Factors Associated with Well-to-Well Variation in Nitrate Concentration of Groundwater in a Nitrate-Polluted District in Miyakonojo Basin, Southern Kyushu, Japan

Abstract

This study monitored nitrate levels in well water and analyzed their association with well attributes (physicochemical parameters of water, location, livestock farming conditions) in a nitrate-polluted, animal industry district in central Miyakonojo Basin, southern Kyushu, Japan, to characterize the nitrate status of groundwater in the district. Water quality varied considerably among the wells, with nitrate-N concentration and natural nitrogen-15 abundance in nitrate-N (δ15N-NO3) ranging from 1.1–44.6 mg L−1 and 4.2–17.8‰, respectively. There was a significant positive correlation between nitrate-N concentration and δ15N-NO3. Nitrate-N concentration was higher in wells located at higher elevations, having larger areas of livestock barns within a 100-m radius and with higher animal populations. Wells in pig farms showed a higher nitrate tendency than those in the other situations (cattle farm, poultry farm, non-livestock farm and non-farmer). The results show that the nitrate status of groundwater in the district has not been drastically changed since 1996, and the nitrate in the wells is of multiple origins (e.g. chemical fertilizer, animal wastes) with a tendency for higher contribution of animal wastes in more heavily polluted wells. The results also highlight a need for further regular monitoring of groundwater quality in the district particularly for wells; (1) located at higher elevations, (2) with a large area of livestock barns nearby, (3) in farms with a high animal population and/or (4) in pig farms.