Abstract
Ⅰ Introduction
Research on water environment change has been conducted for many years on many islands, but there are few research and research on islands in Nagasaki prefecture, and since 2014 we began surveying the Goto Islands and began research with Tsushima, Iki and Hirado It was. The investigation of several years has revealed features of each island including seasonal change and sea salt influence. This time, we will clarify the water environment in each area from relation with terrain / altitude and analysis by small watershed.
Ⅱ target area
Iki is rugged with a maximum altitude of 213 m, and there are numerous reservoirs in various parts of the island. Tsushima is about 50 km from Korea, the altitude of the whole island is relatively high, and the mountains occupy about 89%. The Goto Islands Island consists of about 140 large and small islands that are complex and rich in variety, and the geology is quite different on each island. The Hirado Islands have many mountains while the fields are also relatively large. In all areas the population penetration rate of the sewage treatment population is as low as 20-40%, and the population decline continues.
III Research method
After organizing and examining existing research, the field survey was conducted four times from 2014 in Goto Islands, seven times in Iki from 2015, seven times from Tsushima, seven times in 2016 and four times in Hirado in 2017. In the field, water temperature, temperature, electrical conductivity (EC), colorimetric pH and RpH, COD (May 2017, Iki, Tsushima, Hirado only) were measured and collected to measure the total organic carbon and the major dissolved components Was analyzed. Rainwater is collected every month at Iki ・ Hirado 3 places, 4 Tsushima places, Goto islands ・ Shimabara each one month and analyzes it.
IV Results and Discussion
Sea salt influence was seen on almost all islands, but many factors excluding sea salt are outstanding. In Iki the influence of agriculture appears in EC and TOC, but it is interesting that there is almost no effect of nitric acid. It is thought that groundwater of agricultural water contributes greatly to the higher concentrations of dissolved components even in the upstream area compared with Tsushima. On the Goto Islands, there was a place where the contribution of geology strongly occurred in Fukue Island, and a lot of nitric acid was detected. It is thought that there is a factor in paddy fields in Iki, and upland fields in Goto Islands. Tsushima has a steep topography and the flow velocity of river water is fast and short, so EC and dissolved component concentrations are relatively low, and the concentration has increased with flowing down. Shimoshima was particularly influenced by wind salt transfer at the upstream point, and the seasonal change also appeared greatly. In Hirado Island, especially in the southern part, there are many points where the influence of the geology is considered to be large, the concentration tended to rise with the falling, but the influence of sea salt was strongly seen in Lucerne Island and Kayama Oshima. The rainwater tends to rise in EC and rise in pH around March and October, but the relationship with transboundary contamination is not clear.
Ⅴ Conclusion
From the above, it is considered that the difference in the quality of the islands is greatly influenced by the difference of geology, topography and agricultural form. From now on, it is necessary to further analyze and consider each small watershed, and to clarify the features of the water environment on each island.
