Emily Gravens, Montana State University, Bozeman

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This study examines two simple nitrogen loading models, an excel spreadsheet based nitrogen loading model and a web-based pollution runoff model, applied to two small watersheds within the larger Chesapeake Bay watershed. The values for nitrogen runoff generated by the models are compared to nitrogen runoff values from field studies. The Nitrogen Loading Model, NLM, overestimated the observed value by 17.5% while the Long Term Hydrologic Impact Analysis model, L-THIA, underestimated the observed value by 37%. For a watershed with an area of just over 36 km2 the NML predicted, 17,382 kg N/yr and the L-THIA model predicted 10,797 kg N/yr, field studies showed 14,789 kg N/yr. These results suggest the usefulness of the models for local management, but still require the input of specialists and continued field analysis to determine long-term impacts of land management decisions.