地球科学进展

地球科学进展  2018 , 33 (7): 675-686 https://doi.org/10.11867/j.issn.1001-8166.2018.07.0675

生态水文学与水安全

河流梯级开发生态环境效应与适应性管理进展

李哲1, , 陈永柏2, 李翀2, 郭劲松3, 肖艳1, 鲁伦慧1

1.中国科学院重庆绿色智能技术研究院,中国科学院水库水环境重点实验室,重庆 400714
2.中国长江三峡集团有限公司,北京 100038
3.重庆大学,城市建设与环境工程学院,重庆 400045

Advances of Eco-environmental Effects and Adaptive Management in River Cascading Development

Li Zhe1, , Chen Yongbai2, Li Chong2, Guo Jinsong3, Xiao Yan1, Lu Lunhui1

1.Key Laboratory of Reservoir Environment, Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences, Chongqing 400714,China
2.China Three Gorges Corporation, Beijing 100038,China
3.College of Urban Construction and Environmental Engineering, Chongqing University, Chonging 400045,China

中图分类号:  P343.1;TV213.4

文献标识码:  A

文章编号:  1001-8166(2018)07-0675-12

收稿日期: 2018-03-30

修回日期:  2018-05-8

网络出版日期:  2018-07-20

版权声明:  2018 地球科学进展 编辑部 

基金资助:  *国家自然科学基金项目“碳在金沙江梯级水库过坝下泄中的迁移转化及其通量研究”(编号:51679226)中国长江三峡集团重点科研项目“三峡水库温室气体源汇通量监测与分析研究”资助.

作者简介:

First author:Li Zhe(1981-), male, Zhangzhou City, Fujian Province, Professor. Research areas include reservoir aquatic environment. E-mail:lizhe@cigit.ac.cn

作者简介:李哲(1981-),男,福建漳州人,研究员,主要从事水库水环境研究.E-mail:lizhe@cigit.ac.cn

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摘要

筑坝蓄水将迫使淹没区陆生生态系统退化消失,改变其下游受影响河段的环境与生态,破坏自然河流连续性与连通性,是影响河流生态系统显著且强烈的人类活动。河流梯级开发对其生态系统的影响可能存在“累积效应”,即将大坝拦截阻隔对河流生态系统的影响逐级“放大”。然而,“累积效应”的作用对象、途径与水文生态机制目前仍不明晰。不仅如此,河流梯级开发的适应性管理的对象、目标、时空范围与作用途径等已不能简单地参照或套用当前以恢复水文自然情势来修复河流生态系统为主线的实践模式,其适应性管理取决于对河流—水库系统生态结构功能、演替规律的科学认识,也受到多利益主体的制约和影响。长江上游梯级开发在全球大河流域开发中独树一帜,将深刻改变长江上游河流生态格局。对长江上游梯级开发的适应性管理应以优化河流—水库生态结构功能、维持河流—水库生态系统健康为目标。揭示长江上游梯级开发“累积效应”的作用对象与形式,通过优化提升生态系统服务以权衡多利益主体诉求,构建长江上游绿色水电运营管理新体系,值得进一步探索。

关键词： 河流—水库系统; ; 累积效应 ; 变化水文环境 ; 生态系统结构功能 ; 水库生态学

Abstract

As a kind of anthropogenic activity with significant impact on river ecosystem, dam construction and reservoir creation will result in the degradation and disappearance of terrestrial ecosystem in its flooded area. It will cause the significant change of downstream eco-environment and disrupt the continuity and connectivity of natural rivers. There may be “accumulative effects” on the impact of river cascading development on its ecosystems, which is to “amplify” the impact of damming on river ecosystems step by step. However, the role, approach, and hydro-ecological mechanisms of the “accumulation effect” are still not clear. Additionally, this will also result in the uncertainty in the objective, targets, spatio-temporal scope and action path of adaptive management of river cascading development. In river cascading development, the current adaptive practice on restoring natural hydrological processes and river ecosystem may no longer be effective. There is need to understand the function and structure of river-reservoir system and its succession. The trade-offs between multi-stakeholders of river-reservoir system shall be also taken into consideration. The upper Yangtze River has experienced intensive cascading development, which is unique among the world’s rivers and will profoundly change the ecosystem in the upper Yangtze. The adaptive management of upper Yangtze should aim at optimizing the ecological structure of rivers and reservoirs and maintaining the health of river-reservoir ecosystems. Future research could be focused on the role and form of “accumulative effects” in upper Yangtze, and the trade-offs among multiple stakeholders. These will construct a new paradigm for the operation and management of green hydropower in the upper Yangtze.

Keywords： River-reservoir system ; Accumulative effect ; Changing hydrological environment ; Ecological structure and function ; Reservoir ecology.

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李哲, 陈永柏, 李翀, 郭劲松, 肖艳, 鲁伦慧. 河流梯级开发生态环境效应与适应性管理进展[J]. 地球科学进展, 2018, 33(7): 675-686 https://doi.org/10.11867/j.issn.1001-8166.2018.07.0675

Li Zhe, Chen Yongbai, Li Chong, Guo Jinsong, Xiao Yan, Lu Lunhui. Advances of Eco-environmental Effects and Adaptive Management in River Cascading Development[J]. Advances in Earth Science, 2018, 33(7): 675-686 https://doi.org/10.11867/j.issn.1001-8166.2018.07.0675

1 引 言

河流是孕育人类社会的摇篮。人类社会的繁衍与发展都依赖于河流提供生计、住所、商业并维持生态功能。筑坝蓄水通过拦蓄调节流域淡水资源的时空配给,发挥灌溉、发电、防洪、供水、养殖、航运、旅游等多种功能,服务人类社会经济发展[1]。作为保障人类水安全的重要工程手段,筑坝蓄水几乎与整个人类文明的演进史相伴相行,在人类发展史中的重要性并不亚于火的发现与使用。目前,全球已建有各类大坝(坝高超过15 m)约58 000座[2],所形成的水库总库容为7 000~8 300 km3,已接近全球陆地天然湖泊储水总量的10%,是全球河流入海总量的1/6[2]。若考虑各类小型水库、堰塘的蓄水规模,可大致推算出目前全球各类水库所形成的总库容约为15 500 km3,是全球河流年径流总量(55万亿m3/a)的27.3%。

