Study On The Hydrological Situation And Ecological Water Level Threshold Of Dongting Lake Wetland

Dongting Lake is the first great lake in the middle and lower reaches of the Yangtze River and an important wetland nature reserve in the world.Its special geographical location makes up the special water system structure of the river-river-lake connection.The region is rich in freshwater resources,fertile land,a wide variety of plants and animals,with good wetland ecological benefits.In recent years,due to the impact of climate change and human activities,the ecological environment of the wetland in Dongting Lake has been seriously damaged.Therefore,in order to alleviate the continuous deterioration of the ecological environment of the Dongting Lake wetland,we studied the evolution law of the eco-hydrological situation and the ecological water level threshold of the Dongting Lake wetland.Firstly,this paper summarizes Dongting Lake from three aspects of geography,landform and climate,and introduces its biological status and ecological problems,highlighting the importance of ecological construction.In order to carry on the scientific research to Dongting Lake comprehensively,we divided the whole Dongting Lake into three regions: east,south and west,each region takes two hydrological.The long-term hydrological data of each hydrological station are studied,and the characteristics of hydrological situation change in Dongting Lake for many years are analyzed in detail.,through to the spatial and temporal variation characteristics of Dongting Lake and the water level trend,periodic and paroxysmal analysis we concluded that the west and low in water distribution pattern in Dongting Lake.The water level difference of each lake area is small and the water level difference is large in dry season.The reason is that water level connectivity decreases in dry season,the water exchange weakened;The water level of Dongting Lake began to rise from March to May,rose sharply from June to August,reached its peak in July,and decreased from November to February to enter the dry season.According to the Mann-Kendall trend test,the water level of eastern and southern Dongting Lake showed a trend of increasing from 1959 to 2016,among which the Chenglingji Hydrographic Station showed an obvious trend of increasing and passed the 99% confidence test,while the water level of Western Dongting Lake showed a decreasing trend and the decreasing trend was obvious and both passed the 90% confidence test.According to the wavelet analysis,the water level periods of Dongting Lake in the east,south and west are 26,26 and 32 years respectively.Through the comprehensive analysis of Mann-Kendall mutation test,sliding T test and cumulative anomaly method,the water level variation points of Dongting Lake in the east,south and west are 1979 and 2003.Therefore,1959-1978 is considered as the hydrologic morphology of the lake in a near-natural state.1979-2002 is the first variation stage,and 2003-2016 is the second variation stage.In order to explore the causes of hydrological variation,the contribution rate of human activities and climate change in hydrological variation was calculated by the method of cumulative slope change rate.In the south of Dongting Lake and west Dongting Lake from 1979 to 2002 is given priority to with human activities cause the phase change,east Dongting Lake is given priority to with rainfall factors lead to the phase change;From 2003 to 2016,the variation of south Dongting Lake and west Dongting Lake was mainly caused by rainfall,while the variation of east Dongting Lake was mainly caused by human activities.Secondly,in order to discuss the degree of Dongting Lake in the hydrological variation of hydrological change and the impact on the ecological,by IHA index system,with the method of variable scope(RVA)and histogram matching method(or HMA,the Dongting Lake each hydrological station in the 1979-2002 period(T1),and 2003-2016 period(T2)of hydrology change degree was calculated,the result showed that: East Dongting Lake Chenglingji Station had moderate changes in period of T1,T2,Lujiao had low changes during T1 period and antlers had moderate changes during T2 period;The stations of Yangliutan and Yingtian in south Dongting Lake changed at a low degree in T1 and T2 periods.The changes of Nanzui and Xiaohezui in west Dongting Lake were low in T1 period and moderate in T2 period.Finally,based on the hydrological change index method and range method commonly used in the calculation of river ecological discharge,constructed including the lowest ecological water level,the annual high and low water level,the time of of high and low water level,the duration of high and low water level and the change rate of water level in special period,a total of eight indicators index system of ecological water level,and calculated the average and range of each index in detail.The research results are different from the previous research on only a single ecological water level value,it highlights the fluctuation range of ecological goals,conforms to the actual requirements of ecological development,and can also provide a more scientific theoretical basis for the local government to regulate the amount of water.