Recommended Indicators of Estuarine Water Quality For Georgia
Sheldon, Joan E.
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Increasing nutrient input and subsequent eutrophication and hypoxia are concerns in many estuaries, and the U.S. EPA has mandated the development of numeric nutrient criteria to assess the status of U.S. coastal waters. However, they recognize the need for regionally appropriate criteria, as previous national-level efforts have often relied on criteria that are not equally relevant in all waters. Two pathways to eutrophication have been suggested to exist in Georgia waters: the classic phytoplankton- mediated pathway in stratified waters and an alternate pathway in which excess nutrients stimulate microbial respiration directly, resulting in low dissolved oxygen throughout a well-mixed water column. We propose a suite of seven indicators, as well as basic ancillary data (water temperature, salinity, specific conductance), that are intended to help classify and understand the causes of water quality degradation in Georgia. We recommend two immediate indicators of poor water quality (pH and dissolved oxygen) that may indicate that a stressful and potentially lethal condition is already in progress. The remaining five (nitrogen, phosphorus, chlorophyll a, transparency, and biochemical oxygen demand (BOD)) are “early warning” indicators of potentially poor water quality that should be measured in order to anticipate problems and make appropriate management decisions. These indicators, which cover the progression of eutrophication from nutrient over-enrichment to algal overgrowth (if present) to enhanced microbial respiration and hypoxia, will help to ensure that problems will not be missed due to limited sampling frequencies. We present the rationale for choosing these indicators and the considerations for developing evaluation criteria.