Fish were sampled from 35 drainage and seepage lakes in the upper Michigan peninsula and Wisconsin in conjunction with Phase II of the U.S. Environmental Protection Agency's Eastern Lake Survey to explore the relationship between physicochemical characteristics of lakes and mercury concentrations in fish tissue. The lakes were selected using a stratified random design weighted for low pH to assess acidification effects on mercury bioaccumulation. Muscle tissue from yellow perch (Perca flavescens), northern pike (Esox lucius), white sucker (Catostomus commersoni) and largemouth bass (Micropterus salmoides) was analyzed for total and methylmercury. Differences in mercury concentrations were found between species, and methylmercury accounted for 99% of total mercury. Relationships were examined between tissue concentrations of mercury in yellow perch and lake physicochemical variables including pH, acid neutralizing capacity (ANC), calcium, conductivity, aluminum, total phosphorus, dissolved organic carbon, color, sulfate, lake area, lake depth, watershed area, Secchi depth and elevation. Mercury concentrations were negatively correlated with pH and ANC for both seepage and drainage lakes, but correlations with other water‐quality characteristics varied with lake type. Dissolved organic carbon had a negative correlation with fish mercury accumulation in seepage lakes, but not in drainage lakes. Mercury concentrations had a positive correlation with age, weight and length in yellow perch.
The sustainability of water resources in future decades is likely to be affected by increases in water demand due to population growth, increases in power generation, and climate change. This study presents water withdrawal projections in the United States (U.S.) in 2050 as a result of projected population increases and power generation at the county level as well as the availability of local renewable water supplies. The growth scenario assumes the per capita water use rate for municipal withdrawals to remain at 2005 levels and the water use rates for new thermoelectric plants at levels in modern closed-loop cooling systems. In projecting renewable water supply in future years, median projected monthly precipitation and temperature by sixteen climate models were used to derive available precipitation in 2050 (averaged over 2040-2059). Withdrawals and available precipitation were compared to identify regions that use a large fraction of their renewable local water supply. A water supply sustainability risk index that takes into account additional attributes such as susceptibility to drought, growth in water withdrawal, increased need for storage, and groundwater use was developed to evaluate areas at greater risk. Based on the ranking by the index, high risk areas can be assessed in more mechanistic detail in future work.
Recently developed models for the estimation of risks arising from the release of toxic chemicals from hazardous waste sites are inherently complex both structurally and parametrically. To better understand the impact of uncertainty and interaction in the high‐dimensional parameter spaces of these models, the set of procedures termed regional sensitivity analysis has been extended and applied to the groundwater pathway of the MMSOILS model. The extension consists of a tree‐structured density estimation technique which allows the characterization of complex interaction in that portion of the parameter space which gives rise to successful simulation. Results show that the parameter space can be partitioned into small, densely populated regions and relatively large, sparsely populated regions. From the high‐density regions one can identify the important or controlling parameters as well as the interaction between parameters in different local areas of the space. This new tool can provide guidance in the analysis and interpretation of site‐specific application of these complex models.
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