W F Vincent, Laval University, Quebec City, QC, Canada © 2009 Elsevier Inc. All rights reserved.
Lake ecosystems are vital resources for aquatic wildlife and human needs, and any alteration of their environmental quality and water renewal rates has wide-ranging ecological and societal implications. The increasing accumulation of greenhouse gases in the atmosphere as a result of human activities has begun to affect the structure, functioning, and stability of lake ecosystems throughout the world, and much greater impacts are likely in the future. Current global circulation models predict an increase in air temperatures of several degrees by the end of the twenty-first century, combined with large changes in the regional distribution and intensity of rainfall. These changes will also be accompanied by massive disruption of the cryosphere, the ensemble of ice-containing environments on Earth. These shifts in climate forcing appear to have already begun, and the onset of changes in the physical, chemical, and biological attributes of lakes is affecting their ability to maintain the present-day communities of aquatic plants, animals, and microbes, and their capacity to provide ecosystem services such as safe drinking water and inland fisheries (Figure 1).
Lakes have always been subject to the impacts of climate change, and natural climate variations in the past have been one of the main reasons that lakes are ephemeral features of the landscape. Most of today's lakes are the result of climate amelioration and the retreat of the Pleistocene glaciers some 10 000 years ago, and so most present-day lakes are relatively young. A powerful approach toward understanding the potential impacts of future climate change on lakes is the application of paleolimnological methods in which lake sediment cores are dated and analyzed to infer climate impacts in the past. Most such analyses have been restricted to the time period of the last few 1000 years; however, detailed records of greater than 100 000 years are becoming available from studies of ancient lakes. Studies of present-day lakes of different ages (chronosequences) and across latitudinal gradients are also providing valuable insights into the consequences of climate change. Additional knowledge about climate impacts is coming from modeling and experiments, combined with multi-decade, regional analyses of lakes that are currently experiencing shifts in temperature and precipitation.
Some of the most striking examples of climate impacts to date are from limnological and paleo-limnological studies in the polar regions. Global circulation models predict that the fastest and most pronounced warming will be at the highest latitudes because of a variety of feedback processes that amplify warming in these regions. These include the capacity of warm air to store more water vapor, itself a powerful greenhouse gas, and the reduced albedo (reflection of sunlight) as a result of the melting of snow and ice, leaving more solar energy to be available for heating. Some of the immediate impacts of climate change on high-latitude lakes include loss of perennial ice cover, increasing duration of open water conditions, increasing water temperatures, stronger water column stratification and shifts in water balance, in some cases leading to complete drainage or drying up of the waterbodies.
Changes in air temperature and precipitation have direct effects on the physical, chemical, and biological characteristics of lakes, and they also operate on lakes indirectly via modifications in the surrounding watershed, e.g., through shifts in hydrological flow pathways, landscape weathering, catchment erosion, soil properties, and vegetation. Of particular interest to limnologists (lake and river scientists) are the interactions between variables, the feedback effects that accelerate or dampen environmental change, and threshold effects by which lakes may abruptly shift from one environmental state to another.
Changes in the precipitation regime that accompany climate change have the potential to cause shifts in the connectivity of lakes (with biological implications, e.g., for migratory fish species), as well as in erosion rates that could affect the inflow and outflow dynamics of lakes. The latter effects are particularly conspicuous in the tundra permafrost. Many thaw ponds (also called thermokarst ponds) on the Siberian and Alaska tundra are draining as a result of increased melting of the permafrost, while certain thaw ponds further south in discontinuous, subarctic permafrost have begun to expand as a result of the differential melting of such
Climate forcing -M-
; Thermal regime and mixing |
! Underwater solar radiation I
P/E, water volume and residence time
; Ecosystem services !
; Water supplies |
Flood control Fishing and hunting Waste treatment Hydroelectricity Water sports Aesthetics
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