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CHESAPEAKE BAY 2007 RE-EVALUATION
The objective of this work is to contribute to multimedia studies and assessments by applying state-of-the-art atmospheric models, estimating the atmospheric contributions to multimedia issues and the sources of those contributions, and evaluating the models strengths and weaknesses. A sub-objective of this work is to provide the Chesapeake Bay modeling and assessment team with projections of anticipated reductions in atmospheric nitrogen deposition due to implementation of Clean Air Act regulations to assess the potential contribution these reductions can make to the Bay restoration goal. A sub-objective is also to provide an assessment of each Bay state's relative contribution to oxidized-nitrogen atmospheric deposition to the entire watershed to clarify the potential for voluntary efforts within each state, as part of a tributary strategy, to support the Bay restoration goal. A sub-objective is also to test aspects of linking atmospheric and watershed models for further research development and to test the more advanced versions of the one-atmosphere model to understand how better to reduce uncertainties.
A long term goal of multimedia environmental management is to achieve sustainable ecological resources. Progress towards this goal rests on a foundation of science-based methods and data integrated into predictive multimedia, multi-stressor open architecture modeling systems. The strategic pathway aim is to progress from addressing one stressor at a time to a comprehensive multimedia assessment capability for current and projected ecosystem health. The multimedia tasks in AMD address a number of issues that arise in multimedia modeling with an emphasis on interactions among the atmosphere and multiple other environmental media. While the watershed is a fundamental unit of ecosystem analysis, due primarily to its containment of the hydrologic cycle and related stresses, the relevant atmospheric scale of modeling and analysis for linking to watersheds is regional/continental in scope, encompassing multiple States and/or watersheds. The interaction between the atmosphere and the underlying surface is increasingly being recognized as an important factor in multimedia issues. Targeted development, evaluation and application of state-of-the-art, multi-pollutant atmospheric models of nitrogen and mercury to multimedia issues help determine how to further improve the one-atmosphere models and support ongoing ecological assessments. Software tools are needed to support linkage of models across media and specialized multimedia data analysis applications. This multimedia work helps to bring the results of air pollution control, that primarily stem from addressing human health effects, into the management purview for addressing multimedia or ecosystem problems. The multimedia tasks support Goal 4 (Healthy Communities and Ecosystems) and its Long-Term Goals ECO-3, Restoration - develop scientifically defensible methods to protect ecosystem conditions, and HG-3, Transport and fate - understand the transport and fate of mercury from release to the receptor.
Targeted applications that link the state-of-the-art models of nitrogen deposition with watershed and estuarine models in support of assessments provide an important test bed for learning what capabilities are required of the atmospheric models to support multimedia assessments. Past linkage work has shown that it is important that atmospheric deposition be able to be related to climatological averages. This work has also shown atmospheric models fill a critical gap for provision of dry deposition estimates for both oxidized and reduced nitrogen to provide the needed input of total, wet + dry, atmospheric deposition. This integrated experience contributes to multimedia science and helps define better predictive multi-stressor, open architecture approaches. This work also helps to identify further air-surface exchange needs, particularly related to dry deposition, for defining priority air-surface exchange work in the companion AMD multimedia Task 20472, performed in coordination with the CMAQ development task, and helps define specialized needs for multimedia tool development in multimedia Task 20477.
Atmospheric deposition of nitrogen to the Chesapeake Bay watershed and Bay surface is important. The atmosphere is estimated to contribute a quarter to a third of the nitrogen loading to the Bay, affecting current conditions and needing to be addressed in Bay restoration efforts. Chesapeake Bay has been placed on EPA's list of impaired waters, with a TMDL plan required in 2011. The Chesapeake 2000 agreement calls for preempting the need for a TMDL plan by cleaning up the Bay by 2010. The Bay 2007 Re-evaluation is a critical step in the process towards the 2010 cleanup and delisting. To provide the best modeling science for the 2007 Re-evaluation, a major upgrade of the Chesapeake Bay Watershed model will be used as well as the latest version of CMAQ and the upgraded Aggregation method to create climatological average deposition. This atmospheric modeling will be a major update from earlier use of the Extended RADM and the original Aggregation method. The CMAQ modeling for the 2007 Re-evaluation has two major foci: (1) development of scenarios estimating the deposition reductions expected by 2010 and 2015 due to Clean Air Act regulations, such as the Clean Air Interstate Rule, and (2) estimation of the relative contribution the nitrogen oxide (NOx) emissions from each Bay state make to the atmospheric deposition of oxidized nitrogen to the Bay watershed and Bay surface.