1:45 PM - 3:15 PM
[O08-P78] Water quality of Tairo-Ike Pond in the Miyake-jima Island, Izu-Bonin Arc
Keywords:Groundwater, Water quality surveys, Miyakejima Island
Located in the southern part of Miyake Island in the northwest Pacific, Tairoike is a freshwater lake formed approximately 2300 years ago by a volcanic eruption. There are no rivers flowing in or out of the lake's surface (Arai et al., 1977). Research on the water quality of Tairoike has been conducted by Arai et al. (1977), Kodera et al. (2014), Sato et al. (2020), and others. However, to the best of the author's knowledge, there have been no studies focusing on the diurnal and seasonal variations in the hydraulic characteristics of Tairoike. Therefore, this study aimed to clarify the hydraulic characteristics of Tairoike by conducting water quality surveys on August 2, 2023, and January 17, 2024.
Water quality surveys were conducted at two locations along the lake shore on August 2, 2023, and at six locations on January 17, 2024. The measured parameters were air temperature, water temperature, pH, RpH, electrical conductivity, and Na+. In addition, fixed-point observations of air and water temperature were conducted at a pier on the north side of Tairoike from the morning of January 17 to the morning of January 18. Isopleth maps were created for water temperature, pH, electrical conductivity, and Na+ based on the measurements taken in January 2024 (Figure 1).
As a result, the values of pH, electrical conductivity, and Na+ were consistently lower at all times compared to other observation points within Tairoike. This indicates a reduction in the proportion of ions in the water for some reason in the northwest part of Tairoike. The cause of this phenomenon will continue to be investigated in the future, but the current hypothesis includes a decrease in ion concentration in the water due to aquatic plants growing in the northwest part and the influence of the surrounding topography and ocean.
Water quality surveys were conducted at two locations along the lake shore on August 2, 2023, and at six locations on January 17, 2024. The measured parameters were air temperature, water temperature, pH, RpH, electrical conductivity, and Na+. In addition, fixed-point observations of air and water temperature were conducted at a pier on the north side of Tairoike from the morning of January 17 to the morning of January 18. Isopleth maps were created for water temperature, pH, electrical conductivity, and Na+ based on the measurements taken in January 2024 (Figure 1).
As a result, the values of pH, electrical conductivity, and Na+ were consistently lower at all times compared to other observation points within Tairoike. This indicates a reduction in the proportion of ions in the water for some reason in the northwest part of Tairoike. The cause of this phenomenon will continue to be investigated in the future, but the current hypothesis includes a decrease in ion concentration in the water due to aquatic plants growing in the northwest part and the influence of the surrounding topography and ocean.