We clarified the spatio-temporal variations of the remarkably degraded water chemistry of the Miyajimanuma lake (a Ramsar site in Japan) and the contributing factors. The spatio-temporal data were obtained using an autonomously operated boat equipped with a water quality sensor and an automatic water sampler installed in the lake. This monitoring was monthly performed according to the agricultural activities in the surrounding area. All water chemical data were evaluated using principal component analysis (PCA), which showed heterogeneity of the water chemistry due to the inflow of effluent water from paddy fields via drainage ditches. The PCA scores derived from chemical fertilizers and river water increased at the fringe of the inlet ditches during the puddling (May) and irrigation periods (July), respectively, corresponding to the rice paddy cultivation. In contrast, the score indicating dissolved organic carbon, which was derived from groundwater of peatland, increased along the shoreline during the non-irrigation period (August). The spatio-temporal monitoring revealed point and non-point sources. This information combined with a sampling technique based on an autonomously operated boat could be a powerful tool for future environmental monitoring.

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Using geographic information system (GIS), potential habitats in Japan were identified by applying the environmental conditions of otter habitats in Korea. A land use map of Korea was classified into four categories: city, grassland, forest, and water body. Based on the distribution of otter spraints, the optimal habitat conditions for otters were determined. The optimal habitat determined in Korea and Japan was similar to each other. It is unclear if mountain areas would be suitable as they were not surveyed. These findings confirmed that the current environmental conditions of Japan satisfied the conditions for otter survival.

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Changes in the vegetation communities in Lake Izunuma-Uchinuma located in the northern part of Miyagi prefecture, was investigated using aerial photographs in 1976 and 2012. After a flood in 1980, the communities of Indian rice was drastically reduced, and then, disappeared in the most of bank areas by the erosion following the high water level management. In addition, a part of the reed community also decreased from the shoreline side due to erosion. As a result, the area of the lake shore vegetation has decreased from 122.3ha to 59.9ha. Before the 1970s, paddy fields distributed in the lakeside, and there was a traditional use about common reed etc. Thereafter, the paddy fields became renaturalization after the municipalization of the lakeside. Due to these changes in vegetation, there are some problems such as the influence on the ecosystem and the decrease in the association with the local community. In the nature restoration project of Lake Izunuma-Uchinuma, it seems important to properly manage plant communities based on various viewpoints toward solving these problems.

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[in Japanese]

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