Surface water chemistry in Shimabara, Nagasaki Prefecture, Japan

Abstract

Shimabara city has been experiencing serious nitrate pollution in groundwater. To evaluate nitrate pollution and water chemistry in surface water, water samples were collected at the 42 sampling points in Shimabara including a part of Unzen city. Spatial distribution of water chemistry was assessed by describing hexa and trilinear diagrams using major ions concentrations. Most of the samples showed Ca-HCO₃ or Ca-(NO₃+SO₄). It corresponds to groundwater chemistry. Some samples were classified into characteristic water types such as Na-Cl, (Na+K)-HCO₃, and Ca-Cl. This results represent sea water mixing and anthropogenic pollution. At the upstream of Nishi river, although water chemistry was Ca-HCO₃, ions concentrations were higher than that of the other rivers. It indicates that this site was affected by the peripheral anthropogenic activities.