Characteristics of water conditions in the inner part of Ariake Bay with hypoxic water and red tide and causes of decline of the ecosystem on the tidal flats faced to the bay.

从2005年4月至2007年12月，在有莱克湾内部的9至12个采样点每月或每两周监测一次水质情况。在位于海湾最深处的四个采样站，在相同的采样时刻对底栖生物群落进行了定量评估。在这个海湾，每年雨季后的7月底到8月，深度不到20米的最里面都会出现低氧水。2006年8月5日，这几个地区的DO下降最为严重。在水的中层，形成了缺氧水，底层水的DO也降到了1 mg/L以下，此时地表水停留在30℃以上，浮游植物，主要是雨季繁殖的硅藻，由于极高的水温而死亡。浮游植物的身体变成了大量悬浮在水中的死亡有机颗粒，并正在分解，消耗…在水里做更多的运动。这一现象表明，低氧水是由于海底DO消耗的增加和沉积物的有机富集所引起的，但近期全球变暖导致的水温升高正在成为另一个因素，增加了水中的氧气消耗，导致海湾缺氧或缺氧的进展。由于出现了更严重的缺氧或缺氧水，湾内最深处的底栖动物群落逐年明显下降。它们重复着密度和生物量的周期性波动，夏季迅速减少，秋季到冬季恢复。然而，在寒冷的季节，底栖动物群落并没有完全恢复。底栖动物群落由限制成员组成，包括小型螺旋体多毛类和小型双壳类，对环境波动具有很强的适应性。因此，春季底栖动物群落的总生物量很低(小于10g/m^2)，在春季趋于高峰。如果夏季继续保持大范围赤潮发生后有机排放增多、水位和面积出现低氧水的底栖生物条件，在不久的将来，湾内底栖生态系统将受到严重破坏。较少

The water conditions were monitored monthly or biweekly at 9 to 12 sampling stations in the inner part of Ariake Bay from April 2005 to December 2007. At four of these sampling stations, which are located in the innermost areas of the bay, the benthic communities were assessed quantitatively at the same sampling occasions. In this bay, hypoxic water occurred between the end of July after the rainy season and August in the innermost areas of less than 20 m in depth every year. On August 5, 2006, the most severe decrease of DO occurred in these areas. In the middle layer of the water, anoxic water was formed, and DO of the bottom water also fall to the levels of less than 1 mg/L. In this time, the surface water stood over 30℃, and the phytoplankton, mainly diatoms that bloomed during the rainy season, died due to the extremely high water temperature. The dead body of the phytoplankton became large amounts of dead organic particles suspended in the water, and was being decomposed, consumi … More ng DO in the water. This phenomenon indicate that the hypoxic water has occurred by the increase of DO consumption from the sea floor with organic enrichment of he sediment, but also the increase of water temperature due to the recent global warming is becoming another factor that increase oxygen consumption in the water and results in the progress of hypoxia or anoxic in the bay. The benthic communities in the innermost areas of the bay were declining markedly year to year due to the occurrence of the severer hypoxic or anoxic water. They repeated a cyclic fluctuation in density and biomass, that they decreased rapidly in summer, and recovered from autumn to winter. However, the benthic communities did not recover fully in the cold seasons. The benthic communities consisted of restricted members including small spionid polychaetes and small bivalves that had high adaptability against the environmental fluctuations. Therefore, the total biomass of the benthic communities were very poor (less than 10g /m^2) in spring, when they tended to reach a peak. If the present benthic conditions with increasing organic discharge from the occurrence of large scales of red tide and developing hypoxic water in levels and areas continued in summer, the benthic ecosystem in the inner parts of the bay would be seriously destroyed in near future. Less