Evaluation of trophic state of eutrophicated lake and biotic response fromalgal community level

Trophic state indices were developed according to the comprehensive assessm ent approach. The results of the average trophic state index at four sampli ng stations with different contamination situations in Lake Kasumigaura, Ja pan, showed that trophic state index ranged monthly from 55 to 75, and the limiting factors were chemical oxygen demand and total phosphorus. Further, two empirical expressions indicating the trophic state of total nitrogen a nd total phosphorus were established by regressing with Carlson index. To a nalyze the biotic responses from algal community level, the correlation bet ween the chlorophyll-a (representing the total biomass of phytoplankton), S hannon's diversity index (representing the information content), and trophi c state indices of main water quality factors were studied. It was found th at chlorophyll-a was suitable as one biological indicator to show the trend of eutrophication of Lake Kasumigaura. However, it will be limited as dive rsify index is employed to test the biotic response to the change of wares environment only.