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Tracing nutrient and organic matter sources and biogeochemical processes in the Sacramento River and Northern Delta: proof of concept using stable isotope data

Carol Kendall*, Megan B. Young, Steven R. Silva (USGS-Menlo Park); Tamara Kraus (USGS-Sacramento); Sara Peek (USGS-Menlo Park); Marianne Guerin (RMA-Fairfield)

Citation: Kendall, C., Young, M.B., Silva, S.R., Kraus, T.E.C., Peek, S., and Guerin, M., 2015. Tracing nutrient and organic matter sources and biogeochemical processes in the Sacramento River and Northern Delta: proof of concept using stable isotope data. U.S. Geological Survey, Data Release, http://dx.doi.org/10.5066/F7QJ7FCM

Abstract

Isotope and chemical data for samples collected during several overlapping studies in the Sacramento River and Delta conducted 2009-2011 is presented to evaluate the potential usefulness of stable isotope techniques for testing hypotheses about sources of nutrients and algae, and biogeochemical processes in section of the San Francisco Estuary. These data are used to provide an independent test of the hypothesis that ammonium derived primarily from waste-water treatment plants was inhibiting phytoplankton uptake of nitrate. These data represent approximately monthly samples from 15-20 sites along transects of the river and delta and were analyzed for the stable isotopic compositions of ammonium, nitrate, particulate organic matter, dissolved organic carbon, and water then used to demonstrate the viability of assessing the temporal and spatial variations in the sources, transport, and sinks of nutrients and organic matter in the Sacramento River and Delta Another main focus was to assess whether there were significant differences between the chemistry and isotopic compositions of mainstem Sacramento River samples and (1) samples from tributaries within the Cache/Yolo Slough Complex, and (2) samples from the main two distributaries of the Sacramento River downstream of the waste-water treatment plant: Miner Slough and Steamboat Slough.

Using these data we present (1) "proof of concept" of the usefulness of isotope techniques combined with water chemistry and hydrological modeling in this ecosystem, (2) key findings from some of the ongoing parts of the studies, and (3) downloadable Excel files of the relevant isotope and chemistry data with associated metadata to facilitate these data being used for other investigations. The rationale was that if isotope techniques showed promise in identifying sources and processes in this ecosystem, a comprehensive multi-isotope approach would later be used for quantifying nutrient and organic matter sources and biogeochemical processes relevant to questions about causes of environmental problems. These more quantitative assessments are in progress.