PREDICTIONS OF ECOLOGICAL EFFECTS OF ARTIFICIAL UPWELLING IN SEMI-ENCLOSED BAY AND ENCLOSED LAKE

An apparatus, which mixes waters in upper and lower layers in density stratification and discharges the mixture at the middle depth, has made a remarkable success in enhancing water quality for ecosystems in a small semi-enclosed bay and an enclose lake in Japan. In this study, we conducted numerical simulations by using a three-dimensional tidal current model and an ecosystem model to predict the effects of the apparatus in two different waters: a larger semi-enclosed bay and an enclosed lake. Isahaya Bay in Ariake Sea was chosen as the former case to see how effectively the apparatus can reduce oxygen-deficient water, and Feng-Shan dam-lake located in South Taiwan represents the latter case, where we are interested in the effect of the apparatus on reduction of Microcystis aeruginosa, which is harmful blue-green alga and causes environmental problems in the neighbouring area. As a result, it is suggested that the apparatus averages temperature of water vertically in its vicinity and this increases phytoplankton in the lower layers resulting in reducing oxygen-deficient water in lsahaya Bay. However, it is not very effective in reducing the blue-green alga in the Taiwanese lake because the temperature in the lower layer is still preferable for the alga even after the mixing..