但是,筑坝蓄水会不同程度地改变陆地水循环、调节河流水文情势,对河流生态系统产生深刻的影响。自20世纪60~70年代以来,部分观点认为筑坝蓄水对河流生态系统的负面影响大于其正面效应,在很多情况下会导致物种和生态系统不可逆的丧失[3]。一些研究成果被自然保护主义者广泛引用,成为世界反坝运动的重要依据。然而,在全球变化的大背景下,因在淡水资源保障(水安全、粮食安全)、低碳能源供给(能源安全)等方面呈现突出的服务功能,大坝修建和水电开发已成为具有减缓气候变化不利影响的重要途径,被各国政府纳入基础设施投资建设的优先项目清单[4,5]。在后巴黎协议时代[5],如何有效减缓大坝对河流生态系统的不利影响,如何优化大坝管理运行以可持续地发挥其对人类社会福祉的贡献,依然成为当前地球科学研究领域的重要问题,备受关切。

长江是中国的母亲河。长江上游水能资源丰富,其干支流水能理论蕴藏量约为2.68亿kW,能开发量约为1.97亿kW,年发电量约为10 270亿kW·h,占全国可开发总量的53.4%。其中,宜昌以上的长江上游水能资源蕴藏量约占流域的80%,可开发的水能资源则占全流域的87%。特别是宜宾以上的金沙江水系,水量丰沛且稳定,落差大而集中,是我国水能资源的“富矿”区。目前,金沙江规划开发的水电总装机容量为77 000 MW,规划年发电量为3 530亿kW·h,是实现我国“西电东送”战略目标的重要能源基地,位居我国十四大水电基地之首。预计在金沙江干流直门达—宜宾2 326 km干流河段,未来可能建设超过20座大型水电站,平均约100 km河段便有1座水电站。如此高强度的河流梯级开发在全球大河流域开发中独树一帜,不仅将深刻改变长江上游生态格局,也将对长江流域社会经济可持续发展产生深远影响。

本文梳理近年来筑坝蓄水生态环境效应研究进展,分析河流梯级开发可能产生的“累积效应”,综述大坝拦截下河流适应性管理研究与实践进展。文章以长江上游梯级开发现状为重点,探讨长江上游未来适应性管理的科研需求,为长江上游梯级开发的水环境保护与水生态管理提供建议。需特别指出,本文所指的“生态环境效应”仅涉及水环境与水生态。

2 筑坝蓄水的水环境与水生态效应

2.1 筑坝蓄水的生态环境效应研究进展

筑坝蓄水将迫使河流生态系统不同程度地呈现出以下4个方面的变化:

(1)水库蓄水污染物释放[6]:筑坝蓄水将导致部分陆地受淹,迫使淹没区陆生植被逐渐死亡、有机质(动植物残体、土壤中有机碎屑和腐殖质等)降解、养分与各种污染物(如汞、镉和砷等)溶出释放到水库[7]。因养分溶出,易造成水库营养水平在蓄水初期(通常为3~5年)呈现显著升高的“上涌”现象(trophic upsurge)[8]。

(2)水库生态系统形成与发育、演变[9]:蓄水后,在原有河流本底状态基础上发育演变形成了“新生”的水库生态系统。在空间上,系统各要素呈现由“河相”向“湖相”过渡的梯度变化(图1)[10]。

显示原图| 下载原图ZIP| 生成PPT

图1   水库生态系统各要素的纵向变化概念性模型(据参考文献[9]修改)

Fig.1   Conceptual framework of longitudinal gradients of reservoir ecosystem(modified after reference[9])

在时间上,“新生”水库在经历初期“上涌”阶段后[8],随库龄延长逐渐发育并趋于稳定,且受上游来水和水库运行交叠影响呈现出演变规律[9]。

(3)下游受影响河段环境与生态的改变[11,12]:大坝下游河段形态、水沙关系和冲淤情势等均受制于上游大坝运行,径流量呈现下降趋势或非自然节律的变化特征,驱动环境与生态各要素发生改变,例如,河流底栖生物种群变化[13]、鱼类栖息地与产卵场消失[14]、河岸崩塌与河滩地退化[15]和河口海岸生态环境变化等[16]。

(4)河流连通性与连续性被破坏[17,18]:大坝拦截和生态阻隔将不可逆地影响鱼类洄游,改变流域鱼类种群结构、生物多样性及生物资源总量,最终影响流域中陆生、水生系统的物种组成与食物网格局,形成诸如外来物种入侵等生态环境问题[17]。

围绕筑坝蓄水生态环境效应的研究,可大致梳理成2条有显著区别的学术发展路径。

第一条路径起始于20世纪30年代,围绕水库修建可能产生的“土地淹没、水文调节、生态阻隔”3个方面的生态环境影响开展研究,至60~80年代形成了研究热潮并持续至今。该路径侧重于对水库修建、蓄水和运行过程中的具体生态环境问题,分议题开展针对性研究,如:水库淹水后污染物释放(营养物、重金属)的生态效应、水库中变价有害金属物质的生态毒理效应与生态风险、大坝拦截对河流营养物质输送和鱼类洄游的影响、物种入侵和滨岸带生态系统恢复等。尽管研究议题相对较分散且学科间交叉明显,但该路径的总体思路和目的却十分清晰,即甄别水利工程对河流生态系统的影响并开展“点对点”研究,故该路径从某种意义上可称之为 “大坝生态学”。

