HR: 0800h
AN: H31D-1337    [Abstracts]
TI: Estimating Sources and Rates of Internal Cycling of DOM Using Radiocarbon in the San Joaquin-Sacramento Delta
AU: * Sickman, J O
EM: jsickman@ufl.edu
AF: Soil and Water Science Department, University of Florida, Gainesville, FL 32611 United States
AU: DiGiorgio, C L
EM: caroldi@water.ca.gov
AF: Office of Water Quality, California Department of Water Resources, Sacramento, CA 95814 United States
AU: Davisson, M L
EM: davisson2@llnl.gov
AF: Health and Ecological Assessment Division, Lawrence Livermore National Laboratory, Livermore, CA 94550 United States
AU: Lucero, D M
EM: dlucero@ufl.edu
AF: Soil and Water Science Department, University of Florida, Gainesville, FL 32611 United States
AB: Uncertainties in sources and transformations of dissolved organic matter (DOM) typically cannot be overcome using stable isotopes of carbon due to low natural variability of δ13C in sources and relatively small isotopic discrimination for the major processes producing or consuming DOM in large riverine systems. Radiocarbon, in contrast, has the potential to be a powerful tool in unraveling DOM dynamics owing to substantial variations in 14C content of autochthonous and allochthonous DOM sources to rivers. In addition, coupling radiocarbon fingerprints to DOM mass fluxes produces a powerful tool to measure internal rates of DOM turnover in complex riverine systems. Radiocarbon and stable isotopic composition of three fractions of DOM (whole water, hydrophobic and hydrophilic) were measured over a one-year period at six locations in the in the Sacramento-San Joaquin Delta of California including the California Aqueduct. Overall variation in radiocarbon concentrations ranged from 0.6 to 1.3 fmc. DOM in agricultural runoff was more 14C depleted (0.78 and 0.79 fmc for mean whole water and hydrophobic fractions) than riverine DOM inputs (0.83 and 0.98 fmc respectively). In many samples collected during the growing season, whole-water DOM 14C content was lower than in hydrophobic fractions indicating a substantial contribution of old, non-humic substances to riverine DOM loads. Coupling this wide range of radiocarbon variability to DOM fluxes reveals that the major source of organic matter to the California Aqueduct is riverine input. Furthermore, the mixing analysis suggests that a substantial amount of DOM from agricultural sources is retained within the Delta through a combination of biotic and abiotic processes.
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0496 Water quality
DE: 1040 Radiogenic isotope geochemistry
SC: Hydrology [H]
MN: Fall Meeting 2005