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关闭窗口 【摘要】 本文从河流的连续性特征出发分析了大坝对于河流生态系统的胁迫问题。指出要在自然－社会－经济复合生态系统中全面权衡筑坝的利弊得失。采用生态工程的方法对于筑坝河流进行生态补偿是可行的。开展河流生态系统功能价值评估，建立生态补偿的合理机制。
【关键词】 大坝 河流 生态补偿生态工程学 生态水利工程学 补偿机制
Ecological Compensation for Rivers in which Dams Build
DONG Zheren
(China Institute of Water Resources and Hydropower Research)
Abstract
Abstract: The paper presents the stresses on rivers in which dams build base on the river continuum concept. It is pointed out that analysis of advantages and disadvantages of dams construction should be in the nature-society-economy compound ecosystem. It is possible that ecological compensation applying ecological engineering for rivers in which dams build. It is very important to evaluate value of the river’s ecosystem services and natural capital, which the cost of ecological compensation should be confirmed according as.
Key words: dam; river; ecological compensation; Ecological engineering; Eco-Hydraulic Engineering; compensation mechanism
近来，国内有专家对于我国西南河流的水电开发计划提出了质疑，主张“保留一条生态河流”。还有专家认为西方国家都在拆除大坝，我国为什么还要建设大坝？看来，20世纪70年代在西方国家出现的大坝建设的利弊之争，经过30年后终于波及到中国。
据统计，截至2003年，全世界坝高超过
本文讨论的问题是：大坝对于河流生态系统是否存在负面影响？如何权衡人类社会发展经济与维护自然生态系统健康之间的利弊得失？对于筑坝的河流进行补偿是否可行？如何形成补偿机制？
1.大坝对于河流生态系统的胁迫
大坝工程对于满足人类社会的防洪、发电、灌溉、供水、航运等需求的作用巨大，为社会安全和经济发展提供了保障。大坝对于生态系统的作用是双重的，一方面水库为生物生长提供了丰富的水源，也缓解大洪水对于生态系统的冲击等，这些因素对河流生态系统是有利的。另一方面，大坝对于河流生态系统产生干扰。自然界或人类对于生态系统的干扰,在生态学中称为“胁迫”（stress）。水利水电工程对于河流生态系统的胁迫主要表现在两方面：一是自然河流的渠道化。二是自然河流的非连续化[3]。大坝工程属于第二类问题，即顺水流方向的非连续化问题。这里提出河流的“连续性概念”( continuum concept)，用以说明河流生态系统是一种开放的、流动的生态系统，其连续性不仅指一条河流的水文学意义上的连续性，同时也是对于生物群落至关重要的营养物质输移的连续性[4]。营养物质以河流为载体，随着自然水文周期的丰枯变化以及洪水漫溢，进行交换、扩散、转化、积累和释放。沿河的水生与陆生生物随之生存繁衍，相应形成了上中下游多样而有序的生物群落，包括连续的水陆交错带的植被，自河口至上游洄游的鱼类以及沿河连续分布的水禽和两栖动物等，这些生物群落与生境共同组成了具有较为完善结构与功能的河流生态系统。研究成果还表明，洪水周期变化对于聚集在河流周围的生物是一种特殊的信号，这些生物依据这种信号进行繁殖、产卵和迁徙，也就是说河流还肩负着传递生命信息的任务。概括地讲，河流是生态系统物质流、能量流和信息流的载体。河流的连续性，不仅包括水流的水文连续性，还包括营养物质输移的连续性、生物群落的连续性和信息流的连续性。大坝将河流拦腰斩断，形成了河流的非连续性特征，改变了连续性河流的规律。
从现象上看，大坝对于河流生态系统的影响包括两个方面：一是大坝与水库本身带来的负面影响，二是在大坝运行过程中对生态系统的胁迫。前者的影响主要是造成大坝上下游河流地貌学特征的变化。后者的影响主要是造成自然水文周期的人工化。
