Evaluation of the phosphorus index in watersheds at the regional scale.
Agricultural losses of phosphorus (P) in runoff are a primary cause of eutrophication in many freshwater systems. A modified version of the P Index originally developed jointly by the USDA (Agricultural Research Service [ARS], Cooperative State Research, Education, and Extension Service [CSREES], and Natural Resources Conservation Service [NRCS]) was used to prioritize P loss vulnerability at the regional scale from 60 watersheds located within Minnesota using readily available data related to the transport and sources of P. This modified version of the P Index was created for a regionally based analysis of the index. Validation of the P Index rating was conducted using long-term water quality monitoring data consisting of total P concentrations collected from watersheds and lakes. The modified version of the P Index produced a strong correlation between P Index rating and total P stream monitoring data in watersheds (r2 = 0.70) excluding the Red River Basin. An equally strong relationship was observed between P Index rating and lake water quality (r2 = 0.68) using the modified P Index. The P Index ratings for the Red River Basin showed good correlation with observed total P stream monitoring data (r2 = 0.51); however, the P Index ratings were smaller than in other basins. The results of this study suggest that, with certain limitations, the P Index can be used at the regional scale to prioritize P loss vulnerability using state and national databases. Regional P Index ratings represent the average risk for agricultural land within the entire watershed.
Birr
A S
AS
Department of Soil, Water, and Climate, Univ. of Minnesota, St. Paul 55108, USA.
Mulla
D J
DJ
D000383:Agriculture; D016208:Databases, Factual; D004784:Environmental Monitoring; D005068:Eutrophication; D005544:Forecasting; D008962:Models, Theoretical; D010758:Phosphorus / Q000032:analysis*; D012680:Sensitivity and Specificity; D014872:Water Movements; D014873:Water Pollutants / Q000032:analysis*
D014873:Water Pollutants; D010758:Phosphorus