| 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 wetland and the largest habitat for wintering birds in Eastern Asia.Since the new century,the hydrological drought trend of Poyang Lake happened in autumn and winter seasons has not only posed profound threats to the local freshwater/wetland ecological security,but also attracted extensive attention from the public during recent years.It is therefore of great significance to precisely monitor hydrological changes in Poyang Lake and reveal the underlying drivers.This paper studies the causes of hydrological aridification in Poyang Lake from the aspects of reservoir construction,the difference of flooding characteristics of Poyang Lake,the operation of the Three Gorges Reservoir and the sand mining in Poyang Lake.The results show:(1)Since the beginning of the new century,the dry season of Poyang Lake has been advanced,the characteristics of low water level have prolonged,and the water surface slope of the river into the river has decreased,but the rate of discharge from the lake has increased.(2)Between 1955 and 2010,the“Five Rivers”into the lake totaled6788.389×10~9m~3,of which Minjiang(accounting for 55.58%)>Xinjiang(accounting for 14.41%)>Fuhe(accounting for 10.38%)>Xiuhe(9.82%)>Rao River(accounting for 9.81%);the water volume of the lake at the mouth of Poyang Lake is 8183.758×10~9m~3;(3)Benefiting from the flood-preserving and water-storing effect of reservoir construction in the basin,increasing the coverage of forest vegetation by ecological engineering construction,and improving the water conservation function,the proportion of runoff into the lake during the dry season is increasing,and there is a drought in the autumn and winter of Poyang Lake.Mitigation;(4)The annual total precipitation is the root cause of the change of the annual total lake runoff.Despite the influence of the Yangtze River top support and back irrigation,the total annual runoff of the“Wuhe”into the lake and the annual runoff of the lake and the corresponding basin year.The relationship of total precipitation is consistent in different years;(5)The results of remote sensing extraction of the number of sand mining vessels,sand mining scale and sand mining orientation show that the quantity and scale far exceed the scale of the planning quota and are expanding.The sand mining scope has been expanded to the southernmost tip of Poyang Lake and is in the ecological The sensitive areas appear,showing the disorderly state of indiscriminate mining,stealing and over-exploitation;the sand mining in Poyang Lake leads to the deepening and widening of the river into the river,which is one of the main reasons for the change of hydrological characteristics in the autumn and winter of Poyang Lake;(6)Remote sensing extraction of spatial distribution map of Poyang Lake flooding in 2001-2018 shows that Poyang Lake is located in the middle and north of Poyang Lake in the long-term flooding area of each year,including the northern part of the lake center and north of Songmenshan Island.The narrow river channel;in different hydrological years,the flooding characteristics of the grassland area in the Poyang Lake wetland are very different.In the wet season,the flooding time of the Poyang Lake wetland grassland is relatively long,The flooding time of the Poyang Lake wetland grassland in the dry year is relatively short;(7)The spatial distribution of NDVI in Poyang Lake wetland is related to the flooding characteristics of Poyang Lake.The longer the flooding time,the less the biomass accumulation of wetland plants.The growth of grassland in Poyang Lake wetland and the frequency of flooding in Poyang Lake wetland are significantly negative.Correlation;the wetland grassland area under the same hydrological conditions has an increasing trend,especially in the low water level,the Poyang Lake wetland grassland advances toward the lake center. |
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