Funding by YSI Minding the Planet Grant. Water quality monitoring data will be analyzed using two different modeling approaches to estimate primary production and net ecosystem metabolism (NEM) in 4 estuaries in the eastern Gulf of Mexico (Grand Bay, MS; Weeks Bay, AL, Apalachicola Bay, FL; Rookery Bay, FL) and one on the Atlantic coast of Florida (Guana Tolomato and Matanzas). First, primary production and NEM will be calculated using the open water oxygen method from continuous records of DO. Second, phytoplankton production will be calculated from chlorophyll a concentrations and light attenuation data using the Cole and Cloern BZI method. The frequency and duration of hypoxia and anoxia will be determined for each estuary from continuous DO records. While inter-system comparisons of primary production among different estuaries have been made before, this study has the advantage of using identical methodologies to compare systems over similar periods of time. There are multiple years of continuous and seasonal data at all sites, with some extending back to 1992, so both seasonal and interannual variability can be addressed. The major goals of this project are: 1. Compare seasonal and interannual rates of primary production and net ecosystem metabolism in the 5 estuaries from the NERR system 2. Determine frequency and duration of anoxia and hypoxia in estuaries with continuous DO records 3. Compare estuary wide versus site specific estimates of primary production (BZI model versus continuous DO) 4. Perform time series analyses for the longer records to examine the influence of river flow, precipitation, population growth on primary production and NEM. 5. Examine the effects of nutrient loading on primary production and NEM