長江上游水電開發(fā)對流域生態(tài)環(huán)境影響初探

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1、 長江上游水電開發(fā)對流域生態(tài)環(huán)境影響初探*基金項目：水利部現(xiàn)代水利科技創(chuàng)新項目專題（XDS2004-02-3)資助； 作者簡介：陳 進（1959~ ），男，湖北武漢人，博士，教授級高工，主要從事流域水資源研究。 陳 進1 翁立達2 1長江水利委員會長江科學(xué)院，武漢，430010 2長江水利委員會長江流域水資源保護局，武漢，430010 摘 要 長江水能資源豐富，其中上游地區(qū)水能蘊藏量占全流域近90%，未來20年，長江上游地區(qū)將有一大批水電工程開工建設(shè)，屆時在長江上游干支流將形成較大規(guī)模的梯級水電站群，這些水電站及水庫投入運行

2、后，將對長江上游及全流域的生態(tài)與環(huán)境產(chǎn)生重要影響。本文根據(jù)已有規(guī)劃成果，預(yù)測未來長江上游梯級水電工程的格局；討論上游地區(qū)生態(tài)與環(huán)境對水電站建設(shè)的制約因素；初步分析梯級水庫群對于長江水生生物，特別是魚類的影響；最后提出減緩梯級水庫群對流域生態(tài)與環(huán)境影響的對策。 關(guān)鍵詞 長江上游，水電站，梯級水庫，生態(tài)與環(huán)境，洄游性魚類 1 前 言 長江水量豐富，水流落差大，水能資源豐富，根據(jù)近期普查成果，全流域水能資源理論蘊藏量平均功率27781億kW，年發(fā)電量24336億kWh，約占全國總量的40%，其中技術(shù)可開發(fā)量25627億kW，年發(fā)電量11879億kWh，約占全國總量的48%，經(jīng)濟可開發(fā)

3、量22832億kW，年發(fā)電量10498億kWh，約占全國總量的60%。長江流域水能資源的89.4%集中在上游地區(qū)。開發(fā)可再生的水能資源對于我國能源發(fā)展戰(zhàn)略無疑具有重要意義，但大規(guī)模的梯級水庫的建設(shè)和運行將顯著改變長江天然的水文過程、水沙分配比例，生境的改變將對流域生態(tài)系統(tǒng)與環(huán)境產(chǎn)生重大影響。如果規(guī)劃的水電工程全部實施，長江上中游干流和相當(dāng)多的支流將被部分渠化或完全渠化，自然河流將轉(zhuǎn)變?yōu)榘胩烊缓恿骰蛉斯た刂频暮恿鳎@種變化將給長江的生態(tài)系統(tǒng)和環(huán)境帶來長期的影響。健康的長江不僅應(yīng)該為人類服務(wù)，而且也應(yīng)為流域自然生態(tài)系統(tǒng)提供良好的環(huán)境，流域水文循環(huán)和生態(tài)系統(tǒng)的維持需要自然的長江。所以，在開發(fā)和利用長

4、江的水能時，應(yīng)該充分認識到長江本來是水文循環(huán)的產(chǎn)物，水文循環(huán)的基本特征是水流的連通性、動態(tài)性、可循環(huán)性，應(yīng)該維持自然的水文循環(huán)。本文針對長江上游水電開發(fā)現(xiàn)狀及未來水電規(guī)劃，分析長江上游地區(qū)未來水電站的格局；討論梯級水庫建設(shè)對水沙過程等環(huán)境因素引起的變化；探討這種變化對長江自然生境的影響，以魚類為典型水生生物，討論梯級水庫群對生態(tài)與環(huán)境的影響方式和問題；最后提出減小水電工程對生態(tài)與環(huán)境影響的對策。 2 長江的水電站及水庫建設(shè) 長江流域第一座水電站——石龍壩建于1910年，到1949年全流域共建成31座水電站，全是小水電，總裝機容量僅13.4MW。解放后，水電站及水庫建設(shè)發(fā)展迅速，50-60

