Evaluation of AnnAGNPS Wetland Nitrogen Removal Component on Farmed Prairie Potholes

Abstract

Highlights AnnAGNPS offers a wetland module (AgWET) to simulate farmed prairie potholes soluble nitrogen dynamics. Three key parameters of the AgWET nitrogen removal components show high and very high Relative Sensitivity (Sr ). AnnAGNPS tends to underestimate the soluble nitrogen concentration at the beginning of the cropping season. Abstract. Farmed prairie potholes are common in northern Iowa and have been considered an impediment to agricultural development. Potholes have distinctive wetland characteristics where they might contain a high concentration of soluble nitrogen coming from agricultural upland runoff. With sub-surface drainage underneath them, providing short circuit nutrient transport downstream, Iowa poses a significant threat to nitrogen export to the Gulf of Mexico. Watershed models, such as AnnAGNPS, developed a wetland module allowing users to find the possible BMPs to accomplish nutrient reduction targets. Previous research indicates that AnnAGNPS may be used to mimic inundation depth fluctuations in potholes with moderate success. However, there has been little research on the wetland nitrogen removal components of the model. This study aims to evaluate the AnnAGNPS wetland module's performance in simulating the soluble nitrogen concentration in three farmed prairie potholes by comparing the simulation output with the observed data. The sensitivity analysis of the three key parameters of the model shows high and very high levels of sensitivity, with the temperature coefficient's relative sensitivity ranging from -6.7 to 8.6. Attempts in parameterization on the three targeted parameters indicated that the model poorly simulated the soluble nitrogen concentration. The comparison between observed and simulated data shows that the model fails to predict the high concentration of soluble nitrogen in the early cropping season. This conclusion is consistent with earlier research indicating that AnnAGNPS tends to underestimate the nitrogen concentration during the cropping season. Keywords: AnnAGNPS wetland module, Farmed prairie pothole, Soluble nitrogen concentration.