Abstract
We calculated long-term estimates of the chemical oxygen demand (COD), and nitrogen and phosphorus loads of Ariake Bay using a simplified model with data from 1979 to 2003. After confirming small changes in land use and population around the bay during that term, we calculated the yearly changes of loads with some assumptions and the formula L=a×Qb (L: load, Q: amount of river flow, a,b: parameter) applying the parameters provided from the Koku-cho-hi simulations, which were carried out in 2000 and 2001 by four ministries of Japan; The Ministry of Agriculture, Forestry and Fisheries, The Ministry of Economy, Trade and Industry, The Ministry of Land Infrastructure and Transport, The Ministry of the Environment. We confirmed that the loads calculated in our simple estimation showed good agreement with the observed data, by comparing of the calculated and observed water qualities of rivers. We found that the river discharges and loads ranged from 0.5∼1.5 fold the averages for these 24 years and the loads of COD in years with rich precipitation seemed to be higher than the average comparing with the cases of nitrogen and phosphorus loads.
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