Optimising hydrological conditions to sustain wintering waterbird populations in poyang lake national natural reserve: Implications for dam operations

Poyang Lake is the largest freshwater lake in China and is of global importance for the conservation of migratory waterbirds of the East Asian - Australasian Flyway. Recent dam construction on the Yangtze River and its tributaries for agriculture and hydroelectric power has affected the hydrological regimes in downstream lakes. The Three Gorges Dam changed the hydrological regime of downstream lakes by reducing wet season flooding and expanding water storage in the dry season. Despite the critical role of Poyang Lake in regional and global biodiversity conservation and the potential adverse ecological impacts of the Three Gorges Dam on downstream lakes, there have been few studies of the hydrological requirements of wintering waterbirds in the middle Yangtze floodplains. We assembled a predictor matrix including three hydrological variables (annual inflow, maximum water level in high water season or MaxWL and minimum water level in low water season or MinWL) and two climatic variables (annual rainfall and biological cumulative temperature or BioT). Using the predictor matrix and annual waterbird census, we built group-specific generalised additive models (GAM) to investigate how waterbird population variations were related to climatic and hydrological factors in the Poyang Lake National Natural Reserve. We then used the modelled predictor-response curves to identify the optimal lake water levels for each waterbird group. The community-level model selected group and the group-varying-coefficient term of BioT, Inflow and MaxWL as explanatory variables. At group level, tuber eaters and sedge foragers responded positively to BioT and MinWL. Seed eaters, invertebrate eaters and fish eaters responded positively to Inflow and negatively to MaxWL and MinWL. Based on the modelled predictor-response curves, we propose the following optimal water level ranges for Poyang Lake wintering waterbird conservation: a) maximum high water season level should be less than 17.4 m; and b) minimum low water level should be between 8.2 m and 8.8 m.