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I TA L I A N H A B I TAT S Mountain streams 5 Italian habitats Italian Ministry of the Environment and Territory Protection / Ministero dell’Ambiente e della Tutela del Territorio Friuli Museum of Natural History / Museo Friulano di Storia Naturale · Comune di Udine I TA L I A N H A B I TAT S Scientific coordinators Alessandro Minelli · Sandro Ruffo · Fabio Stoch Editorial commitee Aldo Cosentino · Alessandro La Posta · Carlo Morandini · Giuseppe Muscio “Mountain streams · Life in running waters” edited by Fabio Stoch Texts Marco Cantonati · Valeria Lencioni · Bruno Maiolini · Mauro Marchetti · Karin Ortler · Mario Panizza · Sergio Paradisi · Margherita Solari · Fabio Stoch English translation Elena Calandruccio · Gabriel Walton Illustrations Roberto Zanella Graphic design Furio Colman Photographs Archive Museo Friulano di Storia Naturale (Ettore Tomasi) 47/1, 47/3, 48, 50/1, 50/2, 50/3, 51/1, 51/2, 51/3, 54/1, 54/2, 55/1, 55/2 · Marco Cantonati 31/1, 31/2, 32/1, 32/2, 32/3, 34/1, 34/2, 35/1, 35/2, 39 · Massimo Capula 134 · Ulderica Da Pozzo 9, 10, 27, 28, 46, 58, 110, 139, 148, 151, 153 · Adalberto D’Andrea 6, 64, 132 · Massimo Domenichini 141 · Maria Manuela Giovannelli 60/2 · Luca Lapini 90, 92, 98, 99 · Valeria Lencioni 20, 100 · Bruno Maiolini 56, 60/1, 65/2, 68, 71, 74/1, 74/2, 79/1, 112, 145 · Mauro Marchetti 124 · Michele Mendi 95 · Andrea Mocchiutti 23 · Giuseppe Muscio 26, 42, 52, 119, 120, 130, 135, 136 · Karin Ortler 40, 45, 49, 53 · Sergio Paradisi 85, 87 · Natural Park of Foreste Casentinesi (Nevio Agostini) 7, 18, 29, 80, 122, 129, 147 · Roberto Parodi 96, 97 · Ivo Pecile 13, 66 · Margherita Solari 47/2, 59, 116, 150 Fabio Stoch 62, 102, 103/1, 103/2, 114, 115, 138 · Roberto Zucchini 65/1, 67, 70, 79/2, 91, 93, 127 Mountain streams Life in running waters ©2003 Museo Friulano di Storia Naturale · Udine All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, without the prior permission in writing of the publishers. ISBN 88 88192 10 7 Cover photo: springs of Arzino in Carnia (Friuli, photo by Ulderica Da Pozzo) M I N I S T E R O D E L L’ A M B I E N T E E D E L L A T U T E L A D E L T E R R I T O R I O M U S E O F R I U L A N O D I S T O R I A N AT U R A L E · C O M U N E D I U D I N E Italian habitats Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Sergio Paradisi Hydrogeology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Mauro Marchetti · Mario Panizza 1 Caves and karstic phenomena 2 Springs and spring watercourses 3 Woodlands of the Po Plain 4 Sand dunes and beaches 5 Mountain streams Flora and vegetation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 Marco Cantonati · Karin Ortler Invertebrate fauna . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 Bruno Maiolini · Valeria Lencioni Vertebrate fauna . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 Sergio Paradisi 6 The Mediterranean maquis 7 Sea cliffs and rocky coastlines 8 Brackish coastal lakes 9 Mountain peat-bogs 10 Realms of snow and ice Ecology of mountain streams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 Fabio Stoch Conservation and management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121 Mauro Marchetti · Mario Panizza · Sergio Paradisi · Fabio Stoch Suggestions for teaching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149 Margherita Solari Select bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155 11 Pools, ponds and marshland 12 Arid meadows 13 Rocky slopes and screes 14 High-altitude lakes 15 Beech forests of the Appennines Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156 List of species . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157 Introduction SERGIO PARADISI Mountains undoubtedly take on fascinating aspects when the sight of snowclad peaks rising into the sky, high meadows carpeted with beautiful spring flowers, and mysterious, aweinspiring forests are accompanied by water as an additional feature in a grandiose landscape. Man has always been attracted to running water, whether as a turbulent rush of power gushing from the tongues of glaciers, as myriads of silvery streams spreading down hilly slopes, as the pleasure experienced upon seeing a clear stream flowing across a meadow, or as the deafening roar of waterfalls. In the past, man exploited mountains The Acquacheta in the northern Appennines for some of his activities; nowadays he views them as “picture postcard” landscapes, sufficiently far from large towns to be considered uncontaminated and rustically serene. In fact, this oleographic picture is far removed from reality. Steep slopes and the resulting high speed of water flow, the low or very low temperatures, and reduced trophism all mean that mountain streams are rigorous and selective environments. Their animal and plant communities are poorer than those found in lowland rivers, and are made up of specialized components. However, as specialization also implies vulnerability, high-altitude streams are essentially vulnerable environments, by their very nature. Here, meteoric events produce an almost continual renewal in the landscape, preventing animal and plant populations from reaching a settled maturation stage: as if the stream biocoenoses were perpetual pioneers. In such a context, any unwise human intervention, albeit on a small scale, may upset the delicately contrived balance which makes Mountain streams have always attracted man 7 8 forms of life possible. The traditional activities of mountain people (livestock rearing, forestry) had generally limited consequences on the stream ecosystem, as at high altitudes there are few polluting sources and villages or towns are small. In recent years, the well-known phenomenon of abandonment of mountain areas (particularly high mountain ones) has greatly reduced human activities. At the same time, and as a consequence of this demographic trend, various kinds of interventions were needed. They were neither small nor uninfluential, and often deprived the stream and its landscape of the heavenly aura we have attributed to them so far. Dams, canalizations, various kinds of hydraulic arrangements, deviations and embankments all have a strong environmental impact aimed at controlling water flow, to be balanced against their value for the safety of human settlements and hydraulic requirements. Streams are often viewed - paradoxically, since they are commonly perceived as absolutely natural - as nothing more than sterile conveyors, preferential ways in which melted ice from glaciers or rainwater choose to reach the valley. The animal and plant communities which populate streams are not considered when hydraulic operations are executed, and these often deeply modify and sometimes jeopardize those communities forever. The present volume deals with this issue, and also examines the geological, botanical and faunal aspects of Italian high mountain streams. When speaking of streams, we do not refer to a single, homogeneous habitat, but a complex network of environments which often reveal very different geological and biological aspects. Watercourses in the Alps and Appennines are mountain streams, as are those flowing down the lava spurs of Mount Etna and the small, temporary rivers of inland Sardinia, the geological history of which has created a completely different biogeographical world from that of the Italian peninsula. The icy, fastflowing watercourses which descend from Alpine glaciers are streams, like rivers which on hot summer days are reduced to gravel beds and look more like deserts than watercourses. This is why this volume does not cover all the environmental themes that the “stream” ecosystem provides. The present work is devoted to mountain streams in the strict sense of the word, defining the geographical area of the Alps and northern Appennines and, further south, the streams of the Abruzzi and Latium regions. The volume covers all naturalistic aspects of streams, but also analyses the dangers which threaten the survival of their frail populations. We hope that the spread of knowledge may make us more aware of what we are about to lose and stimulate our will to preserve it. 9 An Alpine stream in winter Hydrogeology MAURO MARCHETTI · MARIO PANIZZA Waters flowing on the Earth’s surface make up the so-called superficial flow, a subject studied by branches of Earth Sciences such as hydrology, hydraulics, and geomorphology. Parameters relating to fluid physics (the field of hydraulics), river geometry and the development of the hydrographic network (hydrology), the structural factors of the catchment basin (lithology, degree of fracturing, etc.) and climatic conditions, which influence river modelling processes (geomorphology) are all necessary to understand the characteristics and evolution of watercourses. Rivers in the Italian Alps and Appennines differ greatly from one another, as they are considerably influenced by the very varying rocks which outcrop in their respective basins, and by very different relief energy, generally higher in Alpine basins. The Alps and Appennines also have different climates, as the former are often located at higher altitudes, where the periglacial environment dominates. ■ Geological setting Italy is particularly rich in mountains and hills, which respectively represent 35.2% and 41.7% of the entire surface area of the country. As is well-known, the mountains of the Alpine and Appennine chains belong to a very long mountain system stretching from the Straits of Gibraltar to Indonesia. The evolution of this mountain system is extremely complex: as regards the circum-Mediterranean area, the various portions of the chain are a series of tectonically deformed stretches, in which the processes of shortening and overthrusting of the continental crust did not take place in a homogeneous way. These phenomena date back to the Jurassic-Cretaceous boundary (about 150 million years ago). Subduction of the ocean floor ceased in the Cretaceous and the two edges of the Eurasian and African continents collided. Overthrusting began to involve increasingly longer parts of the continental crust. The most active phase in the Alps occurred during the Upper Eocene-Oligocene (40-20 million years ago). The orogenetic phase continued into the Neogene and was particularly Ravines are typically created by streams flowing across hard rocks 11 12 intense during the Miocene in the Tuscan Appennines, and in the Plio-Pleistocene in the external Appennines. Mountain chains in southern Europe are formed of overturned north-running faults: their structure is highly asymmetric, as they are composed of overlapping faults translated sometimes hundreds of kilometres. The Appennine chain overthrusts towards the Adriatic. The Alps are a well-defined geographical unit, about 1000 km long and 150200 km wide, characterized by numerous peaks exceeding elevations of 3500 m. The intense tectonic event in the Oligo-Miocene, which formed the Alps, was followed by an erosive phase which reduced the chain to a series of low reliefs in the late Upper Miocene. The present conformation is due to later uplift in the Plio-Pleistocene. The Appennine chain is about 1000 km long and only a few of its peaks exceed 2000 m: the highest ones lie between the Abruzzi and Latium regions (e.g., Gran Sasso, 2912 m). Mount Etna is the highest (3223 m). The greatest differences between the Alps and the Appennines lie in the extent of their tectonization, i.e., their degree of uplift and the ductile or fragile behaviour of their rock formations. These factors directly or indirectly interact with others, such as the erodibility of rocks and climatic conditions, determining an erosion rate which varies significantly according to area. The most significant difference in the evolution of mountain streams is certainly the different lithogical composition of the outcropping soils in the Alps and Appennines. Despite their complexity, hard, erosion-resistant rocks outcrop throughout the Alps: intrusive and metamorphic ones in the west, calcareous in the centre HELVETIC PREALPS CERVINO EXTERNAL DOMAIN Geological sketch of a section of the Western Alps, showing overlapping nappes in the mountain chain. The Alps rest on a pre-Triassic basement composed of granite or metamorphic rocks which are harder than the sedimentary cover. This hard basement outcrops in the Western Alps. The Southern Alps, which comprise almost all the central and southern Alps, are calcareous, and rest on a paleo-African basement overlaid by M. ROSA 13 SESIA SIMPLO - TICINES NAPPES layers of sediments (and rare vulcanites) over 10 km thick. Compression during the formation of the Alps and the development of a series of sliding planes (faults) in the north gave rise to the subsequent thrusting, folding and shrinking southwards of these layers. Yellow: Helvetic domain; green: Penninic domain (light blue: Piedmont area); orange: Austro-Alpine domain. A stream carving its way through mountains in the Aurina Valley (province of Trento) 14 and east, and volcanic or dolomitic in the Veneto-Trentino (province of Trento) area. In the Appennines, lithologies are less coherent, being composed of clay, marl and sandstone, with few crystalline or metamorphic rocks. In some areas, volcanic rocks occur, in places made up of tuff and ash with low resistance to erosion. However, less erodible lithologies stand out in the Appennines where the landscape generally has gentle slopes: among these are the Latium volcanic APPENNINE EXTERNAL FRONT I P L ALPINE/SOUTH ALPINE LIMIT FOREDEEPS PO PLAIN A FORELANDS ADRIATIC FOREDEEP GARGANO FORELAND BRADANIC FOREDEEP I UR LIG AN BA SI N OP EN IN G UP .O LIG ./M ID. M IOC. H TYRR N ENIA NIN OPE P ./ IOC P. M GU .-P LIO IS LE T. SALENTO FORELAND GELA - CATANIA FOREDEEP IBLEI FORELAND The Appennines, at the edge of the western African promontory (Adria microplate) feature foredeeps (Po Plain, Adriatic, Bradanic, GelaCatania), later filled with sediments, on the edges of which are marginal continental areas (forelands: Gargano, Salento and Iblei). The Appennines are composed of faults which originated in the Cretaceous, when the ocean closed up, continental plates collided, and the Liguria-Provence and Tyrrhenian basins were formed. Compression caused tectonic plates to form, which became detached from the crust beneath and overlapped. Orogenesis in the Appennines gave rise to anti-clockwise rotation of the Appennines and the SardinianCorsican unit, which caused the Liguria unit to slide over the Tuscan one during the Oligocene. The southern Alpine and northern Appennine margins warped downwards and came into contact under the Plio-Quaternary marine and fluvial deposits of the Po Plain. covers, sandstone in the Tuscan-Emilian and Romagna ridge, limestone in the Umbrian-Marches sequence, the crystalline and metamorphic rocks of the Apuan Alps, and the remains of the metamorphic basement with granitoid intrusions (which formed during the Hercynian orogenesis, dating back to the end of the Carboniferous, about 300 million years ago) of the CalabrianPeloritan arc. This variety of rocks implies varying resistance to external agents and surface water flow, and thus also influences solid transport by watercourses. The total solid transport of the Appennine rivers has a higher percentage of suspended components than bottom sediments, in comparison with Alpine ones. Another difference lies in the general distribution of relief energy, also defined as relative altitude. The mean altitudes of the various catchment basins are greater in the Alps, as shown by the highest peaks of the two chains. High altitudes influence the microclimate of catchment basins and therefore the type of water supply: the highest ones have nivo-glacial situations. Ice and snow also imply considerable physical disintegration (cryoclastism), capable of forming great quantities of debris. This is carried to rivers by surface water flow, the force of gravity and avalanches. Alpine catchment basins are also usually larger than Appennine ones, and this generally influences the supply, flow and length of watercourses. The two mountain chains also underwent different glacier modelling processes. During the last glacial maximum, which ended about 15,000 years ago, the Alps were buried under a single ice cap, from which only the highest and sharpest peaks emerged, whereas the Appennines had small glaciers which originated near the highest north-facing ridges. Glaciers have not only modelled the main valleys, but have also produced huge amounts of sediments, most of which are still stored in catchment basins. This debris is easily carried by streams in far larger quantities than those deriving from physical disintegration in present-day morpho-climatic conditions. ■ Hydrography Catchment basins. Water flowing on relief surfaces is organized in hydrographic networks, and all watercourses, including occasional ones, drain a certain catchment basin. This basin is the area in which - assuming nil infiltration and evapotranspiration, that is, imagining surface impermeable and devoid of vegetal cover - any liquid or solid precipitation (rain, snow, hail, etc.) is conveyed to the main channel subtending water flow in the whole area. 15 17 16 3rd ORDER BASIN 5 th ORDER BASIN LIMIT 2 2 nd ORDER BASIN 2 2 2 2 3 3 1st ORDER BASIN 2 3 2 3 2 a b c d e f 2 4 2 2 2 2 2 2 3 2 2 4 5 3 3 2 2 2 5 2 1st ORDER 2nd ORDER 3rd ORDER 2 2 2 4 th ORDER 5th ORDER 4th ORDER BASIN 0 2 4 km BASIN LIMIT Catchment basins and hydrographical networks may be analysed from the morphometric point of view by dividing them into hierarchically organized streams. First-order streams are fed by springs or streams; two first-order streams unite to form a second-order stream; two second-order streams unite to form a third-order stream, and so on. Second-order streams subtend basins of the same order. These basins constitute sub-basins of higher order basins, e.g., the catchment basin of the stream Isorno, between Piedmont and the Canton of Ticino (Switzerland) and its catchment basin. One catchment basin borders on others and is separated from them by a boundary called a watershed. Surface and subterranean watersheds do not always coincide, as infiltration may produce subterranean flows towards other basins (loss) or from them (gain). The pattern of the hydrographic network of a basin, composed of the main watercourse and its tributaries, is