鄱阳湖水文干旱化发生的机制研究

近年来,鄱阳湖呈现显著的秋冬季干旱化趋势,对鄱阳湖水生态安全和湿地生态安全都产生了显著影响,引起广泛的社会关注。揭示鄱阳湖水文情势发生变化的原因,对鄱阳湖科学管理具有重要的意义。利用Landsat卫星系列遥感影像分析2000年以来鄱阳湖采砂基础上,结合长时间序列水文资料,分析鄱阳湖水文特征变化,探讨了鄱阳湖水文特征变化与采砂之间的关系。得到以下结论：（1）从采砂船数量、采砂规模和采砂方位等来看,数量和规模远超规划限额的规模,并且呈扩大趋势,采砂范围已经扩大到鄱阳湖最南端,并在生态敏感区出现,表现出滥采、盗采和超采的无序状态。（2）新世纪以来,鄱阳湖枯水期提前、特征低枯水位时间延长,入江河道的水面坡降呈减小趋势,但泄流出湖速率呈增加趋势。（3）长江三峡水库运行对中下游水位的影响,以及长江中下游含沙量降低造成清水侵蚀,河床下降削弱长江水对鄱阳湖泄流的顶托作用,也是鄱阳湖水文干旱化变化的潜在原因。（4）鄱阳湖采砂导致入江河道加深、加宽,是鄱阳湖秋冬季水文干旱化的原因之一。研究结果对于如何应对鄱阳湖秋冬季水文干旱化,开展鄱阳湖综合治理具有参考价值。

Research on the causes for hydrological drought trendin Poyang Lake

Poyang Lake is the largest fresh water lake in China. Seasonal fluctuation of water level is a typical hydrological feature of Poyang Lake. And Poyang Lake wetland is one of the most important international wetlands and the largest habitat for wintering birds in East Asia. Since the beginning of the 21st century, the hydrological drought trend of Poyang Lake that emerged in autumn and winter seasons has not only posed serious threats to the local freshwater/wetland ecological security, but also attracted wide attention from the public. It is therefore of great significance to precisely monitor hydrological changes in the study lake and reveal the underlying drivers. Some studies suggest that the drought trend of Poyang Lake is related to the decrease of precipitation in the basin or the running of Three Gorges Dam (TGD) displaced in the middle reach of Yangtze River. Lai et al. argued theoretically that the drought trend in Poyang Lake was caused by sand minning in the lake. In this study, we used the long term records of LANDSAT images to locate and analyze sand mining in Poyang Lake during 2000-2016. On this basis, long time-series hydrological data were used to analyse hydrological changes. Finally, we combined these two datasets to investigate the impact of sand mining on the drought trend of Poyang Lake. Our results showed that: (1) During 2000-2016, an increasing number of vessels involved in sand mining was observed in the lake, and the sand mining has been extended to the whole lake region, including its southernmost tip and ecologically sensitive areas; (2) The drought period of Poyang Lake tended to be prolonged, and a decreasing water surface gradient and an increasing outflow from Poyang Lake into Yangtze River at similar water level happened in these years; (3) Sand mining, causing river channel connecting Poyang Lake with Yangtze River becoming deeper and wider, contributed to the hydrological drought in autumn and winter of the lake. (4) Three Gorges Dam (TGD), which reduced the water level in downstream, and weakened the backwater effect to Poyang Lake drainage from Yangtze River, could also be one of the reasons for hydrological change in Poyang Lake. In recent years, Jiangxi provincial government has been promoting Poyang Lake Water Conservancy Project to deal with the drought trend. We should urge the departments concerned to formulate a comprehensive management scheme for Poyang Lake according to the main causes for hydrological changes.