Hydro-geographical study on the characteristics and utilization of the water environment of Sado Island

<p>Ⅰ Introduction</p><p>It is important for islands to understand and conserve the current state of water resources centered on drinking water, and to understand how substances circulate and flow out to the surrounding sea area in the water cycle centered on rivers. It is also necessary for the marine environment and marine resources to do. Comprehensive research using the theory of hydrological science, which clarifies the material cycle that accompanies the water cycle, and the method of "hydrological geography," which elucidates the effects of humans based on "natural magazines," is an island. It is effective for water environment research in Japan, and has been conducting continuous research on various islands. Although Sado Island has the second largest area in Japan after the main island of Okinawa, it has not necessarily been sufficiently researched on the water environment, and field surveys were conducted three times in 2019 and once in 2021. Therefore, based on the results, we grasped the current situation and considered the effective and continuous utilization in the future from the viewpoint of hydrology. </p><p>Ⅱ Research method</p><p>First, after organizing various information related to the water environment regarding Sado Island and creating a "hydrological magazine", February, June, September, and 2021 of 2019 at about 80 to 100 points of various rivers on Sado Island. In November, we conducted on-site hydrological observations and analyzed the spatial distribution of water quality. The on-site observation items are temperature, water temperature, electrical conductivity (hereinafter referred to as EC), pH, RpH, and flow rate. After sampling, the total dissolved carbon content by the TOC analyzer and the main dissolved components by the ion chromatograph are used. Analysis etc. was performed. </p><p>Ⅲ Results and consideration</p><p>(1) Use of water The water supply penetration rate of Sado City is about 99%, and water can be used in almost the entire area. The issues such as water supply and earthquake resistance have become issues. The sewage treatment population penetration rate is 64.8%, the sewage treatment population penetration rate including septic tanks and agricultural settlement wastewater is 79.1%, the national average is 79.7% and 91.7%, and the prefecture average is 76.4% and 88.3%, respectively. The sewerage connection rate was 64.2%, which is far below the prefecture's average of 88.9%, and it is thought that this has an impact on the water quality environment in the region. Since agricultural water relied on small and medium-sized rivers and small reservoirs, the Ogura Dam and Toyama Dam were constructed by the state-owned irrigation and drainage project to prevent floods. (2) Hydrological observation results EC was mostly 100-200 μS / cm throughout the period, and reached about 94% of all points in November 2021, when the variation was particularly small. On the other hand, points exceeding 250 μS / cm were distributed in the northeastern / western and southwestern coasts and in the central urban area. It is thought that the influence of sea salt in the coastal area and the low penetration rate of wastewater treatment facilities in the urban area have an influence. There are also differences in water quality, which are thought to be differences in geology and land use, so detailed examination is required. </p><p>Ⅳ</p><p>By conducting a field survey in November 2021 in addition to the three times in 2019, we were able to grasp the water quality of another season, but unfortunately we were hit by bad weather, and light rain and hail occurred throughout the period. Due to the rainy weather, we should investigate the stable period, but on the contrary, it became a record of the rough season.</p><p>View PDF for the rest of the abstract</p>