Study On The Impact Of Key Environmental Factors On The Dynamics And Diversity Of Anatidae In Dongting Lake

The number of waterfowl worldwide is declining.Waterbirds are one of the sensitive and vulnerable groups of wetlands.Waterbirds,one of the most sensitive and vulnerable groups,are a key criterion for Ramsar-listing of wetlands and also the most symbolic ecological indicators in assessing wetland quality.According to the literature,the diversity of waterbirds is susceptible to environmental factors such as hydrological change,climate change,and the availability of food resources,which make their reproduction,migration and foraging under pressure.Non-biological factors are vital to the availability of food resources in interconnected river-lake systems,so in addition to identifying the ecological response to the driving factors,it is also important to analyze and quantify relationships between drivers.In order to explore the impacts of these drivers on the wintering waterbirds,we selected Dongting Lake as a study area,which is a typical interconnected river-lake system in the middle and lower reaches of the Yangtze River Floodplain.The Anatidae species,most of which are herbivorous,were chosen as the representative waterfowl.Firstly,the data of the abundance,distribution,and diversity of Anatidae in Dongting Lake wetland from 2000 to 2015 were collected and analyzed.Then,the topographic data of Dongting Lake and the water level and flow data representing hydrological stations were collected.Based on the hydrodynamics module of MIKE model,the spatial distribution changes of water recession time were obtained.Combined with NDVI data and remote sensing image maps,the changes of the beginning and ending time of water recession were obtained by means of remote sensing interpretation.The independent sample t-test was used to compare whether there are significant differences in the abundance,distribution and diversity of Anatidae under normal or abnormal water recession.The results show that Unseasonably early or late water recession had a negative impact on the diversity of the Anatidae,and in particular affected population dynamics of the Lesser White-fronted goose Anser erythropus(p<0.05).Then,Pearson correlation coefficient analysis method was used to screen key environmental variables that are significantly related to waterfowl population dynamics(including distribution and abundance)and diversity changes.The selected environmental variables included: the beginning time of water recession,the ending time of water recession,the interval time of water recession,the vegetation coverage at important time nodes in the water receding stage(at the beginning time of water recession,at the ending time of water recession,when overwintering waterbirds arrived in Dongting Lake wetland,and when waterfowl were investigated in winter),as well as environmental variables such as the maximum and average vegetation coverage.The results of correlation analysis showed that the diversity of Anatidae was positively correlated with the maximum vegetation coverage(r=0.53,p< 0.01).The abundance of Bean goose Anser fabalis was positively correlated with the interval of water recession(r=0.68,p<0.1).The abundance and distribution of Lesser White-fronted goose Anser erythropus were negatively correlated to the maximum vegetation coverage(r=-0.31,p< 0.1)and the interval of water recession(r=-0.43,p<0.1),respectively.Finally,combining water level,flow,precipitation and temperature data,structural equation models were used to quantify the relationship between key environmental driving factors.The results of structural equation model showed that water level and flow of Dongting Lake had a positive and direct impact on the maximum vegetation coverage,which was intermediated by the interval of water recession.Precipitation had a negative and direct impact on the interval of water recession,but little indirect effect on the maximum vegetation coverage.The explanation ratio of the variation of the maximum vegetation coverage by water level,flow and the interval of water recession was 71%.The results of this study show that there might be a kind of hydraulic interaction between the mainstream and the lake area which affects the inundation pattern and vegetation growth stage after the flood season in the whole lake,and thus affects the foraging suitability of waterbirds.It is suggested that water compensation should be carried out within an appropriate hydraulic gradient range to optimize the timing of water recession and improve the suitability of habitat effectively.