called drainage pattern. It may take on many different forms, mainly according to geological structure. Evolution of a hydrographic network. The development of the hydrographic network of the entire circum-Mediterranean area, including the Italian reliefs, was greatly influenced by an important event which occurred during the Messinian (Upper Miocene, 4-5 million years ago), when the Mediterranean was isolated from the Atlantic Ocean. Until then, the two had communicated with each other through two passages, one north of the Betic chain, in present-day southern Spain, and another south of the Rif chain, in present-day Morocco. The approach of Africa to Europe closed both passages (first north, then south) in a few tens of thousands of years. The result of this closure was the almost total evaporation of the Mediterranean during a hot period, to such an extent that evaporites (especially gyp- Dendritic drainage patterns (a) are typical of soils containing homogeneous clay, such as the hills of the northern Appennines. Parallel networks (b) are influenced by highgradient slopes, like those of Alpine valleys. Rectangular networks (c) are associated with faults and fractures and are typically found in the Trentino Prealps. Radial networks characterize isolated reliefs, e.g., the Euganean Hills (centrifugal, d), or depressions such as the volcanic lakes of Latium (centripetal, e). Deranged networks are found in geologically young or particularly eroded areas, such as the Carso (f). sum) were deposited in some areas. At the same time, in land emerging above sea level, hydrographic networks receded, due to regressive erosion starting from the lowest sea level. The extent of this deepening of the hydrographic network may be fully understood if we consider that the depression base of the main pre-Alpine lakes (Garda, Maggiore, Como, Iseo) is more than 500 m below the present-day sea level. Even though these lake depressions have been filled in by sediments over the last 5 million years, their bottoms are still below sea level. Other critical periods for the Alpine and Appenine hydrographic networks were the great Pleistocene glaciations (1,800,000-10,000 years ago). In the Alps, glacial deposits identify at least five peaks which correspond to the great glaciations, called Donau, Günz, Mindel, Riss and Würm. During cold phases, catchment basins underwent complex, non-homogeneous situations all along the Italian peninsula. The Alps, for example, were covered by a single great ice cap extending to the Po Plain, from which only the highest reliefs emerged. Precipitation was less abundant than now, due to the establishment of anticyclonic conditions over the glacial mass. The surrounding plains were steppe-like (dry and cold), and reliefs were characterized by intense glacial processes which contributed both to remodelling 18 An Appennine stream (Ponte della Brusia, Bocconi, Forlì) of the main Alpine valleys and to overall deepening of the network. In these periods, many base levels were reshaped; glacial excavation of the main valleys and the settling in them of very thick layers of ice supported higher base levels for side tributaries, producing what today are suspended valleys, where the tributaries flow into the main valley over a “throw”, giving rise to sometimes spectacular waterfalls. During the glacial epochs, debris was produced in great quantities and the network deepened; huge deposits of sediments, for instance, accumulated in the valleys at outlets to the plain, as far as the Po itself. The sea, the level of which was about 110 m lower than it is today, did not influence the mountain portion of the network to any significant extent. During the glacial phases in the Appennines, there were no large glaciers, and not even tongues of ice reached the surrounding plains. The landscape was dominated by periglacial (cryonival) conditions; only in the innermost areas of the northern Appennines (Tuscan-Emilian ridge) and on the Abruzzi reliefs did small or medium-sized glaciers appear. Periglacial conditions implied intense physical disintegration, which was not followed by corresponding deepening of the hydrographic network. The latter could not remove all the sediments produced on its flanks and conveyed to its watercourses. “Grèzes litées” are the characteristic deposits still found on the flanks of the Umbrian-Marches regions. In the Po Plain, for instance, during the last glacial maximum, gravel forming alluvial fans was deposited, and now makes up the feed area for the Emilian plain. After the last glaciation (Holocene), changes in the network were minimal and influenced the type of vegetal cover, and particularly its density. This was partly conditioned by the climate, with slight variations in temperature and humidity during the Holocene, but mostly by the rise in human populations and their relative activities, starting from the Neolithic and even more in Roman times. Several periods may be identified: severe network erosion following deforestation (especially in the Neolithic, in Roman times and the modern age), and minor erosion, in the event of stability, following mountain abandonment and deforestation, as in the early Middle Ages or the second half of the 20th century. The latter period is one of the most difficult to interpret, as abandonment of mountain areas, which causes reafforestation, accompanied other human actions, with contrasting effects. Abandonment itself, for instance, produces increased soil erosion in the short term, as woodland and slope maintenance are not carried out; lack of control and economic interests may give rise to the practice of deliberately setting fire to vegetation, resulting in large-scale erosion in the rainy season. Artificial operations (works to regulate water flow, artificial reafforestation, etc.) have the opposite effect, i.e., they thwart erosive processes. Watercourse supply. Supply to watercourses is one of the most important parameters which determine the quantity and quality of available waters in streams, as well as their regimen, or seasonal flow capacity. Watercourses which drain small basins with homogeneous lithologies are characterized by simple supply due to precipitation, melting of ice or snow, or the emergence of aquifers. In larger basins, water supply is complex, and is influenced by the various types of flow supplied by tributaries. There may be pluvial supply when the water flowing in rivers comes from rainfall. Rivers with this kind of supply have regimes characterized by high or low waters, according to periods of maximum rainfall or dry seasons respectively. This seasonal trend is therefore influenced by the general climatic conditions typical of the catchment basin. In the northern Appennines, where feed is typically pluvial, high waters are more common in autumn than in spring. Low waters are typical of winter and especially summer, as a consequence of both high evapotranspiration and reduced supply. In areas with particular climatic conditions, like Liguria or southern Piedmont, the proximity of the Alpine and Appennine chains to the coast interferes with air masses coming in from the Atlantic, which may cause 19 20 intense, late summer storms which are responsible for catastrophic floods. Similar situations are typical of the Calabrian region and to a certain extent the whole western Appennine chain. Another peculiar situation may be found in the Friuli and Veneto Prealps, where cold air masses wedge in from central Europe and sometimes Siberia. These cause fronts to settle in the area for long periods, especially in autumn, when they give rise to abundant rainfall. Glacial supply occurs when watercourses derive from the melting of ice. In this case, high waters are recorded in periods when melting is intense, Meltwater is a form of supply for mountain streams i.e., in summer, whereas low waters are typical of winter. When water supply does not depend on the melting of ice but of snow, high waters are anticipated to spring and decrease in warmer periods, when the snow cover is reduced. Snow supply prevails in the high-altitude basins of the Italian mountain regions; high waters peak in May-June and then decrease until the following spring. Watercourses with snow supply may be found at high altitudes in the Western Alps, and the water consists of melted ice and snow. Many tributaries of the Dora Baltea, Dora Riparia, Sesia and Ticino are supplied in this way, as well as some tributaries of the Adige along the Eastern Alps. Springs. In mountain streams, springs may determine the regime of watercourses. When the quantity of water only amounts to a trickle, the result is a small pool; when the flow may be gauged, it is called a “true spring”. Many names are given to water originating from springs: true springs, “fountainheads”, “veins”, and in the case of anthropic intervention, “fountains”. Streams carry water emerging from aquifers. In the case of permeable rocks, aquifers originate in sediments in which the speed of water flow depends on the slope and permeability of the terrains crossed. Springs originate when the roof of the aquifer meets the topographic surface. A spring is thus an area, small or large, where the subterranean aquifer meets the surface of the Types of springs Mauro Marchetti · Mario Panizza Emergence springs ( a ) have various locations and may temporarily disappear as the flow of the aquifer varies during the year. If they emerge in a valley, they appear at lower altitudes as the watertable sinks, and reach high altitudes during maximum level phases. If they are in a cavity, they may disappear during low watertable levels. Overflowing springs ( b ) originate where waters in subterranean chambers touch an overflow threshold or reach the surface. Contact springs ( c ) are very common and flow out when the aquifer flows in permeable soil after touching an impermeable formation. This contact may be stratigraphic (transgressions, etc.) or tectonic in origin (overthrusts, faults, etc.), or due to recent forms and deposits (landslides, moraines, a b e d floods, etc. on less permeable lithotypes underneath). These springs have fixed locations which cannot be altered by changes in watertable level. When the latter changes, they may vary in flow, or gush out only when the watertable level is high. Karstic springs ( d ) in carbonatic massifs are a typical example: here, permeability is principally due to flow in cracks and fractures rather than to the permeability of the rock itself. Barrage springs ( e ) result from subterranean water that emerges when impermeable obstacles hinder its flow. Fissure springs are caused by the presence of faults, fractures and any other type of preferential course, e.g., karstic conduits, which allow water to flow out at a precise spot. c 21 22 ground and emerges. Water may leave the aquifer because it filters through sediments, porous rocks, or preferential conduits, generally discontinuous surfaces (stratified surfaces, formations with different degrees of permeability, cracks, faults, etc.). There are many kinds of mountain springs, among which are emergence, overflowing, contact, barrage, and fissure springs. Springs may be isolated, grouped in restricted areas, or aligned along particular geological structures (for instance, between permeable and impermeable formations). These alignments may be particularly frequent, as flysch in the Appennines or sandstone overlying the fine, impermeable rocks of the high Emilian Appennines (e.g., at the foot of the “Pietra di Bismantova”). Chemico-physical characteristics of water. Mountain stream waters are characterized by a thermal regime which depends on their supply, and by chemical composition which depends on the surface terrains they cross and, particularly for spring waters, on the composition of the rocks crossed before reaching the surface. Water chemistry is determined by dissolved ions. Their transport in solution does not depend on watercourse energy, i.e., water flow and speed, but rather on the composition of the rocks crossed and their aggressivity (pH). The most common dissolved ions are carbonate (CO3=), chlorine (Cl-) and sulphate (SO4=) ions, as well as sodium (Na+), potassium (K+), calcium (Ca++) and magnesium (Mg++) cations, and dissolved silica (SiO2). The predominance of some ions over others depends on the terrains crossed, for example, waters flowing inside carbonatic massifs have basic pH and are rich in calcium ions and carbonates in general. Waters that cross crystalline massifs where quartz and feldspars abound (e.g., granite, gneiss and schist), have acid pH and are rich in silica, like those of the innermost part of the Alpine chain. Waters crossing a particular terrain, like Triassic gypsum in the Umbrian-Marches chain, are rich in calcium and sulphates. Sodium and chlorine waters are found in salty soil recently abandoned by the sea (generally in coastal plains) or areas with mineral springs. Higher concentrations of magnesium ions are recorded in areas rich in this element, as in the Dolomites. Transport in solution is gauged through laboratory tests which determine the contents of dissolved ions; this datum is expressed in different units of measurement. One of the most common is hardness, i.e., the content of calcium and magnesium in water (total hardness). Hardness is measured in hydrotimetric degrees, the most common of which 23 High-altitude karstic area (Julian Alps) without surface drainage network are French degrees (1°F corresponds to 10 mg/l of Ca++ ion). According to this unit of measurement, waters are classified as: very soft (0-7), soft (7-14), moderately hard (14-22), quite hard (22-32), hard (32-54) and very hard (>54). Total solid residues at 180°C are easy to find: a litre of water evaporates at 180°C. Waters derived from the melting of snow are particularly acid, due to few dissolved cations and abundant carbonic acid. In some areas of the Italian reliefs water chemistry may be modified by anthropic causes, mainly related to the intense exploitation of Alpine areas by tourists. The consequences of this great demographic pressure has led to sometimes significant increases in pollutants: coliform organisms, heavy metals, nitrates and phosphates. Abnormal increases in hydrocarbon and chloride are recorded near main roads, due to the scattering of chlorinated salts for de-icing. Livestock farming areas (cattle-breeding in the Alps and sheep-breeding in the Appennines) lead to high values of dissolved nitrates and nitrites. Hydraulic systems. Watercourses may be divided into two groups: rivers and streams. The two groups partially overlap over a wide transition area. A river is a perennial watercourse with low speed and slope (less than 0.5% gradient). Streams or seasonal torrents are characterized by higher speeds and gradients; the term torrent, in Latin torrens, derives from “torreo”, or bubbling. Velocity and stream discharge Mauro Marchetti · Mario Panizza Velocity Stream discharge Water velocity is the best indicator of stream energy. The faster waters flow, the more intensely stream beds are eroded; slow-moving waters give rise to sedimentation processes. Velocity is not constant or regular along streams; in rectilinear stretches, fast waters usually concentrate in the middle of the channel, just under the free surface; in curved ones, they concentrate near the concave bank. Stream discharge (Q) is the volume of water flowing in a stream in a specified unit of time, and is expressed by the formula: Q=Av in which A is cross-section area and v is average stream velocity. Stream discharge is measured in m3/sec or sometimes in l/sec, by calculating the hydrometric level of water. Their trends in time are analysed with diagrams called hydrograms. 1000 cm/sec RECTILINEAR STRETCH + EROSION 100 10 CURVED STRETCH TRANSPORT + NV EX NK CO BA 1 BA This term is often also used in a figurative way to describe the intensity of flow in particular circumstances, like “a torrent of words”. The speeds of mountain streams vary and are affected by water flow and type of supply. Low waters may be perfectly calm and their speed very low, about 0.1 m/s, whereas high-altitude waters have a high speed, over 10 m/s. Therefore, even if streams have minor total flows, they have a far greater competence. Watercourse competence is determined by the maximum size of the single clastic rocks carried. This size is strictly controlled by the stream speed and its depth. Instead, total solid transport is proportional to the water flow. Increased volume of transported material (solid load) and corresponding decrease in the particle size of transported material (competence) are observed as springs flow from the upper parts of their catchment basins to the river mouth. The collection and sedimentation which occur along streams change their longitudinal profile. Erosion along a portion of the stream lowers the gradient of the watercourse downstream and raises it upstream, increasing the erosion rate upstream and lowering it downstream. Similarly, sedimentation along a portion of the stream lowers its gradient upstream and raises it downstream. When every part of the longitudinal profile maintains the same gradient over a sufficiently long period (e.g., one year), the watercourse is said to have reached balance. Streams reach their characteristic balanced profile through erosion and sedimentation processes. When this occurs, the whole volume of debris which reaches the stream bed from nearby slopes and upstream, is carried away downstream. From the viewpoint of transported sediments, a balanced stream therefore has a nil balance. A diagram with the ordinates showing elevations above sea level and the abscissa the distance from springs, will show that the longitudinal profile of a balanced watercourse is theoretically hyperbolical, with gradients steadily falling from spring to river mouth. The river mouth is a fixed point of reference, called base level, below which watercourses cannot deepen their beds. The general base level is the sea, although there may be local base levels due to the confluence of streams in hierarchically more important watercourses, or their flow into natural or artificial lakes. Huge clastic concentrations, larger than those of stream competence, are visible along mountain streams. These large pebbles or boulders are not carried by the stream water, but by gravity along its flanks or exhumation by water of smaller clastic rocks, until the channel banks and bottom are almost NK SEDIMENTATION VE 24 CO A NC 0.1 0.001 0.01 0.1 1 10 mm 100 Distribution of lines connecting points where the current has equal velocity in rectilinear (up) and curved stream beds (down). Fast currents are shown in red: in a curved strectch they are close to the concave bank Hjulström’s diagram, showing that erosion, transport and sedimentation all depend on water velocity. x: diameter of debris in mm; y: current velocity in cm/sec In the early 20th century, it was already clear that erosion, transport and sedimentation all depend on water velocity, as shown in Hjulström’s diagram of 1935. This demonstrates that the finest particles (diameter less than 0.05 mm) are not sedimented, even if the water is almost still, but float in suspension as far as the streams reach the lakes or seas, which represent base levels In Italy, the National Hydrographical Service provides many measuring stations, and the data collected are published. Past floods recorded over long periods and then statistically processed, can predict peak stream discharges in 100, 200 or even 1000 years. Those with particular return periods are used to design special works along watercourses. 