Biogeochemistry

, Volume 94, Issue 1, pp 43–62

Influences of climate, hydrology, and land use on input and export of nitrogen in California watersheds

  • Daniel J. Sobota
  • John A. Harrison
  • Randy A. Dahlgren
Article

DOI: 10.1007/s10533-009-9307-y

Cite this article as:
Sobota, D.J., Harrison, J.A. & Dahlgren, R.A. Biogeochemistry (2009) 94: 43. doi:10.1007/s10533-009-9307-y

Abstract

Human activities have greatly increased the input of biologically available nitrogen (N) from land-based sources to aquatic ecosystems; yet few studies have examined how human actions influence N export in regions with a strong seasonality in water availability. In this study, we quantified N inputs and outputs for 23 California watersheds and examined how climate, hydrology, and land use practices influenced watershed N export. N inputs ranged from 581 to 11,234 kg N km−2 year−1 among watersheds, with 80% of total input for the region originating from agriculture (inorganic fertilizer, manure, and legumes). Of the potential N sources examined, mean annual concentrations of dissolved organic N and dissolved inorganic N in study rivers correlated most strongly with manure N input (r2 = 0.54 and 0.53, respectively). Seasonal N export varied by basin and was correlated with climate, anthropogenic N inputs, and reservoir releases. Fractional export of watershed N inputs by study rivers annually was small (median of 8%) and scaled exponentially with runoff (r = 0.66). Collectively, our results show that anthropogenic activities have altered both the magnitude and timing of watershed N export in California and suggest that targeted management in specific locations and times of the year could reduce N export to downstream systems in the region.

Keywords

Agriculture California Denitrification Nitrogen Nutrient budget Watershed Mediterranean climate 

Copyright information

© Springer Science+Business Media B.V. 2009

Authors and Affiliations

  • Daniel J. Sobota
    • 1
  • John A. Harrison
    • 1
  • Randy A. Dahlgren
    • 2
  1. 1.School of Earth and Environmental SciencesWashington State UniversityVancouverUSA
  2. 2.Department of Land, Air and Water ResourcesUniversity of CaliforniaDavisUSA

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