Abstract
The high water quality of Lake Inawashiro is due to the low concentration of phosphorus, for example, 0.003mg · l-1. In acidic Nagase River, a floc is produced which coagulates and forms as phosphorus sediment in Lake Inawashiro. We studied the mechanism by which the floc is produced. The major findings are as follows : (1) There are two processes involved in floc production in the Nagase River. (1) The first is the dissolution of Fe, Si, Ca, Al and other conpounds into the acidic water in the Iou River. (2) The second is the neutralization of the water by dilution, producing floc. (2) Iou River water was neutralized with an NaOH solution, then floc was precipitated. The resulting floc has almost identical chemical elements and particle size distribution as floc found at the mouth of the Nagase River. (3) Nine conglomerate samples from the Iou River were soaked in an aqueous solution of H2SO4, and the levels of chemical elements were measured. Then, these solutions were neutralized with a NaOH solution, artificially producing floc. This floc has almost the same composition of chemical elements and particle size distribution as floc found at the mouth of the Nagase River.
