密西西比河干流大坝建设对鱼类的影响及保护措施

IMPACTS OF CASCADE DAMS ON FISH IN THE MAINSTREAM OF MISSISSIPPI RIVER AND THE MITIGATION MEASURES

如何减轻大坝阻隔对鱼类等水生生物的影响以及制定有效的恢复措施一直是河流生态保护的主要内容。文章通过文献调研、资料收集等方式对美国密西西比河干流大坝建设状况及其对鱼类的影响进行梳理,总结了当前美国所采取的相关保护措施和效果。统计结果显示,密西西比河干流共建有梯级闸坝41座,均分布在干流的上游,多数大坝坝高不超过15 m,库容小于0.3 km3。这些弱调蓄能力的低水头坝阻隔了密西西比河鱼类洄游,但目前仍未修建过鱼设施。相关研究证实,密西西比河洄游性鱼类可以利用泄水闸门完成上行和下行,但过鱼效率随着大坝梯级的递增逐级下降,尤其是鲟类,仍难以抑制其种群的衰退。受长期蓄水影响,密西西比河上游鱼类群落产生了空间分化,但仍保持着较高的物种多样性。1986和2000年,美国分别实施了上密西西比河生态系统环境管理计划(UMRS-EMP)和上密西西比河生态恢复和维持策略(UMRS-RMS),采用渔业资源长期监测计划(LTRMP)及9项栖息地修复措施,从生态系统层面保障了密西西比河鱼类资源的持续稳定。这种系统性修复方式可为我国筑坝河流鱼类资源保护与河流生态修复提供参考和示范。

How to mitigate the influence of dam construction on fish diversity and develop effective conservation and restoration measures are the main content of river ecological protection.This study overviewed dam constructions in the mainstream of Mississippi River and their influence on fish.Additionally,the conservation measures of fish resources and their effectiveness were analyzed and summarized.It was found that 41 lock and dams were constructed in the upper Mississippi River.The height of most dams were no more than 15 m and their capacities were less than 0.3 km3.These dams blocked the migration path of fish in the Mississippi River but no one had fish passage facilities.Many studies showed that navigation dams in the Mississippi River may function similarly to weirs,because most are lowhead dams with bottom release gates that allow fish to pass under some conditions.However,increased dams decreased the passage efficiency,and they had less effect in maintaining the fish population,especially for sturgeon species.Influenced by the impoundment of dams,the spatial variation of fish composition in the upper Mississippi River suffered a community-level fragmentation.In 1984 and 2000,the Upper Mississippi River System-Environmental Management Program(UMRS-EMP)and the Restoration and Maintenance Strategies(UMRS-RMS)were implemented respectively,including the long term fish recourses monitoring program(LTRMP)and 9 habitat restoration measures.Benefiting from these measures,the Mississippi river still maintains high species diversity.This can provide us with successful experience in future fish resources protection and watershed management in dammed Chinese rivers.