25 26 completely made up of immovable material. In such conditions, channels cannot be eroded further, as the coarse clastic rocks protect underlying deposits with finer particle sizes from erosion. The arrangement of large rocks in mountain streams is very important because it contributes to the formation of clastic aggregates supported by larger blocks. These determine the typical terraced profile which AngloSaxons call “step and pool”. The spacing and relief of this type of discontinuity is important both to assess the dispersion of energy in the stream, due to the roughness of the river bed Large amounts of solids make waters milky (Savio stream, northern Appennines) and the hydraulic throws which are responsible for downstream deceleration at every step, and for the ecology of the stream itself, as shallow, fast stretches alternate with calm, deep ones. Solid transport in mountain streams is deeply affected by the rocks of the catchment basin, the stability of flanks near the stream, active processes prevailing in those reliefs, and the type of feed of the stream itself. Prevailing types of solid transport are thus impossible to define according to hydraulic characteristics (e.g., flows and speeds). Streams crossing easily erodible fine rocks, like those of the Emilian Appennines, have higher suspended transport than their bottom sediments. In such areas, mainly during intense autumn rains, the waters become cloudy following surface leaching of rocks in the supply basin and slow gravitational processes along flanks. In streams supplied by ice meltwater, suspended transport makes waters milky-blue in colour. Streams which cross areas with outcropping competent rocks - calcareous, dolomitic or crystalline - have more bottom sediments than suspended components, especially if the material reaching the river bed derives from cryoclastism and if transport down slopes is due mainly to collapse rather than to surface leaching. Generally, there is a clear difference in types of transport during high and low water phases. Low waters are characterized by little bottom transport, whereas suspended transport continues, particularly if clay or fine sediments are occur along the river bed. 27 Steps and pools Flora and vegetation MARCO CANTONATI · KARIN ORTLER ■ Algae and aquatic lichens In normal conditions, i.e., when disastrous events like sudden, great floods or chemical pollution have not occurred, the bed of a stream sparkles with shades of colour ranging from dark brown or black, to reddish, to all nuances of green and blue-green. Streams owe their bright colours to algae, aquatic lichens and mosses (whereby German scholars use the Vegetation along the banks of a stream term Vegetationsfärbungen = colours due to aquatic vegetation). The banks, unless artificially straightened or reinforced with concrete, are never bare, but richly covered with aquatic plants, bushes and trees which need increasingly less water and become more and more intolerant of submersion with distance from the stream. While aquatic and hygrophilous mosses are frequent in spring areas, and higher aquatic plants prefer slow-moving waters with sandy or muddy bottoms typical of large plain rivers, mountain streams with fastmoving waters are characterized by algae. These organisms are generally associated with beaches, or sometimes lakes, not with mountain streams. However, even if often overlooked, they are quick at colonizing any watercourse, whether small or impetuous, in plains as in mountains. The term “algae” is commonly used, but it often inappropriately identifies true higher plants which have adapted to life in an aquatic environment, such as the water buttercup. The term is inaccurate also from a strictly systematic point of view, and is nowadays mostly used informally to indicate a highly varied group of organisms. “Algae” better defines aquatic plants of various sizes and with heterogeneous organization, without specialized vascular tissues, and not separated into the usual roots, stem and leaves (i.e., they are thallophytes, not higher plants). Springs of Arzino in Carnia (Friuli): algae and lichens cover most of the emerging rocks 29 Algae range in size from few thousandths of a millimetre in the case of cyanobacteria (blue-green algae) to tens of metres in giant brown algae (Macrocystis), which grow on ocean shores. The cells of these plants present the two main structural patterns of the animated world: prokaryotic, having cells without a differentiated nucleus, typical of bacteria and cyanobacteria, and eukaryotic, with a nucleus clearly distinguished from the cytoplasm and enveloped in membranes, typical of all other organisms. The feature these algal types have in common is the way in which they procure energy for life, through oxygenic photosynthesis, by means of a green photosynthetic pigment called “chlorophyll a”, typical of both cyanobacteria and plants. However, individual algal groups differ enormously for the other pigments they contain (accessory and photoprotective), as well as for their ultrastructural, physiological and biochemical characteristics and reproductive system, in the same way as man is different from a sea-urchin or an insect. CYANOBACTERIA DIATOMS GREEN ALGAE MARCH 1 mm 30 APRIL MAY - JUNE Seasonal variations in algal populations (sizes of the individual algae are indicative and colours are only evocative) on stream rocks and pebbles (microscopic aspect) ■ Seasonal variations of algae in streams In temperate climates, seasonal trends affect the presence and development of many species of algae in streams. The cyanoprokaryote Phormidium autumnale, as its name suggests, is usually found in autumn; the chrysophyte Hydrurus foetidus prefers the cold months of autumn and winter; the rhodophyte Bangia atropurpurea develops in early spring. The variations in the abundances of these macroalgae are macroscopically visible and can be quantified by measuring cover and thickness on the spot. As regards diatoms, this is only possible for exceptional blooms of some species occurring in specific seasons (e.g., Diatoma spp., Gomphonema olivaceum var. calcareum, Melosira varians). Many works devoted to streams indicate that variations of the most abundant species in diatom associations, in percentual terms, are not very great. Algal groups in mountain streams Cyanobacteria. Cyanobacteria often colonize the most inhospitable areas of streams, where environmental conditions are the most severe, e.g., areas where water may flow suddenly, change and periodically cease entirely, or rocks along the banks that are only occasionally splashed or sprayed by turbulent waters. Cyanobacteria are also called cyanoprokaryotes, as they do not have an eukaryotic structure like algae, but are prokaryotic, like bacteria. Unlike photosynthetic bacteria which contain bacteriochlorophyll, they contain chlorophyll a, and their photosynthesis is oxygenic like that of algae, mosses and higher plants. Many of them have a sufficiently high number of characteristics to be taxonomically analysed with methods traditionally applied to algae, i.e., morphological observations by optical, Scanning or Transmission Electron Microscopyes. So far, cyanobacteria have therefore been studied by phycologists as “blue-green algae” or “cyanophytes”. Marco Cantonati However, “los bacteriólogos chauvinistas”, as the well-known Spanish ecologist and phycologist Ramón Margalef defined them, claim that cyanobacteria should only be studied using methods applied to bacteria. This controversy is based on the structural (prokaryotic) simplicity of these organisms, which resembles that of bacteria and enables them to colonize inhospitable environments like the Arctic tundra, rocky mountain slopes and hightemperature waters (for this very reason, bacteria were among the first organisms to appear on the Earth billions of years ago). In these environments, cyanobacteria are subject to intense solar radiation, particularly by ultraviolet light, which can seriously damage their DNA. They react with a whole series of adaptations, like actively moving away from excessive light, generating efficient mechanisms to repair molecular damage, and producing photoprotective substances. Nowadays, concern for the reduced ozone in the upper atmosphere Dark brown spots are colonies of Chamaesiphon geitleri, a cyanobacterium typically found in mountain streams with carbonate substrates and clean, gushing waters. Right: cells of the cyanobacterium enveloped by an irregular sheath, as seen under the microscope (1000 X) 31 32 requires deeper knowledge of contrivances adopted by organisms to protect themselves from ultraviolet radiation, and these physiological and biochemical aspects are therefore studied very closely. The main accessory pigments of cyanobacteria are blue phycocyanin and red phycoerythrin, which endow mountain stream beds with bright colours: red or reddish in some areas or on rocks; small, dark brown or turquoise spots glowing under stones, and dark green spots on pebbles. Some species protect themselves from dehydration with strong sheaths enveloping their cells, like Chamaesiphon polonicus, which is generally found in areas of the stream characterized by occasional or seasonal low water or even none at all. Stream cyanobacteria prefer epilithic substrates, i.e., rocks and pebbles. They may also grow on other substrates, such as moss, aquatic plants, or other cyanobacteria (like Chamaesiphon amethystinus, which is found on the filaments of another cyanoprokaryote, Tolypothrix distorta). Most taxa (= taxonomic groups, like genera and species) are widespread. However, there are also very rare species, such as the above-mentioned Chamaesiphon amethystinus. In 1999, Eugen Rott and co-workers identified algae in Austrian waters (analysing 225 watercourses from various aspects), and classified almost half the cyanobacteria as “very rare” on the basis of their frequency. Many taxa are good indicators of water quality. Diatoms. Diatoms make up the largest group of algae as regards number of species and individuals in a stream and, generally, in aquatic environments. There are few kinds of watercourses which diatoms do not colonize, among which Banks of a mountain stream covered by the efflorescence of the microalga Diatoma. Bottom right: bands formed of algal cells (about 60 X); top right: the silicic frustules of these diatoms have a rectangular section when seen from the side (400 X) are “typical” glacial streams, characterized by high discharge (especially in the hottest hours of the day in spring and in summer), and rich in suspended sediments (glacial flow). Otherwise, these algae are found in almost any humid area, from cracks in the desert floor to the oceans. They are microscopic (a few thousandths of a millimetre) unicellular organisms, but they may aggregate in large groups which, when they bloom, form golden to dark brown patinas, velvety covers, or thin filaments. This is the case of species belonging to the genus Diatoma, whose cells adhere to one another forming long bands and, in particular conditions, accumulating to cover the beds of slowmoving watercourses. Every diatom cell is contained in two valves made of amorphous silica, structurally very similar to opal and glass. These valves fit together like the box and lid of a shoe box: bilateral and radial symmetries are the most common types among diatoms. According to this simple criterion, diatoms are subdivided into two large groups, Pennales and Centrales. This subdivision has deep ecological and morphological significance, as it is based on the two large habitats colonized by diatoms: benthic, i.e., shores and watercourse bottoms, and planktonic, i.e., free waters typical of lakes and oceans. Diatoms are so small that they are little known to non-specialists, but they are very important in aquatic environments. They frequently dominate oceanic plankton and constitute the basis of the food chains on which large-scale sectors of the fishing industry, and therefore the nourishment of entire human populations, depends. They make up about a quarter of global primary production, exceeding rainforests and savannahs which are by far the most productive terrestrial biomes. The elegant shapes of diatoms are still a source of inspiration for artistic works, in which valves are embedded in resin and juxtaposed on slides. The valves owe their beauty to the rich and complex series of their morphological details (spots, lines, bands, etc.) which are the signatures of the various species. Identification is carried out by arranging the valves on slides after cleaning them of organic substances and carbonates. Identification of diatom species is therefore based on the structural details of the silicic “box” which contains their cells. One of the most evident structural characteristics of Pennales is the thin slit, called raphe, which runs along the valve. It has long been thought that this structure enables certain diatoms to move, but the exact mechanism is very complex and is still being studied. The cell seems to emit “small molecular rods” from the raphe opening: these rods adhere to the substratum at one end, and hook themselves to the cell membrane on the other. The cell moves forward by contracting, the rods unhook, and then the process is repeated. The ability to move actively is particularly important for species living on mud (epipelic habitat) or other soft substrates, as the micro-algae are enabled to move to illuminated surfaces when they need to (species of the genera Navicula and Nitzschia are typically mobile and epipelic). Other species (like those of the genus Cocconeis) have a raphe only in one of the two valves, and anchor themselves firmly to hard substrates (e.g., stones 33 34 and rocks, epilithic habitat) by means of mucilage produced by the raphe itself. In yet other cases, they adhere with strong mucilaginous stalks which are secreted by pores at one or both ends of the valve. The variety of movement and adherence mechanisms enables diatoms to colonize all areas of mountain streams: central zones with fast-moving water, or small side bays where organic material collects easily. The many species and their different ecological needs allow the colonization of various kinds of streams, from waters with very little mineralization to those rich in carbonates, from clean waters to others organically polluted or contaminated with heavy metals. Chrysophytes. Chrysophytes, or goldenbrown algae, are similar to diatoms as regards their accessory pigments and reserve substances, and include planktonic species with silicic scales which form typical silicified cysts. However, only one species of this group lives in mountain streams, Hydrurus foetidus. Fringed filamentous structures, several tens of centimetres long, which characterize these chrysophytes and turn the beds of mountain streams almost black, particularly on carbonatic rocks, are often seen in autumn or winter. Great quantities of these algae may even be smelled in areas with a moderate increase in algal nutrients (e.g., near an Alpine cattle barn). This smell (unpleasant, recalling that of rotten fish) becomes pungent if one of these filamentous, mucilaginous structures is squashed - hence its name “foetidus”. Microscopic examination reveals that the cells of this alga, which are greenish and golden-brown ovoid structures a few thousandths of a millimetre in size, are actually immersed in a mucilaginous matrix inside the filamentous structure, technically called coenobium. The species is usually found in cold waters, from the mouths of glaciers to medium altitudes. Flow and light may play an important role in the development of this alga, since it tends to reduce its presence in summer even in mountain springs where water temperature is almost constant and low also during summer. Chlorophytes. In mountain streams, the brown shades of diatoms and chrysophytes alternate with the bluegreen, turquoise or reddish cyanobacteria and, in particular, when organic pollution The filamentous structures are cenobia of Hydrudus foetidus, typical of fast-flowing stream stretches, particularly in autumn and winter. Right: the cells of Hydrudus foetidus (green ovoid structures) under the microscope; the elongated, arched shapes on the right are cells of the Diatoma Fragilaria arcus occurs and in summer with patches of greenish filaments or green crusty covers. Tufts of green filaments frequently grow on aquatic moss. These algae belong to the large group of green algae or chlorophytes, the only ones to contain the same chlorophyllic pigments (chlorophyll a and b) and the same reserve substance (starch) as mosses, ferns and higher plants. Areas of the stream subject to flow variations reveal unbranched filaments of green algae of the order Ulotrichales. Those belonging to the order Zygnemales are found in calm, clean water. Microscopic examination easily identifies the three most common genera of this group according to the shape of their chloroplasts: spiral in Spirogyra, band-like in Mougeotia and star-shaped in Zygnema. Representatives of the Desmidiales are rare in