Journal of Japan Society on Water Environment

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Nitrate loading through baseflow during a storm event was calculated by the hydrograph separation. The hydrograph generated by a 54-mm rainfall in the Fuefuki River watershed in Yamanashi Prefecture (Japan) was separated into two components, namely rainwater and prestorm water, using water-oxygen isotope values. The stormflow discharge was 159 hours long. During this period, the water released from prestorm water was 87% of the total discharge and that released from rain water was 13%. The average concentrations of nitrate in the rainwater and prestorm water were 0.8 and 5.6mg · l^-1, respectively. The nitrate concentrations were determined from riverwater collected during the storm flow event, which were between 4.8 and 5.6mg · l^-1. The nitrate loading is mainly from prestorm water. The origin of the prestorm water was identified to be baseflow on the watershed. These results suggest that baseflow is the main source of nitrates in the Fuefuki River.

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