Thomas M. Grieb

Projecting Water Withdrawal and Supply for Future Decades in the U.S. under Climate Change Scenarios

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.

Mercury in the San Francisco Estuary

This review presents some of the published and other important literature on mercury contamination in San Francisco Estuary. Studies on human consumption of contaminated sportfish and on detecting ecological impacts of this contamination in wetland areas validate concerns regarding mercurys toxicity in this system. Mining, industrial, and environmental uses of mercury have occurred for more than a century, resulting in its large historic and continuing transport to the estuary. Consequently, there is a widespread distribution in the estuary, but more work is needed to show its relative chemical and biological availability from these sources. The uptake of mercury in the estuary has been shown in phytoplankton, but studies on biomagnification in local food webs have yet to draw a clear path to impairment in sportfish and waterbirds. In light of these concerns of impairment and the need for further information, large restoration activities planned for the estuary will require new technical approaches to solve important management questions, such as the location of key areas of methylmercury production.

A model framework for assessing the effects of selenium on aquatic ecosystems

A model framework is being developedto assess the effects of Se toxicity on aquatic ecosystems. The framework integrates several types of model components including a biogeochemical model, a pharmacokinetic model, a food web transfer model, a toxic effects model, and an ecosystem effects model that addresses both population dynamics and bioenergetics. The model is being used to identify data gaps and to test hypotheses concerning the biological cycling and toxic effects of different chemical forms of Se. An experimental research program is being conducted in conjunction with the model development to quantify Se cycling and toxicological processes, and to provide data to parameterize the model.

Modeling Fate, Transport, and Biological Uptake of Selenium in North San Francisco Bay

Selenium behavior in North San Francisco Bay, the largest estuary on the US Pacific coast, is simulated using a numerical model. This work builds upon a previously published application for simulating selenium in the bay and considers point and non-point sources, transport and mixing of selenium, transformations between different species of selenium, and biological uptake by phytoplankton, bivalves, and higher organisms. An evaluation of the calibrated model suggests that it is able to represent salinity, suspended material, and chlorophyll a under different flow conditions beyond the calibration period, through comparison against long-term data, and the distribution of different species of dissolved and particulate selenium. Model-calculated selenium concentrations in bivalves compared well to a long-term dataset, capturing the annual and seasonal variations over a 15-year period. In particular, the observed lower bivalve concentrations in the wet flow periods, corresponding to lower average particulate selenium concentrations in the bay, are well represented by the model, demonstrating the role of loading and hydrology in affecting clam concentrations. Simulated selenium concentrations in higher organisms including white sturgeon and greater scaup also compared well to the observed data in the bay. Finally, a simulation of changing riverine inflows into the bay that might occur as a consequence of proposed hydrologic modifications indicated significant increases in dissolved and particulate selenium concentrations in the bay. The modeling framework allows an examination of the relationship between selenium loads, variations in inflow, in-bay concentrations, and biota concentrations to support management for limiting wildlife impacts.

PREDICTION OF LAKE RESPONSE TO INDUCED CIRCULATION

ABSTRACT The outcome of any lake restoration project depends on numerous variables: e.g., lake morphometry, initial water quality, composition of the biological community, and engineering specifications of the restoration technique. Consequently, a variety of lake responses to restoration attempts can be expected, ranging from complete success to at least partial failure. For example, artificial circulation has improved water quality in many cases, but has often caused adverse ecological impacts, such as increased turibidity or nuisance algal blooms. The benefits of lake restoration can be realized only through accurate prediction of lake responses to alternative management schemes or experimental manipulations. Numerical classification of previous case history data can be used to enhance this predictive capability and to refine lake restoration techniques. By applying Mulitple Discriminant Analysis to case histories of artificial circulation, we defined the critical attributes of a successful restoration...