Modeling sediment and phosphorus loading in a small agricultural watershed

Agricultural nonpoint source pollution is considered the leading cause for water pollution in the United States. Sediment and phosphorus are two major pollutants that are responsible for water pollutions. While soil erosion degrades soil productivity, it causes water quality problem through sediment and nutrients. Excessive fertilization, particularly from phosphorus, leads to eutrophication which deteriorates surface water quality. Efforts have been made to minimize agricultural nonpoint source pollution by, for example, implementing best management practices. Controlling agricultural nonpoint source pollution requires good information and knowledge on identifying the source areas and quantifying the pollutant loadings. A water monitoring program is helpful but costly. A scientifically based model can provide an alternative approach to provide a quantitative estimation on soil erosion, sediment and nutrient loadings, and to help identify the source areas.; The goal of this research is to investigate various agricultural nonpoint source pollution models, and develop a GIS based and spatially distributed approach to better estimate soil erosion, sediment and phosphorus loading in an agricultural watershed context.; A small agricultural watershed, Marshall Drain Watershed, was selected as the study area. This watershed is approximately 400 acres with 90 percent agricultural land use. It is a subwatershed of the Sycamore Creek watershed, located in Ingham county, Michigan. Agricultural nonpoint source pollution, particularly sediments, has been identified as the major cause of water pollution in the watershed. A multi-year water quality and land use/tillage management monitoring program has been conducted in the watershed from 1990–1997. Data from this monitoring program are used in this study.; A Spatially Explicit Sediment Delivery Model (SEDMOD) and the modified Revised Universal Soil Loss Equation (MRUSLE) are used in this study. These two models are integrated into Sediment and Phosphorus Loading Model (SPLM). It is GIS based and capable of calculating soil erosion, sediment yield and phosphorus loading. The results showed SPLM estimated sediment and phosphorus loading with an improved accuracy compared to other models. Input data required to run the model are minimum and readily available. The results of this research demonstrate the benefits of using a spatially explicit model combined with GIS technology. SPLM allows users to identify the source areas and estimate NPS loadings which may lead to a cost-effective watershed planning and management for minimizing agricultural nonpoint source pollution.