Projections of Watershed Pollutant Loads Using a Spatially Explicit, Agent-Based Land Use Conversion Model: A Case Study of Berkeley County, West Virginia

Abstract

This research presents a methodology to make projections of land use conversions in Berkeley County, West Virginia and then utilizes these projections to estimate water quality impacts on the Opequon Creek in Berkeley County. Empirical estimates for factors that influence the land use conversion probability are captured using parameters from a spatial logistic regression (SLR) model. Then, an agent-based, probabilistic land use conversion (APLUC) model is used to explore the impacts of policies on land use conversion decisions using estimates from actual land use change from 2001 to 2011 in SLR model. Three policy scenarios are developed: (1) no policy implementation, (2) a 15.24 m (50 ft) buffer zone policy of no development applied to all streams, and (3) 15.24 m buffer policy applied only on critical source area (CSA) watersheds. The projected land use patterns in the APLUC model are driven by individual land conversion decisions over 50 model runs of 10 iterations each under each policy scenario. The results show that with no policy scenario, most conversions occurred near existing residential land use and urban centers. Residential land use conversions are greatly reduced in a 15.24 m buffer policy around all streams in watershed. Spatial patterns generated under a 15.24 m buffer policy in CSAs only showed that future projected land use changes occurred close to major highways and shifted the residential development to the northern part of the Opequon Creek. Finally, the impacts of these three policies on water quality are estimated using an ArcSWAT model, a graphical user interface for SWAT (Soil and Water Assessment Tool). This model indicates that the 15.24 m buffer policy in CSAs is most effective among the three policies in reducing the pollutant loads. This study suggests that carefully designed policies which discourage residential land use conversions in CSAs, result in less pollutant loads by shifting the location of residential conversions to less critical areas where agricultural land is dominant in the watershed.