Study on the long-term monitoring of the marine environments in the Seto Inland Sea and their predictions

本项目利用自主监测系统对萨达半岛顶端的水质包括营养物进行了长期监测。利用历史资料和沉积物样品分析了附近地区的长期环境变化。并对目前生态系统的结构进行了调查。有关濑户内海营养环境的主要研究结果如下：(1)濑户内海中60%以上的氮、磷来源于太平洋。就本戈海峡而言，来自太平洋的营养物质的供应主要是通过通道以南陆架斜坡区底层的冷的、富含营养物质的水团的侵入来进行的。(2)在年代际尺度上，营养物质侵入本果水道的程度是不同的。1980 - 2000年总体呈下降趋势，导致iomo - nada海域营养物浓度和浮游植物种类多样性下降。这些结果显示了濑户内海的营养状况和生态系统很可能会因全球海洋环流的变化而发生变化，并支持了我们长期营养监测的意义。对本戈海峡沉积物样本的分析揭示了由于养鱼造成的有机物和有机锡污染的最新状况。通过对Seto Inaldn海特有沙丘区域的调查，分析了沙丘在促进初级生产和物质循环中的作用。此外，本古海峡的微生物调查还揭示了由于海洋扰动（如九代潮和海底入侵）造成的微生物环的部分变化。这些结果将为验证濑户内海环境和生态系统的长期变化提供重要的参考数据。

In this project, long-term monitoring of water quality including nutrients was conducted at the tip of Sada Peninsula by using the autonomous monitoring system. The long-term environmental variations of nearby areas were analysed by using the historical data and the sediment samples. Moreover, the structure of the ecosystem at present were surveyed.The major results relating to the nutrient environments of the Seto Inland Sea are as follow. (1) More than 60% of the nitrogen and phosphorous in the Seto Inland Sea are originated from the Pacific ocean. In case of Bungo Channel, supply of the nutrients from the Pacific Ocean is mainly carried out by the intrusion of cold, nutrient-rich water mass from the bottom layer of the shelf slope region south of the channel. (2)The intrusion of the nutrients into Bungo Channel varied at the decadal time scale. It generally decreased from 1980 to 2000, resulting in the decreases of the nutrient concentration and the spieces diversity of phytoplankton in Iyo-Nada.These are very important results showing the high possibility that the nutrient conditions and the ecosystems in the Seto Inland Sea can vary due to the variations of global ocean circulation, and supporting the significance of our long-term nutrient monitoring.The analyses of the sediment samples in the Bungo Channel revealed the state of recent pollutions by organic matter and organotin due to the fish culture. Surveys of the sand dune areas peculiar to the Seto Inaldn Sea were conducted, and some roles of the sand dunes in the enhancement of primary production and material cycling in the ecosystem. Moreover, the microbe surveys in Bungo Channel revealed some part of the variations of microbial loop due to the oceanic disturbances such as the kyucho and the bottom intrusion. These result will provide the important reference data in the future research verifying the long-term variations of the environments and ecosystems in the Seto Inland Sea.