2018 Volume 41 Issue 5 Pages 115-122
In Lake Biwa, annual changes in species composition and abundance of the phytoplankton community have been frequently examined. However, it is not well understood how the seasonality of phytoplankton has changed over the past several decades. In this study, we analyzed the monitoring data of the phytoplankton community collected twice a month from 1978 to 2014 in the north basin of Lake Biwa and categorized seasonal change patterns of the phytoplankton community using the Bray-Curtis similarity index. Then, the seasonal patterns were compared with those of phytoplankton communities described in the Plankton Ecology Group (PEG) model and examined in relation to the long-term changes in the water quality and nutritional state of Lake Biwa. The results showed that the seasonality of the phytoplankton community in Lake Biwa changed from one typical of a eutrophic condition to one typical of an oligotrophic condition and was found, in specific years, to deviate from these patterns. Thus, the seasonal pattern of the phytoplankton community is a useful and sensitive gauge for evaluating the water quality, nutritional state, and trophic condition of Lake Biwa.
