Modeling the effect of artificial flow and sediment flux on the environment and plankton of an estuary

Abstract

Estuarine environments are influenced by both river flows and oceanic tidal movement of water, sediment, and nutrients, often forming ecosystems that are rich in resources and biodiversity. The Yellow River once carried the world's largest sediment load, but artificial structures have transformed its hydrodynamic processes. An annual Water–Sediment Regulation Scheme (WSRS) was introduced to flush accumulated sediment from the Xiaolangdi Reservoir, which provides flood control and water storage. However, the effect of the WSRS process on the runoff and sediment conditions, nutrients, and ecological environment of the Yellow River Estuary and adjacent ocean are not well understood. In the current study, a coupled hydrodynamic–nutrient–plankton ecosystem dynamics model (FVCOM–FABM–NPZD) was constructed to simulate changes in the ecological parameters and in the vertical response in the Yellow River Estuary before, during, and after the WSRS, This model also was used to quantify the effects of changes in the incoming material flux on the hydrodynamic and ecological environment of the estuary, using the Yellow River Xiaolangdi Reservoir water transfer and sand transfer as an example. The study found that the WSRS changed the spatial and temporal distribution of temperature, salinity, sediment, inorganic nitrogen, and phytoplankton in the Yellow River Estuary and adjacent waters. It also had a significant effect on the temperature, salinity, and ecology of the adjacent near-shore marine environment. The spatial and temporal responses of zooplankton and phytoplankton to the WSRS differed. Zooplankton showed a lag in response to the WSRS and were mainly influenced by temperature and phytoplankton. The phytoplankton concentration was positively influenced by inorganic nitrogen and negatively influenced by salinity and sediment. In the current study, the effects of changes in the flow and sediment flux from the WSRS on environmental factors and zooplankton in the Yellow River Estuary were simulated, providing a theoretical basis for scheduling the release of water and sediment in the Yellow River basin and providing a reference for water and sediment regulation in other reservoirs upstream of the estuary.