Water level management plan based on the ecological demands of wintering waterbirds at Shengjin Lake

Abstract

A reasonable hydrological regime is of great significance for ecosystem services and wildlife habitat management in river-connected lakes. Shengjin Lake is a Ramsar site with international importance for wintering migratory waterbirds. Since the Huangpen River sluice began operations, the lake’s hydrological rhythm was changed. We investigated the effect of different hydrological conditions under water level control on the abundance of waterbird foraging guilds using habitat as an intermediary. First, linear models of 12 years dataset (2008–2019) based on waterbird surveys and satellite remote sensing images were constructed to analyse the relationship between habitat area and water level. 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 guild was predicted at intervals of 0.10 m at the water level. Overall, 60% of the abundance of waterbird foraging guilds could be explained by water level with habitat as an intermediary, and this was affected by the rate of change of their preferred habitat area with water level increase. When the water level was less than 10.2 m, the meadow area was negatively correlated with the D80 water level (average water level of 71–80 days before waterbirds wintering), which was the main factor that affected tuber foragers and seed foragers/dabbling waterbirds. The abundance of food for these herbivorous waterbirds during the middle wintering was affected by the exposed tidal flat area in October, which provided suitable conditions for the secondary growth of grass. Starting from 10.20 m, waterbird abundance rapidly reduced with a sharply increasing water area, which was influenced by artificial sluice control and reduced rainfall. Therefore, management should be focused on appropriately lowering the water level in the early wintering period. Considering the suitable habitat area, hysteresis of meadow growth, and residential water demand, a water level control scheme was recommended to be 8.65–9.50 m in the early wintering period, 8.11–8.80 m in the middle wintering period, and 8.09–9.40 m in the late wintering period. The results of this study will help to promote the reasonable water level control for the lakes as the wintering grounds of migratory waterbirds.