streams, although they may be found in small side bays where sand and organic substances are deposited. These are considered among the most beautiful of all algae. Desmids are frequently found in environments like peat-bogs, and are characterized by cells symmetrically arranged on both sides of a narrow waist or isthmus, with a richly decorated cellulose wall which makes them look like tiny jewels. Springs and streams on carbonatic rocks may sometimes reveal the presence of Oocardium stratum, a rare, clearly declining species. Its cells are inserted like plugs in tubular calcareous deposits. Members of the Cladophorales are frequently found at mid-low altitudes, particularly on limestone rocks or in water rich in nutrients, where they cover surfaces with their dense, branching filaments. Their most common genus is Cladophora, which is characterized by particular branching and multinucleate cells, as microscopic examination reveals. Green algae, however, do not necessarily turn streams green. In spring and summer, the banks of at least seasonally fast-flowing and turbulent mountain streams are coloured orange and red. The colour is actually due to green algae of the order Trentepohliales, located on the evolutionary line which led to the higher terrestrial plants. Their cells are filled with a mixture called hematochrome, containing carotenoid pigments. Charophytes. In the past, charophytes were classified as green algae, as they share the same pigments (chlorophyll a and b) and reserve substances (starch). Today, charophytes or stoneworts are A fast-flowing mountain stream. The felty red covers on rocks are due to the green alga Trentepohlia sp. Right: enlarged photograph showing branched filaments, which owe their red colour to the presence of carotenoid pigments 35 generally considered an independent group, especially because of the peculiar structure of their thallus and reproductive structures. They generally live in still water, but may be found on the sides of streams, in secondary channels, or areas where the current is slow and fine sediments deposit. They definitely prefer clean waters and carbonatic substrates. Although non-specialists often confuse them with aquatic higher plants, they are macroalgae. They look like, long, small plants, extending for several tens of centimetres, with multi-cellular thalli made up of elongated internodal cells and shorter nodal cells bearing whorls of branches, each of limited growth. The plant is usually covered by carbonate precipitates, which must be removed with dilute hydrochloric acid prior to examination. Many species typically smell of garlic. The most common genera are Chara and Nitella, which may form submerged meadows. Xanthophytes. Green thalli of peculiar shape may be found in streams, sometimes so densely packed that they resemble that kind of stiff synthetic sponge used by florists for flower compositions. They are not green algae, but a species of the genus Vaucheria, belonging to the xanthophytes or yellow algae. This group does not contain chlorophyll b and its reserve substance is not starch but chrysolaminarin. Xanthophytes may be distinguished from green algae by using reagents which colour starch, like iodine. Equally important and widespread, the genus Tribonema has very different morphology. It includes several species which form long, unbranched filaments in mountain streams. Rhodophytes. Red algae or rhodophytes are very often found in seawater, and their presence in fresh water is relatively rare and limited to a few, albeit very interesting species. Hildenbrandia rivularis forms beautiful, bright red circular spots, especially in low-altitude streams. Lemanea fluviatilis has thalli with nodose structures separated by internodes. It is a rheophilous species (adapted to the current) with a wide distribution in streams and which may even appear in glacial streams at high altitudes. The most peculiar species is Bangia atropurpurea, a red filamentous alga, almost identical forms of which inhabit areas of varying altitudes, ocean, sea and lake shores, rocks and other hard substrates in various types of streams. In the last few decades, detailed studies on its morphology, reproductive cycle, ecophysiology (adaptation to different degrees of salinity in cultures in the laboratory), karyology (analysis of chromosome number, form and size) and lately, biochemistry and molecular genetics, have aimed at determining if these sea and fresh water forms alike belong to the same species, or if they are to be viewed as separate entities. Audouinella hermanni is frequently found in mountain streams. It lives on rocks or other aquatic plants, where it forms purple-violet thalli a few millimetres long. Phaeophytes. Very many species of phaeophytes or brown algae live along sea and ocean coastlines, including the largest of all algae. Their presence in fresh water is limited to a low number of species (e.g., Heribaudiella fluviatilis), mainly found at low altitudes. ■ Biogeography of algae in streams and endangered species The importance of biogeography in explaining algal distribution is difficult to interpret. The same species may be common to several mountain chains in different continents (e.g., the Alps and the Himalayas), whereas others seem to live only in a single mountain massif. Some species of diatoms, for instance, although widely distributed, cannot be found in some areas: Fragilaria arcus var. recta lives in Arctic and Antarctic areas and in eastern Asia, but not in the Alps. Generally speaking, as most groups of algae develop resistance forms which can be efficiently carried by the wind, aquatic birds, etc., most species are cosmopolitan and widely distributed. As regards diatoms, this is particularly true of species living in polluted or moderately contaminated waters. Methods for evaluating the quality of waters based on diatoms are therefore easily applicable or adaptable to streams throughout the world. It is not surprising then, that there are no great differences between the algal flora of Alpine and Appennine streams. In the Appennines, longitudinal distribution areas of algal species, detectable along watercourses, are compressed and located at lower altitudes with local variations. Natural causes and phenomena of organic pollution which generally increase EPIPHYTIC EPILITHIC ENDOLITHIC 36 sand mud EPIPSAMMIC EPIPELIC The main habitats of microalgae in streams, showing algal populations typically associated with substrates, including those which may pierce through carbonatic rocks to reach the interior (endolithic habitat) 37 downstream, give rise to the typical longitudinal distribution of algal species along watercourses. High altitudes are characterized by epiliChamaesiphon geitleri thic species which live in clean, cold, fast-flowing waters (e.g., the cyanobacterium Chamaesiphon polonicus, 6 Hydrurus foetidus 4 diatoms like Diatoma mesodon and 2 0 Fragilaria arcus, the chrysophyte 6 Hydrurus foetidus and the rhodophyte 5 4 Lemanea fluviatilis). 3 Medium altitudes are marked by 2 1 species which require some nutritive 0 salts and can withstand variations in 10 8 °C temperature (e.g., diatoms like Cym6 4 bella affinis and Cocconeis placen2 0 J F M A M J J A S O N D J F M tula, the chlorophyte Cladophora glo1989 1990 merata and the xanthophyte Vaucheria Seasonal variations in the surface cover of geminata). Species which can tolerate some algal species, corresponding to variations in discharge (m /s) and temperature (°C) high quantities of nutritive salts and higher temperatures (e.g., the cyanobacteria Oscillatoria spp., diatoms Navicula spp., Nitzschia palea and Surirella ovata, and desmids Closterium leibleinii and Staurastrum punctulatum) are found at low altitudes. In view of the often wide distribution and intimate relationship between environmental conditions and algal species, attempts at drawing up “Red Lists” (i.e., of endangered species) for algae and particularly diatoms, have led to the identification of some of the endangered aquatic environments in which these algae live. For diatoms, these are mainly nutrient-poor (oligotrophic) freshwaters. According to Horst Lange-Bertalot, who drew up the Red List of diatoms in Germany, protection of these environments is particularly difficult, as they undergo not only direct impacts (e.g., organic pollution), but also receive supplies of atmospheric pollutants (some of which may be nutrients) with precipitation. As regards the distribution and rarity of algal species, much still remains to be done, especially in Italy, since the algal flora of large areas has not yet been explored or is still scarcely known. The presumed rarity and distribution of certain taxa may therefore be due to lack of available information. 14 12 10 8 6 4 2 0 8 6 4 2 0 Phormidium autumnale m3/sec 38 3 ■ Aquatic lichens Not all the patinas and colourful crusts found in mountain streams are due to algae and cyanobacteria: many are composed of aquatic lichens. These organisms have not yet been studied thoroughly, and available information is scarce. Aquatic lichens, like all lichens, derive from the association (symbiosis) of an alga (chlorophyte or cyanophyte) with a fungus A lichen of the genus Verrucaria (ascomycete). The alga provides glucids (sugar) through photosynthesis, and the fungus offers a protected environment and supplies sufficient water and salts from outside. Covers with variously well-defined edges may often be seen in streams. The colours of their thalli range from grey, black and dark brown to greenish, and they bear black ovoid structures. These are called perithecia and contain the spores of the fungus. The perithecia may be very obvious and look like verrucas or warts - hence, the common name of the widespread genus Verrucaria. Its different species colonize siliceous and carbonatic substrates and fast-moving areas of streams, as well as marginal ones barely sprayed by water. Light conditions are very important in the distribution of aquatic lichens. Among the species which can tolerate reduced light are Verrucaria hydrela and Porina chlorotica. Toleration to drought varies according to species. Some (e.g., Verrucaria funckii) cannot withstand even short periods of subaerial exposure. Others are sensitive to prolonged submersion (e.g., Dermatocarpon luridum, which colonizes areas that are submerged only during floods). The result is vertical zonation of species with respect to low and high water, which becomes particularly evident on rocks with large homogeneous surfaces which are partly bathed by water. This kind of vertical distribution is also typical of aquatic and hygrophilous mosses and will be discussed later. Some lichen form typical associations with species of moss and hepaticas in small streams at medium altitudes, especially on siliceous substrates. Analysis of these associations provides useful information about the quality and integrity of such mountain streams. 39 40 ■ Bryophytes and higher plants Mountain streams have fast, turbulent waters, undergo intense erosion and are cold - all unfavourable to the development of bryophytes and vascular plants. Although fast-moving waters do limit the growth of mosses and aquatic plants, many species are widespread. Current speed and substratum lithology (the latter influences water chemistry: acid, around neutral or alkaline waters) are the main factors in determining which plant communities can adapt to life in streams. Vegetation on banks and beds is more highly developed. As water flow undergoes seasonal changes, there may be different types of plant associations. These parts of stream beds which frequently undergo small variations in water level are colonized by pioneer plants, capable of growing and fructifying rapidly during periods of low water, before later floods submerge the area again. The edges of this vegetation, in areas subjected to seasonal regular (but less frequent) variations in water level, is characterized by bushes which can tolerate flooding, such as willows. In areas which are only flooded occasionally, colonies of bushes and trees make up the riverbank woodland. In order to survive in these particular environmental conditions, subjected to considerable changes over the seasons, higher plants have had to adapt themselves to both flooding during high water, and drought during periods of little or no water. The following paragraphs explain what mechanisms they exploit. The distinctive and perhaps most fascinating feature of these environments is their remarkable dynamism. During high waters, the stream shifts its bed, carries considerable quantities of large-sized material (up to one-third of the water volume!), reshapes the course of its channels by submerging old obstacles and creating new ones, and erodes its banks and the foot of mountain slopes while depositing coarse material in plain areas. This continual, extreme dynamism contrasts with the need for stability of man’s villages and his works. People living near watercourses, whether in the Alps or in the Appennines, have often had to face the consequences of hydrogeological disorders such as landslides, instability, solid transport and erosion. The vegetation growing on banks outside the area flooded during high water (alluvial plain), is not especially linked with the watercourse (except for some species which reveal the humidity of the undergrowth in these areas). A typical mountain stream bed In mountain streams, various kinds of vegetation colonize areas which are frequently flooded 41 43 42 Comparison between natural and semi-artificial stream environments Bank vegetation Disorders caused by streams, such as erosion at the foot of slopes, may be remedied by planting suitable grasses, shrubs and trees on the banks. Unlike rthe zonal vegetation which, if undisturbed, depends on local climatic conditions and is therefore restricted, the vegetation which is closely linked with watercourses depends to a lesser extent on climate and is therefore very uniform in its essential structure throughout central Europe. Mountain streams in general must be considered as habitats deserving rigorous protection. Streams in natural conditions, like those described in this chapter, the flow rates of which vary greatly and are colonized by great quantities of bank bushes and trees, are becoming more and more rare. Human intervention has had a strong impact: besides causing pollution, man has redesigned the course of streams, constructed artificial banks, or lowered their beds by excavating sand and gravel from them. Many specialized plants can no longer survive in such revolutionized environments. In natural conditions, the bank vegetation of a mountain stream carries out essential functions: it offers food and shelter to the local fauna, contributes to the removal of nutritive salts (nitrates and phosphates) which flow into the stream from the catchment basin, and reinforces banks. The valleys of watercourses are also important channels for the diffusion of plants belonging to different vegetational and floristic areas. 44 Many factors contribute to this process: the fact that moving water does not only carry seeds and vegetative propagules, but also whole plants or fragments of them; the reduced competitive pressure of alluvial deposits and temporarily flooded areas; the formation of new soil during high water; an efficient supply of nutrients and water which enable sometimes very demanding plants to develop; and the ability of animals living near streams to transport seeds (essential for the colonization of upstream areas). Aquatic flora. There are no vascular plants adapted exclusively to life in Bryophytes on the calcareous banks of a fast-running waters. mountain stream. Aquatic bryophytes, such as Platyhypnidium riparoides ( 1 ) live underwater. Some species, typical of still waters, Just above the level of mean flow are Cratoneuron filicinum ( 2 ) and Dichodontium may also be found in streams, but pellucidum ( 3 ), followed by Brachythecium only in areas where the water is calm. rivulare ( 4 ) and Didymodon spadiceus ( 5 ). Hygrohypnum luridium ( 6 ), Fissidens Their distribution is irregular and cristatus ( 7 ) and Ctenidium molluscum ( 8 ) are found at maximum flow level. Thallose depends on environmental condiliverwort (Conocephalum conicum) ( 9 ) grows tions, which change with any marked in areas which are never splashed by water increase in flow. The reproduction of vascular aquatic plants is mainly vegetative, since their seeds cannot germinate in running water. In this case, colonization occurs through fragmentation, i.e., plant parts which are able to generate new individuals are carried by the current. Instead, the reproduction of bryophytes (mosses and liverworts) depends on water. Mosses do not reproduce by means of flowers and seeds, but from male and female gametes born on the protonema. This is a thin, green, primordial filament which forms only when spores germinate. Male gametes need water - even just a drop of rain or dew - to reach and fecundate female gametes, from which a new bryophyte will develop. Unlike vascular plants, bryophytes cannot regulate their transpiration processes actively, and therefore live in more or less humid environments. They avoid areas with fast-moving waters and prefer calm waters (springs), where they carpet large areas, both submerged and emerging. Bryophytes are systematically placed between algae and vascular plants (pterydophytes and higher plants) and include liverworts and mosses. Liverworts - the most primitive group - may have either a thallose form with a lobed structure, or a foliated form with stalks and leaves without ribbing, as in Scapania undulata. The delicate morphology of aquatic liverworts makes them vulnerable to fast-moving water and the material it carries. Unlike liverworts, mosses have a more complex structure, with clearly differentiated leaves and stalks, more similar to that of vascular plants. HowLiverwort Scapania undulata ever, aquatic mosses living in running water also have to be considerably flexible and traction-resistant, as an efficient anchoring system may be fundamental for their survival. Some species (e.g., Fontinalis antipyretica) carpet pebbles thickly by adhering to them with their primitive rhizoids. The leaves of aquatic mosses are often dense and unilaterally arranged. Stalks and branches are elongated and the tips of leaves are