另一条路径起始于20世纪80年代,依托经典湖沼学理论和方法体系,以水质保障与管理为出发点发展而成。1980年美国明尼苏达大学和美国土木工程学会(The American Society of Civil Engineers,ASCE)资助召开了水库专题研讨会(Symposium on Surface Water Impoundments),共收集了160篇论文,涵盖水库历史、社会价值、环境管理法规、规划与设计运行、物理化学与生物过程等方面[19]。1987年于捷克斯洛伐克召开了第一届国际水库湖沼学与水质管理大会[20]。1990年美国学者出版了专著《水库湖沼学:生态学视角》,该专著以美国水库为对象,从地理分布特征、水文水动力过程、泥沙输移沉积过程、初级生产与次级生产以及鱼类动态等方面描述了水库生态系统各组分基本特征及其过程,勾勒出了水库生态系统总体框架和水库生态学的基本体系,成为了水库湖沼学系统化的重要标志[21]。该路径延续了现代湖沼学的研究思路和基本观点,侧重于以水库生态系统作为独立单元,强调将水库视为有别于天然湖泊、河流的半人工半自然水体和面向水库水质管理(主要是N和P控制与水库富营养化防治)而开展研究实践[22,23],故其问题边界与涵盖内容也少于第一条路径。

上述学术路径的差别在一定程度上归因于水库生态系统“自然—人工”的双重属性。第一条路径强调了大坝建设、水库运行的“人工”属性,认为水库是具有明确服务功能的人工生态系统,显著地受到人类活动胁迫或干预而有别于蓄水前的自然河流特征。第二条路径强调了水库生态系统仍具有同其他自然水生态系统相同的基本结构和要素,但物理生境差异迫使其生态系统呈现出独特的功能特征和发育演替模式。尽管研究方向与定位上存在差异,但上述2条路径并不矛盾,且逐渐呈现出融合趋势。近年来在全球变化研究兴起大背景下,筑坝蓄水对河流生态系统影响依然热度不减,细化衍生出例如水库碳循环、碳通量与水电碳足迹等研究热点,并注重从基础研究过渡到适应性管理实践以减缓筑坝蓄水对河流生态系统的不利影响。

2.2 河流梯级开发对其生态系统“累积效应”的研究进展

河流梯级开发,通常是指从河流或河段的上游到下游,呈阶梯形地修建一系列大坝,以最大限度依托河流落差充分利用水资源(水能、航运和防洪等)[24]。河流梯级开发迫使其“原生状态”消失殆尽,取而代之的是一系列由大坝拦截蓄水形成河流—水库串联交错的生态系统(简称“河流—水库系统”),显著改变流域水生态格局。在河道水文形态(hydromorphology)方面,一部分河段受水库回水影响,水位升高、过水断面扩大、流速放缓,水体滞留时间显著延长;另一部分河段尽管未受回水影响,但径流过程、水动力条件受上游大坝运行约束而呈非自然节律。河流梯级开发逐渐形成了急流型生境(lotic type)和缓流型生境(lentic type)交错序列,水体光热条件、养分等生境要素的配置亦受上下游大坝运行影响显著,迫使河流生态结构、功能显著迥异于自然河流,也显著差别于单一水库的纵向梯度变化。特别是在首尾相连的梯级水库或水库群中,河流将受到上游大坝下泄流量、下游水库顶托以及上下游水库联动运行调节的交叠影响,水文水动力条件、分层—混合格局、生物—非生物要素时空分布更具有复杂性和不确定性[12,25]。

国内在澜沧江开展相关研究的团队主要为杨志峰团队[26,27]和何大明团队[28,29],侧重于从鱼类、浮游生物等生物要素的时空分布、变化与演替的角度,阐释梯级水库建设运行对生态系统的影响。而在乌江水系梯级水库的研究则主要来自汪福顺和刘丛强团队[30,31]等,着重从生源物质(C,N和P等)的生物地球化学过程入手阐释梯级水库生源物质循环机制与通量变化。此外,国内亦有不少学者对河流梯级开发的生态环境累积效应进行了研究讨论[32,33,34,35,36,37,38,39,40]。目前,学界观点倾向于认为,梯级水库建设运行对河流生态系统的影响存在“累积效应”[41],即将大坝拦截阻隔对河流生态系统各种影响逐级“放大”。如河流泥沙输送量因大坝数量增加而逐渐下降、水库温度延滞效应逐渐加大等。在生物群落方面,Li等[27,42]发现澜沧江中段梯级水库逐级修建后浮游植物丰度呈现逐级升高、生物完整性呈现显著下降的“累积”特征。Zhai等[43]认为澜沧江梯级水库建设将迫使河流生态系统完整性逐级下降。Serafim-Junior等[44]报道了轮虫、微型甲壳类生物多样性在天然河道中呈现明显的空间梯度变化,但因梯级水库修建而逐渐消失,生物群落组成呈现均质化趋势(homogenization)。亦有研究认为,梯级水库对生态系统影响的“累积”,同大坝相对位置、水库形态与运行方式等密切相关[25]。Lacerda dos Santos等[45]发现梯级水库运行导致局地生境变化是改变物种分布、生物多样性与营养水平的关键。王光谦等[46]认为梯级河流开发导致的生境格局和生源物质循环异变是当前研究的挑战[46]。水库群对径流调节的耦合作用使河流生境格局和生源物质循环异变呈现表现出多要素、多过程、高度不确定性的复杂过程特征。

目前,阐释筑坝蓄水对河流生态系统影响的经典理论模型是由Ward和Stanford在河流连续性概念(River Continuum Concept, RCC;图2)[47]基础上提出的序列非连续性概念(Serial Discontinuity Concept, SDC;图2)[41]。SDC的理论模型已通过不少研究予以验证[13,41,48,49],并主要应用于对坝下受影响河段开展生态修复与适应性管理[50,51]。在SDC基础上,巴西学者Barbosa等[25]在1999年提出了梯级水库连续体概念(Cascading Reservoir Continuum Concept, CRCC),并主要用以描述梯级水库水环境变化过程。CRCC认为河流梯级开发不仅促使河流纵向生态要素呈现迥异于单一水库的变化特征,如温度逐渐升高、浊度逐渐下降、叶绿素a浓度升高、富营养化加重等,生态要素在梯级水库的横向和垂向方向上也呈现出有序列的变化特征。尽管原文中并未使用“accumulative effects”定义因梯级水库导致的上述变化,但作者强调了梯级水库中将迫使生态要素各种变化得以“增殖”(proliferation)。

