Decomposition approach of the nitrogen generation process: empirical study on the Shimabara Peninsula in Japan.

Groundwater nitrate pollution is one of the most prevalent water-related environmental problems worldwide. The objective of this study is to identify the determinants of nitrogen pollutant changes with a focus on the nitrogen generation process. The novelty of our research framework is to cost-effectively identify the factors involved in nitrogen pollutant generation using public data. This study focuses on three determinant factors: (1) nitrogen intensity changes, (2) structural changes, and (3) scale changes. This study empirically analyses three sectors, including crop production, farm animals, and the household, on the Shimabara Peninsula in Japan. Our results show that the nitrogen supply from crop production sectors has decreased because the production has been scaled down and shifted towards lower nitrogen intensive crops. In the farm animal sector, the nitrogen supply has also been successfully reduced due to scaling-down efforts. Households have decreased the nitrogen supply by diffusion of integrated septic tank and sewerage systems.