HR: 0800h
AN: B41A-0030    [Abstracts]
TI: Isotopic evidence for the source and fate of P in the Everglades wetlands
AU: * Li, X
EM: xli@mail.magnet.fsu.edu
AF: Department of Geological Sciences,Florida State University & NHMFL, 1800 East Paul Dirac Drive, Tallahassee, FL 32310, United States
AU: Wang, Y
EM: ywang@mail.magnet.fsu.edu
AF: Department of Geological Sciences,Florida State University & NHMFL, 1800 East Paul Dirac Drive, Tallahassee, FL 32310, United States
AB: High phosphorus (P) influx into wetland ecosystems in the Florida Everglades continues to be a problem. The increased P loading has been linked to changes in flora and fauna and the degradation of water quality in the wetlands. The number and species of animals have dramatically declined due to the agricultural and urban development since 1900. The plant community has also shifted from P-limited sawgrass (Cladium) to P-adapted cattail (Typha) in areas impacted by agricultural runoff. Although the effects of P loading on ecosystem have been recognized, little is known about how those changes affect the biogeochemical processes regulating P availability and cycling in freshwater ecosystems. The P-O bond in phosphate is resistant to hydrolysis in inorganic systems. However, the P-O bond can be easily broken in enzyme-mediated biochemical reactions, resulting in rapid oxygen isotope exchange with surrounding water within organisms. Thus, oxygen isotopic composition of phosphate should indicate the environment and processes of its formation. Oxygen isotopes in phosphate may provide a useful tool for tracing the source and recycling of phosphorus in aquatic systems. Here, I present the results of an oxygen isotopic study of phosphate in a constructed wetland (Storm water Treatment Area STA-1W) in northern Everglades as well as in a relatively pristine wetland in the Everglades National Park (ENP). Oxygen isotopic compositions of dissolved inorganic phosphate (DIP) in water and of total phosphate in sediment were determined using a High Temperature Conversion Elemental Analyzer (TC/EA) interfaced to a Finnigan MAT Delta Plus XP stable isotope ratio mass spectrometer (IRMS) at NHMFL. The data show: 1) there is no clear relationship between the d18O of DIP and P concentration in the water; 2) the d18O value of DIP is correlated with hydrological data (what kind?); 3) d18O value of DIP is not in equilibrium with water. The DIP samples collected in July are closer to isotopic equilibrium with environmental water than in April, indicating a faster biochemical cycling in the summer than in the spring. Our data also show that the d18O values of total phosphate in sediment cores from both STA1W and ENP display a very similar pattern, likely reflecting the interaction of remineralization and influence of anthropogenic P input (e.g. fertilizer).
DE: 0330 Geochemical cycles (1030)
DE: 0470 Nutrients and nutrient cycling (4845, 4850)
DE: 0497 Wetlands (1890)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting