Effects of Land Use Type on Water Quality and Organisms in a Small River of the Shizukuishi River Basin, Iwate Prefecture, Japan

Abstract

Several small distributary rivers exist downstream of the Gosho Dam in the Shizukuishi River of the Kitakami River system. Although there are human-influenced areas surrounding these rivers, such as pastures, fields, residential areas, major national roads and highways, many rare aquatic organisms exist, including Margaritifera laevis. This rare aquatic organism is decreasing in number and increasingly threatened presumably because of the presence of various type of human activity. Therefore, we attempted to evaluate the effects of land use type on water quality on the basis of relationship between the land use classification of areas within the watershed and the results of water quality surveys conducted once a month for one year at several locations along a small river. The results of this study revealed that in addition to the effects of fertilizers from fields and pastures, drainage, and treated water from residential areas, along with the strong effects of antifreezing agents applied to roads during the winter were observed. Small streams are susceptible to inflow loads because of their low flow rate and limited dilution effects. If aquatic life conservation is regarded as important, then measures must be taken to address road drainage problems.