5、年代，水電開發(fā)主要集中在交通便利和經(jīng)濟相對發(fā)達的中下游地區(qū)，60年代到80年代，上、中、下游地區(qū)水電建設(shè)全面展開，到20世紀(jì)后期至本世紀(jì)，為適應(yīng)西部大開發(fā)戰(zhàn)略和“西電東送”要求，我國水電開發(fā)的重點轉(zhuǎn)移到水能資源豐富的長江上游和西南諸河等地區(qū)，到2001年底，全流域已建和在建水電站2441座，裝機容量69727.1MW，年發(fā)電量2924.96億kWh，占全國水電裝機容量的70%左右。全流域已建、正建水電站裝機容量和年發(fā)電量分別占經(jīng)濟可開發(fā)量的30.5%和27.9%。從地區(qū)分布來看，中下游地區(qū)水能開發(fā)利用程度已經(jīng)超過50%，上游地區(qū)不到20%，而長江江源至宜賓河段，水電開發(fā)不到經(jīng)濟可開發(fā)量的5%，

6、所以，今后20年，長江水電開發(fā)的主戰(zhàn)場在長江上游地區(qū)。 從水庫建設(shè)規(guī)模來看，到2000年為止，長江流域已經(jīng)建設(shè)水庫4.4萬座，總庫容1373.37億m3，其中大型水庫109座，總庫容667.42億m3，中型水庫997座，總庫容242.00億m3，如果加上在建的大中型水庫，總庫容超過2113億m3。表1給出了長江上游地區(qū)主要干支流上規(guī)劃和建設(shè)的大中型水電站水庫庫容統(tǒng)計情況，從已建和在建水庫來看，烏江流域和上游干流區(qū)間河段水電開發(fā)程度比較高，而其他流域水電開發(fā)程度還比較低，但各河段規(guī)劃的水庫較多，特別是金沙江流域規(guī)劃的水庫總庫容將達到徑流量的83%。隨著規(guī)劃水電站的逐步實施，長江上游地區(qū)水庫總庫

7、容將達到河川徑流量的61%，如果考慮大量的小型水庫和塘庫，水庫控制的地表徑流量將超過年徑流量的70%以上，除赤水河等少數(shù)支流外，長江上游干流決大多數(shù)河段都將布滿梯級水庫，相當(dāng)多的天然河流將轉(zhuǎn)為人工控制的河道。 表1 長江上游大中型水庫建設(shè)情況（2001年為止） 流域 年徑流量（億m3） 已建水庫總庫容 （億m3） 在建水庫庫容 （億m3） 已建在建水庫庫容（億m3） 已建在建水庫占年徑流量的比例（%） 規(guī)劃水庫庫容 （總庫容） （億m3） 總庫容占年徑流量的比例（%） 金沙江 1565.2 0 0 0 0 1300（1

8、300） 83 岷沱江 1065.0 5.9 70.0 75.9 7 260（335.9） 32 嘉陵江 698.8 37.1 25.3 62.4 9 171.6（234.0） 33 烏江 551.1 30.5 166.0 196.5 36 73.5（270.0） 49 宜賓至 宜昌 634.8 42.9 479.6 522.6 82 83.3（605.9） 95 長江上游合計 4514.9 116.4 740.9 857.4 19 1887.6（2745） 61 3 上游地區(qū)水電開發(fā)的制約因素 長江上游

9、流域面積約100萬km2，不僅水能資源豐富，而且森林、礦產(chǎn)和旅游等資源也十分豐富，同時，長江上游區(qū)處于我國地形第一和第二階梯，地勢陡峻，山高谷深，土層淺薄，地質(zhì)構(gòu)造活動強烈，外動力地質(zhì)現(xiàn)象如泥石流、滑坡、山崩等災(zāi)害嚴(yán)重，生態(tài)與環(huán)境脆弱。 長江上游地區(qū)森林資源十分豐富，是我國僅次于東北的第二大林區(qū)，也是長江水土資源保護的重要屏障。森林主要分布在金沙江、岷江、大渡河、嘉陵江等河流的上游。多年來，由于不合理開發(fā)，重伐輕造，森林植被銳減。不少地區(qū)的森林已經(jīng)破壞，有些演替為草灌群落，生態(tài)系統(tǒng)自我調(diào)節(jié)能力大為下降，土地退化和水土流失面積不斷擴大。 長江上游地區(qū)礦產(chǎn)也十分豐富，銅、鉛、鋅、銻、鎢、鈷、錫

