title: Linking dissolved and particulate phosphorus export in rivers draining California's Central Valley with anthropogenic sources at the regional scale.
abstract: 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 yr 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 yr) 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.
authors.affiliation: Washington State University, Vancouver, WA, USA. Sobota.Dan@epa.gov
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Sobota
authors.forename: John A
authors.initials: JA
authors.lastname: Harrison
authors.forename: Randy A
authors.initials: RA
authors.lastname: Dahlgren
mesh_terms: D000383:Agriculture; D002140:California; D002947:Cities; D004784:Environmental Monitoring; D005308:Fertilizers / Q000032:analysis; D008372:Manure / Q000032:analysis; D010758:Phosphorus / Q000032:analysis*; D045483:Rivers / Q000737:chemistry*; D012621:Seasons; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D005308:Fertilizers; D008372:Manure; D014874:Water Pollutants, Chemical; D010758:Phosphorus