In the Shishizukaoike pond, Ibaraki Prefecture, the Nelumbo nucifera community disappeared in 2020. This disappearance is attributed to foraging by the American red swamp crayfish, Procambarus clarkii, whose population dramatically increased after the decline of largemouth bass, Micropterus salmoides. To examine whether there are other animals that prey on the crayfish in the ecosystem, and whether the crayfish eat aquatic plants such as lotus, we analyzed carbon and nitrogen stable isotope ratios that were sampled before the disappearance of the lotus community. It was confirmed that American red swamp crayfish feed on aquatic plants, including lotus. Largemouth bass less than 10 cm in length eat the crayfish and bullfrog (Lithobates catesbeianus) tadpoles. These tadpoles also feed on aquatic plants. Although the crayfish were imported to Japan as food for bullfrogs, it is presumed that the bullfrogs in Shishizukaoike pond did not mainly feed on crayfish. Therefore, without largemouth bass in Shishizukaoike pond, there would be no animals that feed mainly on crayfish and bullfrog tadpoles, which would make it difficult for aquatic plants, including lotus, to grow.

　To evaluate the effect of an artificially constructed bank road on nutrient cycling in mire ecosystems based on chemical and microbiological properties, a field survey was conducted in Kushiro Mire, Hokkaido, with the following results:
　A bank road constructed in Kushiro Mire influenced the chemical properties of peat soils and surface water. Calcium, magnesium, and silicon concentrations, as well as electrical conductivity values of surface water increased approximately 180 m from the bank road. Mineral ash and inorganic phosphorous contamination in peat soils were observed in the vicinity of the bank road. Hydrolase activities, such as cellulase, xylosidase, and phosphatase activities in soils adjacent to the bank road increased. In addition, decomposition rates of organic materials, such as cellulose paper and woody sticks, increased. Such alterations in nutrient cycling in mire ecosystems may influence vegetation by altering nutrient supply to plants. In conclusion, soil enzyme activity could be used as an index for disturbance and eutrophication in mire ecosystems because it is directly associated with nutrient cycling in soils.　

　In the euphotic layer of a dam lake (reservoir), we discovered a phenomenon that hydroxylamine (NH₂OH) accumulates at a high concentration at the same time as the increase in Chl-a, which is an indicator of phytoplankton biomass. Therefore, to investigate the presence or absence of NH₂OH production by phytoplankton, we conducted a culture experiment using a single sterile strain of cyanobacteria isolated from the dam lake. Our results confirmed that NH₂OH increased with the increase in Chl-a, and the ability of cyanobacteria to produce NH₂OH was clarified. This result suggests that NH₂OH detected in the euphotic layer during the dominance of cyanobacteria in summer is produced by the cyanobacteria.

　This report illustrates a novel trial to use a drone equipped with both visible light and infrared cameras to measure river surface temperature to locate a site where groundwater is being directly discharged into the river. The water at the site was distinguished from the surrounding river water by its temperature. It was compared with the water in the middle of the river in terms of physical and chemical properties, including via an examination of stable isotopes. In addition, microbial DNA analysis was applied to estimate the variations in dominant prokaryotes in the water sample. The site where groundwater is discharged directly into the river may provide a unique habitat where temperature does not fluctuate through the seasons. Discharged groundwater may also affect the surrounding water though the area of this effect would be limited. In terms of the hydrological cycle, evaluating the influence of the direct discharge of groundwater into a river system is an essential step in river management. Therefore, measurement of river surface temperature by drones is a useful tool.

This paper describes the limnological features of the Sasahana-ike pond, which emerged circa 1990 due to a depression in the Nakaikemi wetland, Japan. We discuss the merit of the pond as an aquatic habitat for the native wetland biota. The pond has developed into an area covering 1.9 ha, with a depth of 3.9 m. The pond classifies as a eutrophic and humus rich lake, although its colour, light attenuation, pH, and algal biomass show wide seasonal fluctuations. In comparison with other limnetic wetlands, the pond water, derived from limestone bedrock, showed high pH, conductivity, and hardness. The bowl-like landform, which weakens the effect of wind turbulence and the underground inflow of cool water, maintained a stable thermal stratification during summer. The resulting vertical mixing obstruction and a high productivity of planktonic algae cause bottom hypoxia. The surface water oxygen was also undersaturated throughout the study period. We concluded that the ponds’ hypoxia and high pH conditions are not suitable for native wetland biota. The water level increased in winter due to heavy snowfall. Long-term observations of the pond depths from 2012 to 2017 and reports from residents indicated that the pond is still expanding and deepening.