HR: 1340h
AN: H13A-0961    [Abstracts]
TI: Diurnal variability in riverine dissolved organic matter composition determined by in situ optical measurement in the San Joaquin River, California.
AU: * Downing, B D
EM: bdowning@usgs.gov
AF: U.S.Geological Survey, 6000 J Street Placer Hall, Sacramento, CA 95819, United States
AU: Spencer, R G
EM: rgspencer@ucdavis.edu
AF: Department of Land, Air and Water Resources, University of California, Davis, One Shields Ave, California 95616, Davis, CA 95616, United States
AU: Pellerin, B A
EM: bpellerin@usgs.gov
AU: Bergamaschi, B A
EM: bbergama@usgs.gov
AF: U.S.Geological Survey, 6000 J Street Placer Hall, Sacramento, CA 95819, United States
AU: Kraus, T E
EM: tkraus@usgs.gov
AF: U.S.Geological Survey, 6000 J Street Placer Hall, Sacramento, CA 95819, United States
AU: Dahlgren, R A
EM: radahlgren@usdavis.edu
AF: Department of Land, Air and Water Resources, University of California, Davis, One Shields Ave, California 95616, Davis, CA 95616, United States
AU: Hernes, P J
EM: pjhernes@ucdavis.edu
AF: Department of Land, Air and Water Resources, University of California, Davis, One Shields Ave, California 95616, Davis, CA 95616, United States
AB: Rivers have been commonly perceived as homogeneous with respect to dissolved organic matter (DOM) concentration and composition, particularly under steady flow conditions over short time periods. Few studies have evaluated the impact of short term variability (<1 day) on DOM dynamics. Here we present results from a 2006 study in the San Joaquin River (California) where we evaluated the efficacy of using in situ optical measurements of absorption and fluorescence to elucidate changes in DOM composition. The in situ optical measurements used in this study clearly showed diurnal variations in DOM, which have previously been related to both composition and concentration, even though diurnal changes were not well reflected in bulk dissolved organic carbon (DOC) concentrations. An apparent asynchronous trend of DOM absorbance and chlorophyll-a in comparison to chromophoric dissolved organic matter (CDOM) fluorescence and spectral slope S290–350 suggests that no one specific CDOM spectrophotometric measurement explains absolutely DOM diurnal variation in this system; the measurement of multiple optical parameters is therefore recommended. The observed diurnal changes in DOM composition, measured by in situ optical instrumentation likely reflect both photochemical and biologically-mediated processes. The results of this study highlight that short-term variability in DOM composition may complicate trends for studies aiming to distinguish different DOM sources in riverine systems and emphasizes the importance of sampling specific study sites to be compared at the same time of day. The utilization of in situ optical technology allows short-term variability in DOM dynamics to be monitored and serves to increase our understanding of its processing and fundamental role in the aquatic environment.
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0428 Carbon cycling (4806)
DE: 0469 Nitrogen cycling
DE: 0470 Nutrients and nutrient cycling (4845, 4850)
DE: 0483 Riparian systems (0744, 1856)
SC: Hydrology [H]
MN: 2007 Fall Meeting