Study On The Impact Of Water Level Fluctuation On Avian Community In The Hanfeng Lake Of The Three Gorges Reservoir

Water is the core element of wetland ecosystem,and determines the structure and function of wetland ecosystem.Water level fluctuations in the wetland,especially their extent,frequency and duration,are dominant forces controlling the functioning of the ecosystem.Species in the wetland are affected directly or indirectly,and form the corresponding adaptive strategies and response mechanism.Comparison with the general reservoirs,lakes,rivers,the Three Gorges Reservoir has the characteristics of anti-season water lever change and high water level drop,whose habitat structure between the high water level and the low water level are quite different with the continuous and dynamic changes.The impact of the construction and operation of the Three Gorges Reservoir on biodiversity has attracted the attention of researchers both at home and abroad.In order to study the response relationship of bird community structure,diversity and spatial distribution pattern to water level changes after the impoundment of large reservoirs,we conduct surveys on the avian community and diversity at the different water levels of the Hanfeng Lake,located at the center of the Three Gorges Reservoir,from June 2013 to January 2017,aiming at accumulating the long-term change data of biodiversity under the influence of water level fluctuations by the Three Gorges Reservoir,and providing scientific basis for biodiversity conservation and management decision-making of large reservoirs at home and abroad.The results of the thesis are articulated as below:(1)A survey on the avian community and its diversity had been conducted In February 2014-January 2017.126 bird species were recorded,belonging to 34 families of 13 orders,62 of which were wetland birds,containing waterfowls(23 species),shorebirds(21 species),egrets(8 species)and rallidaes(6 species).(2)The research showed that the avian community structure and diversity were affected significantly by the water level fluctuation in the different seasons.During the low water level period in summer(August,at the water level of 152.50m),avian richness(34 species)and Shannon-Wiener index were the highest,and the carnivore and insectivore ones were main feeding functional groups;due to diverse types of habitats,vigorously growing plants and abundant food resources.This period provided suitable habitats for passeriformes,egrets,rallidaes,and so on.During the high water level period of the Hanfeng Lake in winter(December,at the water level of 174.50m),avian Shannon-Wiener index and Pielou index were the lowest and the herbivores birds were the main feeding functional group;however the number of birds was the largest due to the open water with single type of habitat in this period,and the open water was favorable for ducks clustering to overwinter.(3)Avian diversity was significantly different along the elevation gradient.The change trend of species richness,abundance,Shannon-Wiener index,Pielou evenness index was the same along the elevation gradient: ? zone(165.00-175.00m)>?zone(152.50-155.00m)> ? zone(155.00-165.00m).Egrets and rallidaes distributed mainly in the?zone with water mainly and diversity types of habitats,passeriformes distributed mainly in the ? zone with richest herbaceous plant community diversity.Avian diversity was the lowest in the ? zone with single type of habitat,Canodon dactylon as the dominant vascular plant,grass seeds and insects deficient.Dike-ponds in the ? zone could provide refuges and rich food resources for egretsand rallidaes,therefore to increase the avian diversity in summer.(4)Compared with the summer at the low water level,it was at the high water level in winter and the horizontal pattern distribution of the avian community structure was different significantly.Besides,the horizontal pattern distribution changed at the same time with the water level fluctuation.Due to the complex habitat structure and far from the urban residential areas,Wuyang Ba was the main wintering habitat of ducks,where the number was more than eighty percent of birds in winter.Due to the water releasing,shallow water swamp contained plentiful plant residues,which were important food resources for ducks.The Hanfeng Lake released water level from the 175.00 m,Shuidong Ba and Toudao river estuary generated a certain area of shallow water marsh wetlands,where abundant plant residues available for ducks feeding,with islands for birds resting.Therefore,As a result,they attracted nearly two hundred ducks to forage and rest.The abundance of birds and the number of individuals in these two sampling sites increased significantly.Water level fluctuations led to changes of the habitat structure,and thus affected the original avian spatial pattern of the Hanfeng Lake.