| Hydrological regime is one of important environmental elements in wetland ecosystem and its change could directly affect the structure pattern and ecological functions of wetland ecosystem.This thesis chose Dongting Lake was study area,and focused on the variation features of hydrological regimes under the background of climate change and human activity.And then,qualitative or quantitative analyses were carried out to study the effects of climate change and human activity on hydrological regimes.Last,wetland conservation measures under the changing environment were proposed to provide scientific theory basis for water resource conservation and habitat management.Firstly,statistical analysis and Mann-Kendall test were applied to reveal the change features of water level and streamflow in Dongting Lake,and explore the possible influence factors.The results showed that water level decreased during the period of 1961-1980,while increased during the period of 1981-2002.Moreover,the variation trend of water level after 2002 increased at the 5%significance level.The variation in the dry season was more obviously than that in the wet season.The date when water level was firstly below 24 m during the period of 2003-2010 appeared about 27 days earlier than usual,and the date was even advanced to mid-September in 2006.As for the duration,water level was below 24 m for about 185 days in the period of 2003-2010 and 30-40 days longer than the period of 1961-1980 and 1981-2002.The trend of streamflow of "four waters" was stable and changed obviously during the period of 1983-1994.Meanwhile,the trend of streamflow of“three outfalls”and Chenglingji decreased especially after 2002.The result of MK test showed that 2003 was the common change point of streamflow and climatic variables.Compared with the period of 1961-2002,the ratio of "four waters"streamflow in the regional water balance during the period of 2003-2010 increased while the ratio of "three outfalls" streamflow,climatic variables and other human activities reduced by 25.66%,40.48%and 6.78%respectively.In conclusion,hydrological regimes might be influenced by a combination of anthropogenic and climatic factors in Dongting Lake.Secondly,sensitivity analysis based on Budyko type equations was applied to reveal the contributions of climate variability and human activity on streamflow variation.The time series(1961-2010)was divided into three periods,namely natural period(1961-1980),change period I(1981-2002)and change period II(2003-2010).The results showed that during the change period I,climate variability was the main factor responsible for streamflow alteration in most parts of Dongting Lake,accounting for 60.07%-67.27%.However,the impact of climate variability was slightly smaller than that of human activity in West Dongting Lake(the former accounting for 43.20%while the latter accounting for 56.80%).For the change period?,human activity was the dominate factor for streamflow alteration,accounting for 58.89%-78.33%.The impact of climate variability gradually decreased while the impact of human activity gradually increased.Along with the intensification of the human activity,the impact of it became more dominant.Finally,Redundancy Analysis combined with forward selection procedure was applied to select the hydrological and climatic variables with significant influences.Then,Response Surface Methodology was carried out to identify the thresholds of the variables.To better interpret the ecological significance,we divided the bird species into five functional groups on the basis of their typical feeding habits.The results showed that inflow and water level were probably the two critical variables accounting for 52.13%(P = 0.001)and 47.87%(P = 0.021)of the variation in the bird species,respectively.As for the group-level,different functional bird groups had different reflections to inflow and water level.Minimal guaranteed values of the two variables were identified as 3518.82-3736.28 m~3/s and 22.61-23.49 m respectively based on the hydrological requirements and the weights of all groups(namely,0.010.37?0.33?0.20 and 0.09).The results highlighted that the minimal requirements of inflow and water level should be satisfied to provide appropriate habitats for waterbirds.Besides,the regulatory authorities and environmental protection agencies should develop relevant law or regulation to protect waterbird habitats from human destruction especially the activities which could change the hydrological regime.The results could provide a reference for water resources planning and management decisions.As for wetland conservation,under the circumstance of uncontrollable climate change,effective measures for reservoir operation should be put forward to maintain the ecological integrity and ensure water release and storage capacity of aquatic ecosystems.Moreover,reasonable measures should be taken to protect and optimize wetland landscape,such as return part of area to river,expand the flood channel,and enhance the capacity of the discharge river flood.Meanwhile,in some important habitat,excessive development should be prohibited and closed management should be put forward based on the identification the priority protection area and the core protection area. |
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