small, with reinforced ribbing. Mosses are very sensitive to drought, but few bryophytes grow directly in water: most of them prefer only periodically wet or submerged areas. Bryophytes have also adapted to the typically low temperatures of mountain streams. Their photosynthesis requires free carbon dioxide, which is dissolved in higher quantities in cold waters. Recent studies show that the photosynthetic rate of mosses adapted to life in cold streams decreases with increasing water temperature. The type of substratum is essential in determining the presence of many species of bryophytes in streams. Thus, the genus Cratoneuron is only found on calcareous substrates and Scapania undulata on siliceous ones. Bryophytes also feature indifferent species, like Brachythecium rivulare. Communities of aquatic mosses are quite homogeneous in Italy and central Europe. The Italian Alps and Appennines host communities of Platyhypnidium riparioides (which adheres to rocks, forming sometimes quite large tufts), 45 46 Mosses may cover most of the rocks on river banks with its partner species Fontinalis antipyretica and Brachythecium rivulare. The extent of cover may vary considerably, according to the environmental characteristics of specific areas (especially current speed). Pioneer vegetation of stream beds. When the banks and beds of mountain streams are frequently submerged even in periods with low water level (ansd so enriched with nutritive substances), we find communities of annual grasses, such as several species of polygons (Polygonum spp.). In natural conditions and in periods of low water, grasses colonize the beds of streams. This pioneer vegetation is organized mosaic-wise, as it depends on the distribution of gravel and sand deposited during periods of high water, according to current speed. Orophilous species like alpine gypsophila (Gypsophila repens), alpine toadflax (Linaria alpina) and alpine willowherb (Epilobium dodonaei) may also be found in streams. These plants - called in German Alpenschwemmlinge - are typical of Alpine and sub-Alpine gravelly debris. The seeds of these plants are carried by currents to alluvial areas, find the proper conditions for their development. There they have to germinate, flower and fructify quickly. Rapid, abundant production of seeds guarantees efficient recolonization after a possible increase in water level. If there is a violent storm, for instance, the level of the stream may rise and submerge plants, which are then carried away by the current, but their seeds may start a new life-cycle. In this environment, herbs do not only have to tolerate periods of submersion, but also drought. This is why their roots follow the level of the aquifer, or why they reduce their transpiration both through the xeromorphic structure of their leaves and their own shape, which is similar to that of dwarf shrubs. This is the case of mountain avens (Dryas octopetala), which forms low carpets with creeping woody stalks. Its horny leaves look like those of oak trees: they are oblong-elliptical, dentellated, and up to 3 cm long, with white down on their underside. This grass produces single, cup-shaped, creamy-white flowers with upturned corollas up to 4 cm wide, with yellow stamens. Its feathery silver fruit is equally beautiful and lasts all summer. Pioneer vegetation alternates with areas of thicker vegetation, made up of stretches of steppe-like meadows with grasses like Calamagrostis pseudophragmites, typical of Calamagrostietum pseudophragmitis, an association generally found in south-eastern Europe. Its erect, leafy culm may reach a height of 1.5 m, and its underground offshoots enable it to colonize new sandy areas very quickly, even after 47 Alpine toadflax (Linaria alpina) Alpine willowherb (Epilobium dodonaei) Mountain avens (Dryas octopetala) 48 being submerged. It may surface again after being covered by gravel and sand. The alluvial plains of streams are therefore a meeting point for species coming from other, different environments, which give rise to very peculiar vegetation. Areas which undergo seasonal variations in water level. Areas which are less frequently submerged by seasonal variations in water level are colonized by thickets. Seeds of willows and other shrubs may develop into plants of a certain height before the next flood. Purple willow (Salix purpurea) Many species of willows have adapted to environmental conditions of streams and, while submerged, withstand the power of the current by means of efficient anchoring systems - networks of roots, lanceolate leaves, and considerable flexibility of branches and trunks. Frequent floods generally do not only imply accumulation of debris, but also ability to regenerate: these willows quickly start growing again by developing strong new shoots from their collet and adventitious roots. High waters may give rise to anaerobic conditions, during which plants adopt another contrivance aimed at avoiding damage caused to roots by insufficient oxygen. The possible accumulation of ethanol, a toxic product of anaerobic respiration, is avoided in many ways. Numerous lenticels in the lower part of the trunk facilitate the diffusion of both oxygen to the roots and of ethanol towards the surface of the trunk. Many species of willows may produce non-toxic metabolites like pyruvic and glycolic acids. Streams in the hills and mountains of the Alps and northern Appennines are flanked by pure and mixed willow groves, whose dominant species are purple willow (Salix purpurea) and riparian willow (Salix elaeagnos). Wet and cool Appennine ravines typically contain Appennine willow (Salix apennina). Purple willow and Alpine tamarisk (Myricaria germanica) are found in sandy and silty soils which are frequently flooded. Purple willow (Salix purpurea) looks like an expanded shrub, with easily recognizable thin, flexible, purpleshaded branches. Its oblong, dark to blue-green leaves, up to 8 cm long, have serrated apexes. Its delicate catkins appear in early and mid-spring before the leaves; the males have purple, then yellow anthers. Alpine tamarisk (Myricaria germanica) is very elegant, with light, glaucous leafy fronds, pale pink flowers, and seeds characterized by tufts of stipitate hair. It is sensitive to drought and in the gravelly beds of high mountain streams, where the level of the water table varies considerably and is particularly dry in summer, it is replaced by riparian willow (Salix elaeagnos). Alpine tamarisk (Myricaria germanica) These are thick, erect shrubs with delicate, velvety grey shoots. Their linear, whole leaves are up to 20 cm long, grey when young, then dark green and downy on their underside. Their edges are parallel and revolute with acute apexes. In spring, delicate, green catkins 3-6 cm long flower with the leaves. The males have yellow anthers. According to changing climatic, geomorphological and pedological conditions, these species are associated with more thermophilic shrubs, such as almond leaved willow (Salix triandra), continental forms like dark leaved willow (Salix myrsinifolia), or typically mountainous ones like violet willow (Salix daphnoides, the Salicetum elaeagno-daphnoidis association, one of the most typical vegetal communities of Alpine valleys and therefore among the first to be described). Plants must also withstand drought during low water and their roots follow phreatic water. In particular, sea buckthorn (Hippophae rhamnoides) reduces transpiration through the xeromorphic structure of its leaves. This shrub has thorny shoots bearing linear grey to green leaves up to 6 cm long, with silvery-bronze scales on both sides. In spring, it produces tiny yellow-green flowers on racemes up to 2 cm long. In female plants, flowers are followed by round, bright orange fruit 8 mm across, particularly rich in vitamin C, which last until the following spring. Hippophae rhamnoides colonizes silicic terraces above high water level, and is particularly lush in south-facing valleys. 49 50 Willows Willows, of which there are about 300 species, usually prefer open areas in northern temperate regions, although they may be found all over the world, except in Australia. High-altitude, boreal regions, are colonized by strong and cold-resistant shrubby types, which grow tree-high in milder climates. A large number of species live on fluvial, alluvial and open soils. As willows grow rapidly and develop strong new shoots from its collets, many species are used to consolidate stream and river banks or highly eroded mountain flanks. Willows growing in dry environments have ovate leaves, which are lanceolate in species colonizing stream banks. The shape of their leaves and the considerable flexibility of their branches and trunks allow willows to bend with the current during floods, so that they avoid being broken or uprooted. In the past, the great flexibility of the twigs of almond leaved willow (Salix triandra) and purple willow (Salix purpurea) lent themselves to many forms of wickerwork. In late winter, the small flowers of willow appear before or at the same time as the leaves. Flowers do not have petals and are borne in female and male catkins on different trees. Male catkins are usually more conspicuous than female ones, and their pollen is carried by the wind. Willows also have important melliferous (honey-producing) species which produce nectar in early spring, when other flowers are rare. Small seeds develop in female capsules and are carried by the wind. They are permeable, and germinate immediately when the climate and season are favourable. This enables willow to colonize broad areas with surface Karin Ortler watertables, but it has fatal consequences when seeds fall in shady areas or insufficiently damp soils, because the small plants die immediately. In the past, the cultivation of willows was important, especially in the Po Plain, where various species were grown to produce fuel for bakeries, and were also used for basketwork, carpentry, tools, etc.. Wickerwork was not restricted to the production of baskets, but included other products such as fish traps, supports for vines and other woody plants which grow on espaliers, and strings to tie and fix the thatched roofs of country cottages. It is also worth remembering the pharmaceutical use of the glycoside salicin as an efficient febrifuge (antifever agent). This substance is extracted from the bark of almost all willow species, from which salicylic acid (now a component of aspirin) was obtained in the past. Riparian willow (Salix elaeagnos) Leaves of riparian willow (Salix elaeagnos) Morphological adaptations to currents of leaves of various types of willows. From left to right: white willow (Salix alba), crack willow (Salix fragilis), laurel or bay willow (Salix pentandra),almond leaved willow (Salix triandra discolor and Salix triandra triandra), common osier (Salix viminalis), European violet willow (Salix daphnoides), riparian willow (Salix elaeagnos), purple willow (Salix purpurea) Purple willow (Salix purpurea) Purple willow (Salix purpurea) White willow (Salix alba) White willow (Salix alba) 51 52 Areas flooded only during high water. Along mountain streams, bushes are followed by grey alder (Alnus incana association: Alnetum incanae, especially in the valleys of high-altitude mountains and dominating areas with very little humus), is replaced by black alder (Alnus glutinosa) in areas where winters are milder. These trees may grow where willow groves and Hippophae rhamnoides have previously prepared the soil by gradually collecting sand and gravel. Alders have adapted both to occasional high water and insufficiently aerated wet soil. Lenticels in the lower part of the trunk provide air to superficial, submerged roots. Roots have tubercules which contain bacteria, living in symbiosis with the plant. These absorb nitrogen from the air, compensating for the lack of nitrogen in the soil. The combination of certain conditions determines which species colonize particular areas after floods. Alder seeds germinate in the summer, when water levels decrease and enable the growth of alder. The seeds of white willow (Salix alba association, Salicetum albae, the vegetal community of alluvial plains which flanks the main rivers of the Po Plain and central Italy) and crack willow (Salix fragilis) flower in June, when mountain stream waters are high and areas for colonization are not yet available. The germination period of these seeds is limited to a few days, and they cannot be carried by water. They find more favourable conditions for their development along the lower stretches of watercourses, on sandy and silty soils, where they form thick riverbank forests. Low winter temperatures also play a fundamental selective role. Pioneer plants and willows which usually live near streams and prefer sunny areas may no longer live in the shady underbrush of alder woods. The soils of these habitats, although still at an early evolutionary stage, are enriched in nutritive substances at every flood. Thus, associations of megaphorbies (term derived from the French megaphorbiées) are usually found at the edge of alder woods and glades, e.g., bishop’s weed (Aegopodium podagraria) and figwort (Scrophularia White willow (Salix alba) nodosa). Alder In Italy, there are four spontaneous species of alder: grey alder (Alnus incana), found in alluvial soils of central-northern Italy; black alder (Alnus glutinosa, see photo), which colonizes river and stream banks and brackish woodland; green alder (Alnus viridis), typical of the Alps, usually covered with snow, where avalanches are frequent; and Italian alder (Alnus cordata), which lives in mountain woodland in southern Italian regions. Alder is suited to very damp soils and perhaps this is why many botanists believe that the Latin word Alnus derives from the Celtic “al lan”, meaning “living near banks”. Since black alder wood hardens if submerged for lengthy periods, it was commonly used for piles and other hydraulic works. Alder wood turns deep orange when freshly cut, and was thus endowed with symbolic meanings, e.g., the tree of life after death. Black alder may be higher than 30 m, round or pyramidal in shape and very strong, with easily recognizable leaves. The oval, round leaves are irregularly serrated and without a proper apex, which is usually gently lobed. The upperside is a dark, glossy green; the underside is a lighter, matt green with rusty tufts of hairs where the main veins branch. Grey alder, which grows to 10-15 m, is recognizable by its dark grey bark. Its oval leaves are up to 10 cm long and 5 cm wide, doubly serrated along the margins, with sharp apexes. The upperside is dark green and the underside grey and downy. Female and male flowers are born on separate catkins on the same tree, Karin Ortler and form in late winter or early spring, before the leaves open. Male catkins are about 10 cm long and hang in groups from the tips of branches. Their pollen is carried by the wind. Clusters of female catkins, oval and about 1-2 cm long, produce small, woody, dark brown fruit about 2 cm long. These woody nutlets stay on the tree throughout the year. Their seeds have a special structure full of air, which enables them to be easily carried by running water. Winds carry them for about 30-50 m, and they may germinate for 12 months. As alder is a pioneering plant, it grows rapidly during its juvenile stages, but seldom lives for longer than 100-120 years. Alder wood, which hardens in water, is used for hydraulic constructions. It is sensitive to exposure to air and is seldom used as fuel or as carpentry material. Its bark is rich in tannin and was once used for tanning hides. 53 54 These hygrophilous and nitrophilous plants grow rapidly to over 1 m. Among the flora of the underbrush is ostrich fern (Matteuccia struthiopteris), up to 1.5 m high, and butterbur (Petasites spp.), whose dense stalks in spring bear round, purple and white, male and female flowers on different plants. Base heart- or kidney-shaped leaves grow after flowering. Their diameter is about 60 cm and they form dense herbaceous communities. Ostrich fern (Matteuccia struthiopteris) Areas which are not subject to floods are colonized by alder and also by trees typically found in riverbank forests of hilly areas, like common ash (Fraxinus excelsior), white poplar (Populus alba) and black poplar (Populus nigra). Common ash has pinnate leaves about 30 cm long, with 9-13 small, oblong, ovate leaves, about 10 cm long and 3 cm wide. Its flowers are delicate, violet, without petals, and bloom in spring, before the leaves, from almost black buds. Its winged, hanging fruit is greenish, then light brown, and ripens in thick bunches. Poplars belong to the willow family. Their flowers, like those of willows, have hanging male and female catkins about 5 cm long (in black poplar) or 10 cm long (in white poplar). However, their seeds are larger: the small, green capsules open to release seeds covered with a white down similar to raw cotton, which are easily carried by the wind. The leaves of black poplar are triangular or ovate, about 10 cm long and wide, with glossy uppersides and Black poplar (Populus nigra) opaque undersides. The leaves of white poplar have 2-5 lobes, and are about 10 cm long and 7 cm wide. When ripe, their surface is glossy, and a dense, white down covers their underside. Another type of riverbank forest grows along streams and is characterized by Scotch pine (Pinus sylvestris). These conifers, together with willows, colonize calcareous, alluvial streams, which are submerged for only 1-2 days during exceptional years. Although Scotch pine has great ecological value (it grows in peat-bogs, on dry soils of rocky slopes or on alluvial debris), it cannot withstand floods lasting more than a few days. Butterbur association (Petasites spp.) Black poplar (Populus nigra) 55 Invertebrate fauna BRUNO MAIOLINI · VALERIA LENCIONI Benthic invertebrates are defined as small animals which live close to the substratum for at least a period of their life. Those of larger size (over 1 mm long), are called “macroinvertebrates”, of which insects constitute the most important part. In mountain streams, orders of dipterans, plectopterans, ephemeropterans and trichopterans prevail. Invertebrates in mountain streams have to face two life-threatening obstacles: current speed and cold temperature, which they overcome by contriving extraordinary adaptations. In order to contrast the current, these animals may have flat bodies (like heptageniid ephemeropterans), strong suckers (blepharicerid dipterans), and crown-shaped hooks (simuliid dipterans). The current is not only obstacle, but also produces a constant flow of food downstream, and is a good mean for dispersion. It is far more difficult for invertebrates to adapt to the cold. Many scientists consider temperature the main factor determining the ecology and evolution of aquatic and terrestrial invertebrates (egg-laying and hatching, growth rates, mating, reproductive strategies, activity models, types of food). Invertebrates living at high altitudes and latitudes have adopted various strategies to overcome the long, cold winters. Snow and ice, drought, wind, cold and little food are their most feared enemies. Aquatic invertebrates may exploit the current to move downstream and avoid freezing or drying up, or they may shelter in underground waters. But they frequently spend winters in the same place: the capacity of these organisms, particularly insects, to survive in these harsh environments is due to a series of physiological, biochemical, morphological, behavioural and ecological adaptations. Among these is the production of melanin, their small size and hairiness, capacity for feeding and mating on the ground instead of in flight (they therefore have small or totally absent wings), the building of cocoons, quiescence, diapause, and resistance to cold. Quiescence is a direct, temporary reaction to unfavourable conditions, which is interrupted as soon as conditions become favourable again. Diapause is a direct reaction to unfavourable conditions which cannot be interrupted until after a certain period of time. For aquatic insects, diapause regards eggs and mature larvae, seldom pupae, and almost never adults. Day length (photoperiod) Stonefly larva 57 59 58 Cold challenges mountain stream invertebrates Currents: obstacles for invertebrates, but also efficient means of transport is one of the factors which governs the transition between different physiological states. In Arctic environments, prolonged diapause has been recorded, i.e., organisms may even protract their inactivity for even many years, until environmental conditions are favourable (the life-cycle of some dipterans of the chironomid family may last 6-7 years). Organisms resistant to cold, i.e., able to survive to temperatures below 0°C for long periods (even many months at -40/-50°C), without damage, apply two strategies: hibernation and supercooling. Hibernation freezes their haemolymph and all their cell fluids except the cell matrix. The temperature at which crystals form and the duration of hibernation are controlled by chemical substances, such as polyhydric alcohol, sugars, amino-acids, and complex proteins of high molecular weight called THPs (Thermal Hystereris Proteins), which lower the freezing-point of body fluids by raising their density and, linking with water molecules, prevent the formation of ice crystals. Spring “awakening” is usually a quick process, whereby the same substances which enabled hibernation now provide amino-acids and carbon at thaw, when there is still little food in the environment. Hibernating insects die only when exposed to very low temperatures (-30/-50°C) for many months, when the temperature drops further (-60/-80°C) even for short periods, or when freezing and thawing cycles alternate. Super-cooling, the most typical strategy of aquatic insects, enables them to survive when temperatures drop below 0°C (maximum –20°C) for long periods, during which their body fluids remain liquid. The freezing point of these insects shifts from –5/-10°C (as in most insects) to –20/-25°C, as they may eliminate or reduce substances which favour the formation of ice, and their body fluids take in anti-freeze substances similar to those used by hibernating insects. Glycerol is frequently accumulated as an anti-freeze, and may constitute up to 10-14% of the weight of the animal. 60 Taxonomy of invertebrates Triclads. Triclads, or planarians, are characteristically found in cool, mountain streams rich in oxygen, especially if small and of spring origin. These small animals are easily identified by their extremely long and flat bodies which remain tenaciously attached to the substratum, even in particularly fastflowing waters. They prey on small invertebrates such as insect larvae, crustaceans, gastropods and annelids, but may also feed on carrion. In the upper course of mountain streams, the most common species is Crenobia alpina, well adapted to fast water speeds and low temperatures. Further down, we find Dugesia gonocephala and Polycelis felina. Although fewer than 20 species are known in Italy, mostly typical of slowflowing or standing waters, their presence in streams may be relevant Planaria Bruno Maiolini · Valeria Lencioni with regard to population density and influence on macrobenthic communities, as they are specialized predators. Molluscs. There are few molluscs in mountain streams, as most freshwater species prefer still or slow-flowing waters, due to their scarce mobility and found in areas of submerged vegetation. They crawl on the bottom or swim freely in water among aquatic plants. They are detrivorous, herbivorous, or even carnivorous. Tubificids and lumbriculids are generally found in fine sediment, feeding on bacteria associated with the sediment itself. Tubificids may abound in sediments rich in organic debris and are generally dominant at depths exceeding one metre. Enchytraeids, which may also colonize terrestrial environments, are present where waters are rich in oxygen, particles are coarse and currents fast. Among the oligochaetes which populate running waters, only naidids, lumbriculids and tubificids are strictly aquatic families, of which the first two are generally found in glacial and non-glacial reaches above the tree-line. Ancylus fluviatilis difficulty in finding the right food. A few species constitute an exception, one of which is the pulmonate Ancylus fluviatilis. Middle-shallow reaches feature species of the genus Pisidium, small freshwater mussels which live in sandy or pebbly substrates. Oligochaetes. Oligochaetes colonize various freshwater environments and are found in several stream microhabitats: sandy or muddy bottoms, hard, pebbly or gravelly substrates, areas with deposits of organic debris or submerged vegetation, etc.. Small oligochaetes (some naidids, for example), may also colonize interstitial environments. Naidids are frequently Hirudineans (leeches). Hirudineans, better known as leeches, are mostly freshwater species found in running and standing waters. They adhere to the substratum and move by means of suckers, thus requiring environments with hard substrates like rocks, stones or pebbles. The torrential reaches of rivers are therefore optimal for species which prefer running water. Their presence is limited upstream by temperature (they cannot reproduce at temperatures below 10-11°C) and downstream by increased sandy or muddy substratum. Few species are found in intermediate stretches, like Erpobdella testacea, E. octoculata and Dina lineata, all preying on other benthic invertebrates and resistant to moderate organic pollution. Other species (Dina krasensis, Trocheta bykowskii) may live in streams at low altitudes, even in large numbers. Mites. Mites (see drawing) are arachnids a few millimetres long; they abound in soil fauna, particularly in stream beds, where they provide an excellent example of adaptive radiation, with tens of thousands of known species. Only a few families have adapted to life in freshwater (water mites). A group of families, known as hydrachnids, count thousands of species in freshwaters, and even halacarids, a sea taxon, may be found in freshwaters. Mountain springs and interstitial environments are among the freshwater environments colonized by the most interesting water mites. In springs, water mites constitute an important part of the so-called crenal fauna, typical of these habitats, which requires perennial, clean springs. In the interstitial environment, i.e., in gravelly and sandy stream beds, species have devised adaptations for life in subterranean water: they have no eyes and are colourless. The biological cycle of freshwater mites is extremely complex, being exceptional right from the beginning: eggs do not originate larvae; rather, pre-larvae develop inside eggs. The latter turn into larvae which leave the eggs and become parasitic on aquatic insect larvae (especially chironomids), the internal liquids of which (haemolymph) they suck. Insect larvae are also exploited as “means of transport” which carry larvae 61 62 to new habitats (phoresis). From this point onwards, the cycle becomes even more complex and develops in three successive steps (protonymph, quiescent; deuteronymph, similar to an adult but with three pairs of legs, free and predatory; tritonymph, quiescent again). Tritonymphs finally develop into adults with four pairs of legs, like all arachnids, bodies divided into two parts, front (gnatosome, bearing mouth parts) and rear (idiosome, bearing legs). The body surface is covered with bristles and glands, which probably emit an unpleasant smell and protect water mites from predators. All water mites prey on other aquatic invertebrates and are very sensitive to water quality. Italian springs and streams are colonized by many genera and species, the most common of which are Lebertia, Hydrovolzia, Partnunia, Sperchon and Thyas. The phoretic or transport stage of their life-cycle explains why endemic species of mites are so rare; most aquatic species are widely distributed and may be found randomly almost everywhere in the Alps and Appennines. Alpine streams; they are absolutely the most common organisms of our planet, and have colonized all habitats containing water (seas and oceans, lakes, ponds, marshes, rivers and streams, even tiny pools in tree-trunks, mosses and wet soil, caves, interstitial waters, and even the small lakes which form in favourable conditions in Himalayan glaciers at 5000 m a.s.l.). These crustaceans have unmistakable features: they have only one eye (Cyclops is one of the most common genera) and their bodies have two long antennules and two short antennae, with five pairs of legs (the term copepod derives from the Greek meaning “oarfeet”) ending in a pair of caudal rami bearing long bristles. The female bears one or two egg-sacs; the eggs hatch to become larvae (nauplia), which are very different from the adults and, after a number of moults (generally five) they turn into sub-adults (copepodids), which do not reproduce. After five further juvenile stages, copepods become adults after the sixth moult. Sexes are easy to determine because most male copepods in Italian streams Crustaceans. In mountain streams, most crustaceans are less than 1 mm long, and belong to the so-called “meiofauna”. These organisms live on the bottom of slow-flowing watercourses, in close contact with the substratum (epibenthic) or inside it, between gravel and sand granules (interstitial fauna), even at considerable depths. Copepods are undoubtedly the most numerous crustaceans in springs and Harpacticoid copepods (Bryocamptus tatrensis) mating have swollen, prehensile antennules which they use to seize females during mating. Moss and interstitial species which are frequently found in high-altitude streams and springs belong to the harpacticoids (particularly to the genera Attheyella, Bryocamptus, Maraenobiotus, Hypocamptus, Moraria and Parastenocaris). Some species are very rare and only found in restricted areas of the Alps and Appennines; others are typically boreoalpine, distributed in areas including northern Europe and the Alps (seldom in higher mountains on the Appennines) traces which reveal their much wider distribution during glaciations. Cyclopoid copepods prefer downstream reaches, and many members of the genera Acanthocyclops, Diacyclops and Speocyclops are found in interstitial environments. Besides copepods, spring and interstitial habitats typically contain other small crustaceans. In karstic springs, ostracods may be locally found in large numbers. Their body is enveloped in a bivalve carapace (ostracod derives from the Greek word meaning shell) which protects the soft parts of the body and its appendices. They are round or beanshaped. Ostracods also feature blind and depigmented interstitial species. Among the most common genera in the Dolomites (large quantities of calcium are indispensable for the development of their carapace) are Potamocypris, Pseudocandona, Cypria (see drawing), and the rarer Cavernocypris and Cryptocandona. In interstitial habitats, other taxonomic groups of crustaceans are only occasionally found, such as cladocerans, widely distributed in surface environments, and exceptionally, the blind depigmented members of the order Bathynellacea which, although limited to subterranean waters, have recently been found in the Alps at high altitudes. Larger crustaceans are more common in some streams, particularly amphipods, which are found in large numbers downstream. Their biomass makes them one of the most important food sources for fish. They are generally associated with middle-shallow stretches and slowflowing waters. At high altitudes, they are present only in a few relict sites. Along the Alpine chain, Gammarus fossarum, G. balcanicus and Echinogammarus stammeri are common species. In the Appennines, they are replaced by Gammarus aff. italicus, Echinogammarus veneris and E. tibaldii. Other crustaceans found in springs and interstitial habitats are completely blind and depigmented, and belong to the genus Niphargus, with about 100 species in Italy. N. strouhali often lives in mountain streams and prefers elevations exceeding 2000 m a.s.l.. This genus has recently been found in interstitial environments at high altitudes, e.g., in glacial streams at the foot of the Bernina massif (Switzerland). Other crustaceans colonize low-altitude streams, and are only exceptionally found in mountain stretches. 63 64 Freshwater crayfish (Austropotamobius pallipes fulcisianus) Among these, freshwater crayfish (Austropotamobius pallipes fulcisianus) are widely distributed. They belong to the decapod order and prefer clean, well-oxygenated stretches at low elevations, but in particular conditions (Trentino), they may be found at 1500 m a.s.l. Crayfish are common in northern Italy and colonize the Appennines down to the Basilicata region, decreasing in number southwards. In the past, they were much more numerous and widely distributed, but were harvested indiscriminately for long periods, since they are delicious to eat. In recent years, their numbers have fallen still further, partly owing to their sensitivity to worsened water quality. Today, many regional laws forbid them to be taken, and they are further protected by the Habitat Directive of the European Community. Ephemeropterans (mayflies). Ephemeropterans owe their name to the short span of their adult life (in Greek, ephemeros = lasting one day, and pteron = wing). The masticatory apparatus of adults does not often function and they can only live as long as their store of energy, accumulated during their aquatic larval stage, lasts. They are found in lakes, marshes and ponds, but also running waters, preferably at middle-low altitudes. Many species tolerate moderate organic pollution, and considerable numbers may therefore be found in quite poor-quality watercourses. In Italy, 94 out of 300 European species are found. Mayflies are considered a primitive order, similar to odonates, with a hemimetabolous development. The ecological role of mayflies in mountain streams is one of considerable importance and, if conditions are favourable, they may prevail over the macrobenthic community, both in number of individuals and total biomass. Most nymphs are herbivores and are an important source of food for other aquatic invertebrates and fish. After emergence, they become the prey of many birds, bats and fish which catch them during the delicate stage of metamorphosis, often on the water surface. Fishermen are aware of this, and adult mayflies are the most imitated in the refined art of artificial bait construction. Mayflies occour in various fluvial microhabitats and resort to peculiar morpho-physiological adaptations. Four genera belong to the heptageniids (Epeorus, Rhithrogena, Ecdyonurus and Heptagenia) and, as nymphs, share dorso-ventral flattening. Their hydrodynamic aspect, with flattened head, abdomen and legs, is enhanced by the shape and position of abdominal gills, used as efficient suckers to increase their adherence to the substratum. Thus, nymphs can tolerate strong currents by remaining in the thin Mayfly nymph of the genus Baetis layer close to the substratum where water flow is slow. The most common species found in high-altitude stretches belong to this family: Epeorus alpicola, E. sylvicola, Rhithrogena loyolaea, R. alpestris and Ecdyonorus helveticus. The only Italian species of the oligoneuriid family - Oligoneuriella rhenana - has characteristics similar to those of the heptageniids, and lives in fast-flowing Alpine and Appennine streams. The nymphs of these two families are generally flat-bodied, and are also called lithophilous, as they live on the surface of stones and submerged rocks. A second group (hyponeophiles) of families includes water nymphs, whose tapering, hydrodynamic body has three strong, fringed caudal filaments, used as efficient rudders or oars. Baetids and siphlonurids belong to this group, the latter represented in Italy by only one species. They are typically found in lakes and slow-moving waters. The many species of the large family of baetids usually live in the middle-low stretches of mountain streams. Some, like Baetis alpinus, which is found in many Italian regions, may colonize upstream reaches. B. rhodani is also common in streams and has great ecological value, being found in both polluted and unpolluted downstream stretches. A third group of nymphs has adapted to crawling on the bottom (herpophiles) and includes the caenid, leptophlebiid and ephemerellid families. These mayflies are generally associated with slow-moving waters rich in organic sediments, but may locally abound at middle-low altitudes. There are also burrowing nymphs (oryctophiles), belonging