Simulating the Long-Term Impact of BMPs on the Off-Site Transport of Sediment and Phosphorus Using the Agricultural Policy Environmental eXtender (APEX) Model.

Land use may be the single greatest factor that affects the quality of natural resources. Nonpoint source pollutants, such as phosphates and sediment, from agricultural lands have the potential to degrade surface waters.  Best management practices (BMPs) have been implemented to reduce these pollutants at Chesapeake Farms, however, no follow up monitoring has been completed to determine the effectiveness of the BMPs. There is a need to have a quantitative estimate of the impact of land use practices on pollutant loadings to surface waters.  The Agricultural Policy Environmental eXtender (APEX) Model is designed to simulate field scale and small watershed level landscape dynamics.  Components for crop growth, surface hydrology, erosion, and plant nutrient dynamics are simulated.  The objective of this research was to quantify the amount of off-site transport of phosphorus and sediment from the Chesapeake Farms watershed using the APEX model.

Based on site specific conditions, soil, long-term weather, crop and land management input databases were developed for the APEX model.  Cropping and nutrient management systems and grassed waterways, which have been implemented at Chesapeake Farms over a 30 year period, were integrated into the APEX model. Simulations were completed for 30 years and comparisons between BMPs and no BMPs were analyzed using a paired-t test.

The APEX Model appeared to be well suited to simulate the effectiveness of BMPs on off-site transport of sediment and phosphorus.  Multiple fields can be interlinked and hydrology, sediment and nutrient dynamics can be routed from one sub-watershed to neighboring sub-watersheds. Conservation practices designed to reduce nonpoint source pollution loading to nearby surface waters can be investigated.  The APEX model appeared to be effective as an environmental diagnostic tool.