10、、鐵、錳、鋁等儲量，約占全國的30％-50％；鎂、釩、鈦、汞儲量占全國80％左右，磷礦幾乎全部在長江流域，一塊占全國土地總面積0.7％的攀西地區(qū)，就蘊藏著占全國95％的鈦、54％的釩、20％的鐵。 長江現(xiàn)有魚類370種，分別屬于17目、52科、178屬，其中純淡水魚類294種，咸淡水魚類22種，海淡水回游魚類9種，海水魚類45種。上游地區(qū)的魚類種類繁多，共有魚類230種，其中僅見于上游水體的有103種，如中華腹裂魚、重口腹裂魚、布氏哲羅魚等受到特殊的自然條件影響，僅在上游地區(qū)形成優(yōu)勢種群。 長江上游地區(qū)是水系、山脈、生物和人文的綜合體，風(fēng)景名勝和人文古跡眾多，具有自然遺產(chǎn)、觀賞和科學(xué)研究等

11、價值。如有三峽、九寨溝、黃果樹、三江并流等自然奇觀，有國寶大熊貓棲息地。到2003年為至，已經(jīng)建立國家級自然保護區(qū)32個，保護區(qū)面積達到200萬公頃。長江上游每一條河流由于所處的地理位置不同，景色各異，自然風(fēng)光具有唯一性。長江上游地區(qū)人類活動已經(jīng)有100萬年的歷史，有各類重要遺址數(shù)十處，文物點更是數(shù)不勝數(shù)，僅受三峽水庫影響的文物點就達1087處。 所以，在進行梯級水庫規(guī)劃和建設(shè)時，特別是大型水庫建設(shè)時，應(yīng)該深入了解上游地區(qū)生態(tài)與環(huán)境敏感點，充分考慮所在河流生態(tài)、資源、環(huán)境和人文等方面的制約因素，避免或減少水電開發(fā)對生態(tài)與環(huán)境的影響。 4 梯級水庫帶來生境的變化 生態(tài)系統(tǒng)包括非生物部分（

12、即生境）和生物部分，梯級水庫對生態(tài)與環(huán)境的影響首先體現(xiàn)在對生境的改變，包括河流水沙輸移過程、水體的連續(xù)性、流態(tài)、流速、水溫、溶解氧和透明度等環(huán)境要素的變化，主要影響在以下幾方面： （1）梯級水庫對河流最直接的影響是破壞了河流的連續(xù)性。長江上游是許多洄游魚類的重要棲息地，洄游魚類需要三場一道（繁殖場，育肥場、產(chǎn)卵場，洄游通道），梯級水庫的建設(shè)造成洄游魚類等水生生物的生命通道阻隔，相當(dāng)多的洄游魚類可能滅絕。由于修建魚道不僅增加工程成本和技術(shù)難度，而且較難評價其效果，所以目前已建和在建大壩基本上沒有考慮修建魚道。徑流式電站雖然河流水文過程影響較小，但水流利用率一般很高，河道水流基本上通過引水管道和

13、水輪機流過，也會對魚類等水生生物帶來毀滅性打擊。例如，岷江上游建設(shè)了大量引水式水電站，雖然沒有建高壩大庫，但造成相當(dāng)長的河段，在枯季完全脫流，全部河水都從壓力管道流過，對洄游魚類等水生生物有致命打擊，如珍稀魚類-虎嘉魚已經(jīng)基本消失。洄游魚類是水生態(tài)系統(tǒng)中關(guān)鍵生物指標(biāo)物種之一，它的滅亡將影響整個河流生態(tài)系統(tǒng)的結(jié)構(gòu)和生態(tài)系統(tǒng)的完整性。 （2）大中型水庫的人工調(diào)節(jié)雖然顯著提高了人類利用水的保證率，但同時也使自然河道的洪枯過程減弱，甚至消失。而相當(dāng)多的水生生物需要河流的洪枯變化。洪水是自然現(xiàn)象，河流和河道的形成需要洪水，沒有洪水，就沒有河流，河道就會萎縮，河流的生態(tài)功能就會下降。洪枯變化帶來了河流水

14、位、水溫、水量、含沙量和消落帶等的變化，生物多樣性常常與生境的復(fù)雜性直接相關(guān)，這些現(xiàn)象是河流生境的體現(xiàn)，是生物多樣性需要的自然環(huán)境。當(dāng)然，特大洪水對人類和自然生態(tài)都有巨大的破壞，但一般性洪水卻是自然生態(tài)所需要的，許多水生生物和兩棲生物需要在河灘上產(chǎn)卵，如果河水常年不上灘，生物棲息地將大為減少。研究表明，降雨與徑流的依時變化是河流和濕地的植物、無脊椎動物和魚類生命循環(huán)的主要驅(qū)動力，季節(jié)性高峰流量的喪失會導(dǎo)致魚類產(chǎn)卵、孵化和遷徙激發(fā)因素的中斷，一些魚類遇洪水或急流才能刺激產(chǎn)卵和幼苗生長。河流洪水過程的減弱，使魚類較難進入濕地或回水區(qū)，改變了水生生物的食物網(wǎng)結(jié)構(gòu)，岸邊植被復(fù)原能力降低或消失，植被生長

