Lakes Sagami and Tsukui are reservoirs of nearly equal size, with a short residence time and constructed by connection to the Sagami River. Because of eutrophication of the lakes, cyanobacteria appear every year. However, the occurrence of cyanobacteria in each lake was different. Therefore, in order to investigate these factors, we conducted both biotic and abiotic investigations and compared defined parameters over the past 40 years. Cyanobacteria are found in the surface layer of the lakes. In Lake Sagami, the surface layer was not largely retained and some of the cyanobacteria were found in the outflow water. When the surface layer became disturbed, Dolichospermum dominated, and Microcystis dominated when the layer stabilized due to weather effects. The outflow from Lake Tsukui was taken from a deep layer (depth 24-32 m) and the cyanobacteria were not affected by the outflow. Prior to the installation of the aeration systems, Microcystis dominated, and after the installation, the cyanobacteria were dispersed and Nostocales dominated, but Microcystis still dominated when the surface layer stabilized owing to the influence of the weather. As a result, the influence of nutrients and water temperature was limited and the changes in the abundance and dominant species of cyanobacteria may be influenced by the weather, the difference in the outlet structure, and ancillary facilities such as aeration systems.

　Eutrophication and cyanobacterial blooming are still a worldwide problem. Our knowledge of lake restoration has improved extensively in the past couple of decades owing to geo-engineering studies. Furthermore, newly developed analytical techniques have clarified the processes behind elemental cycling. In this review, I have discussed several environmental restoration methods developed for restoration of dams and shallow eutrophic lakes in Japan; the importance of each process in phosphorus (P) cycling has been ascertained. Furthermore, I have also reviewed the cycling of inorganic and organic P based on the restoration measure applied. Finally, I have discussed future perspectives by incorporating information on lake restoration techniques and P cycling studies from recent literature.

　Recent studies have provided evidence that consumers such as benthic larval chironomids assimilate methane-derived carbon (MDC) by foraging on methane-oxidizing bacteria in lake ecosystems. Trophic transfer of MDC can be detected by measuring carbon stable isotope ratios in consumers as biogenic methane is extremely ¹³C-depleted. In this paper, I review trophic transfer of MDC mediated by larval chironomids.
　Trophic transfer of MDC is closely related to methane cycles (i.e. methane production and oxidation) in sediment, and is often enhanced by depletion of dissolved oxygen above the lake bottom. The robust tube built in sediment by larval chironomids could function as a microhabitat for methane-oxidizing bacteria, and promote trophic transfer of MDC. In stratified dimictic lakes, autumnal supply of oxygenated water to the lake bottom can stimulate the activity of methane-oxidizing bacteria, resulting in enhanced trophic transfer of MDC. In shallow polymictic lakes, transfer of MDC can be enhanced in late summer or early autumn when methane production increases. As dissolved oxygen could be depleted within aquatic plant vegetation even in shallow waters, seasonality of trophic transfer of MDC within vegetation could be similar to that in dimictic lakes. Although some studies reported that fish assimilated MDC, the extent to which MDC is transported to lake food webs is unclear. Trophic transfer of MDC has been mainly studied in deep stratified lakes. MDC may be transferred to aquatic consumers in shallow waters which are a hot spot of methane production, though further studies are necessary.

　The term “spring-fed marshes” characterizes wetlands without peat accumulation on the bottom gravel layer, contrasting with “peat mire”. Because this type of wetland is usually small and has a very short lifespan as an isolated habitat, it received little attention until the 1990s; even now information is quite limited. We herein describe the limnological features of spring-fed marshes distributed in Oomori-okuyama (Kani City, Gifu Prefecture, Tokai Region, Japan). These marshes develop on hill slopes, in gradients of 5-20°. They receive oozing waters at their upper margins, and typically lack inflowing waterways. The water flows over hill surfaces or as ground water in a shallow layer over an impermeable ground layer composed of Oniita (plate-like limonite). The volume of water decreases as it flows downstream. As a result, the wetland develops a fan-like shape. The water is characterized by low pH and low conductivity, and the small algal communities are dominated by filamentous Tribonema affine (Xanthophyceae) and desmids. These features are common in dystrophic environments distributed in high and cool regions in Japan. In contrast, the aquatic insect communities are composed of taxa that also inhabit ponds and swamps from lower altitudes.