Application of AnnAGNPS to model an agricultural watershed in East-Central Mississippi for the evaluation of an on-farm water storage (OFWS) system

Annualized Agricultural Non-Point Source Pollutant Model (AnnAGNPS) is a watershed-scale, continuous simulation, physical model that has been widely used to simulate runoff, nutrients, sediment, and pesticides in different watersheds. This study applied AnnAGNPS to simulate runoff, nutrients (total Nitrogen and total Phosphorus), and sediment from an agricultural watershed of 30.3 ha in East-Central Mississippi. AnnAGNPS was then used to evaluate an On-Farm Water Storage (OFWS) system as a Best Management Practice (BMP) for nutrient and sediment loading control from agricultural fields within this watershed and as a source of water for irrigation. An R2 of 0.85 and E of 0.82 in daily runoff estimation showed that the model can adequately simulate runoff from watersheds in East-Central Mississippi. In addition, an R2 of 0.88 and E of 0.67 for event-based sediment estimation and an R2 of 0.74 and E of 0.54 for monthly phosphorus estimation also showed that the model can satisfactorily simulate sediment and phosphorus. However, the model was not able to simulate nitrogen at a monthly scale, with an R2 of only 0.15 and E of −0.107, because of the lack of site specific and accurate input data. After AnnAGNPS successfully simulated runoff, sediment, and phosphorus, an evaluation of the OFWS system showed that the system was able to capture 220,000 m3 of runoff from the monitored watershed that can be stored and used for irrigation. AnnAGNPS estimated that the OFWS system also captured 46 tons of sediment and 558 kg of phosphorus during the monitoring period, preventing downstream nutrient and sediment pollution.