Abstract
Lakes Inawashiro, Hibara, Onogawa, and Akimoto are located around Mt. Bandai in Fukushima Prefecture, northeastern Japan. The changes in phytoplankton community composition in the acidotrophic lake Inawashiro, where neutralization in pH was observed in recent years, were estimated by analyzing the long-term dynamics of phytoplankton communities in these four lakes by using multivariate analyses. Canonical correspondence analysis (CCA) suggested that the differences in phytoplankton community composition across the four lakes could be predominantly explained by five environmental factors: pH, zooplankton density (ZOO), total nitrogen concentration (T－N), average monthly photosynthetically active radiation within the mixed layer (PAR.m), and nitrogen/phosphorus (N/P) ratio. The niche of species according to the habitat designated by six environmental factors, including water temperature (W.T.), was assessed by conducting outlying mean index (OMI) analysis, and 48 phytoplankton species were classified into the following four groups: widely distributed species, acidophilous species, circumneutral mesotrophic species, and circumneutral oligo-mesotrophic species. The niches of the four groups suggested that circumneutral mesotrophic species such as Microcystis sp. would occur in Lake Inawashiro and the phytoplankton community composition of this lake would approach that of Lakes Hibara, Onogawa, and Akimoto if eutrophication occurs in Lake Inawashiro.
