In regions with steep slopes, underlain by a shallow restrictive layer, runoff losses can be significant. Suburban developments present significant areas of impervious surfaces, which prevent runoff from infiltrating the soil, and increases runoff losses. Fertilized home lawns, wooded lots, sports field, parks, and construction sites can contribute significant phosphorus to surface water bodies causing impaired water quality. The Soil Moisture Distribution and Routing Model (SMDR) was used to model the soil moisture distribution and the ensuing effect on stream flow and dissolved phosphorus (DP) transport in a sloped suburban watershed in Ithaca, NY. Following parameterization of the hydrological portion of the model (E=0.76) the dynamics of DP transport in and from the watershed was modeled and assessed. Landuse in the watershed was divided into representative units (fertilized lawns, unfertilized lawns, wooded areas, impervious) which were assigned P export coefficients based on soil test P and measured DP runoff concentrations from the landuses in the watershed. SMDR running on a daily time step with a grid cell size of 10 m was able to adequately capture the dynamics of DP concentrations and stream loads. Since the model assumes that all precipitation falling on pervious surfaces infiltrates, there were several Hortonian flow events where the DP concentration was underestimated (E=0.61). However, since runoff losses from these events were generally small, the DP flux was captured well (E=0.74). As a result of high runoff losses impervious surfaces and unfertilized areas had disproportionate DP losses. Modeled DP loads from the six largest runoff events were within 8% of the observed loads. These results indicated that SMDR is a valuable tool to assess P losses from diverse landscapes found in suburban areas.
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