HR: 1340h
AN: H13F-1378    [Abstracts]
TI: A Comparison of Isotopic Variation of Particulate Organic Matter on Daily and Seasonal Scales in the San Joaquin River
AU: * Silva, S
EM: srsilva@usgs.gov
AF: U.S. Geologic Survey, 345 Middlefield Rd. M/S 434, Menlo Park, CA 94025 United States
AU: Doctor, D
EM: dhdoctor@usgs.gov
AF: U.S. Geologic Survey, 345 Middlefield Rd. M/S 434, Menlo Park, CA 94025 United States
AB: Water quality issues, in particular trihalomethane production and low dissolved oxygen (DO) concentrations in the Stockton channel, are affected by the temporal and spatial variation in the cycles of phytoplankton production and decay. An understanding of phytoplankton growth and decay is necessary for the development of appropriate management strategies for the purpose of controlling associated water quality problems. Carbon isotopic analyses and C:N ratio of particulate organic matter (POM) in the San Joaquin River indicate that POM is largely composed of phytoplankton. The carbon and nitrogen isotopes of POM and the nitrogen and oxygen isotopes of nitrate collected between June and October in 2000 and 2001 from an array of stations along the river have proven useful in discerning sources of phytoplankton and the nutrients supporting them. Isotope and other data from two recent diel sampling (48 hours) events at single stations on the San Joaquin River have yielded additional information not apparent from the multi-station seasonal studies. The diel studies illustrate the dramatic effects of (1) phytoplankton photosynthesis on DO production and (2) bacterial and other in-stream respiration on DO reduction. In addition, diel trends of C:N ratios, d13C of POM, and chl-a measurements suggest consumption of a large fraction of phytoplankton at night, presumably by zooplankton. These findings indicate that phytoplankton is generated locally and has a primary role in the control of dissolved oxygen. The comparison of these studied illustrates the utility of collecting data over different time and spatial scales.
DE: 0454 Isotopic composition and chemistry (1041, 4870)
SC: Hydrology [H]
MN: Fall Meeting 2005