Evaluating Agricultural Nonpoint‐Source Pollution Using Integrated Geographic Information Systems and Hydrologic/Water Quality Model

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Abstract
Considerable progress has been made in developing physically based, distributed parameter, hydrologic/water quality (H/WQ) models for planning and control of nonpoint‐source pollution. The widespread use of these models is often constrained by the excessive and time‐consuming input data demands and the lack of computing efficiencies necessary for iterative simulation of alternative management strategies. Recent developments in geographic information systems (GIS) provide techniques for handling large amounts of spatial data for modeling nonpoint‐source pollution problems. Because a GIS can be used to combine information from several sources to form an array of model input data and to examine any combinations of spatial input/output data, it represents a highly effective tool for H/WQ modeling. This paper describes the integration of a distributed‐parameter model (AGNPS) with a GIS (ARC/INFO) to examine nonpoint sources of pollution in an agricultural watershed. The ARC/INFO GIS provided the tools to generate and spatially organize the disparate data to support modeling, while the AGNPS model was used to predict several water quality variables including soil erosion and sedimentation within a watershed. The integrated system was used to evaluate the effectiveness of several alternative management strategies in reducing sediment pollution in a 417‐ha watershed located in southern Iowa. The implementation of vegetative filter strips and contour buffer (grass) strips resulted in a 41 and 47% reduction in sediment yield at the watershed outlet, respectively. In addition, when the integrated system was used, the combination of the above management strategies resulted in a 71% reduction in sediment yield. In general, the study demonstrated the utility of integrating a simulation model with GIS for nonpoint‐source pollution control and planning. Such techniques can help characterize the diffuse sources of pollution at the landscape level.

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