Use of GIS and remote sensing to develop indicators of phosphorus non-point source pollution in the Pike River basin

The Pike River is amongst the main watercourses discharging into Missisquoi Bay, a spur of Lake Champlain extending into Quebec. Its watershed drains some 630 km(2), of which 99 km(2) are located in Vermont. The objective of this study is to adapt agrienvironmental indicators to the landscape scale to provide an holistic perspective of phosphorus sources and transfer in the Pike River watershed. The development of agrienvironmental indicators of non-point P pollution was supported by remote sensing, spatial integration of data and the Soil and Water Assessment Tool (SWAT). These indicators were evaluated on subwatersheds of about 5 km(2). The validation of the indicators at the subwatershed scale was supported by water quality records from the monitoring of 18 tributaries and sections of the Pike River. The agricultural land use, topographic attributes, the runoff SCS curve number, the mass balance of P and the P soil saturation were significantly correlated with P concentrations measured under peak streamflow conditions, in response to spring and fall long-duration precipitations, snowmelt and saturated or frozen soil conditions. It was found that 73 % of the variation for bioavailable P sampled within the hydrological network is explained by the P mass balance and subwatershed agricultural land use.