首先是河谷变成了水库，原有陆地及丘陵生境被破碎化、片断化，陆生动物被迫迁徙。流动的河流变成了相对静止的人工湖，流速、水深、水温及水流边界条件都发生了变化，水库中出现明显温度分层现象。由于水库泥沙淤积，也截留了河流的营养物质，促使藻类在水体表层大量繁殖，可能产生水华现象。在热带和亚热带地区的森林被水库淹没后，还会产生大量的二氧化碳、甲烷等温室气体。由于水库的水深高于河流，在深水处阳光微弱，光合作用也弱，与河流相比其生物生产量低。另外，不设鱼道的大坝对于洄游鱼类是致命的屏障。在大坝下游，因为水流携沙能力增强，加剧了水流对于河岸的冲刷，可能引起河势变化。由于水库泥沙淤积及营养物质被截流，大坝下游河流廊道的营养物质输移扩散规律也发生改变。这些因素都会使生物栖息地特征发生改变。另一方面，自然河流的水文周期年内有明显的洪－枯变化，河流生物同样随之呈现脉冲式的周期变化。而大坝运行期间，水库的调度服从于发电和防洪等需求，使年内径流调节趋于均一化，这些都会对河流廊道产生压力。另外，如果从水库中超量引水用于供水、灌溉等目的，使大坝下游水量锐减，引起河流干涸与断流，也会导致生态系统的退化。最后，兴建水库造成移民搬迁，淹没文物古迹或改变自然景观，这不仅涉及社会和文化问题，从宏观上看是造成一种社会－经济－自然复合生态系统的综合问题。
从机理分析看，河流、湖泊和水库都是生物地球化学循环过程中物质迁移转化和能量传递的“交换库”。而在湖泊与水库中往往滞留时间长，一些物质的输入量大于输出量，其滞留量超出生态系统自我调节能力，由此导致污染、富营养化等，这种现象称为“生态阻滞”。
总之，大坝对于河流生态系统的胁迫是客观存在的事实，不容回避。但是，在我国水利水电建设中，不仅需要正视这种负面影响，更重要的是主动研究对于河流生态系统的补偿的政策、技术和管理措施问题，探索与环境友好的大坝建设的新模式。
2. 在自然－社会－经济复合生态系统中选择优化策略
在国际资源与环境研究领域有两种对立的理论，一种称之为资源主义（Resourcism），主张最大限度持续地开发可再生资源。另一种称之为自然保护主义（Preservationism），其主要观点是对于自然界中的尚未开发区域，反对人类居住和进行经济开发。资源主义强调了满足人类经济发展的重要性，却忽视了维护健康生态系统对于人类利益的长远影响。而保护主义虽然高度重视维护生态系统健康问题，但是反对一切对自然资源的合理开发利用，其结果往往会脱离社会经济发展的实际而成为空洞的观点。可以说，这两种理论都带有相当的片面性。比较现实的思维方法是放大研究问题的尺度，把问题放到自然－社会－经济复合生态系统中去考察，分析如何在既满足人类社会经济需求又不损害或较少损害生态系统健康中寻找平衡点，实现可持续发展的目标。讨论问题的方法也要结合各国的国情，不同的自然、社会与经济状况，需要采取不同的对策，不存在各国统一的准则。
如果简单地反对一切大坝建设，主张大范围地拆坝，肯定脱离了社会经济发展实际，是一种因噎废食的观点。相反，回避大坝给生态系统带来的胁迫问题，忽视对于生态系统的补偿，无疑会给人类长远利益带来损害。世界上不存在百利而无一害的工程技术，权衡利弊，趋利避害是辩证的思维方法。实践表明，大坝对于河流生态系统的负面影响，可以通过工程措施、生物措施和管理措施在一定程度上避免、减轻或补偿。寻找相对优化的技术路线是解决问题的合理思维方式。
我国筑坝的目的是防洪、发电、灌溉、供水及航运等，多数大坝工程具有综合效益。我国水资源的特点之一是时间年内分布不均匀，降雨集中在夏季，而冬季是枯水季节，我国大部分水库的建设目的就是调节水量丰枯，满足社会需求。
我国建设的高坝多数以水力发电为主要效益，而高坝对于河流生态系统的影响相对要大。发展水电会造成生态环境问题，那么有什么可以替代的能源形式对于生态环境影响相对要小呢？分析我国的能源结构，2002年我国一次能源产量为1.387×109t标准煤。其中煤炭产量1.38×109t，居世界第一位。发电装机容量3.57×105MW，发电量1.654×109 MW.h，居世界第2位，其中水电发电量2.28×108 MW.h，居世界第四位。我国已成为世界第二大能源消费国。
我国在能源发展上面临着环境污染的严重挑战。其中尤以大气污染严重。我国二氧化硫排放量居世界第一位，二氧化碳排放量仅次于美国居世界第二位。造成大气质量严重污染的主要原因是我国以煤为主的能源结构，烟尘和二氧化碳排放量的70%、二氧化硫的90%、氮氧化物的67%来自于燃煤。有专家对于2020年我国对于能源的需要预测指出：2020年我国一次能源的需求在25-33×108t标准煤之间，至少是2000年的两倍。据专家预测，到2020年，即使按照污染物产生量最少的情景，如不采取脱硫脱氮措施，二氧化硫、氮氧化物预计分别达到4×107t和3.5×107t。到2030年前后,在全球气候变化问题上我国会面临更大的国际压力。
至于选择其它能源技术的可能性，发展核电会遇到安全性、经济性和核废料处理问题。发展风力发电和太阳能光电的困难是单位千瓦造价高难于形成规模。至于利用氢能技术，目前还处于探索阶段。从我国的能源资源结构看，水能资源居世界第1位，煤居第3位，石油第12位，天然气第22位。我国水电开发的程度相对发达国家较低，目前为23％。发达国家的水电开发程度已经很高，平均在60％以上。其中美国为82％，加拿大为65%，德国为73％。我国具有如此丰富的水电资源，开发水电资源自然成为能源战略的必然选择。我国水能的技术可开发量约4×105MW，如果开发其50％，相当于减少年烧煤约6×108t，接近于2002年我国实际燃煤总量的1/2。这对于大幅度减少温室气体排放意义重大，这不仅仅是对中国，也将是对全球环境保护的重大贡献。
