基于环境同位素的鄱阳湖与长江关系变化解析

在气候变化和三峡工程调节的双重影响下,长江中下游通江湖泊江湖关系发生显著改变,而最大的通江湖泊—鄱阳湖—水情的变化及其引发的一系列生态和环境问题受到了高度重视和关注。为了揭示不同时期鄱阳湖与长江间的江湖关系,并初步分析三峡运行对鄱阳湖水情的影响,通过对鄱阳湖北部通江水道湖水、降水和九江段长江干流水同位素特征进行调查并探讨长江水与湖水同位素联系。结果表明:湖水、降水和长江水中δ~(18)O和δ~2H值存在明显的季节和空间变化,可用于揭示湖泊与长江间的关系。在三峡调洪削峰期(7月)湖水δ~(18)O和δ~2H值明显要高于长江水,且湖水主要以外排形式补给长江为主,其比例达75%;在三峡蓄水期(10月)长江水位高于湖口水位,从鄱阳湖出口到老爷庙湖水与长江水同位素值具有较高的相似性,表明了此水域受长江水倒灌影响;而在三峡蓄水期(11和12月)湖水同位素值偏大说明了其受到一定较强的蒸发富集影响。三峡水库运行明显改变了长江水位和流量,进而影响了鄱阳湖与长江的补排关系,调洪削峰调度阶段,较高的长江水位对鄱阳湖存在一定的顶托作用,导致湖水难以排泄。因此,三峡水库的调度需要考虑到鄱阳湖流域水情,以免加重该流域丰水期的洪涝灾害和枯水期的水资源短缺。

Variations of Stable Water Isotopes from the Channel Connecting the Lake Poyang and the Yangtze River and Their Factors

Under the combined influence of climate change and regulation of Three Gorges projects, the relationships between Poyang Lake and Yangtze River have been remarkably altered in the middle-lower reaches. A series of existing ecological and environmental problems were induced by the changes of water regimes of Poyang Lake, which have been attracted worldwide attentions. Hence, this study initially investigated the variations of stable water isotopes of precipitation, lake and river water from the channel connecting the Lake Poyang and the Yangtze River, in order to identify the isotopic connections between Yangtze River and Poyang lake water and to analyze the influence of the regulation of Three Gorges projects on the water regimes of Poyang Lake. The results showed that the isotopic compositions of rivers and lakes characterized a remarkably seasonal and spatial distributions, which could be used to reveal the relationship between Poyang Lake and Yangtze River. During the flood regulation period of July, higher δ18O and δ2H values were observed in Poyang lake water compared with Yangtze River water. Moreover, lake water mainly discharged into Yangtze River and its proportion accounted to 75%. During the flood storage dispatching period of November and December, the highest isotopic values were showed due to the stronger enrichment of isotopic compositions. Water level and discharge were obviously changed due to the regulation of Three Gorges projects and affected the relationships between Poyang Lake and Yangtze River. During the flood regulation period, the high water level of the Yangtze River restrained the discharge of lake water. Hence, the water regimes of the Poyang Lake basin should be taken into consideration during the dispatches of the Three Gorges Reservoir, alleviating possible floods in wet seasons and droughts in dry seasons.