Climate change and the effects on freshwater ecosystems

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Much attention has been focused on the effects of climate change  on forests, farms, freshwater sources and the economy. But what about the ocean?

Fresh waters are particularly vulnerable to climate change because (i) many species within these fragmented habitats have limited abilities to disperse as the environment changes; (ii) water temperature and availability are climate-dependent; and (iii) many systems are already exposed to numerous anthropogenic stressors. Most climate change studies to date have focused on individuals or species populations, rather than the higher levels of organization (i.e. communities, food webs, ecosystems)

Climate change is likely to further stress sensitive freshwater and coastal wetlands, which are already adversely affected by a variety of other human impacts, such as altered flow regimes and deterioration of water quality. Wetlands are a critical habitat for many species that are poorly adapted for other environmental conditions and serve as important components of coastal and marine fisheries.

Evidence shows that many of the effects of changing climate are already occurring. These include: (i) an increase in the surface water temperature of lakes and streams across Europe, especially those at high altitudes and latitudes; (ii) an increase in hypolimnetic temperature of large deep lakes; (iii) a reductionin lake ice-cover; and (iv) the melting of mountain glaciers and permafrost causing changes to discharge regimes in mountain streams and release of solutes and pollutants to surface waters. In the future it is likely that these trends will continue and it is probable that (i) there will be changes in the flow regime of streams and rivers associated with projected changes in the amount, seasonality, intensity and distribution of precipitation, causing an increase in the transport of sediments and nutrients downstream to lakes and the coastal zone; (ii) there will be changes in precipitation, evaporation and flooding dynamics that will cause changes in water levels, habitat structure and water residence times in wetlands; (iii) small intermittent streams and small lakes in warm dry areas may disappear, while flow in permanent streams may become intermittent and lakes may become more saline; and (iv) systems already ata threshold between two different conditions may change abruptly, e.g. may switch from permanent to intermittent streams, from freshwater to permanently saline lakes, from non-stratifying to stratifying lakes, or from dimictic to monomictic regimes.

Increases in water temperatures as a result of climate change will alter fundamental ecological processes and the geographic distribution of aquatic species. Such impacts may be ameliorated if species attempt to adapt by migrating to suitable habitat. However, human alteration of potential migratory corridors may limit the ability of species to relocate, increasing the likelihood of species extinction and loss of biodiversity.

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