15、的速度減緩。 （3）大水庫的建設(shè)對庫區(qū)生境影響巨大。庫區(qū)水流速度減小，水體納污能力和自凈能力下降，特別是在水庫支汊區(qū)域，水體污染物很難擴散。水庫淹沒大量灘地，魚類和兩棲動物的棲息地減少。水庫水體深度較大，水溫會產(chǎn)生分層，水庫下泄的低溫水對下游水生生物和農(nóng)田灌溉都會產(chǎn)生不利影響。泥沙淤積將影響水庫的使用壽命，庫尾淤積將影響回水變動區(qū)航運和碼頭。 （4）梯級水庫的建設(shè)和運行將在相當(dāng)長的時間內(nèi)使中下游河道輸沙量和水體的含沙量減少。正常的河流需要平衡輸沙，河岸穩(wěn)定、河口演變、營養(yǎng)物的輸送、水體凈化和生態(tài)維持都需要一定的輸沙。例如，三峽水庫的清水下泄，長江中下游河段將發(fā)生長時間的沖刷，河床下降，沿岸

16、地下水位也會下降，使河勢變化和沿岸濕地生境受到影響。在平原湖區(qū)，由于長江水位下降，進入洞庭湖的洪水會減少，洞庭湖會加速退化，江湖關(guān)系將發(fā)生變化。清水下泄，對河岸會產(chǎn)生侵蝕，江水對周邊濕地下水交換將減少，同時可能對兩岸堤防安全構(gòu)成威脅。長江河口地區(qū)由于長期缺乏泥沙的補給，岸線將受海潮的侵蝕，河口自然演變規(guī)律和生境發(fā)生變化，同時對河口岸線利用也將產(chǎn)生不利影響。尼羅河三角洲在阿斯旺水庫修建后，進入河口的泥沙減少，導(dǎo)致海岸線不斷后退和侵蝕。因此，河流的沙多了不好，沙少了也不行，應(yīng)該重視水體含沙量減少帶來的新問題。 （5）大規(guī)模的水庫建設(shè)對區(qū)域氣候、水文循環(huán)和環(huán)境變化有一定影響。水庫的建設(shè)，將增加水的

17、蒸發(fā)和滲漏損失，使下泄徑流量減小，如漢江流域，丹江口水庫建設(shè)后，90年代以來上游來水量減少了10%以上，原因有區(qū)域氣候變化的影響，也有水庫蒸發(fā)和滲漏的影響。再如，阿斯旺水庫每年蒸發(fā)和滲漏損失水量達210億m3，達到水庫總庫容的10%以上。隨著長江上游大規(guī)模的水電站建設(shè)，已經(jīng)開始擔(dān)心水庫蓄不滿水的問題。因為長江雖然水資源豐富，但大部分是洪水，非汛期水量并不多，而大部分水庫都是汛后開始蓄水，將加劇枯季人類用水和生態(tài)用水的矛盾。另一方面，水庫的建設(shè)，淹沒大量土地，移民搬遷將改變庫區(qū)土地利用方式，地下水位抬高，氣溫及氣候?qū)a(chǎn)生變化，區(qū)域水文循環(huán)和生境也將發(fā)生改變。另外，水庫還可能誘發(fā)地震、滑坡等地質(zhì)

18、災(zāi)害。 5 梯級水庫對生物的影響 梯級水庫對生物的影響是一個長期和復(fù)雜的過程，自然生境的破壞，人工環(huán)境的產(chǎn)生，一些生物會通過自身的調(diào)整逐步適應(yīng)新的環(huán)境，繼續(xù)生存和發(fā)展，而另外一些生物會不適應(yīng)新的環(huán)境而出現(xiàn)物種退化或消亡。生態(tài)系統(tǒng)中任何生物的存在都有其特定的地位和作用，不同生物之間相互依存，一個生物的消亡，必然影響其它生物的存亡和整個生態(tài)系統(tǒng)的完整性。所以，大壩及水庫對生物的影響及生物對水庫建設(shè)的響應(yīng)是一個十分復(fù)雜的過程，需要長期觀測和研究才會有定量的成果，這里以魚類為例，說明生物受水庫影響的情況。 長江水系有浮游植物321種，常見的近330種，浮游動物330種，常見種類130種，底棲動

