Sediment Inventory and Phosphorus Fractions for Water Conservation Area Canals in the Everglades

摘要

Nutrient loading from the Everglades Agricultural Area and nearby urban communities plus water flow rate and canal size have significantly influenced the amount of sediment and phosphorus (P) pools stored in the Water Conservation Area (WCA) canals in the Everglades. A study was conducted to characterize the potential impact that sediments might have on the overlying water column by conducting an inventory of total P (TP) and major P forms in sediments of all major canals in the WCAs. Sediment samples and sediment depth measurements were taken at transects every 1.6-km along all canals reaches. A total sediment volume of about 6.8 million m3, with a P mass of approximately 1808 Mg was estimated to be stored within all WCA canals, with the eastern canal accounting for 71% of the total sediment volume and about half of TP mass. Phosphorus fractions associated with Ca- and Mg-compounds and residual organic P (Po) were the dominant forms stored in these canals, with the greatest P mass observed in the western side of the WCAs. These results indicates that >80% of the TP mass stored in surface sediments in the WCAs is fairly stable, and represent an important long-term sink for P. Canal sediments from the eastern side of the WCAs were low in bulk density, highly organic and more susceptible to resuspension and transport during strong drainage events. These sediments showed higher Fe- and Al-bound P and organic-bound P fractions, making them more susceptible to changes in the redox potential of the sediments that could result in the long-term release of Fe-bound P to the overlying water column.