Abstract
Historically the water quality of Lake Inawashiro has been kept very good in terms of COD and other variables. The reason for this is due to the very low concentration of phosphorus in the lake for example, 0.003mg · l-1. Additionary, the primary production of phytoplankton is controlled at very low level. The authors studied the mechanism by which floc removes phosphorus that is produced in the acidic Nagase River. The major results obtained from this study are as follows : (1) The floc produced in the Nagase River coagulate and then settle as phosphorus sediment. (2) The floc has a particle size distribution that is effective for coagulation and then for phosphorus sedimentation. (3) The main components of the floc are Fe, Ca and Al. (4) When floc was added to the river water, the concentration of phosphorus decreased and the AGPM also decreased.
