Estimation of the Load of Total Nitrogen and Total Phosphorus in the Enclosed Bay Watershed using GIS

Nutrients run-off from land causes environmental problem due to the eutrophication of rivers, lakes or reservoirs. These run-off are considered to affect not only water quality but sea bottom soil status in enclosed bay which has little exchange of sea water to and from outer sea. This study describes estimation of the load of total nitrogen and total phosphorus in Ago bay and its watershed which is typical enclosed bay in Japan, using geographical information system. First, we describe the model of discharged load on mesh base. Then generation of land use map and digital elevation model are introduced. Finally, the load of COD, TN, TP of watershed are estimated by the mesh model and per unit production method. The result of the two methods is compared.