Process-based modeling to reveal spatio-temporal variations of coastal wetland-mediated nutrient removal.

Nutrient pollution intensifies the strain on coastal ecosystems globally. Despite wetlands' significant nutrient removal potential, process-based assessments of nutrient removal in large-scale coastal wetlands face limitations that hinder accurate quantification of water quality improvements. This study proposes a novel quantitative approach by developing a coupled hydrodynamic-water quality-wetland biogeochemical model. The spatio-temporal distributions of water-sediment-vegetation nutrients in a coastal wetland and bay were simulated over an annual cycle, with model parameters and results calibrated and validated through field investigations and laboratory experiments. The findings show distinct spatio-temporal characteristics of nutrient pollutant reduction in coastal wetlands. In the Liaohe estuarine tidal wetland, a large-scale coastal wetland in China, nitrogen and phosphorus reduction fluxes reached 1184 t·yr and 53 t·yr, accounting for 19 % and 12 % of the river's fluxes to the sea, respectively. These results underscore the critical function of coastal wetlands in mitigating coastal nutrient pollution. This study presents a novel framework for quantifying coastal water quality improvements by wetlands on a larger scale.