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Lake Baikal as possible sentinel of the Climate Change SILOW Eugene Scientific research institute of Biology, Irkutsk State University, POBox 24, Irkutsk-3, 664003, Russia [email protected] Abstract: Now it is relatively well known – what changes must have place in the lakes if the Global Change is real. There must be increase of surface temperature, more expressed and longer direct stratification, shorter period of ice cover and other hydrological changes. Among biological changes there must be decrease of share of large cell alga, increase of small cell phytoplankton, changes in zooplankton community etc. These changes now are observed in many lakes around the world. At the same time we can observe directly opposite changes of parameters, causing doubts in paradigm shift in limnology. The lakes are supposed to be the sentinels of the Climate Change. They have many advances in comparison with other indicators. Ecological processes in lakes are more closely related with temperature, even the structure of water body, the seasonal changes, the freezing of surface etc. depend on temperature. The lake Baikal is the largest, deepest, one of the oldest lakes of Earth. Its systems must be very inert, as there are enormous efforts necessary to cause shifts in the lake Baikal ecosystem. Nevertheless we observe the changes in air temperature, changes of the temperature of the surface and deep layers of water, changes of the period of ice cover. Simultaneously we observe some biological changes – decrease of share of large spring alga, increase of biomass of summer phytoplankton, changes in zooplankton structure, appearance of invasive species. Are this changes (including climate) connected with Global Change, or with local disturbances (e.g. creation of system of enormously large reservoirs near Baikal), or with some extra long-term natural cycles – this is the problem to be solved. Keywords: Lake Baikal, Plankton, Climate Change, Temperature, Stratification 1. Global Change and Lakes Global average land temperature has increased by 0.7 – 0.8 °C and ocean temperature by 0.5 °C since 1880, the decade of 1998-2007 is the warmest on record. According to the most recent data the global temperature trend is 0.12 °C·decade-1 for surface [Nodvin, 2009]. Let us observe the possible shifts in lakes ecosystem which can follow the Global warming from the positions of general limnology [Hutchinson, 1957, 1967; Kalbe, 1997; Wetzel, 2001; Kalff, 2002; Schwoerbel, Brendelberger, 2005; Lampert, Sommer, 2007]. The increase of air temperature must cause the increase of the surface lake temperature and, consequently, to make temperature stratification more strong. The temperature of epilimnion and its volume (depth of thermocline) will increase. Changes in hydrophysics will cause shifts in the lake chemistry, as follows – increase of nutrient (particularly phosphorus and nitrogen) concentrations, decrease of oxygen content, increase of DOM concentration. Consequently, the changes in biotic components must be observed – increase of phytoplankton biomass and production, the growth of the small cell phytoplankton share, changes in zooplankton composition and disturbances at higher trophic levels (predatory zooplankton, planktivorous fishes etc.). Actually all these phenomena occur in different lakes, the excellent reviews are given by [Livingstone, 2008, Nöges et al., 2008]. The increase of temperatures (both surface and deep water), thermocline depth, nutrients and DOM concentrations, often decrease of oxygen, phytoplankton blooms, zooplankton structural changes, trophic balance deviations are observed throughout the world. 2. Paradigm Shift in Limnoecology These phenomena produced the paradigm shift in limnoecology [Livingstone, 2008; Gerten, 2008]. Authors and protagonists of this doctrine postulate that earlier limnology was based on two basic assumptions. The first (tacit assumption of individuality) is though the physical processes in all lakes are principally the same, the differences of their geographical positions, external (particularly climatic) influences, different morphometry and properties of watershed make every lake unique. The second (tacit assumption of stationarity) is despite high temporal variability of the lake parameters they are fluctuating within some limits, also individual for every lake. New paradigm proclaims invalidating of both assumptions and confirms that lakes are subjected to large-scale climatic and human-induced pollution forcing, just modulated by local external conditions. So, two old assumptions are replaced with two new ones: the concept of spatial coherence and the concept of temporal non-stationarity. Here it is necessary to stress that many lakes in the world now behave in the way often contrary to predicted by the “Global Warming & Lakes” scenario. New paradigm godfather himself writes that physical parameters change in good accordance with this theory, but the more complex and vital is the parameter; the less coherent and unidirectional is its dynamics [Livingstone, 2008]. There are many reports of changes of lake parameters contrary to predictions. The Lake Ladoga, for example, ice observations since 1943 has shown an earlier freeze-up (14 days) and does not demonstrate any trend for the timing of break-up [Karetnikov, Naumenko, 2008]. The decrease of epilimnion volume, connected with the decrease of thermocline depth, is observed in Lake Tahoe [Coats et al., 2006]. In deep lakes the decrease of silicates and phosphates concentration before phytoplankton blooms is observed [Goldman et al., 1989;, Salmaso, 2005]. The decrease of available phosphorus and, consequently, of phytoplankton biomass and production is observed in Alp and Swedish lakes [Parker et al., 2008; Weyhenmeyer, 2008]. In three Australian lakes the temperature increase negatively affects