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AGU: Journal of Geophysical Research, Biogeosciences

 

Keywords

  • phosphate oxygen isotopes
  • nutrient source
  • nutrient cycling
  • estuary

Index Terms

  • Biogeosciences: Nutrients and nutrient cycling
  • Oceanography: Biological and Chemical: Stable isotopes
  • Oceanography: General: Estuarine processes
  • Biogeosciences: Biogeochemical cycles, processes, and modeling
  • Biogeosciences: Diel, seasonal, and annual cycles
Abstract
Cited By (3)
 

Abstract

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 111, G03003, 12 PP., 2006
doi:10.1029/2005JG000079

Phosphate oxygen isotope ratios as a tracer for sources and cycling of phosphate in North San Francisco Bay, California

Karen McLaughlin

Department of Geological and Environmental Sciences, Stanford University, Stanford, California, USA

Carol Kendall

United States Geological Survey, Menlo Park, California, USA

Steven R. Silva

United States Geological Survey, Menlo Park, California, USA

Megan Young

Department of Geological and Environmental Sciences, Stanford University, Stanford, California, USA

Adina Paytan

Department of Geological and Environmental Sciences, Stanford University, Stanford, California, USA

A seasonal analysis assesing variations in the oxygen isotopic composition of dissolved inorganic phosphate (DIP) was conducted in the San Francisco Bay estuarine system, California. Isotopic fractionation of oxygen in DIP (exchange of oxygen between phosphate and environmental water) at surface water temperatures occurs only as a result of enzyme-mediated, biological reactions. Accordingly, if phospate demand is low relative to input and phosphate is not heavily cycled in the ecosystem, the oxygen isotopic composition of DIP (δ18Op) will reflect the isotopic composition of the source of phosphate to the system. Such is the case for the North San Francisco Bay, an anthropogenically impacted estuary with high surface water phosphate concentrations. Variability in the δ18Op in the bay is primarily controlled by mixing of water masses with different δ18Op signatures. The δ18Op values range from 11.4‰ at the Sacramento River to 20.1‰ at the Golden Gate. Deviations from the two-component mixing model for the North Bay reflect additional, local sources of phosphate to the estuary that vary seasonally. Most notably, deviations from the mixing model occur at the confluence of a major river into the bay during periods of high river discharge and near wastewater treatment outlets. These data suggest that δ18Op can be an effective tool for identifying P point sources and understanding phosphate dynamics in estuarine systems.

Received 28 July 2005; accepted 21 April 2006; published 19 July 2006.

Citation: McLaughlin, K., C. Kendall, S. R. Silva, M. Young, and A. Paytan (2006), Phosphate oxygen isotope ratios as a tracer for sources and cycling of phosphate in North San Francisco Bay, California, J. Geophys. Res., 111, G03003, doi:10.1029/2005JG000079.

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