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Complementary Monitoring Designs to Document Regional Gradients and Temporal Variations of Dissolved Oxygen in Estuarine Waters

Henry A. Walker 1, John A. Kiddon 1, Christopher F. Deacutis 2, Donald J. Cobb 1, Dana R. Kester 3, Candace A.Oviatt 3, John F. Paul 4, Gerald G. Pesch 1, Richard B. Moore 5, Keith W. Robinson 5.

1 U.S. EPA, Office of Research and Development, National Health and Environmental Effects Research Laboratory, Atlantic Ecology Division, Narragansett, RI, USA 02882
2 University of Rhode Island, Coastal Institute, Narragansett, RI, USA 02882
3 University of Rhode Island, Graduate School of Oceanography, Narragansett, RI, USA 02882
4 US EPA, Office of Research and Development, National Health and Environmental Effects Research Laboratory, Research Triangle Park NC, USA 27709
5 US Geological Survey, New Hampshire / Vermont District, 361 Commerce Way, Pembroke, NH 03275-3718

The US EPA National Coastal Assessment program is designed to address two broad questions: 1) what are the conditions of estuarine resources, how are they changing, and what causes those changes; 2) which monitoring designs, indicators, and protocols are appropriate for assessing estuarine conditions, particularly for assisting State efforts to comply with the Clean Water Act requirements. To document baseline conditions, estuarine data have been collected in the US over a two year period (2000-2001) using a probability-based survey design. Assessment of estuarine dissolved oxygen (DO) concentrations have been made using the following EPA Marine Water Quality Criteria for the Northeast: £ 4.8 mg/L (chronic criterion), £ 2.3 mg/L (acute criterion). In the summer of 2000 in estuarine bottom waters of the Gulf of Maine, DO concentrations were always > 4.8 mg/L, while lower concentrations were observed in stratified waters south of Cape Cod (Narragansett Bay, Long Island Sound, NJ coastal bays, & Chesapeake Bay). In the subsequent summers (2002, 2003) complementary monitoring designs in Narragansett Bay utilized moored instrumentation to capture the spatial and temporal aspects of the formation and transport of low DO water, and additional targeted sampling during periods of increased water column stratification (minimum neap tides) to document the spatial extent of anticipated hypoxic / anoxic events. Targeted sampling following the minimum neap tides in August during both very dry (2002) and very wet (2003) summers detected large areas of bottom water below the acute 2.3 mg/L DO concentration. Both events were accompanied by localized fish kills.

Keywords: Monitoring Coastal Conditions, Northeastern US, Estuaries, Dissolved Oxygen,
Spatial and Temporal Variations, Probability Based Surveys, Hybrid Monitoring Designs.

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