Sources of nitrate in rivers draining sixteen watersheds in the northeastern U.S.: Isotopic constraints

  • Bernhard Mayer
  • Elizabeth W. Boyer
  • Christine Goodale
  • Norbert A. Jaworski
  • Nico Van Breemen
  • Robert W. Howarth
  • Sybil Seitzinger
  • Gilles Billen
  • Kate Lajtha
  • Knute Nadelhoffer
  • Douwe Van Dam
  • Leo J. Hetling
  • Miloslav Nosal
  • Keith Paustian


The feasibility of using nitrogen and oxygen isotope ratios of nitrate (NO 3 ) for elucidating sources and transformations of riverine nitrate was evaluated in a comparative study of 16 watersheds in the northeastern U.S.A. Stream water was sampled repeatedly at the outlets of the watersheds between January and December 1999 for determining concentrations, δ 15N values, and δ 180 values of riverine nitrate.

In conjunction with information about land use and nitrogen fluxes, δ 15Nnitrate and δ 18Onitrate values provided mainly information about sources of riverine nitrate. In predominantly forested watersheds, riverine nitrate had mean concentrations of less than 0.4 mg NO 3 -N L−1,δ 15Nnitrate values of less than +5‰, and δ 18Onitrate values between +12 and +19‰. This indicates that riverine nitrate was almost exclusively derived from soil nitrification processes with potentially minor nitrate contributions from atmospheric deposition in some catchments. In watersheds with significant agricultural and urban land use, concentrations of riverine nitrate were as high as 2.6 mg NO 3 -N L−1 with δ 15Nnitrate values between +5 and +8‰ and δ 18Onitrate values generally below +15‰. Correlations between nitrate concentrations,δ 15Onitrate values, and N fluxes suggest that nitrate in waste water constituted a major, and nitrate in manure a minor additional source of riverine nitrate. Atmospheric nitrate deposition or nitrate-containing fertilizers were not a significant source of riverine nitrate in watersheds with significant agricultural and urban land use. Although complementary studies indicate that in-stream denitrification was significant in all rivers, the isotopic composition of riverine nitrate sampled at the outlet of the 16 watersheds did not provide evidence for denitrification in the form of elevated δ 15Nnitrate and δ 18Onitrate values. Relatively low isotopic enrichment factors for nitrogen and oxygen during in-stream denitrification and continuous admixture of nitrate from the above-described sources are thought to be responsible for this finding.

Key words

denitrification nitrate nitrate sources rivers stable isotopes δ15Nnitrate δ18Onitrate 


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Copyright information

© Springer Science+Business Media Dordrecht 2002

Authors and Affiliations

  • Bernhard Mayer
    • 1
  • Elizabeth W. Boyer
    • 2
  • Christine Goodale
    • 3
  • Norbert A. Jaworski
    • 4
  • Nico Van Breemen
    • 5
  • Robert W. Howarth
    • 6
  • Sybil Seitzinger
    • 7
  • Gilles Billen
    • 8
  • Kate Lajtha
    • 9
  • Knute Nadelhoffer
    • 10
  • Douwe Van Dam
    • 5
  • Leo J. Hetling
    • 11
  • Miloslav Nosal
    • 12
  • Keith Paustian
    • 13
  1. 1.Departments of Geology & Geophysics and Physics & AstronomyUniversity of CalgaryCalgaryCanada
  2. 2.College of Environmental Science and ForestryState University of New YorkSyracuseUSA
  3. 3.Department of Plant BiologyCarnegie Institution of WashingtonStanfordUSA
  4. 4.USEPA (retired)SanfordUSA
  5. 5.Laboratory of Soil Science and Geology and Wageningen Institute for Environment and Climate ResearchWageningen UniversityWageningenthe Netherlands
  6. 6.Department of Ecology & Environmental BiologyCornell UniversityIthacaUSA
  7. 7.Institute of Marine and Coastal Sciences, Rutgers/NOAA CMER ProgramRutgers UniversityNew BrunswickUSA
  8. 8.UMR SisypheUniversity of Paris VIParisFrance
  9. 9.Department of Botany and Plant PathologyOregon State UniversityCorvallisUSA
  10. 10.Marine Biological LaboratoryThe Ecosystems CenterWoods HoleUSA
  11. 11.Department of Energy and Environmental EngineeringRensselaer Polytechnic InstituteTroyUSA
  12. 12.Department of Mathematics and StatisticsUniversity of CalgaryCalgaryCanada
  13. 13.Natural Resource Ecology LaboratoryColorado State UniversityFort CollinsUSA

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