GIS-based spatial indices for identification of potential phosphorous export at watershed scale

ABSTRACT:

Spatial indices for identifying potential pollution resulting from manure spread on agricultural lands were developed for evaluating lands in support of decision- and policy-making. An existing nutrient-delivery ratio was modified by calculating actual distance that water would have to travel to reach a stream and was further tailored to better represent runoff source areas in New York state by incorporating soil drainage class. The Animal Manure Potential Pollution Index (AMPPI) was derived from this modified delivery ratio and animal population census data. The AMPPI and other derived indices use geographical information and nutrient application data to identify and rank geographical areas with respect to potential nutrient export to streams. These indices were applied in the Cannonsville Reservoir Basin in Delaware County, New York. Results demonstrate the potential for using the AMPPI and its derivative indices for selecting priority areas for implementing conservation practices or enrolling lands in programs such as the Conservation Reserve Program. For example, conservation practices would result in large reductions of potential pollution per unit of area when implemented in identified areas of croplands with high AMPPI. Additionally, an efficient way to reduce total nutrient concentration in those streams that have high nutrient loading would be to enroll in conservation programs those farms located in subbasins with high nutrient export per unit area, which correspond to areas with high animal density. Farms located in subbasins that have high ratios of nutrient loss per animal unit would benefit from improved manure-management practices, such as improved manure allocation.