Estimating Nitrate-Nitrogen Sources Through Long-Term Observations of Spring Water in the Southern Part of Terrace Land of Akiruno District, Japan

Abstract

This study aimed to estimate the contribution of nitrogen loading due to anthropogenic influences, which is based on intermittent observations of the process of decreasing NO3- concentration in a spring in the southern Akiruno Plateau in Akiruno City, Tokyo. This study used measured data intermittently from 1994 to 2020. The Cl- and NO3- concentrations showed significant decreasing trends from 1994 to 2020 and from 2000 to 2020, respectively, and each of them was synchronized with the decrease in the population of the city of Akiruno without sewerage system coverage. The Cl- concentration of 51 µmol/L, NO3- concentration of 159 µmol/L, and δ15N for NO3- of 4.4‰, were estimated as having no effect from sewerage wastewater and δ15N of 9.4 ± 1.4 (mean ± sd) ‰ was estimated for the sewerage wastewater sources.