Seasonal variation enhances dissolved arsenic dynamics in aquaculture lake at the sediment-water interface.

Aquaculture promotes the accumulation of substances in sediments and alters the microenvironment state of sediment-water interfaces (SWI). However, the response mechanism of arsenic (As) dynamics in sediments to these changes remains unclear. In this study, we employed high-resolution techniques to investigate the seasonal dynamics of As at the SWI in aquaculture-impacted lake zones, systematically analyzing its mobilization pathways and associated driving mechanisms. Our findings revealed that seasonal variability significantly influenced both dissolved As concentrations in sediment porewater (ranging from 3.54 to 88.14 μg/L) and As diffusive fluxes (ranging from 1.22 to 95.58 μg·m⁻²·d⁻¹). Dissolved As were consistently higher in the aquaculture zones than non-aquaculture areas during both spring and summer. Sedimentary As fractionations differed markedly between aquaculture and non-aquaculture zones, with aquaculture sediments exhibiting higher proportions of both non-specifically adsorbed As (F1) and specifically adsorbed As (F2). Correlation analysis indicated that F1 and poorly crystalline oxyhydroxide-bound As (F3) were major contributors to As mobilization into porewater in aquaculture zones. Partial least squares path modeling revealed distinctive key mechanisms: in non-aquaculture zones, Fe/Mn (oxyhydr) oxides dominated As dissolution processes, whereas in aquaculture zones, elevated nutrient levels modified dissolved organic matter (DOM) composition, thereby altering As speciation and enhancing its dissolution. Collectively, our study advances the understanding of As biogeochemistry at the SWI in aquaculture environments and underscores the potential amplification of As mobilization due to seasonal variability, highlighting the need for continuous monitoring and management.