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图2   河流连续性概念(RCC)和序列非连续性概念(SDC)(据参考文献[41,47]修改)

Fig.2   Conceptual model of River Continuum Concept (RCC) and Serial Discontinuity Concept (SDC) (modified after references[41,47])

尽管如此,目前,河流梯级开发对其生态系统的“累积效应”,还尚难以通过SDC或CRCC界定或阐释。一方面,筑坝蓄水对河流生态系统的影响,其本质是导致生态要素(生物、非生物)时空分布产生“重置”或“错配”,最终驱动河流生态系统结构功能发生显著变化。但河流生态系统能否“消纳”上述变化并恢复到自然状态却难以通过SDC或CRCC概念性框架验证或阐释,故“累积效应”在SDC或CRCC的理论框架下是难以判别或衡量的。Ellis等[49]强调坝下受影响河段物理生境(如水温)恢复过程可长达近百公里,而生源物质可在较短空间范围内恢复至原有河段水平,物理生境和化学生境的“错配”导致坝下受影响河段底栖生物类群分布有别于原有天然河道并影响鱼类种群分布和食物网形成。另一方面,尽管“累积效应”强调梯级开发对河流生态系统的影响相对于单一水库(或大坝)应当是“正馈”的(即逐级放大),但“累积效应”并非作用于所有生态要素。梯级水库对某些特定生态要素的时空变化,可能不具有“累积”影响。Barbosa等[25]发现,浊度、无机磷等在梯级水库中的累积变化响应十分迅速,但亦有生态要素在梯级水库中的响应则显著滞后(如蓝绿藻优势度)或甚至无响应(如无机氮)。一些观点倾向于认为梯级开发将导致有明显梯度的河流生境和生物群落呈现均质化[44,52],这可能是形成“累积效应”的主要原因。但由于梯级水库适生的生物群落发育同生境要素配置变化之间存在时间差,即梯级水库中生物群落发育所需时间可能长于生境要素配置对变化水文环境的响应,因此,梯级水库对河流生态系统结构、功能是否具有“累积效应”,仍值得商榷。例如,假设上游水库水体滞留时间远长于下游水库,在相同流域背景下若上游水库发生藻类增殖的富营养化趋势,但下游水库藻类因水体滞留时间较短难以增殖。故相对于上游水库而言,藻类初级生产并未能够实现“累积”,甚至可能因下游水库水文水动力条件而出现“抵消”。

我们认为,变化水文环境是河流—水库系统(单一水库、梯级水库)水环境与水生态发生变化的根本驱动力(图3)。变化水文环境将从水动力条件(分层—混合特征)、水下光热条件、养分输送(氮磷营养物、异源性与自源性有机物等)等3个方面,构建特定水文环境下河流—水库系统生境配置,逐渐演化形成适生生物群落、生产力格局(初级生产、次级生产、细菌生产等)与生源物质循环模式(图3)。

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图3   变化水文环境对河流—水库系统结构、功能影响的示意图

Fig.3   River-reservoir ecosystem structure and functioning in changing water environment

因此,河流梯级开发对其生态系统的“累积效应”,理论上应是在上述3个方面的驱动力存在“累积”(或“逐级放大”)的基础上,导致的河流—水库系统生物群落、生产力格局与生源物质循环的“累积”变化。甄别河流梯级开发的“累积效应”、揭示“累积效应”作用对象、途径与水文生态机制,是阐明河流梯级开发生态环境效应关键。

3 筑坝河流的适应性管理研究进展

“适应性管理”(adaptive management)最早是由Holling[53]在20世纪70年代末提出的,其核心是“边学边做”,即通过实施监测评价管理方式,验证管理方法与决策的合理性与完整性。河流生态系统适应性管理的经典案例,是美国格伦峡谷大坝(Glen Canyon Dam)为应对下游河流生态系统退化而开展的径流调节实践。通过修正大坝下泄流量方案,增加最小日泄水量,减少日泄水量变幅等措施,构造了格伦峡谷大坝下游河段不同物种的栖息生境[54],对坝下河流生态恢复取得了显著效果[55]。以该案例为起点,20世纪90年代中期美国启动了以淡水生态系统生态修复为主要目标的全国性行动计划[56]。匹配相对完善的生态系统监测网络体系,对河流适应性管理逐渐形成了以坝下河流生态系统修复为主要目标、以“径流调节→替代性方案实践→监测评价与反馈→优化的大坝下泄方案”为主线的适应性管理基本模式[50,57]。

据不完全统计,迄今在全球范围内以“优化大坝运行、实践径流调节”为主要途径的流域适应性管理案例已超过120个[50,57,58]。目前的案例中超过50%以保护珍稀物种和自然生物资源(如鱼类)为出发点[50],约有40%的案例以保护底栖生物、浮游植物、大型水生植物与河滩地植被为目标。在对生境要素的调节方面,约有40%的案例以改善水文水动力条件和水温为目标;另有约30%的案例以生源物质调节、河床形态改造优化为目标。可以看出,绝大多数研究(约95%以上)以大坝下游自然河段为区域,所涵盖的水文变量包括流量、频率、出现时间、持续时间和变化率等[12]。

但目前的适应性管理实践依然存在一些问题。一方面,传统实践中针对单一对象(如单一生物种群、或有限的生境要素)的实践效果并不优[50,54]。限于河流生态系统复杂性,近期的主流观点倾向于认为,实现食物网结构优化可能是河流生态系统修复较佳的方案[15,54,57]最近,Poff等[15]在Science上综述分析了通过电站调峰水流(hydropeaking)优化昼夜水位变幅改善岸栖生境并优化食物网结构的适应性实践,展望认为更精细的大坝选址设计与管理、能够在满足水电效益的同时逐渐恢复河流生态系统功能。但仍缺乏更充分的研究积累指导管理实践[54]。另一方面,河流生态系统对适应性管理的响应具有长期性和不确定性[59]。Olden等[50]认为,目前的实践更倾向于强调完成短期生态目标以满足决策者和利益攸关方的需求,缺乏持续跟踪观测与系统的后效应评估及反馈[50]。

