National Research Program | Isotope Tracers Project

Isotope Tracers Project Personnel

Nina’s main duties are to prepare organic matter samples for C-N-S isotopic analysis, process field samples, prepare media for the microbial nitrate isotope method, and assist with tritium sample distillations.

TB is the lead technician in the tritium laboratory, sharing responsibility for keeping the tritium laboratory running smoothly at maximum capacity; he also prepares organic matter samples for C-N-S isotopes, processes field samples, and prepares nitrate isotope samples.

CHOY, Doug (650-329-4316,
Doug handles much of the responsibility for training and supervising junior team members in the labs, database management, safety issues, instrument maintenance, ordering supplies, running the laser spec and TIC-TOC, and preparing for field trips. Doug also oversees the daily operation of the tritium lab.

KENDALL, Carol (650-329-4576,
Chief of the Isotope Tracers Project. Carol's main field of interest is watershed biogeohydrochemistry, especially in large human-impacted basins. Other interests include: nitrate and organic matter sources and cycling in aquatic systems, the development of new analytical methods and practical applications for CHNOS stable isotopes, and teaching about applications of isotopes for water quality and ecological studies.

MICHEL, Bob (650-329-4547,
Former chief of the Menlo Park Tritium Lab, now retired from the USGS but still part of the team. Bob's main fields of interest are alpine and arid zone hydrology.

MIXON, Rachel (650-329-5603,
Rachel splits her time between field work in the Sacramento Bay, preparing and analyzing ammonium isotope samples, distilling samples for tritium analysis, and helping with data corrections.

PEEK, Sara (650-329-4509,
Sara divides her time between method development, instrument maintenance, analyzing nitrate and other samples for isotopic composition, database management, and helping with ongoing ecological projects.

SILVA, Steve (650-329-4538,
Assistant Project Chief. Steve divides his time between methods development research, several research projects related to nutrient sources and organic matter sources, instrument maintenance, and budget and personnel paperwork. Most of his current methods development research has been on devising new ways to expand project analytical capabilities.

TU, Ying (
Ying’s main duties are to prepare organic matter samples for C-N-S isotopic analysis, process field samples, prepare media for the microbial nitrate isotope method, and help prepare nitrate isotope samples.

YOUNG, Megan (650-329-4544,
Megan specializes in isotope biogeochemistry research, with a focus on nutrient source and cycling dynamics. She also runs the Menlo Park Tritium Laboratory, providing tritium analysis for groundwater age dating and contaminant tracing within the USGS. She is currently working on several different projects using multiple stable isotopes to trace interactions between groundwater, surface water, and anthropogenic nutrient inputs.

Past Team Members

BEMIS, Bryan.
Bryan was an isotope geochemist post-doc. His main interests were applying isotopic ratio techniques to solving environmental problems, including using compound specific isotopic ratio techniques for tracing sources of nutrients to the base of aquatic food webs, food chain reconstructions, mercury bioaccumulation, characterizing sources of DOC to wetlands, and correlating THM formation potential with DOC type. He is now a biogeochemist at Applied Marine Sciences, CA.

CHANG, Cecily.
Cecily divided her time between methods development work, and working with WEBB, NAWQA, and other nitrate-related projects. Cecily developed an improved method for collecting and analyzing nitrate for 18O from very dilute, DOC rich waters that was used in many watershed nitrate studies. She is currently focusing on nitrate sources and cycling in big river systems. She has retired from the USGS.

Dan was an NRC post-doc, and divided his time between working on sources and cycling of carbon (DIC and DOC) at one of the WEBB program sites (Sleepers River VT) using our new automated TIC/TOC analyzer connected to an IsoPrime mass spectrometer, and working on our CALFED-funded projects. He is now a research geologist at the USGS in Reston VA.

Emily was an isotope biogeochemist post-doc working on our NYSERDA and EPRI-funded project on mapping the nitrate isotopic composition of precipitation across the USA, and in particular the state of NY. We were testing the hypothesis that nitrate in precipitation derived from emissions from vehicles and power plants might have distinguishable nitrate isotope compositions. She is now an assistant professor in the geology department of the University of Pittsburgh, in PA.

WANKEL, Scott.
Scott divided his time between managing our laboratory database and helping with method development and ongoing ecological projects, with his thesis work (at Stanford, in collaboration with Adina Paytan). He was especially interested in foodweb ecology at the bottom of the foodweb. His dissertation focused on nutrient sources and cycling in Monterey Bay. He is now a research scientist at WHOI, MA.

Project Contacts:

  • Carol Kendall
    U.S. Geological Survey
    345 Middlefield Rd, MS 434
    Menlo Park, CA 94025

  • Megan Young
    U.S. Geological Survey
    345 Middlefield Rd, MS 434
    Menlo Park, CA 94025

  • Steve Silva
    U.S. Geological Survey
    345 Middlefield Rd, MS 434
    Menlo Park, CA 94025