Use of Multiple Isotope Tracers (d15N, d34S, d13C, d18O) To Track Changes in Denitrification Electron Donors

EPA Grant Number: U915356
Title: Use of Multiple Isotope Tracers (d15N, d34S, d13C, d18O) To Track Changes in Denitrification Electron Donors
Investigators: Mann, Jacqueline L.
Institution: University of Maryland
EPA Project Officer: Michaud, Jayne
Project Period: September 1, 1998 through August 1, 2001
Project Amount: $73,402
RFA: STAR Graduate Fellowships (1998) RFA Text |  Recipients Lists
Research Category: Fellowship - Geology , Ecological Indicators/Assessment/Restoration , Academic Fellowships


The objectives of this research project are to use multiple isotope tracers and chemical mass balance to: (1) evaluate whether the primary electron donor—organic matter or metal sulfide—that participates in the denitrification reaction changes in response to seasonal variations within a coastal plain agricultural watershed; and (2) document the relative importance of these reactions in the overall denitrification budget.


The approach to be used in this research project starts with a detailed study of denitrification mechanisms near an incised headwater stream, where metal sulfides are likely to play an important role in the denitrification budget. Hydrophysical data, in conjunction with multiple isotope tracers (d15N, d34S, d13C, d18O) and geochemical data, will be used to document hydrodynamic responses of the watershed and to characterize the resulting denitrification pathway—organic matter or metal sulfides. Specifically, precipitation, groundwater elevations and gradients, and streamflow will be monitored to characterize the physical hydrologic conditions necessary for denitrification. Stable isotope compositions of the reactants (organic matter, metal sulfides, dissolved nitrate-N) and products (dissolved inorganic carbon, N2, dissolved sulfate-S) will be measured to determine the dominant electron donor source in the denitrification reaction. In addition, major solute concentrations in groundwaters will be measured for chemical mass balances to identify the main denitrification electron donor. Once a geochemical model is established for this headwater site, data will be collected from five to six other headwater sites to evaluate the relative importance of sulfur-induced denitrification in the denitrification budget.

Supplemental Keywords:

fellowship, isotope tracers, organic matter, metal sulfides, dissolved nitrate, denitrification, watershed, coastal plain, electron donors.

Progress and Final Reports:

  • 1999
  • 2000
  • Final