phosphorus (both total and phosphate) and nitrogen (also both total and nitrate) and does not correlate with chlorophyll content, reflecting phytoplankton development [Tibby, Tiller, 2007]. Decrease of nutrients content in epilimnion and, consequently, the depression of phytoplankton development is observed in the Lake Tanganyika, Africa [O’Reily et al., 2003; Verburg et al., 2003;, Stenuite et al., 2007]. Here it is possible to add that not only unidirectional temperature rise, but also cyclic phenomena, such as North Atlantic Oscillation and Arctic Oscillation, sufficiently affect the precipitation amount, air temperature, timing of freeze-up and break-up and the dates of spring phytoplankton blooms both in Europe and Asia [Livingstone, 1999; Todd, Mackay, 2003; George et al., 2007; Gerten, 2008]. In the North America ice break-up date as well as total phosphorus content strongly develop on El Nino South Oscillation [Nicholls, 1998; Kalff, 2002], Pacific Oscillation [Mantua et al., 1997; McGowan et al., 1998], and their interaction [McGabe, Dettinger, 1999]. It is necessary to remind that Earth climate is the result of extremely complex interaction of atmosphere, hydrosphere, cryosphere, and lithosphere and such external for them forces as planet rotation velocity, heat flow from the magma, solar activity and many others. There have been two sustained periods of warming (1910 – 1945 and 1975 – 2010 [author’s suggestion]), but there were also two periods of cooling (1880 – 1909 and 1946 – 1974) [Nodvin, 2009], so it is possible the process we observe is not the unidirectional temperature shift, but just a part of some long-term oscillatory process. It is clearly seen that lakes ecosystem dynamics changes are not coherent or unidirectional. The same external influences can cause quite opposite answers. The existence of “old paradigm” is doubtful itself, as the most researchers always observed lake ecosystem dynamics as result of interaction of several processes – seasonal changes, interannual long-term cyclic fluctuations, and directional changes connected both with internal ecosystem development as well as with external influences. 3. Lake Baikal as Climate Change Sentinel Now lakes are supposed to be good sentinels of climate change [Williamson et al., 2009]. They have many advances in comparison with other indicators. Ecological processes in lakes are more closely related with temperature, even the structure of water body, the seasonal changes, the freeze-up timing, phytoplankton bloom etc. depend on temperature [Livingstone, 2008, Weyhenmeyer, 2008]. They reflect the state of their catchment area, serving as magnifying glass to detect the changes. The changes in small lakes are demonstrated to mimic eutrophication effect, while the large lakes are shown to be more inertial systems [Nöges et al., 2008]. The ecosystems of the latter are similar to oceanic ones, so the changes in large lake ecosystem can be used to predict the changes in the ocean. Lake Baikal is the oldest (25 mln years old), deepest (more than 1600 m) and the largest by volume (23,000 km3), equal to the total volume of Laurentian Great Lakes. It is characterized by low mineralization (96 μg l-1), oligotrophy, high oxygen content even at maximum depth and high degree of its flora and fauna endemism [Kozhov, 1963, Kozhova, Izmestyeva, 1998]. Its plankton community characteristic feature is relative simplicity: about 20 species of dominant alga (mainly endemic diatom under ice-cover and smaller non-endemic alga in summer), one super-dominant herbivorous zooplankton species (Epischura baicalensis), accompanied by Cyclops kolensis and several rotifers, one predatory zooplankton species (Macrohectopus branickii), two planktivorous fishes of the endemic family Comephoridae (95 % of total fish biomass), and seal. Nevertheless, this structure demonstrates rather complex behaviour with two peaks of plankton development (under ice and in summer) during the year and great interannual fluctuations of both phyto- and zooplankton development. This dynamics is supposed to be the product of interaction of annual and interannual cycles and long-term internal succession and evolutionary dynamics as well as external influences. Of course, the detection of changes in such ecosystem, coherent with predicted by “Global Warming & Lakes” model will point to reality of Global Change and its enormously significant degree, as to cause changes in shallow lake and in the Lake Baikal are quite different things. There were several researches, devoted to the influence of global warming on some parameters of the lake Baikal ecosystem state, fulfilled, mainly for ice-cover [Livingstone, 1999; Todd, Mackay, 2003; Kouraev et al., 2007], hydrochemistry [Yoshioka et al., 2002], and phytoplankton [Bradbury et al., 1994; Mackay et al., 1998, 2006; Bangs et al., 2000; Fietz et al., 2005, 2007; Straskrabova et al., 2005; Mackay, 2007]. The necessity of complex analysis of long-term data on limnological and biological parameters as recommended on the basis of world wide experience [Gersten, 2008] is obvious. Our international team just started such the real complex studies of the reaction of the lake ecosystem as whole to the changes of climate forming factors. The first results have revealed the increase of water temperature at different depths, followed by remarkable increase of the summer plankton biomass, structural changes in zooplankton community [Hampton et al., 2008; Moore et al., 2009]. Also we observe some other changes – decrease of share of large spring alga, appearance of invasive species. Are all this changes (including climate) connected with Global Change, or with local disturbances (e.g. creation of system of enormously large reservoirs near Baikal), or with some extra long-term natural cycles – this is the problem to be solved. 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