DEVELOPMENT OF A WATER TEMPERATURE-ECOLOGICAL MODEL TO STIMULATE GLOBAL WARMING EFFECTS ON LAKE ECOSYSTEM

This paper describes a newly developed combined water temperature-ecol ogical (WT-ECO) model which is employed to simulate the effects of glo bal warming on lake and reservoir ecosystems. The WT model includes (i ) variations in the eddy diffusion coefficient based on the degree of thermal stratification and the velocity of wind, and (ii) a sub-model for simulating the freezing and thawing processes of surface water, wa ter temperatures, and the mixing rates between two adjacent layers of water. The ECO model then uses these results to calculate the resultan t effect on a lake's ecological dynamics, e.g., composition of phytopl ankton species, their respective concentrations, and nutrient concentr ations, When the model was benchmarked against Lake Yunoko, a dimictic lake, fairly good agreement was obtained over a 4-yr period; thereby indicating it is suitably calibrated. In addition, to assess the effec ts of global warming on a lake ecosystem, changes in Lake Yunoko's wat er temperature/quality were simulated in response to an increase in ai r temperature of 2-4 degrees C. Results indicate that such an increase will (i) increase thermal stratification in summer, which increases t he nutrient concentrations in bottom water due to nutrient release fro m bottom sediment, (ii) increase the concentration of phytoplankton at the beginning of the autumn circulation period, and (iii) change the composition of phytoplankton species. Copyright (C) 1996 IAWQ.