Estimation and Evaluation of Pollution Load from Water Conservation Forest

Abstract

 Maintenance of the Watershed Forest in the upper stream of the Tama River is necessary for supply of drinking water with safety and tasty. In this study, pollution load from the watershed, where water supply forest is conserved, was evaluated. GIS software was used to grasp the land use of each basin. Its information was provided to calculate unit pollution load for total nitrogen, total phosphorus, and COD. Annual pollution load was calculated for each basin based on water quality monitoring data. To subtract pollution load from point and non-point sources other than forest, land use of the basin, domestic waste water, and fishery effluent were considered. Calculated unit pollution load from the forest was compared with values in database from other watersheds in Japan. Compared with other watershed, unit pollution load was similar or lower. As more than 96 % of target area is covered by forest, calculated value of unit pollution load was further divided by annual rainfall, to compare the relations among unit pollution load index, vegetation and area of watershed forest.