A STUDY ABOUT EFFECT OF SEWERAGE TREATMENT WATER DISCHARGE THAT LET PROCESSING RELIEVE ON NUTRIENT CONCENTRATIONS IN THE NORI CULTIVATION GROUNDS, ARIAKE BAY, JAPAN

We studied the effect of sewerage treatment water discharge that let processing relieve on nutrient such as dissolved inorganic nitrogen (DIN) concentrations in the Nori cultivation grounds, Ariake Bay, Japan. We examined the contribution of the DIN concentrations in the Nori cultivation grounds discharged from sewerage treatment plants by using a mass transfer model that considered advection and diffusion. As a result, we observed an increase in the DIN supply in the Nori cultivation grounds caused by relieving the sewerage treatment in front of these grounds during the winter season. We particularly calculated that the contribution ratio of the DIN concentrations rose from 10% to 20% during the winter season, although there were little rain and limited supply of DIN loads from local rivers. Furthermore, we found that the DIN concentration of the Nori cultivation grounds, which is located in the south of Saga Prefecture, rose by 4% owing to sewerage treatment water discharge, which flowed into the western sea area in Saga Prefecture.