关键词: 水文干旱, 采砂, 鄱阳湖, 三峡水库, 成因探讨

Abstract:

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.

Key words: hydrological changes, sand mining, Poyang Lake, Three Gorges Dam, cause analysis