February Feature: Rivers and Lakes Freshwater ecosystems will be hit by rising temperatures and sometimes drastic changes in water levels and seasonality of flow - especially where they are currently fed from snowmelt and where catchments are small. Shallow streams and lakes could warm drastically, especially if warming also kills bankside vegetation and reduces shading. In many parts of the US even small increases in stream temperatures are predicted to have a major impact in reduced cold-water fisheries. A 2░ C increase would reduce cold-water habitats in the streams of Wyoming, for instance, by about a quarter, making bigger changes in fish populations, including extinctions, likely. Studies of recreational salmon fisheries on the Sacramento River in California suggest a 23% decrease from the early stages of global warming. Again in the US, striped bass may disappear from the southern states, but could enter the Great Lakes, perhaps pushing out salmonid species. Low average river flows will generally reduce fish stocks. This will be especially true where this means floodplains are no longer flooded, a change which typically reduces stocks 1.5 to 4-fold, because of the food-rich habitats lost. Studies in both Arizona and Australia show that in dry years aquatic biodiversity is sharply reduced. Such changes are extremely likely because small changes in rainfall generally produce large increases in flow variability. Meanwhile, unusually large floods scour river beds and reduce biomass for long periods. Learn MORE About Lakes and Rivers... Endangered Seas Campaign Water Information Resources

Copyright 1997, The World Wide Fund For Nature