19、物220種，水生高等植物214種，水生大型動物中除魚類外還有獸類白鱀豚、江豚、爬行類揚子鱷和兩棲類大鯇等珍惜物種，其中國家一級保護動物白鱀豚、中華鱘、長江鱘、白鱘；國家二級保護動物江豚、胭脂魚、川陜哲羅鮭、秦嶺細鱗鮭、松江鱸魚等。梯級水庫對魚類影響可以從以下幾方面來說明： （1）隨著長江干流葛洲壩和三峽水電站的建設(shè)和沿江大規(guī)模筑堤建閘工程，河海間洄游的魚類如鱘魚、鰣魚等珍稀魚類已大為減少。國家一級保護動物中華鱘原產(chǎn)卵地原在長江上游合江至屏山河段，長約800km，原有16處產(chǎn)卵場，葛洲壩電站建成后，雖然在壩下建立了人工產(chǎn)卵場，但僅局限在5km范圍內(nèi)，產(chǎn)卵場面積僅為原來的1-2%。國家一級保護動

20、物白鱘產(chǎn)卵場分布于金沙江下游和重慶以上的長江干流，產(chǎn)卵季節(jié)為3月-5月，習(xí)慣在河灘礫石間產(chǎn)卵。國家二級保護動物胭脂魚產(chǎn)卵場在長江上游岷江和嘉陵江等支流，魚卵具有微粘性、散布在石塊縫隙中發(fā)育，幼魚可隨江飄流到中下游及通江湖泊。如果在這些河段建設(shè)水庫，河灘將淹沒，必將影響到這些珍稀魚類棲息地和洄游通道。 （2）長江上游河段特有魚類，大多數(shù)終生在流水中生活，它們的形態(tài)結(jié)構(gòu)、生理特征和生態(tài)習(xí)性同棲息地的水流、河床物質(zhì)和底棲生物相適應(yīng)，如巖原鯉、圓口銅魚等喜棲息于快速流淌、與大氣接觸面大，含氧量較高的水體，形成水庫后，在靜水中則會因溶解氧不足而死亡。 （3）長江上主要的經(jīng)濟魚類--四大家魚的產(chǎn)卵很大

21、程度上取決于水溫和漲水等環(huán)境因素，在四月底至五月初的繁殖期，如果水溫未達到18℃，即使?jié)q水也不產(chǎn)卵，如達到合適水溫，又遇降雨引起河流水位陡漲，可刺激家魚產(chǎn)卵，產(chǎn)卵規(guī)模和漲水幅度表現(xiàn)出正相關(guān)，魚卵在隨水飄流過程中發(fā)育、孵化，飄流距離可達300-400km，且要求流速在0.2m/s以上，否則魚卵和魚苗會下沉而不能正常發(fā)育，像這樣魚卵飄流性的魚類，在長江干流有20多種。在水庫內(nèi)，因庫區(qū)河灘淹沒，產(chǎn)卵場減少，魚卵也難以飄流孵化。 （4）長江上游梯級水電站中，大部分是低水頭的徑流式電站，雖不是高壩大庫，但水流利用率很高，90%以上的水流流經(jīng)水電站水輪機或壓力管道，魚類等水生生物難以存活。而且徑流式水電

22、站絕大多數(shù)是日調(diào)節(jié)或無調(diào)節(jié)能力河道每日都有斷流時段，魚類無法生存。另一方面，許多高壩大庫下泄水流，通過摻氣進行消能防沖，保護河道，但同時造成水庫下游相當(dāng)長的河段（可達數(shù)百公里）的河水氣體過飽和，幼魚吞食而造成氣泡病大量死亡。 6 對 策 長江上游梯級水電站建設(shè)對流域生態(tài)與環(huán)境的影響十分復(fù)雜，短時間內(nèi)較難看出明顯影響，應(yīng)本著科學(xué)務(wù)實的態(tài)度全面客觀分析，處理好保護生態(tài)環(huán)境與水電開發(fā)的關(guān)系。水電開發(fā)的規(guī)劃、設(shè)計、建設(shè)和管理者應(yīng)該廣泛聽取各方面的意見，鼓勵公眾參與，盡量采取措施，減小水電工程對流域生態(tài)與環(huán)境的影響，建議采用的措施有： （1）政府及各部門、流域管理者、水庫管理者和利益相關(guān)者都應(yīng)

23、該具有生態(tài)與環(huán)境保護的理念，充分認識到水電站建設(shè)和運行給生態(tài)與環(huán)境帶來的不利用影響，同時應(yīng)該認識到問題的復(fù)雜性和長期性。 （2）加強流域統(tǒng)一管理，在長江干支流水資源綜合規(guī)劃中，應(yīng)從長江全流域角度，根據(jù)各河段特點，制定河流生態(tài)基流標(biāo)準(zhǔn)，作為水電站規(guī)劃、設(shè)計、建設(shè)和運行的依據(jù)。水電站建設(shè)必須保持河流必要的生態(tài)基流，并從流域的角度考慮梯級水電站的生態(tài)調(diào)度。 （3）以流域為單元，定期進行生態(tài)與環(huán)境監(jiān)測，進行長期的科學(xué)觀測和科學(xué)研究，對水庫建設(shè)不僅應(yīng)進行環(huán)境影響預(yù)測評價，更重要的是需要建立后評估制度，在工程完成后觀測和分析對流域生態(tài)與環(huán)境的影響。 （4）水電站的規(guī)劃不能僅考慮水能利用的經(jīng)濟指標(biāo)，還

24、要考慮水電站及水庫對各類自然保護區(qū)及生態(tài)與環(huán)境敏感區(qū)的影響，應(yīng)將避免和減少這種影響作為規(guī)劃的重要目標(biāo)。對于已經(jīng)造成影響的，應(yīng)該采取必要的工程和非工程措施進行修復(fù)。 （5）從法律等制度上建立合理的生態(tài)補償機制，需要水電站受益者向受影響的河流生態(tài)和弱勢群體進行補償，建立流域生態(tài)與環(huán)境保護工作和研究費用的投入機制。 參 考 文 獻 [1] 長江水利委員會，長江流域地圖集，北京：中國地圖出版社，1998年。 [2] 陶思明，濕地生態(tài)育保護。北京：中國環(huán)境科學(xué)出版社，2003年。 [3] 水力水電規(guī)劃設(shè)計總院，中國大中型水電站規(guī)劃圖集，1994年。 [4] 長江水利委員會，中國水力

25、資源復(fù)查成果，長江流域-概述，2004年。 [5] 范繼輝，程根偉，張艷等，岷江上游水電梯級開發(fā)存在的問題及建議，中國水利，2005年第10期，47-49。 聯(lián)系地址：武漢市黃浦大街23號，430010，長江科學(xué)院 Email：chenjin12342003@ or cjcjcj@ 電話：027-82829755，13607178977  A Preliminary Approach on Impacts of Hydropower Development in Upper Yangtze River on Ecological Environment

26、Jin Chen1 Lida Weng2 1Changjiang River Scientific Research Institute of Changjiang Water Resources Commission, Wuhan, 430010, Email:chenjin12342003@ 2Yangtze River Valley Water Resources Protection Bureau of Changjiang Water Resources Commission, Wuhan, 430010, Email: wengld@

27、 Abstract There are abundant hydro-energy resources in the Yangtze River (also called Changjiang River), and the hydro-energy reserves in the upper reaches occupy nearly 90% of the whole valley. In future 20 years, a great amount of hydroelectric projects will be constructed in the upper reaches o

28、f Yangtze River, and a large scale of cascade hydropower stations will be formed in the main channel and branches in the upper reaches at that time. After construction and operation of these power stations and reservoirs, some important impacts will be produced on the ecology and environment in the

29、upper areas and even the whole valley. In the paper, distribution of cascade power stations in the upper reaches is forecasted according to completed plans; some restricting factors of ecology and environment on hydropower station constructions in upstream are discussed; the impacts of cascade reser

30、voirs on the habitat and Aquatic Life (such as fishes) in the valley ecosystem are discussed; and finally, some countermeasures for mitigating the impacts arisen from the cascade reservoirs are put forward. Introduction The Yangtze River is rich in water resource, big in water head and abundant

31、in hydropower resources. According to recent general investigation, for the theoretical reserves of hydropower in the whole valley, the average power is 27781×108kW, and annual electricity output is 24336×108kWh, accounting for about 40% of the total China; 90% of the hydropower resources in the Yan

32、gtze River are distributed in upper areas. Undoubtedly, the development of renewable hydropower resources has vital significance for energy development strategy of China, but the construction and operation of large scale reservoirs will make the flow process, water-sediment proportion and ecosystem