可见，观察和研究筑坝环境影响问题，既要研究自然问题，还要考察相关的社会经济问题；既要研究一条河流、一个流域的问题，更要宏观地研究全球尺度的生态环境保护问题。也就是在全球自然－社会－经济复合生态系统中考量我国水电发展和筑坝问题。在各种比选的技术路线中，“两利相权取其重，两害相权取其轻”，寻找相对优化的方案。水力发电不污染大气，不产生废料，只要太阳不熄，水能资源不断。毫无疑问，水电是一种可再生的清洁能源。可是，近年来由于国际反对建坝的声浪高涨，在国内外一些有关能源政策报告中，水电在清洁能源的名单中消失了，这明显是片面的也是不科学的。
3. 对筑坝河流进行生态补偿的可行性
不建设大坝或者拆除大坝，并非是保护河流生态健康的唯一选择。理论与实践表明，通过工程措施、生物措施和管理措施，对于筑坝河流进行生态补偿，可以在一定程度上避免或减轻大坝对于河流生态系统的胁迫，建设与生态友好的大坝工程是完全可能的。
3.1大坝工程项目的环境评估
我国高度重视环境影响评价工作，2003年9月开始实施《中华人民共和国环境影响评价法》（以下简称《环评法》）。《环评法》指出：“环境影响评价必须客观、公开、公正、综合考虑规划或者建设项目实施后对各种环境因素及其所构成的生态系统可能造成的影响，为决策提供科学依据。”《环评法》的颁布实施对于建设与生态环境友好的大坝工程具有重要促进作用。目前我国对于大坝工程的环境评价工作尚有若干问题需要完善和改进。
按照《环评法》规定，环境评价分为两类，一类是区域、流域、海域的建设、开发规划以及包括水利、能源等有关专项规划的环境评价。另一类是建设项目的环境评价。对于大坝工程来说，无论是在河流建设的单座大坝还是梯级开发，建成后对于生态系统的影响范围是全流域的。所以，要按照《环评法》的要求，应重视流域规划中河流建坝后环境影响的分析预测和评估，对于全流域各种生境因子和生物因子间的相互关系进行综合、整体研究。
环境评价的时间尺度也很重要。大坝引起河流生态系统的演进是一个动态过程。一些工程案例表明，经过十几到几十年的时间，大坝对于河流生态系统的影响才逐步显现出来。因此，进行长期的生物、水文监测，掌握长时间尺度的河流生态演变信息，并在此基础上进行动态评估是十分必要的。
大坝环境评价的重点应是筑坝对于河流生态系统的健康和可持续性的影响，内容是对于河流生态系统的结构和功能影响的分析、预测和评估。大坝项目的环境评价应更多关注生物群落多样性的变化。
目前大坝环境影响评价往往是从个别学科或局部功能的需要出发，孤立地研究水库淹没区的濒危或特殊动植物的保护问题，或者孤立地研究对于水质的影响问题等，缺乏对于生态系统各个组分之间的相互作用，相互联系，相互依存，相互转化的系统评估分析。
《环评法》规定：“国家鼓励有关单位，专家和公众以适当的方式参与环境影响评价。”大坝的环境影响评价是一种涉及多专业、多学科和多部门复杂问题，应该提倡多学科的合作，开展相关的科学研究，摸索规律，提高评估工作的科学性。另外，通过论证会、听证会等多种形式广泛吸收社会公众的积极参与，这将有助于推动重大工程项目决策的科学化民主化进程。
3.2探索与发展生态水利工程学
从20世纪70年代开始，面对世界范围内的生态环境恶化问题，各国学者探索系统解决问题的途径，在现代生态学发展的带动下，为促进生态学与工程学相结合，一门新兴的交叉学科－生态工程学（Ecological engineering）应运而生。1993年美国科学院所主办的生态工程研讨会对“生态工程学”定义为：“将人类社会与其自然环境相结合，以达到双方受益的可持续生态系统的设计方法。”生态工程学的范围很广，包括河流、湖泊、湿地、矿山、森林、土地及海岸等的生态建设问题。
河流生态恢复是生态工程学的一个分支。美国土木工程师协会对于“河流恢复”有以下定义：“河流恢复是这样一种环境保护行动，其目的是促使河流系统恢复到较为自然的状态，在这种状态下，河流系统具有可持续特征，并可提高生态系统价值和生物多样性。”[6][7] 在“河流恢复”的总概念下，各国学者提出了以下不同的恢复目标[8]： “完全复原” (Full restoration)， “修复”（Rehabilitation）， “增强”（Enhancement），“创造”，（Creation）， 和“自然化”（Naturalization）。
其中主张“完全复原”的学者，坚持一种极端的观点。他们把河流生态恢复的目标确定为恢复到人类活动以前的原貌，这包括反对建设大坝，主张一律拆除大坝等[5]。许多学者对此持不同意见，他们认为由于河流的自然演变及人类活动影响，已经形成了新的河流生态系统，使其逆转到原始状态是不可能的。实际上，出于现实的原因，西方国家拆除的水坝数量是很小的，比如美国在上世纪90年代共拆除了180座小型水坝，而且其中多数是应该退役的水坝。
现实的方法是承认人类合理利用自然资源的必要性，在当前河流生态系统现状的基础上，采取多种措施促进河流生态系统向健康方向发展。上述河流恢复目标中，修复、增强和自然化大体属于这一类。
