Abstract
A study of groundwater concentrations of nitrate nitrogen was conducted in M City in the Miyakonojo Basin, based on measurements taken over a four-year period from August 1996 to August 2000. Most wells where measurements were taken were shallow wells with a depth of 20 m or less. Groundwater concentrations of nitrate nitrogen at most measurement points remained relatively stable, with few points exhibiting increasing or decreasing tendencies. However, some measured points where levels remained stable exhibited significant fluctuations in nitrate nitrogen concentrations, and the higher the groundwater nitrate nitrogen concentration, the greater the fluctuations. M City was divided into six areas, and mean nitrate nitrogen concentration was calculated for each area. The resulting values ranged from 2-10 mg/L, and the mean concentration of nitrate nitrogen remained relatively stable during the survey period in all areas. Furthermore it turns out that there is an area where the well exceeding 10 mg/L in nitrate nitrogen concentration exists no less than 44%.
