Journal of the Japanese Agricultural Systems Society

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Nitrogen and phosphorus loads generated in the watershed and discharged into the stream were investigated in the east area of Gunma Prefecture where stock-raising activity was high. Most of the nutrients existing in the stream water were nitrate, and the concentration was relatively high with the range of 3-13 mg/L. Nitrate concentration of groundwater was also high with the range of 3-32 mg/L. Chlorine concentration was in the range of 10-40 mg/L, indicating that there is a water pollution by the load generated from a anthropogenic activity. Phosphorus concentration ranged from 0.05 to 4.5 mg/L. A correlation between the ammonium concentration and the area ratio of nursery garden could be found from the statistical analysis based on the water quality of the stream and land use in the watershed. In the research in the case of a rainy weather, the difference in the flowing down times of the nutrients was observed. In addition, run-off ratios based on the nitrogen and phosphorus loads calculated by using the pollutant load factors were in the ranges of 0.1-0.5 and 0.01-0.1, respectively. This result shows the possibility of accumulations of the nutrients in the watershed.

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