HR: 0800h
AN: B11A-0053    [Abstracts]
TI: Microbial Origin and Transformation of Dissolved Organic Matter in the Agricultural Willow Slough Watershed, California: Insights From Amino Sugars
AU: * Journet, S
EM: sjournet@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
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
AB: Understanding the fundamental processes and land management practices affecting dissolved organic matter (DOM) cycling in agricultural watersheds is essential for managing drinking water quality and maintaining ecosystem health. Although dissolved organic nitrogen (DON) is increasingly recognized as a key component of DOM in disturbed watersheds, our knowledge of its origin and reactivity are limited due to multiple sources, microbial uptake, and secondary production. In particular, the effect of microbial processes on DON dynamics remains poorly understood at the watershed scale. The seasonal and spatial variations of DON concentrations in the surface waters of the Willow Slough watershed, a 425-km² agriculturally-dominated catchment in the northern Central Valley of California, USA, were monitored weekly at 8 locations since January 2006. Amino sugars are specific microbial biomarkers and their unique distribution among groups of microorganisms such as bacteria, fungi, and algae allows the distinction between different sources of DOM. Although mean annual DON concentrations were lower at the headwaters (0.18 mg/L) than the outlet (0.45 mg/L), DON constituted up to 90% of the total dissolved nitrogen (TDN) at the headwaters, compared to only 15% of the TDN at the watershed outlet. During winter baseflows, DON concentrations at the outlet were low (0.2 mg/L), while they increased to about 1.2 mg/L during winter storms. Remarkably, DON concentrations increased and remained high at 0.6 mg/L during the summer irrigation season. Preliminary data suggests that winter storm runoff and summer irrigation flows are dominated by DON of terrestrial origin, whereas periods of winter baseflow are mainly composed of algal-derived DON. The concentration of total dissolved amino sugars in the Willow Slough surface waters and the contribution of amino sugars to the DON pool (% DON-AS) will be used to evaluate DON composition and degradation state. In addition, molar ratios of four amino sugars monomers; glucosamine, galactosamine, muramic acid and mannosamine, will provide insight on the origin of DON. Microbial processing is at the heart of nutrient and carbon recycling, and as such, the results of this research will have implications beyond the Willow Slough watershed.
DE: 0420 Biomolecular and chemical tracers
SC: Biogeosciences [B]
MN: 2007 Fall Meeting