to the ephemerid and polymitarcid families, with modified mandibular processes and forefeet which enable them to dig tunnels in river and stream bottoms. A few live in stream stretches, as they prefer slow-flowing waters. The only exception is Ephemera danica, locally abundant, inhabiting gravel and sand streams. Subimago of a mayfly of the genus Baetis 65 This order is divided into two groups, zygopterans or damselflies, and anisopterans or dragonflies. In the former group, only one genus lives exclusively in running waters, Calopteryx, with three Italian species (C. virgo, C. splendens and C. haemorrhoidalis) found at middle-low altitudes. The latter group includes two families with species adapted to running water, cordulegastrids and gomphids. The former has only one Italian genus (Cordulegaster), which includes a few very large species, whose larval stage occurs in slower areas of streams. Gomphid nymphs are flatter and stumpier, and live in the mud and gravel of mountain stream beds. 66 of sound signals, which are produced by drumming the substratum with their abdomen. This phenomenon has been thoroughly studied, and the recording and analysis of sounds reveal that these are true languages. The rhythm of beats and the frequency of sequence repetition differ between species and sexes. In some cases, even “dialects” have been recorded in populations of the same species but geographically apart. Stoneflies of the northern hemisphere (Palaearctic and Neartic) are divided into two large groups: Systellognatha and Euholognatha. The buccal apparatus of adults of the former group does not Cordulegaster bidentatus Odonates (dragonflies and damselflies). Dragonflies and damselflies are the largest insects with larval stages (up to 6 cm long). The adults are excellent fliers and may be seen far from the point of their emergence from the water. They then colonize many aquatic environments including standing or slow-flowing waters. A few species live in stretches or pools at the edge of streams, rich in aquatic vegetation. Nymphs, like adults, prey on other invertebrates and vertebrates, especially tadpoles and fry which they catch with their typical buccal apparatus, called mask. This looks like a pair of pincers, which are kept folded when at rest and snap forward to grasp the prey. Therefore, their method of hunting is by stalking, during which motionless nymphs mimic aquatic vegetation. Plecopterans (stoneflies). Plecopterans, or stoneflies, derive their name from the Greek pleco = fold, and pteros = wing, due to the typical position in which adults keep their wings at rest, folding them scissorswise to cover their abdomen. This is probably the most typical order of benthic fauna in mountain streams, since many species are particularly suited to cold, welloxygenated, clean and fast waters. This, and downstream pollution of rivers, confines stoneflies to streams at altitudes over 600-700 m. Their distribution is not only limited by their strict ecological requirements (stenoecious nature), but also by the poor flying skills of the adults. Over 3000 species are known in the world, 400 of which belong to European fauna. In Italy, 144 species are known, divided into 21 genera grouped in 7 families. One peculiarity of stoneflies is their use Stonefly nymph of the genus Perla function, making it impossible for them to feed. Nymphs are generally omnivorous and good predators in the last stages of their development. Euholognatha include species which feed as adults, meaning that they may lead a subaerial life for some weeks. Both adults and nymphs are phytophagous or detritivorous and feed on algae, mosses and vegetal debris. Their development is hemi-metabolic and their larval stage lasts for about one year, although biennial cycles are known, e.g., in Dinocras cephalotes. A large number of moults is necessary to achieve the adult stage, ranging between 10 and 20, with a maximum of 33 in Dinocras cephalotes, the largest species, the winged females of which are over 30 mm long. When mature, nymphs leave the water and have their last moult, to become adult insects. This generally occurs in spring, but there are many known cases of winter emergence from the water, with flying adults which mate on snowy shores. There is usually only one generation a year (univoltine species), but in favourable conditions, a second autumnal generation may follow the first (bivoltine species), e.g., Nemurella pictetii. Nymphs generally look like mayflies, but have only two caudal cerci and lack leaflike abdominal gills. Nymphs of stoneflies, although typical of mountain streams, are not particularly suited to life in water, and colonize microhabitats characterized by slow currents, like leaf debris, the lower parts of stones and rocks, and the quiet waters of pools. Stoneflies are widely distributed in all mountain streams and, in favourable conditions, constitute more than 50% of the macrobenthic population. After dipterans, they are the group most frequently found in high-altitude streams, even with large species, like Dictyogenus fontium, populations of which have been found in the Alps at elevations over 2800 m a.s.l. Other smaller species living upstream (rheophilous-orophilous species) are Protonemura ausonia, P. caprai, P. elisabethae, P. brevistyla, Nemoura 67 68 Adult stonefly of the genus Chloroperla mortoni, N. obtuse, Leuctra rosinae, L. festai, L. teriolensis, Isoperla rivulorum, Perlodes intricatus, Siphonoperla montana and Chloroperla susemicheli. At middle altitudes, there are medium and large species like Perla grandis, Dinocras cephalotes, D. ferreri, Dictyogenus ventralis, Perlodes intricatus and Isoperla rivulorum. The genus Tyrrhenoleuctra, with only one Italian species - T. zavattarii - deserves special mention. It is found in Sardinian and Corsican streams. Heteropterans (bugs). Bugs are commonly found in aquatic environments, in both larval and adult stages. Their name derives from their two “different wings” (hetero = different; pteros = wing), i.e., partially sclerotized front wings and totally membranaceous rear wings. Nymphs are very similar to winged adults, and turn into adults by means of gradual transformations in shape and size called paurometabolous metamorphosis. Aquatic bugs prefer quiet waters, although many species are found in running waters, near shores, in pools, in calm river sides, and generally where water current is slow. Some bugs called gerrids live on the water surface, and others, nepids, live underwater. The former walk or skate on water surface exploiting the superficial tension, the latter walk on the bottom or swim in the vegetation. Most of them prey on other insects, such as mites and spiders. Larger species suck tadpoles, fry and the eggs of amphibians and fish. Smaller species are omnivorous and also feed on benthic meiofauna, microscopic algae and organic debris. Among the most common genera in streams are Gerris, Aquarius and Velia. Aquarius najas lives exclusively in streams, in calm stretches and pools. Coleopterans (beetles). Beetles represent the largest animal order, with at least 350,000 species, 10,000 of which belong to Italian fauna. Some families are found both in standing and running waters. They are the only holometabolous insects which live in aquatic environments as both larvae and adults. Adult water beetles can always fly and seek better environmental conditions. There are two categories: swimmers, such as diving beetles (Dytiscidae), crawling water beetles (Haliplidae) and water scavenger beetles (Hydrophilidae), and walkers, represented by long-toed water beetles (Dryopidae), riffle beetles (Elmidae), minute moss beetles (Hydraenidae) and another family of crawling water beetles (Helophoridae). The former have fringes of swimming hairs on their legs, and the latter have strong claws to cling to the substratum. Aquatic adults have tracheal respiratory systems like those of terrestrial species, and have contrived adaptations to store air for their quite long immersions. Diving beetles, water scavengers, crawling water beetles, and minute moss beetles sometimes emerge to store air. They adopt different positions in order to store oxygen. Diving and crawling water beetles, for example, stand on their heads, obliquely, until the rear part of their body touches the air-water interface. They then capture an air bubble, which they tuck in the chamber under their wing surface, i.e., in the cavity between abdomen and elytrum. Exhaled gases are released as bubbles. Instead, water scavengers, minute moss beetles (see drawing) tilt their bodies upwards and convey air to the chamber under their wing surface through their antennae. Minute moss beetles are aquatic only as adults, whereas marsh beetles (Helodidae) are aquatic only as larvae. Larvae and adult beetles eat various kinds of food. Among adult water beetles, diving beetles are predators, water scavengers are omnivorous, and the other families are generally herbivorous. Larvae of diving and water scavenger beetles are predators, larvae of crawling water beetles are herbivorous suckers and the other families are herbivorous/detritivorous. Aquatic beetles prefer river bank environments characterized by slow, shallow waters, rich in vegetation and organic matter. This is why they are not found in upstream stretches, where fastflowing water, stream bed instability and severe erosion make colonization difficult. They may live at higher altitudes in perifluvial wet areas, the ecological role of which is that of “refuge areas” where environmental conditions are not so extreme. Dipterans. The order of dipterans includes the highest number of species in the class of insects. With the sole exception of oceans, dipterans colonize almost all environments during the different stages of their life-cycle. They include more than half of all aquatic insects and, in the larval stage, live in a large number of environments - streams, lakes, ponds and marshes. Their development is complete, with terrestrial or aquatic larval stages and subaerial adult stages. Some species are semi-aquatic and live in wet soil, rotting hollows in plants or animal carcasses. Larvae of dipterans feature all nutrition models, including plant feeders, detritus feeders and predators. The name of these animals, “with two wings”, derives from the fact that adults have only one pair of front wings, since the rear ones are transformed into equalizers (appendices with a club shape) which are used as flight stabilizers. According to the shape of the antennae in adults, dipterans are divided into two sub-orders, nematocerans and 69 70 Larvae of non-biting midges (Chironomidae) brachycerans. The former have long moniliform antennae made up of many joints, a slender body like that of mosquitoes and long, thin legs. Brachycerans are characterized by short antennae and a stocky aspect, like flies. Dipterans include a large variety of forms and adaptations, and may colonize highly polluted or environments which are “inhospitable” for most insects, like wastewater, sulphurous and thermal waters and cold glacial streams. This is due to the ability of larvae to tolerate low concentrations of dissolved oxygen, owing to oxygen storage induced by respiratory pigments similar to haemoglobin (e.g., Chironomus of the group thummi), or anaerobic respiration (i.e., without oxygen). Larvae are sub-cylindrical, thin and worm-shaped, or fleshy and stocky (dorso-ventral flattened shapes are rare), and are characterized by jointless legs. They may have pseudopods (false legs) in various positions, with or without hooks, spiracles, tubes or respiratory filaments. During the pupal stage, individuals may be free or enclosed in rigid envelopes, in the water or on the soil. Adults generally live for about one month, during which mating (in flight, on vegetation, the ground or even in water), and egg-laying occur. Dipterans include various haematophagous adult species which attack humans and other warmblooded vertebrates (ceratopogonids, culicids and simuliids are known for their irritating bites), and they may also carry diseases. Although the order features many different forms, single families are characterized by uniformity of shape. Nematocerans have completely sclerotized and evaginated heads (cephalic capsules), which are therefore clearly visible (eucephalous larvae), or small, only partially sclerotized heads, set deep in the thorax (hemicephalous larvae). Larvae of brachyceran species are, with rare exceptions, hemicephalous or acephalous, i.e., their heads are very small, with few sclerotized parts, and partially or completely set inside the thorax. Body segmentation is usually evident, but thoracic and abdominal areas are not clearly distinguished. The larvae of many dipterans, particularly those with aquatic juvenile stages, are little known, and it is often necessary to breed them to their adult stage to identify the species. The most numerous families of nematocerans in mountain streams are net-winged midges (Blephariceridae), biting midges (Ceratopogonidae), non-biting midges (Chironomidae), dixid midges (Dixidae), moth flies (Psychodidae), blackflies (Simuliidae), solitary midges (Thaumaleidae) and craneflies (Tipulidae and Limonidae). Among brachycerans are houseflies (Anthomiidae or Muscidae), snipe flies (Athericidae), long-legged flies (Dolichopodidae), dance flies (Empididae), and soldier flies (Stratiomyidae). Non-biting midges and black flies are the largest groups in high-altitude streams, and the only ones present, apart from a few exceptions, in glacial streams. Proceeding downstream, we find dance flies and crane flies and, still further down, solitary midges, net-winged midges and snipe flies. Chironomids (non-biting midges). The family of chironomids is the largest in freshwater environments, both for number of species and individuals. About 15,000 species are known in the world, 400 of which are found in Italy. They are divided into 8 subfamilies, 5 of which live in Italy: Tanypodinae, Diamesinae, Prodiamesinae, Orthocladiinae and Chironominae. Adults live in an aerial environment but, as larvae, they colonize various freshwater environments, such as lakes and mountain streams, rivers, ponds and pools, clean waters rich in oxygen as well as very polluted ones, both poor (oligotrophic) and rich in nutrients (eutrophic). Some species colonize sea water, particularly areas between low and high tide, and others live on land. Thus, non-biting midges are a definitely cosmopolitan group of insects. They include many species of high ecological amplitude (euryecious), but also stenoecious ones, i.e., they are unable to live in conditions different from those to which they have become adapted. Therefore, they are good biological indicators as they reveal even 71 Larvae of midges (Diamesa, Chironomidae) minimal variations in the environmental conditions in which they live. For example, the presence of Diamesinae larvae in watercourses, and particularly species of the genus Diamesa, such as D. steinboecki, indicates “glacial” conditions, as they are typical of these environments. In mountain streams, non-biting midges are certainly the largest group of dipterans, both in terms of number of individuals and species. At high altitudes and in extreme environments, like the upstream stretches of mountain streams, chironomids are usually the only invertebrates. A clear longitudinal succession is not only evident in species, but also in subfamilies. In upstream stretches, where waters are cool and well-oxygenated, Diamesinae and Orthocladiinae abound. These two subfamilies include several rheophilous and cold stenothermal species, i.e., adapted to life in the fast-flowing, cloudy and always cold waters of glacial streams. In particular, larvae of Diamesa spp. have contrived several adaptations 72 to fast currents and unstable substrates, like a) long and strong claws with which to cling to the bottom; b) elongated rear pseudopods to cling to larger stones and increase the stability of larvae; c) construction of sand “tubes” cemented with saliva to protect themselves from the current. Besides these strategies, many of them colonize small depressions in pebble surfaces, to avoid being crushed by stones rolling in the stream bed. These species feed on organic matter originally carried by the wind (spores, pollen, vegetal fragments, dead insects), which is trapped in ice and released in stream water during the thaw. The length of chironomid larvae ranges from 2-30 mm and their colour from grey to dark yellow, violet, orange, red and green. Some species of the Chironominae subfamily (e.g., Chironomus of the thummi group), are typically red: these are the ordinary “bloodworms” on which aquarium fish often feed. In nature, they live in waters characterized by high organic pollution. Their blood-red colour is due to the presence in their haemolymph of a respiratory pigment very similar to human haemoglobin, which enables them to survive even in poorly oxygenated environments. All larvae are worm-shaped, i.e., have elongated, segmented bodies, often covered with bristles and without real legs. They only have two pairs of hooked “pseudolegs”, front and rear, with which they cling to the substratum. The lives and even the shapes of chironomid larvae are considerably determined by their feeding habits. Some larvae are herbivorous and scratch the algal and bacterial cover of the substrates they colonize; others are detrivorous and collect particles of organic debris from the bottom; and yet others are carnivorous and prey on small animals. These generally belong to the Tanypodinae subfamily. Predatory larvae have contrived various adaptations to this kind of life: a barely sclerotized chin, in order to swallow prey whole, scythe-shaped jaws like pincers, a large, sclerotized tongue which rolls backwards to push the prey down the pharynx, retractile antennae on hydrodynamic heads, and greatly elongated pseudopods to move quickly and jerkily. In other subfamilies, sclerotized chins and oblique-moving jaws scratch algae and debris off submerged surfaces. Non-biting midges living on the sandy-muddy bottoms of lakes generally produce tubes, in which the larvae create currents of water by waving their bodies to and fro. This movement conveys food particles (algae, bacteria, etc.) to a specially constructed net, which is produced with their own saliva and