Water Quality Characteristics of the S River - Effect of Livestock Grazing, Hokkaido, Japan

抄録

Forest grazing, which uses grassland and woodlands for livestock grazing, is generally considered an environmentally friendly method of livestock management. However, its implementation is rare, and the full extent of its environmental impact is poorly defined. Here, we examined the effect of forest grazing on the current state of river water quality. The study site was the S River, which flows through K Farm, located in eastern Hokkaido, Japan. The K Farm offers forest grazing for its beef cattle. River water was collected at nine points on the main S river and at five tributaries that join the main river near the pastureland and upstream of the dam. The mean ion concentration of river water was 8.1-16.4 mg/L for cations and 6.5-11.5 mg/L for anions. The concentrations were relatively low at all the sampling points. The average total nitrogen (T-N) concentration ranged from 0.18 to 0.75 mg/L, which is below the environmental standard of 1.0 mg/L. In the tributaries, the nitrate nitrogen (NO₃-N) ratio was approximately 45%, which was greater than the main river value of 30%. Regarding the relationship between the first and second principal components of the PCA results, the plot trends differed between the main river upstream and downstream and between the tributaries. The overall ion concentration in the main river upstream was low. In contrast, the five tributaries showed a different trend from the main river; in particular, the overall water quality concentration of tributary T2 was high, and K+, PO₄^2-, and T-N were high. It is necessary to conduct long-term observations of seasonal and temporal fluctuations in the tributaries flowing through grazing areas to investigate the effects of grazing.