Impacts of global climate change on the quality of surface waters.

摘要

Current anthropogenic activities, are expected to produce significant changes in the global climate of the earth, micro climates and the landscapes of watersheds. These, in turn, may alter hydrologic responses and ultimately the ecology of aquatic systems. Relatively little attention has been given to the effects of climate change on the quality of surface water bodies, e.g. lakes, and their indigenous ecosystems, which are intimately linked to the circulation and distribution of water on earth and to atmospheric processes. The probable fate of aquatic species, in many cases already stressed near threshold limits of temperature, are yet to be carefully examined in a quantitative framework that will reveal the potential impacts of climate change.; The objective of this research was to assess the consequences of climate change on the water quality of reservoirs, evaluating uncertainties involved by means of water quality models and statistical methods. Emphasis is on water temperature, per se, but the implications for other quality characteristics, e.g., dissolved oxygen, are also evaluated preliminarily. Under projected climate change scenarios, the main sources of water quality uncertainty stem from the primary driving forces, i.e., atmospheric and hydrologic regimens. Both time series analysis and traditional Fourier representation were used to formulate a predictive model that generates hydrologic and atmospheric boundary conditions. Results of this model were used as input to the water quality model WQRRS (Water Quality for River and Reservoir System), chosen specifically because it simulates the key heat exchange mechanisms at water surfaces. Predictive and water quality models were coupled to produce Monte Carlo simulations of key water quality indicators.; A case study of the Shasta Lake watershed, a critical element of the Sacramento River ecosystem, is presented. The consequences of alternative climate change scenarios imposed on the lake are examined. End results are comparisons under present and future climatic conditions of the frequency and severity of exceeding threshold levels of water temperature; probable changes in the duration of critical periods above threshold levels for the survival of chinook salmon; and insight into the impact of reservoir operation strategies for mitigation.