Abstract
The NO3-N concentration and load during a stormy flood event were investigated in a forested, mountainous headwater catchment in the Shimanto River basin. The experimental catchment is covered with a natural forest of predominately Abies firma and Tsuga sieboldii. Investigations during flood events were conducted for five events. Two types of NO3-N concentration variation were found before and after the rainfall event. The NO3-N concentration after the rainfall was almost the same as the concentration before the rainfall in three events, of which total rainfall was less than 100mm. In contrast, the NO3-N concentration after the rainfall was much smaller than that before the rainfall in two events, for which the total rainfall exceeded 150mm. The amount of NO3-N load during flood events increased with increasing of the total rainfall when the total rainfall was less than 100mm. However, for the rainfall events with a total rainfall exceeding 150mm, the increase rate of NO3-N load during flood events to total rainfall tended to reduce.
