Pollution of underground water by nitrate in the western region of the Kasanohara Shirasu plateau in Kagoshima prefecture [Japan]

Water pollution by nitrate has occurred on springs of the western low land area of the Kasanohara plateau. It worsened remarkably water quality of the Kimotsuki River. Underground water is a main source of drinking water for local residents, and the examination to clarify sources of the nitrogen load was done to propose effective countermeasures. The following results were obtained. 1) It was estimated that pollution of spring water by nitrate in the western low land was caused by the contamination of the livestock excretion, based on the analysis of the stable isotope natural existence ratio of nitrogen. 2) The nitrogen load was mostly caused by leaching from the unlined storage pond method as a pig waste management. 2) The abolition of the unlined storage pond method and the making system of composting as a pig waste management were proposed as nitrogen load reduction countermeasures. 3) Although the removal of slurry which has been collected in the storage pond at present is urgently needed, about 400Mg were estimated as the amounts of slurry nitrogen. It is seriously recognized that these amounts of slurry nitrogen are extremely over those to be sufficient for use by reduction on the agricultural land.