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The Biosphere Soils • All forms of life depend on soil. It is a delicate, fragile living resource. It needs to be managed carefully to ensure sustainability. • Soil is the uppermost layer of the earth. Soil is made up of the following: • Mineral Matter (weathered rock) • Organic material (living plants and animals) • Water • Air And what percentages are they? Water 25% Mineral Matter Air 45% 25% 5% organic matter • The mineral matter consists of material derived from the parent rock by physical and chemical weathering. • The organism matter is derived from decaying roots, leaves, needles and the remains of dead organisms. • The other two important components are water and air which fill up the pore spaces. These are found in variable amounts e.g. if a soil is waterlogged it lacks oxygen. What factors affect soil development? • Climate How much water and air enter the soil - and their temperatures - will affect the organic life of the soil and evaporation rates on the surface. Water movement tends to be down through the soil (Leaching). • Relief Different soils will form on different degrees of slope and aspect. Gravity and temperatures will affect the degree of slope movement and weathering. • Parent Material The rock type affects the acidity, texture and fertility of the soil. What factors affect soil development? • Soil Organisms • These are important in decomposing organic material and in mixing up the soil components. They are most abundant in warm, moist conditions. • Time The process of soil formation is very slow yet it can be destroyed very quickly. Soil Profile A soil profile is a vertical section through the soil from the surface vegetation to the bedrock. A fully developed soil profile displays a sequence of layers. Each layer is called a horizon. The A horizon is the top soil. • organic layer made up of decomposed leaf litter called humus. •Contains weathered rock from below. •Soil organisms usually mix up the 2 components. The B horizon is the subsoil. A B C •Contains higher proportion of weathered material. •It is generally less fertile. •Most fertile layer (usually). The C horizon is the regolith. •Weathered rock material which provides the soil with its mineral matter. •Beneath the regolith is the bedrock (Parent material) Soil Classification- Zonal Soils • • • • These are soils that broadly correspond to the main biomes. Influenced by time, climate and vegetation. Examples are: Podzols in the Taiga (coniferous forests) Brown Earth soils in the deciduous forests Tundra Gleys in the tundra Intra-zonal soils These are soils that are influenced by local factors e.g. the parent material in an area or local drainage. The climate is not an important influence. • Example: • Gley soils • Limestone soils Azonal Soils These are young, immature soils which have not developed horizons. Examples: • Alluvial soils deposited by rivers • Boulder clay soils deposited by glacal deposition. • Volcanic soils Ecosystems An ecosystem is a unit which links all living things (plants, animals, people) with each other and with their physical environment (rock, soil, air and precipitation). • The driving force for the whole system is solar energy. • Ecosystems can exist at a variety of scales from a single tree to the major biomes (bioclimatic zones). Solar energy Precipitation Soil Vegetation Man The Ecosystem Temperature Relief Biotic factors Podzols-summary Location- Europe, Northern Asia and North America. Climate- precipitation greater than evaporation= leaching Vegetation- pine woodland, coniferous trees, heather moorland. Low temperatures mean slow decomposition of organic matter producing raw humus. Needles from conifer trees produce raw acid Spring meltwater causes leaching (downward movement of water). Low summer temperatures= little evaporation. Leaching of aluminium and iron oxides leaves a silica (light sandy layer). Red / Brown iron or hard pan. Aluminium oxide deposited in light clay. Thin layer of black humus. Dark staining Shallow roots of coniferous trees take few minerals from the soil. Ash grey Low temperatures mean little earthworm (or other organism) activity, therefore distinct horizons. IRON PAN Yellow / Brown Waterlogging as water cannot penetrate hard pan. leaching is dominant in the A Horizon. The leaching washes down the soluble minerals such as iron, humus and leaves behind a bleaching horizon (insoluble silicates). RAW ACIDICS HUMUS (MOR) & SHALLOW ROOTS B HORIZON IRON PANGLEYING The C horizon is derived from the weathered parent