HR: 13:45h
AN: H52C-01 INVITED     [PDF]
TI: Isotopic Study of the Sources and Cycling of Nitrate and Algae Associated with Low Dissolved Oxygen Concentrations in the San Joaquin River, California
AU: Silva, S R
EM: srsilva@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., Mailstop 434, Menlo Park, CA 94025 United States
AU: Kendall, C
EM: ckendall@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., Mailstop 434, Menlo Park, CA 94025 United States
AU: * Wankel, S D
EM: sdwankel@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., Mailstop 434, Menlo Park, CA 94025 United States
AU: Bergamaschi, B
EM: bbergama@usgs.gov
AF: U.S. Geological Survey, Placer Hall 6000 J Street, Sacramento, CA 95819-6129 United States
AU: Fram, M
EM: mfram@usgs.gov
AF: U.S. Geological Survey, Placer Hall 6000 J Street, Sacramento, CA 95819-6129 United States
AU: Kratzer, C R
EM: ckratzer@usgs.gov
AF: U.S. Geological Survey, Placer Hall 6000 J Street, Sacramento, CA 95819-6129 United States
AB: Fish migration through the deep-water channel in the San Joaquin River near the city of Stockton is inhibited by periodic low oxygen concentrations during the summer and fall. The cause of this condition appears to be decomposition of algae with attendant oxygen consumption. Development of a successful remediation plan requires knowledge of the source areas of algal production, and of the nutrient sources upon which they thrive. To identify the sources of nutrients and algae, samples of seston and water were collected monthly at several river sites during the summers of 2000 and 2001, and along a transect of the entire river-delta-bay system in 2002. These samples were analyzed for major chemical constituents, nitrate d15N, d18O, seston d15N, d13C, and water d18O. Chlorophyll-a and C:N ratios indicate that the seston consisted largely of plankton. The d15N of the plankton usually tracked the d15N of the associated nitrate with about a 5 per mil fractionation in areas of high nitrate concentrations and little or no fractionation in areas of low concentration, as expected for algae using nitrate as a primary nutrient. The d15N of the nitrate was generally between +10 and +15 per mil, which could indicate either denitrification or a nitrate source of animal waste and/or sewage. A multi-isotope approach suggested that the high d15N values were only rarely caused by denitrification, implicating animal waste/sewage as a significant source of nitrate.
DE: 1806 Chemistry of fresh water
DE: 1871 Surface water quality
DE: 4845 Nutrients and nutrient cycling
DE: 4855 Plankton
DE: 4870 Stable isotopes
SC: Hydrology [H]
MN: 2003 Fall Meeting