2013 Volume 26 Issue 6 Pages 285-294
The Kurobe River Basin (682 km2) in Toyama prefecture is located in a snowy temperate climate. The water resource area in this basin is surrounded by the Tateyama mountain range and the northern Alps. Therefore, deposits ofnitrogen oxides in the mountain range are less than those in the plains. The nitrogen oxides of the snow cover flow out intensively by fluctuation of air temperature during the initial stage of melting period. Compacted snows turn into large granular snows with lower concentrations of nitrogen oxides. Nitrogen oxides retained in the soil layer of the mountain slope flow down by snowmelt water at lower concentrations. Moreover, in the spring the forests of Kurobe gorge absorb nitrate nitrogen as nourishment from the forested soil layer. Because of these phenomena, the nitrogen oxide concentrations in river water became lower at the Unazuki site located at the top of the Kurobe alluvial fan during spring - summer. The mean value of annual nitrogen retention of forests is about 4.6 kg/ha/year.The river water from the upper basin infiltrates underground at the middle reaches of the alluvial fan and flows as groundwater. This groundwater springs out at Nyuzen and Ikuji, which are located at the edge of the alluvial fan. Moreover,the groundwater springs out in the seabed in shallow sea areas. The volume of water that sprang out in that manner was15.8 % of surface river water. The nitrogen load springing out in seabed becomes 30 % for the surface river water. The nutrient salt of coastal zone is supplied by snowmelt from plains and hilly areas, spring water of the coastal seabed and precipitation of the sea. Therefore, phytoplankton blooms occur in the coastal zone in March, because solar radiation increases. The cycle of nitrogen with water circulation in the Kurobe River Basin cultivates various ecosystems of the land and coastal zone.