STUDY ON A MATHEMATICAL MODEL FOR PREDICTION OF EUTROPHICATION

ANALYSIS ON TEMPORAL SCALES OF INPUT FUNCTIONS AND SPATIAL SCALES OF SUBMODELS

Abstract

Accuracy of a mathematical model for prediction of eutrophication, which is affected by temporal and spatial scales, has been analyzed in order to provide basic data to determine those scales more objectively. The analysis method is to evaluate accuracy of each submodel for temporal and spatial scales which are different from those in the standard simulation. The following results are obtained.(1) Accuracy of water quality balance model is little affected by temporal scales of proportion of diatoms, water temperature and light intensity.(2) Accuracy of each submodel is strongly affected by a temporal scale of precipitation.(3) Effects of temporal scales on accuracy vary with retention time of a lake. According to the simple model, if retention time is less than 5 times temporal scale of an input function, variation of an output is greater than 10% of that of an input.(4) Accuracy of outputs on water quantity is little affected by a spatial scale of the watershed of South Lake (the southern basin of Lake Biwa), but accuracy of outputs on water quality is strongly affected. Accuracy of load model is more important when determining a spatial scale of a watershed.