Development of a Mathematical Model to Predict the Role of Surface Runoff and Groundwater Flow in Overfertilization of Surface Waters

Abstract

A nutrient enrichment accounting mathematical model was devised for the New Prague watershed in Minnesota. The New Prague watershed is 23.3 square miles in area and is predominately a rural watershed. Model input data was collected over a 2 1/2 year period from a stream gauging station and two automatic sampling stations. Over 800 water samples were analyzed. Extensive effort was placed on better understanding the nitrogen and phosphorus cycles. It is evident that the spring runoff process and accumulative winter fertilizer applications constitute the major portion of diffuse sources of nutrients in the watershed. Point sources from feedlots and municipal and industrial effluents contribute only 11 percent of the annual EN (total nitrogen, four components) and 7 percent TP (total phosphorus). Disperse sources accounted for 89 percent of EN and 93 percent of TP, with spring runoff in the two months of March and April accounting for 79 percent of the annual EN and 64 percent of the TP. The nutrient output from the watershed could be decreased by increasing penetration of the large amounts of EN and TP in snowpacks into the soil through land terracing to restart rapid spring runoffs and sub-surface drains to allow rapid drainage during the crop season.