HR: 0800h
AN: B11A-0052    [Abstracts]
TI: Investigating the Sources and Dynamics of Dissolved Organic Matter in an Agricultural Watershed in California (U.S.A.)
AU: * Dyda, R Y
EM: rydyda@ucdavis.edu
AF: University of California Davis, Department of Land, Air and Water Resources, One Shields Ave, Davis, CA 95616, United States
AU: Hernes, P J
EM: pjhernes@ucdavis.edu
AF: University of California Davis, Department of Land, Air and Water Resources, One Shields Ave, Davis, CA 95616, United States
AU: Spencer, R G
EM: rgspencer@ucdavis.edu
AF: University of California Davis, Department of Land, Air and Water Resources, One Shields Ave, Davis, CA 95616, United States
AU: Ingrum, T D
EM: tdingrum@ucdavis.edu
AF: University of California Davis, Department of Land, Air and Water Resources, One Shields Ave, Davis, CA 95616, United States
AU: Pellerin, B A
EM: bpeller@usgs.gov
AF: U.S. Geological Survey, 6000 J Street Placer Hall, Sacramento, CA 95819, United States
AU: Bergamaschi, B A
EM: bbergama@usgs.gov
AF: U.S. Geological Survey, 6000 J Street Placer Hall, Sacramento, CA 95819, United States
AB: Dissolved organic matter (DOM) is ubiquitous and plays critical roles in nutrient cycling, aquatic food webs and numerous other biogeochemical processes. Furthermore, various factors control the quality and quantity of DOM, including land use, soil composition, in situ production, microbial uptake and assimilation and hydrology. As a component of DOM, dissolved organic carbon (DOC) has been recently identified as a drinking water constituent of concern due to its propensity to form EPA-regulated carcinogenic compounds when disinfected for drinking water purposes. Therefore, understanding the sources, cycling and modification of DOC across various landscapes is of direct relevance to a wide range of studies. The Willow Slough watershed is located in the Central Valley of California (U.S.A.) and is characterized by both diverse geomorphology as well as land use. The watershed drains approximately 425 km² and is bordered by Cache and Putah Creeks to the north and south. The study area in the watershed includes the eastern portion of the foothills of the inner Coast Range and the alluvial plain and encompasses diverse land uses, including orchards, viticulture, dairy, pasture and natural grasslands. The Willow Slough watershed represents a unique opportunity to examine DOC dynamics through multiple land uses and hydrologic flow paths that are common throughout California. Preliminary data show that DOC concentrations at the watershed mouth peak during winter storms and also increase gradually throughout the summer months during the agricultural irrigation season. The increasing DOC concentrations during the summer months may result from agricultural runoff and/or primary production in channel. In addition, initial results using the chromophoric DOM (CDOM) absorption coefficient and spectral slope parameters indicate seasonal differences in the composition of the DOM. Spectral slopes decreased during both the summer irrigation season and winter storms relative to winter base flow, consistent with an increase in terrestrial signature. Biomolecular markers such as lignin phenols provide diagnostic source information on DOM as they are derived uniquely from vascular plants. Lignin can be used to differentiate angiosperm and gymnosperm tissues, but more importantly for this study, carbon-normalized yields can help to constrain the proportions of the increasing DOC during irrigation that come from vascular plants versus in situ production. In addition to supplying useful source information, dissolved lignin phenols undergo rapid photodegradation when exposed to adequate solar radiation, and this process is "imprinted" through increases in the acidic components of lignin and decreases in the syringyl phenols, thus providing insight into DOM cycling in agriculture-dominated watersheds. Data will be presented highlighting the use of a range of analytical and spectrophotometric measurements including lignin phenols, ¹³C of DOC and CDOM in the Willow Slough watershed for investigating sources and dynamics of DOM throughout the watershed.
DE: 0420 Biomolecular and chemical tracers
DE: 0428 Carbon cycling (4806)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting