三峡工程对两湖的生态影响

长江干流的渔业捕捞量从1954年的43万t下降到2011年的8万t,降幅达81%,而两湖(洞庭湖和鄱阳湖)的渔业捕捞量分别在2~4万t之间波动。三峡大坝对洞庭湖三口径流量的影响有限,但使江水倒灌鄱阳湖的天数和水量进一步降低。长江来水占洞庭湖径流量的30%,而在鄱阳湖中仅有0.1%,因此,对维持长江干流的渔业资源(特别是产漂流性卵鱼类)来说,洞庭湖的重要性远超鄱阳湖。干流渔业资源的衰退主要是江湖阻隔的结果,虽然过度捕捞起到了推波助澜的作用,因此,即使在干流休渔十年,也未必能使长江的渔业资源大幅回升。如果在两湖建闸,长江渔业资源的衰退将会进一步加剧,江豚的灭绝可能难以避免,因此,维持两湖与长江的生态联系,对长江干流生物多样性的维持至关重要。

ECOLOGICAL IMPACTS OF THREE GORGES DAM ON LAKES DONGTING AND POYANG

Total catch in the main river declined from 43 × 104 t to 8 × 104 t in 2011,with a reduction of 81％,while in contrast,since 1950s,total catches in Lakes Dongting and Poyang fluctuated between 2-4 104 t,respectively.The impact of the Three Gorges Dam on discharge of the three outlets into Lake Dongting was limited,but it decreased the days and amount of backward flow from the river to Lake Poyang.The inflow of water from the Yangtze River accounts for 30％ of the total runoff of Dongting Lake,but only 0.1％ in Lake Poyang.Therefore,for the maintenance of fishery resources (especially those fishes with drifting eggs) of the main river,Lake Dongting is much more important than Lake Poyang.The decline of fishery resources in the main river was mainly the result of obstructions between the river and lakes,although overfishing has also contributed to this,thus,it is difficult to have a fundamental improvement on the fishery resources in the Yangtze River even fishing is forbidden for ten years.If Lakes Poyang and Dongting are isolated by dams,the fishery resources in the river will further decline,the extinction of the finless porpoise can hardly be avoided.Therefore,it is crucially important for the maintenance of biodiversity in the Yangtze River to keep ecological connections between the river and both lakes.