Potential effects of climate chance on surface-water quality in North America

Data from long-term ecosystem monitoring and research stations in North Ame rica and results of simulations made with interpretive models indicate that changes in climate (precipitation and temperature) can have a significant effect on the quality of surface waters. Changes in water quality during st orms, snowmelt, and periods of elevated air temperature or drought can caus e conditions that exceed thresholds of ecosystem tolerance and, thus, lead to water-quality degradation. If warming and changes in available moisture occur, water-quality changes will likely first occur during episodes of cli mate-induced stress, and in ecosystems where the factors controlling water quality are sensitive to climate variability. Continued climate stress woul d increase the frequency with which ecosystem thresholds are exceeded and t hus lead to chronic water-quality changes. Management strategies in a warme r climate will therefore be needed that are based on local ecological thres holds rather than annual median condition. Changes in land use alter biolog ical, physical, and chemical processes in watersheds and thus significantly alter the quality of adjacent surface waters; these direct human-caused ch anges complicate the interpretation of water-quality changes resulting from changes in climate, and can be both mitigated and exacerbated by climate c hange. A rigorous strategy for integrated, long-term monitoring of the ecol ogical and human factors that control water quality is necessary to differe ntiate between actual and perceived climate effects, and to track the effec tiveness of our environmental policies.