Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/28/2005
Publication Date: 12/1/2005
Citation: Yuan, Y., Bingner, R.L., Theurer, F.D., Rebich, R. A., Moore, P.A. 2005. Phosphorus component in AnnAGNPS. Transactions of the ASAE. 48(6): 2145-2154. Interpretive Summary: Pollution entering a water body can significantly affect the ecological balance needed in maintaining healthy recreational and municipal river or reservoir systems. Producers have to balance the effects of their farming practices on pollution with their economic benefit from those practices. A study was conducted to describe and evaluate the capability of the USDA watershed model, AnnAGNPS, to evaluate the production of phosphorus pollutants from Mississippi Delta farms as part of the Mississippi Delta MSEA Project. Application of the USDA AnnAGNPS watershed model demonstrated that the two critical parameters that impact phosphorus loadings into streams are the initial nitrogen in the soil and the ability of crops to use phosphorus. Actual comparison with measured results showed the model estimated long term dissolved and attached phosphorus loadings within 94% and 72%, respectively, of the measured values. By applying this watershed model to agricultural areas that may contribute to nutrient problems downstream, alternative farming practices can be evaluated before their actual implementation that would demonstrate the approach that reduces any downstream impact on the watershed system.
Technical Abstract: The USDA Annualized Agricultural Non-Point Source Pollution model (AnnAGNPS) has been developed to aid in the evaluation of watershed response to agricultural management practices. The main purpose of this paper is to introduce AnnAGNPS phosphorus (P) component and evaluate the performance of AnnAGNPS on P loadings using comparisons with measurements from the Deep Hollow watershed of the Mississippi Delta Management Systems Evaluation Area (MDMSEA) project. Previous studies have demonstrated the capability of the model to simulate runoff and sediment, but not P loadings. A sensitivity analysis was performed to identify input parameters whose impact is the greatest on P loadings. Sensitivity analysis results indicate that the most sensitive variables of selected for analysis of P loadings are soil initial P contents, the second sensitive variable of selected is P application rate, and the third sensitive variables of selected are plant uptakes. AnnAGNPS simulations of dissolved P loading do not agree well with observed dissolved P loading (R-square of 0.36 and slope of 0.28); AnnAGNPS simulations of total P loading agree fairly with observed total P loading (R-square of 0.76 and slope of 0.78). The difference in the agreement of dissolved P loading may be attributed to the simulation of the P pool movement between solution pool and active pool and between the active pool and stable pool. The uncertainties in choosing input parameters affect the model's performance too. This study introduces the AnnAGNPS P processes contained within the simulation model. It provides model users with better understanding of P processes in AnnAGNPS and information needed for future enhancements of P processes in non-point source pollution models.