(1) Water Unsuitable for Drinking (1968)

In 1968, Kaneshima Kiyoshi of the University of the Ryukyus conducted water quality surveys on Uotsuri Island, Minamikojima Island, and Kitakojima Island, collecting and analyzing seven samples. He established that there were a number of small streams on Uotsuri Island, and that although Minamikojima Island and Kitakojima Island had no springs or streams, puddles had formed where water had dripped down among rocks, but as the water was yellowish-brown and strongly acidic, it was unfit for drinking. The results showed a strong overall influence from seawater, with salt the main additive component of the water, and in all but one case an unusually low pH of between 2.8 and 4.4. Water from Minamikojima Island and Kitakojima Island had low pH and high amounts of phosphorus due to the effects of seabird droppings. Also, some of the samples collected on Uotsuri Island contained sulfuric acid, suggesting the existence of mineral deposits. (Ref. 1)

(2) High Flow Rate Contributes to Potability of Water on Uotsuri Island (1971)

In 1971, Yoshida Kazuharu, Taira Hatsuo, and Tokuyama Akira of the University of the Ryukyus continued research by collecting 45 samples of water from the islands and conducting detailed analysis and investigation. Their survey made the new discovery that high flow rate on slopes in the north of Uotsuri Island contributed to the potability of water, with water here relatively less affected by seawater. Having divided water on Uotsuri Island, Kitakojima Island, and Minamikojima Island into three groups, they made the following estimates as to how their composition had come about. (Ref. 2)

1. Water containing wind-borne salt from seawater, sandstone, and rainwater (Uotsuri Island).
2. Water like 1. that also includes eluted components from seabird droppings (Minamikojima Island).
3. Water like 2. that further includes eluted components from dry grass and humic soil (Kitakojima Island).

In addition, they conjectured that water on Uotsuri Island, Kitakojima Island, and Minamikojima Island may be affected by the islands' slopes, depending on whether it is easy for water, dry grass, and humic soil to accumulate and how long they take to come into contact with each other. They also conjectured that the amount of flora and fauna may be a factor. (Ref. 2)

(3) Water Quality From the Perspective of Potential Development and Usage (1979)

In its 1979 survey regarding potential development and usage, the Okinawa Development Agency conducted water quality surveys. It analyzed samples of surface water from 10 locations and samples taken from boring surveys from 3 locations on Uotsuri Island and 1 location on Minamikojima Island, investigating whether they met water supply quality standards. Samples were all taken from locations near the coast; the results showed that surface water on Uotsuri Island was unsuitable for drinking due to the general bacterial population, E. coli bacteria, and in some cases the pH level. Water from Minamikojima Island was unsuitable because it would require three forms of treatment to make it fit for drinking: adjustment of the pH; purification through flocculation, precipitation, and sand filtration; and sterilization. Water from Kitakojima Island was unsuitable due to its potassium permanganate consumption and its pH level, requiring the same kind of measures to make it drinkable as water from Minamikojima Island. Even on Uotsuri Island, the largest of the Senkaku Islands, the basin area is small at only 14 hectares, meaning it has a high level of evaporation and transpiration and poor water-holding capacity. The survey concluded that the nature of the land makes it difficult overall to secure a stable supply of water for usage. (Ref. 3)

Translated by OPRF

Translated by OPRF

Ref. 1: Kaneshima Kiyoshi, "Senkaku Retto no suishitsu" (Senkaku Islands Water Quality), in Kogyo yosui (Industrial Water) 128, Japan Industrial Water Association. Collated and published by the Senkaku Island Documentary Material Compilation Association in Senkaku kenkyu: Takara gakujutsu chosadan shiryoshu (Senkaku Research: Takara Academic Research Group Materials Collection), 1968.

Ref. 2: Yoshida Kazuharu, Taira Hatsuo, and Tokuyama Akira, "Senkaku Retto no suishitsu chosa" (Senkaku Islands Water Quality Survey), in Senkaku Retto gakujutsu chosa hokoku (Report on the Senkaku Islands Scientific Expedition), based on a survey carried out by the University of the Ryukyus Scientific Expedition Team (Nishihara, Okinawa: University of the Ryukyus, 1971).

Ref. 3: Abridged version of Senkaku Shoto chosa hokokusho: Riyo kaihatsu kanosei chosahen (Report on the Senkaku Islands Survey: Potential Development/Usage Survey) (Okinawa Development Agency, 1980).

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