Abstract
River water quality investigation was carried out for three years on a forested watershed and a livestock farming watershed in southwestern Hokkaido, Japan. The characteristics of pollution load discharge under three river hydrological conditions (normal flow, rainfall runoff and snowmelt runoff) was examined for both watersheds. The water quality concentration and load discharge were much higher under rainfall runoff and snowmelt runoff than under normal flow. The annual river discharge and nitrogen load were compared for each hydrological condition. It was clarified that more than 50% of the annual river discharge flowed out during snowmelt runoff, and 50% of annual T-N load flowed out during rainfall runoff. Furthermore, NO3-N load accounted for most of the T-N load during snowmelt runoff, and T-N load during rainfall runoff was predominantly suspended TON load. The annual T-N load discharge was compared between the watersheds. It was found that the annual T-N load in the livestock farming watershed was 1.8 times that in the forested watershed. It was also shown that most of the T-N load from the livestock farming watershed was discharged during the rainstorm runoff.
