Visualization of nitrate behavior by using 3D groundwater flow simulation in the Miyakonojo Basin

Abstract

A comprehensive 3D groundwater flow simulation was performed by using results of accumulated hydrological observed data and nitrogen load statistical data to understand the 3D behavior of NO₃^－ in groundwater in the Miyakonojo Basin. We firstly constructed 3D groundwater flow model which shows high correlation with the observed data of river discharge and groundwater level in this area. By using this model, nitrate transportation simulation was applied to the study area. The nitrogen infiltration amount was estimated based on statistical data for agriculture and forestry. The simulated NO₃^－ distribution and historical change of NO₃^－ concentration showed good correlation with the observed data under the condition where denitrification were not occurred. This result suggests that NO₃^－ pollution attenuation in groundwater is largely attributed to dilution and diffusion in this area.