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Lessons learned using water quality models to develop numeric nutrient criteria for a Gulf coast estuary
Citation:
Hagy, Jim, D. Beddick, B. Jarvis, AND Rick Greene. Lessons learned using water quality models to develop numeric nutrient criteria for a Gulf coast estuary. Presented at CERF 2013, San Diego, CA, November 03 - 07, 2013.
Impact/Purpose:
The purpose of this abstract is to secure placement of an oral presentation in the program schedule at the CERF conference in November 2013
Description:
Pensacola Bay is a shallow, mesotrophic estuary located in the north-central coast of the Gulf of Mexico, US. In November 2012, the US Environmental Protection Agency (US EPA) proposed numeric total nitrogen (TN), total phosphorus (TP), and chlorophyll-a (chl-a) water quality criteria for this estuary to limit anthropogenic nutrient impacts associated with phytoplankton blooms, seagrass loss, and hypoxia. Analysis using coupled hydrodynamic-water quality models was central to the rationale for criteria development because these models are well-suited to evaluating spatial and temporal distributions of water quality parameters in the context of the dynamic physical regime in estuaries. Seagrass habitats in the Bay have decreased in spatial extent and depth of colonization since 1960 and hypoxia (DO<2.0 mg l-1) occurs in up to 25% of the Bays' bottom waters, trends consistent with nutrient enrichment impacts around the world. Surprisingly, data generated from simulations of Pensacola Bay water quality for 2002-2009 suggested that neither issue could be addressed via nutrient loading reductions. Recognizing the potential value and importance of water quality simulation models as tools for developing numeric nutrient criteria, we are using Pensacola Bay as a test case to further evaluate and improve their use for this purpose. A conceptual model guides selection of potentially important "target processes," which for Pensacola Bay includes optical properties and sediment-water oxygen and nutrient fluxes, among others. We will conclude by suggesting key elements that could be incorporated into recommended approaches for evaluating simulation model applications for numeric nutrient criteria development in estuaries.