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Sediment Pore Water Ammonium and Phosphate Concentrations in Choctawhatchee Bay as?Determined by the Diffusive Equilibration in Thin Films (DET) Technique
Citation:
Burke, R., R. Mckinley, K. Mcneal, J. Martin, AND M. Parsons. Sediment Pore Water Ammonium and Phosphate Concentrations in Choctawhatchee Bay as?Determined by the Diffusive Equilibration in Thin Films (DET) Technique. 10th National Water Quality Monitoring Conference, Tampa, FL, May 02 - 06, 2016.
Impact/Purpose:
In support of the RARE project: "Improving TMDL and Waste Load Allocation Permit Limits by Determination and Application on New Sediment Diagenesis Input Parameters in Current Water Quality Models"
Description:
Choctawhatchee Bay (CB) is a large estuarine ecosystem in northwest Florida that provides quality of life and economic benefits to local residents. The CB watershed is largely forested, but with significant agriculture in its northern part and intense residential and commercial development of the land-estuary interface. In spite of these anthropogenic disturbances, CB is not considered to be nutrient impaired at present, and the current regulatory strategy is to maintain the status quo with respect to nutrients. The rapidly growing human population in the area has the potential, however, to create significant nutrient stresses on the system in the future. To protect the ecosystem from future eutrophication, we will need better estimates of nutrient inputs from the various sources. One source that apparently has not been considered in CB nutrient budgets is flux from the sediments. Diagenesis of organic matter in sediments generally leads to elevated pore water nutrient concentrations, which can then drive sediment-water nutrient flux. In July 2013, we determined pore water ammonium and phosphate concentrations at eight sites scattered throughout CB with diver-deployed sediment probes employing the diffusive-equilibration-in-thin-films (DET) technique. Observed mean pore water ammonium concentrations ranged from about 1.5 to 4.5 mg N/L and mean phosphate concentrations ranged from about 0.25 to 0.75 mg P/L. These concentrations are 5 to 10 times higher than concentrations observed in the water column and suggest the potential for the sediments to be a significant source of nutrients to CB surface waters. Further, pore water N/P ratios ranged from 3 to 8, which is considerably lower than observed TN/TP ratios in the water column (18 to 23). Given that CB algal production is judged to generally be P-limited based on the elevated surface water TN/TP ratios, diffusion or advection of the P-replete pore waters across the sediment-water interface would be expected to stimulate algal production.
