The Ozegahara mire is the largest peatland (approximately 8 km 2 ) on the mainland of Japan. The mire is located on an amphitheater-shaped basin surrounded by mountains that rise 2,000 m asl, and the effects of climate change and flooding on the mire ecosystems were studied. The water level of Kaminoohorigawa was highest between 2016 and 2017, exceeding 7 m from the bottom of the stream after heavy rainfall in autumn 2016, and approximately 2 m from the bottom of the stream after heavy rainfall in early spring 2017. Water level of ground surface in Kamitashiro in snowmelt season was 0.2 m, and that at Kenkyumihonen was 1.6 m in snow coverage. The water level during the snowmelt season at Kenkyumihonen was very high at several times. The water level of the bog pool of KA1-08 increased in March 2018 due to surface water and groundwater inflow. The bog pool KA1-04 had early snowmelt due to groundwater inflow from the middle bog pool. Heavy snow flooding in torrents occurred in May 2019 in the Kamitashiro area. After the flooding, the distribution of the muddy water in the bog pool was obtained by air photography by UAV. A high content of inorganic particles was detected in the peatland sediment of 0.9 m depth layer and estimated by historical flooding a millennium ago. Radio cesium from the Fukushima Daiichi Nuclear Pwer Plant accident was detected as 5,919 Bq m -2 at Nakatashiro and 8,594 Bq m -2 at Kamitashiro. The radioactivity of Kamitashiro in the flooding area was higher than that of Nakatashiro in the non-flooding area because of contaminants from the hydrographic basin.

The Ozegahara mire is the largest raised peat bog in central Japan. Nymphaea tetragona and Nuphar pumila var.ozeensis were the dominant floating-leaved plants in the bog pools. N. tetragona is known to have specific spatial distributions in pools. Forty pools in the Kamitashiro area were surveyed in August 2017 to document the present status of macrophytes. To clarify the factors that cause these specific spatial distributions of N. tetragona in the pools, the growth status of N. tetragona (coverage index, number of floating leaves, and width of leaf blades) and bottom sediment properties (fabric matter, ash, and total phosphorus content) were measured in three study pools in the Kamiatashiro area in August 2018. The survey revealed that an increase in N. tetragona and a decrease in N. pumila var. ozeensis has continued since the 1970s. The results from the three study pools showed that there were no clear differences in the growth status of N. tetragona (coverage index and number of leaves) and in the bottom sediment properties (fabric matter, ash, total phosphorus content, and the thickness of the decomposed peat) between the shore side bottoms and at the central bottoms in the study pool where N. tetragona was distributed all over the bottom (overall type). On the other hand, an obvious increase in the growth status of N. tetragona and the values of the bottom sediment properties were observed toward the central bottoms in the study pools, where N. tetragona was distributed all over the pool, avoiding the shore side bottom (overall without shore side type). The results indicated that the absence of N. tetragona on the pool bottoms was attributed to sediment nutrient infertility.

To clarify the genetic characteristics of the white-spotted char, Salvelinus leucomaenis, which inhabits the Shimoyosaku tributary (which is isolated from the main stream during the normal stage of water), we performed mitochondrial DNA cytochrome b region analysis and microsatellite analysis of 35 individuals sampled from both groups of the isolated tributary (Shimoyosaku) and the main stream. mtDNA cytochrome b region analysis confirmed both groups to have only one haplotype that has been observed in populations of the North Kanto area.Genetic diversity of the isolated group was lower than that of the mainstream group, and gene divergence was greater between groups, suggesting that gene flow between groups was extremely low.