在河流治理方面，西方国家实施生态工程的重点是受人类活动干扰的河流生态恢复。我国情况与此不同，可以预计在未来10年左右将是我国水利水电建设的高峰期。因此我国一方面要重视已经筑坝的河流生态恢复问题。另一方面，更要重视新建大坝工程的生态补偿问题，避免重蹈发达国家在建坝方面的覆辙。在进行水电工程方案比选时，应优先选用对河流生态系统负面影响较小的工程方案，比如高坝大库方案与低坝引水式水电站方案比较，尽管前者经济效益明显，但是如果兼顾生态影响，全面权衡利弊就有可能选择后者，因为低坝方案对于河流生态系统的压力相对要小。进而言之，传统的水利工程是以建设工程设施、改造河流和控制水流为手段，达到开发利用水资源的目的。学科的基础是水文学和工程力学等。传统的水利工程忽略了河流处于一个完整的生态系统之中这一基本事实，孤立地处理水资源中的水量、水质、水能等水文系统中的问题，忽略了河流生态系统中的动物、植物、微生物组成的生命系统。其结果是在给人类带来巨大经济社会利益的同时造成对于河流生态系统的不同程度的胁迫。因此需要改进和完善水利水电工程的规划设计方法，吸收生态学的理论与技术，探索和发展生态水利工程学（Eco-Hydraulic Engineering）。所谓“生态水利工程学”作为水利工程学的一个新的分支，是研究水利工程在满足人类社会需求的同时，兼顾水域生态系统健康与可持续性需求的原理与技术方法的工程学[9]。
河流生态修复的任务有三类，一是水文条件的改善，二是河流地貌学特征的改善，三是濒危或特殊物种恢复。总的目的是改善河流生态系统的结构与功能，标志是生物群落多样性的提高。[10]
水文条件的改善指水量、水质的改善；自然水文周期的模拟等。包括：通过水资源的合理配置维持最小生态需水量；通过污水处理，控制污水排放以及提倡清洁生产改善河流水质；水库的调度除了满足社会经济需求外，尽可能接近自然河流的脉冲式的水文周期等。河流地貌学特征的改善包括：尽可能恢复河流的纵向连续性和横向联通性，保持河流纵向和横向形态的多样性，防止河床材料的硬质化。加强河流生物栖息地建设，注重水库库区的生态重建。
4. 河流生态服务效益价值评估与生态补偿机制
河流生态系统提供的服务功能维持着人类赖以生存的条件，同时还为人类社会提供了各种福利。这包括：维持生物多样性；提供食品、药品和材料；淡水的净化；水分的涵养与旱涝的缓解；局部气候的稳定；废弃物的解毒和分解；种子的传播和养分的循环；人类审美需求的满足等。这些服务功能一部分是实物型的生态产品，比如食品、药品和材料，其经济价值可以在市场流通中得到体现。另一部分是非实物型的生态服务，包括生物群落多样性、环境、气候、水质、人文等功能。这些功能往往是间接的、却又对人类社会经济产生深远、重要的影响。
长期以来，人们认为河流生态系统的服务功能是大自然的无偿恩赐，是可以免费得到的。人类自认为是地球的宠儿，更是受之无愧。特别是在商品社会中，有形的生态产品还能为人们所计及，而大量的非实物型的生态服务价值往往被忽视。当大规模的治河工程给人们带来巨大的、直接的经济利益时，却发现河流丧失了若干服务功能，这对于人类社会经济的影响可能是间接的，但其后果严重。这部分功能的价值如何计算评估，成为当前可持续发展领域的热点课题[11][12]。国际社会认识到需要深入研究生态系统服务功能的效益，量化其经济价值，同时将其纳入国民经济核算体系，才能显示生态系统为人类提供的巨大贡献。1992年联合国环发大会（UNCED）通过的《21世纪议程》明确提出，要开展生态价值和自然资本的评估研究。1994年我国颁布的《中国21世纪议程》提出：“将可持续能力纳入经济决策，首先要比较明确地衡量环境作为自然资本的来源以及作为人类活动所产生的副产物的承载体的重大作用。传统的国民经济衡量指标－国内生产总值（GDP）或国民生产总值（GNP）既不反映经济增长所导致的生态破坏，环境恶化和资源代价，也未计及非商品劳务的贡献，……需要建立一个综合的资源环境与经济核算体系来监控整个国民经济的运行。”
如果对于河流生态服务功能的价值开展评估并进行量化，以法律的形式纳入国民经济核算体系，其作用巨大。首先，在大型水利水电工程立项决策时，可以全面权衡工程的直接社会经济效益与生态系统服务功能损失之间的利弊得失，以避免为获得直接经济效益的短期行为。其次，也可以促使工程项目业主采取更多的生态补偿措施，缓解对于河流生态系统的胁迫，减少服务功能损失的总价值。最后，这种评估也可以定量地提出工程项目业主应该提供的生态补偿资金数额。
在环境保护管理领域，“誰污染，誰付费”的原则，已经得到了国际社会的普遍赞同。参照这个原则，在大坝建设政策方面，建议明确“誰损害，誰补偿”的原则，明确大坝工程业主是负责生态补偿的主体。补偿的标准不仅仅局限在保护濒危、珍稀动植物或者库区植被恢复等资金需要，似应以河流生态系统服务功能损失总价值作为补偿标准的依据。补偿的范围不应仅仅局限于水库和大坝下游局部，应该是针对全流域的。补偿的时间应与大坝寿命一致，也就是说，大坝边运行边补偿。补偿的方式除采取生态工程措施外，还应制定法规，明确规定水库调度方式要有利于河流生物生长繁衍，由此造成的发电量减少的经济损失，也确定为一种补偿方式。
长期以来，在强势的人类活动面前，河流系统的生物群落承受了越来越大的压力。但是生物无言，无力申诉。在这种形势下，政府部门和流域管理部门就应该肩负起河流保护者的责任，成为河流生态系统的代言人。在河流开发利用与生态环境保护工作中建立起一种制约与协调机制。
参考文献
[1] 贾金生等，2003年中国及世界大坝情况[J]，中国水利，2004年第13期，P25－32
[2] 潘家铮，千秋功罪话水坝[M]，清华大学出版社，2000年,P10-48
[3] 董哲仁，河流形态多样性与生物群落多样性[J], 水利学报，2003年第11期,P1-7
[4] Vannote, R. L. et al, The river continuum concept[J], Can. J. Fish. Aqua. Sci., 37:130-137, 1980.