不仅如此,当前多针对单个水库或单一大坝的下游河段径流调节开展适应性管理实践。但在河流梯级开发情形下,因梯级水库水文形态已迥异于“原生”的自然河道,适应性管理的对象、目标、时空范围与作用途径等显然已不能简单地参照或套用当前以恢复水文自然情势来和修复河流生态系统为主线的实践模式(图3)。梯级水库适应性管理取决于对河流—水库系统生态结构功能、演替规律的科学认识,也受到防洪、供水、发电等多利益主体的制约和影响。梯级水库生态系统适应性管理的“基线”(或“基准状态”)是什么?这是梯级水库适应性管理中亟待破解的科学问题。Renofalt等[12]此前曾报道了梯级水库优化运行可实现局部减水河段库岸带与底栖生境恢复并促进食物链形成。然而,目前全球范围内针对梯级水库展开适应性管理的相关研究和实践仍相当匮乏。

4 长江上游梯级开发现状、矛盾与研究需求

长江上游通常指宜昌以上河段,流域面积约100万km2,宜昌站多年平均径流量约14 300 m3/s。长江上游水能资源蕴藏丰富,据不完全统计,其干流与主要支流上已分布有大大小小百余座大型水电站,装机容量超过11 000万kW(图4)。近年来,长江上游还将建一批大型电站,将会深刻改变长江上游生态格局。在长江上游处于“原生”状态自然河段逐渐消失的同时,水电开发也促进了流域社会经济发展。基础设施建设和城镇化加速推进,带动了水产养殖、农业开发、亲水旅游、航运交通、建筑施工、矿山开采等产业或行业发展,使当地人民的生产生活方式由原先“靠山而生”变成了“近水而富”,地方社会发展形态发生根本性改变(图5),衍生形成了多利益主体共同作用的经济—社会—生态多元复合体系,构成了非常复杂的径流调节(供水、防洪、航运、泥沙)、水力发电(水能利用)、环境保护(生态系统健康维持)的互馈关系(图6)。在多利益主体(流域机构、水电企业、地方政府、地方企业与库区移民)的外部驱动作用下,河流—水库系统将可能受到来自以下几个方面的潜在威胁(图6):

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图4   长江上游水电站分布(装机容量大于0.3万kW)

Fig.4   Distributions of hydropower plant in the upstream of Yangtze (Installed capacity > 3MW)

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图5   溪洛渡—向家坝梯级水库近岸的人为活动(拍摄:李哲;时间:2016年) (a)脐橙种植;(a,b)水产养殖;(c)亲水旅游;(d)港航设施

Fig.5   Anthropogenic activities along the Xiluodu and Xiangjiaba cascade reservoirs (photo taken by Li Zhe, 2016) (a) Naval fruits; (a,b) Fish farming; (c) Tourism; (d) Facilities of ports

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图6   长江上游河流—水库系统“径流调节—水力发电—环境保护”互馈关系

Fig.6   The nexus of “river runoff regulation-hydropower production-environmental protection” in the upstream of the Yangtze

(1)梯级开发改变流域水资源总量与时空分布:河流梯级开发将改变局地水—气循环,对径流调节与水资源配置将使局部水资源量与时空分布等发生显著改变。加之气候变化导致长江上游径流产汇不确定性激增,与河流梯级开发对径流调节相叠加,可能加剧下游流域水资源时空变化程度[1]。

(2)水力发电用水与河流—水库生态需水存在矛盾:发电所需要的高水头将导致部分流水河段栖息生境严重破坏、流水生态系统退化。水力发电产生非自然节律的径流脉冲,对河流—水库生态系统产生的强力扰动不可避免,河流—水库生态需水难获满足。

(3)流域开发、人口增长威胁水环境与生态:流域开发、人口增长将诱发污染负荷增加,并加剧流域水土流失。而筑坝蓄水导致水体滞留时间延长、自净能力下降加剧水体环境污染风险。

维持长江上游河流—水库系统生态健康,是切实贯彻执行长江大保护战略、构筑长江上游安全屏障的重要组成部分。但是,长江上游河流—水库系统应维持何种状态可视为“健康”?如何开展河流—水库系统适应性管理以实现流域生态良治?这些是当前长江上游适应性研究与实践中并未系统回答的关键问题。掌握长江上游河流—水库系统生态演替规律是解答上述科学问题、实践流域适应性管理的基础和关键。

长江上游梯级开发已深刻影响其河流生境。我们认为,河流—水库系统的适应性管理,已从简单恢复坝下自然河流水文情势与生物群落为途径,转变至以优化河流—水库生态结构、功能以维持河流—水库生态系统健康为目标[15,60]。结合当前研究进展,未来可能有以下几个方面值得思考:

(1)掌握河流—水库系统发育演替的水文生态机制,厘清并阐明河流—水库系统健康的“基准状态”。生态系统健康,可理解为在人类活动干扰下生态系统本身结构和功能的完整性[61]。健康的生态系统,应该是活跃的、可维持组织结构、具有在压力下能自我恢复的弹性。如何掌握并阐明河流—水库系统发育演替的水文生态机制?如何明晰变化水文环境下外界胁迫对河流—水库系统结构、功能产生的影响,是准确界定河流—水库系统健康“基线状态”的关键基础。厘清并阐明河流—水库系统健康的“基准状态”,是进一步开展保护或修复的重要前提。

(2)揭示“累积效应”作用对象与形式,甄别河流—水库系统适应性对象,合理制定保护或修复措施。有效甄别河流—水库系统适应性管理对象,合理制定保护或修复措施是水电开发生态环境保护的重要工作。在河流梯级开发背景下,揭示“累积效应”的作用途对象与形式,阐明“累积效应”作用于哪些生态要素或生物群落,是甄别适应性对象、制定保护或修复措施的基础,更是破解河流梯级开发生态环境保护难题的重要切入点。

