HR: 16:48h
AN: H44B-05    [Abstracts]
TI: The Influence of Subsurface Processes on the Concentration and Composition of Dissolved Organic Matter
AU: * Aiken, G
EM: graiken@usgs.gov
AF: U.S. Geological Survey, 3215 Marine Street, Boulder, CO 80303 United States
AB: Microbial and geochemical interactions in the subsurface can result in chemical alteration and fractionation of organic matter thereby altering the nature and composition of dissolved organic matter (DOM) in groundwater and in surface waters dominated by ground water inflow. In this paper, the results of a study designed to determine the effectiveness of subsurface processes for removing DOM from two surface waters in Southern California will be presented. The recharge zones immediately underneath two infiltration basins, Anaheim Lake and Kraemer Basin, were found to be very active with respect to changes in the amounts and reactivities of the DOM. In all cases, dissolved organic carbon (DOC) concentrations decrease as water moves from the basins into the regional aquifer system. Data obtained from relatively shallow wells located near the infiltration basins (travel times less than 30 days) indicate that a large amount of DOM is removed during the first stages of transport in the subsurface. Parcels of water from both basins were followed for up to 360 days as the water moved away from the infiltration basins. DOC concentrations and specific ultraviolet absorbance (SUVA), an excellent indicator of aromatic carbon content of DOM, continued to decrease substantially with a general decrease in DOC concentration of about 70%. Regardless of initial DOC concentrations present in the infiltration basins, values decreased to approximately 1.3 mg C/L at the furthest points sampled. Analyses of organic matter isolates obtained by chromatographic methods indicated greater removal of aromatic molecules and preservation of branched chain aliphatic and alicyclic structures more resistant to biodegradation. Compared to samples from a wide range of environments, the DOM in the down gradient wells most closely resembled similar materials obtained from other groundwater systems and those of microbial origin. These results suggest that subsurface processes are significant in the metabolism of terrestrially derived material and contribute to the evolution of DOM pools from ones dominated by terrestrially derived material to those of microbial origin. Ultimately, these processes exert strong controls on the composition and reactivity of DOM in ground water and contribute to the pools of compounds comprising DOM in surface water systems receiving ground water discharge.
DE: 1800 HYDROLOGY
DE: 1806 Chemistry of fresh water
DE: 1831 Groundwater quality
DE: 1871 Surface water quality
DE: 0400 Biogeosciences
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting