Of manatees, mangroves, and the Mississippi River: Is there an estuarine signature for the Gulf of Mexico?

Important parameters of estuarine variability include morphology, flushing times, nutrient loading rates, and wetland: water ratios. This variability both reflects and disguises underlying relationships between the physics an d biology of estuaries, which this comparative analysis seeks to reveal, us ing the Gulf of Mexico (GOM) estuaries as a starting point. A question used to focus this analysis is: are the GOM estuaries unique? The GOM receives the Mississippi River, a uniquely large, world-class river, which dominates the freshwater and nutrient inflows to the GOM continental shelf, whose ma rgins include 35 major estuarine systems. These GOM estuaries have 28% and 41% of the U.S. estuarine wetlands and open water, respectively. Within the GOM, estuarine nitrogen, phosphorus, and suspended matter loading varies o ver 2 orders of magnitude. Anoxic estuarine events tend to occur in estuari es with relatively slow freshwater turnover and high nitrogen loading. Comp ared to estuaries from other regions in the U.S., the average GOM estuary i s distinguished by shallower depths, faster freshwater flushing time, a hig her wetland area:open water area ratio, greater fisheries yield per area we tland, lower tidal range, and higher sediment accumulation rates. The avera ge GOM estuary often, but not always, has a flora and fauna not usually fou nd in most other U.S. estuaries (e.g., manatees and mangroves). Coastal wet land loss in the GOM is extraordinarily high compared to other regions and is causally linked to cultural influences. Variations in nutrient loading a nd population density are very large among and within estuarine regions. Th is variation is large enough to demonstrate that there are insufficient sys tematic differences among these estuarine regions that precludes cross-syst em analyses. There are no abrupt discontinuities among regions in the fishe ries yields per wetland area, tidal amplitude and vegetation range, salt ma rsh vertical accretion rates and organic accumulations, nitrogen retention, or wetland restoration rates. These results suggest that a comparative ana lysis emphasizing forcing functions, rather than geographic uniqueness, wil l lead to significant progress in understanding how all estuaries function, are perturbed, and even how they can be restored.