[5] Hart, D. D. and N. L. Poff, eds. 2002. Dam removal and river restoration: special section[J]. BioScience 52:653-747
[6]ASCE River Restoration Subcommittee on Urban Stream Restoration，Urban stream Restoration[J]，Journal of Hydraulic Engineering ASCE , July 2003, pp 491-493
[7]Brookes,A., Shields JR,F.D., River Channel Restoration[M], John Wiley & Sons, UK, 2001
[8]董哲仁，河流生态恢复的目标[J]，中国水利，2004年第10期,P
[9]董哲仁，生态水工学的理论框架[J]，水利学报，2003年第1期, P1-6
[10]董哲仁，试论生态水利工程的设计原则[J]，水利学报，2004年第10期,P1-5
[11]Costanza R, d’Arge R, Rudolf de Groot, et al. The value of the world’s ecosystem services and natural capital[J]. Nature,1997,387:P253-260
[12]徐中民，张志强，程国栋，生态经济学－理论方法与应用[M]，P110-117, 黄河出版社，2003年。
Ecological Compensations for Damed Rivers
Dong Zheren
（Chair of Global Water Partnership - China）
Abstract
The stresses of dams on river ecosystems are analyzed based on river continuity characteristics. It is pointed out that the pros and cons of dam construction should be comprehensively evaluated in the compound ecosystem of nature, society and economy. It is feasible to implement ecological compensations for damed rivers by adopting bioengineering methods. It is suggested to conduct value evaluation of river ecosystem services for decision-making of large hydraulic and hydroelectric projects.
Recently some domestic experts criticize the hydropower development plan on rivers of southwest
According to statistics of International Congress on Large Dams (ICOLD), there are 49697 dams all over the world by the end of 2003, which are higher than
This paper mainly discusses the following topics. Do dams have any negative effects on river ecosystems? How to evaluate the pros and cons of dam construction on social economic benefits and the health of natural ecosystem? Is it feasible for damed rivers to be compensated and what are the compensation standards？
1. The Stresses of Dams on River Ecosystems
Dam projects play important roles in satisfying the demands of human community for flood control, power generation, irrigation, water supply, navigation, etc. and guaranteeing community security and economic development. Dams have dual influences on ecosystem. In one aspect, reservoirs can provide abundant water for the growth of biology and mitigate the impacts of large floods on ecosystems. This is beneficial for river ecosystems. On the other hand, dams have disturbances on river ecosystems. Disturbances from nature and human society are defined as “stresses” in ecology. The stresses of hydraulic projects on river ecosystems are represented mainly in two aspects: one is the channelization of natural rivers and the other is their discontinuity[2]. The negative impacts of dam projects belong to the second problem, i.e. discontinuity in the direction of water flow. Here the “river continuum” concept is used to illustrate that river ecosystem is an open and flowing one. Its continuum means not only the continuity in the sense of river hydrology, but also the continuous characteristics of nutrient substance transportation, which is very important for biology community [3]. Taking a river as a carrier, nutrient substances interchange, diffuse, transform, accumulate and release along with the changes of floods and low flows in natural hydrological cycle. The aquatic and terrestrial organisms along a river survive and multiply and accordingly form a diversiform and orderly biotic community, which includes the continuous vegetation in terraqueous interlaced zones, fishes migrating from estuary to the upper reaches and waterfowl and amphibian continuously distributed along rivers, etc. Biotic community and habitats compose a river’s ecosystem with perfect structures and functions.
Studies have indicated that periodic changes of flood is a special signal for the biology around rivers to breed, spawn and migrate, which means that rivers are responsible for transferring life information. In a word, rivers are carriers of material flow, energy flow and information flow in ecosystems. River continuum consists of not only hydrological continuity of streams, but also the continuity of mass transportation, nutrition substances, biotic community as well as information flow.
Daming causes river discontinuity and as a result radically changes its natural evolution process that has a history of ten thousands or millions of years and its continuity pattern.
Impacts of dams on river ecosystem mainly consist of two respects, i.e. negative effects caused by dams or reservoirs themselves and stresses on ecosystems during reservoir operations. The former mainly causes the changes of river geomorphology features of the upstream and downstream of a dam. The latter mainly leads to man-designed cycle of natural hydrology.
Firstly a river valley is turned into a reservoir, original habitats of land and hills are fragmentized and terrestrial animals are forced to migrate. Original forests, meadows, croplands of reservoir area and garbage, chemical fertilizer are completely submerged under water. Flowing river is turned into a relatively motionless man-made lake. Water velocity, depth, temperature and current boundary conditions are all changed Reservoir has apparently temperature-zoned characteristics. Because of sedimentation and river nutriments trapped in the reservoir, alga propagates in the surface water easily and this will cause water bloom. The growth of large foliage becomes fade because of the spread of alga, while the dead algae sink in the bottom and be rotten and consume oxygen there. Water body with low dissolved oxygen may cause aquatic organisms to be suffocated. In tropical and subtropical areas, lots of greenhouse gases as CO2, CH4, etc may be produced after forests are submerged in reservoirs. Because reservoir water is very deep and sunlight in deep water is feeble, photosynthesis there is accordingly weak. The quantity of living organism production in a reservoir, compared with that in a river, is much lower and its self-recovery capability is feebler to withstand outside disturbances. In addition, any dam without fishways is a fatal barrier for migratory fish. In the downstream of a dam, the increase of sediment carrying capacity of discharged water makes riverbank be scoured intensely and therefore may cause the alteration of river regimes. Because of sedimentation and trapped nutriments, rules of transportation and diffuseness of nutriments may also change in downstream river corridor of a dam. All these elements will cause the alterations of biotic habitat features.
On the other hand, reservoir operation obeys to the demands for power generation, flood control, etc. and therefore artificializes the hydrological cycle of natural rivers. In a periodically hydrological year of a natural river, living organisms will also present periodically pulsed variations. For instance, in flood season hydrophyte community takes the preponderance in a river, being replaced by hygrophyte after water level descends. This pattern is a kind of pulsed variation of biotic community. It is necessary to artificially regulate runoff to be well-distributed in the whole hydrological year during reservoir operation so as to satisfying the requirements for power generation, flood control and etc. As a result, the hydrological period of a natural river is changed. In the mean time, hydropower plants are subject to the adaptive activities according to load change in an electricity grid. Therefore there is a relatively huge water current change in a day for the short-term operation. All these factors may bring pressure on river corridors. In addition, excess water diversion from reservoirs for water supply and irrigation greatly decreases the water quantity in the downstream of dams and makes river dry up and eventually leads to the degradation of river ecosystems. Besides, resettlement is necessary to build dams. Damming sometimes inundates the historic relics and change natural landscapes. This problem is not merely relates to society, culture, but macroscopically is a compound ecosystem problem.
The ecosystem of a natural water body is an open system from the point view of mechanism analysis. It continuously exchanges substance and energy with external environment and has the tendency to balance the input and output. Input substances in water body transfers, transforms and outputs to constitute the metabolic process through physical, chemical and biological actions. Rivers, lakes and reservoirs are all the exchanging ponds for transferring and transforming substances in geochemistry cycle process. Relatively substances stay short and flow fast in the rivers. On the contrary, substances stay long and flow slowly in lakes and reservoirs and therefore their inputs of substances are greater than the outputs. The quantities of trapped substances exceed the self-adjustment capacity of the ecosystems. As a result, it will cause pollution, eutrophication, salinization and so on, which are defined as “ecological retardarce.”
Although dams are different in scale, natural, economic and social backgrounds, and the effects of projects on river ecosystems are also different with varying degrees, the fact is physically existed that dams have stresses on river ecosystems. Along with scientific development and improvement of ecological environment consciousness, in large-scale hydropower development it is not allowed to blench the negative effects of dams on ecosystems. At present, it is necessary to face up to these kinds of negative effects. However it is more important to actively conduct studies on technologies, policies and measures for river’s ecological compensations and to explore a new mode for environment-friendly dam construction.
2 To choose the optimized strategies in nature-society-economy compound ecosystem
There are two opposite theories in the fields of international resources and environments. One is defined as resourcism that claims to widely and continuously exploit recycled resources in maximum. The other is defined as preservationism that opposites human residences and economic development in non-exploited areas [4]. The focuses of the two theories are on how to deal with economic development of human communities and the maintenance of healthy ecosystems. The former emphasizes the importance of satisfying the requirements of economic development and neglects the importance to maintain a healthy ecosystem for the long-term benefits of mankind. Preservationism emphasizes to maintain the health and sustainability of ecosystems and opposes to any reasonable exploitation and utilization of natural resources, which is impractical for economic development and finally becomes an empty viewpoint. Particularly in developing countries, the exploitation degrees of natural resources are much lower than that in the developed countries. If developed countries force the developing countries to accept their viewpoints, then an opposite situation will be initiated. It can be said that either of the two theories is unilateral. The more actual thinking is to extend the research scale, to put the problem in the compound ecosystem of nature, society and economy, and to analyze how to seek the balance point between satisfying social and economic demands of human communities and causing no or a little damages to ecosystem healthy so as to achieve the target of sustainable development. Discussions of any problem should be based on the specific conditions of different countries. For distinct nature, community and economic statuses, different countermeasures should be taken and there is no universal norm suitable for every country. Moreover, there is only relative and no absolute optimization in the selection of energy resource type and in the comparison of different project schemes.
Dam construction poses threats to river ecosystem, though it can meet many demands for flood control, power generation, irrigation, water supply, navigation and so on. The viewpoint of simply opposing to any dam construction and claiming the decommissioning of dams widely is undoubtedly impractical for economic development of human communities. It is one kind of concept of stopping eating for fear of choking. On the contrary, any action of blenching the stresses of dams on ecosystems and overlooking the compensation for ecosystems will undoubtedly be harmful for the long-term benefits of mankind. There is no engineering technique that has great benefits and no harm in the world. The dialectic thinking is to balance the advantages and disadvantages and to pursue good fortune and avoid disaster. Practices have indicated that the negative effects of dams on river ecosystem can be avoided, alleviated or compensated to a certain extent by adopting structural, biotic and administrative measures. The reasonable way is to make concrete analyses of different problems and seek a relatively optimized project scheme.
The objectives of dam construction in
For other alternatives of energy development, nuclear power development has the problems of security, economy and disposal of nuclear waste. The development of wind and solar energy will be confronted with the problems of high cost per kilowatt and the difficulties to be exploit in large scale. For hydrogen energy, it is still in the primary development phase at present. In the composition of Chinese energy resources, conventional commercial energy resources account 10.7% of that in the world, in which water resources, coal, petroleum, gases take the position of the 1st, 3rd, 12th, 22nd in the world respectively. Hydropower development degree in China is only 23%, lower than that in developed countries, where 60% or more hydropower resources has been developed, such as 82% in the US, 65% in Canada, 73% in Germany. Hydropower is one kind of recycled clean energy resources without any pollution to atmosphere and wastes. As long as the Sun does not extinguish, water resources will be available.
It is thus evident that hydropower development has its incomparable advantages from the point of global ecological environment protection by analyzing the influences of different energy resources on environment based on the actual energy composition of
3. Feasibility to actualize ecological compensations to damed rivers.
Oppositions to dams or decommissioning of dams is not the unique choice to protect ecological healthy of rivers. It has been proved to be feasible in principle and practice to construct environment friendly dams by conduct ecological compensations to damed rivers through engineering, biological and management measures to prevent or alleviate stresses on dams to river ecology system with varying degrees.
