Numerical simulation of water quality response to nutrient loading and sediment resuspension in Mikawa Bay, central Japan: quantitative evaluation of the effects of nutrient‐reduction measures on algal blooms

Abstract

AbstractEutrophication is caused by large influxes of nutrient into closed or semi‐closed water bodies due to agricultural runoff, urban waste disposal, and resuspension from the sediment itself. The objective of this study is to examine how effectively various nutrient‐reduction measures can improve water quality in Mikawa Bay, central Japan. Both hydrodynamic and water quality variables were simulated using a model which includes a series of hydrodynamic equations and 13 mass conservation equations related to water quality, such as chlorophyll‐a, dissolved oxygen, etc. The calculated spatial distribution and temporal variations of the chlorophyll‐a, nutrient, dissolved oxygen, as well as temperature and salinity, showed generally good agreement with field observations. Analysis of various nutrient‐reduction measures suggested that nutrient reduction from sediment resuspension can more effectively reduce chlorophyll‐a compared with nutrient loading reduction through rivers from land areas. For suppression of alga growth in Mikawa Bay, control of inorganic nitrogen, especially that of NH4, was a key factor. That is why a decrease in nutrient resuspension from sediment was more effective for reducing chlorophyll‐a, since nitrogen resuspension occurred mostly in the form of NH4. Copyright © 2004 John Wiley & Sons, Ltd.