筑坝河流磷素的迁移转化及其富营养化特征

人类活动过量营养物质输入是导致河流富营养化的主要原因,而河道过度的人为调控则进一步复杂化了河流的营养状态变化。闸坝是河流人为调控的重要工程措施之一,提高水资源利用效率的同时严重干扰了河流自然的生物地球化学循环,产生诸多负面生态环境效应。磷素的迁移转化对河流的营养限制作用受到越来越多的关注,国内外已有研究在筑坝河流磷的富营养化特征方面,已经取得了较为深刻的认识:水库闸坝建设滞留大量磷素,导致河流水体磷含量升高、营养物质比例变化,沉积物储存过量磷素形成的内源释放威胁,以及进一步浮游植物和有害藻类的生长响应等,使得筑坝河流的富营养化生态风险升高;在此基础上,也提出了根据降雨分配和闸控库区储水,合理设置闸坝泄流方式,以改善筑坝河流富营养化生态风险的重要管理思路。对于闸坝调控作用与水体富营养化的定量关系还有待进一步的探讨,而且随着河流资源开发和人为调控力度的增强,河流闸坝建设所产生的系列生态环境问题日益严峻,对此提出还需要系统研究的方向:闸坝调控作用下河流磷素的富营养化机制及其与氮、碳等元素的耦合作用,筑坝河流沉积物内源污染的综合管理,以及闸控景观河流的生态建设和修复等。

Phosphorus cycling and the associated ecological effects of eutrophication in dam-regulated rivers

The anthropogenic input of nutrients to rivers is the main cause of eutrophication, and both the excessive control and engineering of river channels further complicate the issue. To meet the demand for energy and water resources, thousands of dams, weirs, and sluices have been constructed and affected almost every river, which deeply interferes with the biogeochemistry cycles of nutrients and the ecological function of river systems. Previous research has investigated the ecological effects of eutrophication caused by phosphorus in dammed rivers, since phosphorus limitation of primary production is more predominant in river systems. Dammed rivers can reduce outflow and, hence, sequester a significant amount of phosphorus within the impoundments. As a consequence, river water becomes eutrophic, and the ratios of main nutrients change drastically, owing to the different responses of the nutrients to retention by dams. In addition, sediments in the dammed rivers, which containing high contents of phosphorus, can easily become a potential pollution source, especially under intensive scouring events. At the same time, the abundance of algae communities increases, as certain species bloom in the water column, which aggravates the ecologic effects of river eutrophication and threatens the biodiversity of river systems. Therefore, researchers have found that an efficient management strategy based on annual rainfall storage and dam discharge control can be used to improve the ecological effects of eutrophication in dammed rivers. However, as anthropogenic impacts continue to increase, further studies of dammed rivers are needed to clarify the relationship between artificial control in rivers and river eutrophication, in order to reduce the ecological effects of eutrophication, as well as to quantify the threshold of phosphorus, in order to further understand the eutrophication mechanisms of dammed rivers and the combined effects of nitrogen and carbon, to manage phosphorus within sediments, in order to prevent its release and resuspension, and to address concerns regarding the construction and restoration of landscape rivers with dams throughout China.