Prediction Model of River and Groundwater Nitrogen Contamination Caused by Livestock Manure in a River Basin

摘要

In this study, we have developed a prediction model of river and groundwater nitrogen contamination caused by livestock manure in a river basin, based on field investigations and a hearing survey used to estimate actual nitrogen loading from farm sites and grass farms located in the basin used in this study. The river basin was divided into meshes, and the model predicted average total nitrogen (T-N) concentration in the groundwater and the river every three months, considering water and nitrogen mass balance in each mesh. The water mass balance in the basin was calibrated using data on the flow rates of the river, the groundwater level, and precipitation in the region. The nitrogen mass balance model was calibrated using total nitrogen (T-N) concentration data in the river and groundwater, based on an estimation of the nitrogen loading from various nitrogen sources, such as the application of manure, urine, and mineral fertilizer, and the inappropriate storage of manure. As a result, our prediction model suggested that 1) leaving piles of manure on the ground had a large effect on the nitrogen groundwater contamination, and that 2) application of too large amount of manure (25 t/10a) to grass farms was responsible for high concentration of T-N in groundwater, especially in the spring because of melting snow. Our prediction model can be used as a tool to develop countermeasures for appropriate livestock manure management in a river basin to decrease groundwater nitrogen contamination.