lies on the bottom. Periodically, the larvae swallow this net and replace it with a new one. Some species burrow thin tunnels in the submerged leaves of aquatic plants. Others are symbionts or parasites of other invertebrates. Pupae and larvae have similar sizes and colours, but the front part of their body is swollen with the cases of adult antennae, legs and wings. Pupae may swim freely or, for those species living in tubes, remain partially enclosed in the larval tube itself. The length of adults ranges from less than 1 to about 14 mm and they have very long antennae, feathery in males. Their thin body looks like that of mosquitoes, but chironomids have a humped thorax which partially shields their head, and sucking mouth parts instead of biting ones. This is why chironomids are known as “non-biting midges”. Their long legs shake in a typical way during flight, so that they appear to be “gesticulating” (their name comes from the Greek chironomeo = to gesticulate). Females lay eggs on the water surface or near the shore, gathering them in gelatinous masses which may be free or attached to the substratum. The new-born larvae moult 4 or 5 times before metamorphosis. Emergence may occur in spring, summer and/or autumn. Adult life is short and there is only time to mate and lay eggs. As regards altitudinal distribution of chironomids in streams, higher stretches, where water temperature in summer never exceeds 3-4°C, are dominated by the subfamily of Diamesinae with the genus Diamesa, represented by species like Diamesa steinboecki, D. latitarsis, D. goetghebueri, D. bertrami and D. zernyi. Another Diamesinae found in upstream stretches, and sometimes the most frequent (in non-glacial streams) is Pseudokiefferiella parva. In the same stretches, Pseudodiamesa branickii may also be found, particularly between mosses and algae. Together with Sketch representing the life-cycle of non-biting midges (chironomid dipterans): eggs ( 1 ); larva ( 2 ); pupa ( 3 ); adult or imago (male 4 and female 4 ) 73 74 Diamesinae, there may also be Orthocladiinae, such as Orthocladius rivicola gr., O. frigidus, Eukiefferiella minor/fittkaui, E. claripennis gr. and Tvetenia calvescens/bavarica. At medium altitudes, Orthocladiinae becomes the largest subfamily, for number of individuals, genera and species (Chaetocladius piger gr., Heleniella ornaticollis, Corynoneura spp., Thienemanniella partita, etc.). Diamesinae and Orthocladiinae are replaced downstream by Chironominae, particularly Micropsectra atrofasciata gr. Simuliids (blackflies). Together with nonbiting midges, blackflies are the first colonizers of high-altitude streams, where they may assemble in large numbers if conditions are favourable. Their larval stage is spent in running water, particularly in fast-flowing stretches. Adult specimen of black fly 75 Larvae of black flies (simuliid dipterans) The special technique adopted by blackfly larvae to move upstream They are a very old group, as shown by a fossil pupa which dates back 160 million years, well into the Jurassic period. Today, 1500 species are known, 400 of which live in Europe and 70 in Italy. The life-style of blackflies is particularly interesting at both larval and adult stages. Larvae are typically pearshaped, with a swollen abdomen. They feed on fine organic particles and bacteria, which are filtered by special organs called cephalic or mandibular fans. These derive from the transformation of labial parts which evolved into fans, formed of a series of rami, generally between 30 and 50, upon which many hairs grow, creating an efficient capturing system. The larvae have silk glands which produce a viscous liquid with which they adhere to the bottom, by means also of hooks at the end of their abdomen and on their single thoracic pseudopod. The two series of hooks alternate with new adhering systems, enabling them to move on smooth surfaces upstream, in search of micro-habitats where the current is faster and more water can be filtered. The silk glands are also used when moving downstream. In this case, the larvae stick silt to the substratum and quickly spin a “safety rope”, holding on to it until they reach the desired position. This original system enables the larvae of black flies to occupy even smooth surfaces of rocks exposed to the current, where few invertebrates can resist. Thus, they may avoid competition for space and the danger of being preyed upon. In stream beds with macrophytic vegetation, these larvae adhere to various plant parts, and a single emerging grass stem may host up to 200-300 of them. The larvae have 6-9 instars until they build a triangular envelope in which they begin their metamorphosis. In the Prosimuliinae subfamily, the envelope is very small and its shape is not well-defined. Adults look like small, humped flies, with a “flattened” nose (from which their name derives), and the females of many species are haematophagous (bloodsuckers). A “blood meal” is needed to take on organic iron to ripen eggs. Very restrictive conditions govern which host’s blood is sucked and thus some species attack birds (subgenera Eusimulium, Nevermannia), horses (subgenus Wilhemia) or bovines (Prosimulium latimucro, P. rufipes, Simulium ornatum, S. intermedium, S. variegatum, S. paramorsitans). If cattle are severely attacked, an intense anaphylactic reaction may even kill the animals, and in Alpine areas there have been cases of murrain since the early 1970s. As attacks occur during the day and never in closed areas, serious damage may be avoided by quickly providing shelter. Humans may also be bitten, generally with no complications except for those who suffer from allergic reactions. The development of larval groups of black flies is helped by slightly increased organic pollution, and consequent larger numbers of bacteria and organic particles in the water. High levels of pollution limit the presence of these flies, because smooth surfaces are covered with bacterial and periphytic covers. The altitudinal distribution of species is 76 relatively predictable, as many species are closely linked to their environment (stenoecious). Upstream areas are characterized by the Prosimuliinae subfamily and some species (Prosimulium latimucro and P. rufipes) may colonize the lower stretches of Alpine glacial streams, where the mean temperature is about 0°C. In Appennine areas live P. albense and P. calabrum, the former extending as far as Sicily, the latter proper to Calabrian streams. At lower altitudes, besides Prosimuliinae, there is also the large Simuliinae subfamily which belongs to the subgenus Nevermannia, found in both Alps and Appennines, such as Simulium vernum. Typical Appennine species are S. fucense and S. marsicanum. In medium stream stretches, there are many species of the subgenera Simulium, Eusimulium, Obuchovia and Tetisimulium, of which some (Simulium ornatum and S. variegatum) are tolerant or highly tolerant (S. intermedium) of organic pollution. Limoniids (crane flies). Limoniids are a dipteran family with many species (about 320 in Italy), most of which are found in northern regions; larvae are usually terrestrial although a few live in streams. The larvae of some species typically live on muddy banks, others live in silk tubes covered with debris between emerging plants, and may be herbivorous, detrivorous or carnivorous. The most common genera in high-altitude streams are Dicranota, Rhypholophus and Tricyphona. Thaumaleids (solitary midges). In Italy, there are 14 species belonging to 4 genera, of which Thaumalea is the most common in the Alps. The larvae are very similar to those of chironomids and may easily be confused. They differ for their cephalic capsule, which is slightly flattened, setose and covered with small dorsal protuberances. They have only two pseudopods, front abdominal and rear, and a large sclerotized dorsal plaque on each segment of their body. Thaumaleid larvae are frequently found in mountain streams on rocks either splashed or covered by a thin layer of water (hygropetric larvae). Blepharicerids (net-winged flies). Among dipterans, these are the best suited to life in fast-flowing waters, due to the peculiar and unmistakable “architecture” of their larvae (see drawing). The dorsal part of their body is made up of a series of round arches which can withstand the pressure of the current. Their ventral part has strong suckers which enable them to adhere to the substratum even under powerful waterfalls. Blepharicerids have the most functional and complete suckers of all insects: they have a real air-pump, made up of powerful muscles. This produces a vacuum, enabling them to adhere to the substratum perfectly. Each adhesive disc has a front slit to detach the sucker and to allow movement. They have segmented abdomens and small, conic pseudopods, branchial tufts and lateral appendices. The larvae feed by scratching the bacterial or periphytic covers of the substratum, usually large, smooth surfaces washed by fast-flowing water. Pupae, like larvae, live attached to the substratum in the same environments, and their size is similar to that of mature larvae (5-12 mm). The pupae adhere to the substratum with 3 or 4 suckers located ventrally along both sides of the abdomen. Net-winged midges are considered indicators of good environmental quality, as they are very sensitive to several forms of pollution. This is not only due to their physiological intolerance to chemico-physical variations in water, but also to a series of indirect effects, above all reduced adherence to the substratum caused by the overgrown bacterial covers, filamentous algae and mosses which coat the surfaces of eutrophic environments. The poor mobility of the larvae and their habit of colonizing the upper part of stones makes blepharicerids sensitive to sudden variations in water flow typically streams which are subject to hydroelectric regimes. The presence of these animals indicates good trophic and hydraulic conditions. In Italy, there are 5 genera and 13 species, all living in freshwater. Among these, Liponeura cinerascens with its two subspecies minor and cinerascens, lives at high altitudes, in the Alps and in the ridge between the Appennines and the Maritime Alps. Athericids (snipe flies). This is a small family of brachycerans, with aquatic larvae and adults which sometimes suck the blood of other arthropods or mammals (see drawing). They are frequently found in streams with low or moderate quantities of organic matter. The larvae live in calm areas of the stream, burrowing in sand or gravel, under the bark of submerged branches, or on mosses. The females of many species lay eggs in a peculiar way: many of them gather on the branches of a tree suspended over water, lay masses of eggs, and then die, remaining suspended from the branch. Later, the larvae plunge directly into the water below. Three species are usually found in streams: Atherix ibis, Ibisia marginata and Atrichops crassipes. Empidids (dance flies). This is a large family, with 270 species known in Italy. It is widely distributed and lives in almost all environments, including high altitudes (over 2000 m). The larvae may be terrestrial, aquatic or semi-aquatic. In streams, they live among mosses and stones, or on fine, wet sediments on the bank. Their cephalic capsule is small and their mandibular hooks are particularly welldeveloped. This is due to the feeding habits of the larvae, which prey on simuliids and chironomids voraciously. Other dipteran families. These families include species which live in peculiar environments, like drain residues, waste, thermal and sea 77 78 waters. Among these are moth flies (Psichodidae), biting midges (Ceratopogonidae), houseflies (Muscidae) and soldier flies (Stratiomyidae). These families generally live in areas of streams rich in organic debris, submerged vegetation or fine sediments (sand and silt). Trichopterans (caddisflies). Trichopterans derive their name from the Greek words trichos (hair) and pteros (wing). Flying adults look like butterflies with hairy, light-coloured wings. When at rest, the four wings fold roof-like to cover the animal. More than 300 species are known in Italy, divided into 20 families. Adults are crepuscular or nocturnal, and often fly in large swarms in autumn evenings near watercourses or lights. The life of the larvae is particularly interesting, aquatic in both running and standing waters (except for the genus Enoicyla, which lives on land). The uniqueness of trichopteran larvae lies in their ability to construct variously shaped cases for different purposes. As regards larval shelters, trichopterans may be divided into three groups: with mobile, fixed, or free cases. Most species belong to the first group. They construct cases around their bodies to protect themselves and to increase their resistance to the current. Their constructing technique consists in the production of a silk-like secretion to which inorganic (sand, pebbles; see drawing) or organic materials (mollusc shells, pieces of leaves, stems or twigs) stick. The case is conic, with inorganic material in the sericostomatid, odontocerid, and beraeid families and with organic or mixed material in the brachycentrid, lepidostomatid, leptocerid and limnephilid families. Hydroptilids (microcaddis) make peculiar cases. These tiny species build seed-like cases made of silk and grains of sand. Goerids insert small stones next to cylindrical cases, used as stabilizers to prevent overturning; the cases of glossomatids are like camel humps, with an opening in each apex. The building technique of trichopterans larvae has even been adopted by jewellers who breed larvae in aquariums containing grains, sticks, gold leaf and small precious stones of various kinds, to obtain very original and unique “biological” jewels. The larvae of other families (hydropsychids, polycentropodids, philopotamids) build silk cases not to protect themselves, but to collect food. These are real “cobwebs” with a conic shape, open to the current, which filter, or rather capture dead or living organic matter carried by water. These larvae have pygopods with long bristles which form small “brooms”, used to sweep the nets and collect the catch to eat it. Nets are built under stones, rocks, or where water cannot damage them. Trichopterans also include species (rhyacophilids) the larvae of which do not construct cases, but live free and prey on benthic macroinvertebrates. 79 Larval case of caddisfly (limnephilid trichopteran) Adult caddisfly Their development is holometabolous and when metamorphosis approaches, the larvae, which live in mobile cases, climb rocks or similar projections and fix themselves near the water surface. The front opening closes, and the larva, now a pupa, begins the extraordinary process which will transform it into a winged adult. Long, orderly strings of pupal houses are frequently seen on submerged rocks along the water level. Non-case-building trichopteran larvae pupate inside a specially built silk case, fixed under rocks. The poor mobility of most trichopteran larvae makes them vulnerable to sudden changes in water flow, and they are often miserably stranded after storms, when water retreats. This phenomenon is more frequent in streams subjected to hydroelectric peaking. Variations in flow are considerable and sometimes due to natural causes, as in streams supplied with meltwater from glaciers. Therefore, poor mobility, preference for mediumslow-flowing waters, and their prevailing trophic role as shredders-collectors of coarse organic matter (mostly dead leaves) limit the presence of trichopterans to stretches under trees. However, this does not prevent them from colonizing favourable environments at elevations exceeding 2500 m a.s.l. Higher stretches are colonized by orophilous and stenothermal species of cold waters, like Rhyacophila tristis, Philopotamus montanus, Plectronemia conspersa and Drusus discolor. In downstream stretches live other species of high ecological value, such as Rhyacophila torrentium Hydropsyche instabilis, Potamophylax cingulatus and Sericostoma pedemontaum. Vertebrate fauna SERGIO PARADISI ■ Fishes Salmonids of Italian streams. The species which popular belief immediately associates with mountain streams is trout. However, the distribution of this fish is not limited only to this kind of water, but includes pedemontane streams, large pre-Alpine lakes of glacial origin and plain streams. These environments are all characterized by cool or cold water, with tempe-ratures seldom reaching 20°C, usually well below that figure, and therefore, generally well-oxygenated. It is the oxygen requirement of trout and its very active metabolism which closely link this fish to highaltitude mountain streams, where water turbulence increases the percentage of oxygen to saturation levels. Hydrobiologists classify this stretch as “upper and medium salmonid area”, or simply “trout zone”. As regards fish, trout is therefore the guide-species of these waters, the best suited to these ecological conditions, and sometimes the only one present. But trout is an easy definition. Which trout lives in Italian freshwaters? The answer to this question is all but obvious, and this issue is the basis of research and discussion for many scientists who still have not come to an agreement. According to Tortonese, whose two volumes in the series “Fauna d’Italia”, devoted to bony fish appeared in the early 1970s, all Italian trout belong to the polymorphic and polytypic species Salmo trutta, characterized by variable size, skin and behaviour, with local varieties and ecotypes. The nominal variety Salmo trutta trutta, to which stream or brown (“fario”) trout belongs, is found in all regions (including Sicily and Sardinia). There are also two endemic subspecies: “marble” trout (Salmo trutta marmoratus), found in the river Po and its Alpine tributaries, and the Lake Garda trout (Salmo trutta carpio), typical of the largest Italian lake. The “lacustrine” and “Sardinian” or “macrostygma” trout do not have systematic value. Twenty years after Tortonese’s work, Gandolfi and Zerunian proposed a different systematic interpretation which, however, they did not consider definitive. In their opinion, Lake Garda trout is one species (Salmo carpio) and Lake of Posta Fibreno trout (Salmo fibreni) is another. They proposed calling Salmo trutta a Spectacled salamander (Salamandrina terdigitata) 81