(3)优化提升生态系统服务,权衡多利益主体诉求,构建绿色水电运营管理新体系。河流梯级开发不仅改变了流域水文情势和生态格局,也改变流域人类社会生产生活形态。如何优化长江上游水电运行管理,实现流域生态环境良治,是长江大保护在上游区段亟待解决的关键问题之一。权衡“径流调节—水力发电—环境保护”互馈的多利益主体诉求,构建绿色水电运行管理新体系,是实现流域生态环境长期良治的基础。而优化提升河流—水库生态系统服务,是权衡多利益主体诉求的重要标尺,是构建绿色水电运行管理新体系的理论基础。

5 结论与展望

在气候变化的大背景下,河流梯级开发是实现水资源高效利用、推动低碳清洁能源生产、促进地方社会经济可持续发展的重要途径,是保障国家水安全的重要措施。当前,河流梯级开发已成为我国大河流域(特别是西南诸河)生态格局的新常态。水环境与水生态安全是国家水安全重要的组成部分。如何科学认识河流—水库系统生态结构、功能特征,如何准确评判河流—水库系统健康状态,如何有效开展河流梯级开发的适应性管理实践以实现流域生态良治。这些都是河流梯级开发生态环境保护亟待回答的问题。厘清并掌握河流—水库系统发育演替的水文生态机制、阐明河流梯级开发“累积效应”作用对象与形式,明晰河流—水库系统健康的“基准状态”将可能是破解上述问题的关键。

The authors have declared that no competing interests exist.

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[J]. Northwest Hydropower, 2009,(6):11-14.

[本文引用: 1]     

[寇晓梅, 牛天祥, 黄玉胜, 等.

黄河上游已建梯级电站的水环境累积效应

[J]. 西北水电, 2009,(6):11-14.]

DOI      URL      [本文引用: 1]      摘要

通过对黄河上游梯级开发程度较高的龙羊峡~刘家峡河段水文、水温、水质等环境要素的累积效应 分析,认识水电梯级开发布局、水库规模、水库调节方式对水文情势、水温及水质的累积作用、影响程度和演变规律,以期为黄河流域待开发河段及其它流域水电开 发在水环境影响分析方面提供一些参考。
[38] Chen Junxian,Jiang Renfei,Chen Yan.

Evaluation on the health of river ecosystem under the cascade development of reservoirs

[J]. Shuili Xuebao, 2015,46(3):334-340.

[本文引用: 1]     

[陈俊贤, 蒋任飞, 陈艳.

水库梯级开发的河流生态系统健康评价研究

[J]. 水利学报, 2015,46(3):334-340.]

DOI      URL      [本文引用: 1]      摘要

借助生态学及生态系统健康评价理论，分析了河流生态系统健康影响因子，并构建了河流生态系统健康评价指标体系。通过辨析河流生态系统对水库梯级开发响应内涵，甄别了典型区浮游生物、底栖生物、鱼类对梯级开发的响应过程。之后选取典型河流和代表物种，借助关键物种的生活繁殖习性，通过数据分析并考虑地域性原则，确立出生态健康等级标准，并评价了典型区水库梯级开发的生态系统健康程度以及生态水文过程调控实施效果。结果表明，在水库梯级开发下，径流年内分配趋于均匀化，河流下游悬移质泥沙量减小；喜好浅水、急流的生物栖息地空间减小，该类鱼类资源呈下降趋势，鱼类物种多样性下降；部分河段水质超标。评估河段健康综合状况得分43.7分，健康状况“一般”。
[39] Ji Daobin,Long Lianghong,Xu Hui,et al.

Advances in study on cumulative effects of construction of cascaded reservoirs on water environment

[J]. Advances in Science and Technology of Water Resources, 2017,37(3):7-14.

[本文引用: 1]     

[纪道斌, 龙良红, 徐慧, 等.

梯级水库建设对水环境的累积影响研究进展

[J]. 水利水电科技进展, 2017,37(3):7-14.]

DOI      URL      [本文引用: 1]      摘要

为全面了解梯级水库建设的水环境累积影响,从水环境累积影响的定义、分类和特征三方面对其进行了总结,介绍了目前水环境累积影响研究的常用方法,着重归纳了梯级开发对径流、水质、水温和泥沙等水环境累积影响的研究成果,指出了各方面的影响范围和主要特征,探讨了梯级水库水环境累积影响研究的新趋势。我国梯级水库水环境累积影响研究处于发展阶段,目前的研究多集中于定性评价,急需建立统一的评价标准和评价方法,系统地认识梯级水库建设的环境效应。
[40] Wang Chao.

Research conception of ecological protection and restoration of high dams and large reservoirs construction and hydropower cascade development in Southwestern China

[J]. Advanced Engineering Sciences, 2017,49(1):19-26.

[本文引用: 1]     

[王超.

“西南水电高坝大库梯级开发的生态保护与恢复”研究构想

[J]. 工程科学与技术, 2017,49(1):19-26.]

[本文引用: 1]     

[41] Stanford J A, Ward J V.

Revisiting the serial discontinuity concept

[J]. Regulated Rivers-Research & Management, 2001,17:303-310.

DOI      URL      [本文引用: 3]      摘要

Abstract We revisit the serial discontinuity concept (SDC), which predicts river ecosystem responses to stream regulation in the context of recovery with distance downstream from the dam (discontinuity distance). Many studies have described pervasive interruptions of natural biophysical gradients of dams by comparing conditions in tailwaters to reference or pre-impoundment conditions. But only a few studies provide data or interpretations that explicitly test the SDC within entire stream corridors or along specifically defined reaches where recovery was expected in view of the predictions of the SDC. We present discontinuity distance measures for nine rivers around the world where the predictions of the SDC were substantiated. In two cases, recovery trajectories were overwhelmed by other human sources of disturbance. In one case, the SDC did not hold up, but only biotic measures were made. We conclude that, in general, the SDC is a sound construct that in most cases can be used to predict, or at least clearly articulate, the consequences of new regulation. The next step is to develop better empirical models of the SDC and to validate them experimentally through re-regulation of entire river corridors. Copyright 2001 John Wiley & Sons, Ltd.
[42] Li J, Dong S, Peng M, et al.

