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Oct. 19, 2010
3:00 PM
MSB 110
Environmental isotope tracers: using a multi-isotope approach to understand complex hydrological problems

Megan Young, Isotope Tracers Project, U.S. Geological Survey, Menlo Park, CA


Understanding nutrient and organic matter sources, sinks, and biogeochemical cycling is a critical component in environmental studies for both pristine and human-impacted systems. The scale and complexity of large hydrologic systems present logistical, financial, and interpretive challenges due to the difficulty of constraining both sources and biogeochemical dynamics. The use of multi-isotope (H-C-N-O-S) approaches in monitoring studies can provide critical insights into nutrient behavior over large spatial and temporal scales in both surface and ground water systems. Our studies in the San Joaquin River, Sacramento River, and San Francisco Bay demonstrate how the measurement of stable isotopes in water, nitrate, ammonium, phosphate, and particulate and dissolved organic matter can be used to constrain potential sources and sinks of nutrients, and identify biogeochemical processes that may not be evident through concentration analysis alone. Measurements of nitrate and water isotopes in shallow ground water within California’s Central Valley show strong heterogeneity, but under certain conditions provide clear distinctions between dairy-derived nitrate and nitrate from other sources. I will also discuss ongoing research on the oxygen isotopic composition of dissolved phosphate, a relatively new stable isotope technique which shows strong potential for identifying various sources of phosphate in aquatic ecosystems.

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