Cu behaviors and effects of mine drainage in Kosaka River, Hokuroku mining district, Northeast Japan

Focusing on the origin of the heavy metal, this study aims to build an imputed method to estimate the heavy metal content in river water by making a distinction between the heavy metal of natural origins and that caused by human activities. Supported by GIS, Kosaka watershed within the Hokuroku basin was divided into several sub-watershed polygons and the outflows of water and Cu were calculated for each polygon. Compared with the natural origin, the dominant Cu emissions affected the river water more significantly in local. Based on the mass balance closure, the heavy metal content of Cu in the Kosaka River was estimated by the conflux accumulation of tributaries and mine drainages. The estimated Cu concentrations were checked by comparing with the actually measured values at monitoring points along the Kosaka River and the results are coincidence with each other in general. It is revealed that the mainstream water quality could be estimated by seizing the water quality of upstream tributaries and human drainages.