Natural Abundance Stable Isotope Methods Reveal History and Fate of Nitrogen Cycles at the Watershed Scale

EPA Grant Number: FP917327
Title: Natural Abundance Stable Isotope Methods Reveal History and Fate of Nitrogen Cycles at the Watershed Scale
Investigators: Enders, Sara K
Institution: University of California - Davis
EPA Project Officer: Klieforth, Barbara I
Project Period: September 1, 2011 through August 31, 2014
Project Amount: $126,000
RFA: STAR Graduate Fellowships (2011) RFA Text |  Recipients Lists
Research Category: Academic Fellowships , Fellowship - Ecosystem Services: Terrestrial Systems Soil and Plant Ecology


This research targets the following three questions: (1) How will climate warming of the California Sierra Nevada affect the amount of nitrogen available to fuel forest C storage in the future? (2) Can nitrogen isotope-based mass-balance models be used as a management tool at the watershed-scale—particularly for estimating gaseous N emissions from the soil? (3) Can nitrogen isotopes of soil compounds be used to make inferences about pre-anthropocene nitrogen cycling on modern landscapes?


This work will improve the understanding of climate controls on the nitrogen cycle in modern and past terrestrial landscapes via new nitrogen isotope techniques. This study will first develop an isotope-based model to partition gaseous and hydrologic nitrogen losses at the watershed scale across a rain-snow transition in California’s Sierra Nevada. This work will inform prediction of how warming of the Sierra will affect nitrogen and carbon cycles. Further, this work will develop a novel method to investigate pre-anthropocene terrestrial nitrogen cycling on this and other landscapes through the use of novel paleoisotope techniques.

Expected Results:

Expected results of this work include: (1) development of a watershed-scale model of climate controls on the form of nitrogen losses from a watershed; (2) prediction of gaseous and hydrologic fluxes of nitrogen responses to climate change in the Sierra Nevada; and (3) development of a soil compound-based proxy for terrestrial nitrogen cycling on past landscapes—prior to anthropogenic impact and under past climate conditions. Results will improve understanding of natural and anthropogenic terrestrial ecosystem nitrogen cycling and the ability to manage nitrogenous pollution. Further, this research will make more powerful the tool of natural abundance nitrogen isotopes by increasing the interpretability of nitrogen isotope variations now and in the past.

Potential to Further Environmental/ Human Health Protection

This work will inform efforts to regulate pollution, to value ecosystem services and to predict the ability of the biosphere to absorb increases in atmospheric CO2 as the climate warms.

Supplemental Keywords:

nitrogen, isotopes, soil, denitrification, nitrous oxide, nitrate, California, Sierra Nevada, mountain, forest, snow, climate, forests, biogeochemistry, ecosystem services, terrestrial, paleoclimate, precipitation

Progress and Final Reports:

  • 2012
  • 2013
  • Final