33、 habitat change greatly, and the change of habitat will affect the natural ecosystem and environment significantly. If the planned hydroelectric projects are carried out completely, the main stems and quite a few branches of the upper and middle Yangtze River will be channelized partially or complet

34、ely and the natural rivers will be transformed into semi-natural or artificial controlling rivers, which will result in long-term impacts on natural ecosystem and environment of Yangtze River. Healthy Yangtze River should not only serve the human beings, but also provide good environment for the nat

35、ural ecosystem of valley, and the natural hydrologic cycle and ecosystem maintenance also need the Yangtze River. Therefore, in the development and utilization of hydropower, it should be fully realized that the Yangtze River is originally the product of hydrologic cycle, it need participate in and

36、maintain the natural hydrologic cycle; the basic features of river hydrologic cycle include connectivity, flow dynamic characteristics and periodicity. In the paper, in view of the present situations and the plan of future hydropower stations in the upper Yangtze River, the layout of cascade power s

37、tations of the upper reaches is analyzed; the changes of environmental factors such as water and sediment process etc. produced by the construction of cascade reservoirs are discussed; the impacts on aquatic life, such as fish ,since habitat changes are discussed; and finally, the countermeasures fo

38、r mitigating the impacts arisen from cascade reservoirs are proposed. Construction of Hydropower Stations and Reservoirs in the Yangtze River Shilong Dam, the first hydropower station in the Yangtze River Basin was built in 1910; and up to 1949, 31 dams had been built in the whole valley and all o

39、f them are of small ones, with the total installed capacity of 134mw. After 1949, hydropower stations and reservoirs were developed rapidly in 1950s ~1960s, and the hydropower development was located in the middle and lower areas with convenient traffic and developed economy; from 1960s to 1980s, th

40、e construction of hydropower stations in the upper, middle and lower reaches were in full swing; up to the late 20th century and the early 21st century, in order to meet the requirements of West Development strategies and “West-to-East Power Transmission”, the stress of hydropower development was tr

41、ansferred to the upper Yangtze and the rivers of Southwest China, and up to December of 2001, 2441 hydropower stations had been built or are under construction, with installed capacity of 69727.1mw, and annual electricity output of 2924.96×108 kWh, accounting for about 70% of the total installed hyd

42、ropower capacity in China. The installed capacity and annual electricity output of power stations having been built or under construction made up 30.5% and 27.9% of the economically developable reserves respectively. From the distribution in region, more than 50% of the hydropower in the middle and

43、lower Yangtze have been developed and utilized, while only less than 20% for the upper areas, and for the stretch from headwaters to Yibin, less than 5% of economically developable reserves have been utilized for hydropower development. Therefore, in the future 20 years, the hydropower development o

44、f the Yangtze River will be carried out mainly in the upper reaches. Viewed from reservoir construction, up to 2000, 44000 reservoirs had been constructed in the Yangtze River Basin with total storage capacity of 1373.37×108 m3, including 109 large-scale reservoirs with total storage capacity of 66

45、7.42×108 m3, 997 medium-sized reservoirs with total storage capacity of 242.00×108 m3, and the total storage capacity would exceed 2113×108 m3 inclusive of the large and medium scale reservoirs under construction. Table 1 shows the statistics of storage capacity of existing and planned large and med

46、ium reservoirs in main stems and branches of the upper Yangtze River, it can be seen that the degree of hydropower development in Wujiang River and main stems in upper Yangtze River is quite high, while it is lower in other valleys, but there are more reservoirs in planning for each reach, especiall

47、y in Jinsha River, the total storage capacity in planning will reach 83% of river runoff. With gradual implementation of the planning reservoirs, the total reservoirs storage capacity of upper Yangtze River will reach 61% of river runoff. If a large amount of small scale reservoirs are considered, t

48、he surface runoff controlled by reservoirs will exceed more than 70% of annual runoff; and except a few branches such as Chishui River, cascade reservoirs will be arranged in most of reaches in upper Yangtze River, and quite a few natural rivers will be transferred to artificially controlled river.

