摘要
The Seto Inland Sea experienced eutrophication during the period of high economic growth and then subsequent oligotrophication due to reduction of inflow load. The nutrient concentration in the seawater peaked in the beginning of 1970's, and thereafter, it has been decreasing. Dissolved inorganic nitrogen (DIN) has remarkably decreased in recent years following the decrease in dissolved inorganic phosphorus (DIP). As a result, Nori (Pyropia) production has decreased in recent years due to bleaching of leaves caused by DIN deficiency. Recent slack in fisheries production was also likely influenced by the nutrient depletion as evidenced by the fish catch using a compact trawl. The process of both eutrophication and oligotrophication that occurred in the Seto Inland Sea can be explained by hysteresis. We introduce several countermeasures to the oligotrophication in the Seto Inland Sea. In particular, to improve Nori production, local nutrient supply was experimentally augmented, such as by application of fertilizer, temporary discharge of dam water, sediment plowing, and ad hoc operations of relaxing sewage treatment water.
摘要译文
濑户内海在高经济增长期间经历了富营养化，随后由于流入负荷的减少而进行了低营养。海水中的养分浓度在1970年代初达到顶峰，此后一直在下降。随着溶解无机磷（DIP）的减少，近年来溶解无机氮（DIN）显着降低。因此，由于DIN缺乏导致叶片漂白，近年来Nori（Pyropia）的产量有所下降。最近渔业产量的减少也可能受到养分枯竭的影响，如使用紧凑拖网捕捞鱼类所证明的那样。濑户内海发生的富营养化和低营养过程都可以通过滞后来解释。我们介绍了濑户内海低营养的几种对策。特别是，为了改善紫菜生产，通过实验增加了当地的养分供应，例如施肥，大坝水的临时排放，沉积物犁和放松污水处理水的临时操作。
阿保, 勝之; 山本, 民次. Oligotrophication and its measures in the Seto Inland Sea, Japan[R]. JP: JAXA, 2019