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This article in JEQ

  1. Vol. 40 No. 4, p. 1290-1302
    Received: Jan 5, 2011

    * Corresponding author(s): Sobota.Dan@epa.gov
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Linking Dissolved and Particulate Phosphorus Export in Rivers Draining California's Central Valley with Anthropogenic Sources at the Regional Scale

  1. Daniel J. Sobota *a,
  2. John A. Harrisona and
  3. Randy A. Dahlgrenb
  1. a Science Programs, Washington State Univ., Vancouver Campus, 14204 NE Salmon Creek Ave., Vancouver, WA 98686
    b Dep. of Land, Air and Water Resources, Univ. of California, Davis, CA 95616. Assigned to Associate Editor Paul DeLaune


Pollution of water resources by phosphorus (P) is a critical issue in regions with agricultural and urban development. In this study, we estimated P inputs from agricultural and urban sources in 24 catchments draining to the Central Valley in California and compared them with measured river P export to investigate hydrologic and anthropogenic factors affecting regional P retention and export. Using spatially explicit information on fertilizer use, livestock population, agricultural production, and human population, we calculated that net surface balances for anthropogenic P ranged from −12 to 648 kg P km−2 yr−1 in the early 2000s. Inorganic P fertilizer and manure P comprised the largest fraction of total input for all but two catchments. From 2000 to 2003, a median of 7% (range, −287 to 88%) of net annual anthropogenic P input was exported as total P (TP). Yields (kg P km−2 yr−1) of dissolved inorganic P (DIP), dissolved organic P, particulate P, and TP were not significantly related to catchment-level, per area anthropogenic P input. However, there were significant relationships between mean annual P concentrations and P input from inorganic fertilizers and manure due to the concentration of agricultural land near catchment mouths and regional variation in runoff. Catchment-level P fertilizer and manure inputs explained 4 to 23% more variance in mean annual DIP and TP concentrations than percent of catchment area in agriculture. This study suggests that spatially explicit estimates of anthropogenic P input can help identify sources of multiple forms of P exported in rivers at management-relevant spatial scales.

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Copyright © 2011. Copyright © by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.