49、 Table 1 Large and Medium Scale Reservoirs in Upper Yangtze River (up to 2001) River Annual runoff（108m3） Storage capacity of existing reservoirs （108m3） Storage capacity of reservoirs under construction （108m3） Storage capacity of reservoir in planning (total storage capacity) (108m3) Pe

50、rcentage of total storage capacity to annual runoff (%) Jinsha River 1565.2 0 0 1300（1300） 83 Mintuo River 1065.0 5.9 70.0 260（335.9） 32 Jialing River 698.8 37.1 25.3 171.6（234.0） 33 Wujiang River 551.1 30.5 166.0 73.5（270.0） 49 Yibin to Yichang 634.8 42.9 479.6 83.3（605

51、.9） 95 Total of upper Yangtze River 4514.9 116.4 740.9 1887.6（2745） 61 Some restricting factors on hydropower development of Upper Yangtze River The upper Yangtze River Basin covers the area of 100×104 km2 approximately, with abundant hydropower resources, as well as forest, mineral and to

52、urist resources. In addition, it is located in the first and second topographic cascades of China, with steep terrain, high mountain and deep valley, shallow and thin soil layer, intense geological activity, serious external dynamic geologic disaster such as mud-rock flow, landslide, and landfall, a

53、nd frail ecology and environment. The upper Yangtze River, with extremely rich forest resources is the second forested area in China, next only to northeast China, and also an important barrier for water and soil conservation of the Yangtze River. The forest is mainly distributed in upper Yangtze R

54、iver such as Jinsha River, Minjiang River, Dadu River, and Jialing River and so on. However, the forest has reduced sharply due to unreasonable development, over-cutting and neglect of forestation for many years. Once the forest is destroyed, it is very difficult to restore, and as succession, grass

55、 & shrub degradation will occur quickly, the self-adjustment ability of ecosystem decreases greatly, and land degeneration area expands continuously. The mineral resources are also abundant in the upper Yangtze River, including copper, lead, zinc, stibium, tungsten, cobalt, tin, iron, manganese and

56、 aluminum, approximately making up 30%~50% of the total China; the reserves of magnesium, vanadium, titanium and mercury account for about 80% of the total China, and all phosphate rock distributes in the Yangtze River Basin nearly; only in Panxi, with the area accounting for 0.7% of the total area

57、in China, possesses titanium, vanadium and iron respectively accounting for 95%, 54% and 20% of the total China. In the Yangtze River, there are 370 kinds of fish belonging to 17 orders, 52 families and 178 genera separately, including 294 kinds of pure freshwater fish, 22 kinds of salt freshwater

58、fish, 9 kinds of sea freshwater migratory fish, and 45 kinds of marine fish. There are many kinds of fish in upper Yangtze River, totaling 230, 103 kinds are found only in upper reaches due to the influence of special natural conditions, and a dominant population is formed in upper reaches, such as

59、Chinese sschizothoracin, David’ sschizothoracin, Hucho bleekeri and so on. The upper Yangtze River is a synthesis of river system, mountain chain, biology and human culture, it possesses numerous sceneries and historic sites, and it is valuable in natural heritage, sightsee and scientific research,

60、 such as the natural marvelous spectacles like Three Gorges, Jiuzaigou, Huangguoshu, Three Parallel Rivers, the habitat of giant panda and other protected areas. Up to 2003, 32 national natural protected areas had been established, with the protected area of two million hm2, accounting for about 1/5

61、 of the upstream area. Each river of upper Yangtze River is different in landscape due to different geographic position; therefore, the natural scenery is unique. Long before one million years human activity has existed in the upper Yangtze. There are many important legacies and incalculable cultur

62、al relic spots. The cultural relic spots only influenced by the Three Gorges reservoir reach 1087. Therefore, When planning and construction of cascade reservoirs, especially the large-scale reservoirs, the sensitive points of ecology and environment should be thoroughly understood, the restricting

63、 factors of river ecology, resources, environment and human culture should be taken full consideration, and the impacts of hydropower development on ecology and environment should be avoided or mitigated. Changes of Habitat Caused by Cascade Reservoirs The ecosystem consists of abiotic factor (nam

64、ely habitat) and biotic factor, the impacts of cascade reservoirs on ecology and environment are represented by the change of habitat first, including water and sediment transportation process; river continuity, flow pattern, flow velocity, water temperature, dissolved oxygen and transparency of wat

65、er body, the main impacts involve following aspects: (1) The most direct impact of cascade reservoirs is that continuity of river is breached. The upper Yangtze River is an important habitat of many migratory fishes, and migratory fish need three fields and one pass (breeding field, fattening field

66、, spawning field, and migration pass). But the construction of cascade reservoirs will make the life channel of aquatic life(like migratory fish) obstruct, quite a few migratory fishes may become extinct. Up to now, no any consideration has been given to the ecological pass, such as fish-way, for the dams having been constructed and under construction because fish-way construction make the construction cost and technical difficulties increase, an