Maintaining Mechanism Of Wintering Waterbird Diversity By Ecological Dykes In The East Dongting Lake Wetland

Dongting lake provides an important wintering habitat for migratory waterbirds in the East Asian–Australasian Flyway.The Dongting Lake wetlands have suffered significantly degraded trends in recent decades under the multiple effects of anthropogenic disturbances(e.g.,lake reclamation and the Three Gorges Project)and global climate change.The dykes are widespread in Dongting Lake,posing a great threat to the ecological environment of the lake,but the ecological dykes provide suitable habitat during the wintering period,and thus perform an extremely important function of maintaining waterbird diversity.To restore the natural wetland attributes of Dongting Lake,459 dykes were demolished in 2017,and 14 ecological dykes were preserved with ecological functions including flood control and biodiversity conservation.In the context of the dyke demolition in Dongting Lake,the possibility that the preserved ones can serve the more important function of waterbird diversity conservation has not been fully assessed.Therefore,this paper studied the conservation function of ecological dykes on wintering waterbird diversity and its key mechanisms.In this paper,two ecological dykes(hereinafter referred as “ ecological dyke areas ”)and three dykes with waterbird conservation functions but were demolished(hereinafter referred as “ dyke demolished areas ”)in the East Dongting Lake were selected as the study areas,and wintering waterbirds were used as the study subjects.Based on methods including historical data collection,simultaneous field surveys and remote sensing interpretation,and using various statistical methods including comparative analysis,difference analysis and correspondence analysis,we compared and analyzed the conservation function of ecological dykes in Dongting Lake on the diversity of wintering waterbirds and its key mechanisms.The main results are as follows:1.High waterbird diversity has been maintained in the ecological dyke areas for a long time,mainly at the community level(total number of species,total number of individuals,number of rare and endangered species),foraging guild(especially fish-eaters,insectivores,and omnivores),and species level(critical species other than geese),which all perform significant waterbird diversity maintenance functions.The waterbird conservation function decreased sharply in the dyke demolished areas after dyke demolition,mainly reflected in significantly decreased waterbird diversity at three levels: community,foraging guild,and species.2.During the dry period(the wintering period for waterbirds),the ecological dyke areas can maintain large areas of both water body and mudflat habitat,delaying the exposure of Carex spp.and providing rich and suitable habitat for wintering migratory waterbirds.After dyke demolition in the dyke demolished area,the accelerated rate of water recession resulted that the water body and mudflat habitat areas were significantly decreased and the Carex spp.vegetation area was significantly increased,but Carex spp.NDVI reached the maximum value significantly earlier and Carex spp.phenology phase entered the wilting stage earlier.3.The critical reason for the important waterbird conservation function in the ecological dyke areas is the diversity of suitable habitat available for wintering waterbirds,e.g.,higher percentages of water area and shallow water area,suitable Carex spp.habitat.The critical reason that waterbird diversity maintenance functions decreased in the dyke demolished areas was the rapid decline in the area of diverse suitable habitat(especially the area of water)caused by dyke demolition,which is reducing the availability of food resources and significantly reduces the conservation function of waterbird diversity.In summary,Ecological dykes provide stable and diverse habitats(water,mudflats,vegetation,etc.)for wintering waterbirds by changing the hydrological regimes of Dongting Lake during the dry period with rapidly receding water levels,and serve as a significant "water storage" function,maintaining a large water area for a long time,and maintaining a high diversity of waterbirds,which is the key mechanism of ecological dykes for the conservation of wintering waterbirds.Decreased suitability of habitat in the dyke demolished areas caused by dyke demolition can lead to decreased waterbird diversity.The results of this study have important theoretical implications for revealing the conservation mechanism of ecological dykes for wintering waterbird diversity,and realistic implications for habitat management and wetland restoration of ecological dykes.