Effects of damming on the biological integrity of fish assemblages in the middle Lancang-Mekong River basin

[J]. Ecological Indicators, 2013,34:94-102.

DOI      URL      [本文引用: 1]     

[43] Zhai H, Cui B, Hu B, et al.

Prediction of river ecological integrity after cascade hydropower dam construction on the mainstream of rivers in Longitudinal Range-Gorge Region (LRGR), China

[J]. Ecological Engineering, 2010,36:361-372.

DOI      URL      [本文引用: 1]     

[44] Serafim-Junior M, Lansac-Toha F A, Lopes R M, et al.

Continuity effects on rotifers and microcrustaceans caused by the construction of a downstream reservoir in a cascade series (Iguacu River, Brazil)

[J]. Brazilian Journal of Biology, 2016,76:279-291.

DOI      URL      [本文引用: 2]     

[45] Lacerda dos Santos N C, de Santana H S, Dias R M, et al.

Distribution of benthic macroinvertebrates in a tropical reservoir cascade

[J]. Hydrobiologia, 2016,765:265-275.

DOI      URL      [本文引用: 1]      摘要

The functioning of systems arranged in cascades of reservoirs can be explained by the Cascading Reservoir Continuum Concept, providing a theoretical framework for addressing ecological processes. In this context, this study tested the following hypotheses: (i) the benthic macroinvertebrate assemblage shows a nested distribution along a reservoir cascade; and (ii) local factors explain the structure of the benthic assemblage in every reservoir along the cascade. Macroinvertebrates play essential role in aquatic systems, especially due to recycling and, in reservoirs, as important links in every food chain. Sampling was conducted quarterly between October 2006 and September 2010 in six reservoirs located in the S茫o Francisco River, Brazil. The benthic macroinvertebrate assemblage showed nested distribution in the reservoirs, indicating that a loss of species occurs along the cascade. Each reservoir presented a different set of variables that explained the distribution of macroinvertebrates, showing the importance of local factors determining the composition and distribution of benthic assemblages in the reservoirs. Therefore, there is a clear interaction between the position of a reservoir along a cascade and the macroinvertebrate assemblages, which indicate the importance of considering this pattern during the decision-making process of constructing new dams on rivers already regulated.
[46] Wang Guangqian,Fang Hongwei,Ni Guangheng, et al.

River networks and runoff characteristics in Tibetan Plateau: Advancements and future strategie

[J]. Bulletin of National Natural Science Foundation of China, 2016,(1):27-33.DOI:10.16262/j.cnki.1000-8217.2016.01.007.

[本文引用: 2]     

[王光谦, 方红卫, 倪广恒, 等.

大江大河源区河网结构与径流特性研究前沿和重要基础科学问题

[J]. 中国科学基金, 2016,(1):27-33.DOI:10.16262/j.cnki.1000-8217.2016.01.007.]

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[47] Vannote R L, Minshall G W, Cummins K W, et al.

The river continuum concept

[J]. Canadian Journal of Fisheries & Aquatic Sciences, 1980,37:130-137.

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[48] Miranda L E, Dembkowski D J.

Evidence for serial discontinuity in the fish community of a heavily impounded river

[J]. River Research and Applications, 2016,32:1 187-1 195.

DOI      URL      [本文引用: 1]      摘要

In the Tennessee River, USA, we examined lengthwise patterns in fish community structure and species richness within and among nine reservoirs organized in sequence and connected through navigational locks. Within reservoirs, the riverine, transition and lacustrine zones supported distinct, although overlapping, nearshore fish assemblages; differences were also reflected in measures of species richness. Spatial patterns were most apparent for rheophilic species, which increased in species richness and representation upstream within each reservoir and downstream across the chain of reservoirs. This pattern resembled a sawtooth wave, with the amplitude of the wave peaking in the riverine zone below each dam, and progressively higher wave amplitude developing downstream in the reservoir chain. The observed sawtooth pattern supports the serial discontinuity concept in that the continuity of the riverine fish community is interrupted by the lacustrine conditions created behind each dam. Upstream within each reservoir, and downstream in the chain of reservoirs, habitat characteristics become more riverine. To promote sustainability of rheophilic fishes and maintain biodiversity in impounded rivers, conservation plans could emphasize maintenance and preservation of riverine environments of the reservoir's upper reaches, while remaining cognizant of the broader basin trends that provide opportunities for a lengthwise array of conservation and management policy. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.
[49] Ellis L E, Jones N E.

A test of the serial discontinuity concept: Longitudinal trends of benthic invertebrates in regulated and natural rivers of Northern Canada

[J]. River Research and Applications, 2016,32:462-472.

DOI      URL      [本文引用: 2]     

[50] Olden J D, Konrad C P, Melis T S, et al.

Are large-scale flow experiments informing the science and management of freshwater ecosystems?

[J]. Frontiers in Ecology and the Environment, 2014,12:176-185.

DOI      URL      [本文引用: 7]     

[51] Poff N L, Zimmerman J K.

Ecological responses to altered flow regimes: A literature review to inform the science and management of environmental flows

[J]. Freshwater Biology, 2010,55:194-205.

DOI      URL      [本文引用: 1]     

[52] Petesse M L, Petrere M.

Tendency towards homogenization in fish assemblages in the cascade reservoir system of the Tietêriver Basin, Brazil

[J]. Ecological Engineering, 2012,48:109-116.

DOI      URL      [本文引用: 1]     

[53] Holling C S.

Adaptive Environmental Assessment and Management

[M]. New York: John Wiley & Sons, 1978.

[本文引用: 1]     

[54] Naiman R J, Alldredge J R, Beauchamp D A, et al.

Developing a broader scientific foundation for river restoration: Columbia River food webs

[J]. Proceedings of the National Academy of Sciences of the United States of America, 2012,109:21 201-21 207.

