Japanese Journal of Limnology (Rikusuigaku Zasshi)

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The sulfur isotope ratio (δ³⁴S) has been used as an indicator to determine the origin of sulfur compounds that are air pollutants acidifying freshwater and damaging ecosystems. In this study, the simple in-situ collection/concentration method of sulfate in freshwater was developed for δ³⁴S determination. The quantity of sulfate required for that determination can be readily collected by dipping a mesh bag in water containing a small amount of anion exchange resin. This sampling method is appropriate for research into mountains and remote islands where the long-term research and the transport of large amounts of water samples and bulky samplers are difficult. This method was used in our study of stream water on Yakushima Island. The sulfur isotope ratios of non-seasalt sulfate (_nssδ³⁴S) were higher in the western and mountain regions of the island (+1.1∼+7.5‰) than in the northeastern region (-3.9∼+0.3‰). This suggested that the air mass containing sulfate-sulfur with a high δ³⁴S value emitted by coal combustion in the Asian continent, flowed into the island from the west and northwest and deposited sulfur in the western and mountain regions when the air mass reached high mountains such as Miyanoura-dake (1936 m).

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We studied whether values of a phycocyanin sensor (BGA (Blue-Green Algae)) (YSI Inc.) revealed the total biovolume of cyanobacteria and that of bloom-forming cyanobacteria, respectively, in 64 irrigation ponds, and concluded that the sensor explained 87% of both biovolumes. No cyanobacteria were observed under microscopy with the phycocyanin sensor value of < 10² cells mL^-1, and cyanobacteria were observed in only 40% of ponds with sensor values between 123 and 2,653 cells mL^-1. However, cyanobacteria were always observed with a sensor value of ≥2,758 cells mL^-1. A significant linear regression with a sensor value of ≥2,758 cells mL^-1 was obtained to estimate the biovolume of cyanobacteria. A similar result was obtained for bloom-forming cyanobacteria with a sensor value of ≥6,680 cells mL^-1. In the conclusion, the phycocyanin sensor showed the total biovolume of cyanobacteria and that of bloom-forming cyanobacteria in the field when the phycocyanin sensor value was generally ≥10⁴ cells mL^-1.

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