Water Level Management Plan Based On The Ecological Demands Of Wintering Waterbirds At Shengjin Lake

Hydrological conditions are the foundation for river-connected lakes to maintain their ecosystem services function.A reasonable water level control scheme is of great significance for wildlife habitat management in lakes.As a typical shallow lake in the middle and lower Yangtze River floodplain,Shengjin Lake provide adequate habitat for wintering migratory waterbirds.The construction of the Huangpen Sluice changed the original hydrological rhythm and adversely affected waterbirds.In this paper we investigated the effect of different hydrological conditions under water level control on the abundance of waterbird foraging guilds using habitat as a concern.First,linear models were constructed to analyze the impact of the dynamic changes of water level on the habitat areas through continuous long-term simulation(2012–2019).Then,generalized linear mixed models were used to explore the effects of habitat area on abundance in different waterbird foraging guilds.Finally,the abundance of each type of waterbird foraging guild was predicted at intervals of 0.1 m at the water level through the quantitative relationship of water level-habitat-waterbird foraging guild.Considering the operability of water level regulation,water demand for local resident,the suitable habitat area for waterbirds,and hysteresis of meadow growth,a water level control plan to meet the ecological needs of wintering waterbirds was proposed.The main results were as follows:1.The dynamic change of waterbird community structure changed significantly with the year and month.The average maximum number of waterbirds was 64,264,and total waterbird number reached the maximum in December and January each year.Other community indexes also showed similar temporal patterns,such as density and diversity index.The number of waterbirds foraging guilds in the wintering period increased first and then decreased.Throughout the wintering period,the number of the grass foragers was largest,while the rhizome foragers was the smallest.The waterbirds of fish foragers and zoobenthos foragers accounted for the largest proportion in the early period of wintering.The number of seed foragers was the largest in the middle and late wintering.2.Habitat area was significantly affected by water level changes.There was a significant positive correlation between water level and water area(P<0.05).As the water level rose,the water area slowly increased initially and then rapidly increased after reaching 10.2 m.Up to 11m,the growth rate began to slow down again.When the day water level was?10.2 m,the relationship between water area and the day water level was better fitted(R~2=0.825,P<0.001)with the quadratic regression equation.The mudflat and meadow areas had the greatest correlation with the D80 water level(the average water level value of the 71-80 days before the day)and were explained the best with the quadratic regression model(R~2=0.714,P<0.001)and the exponential model(R~2=0.771,P<0.001),respectively.When the water level of the day was>10.2 m,the habitat area was highly correlated with the day water level.The water area(R~2=0.954,P<0.001)and the mudflat area(R~2=0.933,P<0.001)were better fitted by the quadratic regression model,and the exponential model(R~2=0.506,P<0.001)was better for the meadow area.3.The abundance of different waterbird foraging guilds was affected differently by habitat area.The fish and zoobenthos foragers preferred shallow water.The meadow area was more important for rhizome and seed foragers.A larger meadow area was beneficial to increase the number of these three types of foraging guilds.For the total number of waterbirds,the importance order of habitat was:meadow area>water area>mudflat area.During the whole waterbird wintering period,mudflats and meadows were mainly distributed on the south side of the upper lake and the lower lake of Shengjin Lake.They were the main places affected by water level changes,as well as the main habitats for grass foragers and rhizome foragers.4.The effect of the D80 water level and the day water level varied among different foraging guilds.As the D80 water level increased,fish foragers showed an upwards trend,but the other guilds showed the opposite trend.Except for rhizome foragers and seed foragers who were greatly affected by the D80 water level,other guilds were more affected by the day water level.As the day water level increased,their abundance gradually decreased.Waterbirds showed similar patterns in early and late wintering with the change in water level.After considering the operability of water level regulation,water demand for local resident,the suitable habitat area for waterbirds,and hysteresis of meadow growth,the suitable water levels in the early,middle,and late wintering periods should be 8.65–9.5 m,8.11–8.8 m,8.09–9.4m respectively.