material. The low temperatures means that there is little mixing of the horizons due to the lack of soil biota. Podzols are not naturally fertile soils. Lime needs to be added to counteract the soils acidity and animal manure can improve the poor quality mor humus. Brown Earths Location • These forests are located on the west coasts of continents between approximately 40° and 60° N/S of the equator. Climate • Summers are cool (15-16°C) as a result of the relative low angle of the sun, combined with frequent cloud cover. • Winters are mild. • Precipitation is high (depressions throughout year). • Although snow is common in the mountains it rarely lieslong at sea level. Natural Vegetation • Deciduous trees have a growing season of 6-8 months and they shed their leaves in the winter. • Such species as oak, elm, ash, chestnut and beech are common. They all develop large crowns and have broad but thin leaves. • The forest floor is often covered in a thick undergrowth of brambles, ferns and in the spring, bluebells. Mild climate, rapid decomposition of organic matter. Humus is mild (not raw) and alkaline. Thick leaf debris, much organic matter in soil. Deep roots plus earthworm activity caused by high temperatures results in mixing of the soil and indistinct horizons. Iron pan can develop where leaching is more active. Leaching Iron pan Light Brown The soil biota helped to decompose the leaf litter quickly. The B horizon is not too distinct but is lighter in colour than the A horizon as humus becomes less abundant. The C horizon is weathered parent material. The A horizon is well aerated and dark brown in colour as humus is enriched. These mildly acidic brown earth soils have been extensively exploited for agriculture and have supported a much higher density of population compared with the podzols. Tundra Gley Location • The tundra lies to the north of the taiga. It includes the extreme northern parts of Alaska, Canada, Russia and Greenland. Climate • Summers may have long continuous daylight, but with the angle of the sun so low in the sky, temperatures struggle to rise above freezing point and the growing season is very short. • Winters are long, dark and severe and the sea freezes. • Precipitation is light and mainly falls as snow. Natural Vegetation • There are few species of plant in the tundra. • Most are very slow and low growing such as mosses, lichen and small shrubs. • Most have small leaves to limit transpiration and short roots to avoid the permafrost (permanently frozen sub-soil). • Much of the tundra is waterlogged in summer due to the impermeable permafrost preventing inflation. Mosses, dwarf shrubsshort growing season Little activity from organisms because of low temperatures. Therefore breakdown of material is minimal, plus incorporation of organic matter into the profile is low= infertile. Permafrost layer prevents water from draining downwards therefore waterlogging the soil. Rock Fragments Blue/grey clayed mud. Permafrost Bedrock Slow decaying plant mater results in raw acid humus (slow because of low temperatures). Black in colour. Freeze-thaw action (expansion and contraction) leads to vertical mixing incorporation of rock fragments. Therefore no distinct horizons. The limited plant growth due to the climate produces a small amount of litter. There are few soil biota due to the low temperatures. Spring meltwater may cause a little leaching. If the bedrock is close to the surface the parent material is weathered by freeze-thaw action. There is only a thin layer of peaty humus. The permafrost acts as an impermeable layer, restricting moisture percolation and causes waterlogging and gleying (blue-grey in colour). Shattered angular material can be raised to the surface by frost heave in winter. Intra-Zonal Soil The A horizon is dark in colour due to the organic matter. Slow rate of decay because of anaerobic conditions. B horizon mainly bluey/grey in colour due to continuous waterlogging C horizon (parent material) is an impermeable layer. Gleys can support wetlands, permanent pasture and arable farming once drained and ploughed. When soil is waterlogged for a long time, its pore spaces lose oxygen. Such a soil is called anaerobic and this means that any decay of bacteria is slowed down. Soil Catenas • A soil catena illustrates a sequence variation in soil types down a slope where underlying parent material is the same throughout. Relief of the land • angle affects the drainage conditions which then influences the amount of leaching and gleying. • The underlying parent material should be the