3.1 Environment evaluation of dam projects
Chinese government attaches great importance to EIA. Environment Impact Assessment Law of the People’s Republic of
(1) The scope of environment assessment
According to the provisions of EIAL, it is divided into two sorts. One is on the development and construction planning of regions, river basins, and coastal areas, including relevant professional planning such as water resources and energy, etc. The other is on projects. For dam projects, either single dam or multi-staged dams, the impact scopes will be on the whole river basin. Therefore, according to EIAL, much attention should be paid in river basin planning on the analytical prediction and evaluation of environment impacts by dam construction.
In the EIA of dam project, besides the EIA of dam site, reservoir, and downstream areas, it is also required to conduct the EIA of the whole river basin. The reasons exist in that daming will change the hydrological and biological continuity of a river and as a result cause influences on the whole basin. Comprehensive and integrated study should be conducted on the interrelation of eco-factors and biotic factors of the whole basin.
Temporal scale is also very important. Evolvement of ecosystem caused by dams is a dynamic process. Some project cases have indicated that the impacts of dams on river ecosystem emerge gradually after one to several decades. Because of the limitations of science development level and people’s cognition capacity, it is very difficult to make accurate and comprehensive long-term prediction on this kind of impacts. Therefore, it is necessary to conduct long-term biological and hydrological monitoring in order to get long temporal-scale river ecosystem evolvement data and based on these to carry out tracking evaluation.
(2) Main topics for EIA of dam projects
Emphases of EIA of dam projects should be put on the influences of daming on the healthy and sustainability of river ecosystem, including influence analysis, prediction, and evaluation of river ecosystem configurations and functions. River ecosystem is an integrity composed by organism with its physical, chemical and geographical environment. All elements have relations with each other of inter-dependence, interpromoting and restriction or checking, cause and effect.
In a specific river ecosystem, its ecosystem configuration is formed by the variety and quantity, density, ratio, temporal and spatial distribution and combination of biotic and abiotic components. This configuration forms the functions of the river ecosystem through input and output of material flow, energy flux and information flow. The configuration and functions of an ecosystem determine its quality, productivity, and self-purification ability, etc.
It should be specially stated that the negative impacts of daming are often expressed as the degradation of biocommunity diversity. Therefore the EIA of dam projects should pay much attention on the change of biodiversity. The essential to maintain the river biocommunity diversity is to maintain an appropriate ecosystem configuration and function.
Present EIA of a dam is usually conducted according to the requirement of an individual subject or local function, such as to separately study the protection of endangered or special animals and plants in reservoir inundation areas or to study the influences on water quality, etc. This work lacks of systematic analysis and evaluation on the interaction, interrelation, inter-dependency, reciprocal transformation of all the components of the ecosystem.
(3) To promote interdiscipline collaboration, encourage public involvement, and conduct scientific research
EIAL ordain that: “the state encourage relevant institutes, experts, and the public to take part in EIA in a proper way.” EIA of dam is a complex work related with multi-specialty, multi-discipline, and multi-department. Interdiscipline collaboration should be advocated to conduct relevant scientific research, explore principles and promote the scientificaalness of evaluation. In addition, active public involvement should be facilitated in many forms such as conference activities, workshops, forum, etc. This will help to drive the process towards scientific and democratic decision-making of major projects.
3.2 Explore and develop Ecological-Hydraulic Engineering (Eco-Hydraulic Engineering)
Since
River restoration is a branch of ecological engineering. ASCE defines river restoration as “an activity to environmentally protect and restore a river system to a more natural condition with sustainable features that enhance ecosystem values and biodiversity” [5,6].Under the concept of “River restoration”, there are perhaps five distinct terms that states different restoration goals[7]:
“Enhancement”” is defined as “any improvement in environmental quality”.
“Creation” is defined as “development of a resources that did not previously exist at the site.”
Scholars with “full restoration” preserve an ideal opinion that is rarely practiced. They define their objectives of river restoration to be the pre-disturbance geomorphological state by human being, which lead to the oppositions to dam and decommissioning of all dams. Many scholars have different opinions. They believe that it is impossible to achieve complete restoration for a river to get back to its presettlement conditions because that a new ecosystem has been formed through natural processes and the influences of human activities. Practical methodologies are to realize the necessity for human to reasonably utilize natural resources and to adopt multi-approaches to promote the healthy evolution of river ecosystem.
In the aspect concerning river training, emphases have been put on ecological restoration in developed countries.
There are three tasks for the rehabilitation of river ecosystem. The first is the improvement of hydrological conditions. The second is the improvement of river geomorphological characteristics. The third is the restoration of special or endangered species. The total target is to improve river ecosystem configurations and functions. Its indicators are the increases of bio-community diversity [9] .
Improvement of hydrological conditions means the improvements of water quantity and water quality, as well as the simulation of natural hydrological cycles. It includes the following aspects:
l To maintain the minimum water quantity.
l To control sewage discharge through waste water treatment, and improve river water quality by promoting clean production.
l To simulate natural hydrological cycles in reservoir operation whilst meet the social and economical requirements.
The improvement of river geomorphological characteristics includes the restoration of continuity in longitudinal direction and connectivity in cross direction, maintaining the configuration varieties in both directions and preventing the use of harden riverbed materials.
4. Value assessment of river ecosystem services and ecological compensation policies
The basis of sustainable development is to maintain the sustainability of biosphere and that of ecosystem services. The services provided by river ecosystem maintain the living surroundings that human rely on, and offer various welfares for the communities. These include the maintenance of biodiversity; the supply of food, medicine and materials; the purification of freshwater; water conservation and the alleviation of draught and waterlogging; the stabilization of local climate; the detoxifcation and decomposition of rubbish; the spread of seed and the recycle of nutrient; the satisfaction of human aesthetics demand, etc. One aspect of the services exerts as ecological products in the form of material objects, such as food, medicine and material. Their economic values can be embodied in the market circulation. The other exerts as non-material objects, including the diversity of biological community, environment, climate, water quality, human culture, etc. These functions have profound and significant influences on social economy though they are often indirect.
