Abstract
A method for predicting the change of COD of lake water in response to the reduction of phosphorus loading was newly developed because the existing methods for the purpose are considered inappropriate for application to unusual type of waters like a very shallow water. The method is based on an analysis of the current state of the phosphorus cycling in the specific lake and a diagrammatic expression of every flux and stock of the organic and the inorganic phosphorus considering the production and decomposition of organic matter and the release and settling of phosphorus in the take. This analysis needs extensive field observation. Once it is established, the change of organic phosphorus concentration in response to the change of total phosphorus loading can be predicted by making a simple and appropriate assumption on the change of the related processes in the cycle. When the change of organic phosphorus concentration is predicted, the change of COD can be predicted by utilizing a statistical relation between the organic phosphorus and the COD of water. The relation was found to be simple and reliable in our case. The new method was applied to Lake Teganuma and the result was compared with the results of existing methods.
