Biogeochemistry

, Volume 54, Issue 1, pp 85–114

Dissolved and particulate nutrient flux from three adjacent agricultural watersheds: A five-year study

  • Michael J. Vanni
  • William H. Renwick
  • Jenifer L. Headworth
  • Jeffery D. Auch
  • Maynard H. Schaus
Article

DOI: 10.1023/A:1010681229460

Cite this article as:
Vanni, M.J., Renwick, W.H., Headworth, J.L. et al. Biogeochemistry (2001) 54: 85. doi:10.1023/A:1010681229460

Abstract

Fluxes of dissolved and particulate nitrogen (N) and phosphorus(P) from three adjacent watersheds were quantified with ahigh-resolution sampling program over a five-year period. The watershedsvary by an order of magnitude in area (12,875, 7968 and 1206 ha), and inall three watersheds intensive agriculture comprises > 90% ofland. Annual fluxes of dissolved N and P per unit watershed area (exportcoefficients) varied ∼2X among watersheds, and patterns were notdirectly related to watershed size. Over the five-year period, meanannual flux of soluble reactive P (SRP) was 0.583 kg P ·ha−1 · yr−1 from the smallestwatershed and 0.295 kg P · ha−1 ·yr−1 from the intermediate-sized watershed, which hadthe lowest SRP flux. Mean annual flux of nitrate was 20.53 kg N ·ha−1 · yr−1 in the smallestwatershed and 44.77 kg N · ha−1 ·yr−1 in the intermediate-sized watershed, which had thehighest nitrate flux. As a consequence, the export ratio of dissolvedinorganic N to SRP varied from 80 (molar) in the smallest watershed to335 in the intermediate-sized watershed. Because most N was exported asnitrate, differences among watersheds in total N flux were similar tothose for nitrate. Hence, the total N:P export ratio was 42(molar) for the smallest watershed and 109 for the intermediate-sizedwatershed. In contrast, there were no clear differences among watershedsin the export coefficients of particulate N, P, or carbon, even though> 50% of total P was exported as particulate P in allwatersheds. All nutrient fractions were exported at higher rates in wetyears than in dry years, but precipitation-driven variability in exportcoefficients was greater for particulate fractions than for dissolvedfractions.

Examination of hydrological regimes showed that, for all nutrientfractions, most export occurred during stormflow. However, theproportion of nitrate flux exported as baseflow was much greater thanthe proportion of SRP flux exported as baseflow, for all threewatersheds (25–37% of nitrate exported as baseflow vs.3–13% of SRP exported as baseflow). In addition, baseflowcomprised a greater proportion of total discharge in theintermediate-sized watershed (43.7% of total discharge) than theother two watersheds (29.3 and 30.1%). Thus, higher nitrateexport coefficients in the intermediate-sized watershed may haveresulted from the greater contribution of baseflow in this watershed.Other factors potentially contributing to higher nitrate exportcoefficients in this watershed may be a thicker layer of loess soils anda lower proportion of riparian forest than the other watersheds. Theamong-watershed variability in SRP concentrations and exportcoefficients remains largely unexplained, and might represent theminimum expected variation among similar agriculturalwatersheds.

agricultural watershed nitrogen non-point sources nutrients nutrient flux phosphorus watershed 

Copyright information

© Kluwer Academic Publishers 2001

Authors and Affiliations

  • Michael J. Vanni
    • 1
  • William H. Renwick
    • 2
  • Jenifer L. Headworth
    • 3
  • Jeffery D. Auch
    • 4
  • Maynard H. Schaus
    • 5
  1. 1.Department of ZoologyMiami UniversityOxfordUSA (Author for correspondence; e-mail:
  2. 2.Department of GeographyMiami UniversityOxfordUSA
  3. 3.Department of ZoologyMiami UniversityOxfordUSA
  4. 4.Department of ZoologyMiami UniversityOxfordUSA;
  5. 5.Department of ZoologyMiami UniversityOxfordUSA;
  6. 6.Robert B. Annis Water Resources InstituteGrand Valley State UniversityAllendaleUSA
  7. 7.Department of BiologyVirginia Wesleyan CollegeNorfolkUSA

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