Satellite image-based investigation of the seasonal variations in the hydrological connectivity of a large floodplain (Poyang Lake, China)

Hydrological processes of floodplains in large river-lake systems are subjected to strong flood pulses from catchment flows and lake inundations. Hydrological connectivity (HC) is one of the important characteristics of floodplains that can be used to provide evidence of mass and energy transport that influences the health of ecosystems and the biological productivity of floodplain water bodies. This study used geostatistical methods in combination with remote sensing data (2000-2015) to investigate the hydrological connectivity in a complex river-lake floodplain (Nanji Wetland National Natural Reserve) of the Poyang Lake floodplain, which is naturally connected to the middle Yangtze River. The geomorphic characteristics of the study area were characterized by the connection of surface water bodies including rivers, wetlands, sub-lakes and main lake. Results of this research indicated the apparent seasonal shifts of the dominant hydrological factors that affect the spatial-temporal changes of HC. In particular, we find that the main lake stage plays a dominant role in determining the hydrological connectivity during the lake's flooding and receding periods. We also find the existence of a threshold that causes an abrupt change of HC, i.e., if the main lake stage is below this threshold, the whole system becomes weakly hydrologically-connected. This threshold is related to the local topography, but has ecological implications for the entire floodplain system. The outcomes of this research provide an improved understanding of the hydrological behaviour of the catchment-floodplain-lake system. Considering the encountering of consistent drought of the lakes in the middle Yangtze River, this work may help clarify the intensity of the drought impacts on the ecologically important floodplains, and also assist in optimizing the interactions between the lake and the Yangtze River.