For a long time, people consider that river ecosystem services are free bestows of the nature and could be gained without refunds. People think they are the cosset of the earth and feel no regret while accept them. Especially in commercial society, the tangible ecological products can be considered, while the large amounts of non-material values of ecological service are often ignored. When large-scale river training works bring huge and direct economic benefit for mankind, some services of rivers are lost. Its influences may be indirect, however the consequences are severe. It has been a hot topic in the field of sustainable development that how to assess the values of these functions. International society has realized that it is required to study the benefit of ecosystem services deeply and quantify their values, as well as to integrate them into the national accounting system in order to disclose the huge contributions of ecosystem for mankind. In 1992 “Agenda
It has great significance to evaluate and quantify the values of river ecosystem services, and integrate this into the national economic accounting system by laws. First, the short-term activities for obtaining direct economic benefits can be avoided through comparing its direct social economy benefits with the losses of ecosystem services when make decisions for big hydraulic projects. Secondly, it will help to urge project owners to take ecological compensation measures to alleviate stress to river ecosystem and as a result reduce the total value losses of ecosystem services. Finally, this kind of evaluation can also quantify the amounts of compensation capitals that should be offered by project owners.
In the field of environment protection, the principle of “who pollute, who pay” has gotten widespread approval of international societies. Refer to this principle, it is suggested to clarify the principle of “who damage, who pay” in dam construction policies that the dam owner is the main body responsible for ecological compensations. The determinations of compensation standard shouldn’t only consider the capital need for protecting endangered and rare animals and plants or restoring the vegetation in reservoir area. It seems to be applicable to determine the standard based on the total value loss of river ecosystem services. Compensation scope should not limit to reservoir and its downstream areas. It should be extended to the whole river basin. The compensation period should be accord with dam’s life span, which means that the compensation should be carried out after dam construction. Besides bioengineering measures, the compensation mode should also include law establishment in order to implement reservoir operation modes in favor of river biology growth and multiplication. The induced power loss can also be taken as a kind of compensation mode.
For a long time, riverine and riparian animals and plants are often obliged to migrate or go into exile after damming. Migratory fishes have to stop at the dam and some special plants are inundated. Because of strong human activities, biology has to endure and can say nothing. Whom can they say to and who will say something for them? Under the concept of sustainable development, governments, especially water administration agencies, should undertake the tasks to protect rivers. If a mechanism of restriction and coordination between river development and ecology protection can be established, our country’s hydropower development and dam construction will get on a much healthier development approach than before.
5. Conclusions
1) It is physically existed that dam will cause stresses of varying degrees to river ecosystem. We should treat this with a scientific attitude and advocate to pursue profits and avoid disadvantages. It is not receivable to “give up eating for fear of choking.”
2) It is required to comprehensively evaluate the pros and cons of dam construction in the compound ecosystem of nature, society and economy to seek optimized strategies that will help to satisfy the demands of human society and to avoid or alleviate the damages to ecosystem.
3) It is possible to implement ecological compensations to damaged river. Stresses to river ecosystem can be alleviated by taking bioengineering methods as well as structural, biological and management measures. Interdiscipline research and demonstration project construction should be conducted to develop ecology friendly hydraulic and hydroelectric engineering.
4) It is suggested to legislate in order to conduct value evaluation of ecosystem services of natural rivers and integrate it into the national economic accounting system. The evaluation results can be the basis for decision-making of major hydraulic and hydroelectric engineering. Legislations on ecological compensations are also proposed.
Brief introduction on author: Dong Zheren, Chairman of China technical advisory committee of Global Water Partnership (GWP), Professor of China Institute of Water Resources and hydropower Research (IWHR), Director of Chinese Society of Hydraulic Engineering, Visiting Professor of Tsinghua University,
References
[1] Jia Jinsheng, et al, Introduction on world dams in 2003, China Water, No. 13, 2004, pp25-32.
[2] Dong Zheren, Diversity of river morphology and diversity of bio-communities, Journal of Hydraulic Engineering, No.11, 2003.
[3] Vannote, R. L. et al, The river continuum concept, Can. J. Fish. Aqua. Sci., 37:130-137, 1980.
[4]Mitsch W. J. & Jorgensen S E.，Ecological Engineering and Ecosystem Restoration [M]. PP 134-137, Published by John Wiley & Sons, Inc.,
[5]ASCE River Restoration Subcommittee on Urban Stream Restoration，Urban stream Restoration，Journal of Hydraulic Engineering, ASCE , July 2003, pp 491-493
[6]Brookes,A., Shields JR,F.D., River Channel Restoration, John Wiley & Sons,
[7]Dong Zheren, Objectives of river restoration, China Water, No.10, 2004.
[8] Dong Zheren, Theoretical framework of Eco-hydraulic Engineering, Journal of Hydraulic Engineering, No.1, 2003.
[9] Dong Zheren, Design principles for ecological hydraulic engineering, Journal of Hydraulic Engineering, No. 10, 2004
[10]Costanza R, d’Arge R, Rudolf de Groot, et al. The value of the world’s ecosystem services and natural capital. Nature,1997,387: 253-260
[11]Xu Zhongmin, et al, Ecology Economy-theory, method and application. Yellow River Press, 2003, pp110-117.
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