| Apalachicola Bay is a productive estuary located in the northern Gulf of Mexico. The high productivity is, in part, the result of the Apalachicola River delivering freshwater and nutrients to the Bay. Freshwater moderates salinity in the Bay, which creates habitat for estuarine flora and fauna. Nutrient input supports high levels of phytoplankton productivity, which supports the Bay's secondary productivity. Diversion of water from headwaters of the Apalachicola River during summer has been proposed to satisfy upstream freshwater requirements for recreation and agriculture. Natural droughts in Apalachicola Bay have led to reductions in higher trophic level productivity. The mechanisms through which water diversion are expected to reduce higher trophic level productivity in Apalachicola Bay are, for the most part, unknown.;A major pathway of mass and energy flow in the Bay is through the planktonic food web. The objective of this research was to test the hypothesis that a classical diatom-copepod-fish food chain and a microbial food web characterize planktonic food web structure in low and high salinity waters, respectively in Apalachicola Bay. To achieve these objectives, data were collected within various salinity regimes in Apalachicola Bay during 2003 and 2004.;The temporal and spatial distribution of phytoplankton growth, biomass, productivity, and size composition were determined in Apalachicola Bay. Growth, biomass, and productivity were highest between 26 and 27°C and lowest at temperature minima and maxima. Two conceptual models are proposed to describe the spatial distribution of phytoplankton growth, biomass, and productivity in well- and partially-mixed river dominated estuaries. Apalachicola Bay appears to fit both of these models, but during different time periods. During summer, growth, biomass, and productivity were highest between about 5 and 20 psu, and the phytoplankton community was primarily composed of picophytoplankton. During winter, growth, biomass, and productivity were highest between about 20 and 26 psu, but less than during summer. Picophytoplankton were the main component of the phytoplankton community in low salinity waters during winter. Microphytoplankton, however, were the main component of the phytoplankton community in mid to high salinity waters during winter. Reduced river discharge during summer 2004 led to a large reduction (up to 80% compared to summer 2003) in the areal extent of lower (<20 psu) salinity water where phytoplankton growth, biomass and productivity peaked. Lower river discharge during summer 2004 also led to lower nutrient concentrations, phytoplankton growth and productivity at a particular salinity. (Abstract shortened by UMI.). |