DOI      URL      [本文引用: 4]      摘要

Well-functioning food webs are fundamental for sustaining rivers as ecosystems and maintaining associated aquatic and terrestrial communities. The current emphasis on restoring habitat structure--without explicitly considering food webs--has been less successful than hoped in terms of enhancing the status of targeted species and often overlooks important constraints on ecologically effective restoration. We identify three priority food web-related issues that potentially impede successful river restoration: uncertainty about habitat carrying capacity, proliferation of chemicals and contaminants, and emergence of hybrid food webs containing a mixture of native and invasive species. Additionally, there is the need to place these food web considerations in a broad temporal and spatial framework by understanding the consequences of altered nutrient, organic matter (energy), water, and thermal sources and flows, reconnecting critical habitats and their food webs, and restoring for changing environments. As an illustration, we discuss how the Columbia River Basin, site of one of the largest aquatic/riparian restoration programs in the United States, would benefit from implementing a food web perspective. A food web perspective for the Columbia River would complement ongoing approaches and enhance the ability to meet the vision and legal obligations of the US Endangered Species Act, the Northwest Power Act (Fish and Wildlife Program), and federal treaties with Northwest Indian Tribes while meeting fundamental needs for improved river management.
[55] Melis T S, Walters C J, Korman J.

Surprise and opportunity for learning in grand canyon: The Glen Canyon dam adaptive management program

[J]. Ecology and Society, 2015,20(3).DOI:10.5751/ES-07621-200322.

[本文引用: 1]     

[56] Naiman R J, Magnuson J J, McKnight D M, et al.

Fresh-water ecosystems and their management—A national initiative

[J]. Science, 1995,270:584-585.

DOI      URL      [本文引用: 1]      摘要

Recently, the laws and regulations that govern water quality and endangered aquatic ecosystems have begun being evaluated in light of increased demands on use of fresh water. Naiman et al. point out that much of the research aimed at evaluating this important resource is in need of improvement and coordination.
[57] Kennedy T A, Muehlbauer J D, Yackulic C B, et al.

Flow management for hydropower extirpates aquatic insects, undermining river food webs

[J]. American Institute of Biological Sciences, 2016,66:561-575.

DOI      URL      [本文引用: 3]      摘要

Dams impound the majority of rivers and provide important societal benefits, especially daily water releases that enable on-peak hydroelectricity generation. Such “hydropeaking” is common worldwide, but its downstream impacts remain unclear. We evaluated the response of aquatic insects, a cornerstone of river food webs, to hydropeaking using a life history–hydrodynamic model. Our model predicts that aquatic-insect abundance will depend on a basic life-history trait—adult egg-laying behavior—such that open-water layers will be unaffected by hydropeaking, whereas ecologically important and widespread river-edge layers, such as mayflies, will be extirpated. These predictions are supported by a more-than-2500-sample, citizen-science data set of aquatic insects from the Colorado River in the Grand Canyon and by a survey of insect diversity and hydropeaking intensity across dammed rivers of the Western United States. Our study reveals a hydropeaking-related life history bottleneck that precludes viable populations of many aquatic insects from inhabiting regulated rivers.
[58] Warner A T, Bach L B, Hickey J T.

Restoring environmental flows through adaptive reservoir management: Planning, science, and implementation through the Sustainable Rivers Project

[J]. Hydrological Sciences Journal—Journal Des Sciences Hydrologiques, 2014,59:770-785.

[本文引用: 1]     

[59] Keith D A, Martin T G, McDonald-Madden E, et al.

Uncertainty and adaptive management for biodiversity conservation

[J]. Biological Conservation, 2011,144:1 175-1 178.

DOI      URL      [本文引用: 1]      摘要

Adaptive management of natural resources is widely supported, but in biodiversity conservation there have been few practical applications of the approach in its entirety. Some of the contributions to this special publication examine progress in the implementation of adaptive approaches into conservation policy, while others explore novel theoretical and modeling approaches that seek to accommodate the complexities of real-world applications. Several of the papers address the treatment of uncertainty in adaptive management through innovative approaches to experimentation and monitoring, use and characterisation of expert knowledge and reconciliation of differences of opinion about parameters or systems. Drawing on these contributions, we discuss the major impediments to implementing adaptive management, why adaptive management has been slow to be implemented and how this can be redressed.
[60] Poff N L, Brown C M, Grantham T E, et al.

Sustainable water management under future uncertainty with eco-engineering decision scaling

[J]. Nature Climate Change, 2016,6:25-34.

DOI      URL      [本文引用: 1]     

[61] Liu Yanxu,Peng Jian,Wang An,et al.

New research progress and trends in ecosystem health

[J]. Acta Ecologica Sinica, 2015, 35(18): 5 920-5 930.

[本文引用: 1]     

[刘焱序, 彭建, 汪安, 等.

生态系统健康研究进展

[J]. 生态学报, 2015, 35(18): 5 920-5 930.]

DOI      URL      [本文引用: 1]      摘要

健康的生态系统一般被视为环境管理的终极目标,进行生态系统健康研究对探索区域与生态系统可持续发展具有重要意义。随着国际生态与健康学会(International Association for Ecology and Health)的解体,生态系统健康研究视角出现转型。系统梳理了近年来国际上有关生态系统健康概念及其评估方法、指标的新进展,通过文献统计和重要文献引用揭示了国际生态系统健康研究的发展历程,提出了从生态系统健康到生态健康再到生态文化健康的三大核心框架发展阶段,生态系统健康的研究对象和范围正在不断扩充。资源环境研究领域是国内研究者应用生态系统健康概念与方法的优势领域,在区域尺度上评价生态系统的健康更贴近资源环境和社会文化交互作用的复合表征理念。因此,我国生态系统健康研究的趋向不仅应包括在生态系统尺度上研究的继续深化,也应包含对生态文化健康概念的完善与应用,并发挥地理-生态视角的区域集成研究优势,从而有效指导区域生态与环境政策制定与实施。
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