Numerical study of nutrient responses to environmental factors in complex river-estuary interactions

A three-dimensional hydrodynamic and ecological model was constructed to understand the spatiotemporal distributions of nutrients and their dynamic responses to environmental factors in the Liao River Estuary (LRE) and Daliao River Estuary (DLRE). The simulated results were validated using observed data, demonstrating high simulation accuracy. Nitrogen nutrient concentrations were highest in spring and summer of 2023, while dissolved inorganic phosphorus (DIP) concentrations and Chlorophyll-a (Chl- a ) were highest in summer. Under scenarios of reduced nutrient loads by 10 %–30 %, the dissolved inorganic nitrogen (DIN) concentrations at selected stations decreased by 5.2 %–9.8 % and 14 %–29 %, respectively, while the DIP concentrations decreased by 2.8 %–8 % and 8.4 %–24.4 %. A 20 % discharge increase resulted in reductions of 6.61 % and 6.56 % in DIN and DIP concentrations during summer flood season, respectively. The reclamation for construction promoted the advection and diffusion of pollutants from the LRE into the sea but weakened the migration of pollutants in the DLRE. The study insights can enhance our understanding of estuarine water quality processes and provide valuable guidance for pollutant control strategies. • Nutrient dynamic responses to environmental factors were identified. • River nutrients concentration reduction was more effective in improving estuarine water environments. • High discharge promoted the nutrient migration toward the open sea in the study region. • Land reclamation promoted and weakened the pollutants migration in the LRE and the DLRE, respectively.