Estimating nutrient loads from land use patterns in the North Branch Piscataquog Watershed :a comparative study of export coefficients

Hutchins, Tracy A.
Joy Ackerman, PhD
Department of Environmental Studies
The purpose of this study is to determine the threshold phosphorus and nitrogen loads sustainable by the North branch Piscataquog Watershed. Using pollutant loading coefficients and models, the study determines the annual load of phosphorous and nitrogen contributed by present land uses in the watershed and projects nutrient contributions under future land use scenarios. Nitrogen and phosphorus export coefficients and loading models were gathered from scientific literature and applied to the North branch watershed to determine the total annual Po or N load. Land uses were categorized as urban, forested or rural/agricultural. The models were then applied to various scenarios indicating changes in current land use patterns to estimate the maximum development capacity of the watershed. Phosphorous levels according to models by Rast and Lee and Uttormark et al. do not indicate a significant difference between P levels at 50% of 100% development. Phosphorus levels do not exceed the o.o3 mg/L maximum when river discharge is very low. According to the models and possible land use scenarios, increasing the acreage of open space within the watershed demonstrates the highest flux in N concentrations. The models and coefficients of Uttormark et al. (1974) and Rast and Lee, (1983), compare favorably with the sample water quality data for the North Branch Piscataquoug. Coefficients provided by Frink, (1991), result in nitrogen loads and concentrations three times that of the actual data and compared models.

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