Short-term chronic toxicity tests on acidified Lake Tazawa using responses of three trophic levels of aquatic organisms

Lake Tazawa in Akita Prefecture, Japan, is an acidic lake caused by the inflow of low-pH water from Tamagawa Hot Springs. Because of this anthropogenic acidification, many indigenous fish species and aquatic ecosystem have perished. Although several counter-measures such as artificial neutralization have been implemented against the acidic waters of Tamagawa River flowing into Lake Tazawa, the pH level of the lake remained low. Therefore, a bioassay evaluation of the low-pH lake water is necessary for ecosystem restoration. In this study, short-term chronic toxicity tests were applied to observe biological responses of three trophic levels of aquatic organisms using water samples of Lake Tazawa. As a result, Lake Tazawa water has toxic effect on all tested aquatic organisms. Especially, the fish embryo/larvae was directly affected by low-pH water, while algae and crustaceans were affected not only by low pH but other factors such as fluorine ion and metals. In order to improve the water quality management of Lake Tazawa for ecosystem restoration, further efforts are needed to reduce multiple toxic substances in addition to the pH neutralization of lake water.