GIS-based evaluation of the Conservation Reserve Program in Texas County, Oklahoma

The main goal of this research was to evaluate the long-term environmental benefits of the Conservation Reserve Program (CRP). The GIS-integrated hydrologic model, AVSWAT (ArcView-Soil and Water Assessment Tool), was used to evaluate the potential environmental benefits of the CRP in the Beaver River watershed, Texas County, Oklahoma. In this study SWAT model was used to simulate erosion rates and related stream water quality. The GIS interface of AVSWAT is ideally suited for input data management and output visualization purposes. The Beaver River Watershed was subdivided into 53 sub-basins using the digital elevation model as the base data source. Calibration results using monthly predicted values generally matched well with the observed values of two USGS gage stations in the watershed. The R2 values of 0.65, 0.61 and Nash-Sutcliffe efficiency 0.63, 0.55 of stream flow for the two stations were similar to values found in the literature.; Although the simulated sediment yields was low, it correlated well with the CRP areas. The higher the CRP area the lower the sediment yield with an overall 30% reduction in annual sediment yield for Texas County. Sediment yield was highest from wheat, general agriculture and corn fields with an average of 9.25, 2.40, and 0.25 tons/ha/year respectively. Mapping sediment yield based on data from hydrologic response units determined priority areas for future CRP enrollment. The areal association between sediment yield and CRP area was calculated to be 53%. Correlation analysis also revealed a good inverse relationship between sediment yield and area under CRP. Wheat fields accounted for about 71% of total phosphorus and 77% of total nitrogen lost in Texas County. Results from Patch Analyst showed 7% increase in grassland area, 24% decrease in number of patches, and an increase in average patch size from 24 ha to 36 ha. Analysis of changes in landscape structure indicated that CRP can potentially improve the quality and quantity of wildlife habitat.