Studies on environmental assessment technique on the estuarine ecosystems using multi-tracer

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Chemical analysis of river water and groundwater were carried out for the samples from Izu-Ohshima Island,Hachijyoujima Island and Ogasawara Islands from 1997 to 1999 and from 2005 to 2008. Concentrations of nitrate-N of inland water of Ogasawara Islands werter higher than those in summer. The analytical results show that nutnnt concentrations of the groundwater around the coastal area were increased from Ogasawara Islands to lzu Islands because of land use of agriculture and sewage water from human activity. The analytical results of nitrogen isotope ratio in seaweeds show that the nutrient supply from inland water was decreasing in Hachijyoujima Island. This indicates the importance of nutrient from groundwater seepage for seaweed vegetation in lzu Islands.