HR: 11:50h
AN: B12B-07    [Abstracts]
TI: Phosphate Oxygen Isotopes as a Tracer for Sources and Cycling of Phosphate in San Francisco Bay
AU: * McLaughlin, K
EM: karenmcl@pangea.stanford.edu
AF: Stanford University, Department of Geological & Environmental Sciences, Stanford, CA 94305-2115 United States
AU: Paytan, A
EM: apaytan@pangea.stanford.edu
AF: Stanford University, Department of Geological & Environmental Sciences, Stanford, CA 94305-2115 United States
AU: Kendall, C
EM: ckendall@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd, MS 434, Menlo Park, CA 94025 United States
AU: Silva, S
EM: srsilva@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd, MS 434, Menlo Park, CA 94025 United States
AB: Phosphorous is an essential macro-nutrient for primary productivity, but tracing sources and cycling of P in marine systems has been difficult to assess because P has only one stable isotope and can not be used as an isotopic tracer. Recently a new technique (McLaughlin et al., 2004) has been developed to track sources and cycling of phosphate in aquatic systems. This approach takes advantage of the strong P-O bond in phosphate, which is resistant to inorganic hydrolysis. The exchange of oxygen isotopes therein only occurs due to intracellular biological cycling. Because the d18O of phosphate will largely be determined by the isotopic composition of the water in which it is being recycled and because the isotopic composition of rivers and oceans is significantly different, the d18O of phosphate may be used as a tracer for different sources of phosphate to an estuarine system which is not phosphate limited. Consequently, the d18O of phosphate may be useful for quantifying the mixing of different sources of phosphate in estuarine systems. We applied this method to enhance our understanding of P sources and cycling in the San Francisco Bay. To this end we conducted four sampling transects from Coyote Creek in the South Bay to the Sacramento and San Joaquin Rivers in the North between October 2002 and August 2004. Phosphate d18O ranged from 10.1 to 20.1 per mil, with highest values at the Golden Gate and lowest at the San Joaquin River. Most of the Bay samples showed strong positive correlations with salinity, water d18O, and the inverse of phosphate concentration, suggesting a simple two-component mixing of oceanic and riverine sources. These data suggest that phosphate d18O can be an effective tool for identifying P point sources and understanding phosphate dynamics in the ecosystem.
DE: 4805 Biogeochemical cycles (1615)
DE: 4815 Ecosystems, structure and dynamics
DE: 4845 Nutrients and nutrient cycling
DE: 4870 Stable isotopes
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting