A long-term decreasing trend of the electrical conductivity (EC) has been found (1 % significance by Mann-Kendall rank statistic) in spring waters around Akiru plateau (Shirataki-shrine, Ninomiya-shrine and Moriyama-kaikan), Tokyo, Japan. By investigating water quality at these springs in 2018 and comparing them with observed data in 1994, this study clarified causes for the trend found there. At each spring, pH increased in 2018 (1 % significance by Welch’s test), which is regarded as deriving from the decrease of acidic substances. In 2018, EC, and concentrations of nitrate nitrogen and sulfate ion decreased (1 % significance by Welch’s test). The latter two are regarded as derived from long-term changes of agriculture and domestic wastewater. Since the 1990s in Akiruno City where Akiru plateau is located, farmland has been decreasing; sewage systems have been extended. These have affected water quality at the springs around Akiru plateau including EC. Furthermore, environmental regulation standards of nitrate nitrogen imposed by the Ministry of the Environment in 1999 have affected water quality.

　Environmental factors affect microbial community in shallow groundwater. However, the microbial dynamics in deep groundwater have not been investigated enough. This study aims to elucidate the abundance and constituents of the microbial communities in the groundwater deeper than 700 m, at the coastal area of Hokkaido, Japan. Characteristics of the microbial distribution were discussed considering the hydrologic parameters such as dissolved inorganic materials. The density of prokaryotes shows 2.68 (±0.03) × 10³ cells/mL and the relative ratio of Bacteria to the total abundance of prokaryotes shows 14.9 % at the depth of 715 m, whereas the density of prokaryotes shows 1.87 (±0.03) × 10⁵ cells/mL and the relative ratio of Bacteria shows 48.8 % at the depth of 943 m in the groundwater. The main genus detected by the next-generation sequence shows absolute anaerobic, thermophilic, halophilic and alkalophilic bacteria as the major community constituents at the depth of 943 m. This suggests that the groundwater would have been affected by the seawater. Also, the methane is observed in the groundwater due to the microbial activity. Therefore, the information of the microbial dynamics seems to be important to understand the subsurface environment especially focusing on the groundwater.

　Iran lies in an arid/semi-arid region of the Middle East. The Iranian hydrological statistics from 1968 show that the 50-year average annual precipitation was, earlier, approximately 248 mm, but has gradually decreased to 220 mm over the most recent decade, thus, by almost 11 %; water resources have fallen nationwide. The Iranian population has grown from less than 30 million in the 1950s to more than 80 million in 2019. Furthermore, urbanization and agricultural development have placed increasing demands on water resources; these activities today account for 86 % of annual water usage. Iran currently experiences extreme water stress. Permanent rivers have gradually become seasonal; the groundwater level has decreased nationwide. Therefore, water resource management is critical in terms of the stability and sustainability of future socioeconomic activities. Here, I describe the challenges faced by those who seek to manage Iranian water resources.