1Laboratory of Fisheries and Environmental Microbiology, Shiga 520–0112, 2Metocean Environment Inc., Osaka 550–0002, Japan
The relationships between the eutrophic levels (TN×TP, total nitrogen×total phosphorus), TN, TP, TN: TP ratio, transparency and chlorophyll–a in Japanese lakes were synthetically examined referring to numerous related data. It was observed when TN×TP increased, TN, TP or chlorophyll–a increased consistently with the coeffcient of correlation (respectively, r2=0.96, 0.97 or 0.89), while transparency decreased consistently with the coeffcient of correlation of 0.91 or the TN: TP ratio consistently decreaed.
Based on the values of TN×TP, Japanese lakes and ponds were divided into seven grades of eutrophic levels: extremely oligotrophic lake, oligotrophic lake, weekly eutrophic lake, eutrophic lake, weekly hypereutrophic lake, hypereutrophic lake, and strongly hypereutrophic lake. Then the ranges of TN, TP, TN: TP ratio, transparency or chlorophyll–a in each trophic level were roughly estimated along with the trophic levels of the lakes and ponds where the bloom-forming phytoplankton and fishery organisms were mainly found.