same along the slope. • The climate should also be constant but altitude will vary the climate. Plant Succession • A plant community (ecosystem) is a group of plants that occur in the same place at the same time. • They evolve over time from simple beginnings when pioneer plants colonise new land to even more complex communities (building stage) and eventually climax vegetation. • During a typical plant succession, the ecosystem will go through the following stages: • On a plot of bare ground it is only a short time before basic pioneering plants start to colonise. • pioneer plants stabilise the environment binding the loose material. • plants die and decompose the environment conditions change and humus starts to develop. • Further developments of humus and weathering means that the soil becomes richer and deeper. • competition between the plants may occur. • new plants may be taller and create shady conditions, altering the micro-climate. • Plants continue to compete for the available nutrients, water and space. • Eventually the plant succession reaches climax vegetation. Climax Vegetation This is the ultimate stage of plant succession. It is reached through plant communities going through plant colonisation, competition and stabilisation. It is when the vegetation no longer changes. The vegetation is in a state of equilibrium with the climate and soils of the local environment. Coastal Sand Dunes Sand dunes are formed where: 1. there is a plentiful supply of sand 2. a strong onshore wind 3. there are obstacles to trap the sand at the bern line (high tide mark). • A plant succession on a sand dune is called a psammosere. To study this plant succession from pioneer plants to climax vegetation it is best to look at a transect of coastal sand dunes. Stand Line and Embryo Dune (mobile dune) • Sand may become trapped by seaweed or driftwood on berns. • Windborne seeds may germinate and a pioneer community of annual plants such as sea rocket grow. • plants have to be able to withstand the dry, salty conditions. • plants allow sand to accumulate, The grasses have runners and are extremely salt resistant. • Sea couch cannot grow upwards and though the sand and the sand dunes tend to be low. Sea Couch Grass Embryo and Foredunes at Sandwood Bay Sea Couch Grass colonising foreshore Embryo Dunes at John Muir Country park near Dunbar Embryo Dune Sea Lyme Grass (1) Sea Lyme Grass (2) Yellow Dunes (mobile dune) • They are above the high tide limit, are dry and exposed to wind. • The dominant plant is marram grass. • There is always bare loose sand between the marram grass giving the dune a yellow appearance. Marram grass has adapted to the harsh conditions as: • It is xerophytic • Its leaves are re-rolling inwards to reduce transpiration. • It has long tap roots. • It can grow upwards very quickly. Yellow Dunes at Sandwood Bay Lagoon and Yellow Dunes Marram Grass (1) Marram Grass (2) • Where marram grass dominates the sand dunes will grow very quickly in height to 10 meters. The wind is forced up over the dunes and in the lee of the dune, the speed of the wind drops, and the windblown sand is deposited. • This means the dunes migrate inland. Grey Dunes and Slacks (Fixed Dune) • smaller in size as the grey dunes cease to grow. • As the fresh supply of sand is cut off marram stops growing and begins to thin out. • plants die and decompose which adds nutrients and the ‘soil’ is able to hold more moisture. • In the damp and wet hollows between the dune ridges, where the watertable is close to the surface, dune slacks develop supporting water loving plants such as rushes, iris, reeds and cotton grass. • the dunes mature and becomes more isolated from the sea, new embryo dunes form. Semi-fixed Dunes with Dune Slacks Dune Slacks Snails and Mosses in Dune Slacks Bird’s Foot Trefoil (Fixed Dune) Saltwort (1) Saltwort (2) Ragwort Heathland and Woodland • increasing distance= non-maritime species enter the dune community. • rich grasslands are found depending on amount of calcium carbonate in the dunes as. • where the lime has been leached out leaving the dune acidic, acid loving heathland plants are found such as heather. • The final stage of this plant succession, is mixed woodland where species such as pine, birch and oak are common. • Generally, in a transect through a sand dune certain characteristics occur when moving inland. • Acidity increases • Salinity decreases • Water retention and biomasses increase. • Exposure to wind is reduced • Plant coverage and diversity increases. Wind blown Hawthorn (Fixed Dune) The end