Concentration of sediments in Lake Erie resulting from a large storm. Concentrations are color coded, with the highest shown in red. Winds from storms produce waves, which in turn create bottom currents and turbulence that can cause contaminated bottom sediments to be resuspended in the water column. The shallower the water, the stronger the effects of the wave action. Consequently, sediment concentrations tend to be largest in shallow sections.
High performance computing is crucial to improve decision making on environmental issues. Improved numerical computer models provide more accurate predictions of pollution so that our leaders will be in a better position to make policy decisions involving the environment and economic growth. The accuracy of these models depends upon descriptions of physical, chemical and biological processes that adequately incorporate important causal interactions, nonlinearities, synergies, and feedbacks, as well as capture nonintuitive interactions. The linkage of single media models and the development of megamodels are essential for more reliable management of the environment.
Three areas of environmental decision support have been established as part of EPA's HPCC Program: air pollution, water pollution, and the combined effects of air and water pollution on coastal estuaries that lead to de-oxygenation.
The Clean Air Act amendments mandate State use of air quality models to demonstrate the effectiveness of proposed approaches for reducing air pollution in highly polluted areas. Researchers at EPA and the North Carolina Supercomputing center in Research Triangle Park, NC are developing a decision support system to satisfy a wide range of related air quality modeling, information and analysis needs. New computational capabilities enable improved air quality models to address multipollutant interactions among acidifying species, oxidants and aerosol, and interactions with meteorology. These complex, three-dimensional, time-dependent models are used to evaluate alternative pollution control strategies where interactions at different scales, from urban to regional, are critical and require new approaches made possible only through high performance computing. The North Carolina Department of Environment, Health and Natural Resources is testing an early prototype of an urban airshed modeling system.
Contaminated bottom sediments and the associated decrease in water quality are a major problem in hundreds of rivers, lakes, harbors, estuaries, and near-shore areas of oceans. In order to remediate this problem and evaluate possible management alternatives for the disposition of these toxic sediments, EPA-supported researchers at the University of California- Santa Barbara are developing computer intensive three-dimensional, time-dependent models of the hydrodynamics, particle transport, and sediment bed dynamics coupled with meteorology. Significant biochemical reactions that affect the fate of contaminants are also included in the models. Work currently focuses on the Great Lakes region of the United States. Figure 1 shows that redistribution of toxic sediments in Lake Erie due to a large storm is highly dependent on wind direction and speed, and water depth.
Interactions between pollutant media, such as air and water, often significantly affect the environment. Air and water pollution both contribute to an overabundance of nutrients in coastal estuaries causing lack of oxygen and eventual decline of commercial productivity of the estuaries. Researchers at EPA's Environmental Research Laboratories in North Carolina and Georgia, and the Chesapeake Bay Program Office in Maryland are developing loose linkages between air and water quality models to study the impact of nitrogen deposition by air and water sources on the decline of coastal estuaries of the Chesapeake Bay.
In some cases, only minor feedbacks exist between the different media. Loosely linking current single-medium models retains the known features and complexity of each model. This linkage provides additional information for more effective policy determination by individual pollutant media decision making communities.