福井県北潟湖における夏の水質と珪藻遺骸分布

Water quality and surface sediment diatom assemblages in Lake Kitagata, Hokuriku region, Japan, were investigated in August 2016. Lake Kitagata is a brackish lagoon complex, separated into several sub-basins by narrow channels. Water quality was different in each sub-basin. Surface salinities in each sub-basin of Lake Kitagata were between 4 and 19, and bottom salinities were between 6 and 32 in August of 2016. Anoxic water masses were present in the near-bottom water of the central and a portion of the southern lagoon. The three most dominant diatom taxa in the surface sediments were Cyclotella striata , Cyclotella meneghiniana , and Cyclotella atomus .This probably reflects the high salinity and nutrient conditions of Lake Kitagata in recent years prior to sampling. The number of total diatom valves in surface sediment increased moving from east to west, with decreasing salinity, however, diatom numbers decreased again at the lowest salinity (the westernmost sub-basins). It is likely that other phytoplankton taxa dominated the population in the westernmost area due to low salinity conditions. In Lake Kitagata a strong fresh-water effect is observed not only in the low salinity western area, but also at the mouth of the lake, opening into the ocean. This occurs because fresh water from the Daiseiji River, which empties into the lake at the mouth, moves upstream into the Lake Kitagata system.