Unravelling the spatiotemporal trade-offs and synergies among hydrological ecosystem services in a large floodplain lake

Understanding the dynamics of ecosystem services (ESs) and their interactions is vital for effective environmental management. This knowledge remains limited in highly dynamic systems, however, particularly floodplain lakes. In this study, spatiotemporal relationships were examined among four leading hydrological ESs (i.e., water supply, flood regulation, nutrient retention, and habitat support) in a large floodplain lake (i.e., Poyang Lake, China). Ecologically relevant hydrological variables were derived through two-dimensional hydrodynamic modeling and served as key ESs indicators. Specifically, water supply was represented by lake storage, flood regulation by changes in lake storage, nutrient retention service by TP retention rate calculated through an empirical model, and the habitat support by the area and presence of suitable water depth of two key biodiversity components. Results showed that hydrological processes and topographical gradients regulated the ES dynamics and interactions in Poyang Lake across time and space. The water supply service exhibited a significant co- occurrence relationship with the flood regulation and nutrient retention services, whereas a trade-off occurred with the habitat support service. However, dynamic shifts of trade-offs and synergies occurred among all ES pairs throughout the hydrological year. Spatially, the main lake channel was a hotspot for water supply, flood regulation, and habitat support services, each of which displayed significant synergistic relationships. Trade-offs occurred between water supply and nutrient retention at the southwestern edge of the wetland, as well as between habitat support and the other ESs in the central lake. Moreover, mismatches in the spatial and temporal trade- offs and synergies were identified between water supply and both nutrient retention and the habitat support services, underscoring the need for careful management strategies that can balance the spatiotemporal trade-offs and synergies of multiple ESs. This study offers valuable insights into the dynamic relationships among ESs in floodplain lakes and could provide guidance for coordinated promotion of multiple ESs in Poyang Lake and similar floodplain systems.