The spatial distributions of water quality and load units were determined for each small sub basin of the Iinashi River basin as
a first step in water environment management. In addition, a GIS database was established to comprehensively resolve the issue of water
quality degradation. It was found the concentrations of water quality parameters in the Iinashi River basin were relatively low at almost
all sampling points. The average concentrations of each parameter are 1.86 mg·L-1 of chemical oxygen demand, 0.73 mg·L-1 of dissolved
organic carbon, 18.5 % of biodegradation ability, 6.58 mg·L-1 of silica, 519.8 μgN·L-1 of total nitrogen, and 27.4 μgP·L-1 of total phosphorus.
In addition, the load units discharged from the small watersheds were obtained. The load units varied greatly regardless of similar
land use in the basin. Moreover, discharged loads from observation point 1-31 in the Yamasa River basin were higher than those from
observation point 1-5 in the upstream of the Iinashi River basin regardless of high percentage of forest area (91.51%), low percentage of
agricultural land (2.3%) and low population density (24 people·km-2). Finally, the discharged loads from observation point 1-3 were determined
as 53.2 g·ha-1·day-1 of suspended solid, 45.4 g·ha-1·day-1 of chemical oxygen demand, 20.9 g·ha-1·day-1 of dissolved organic carbon,
8.1 g·ha-1·day-1 of particulate organic carbon, 16.3 g·ha-1·day-1 of total nitrogen, 5.0 g·ha-1·day-1 of dissolved organic nitrogen, 1.3
g·ha-1·day-1 of particulate organic nitrogen, and 0.3 g·ha-1·day-1 of total phosphorus.