Riparian buffers function as bidirectional filters and hotspots for the removal of riverine microcystin

Abstract

Microcystins (MCs), a group of highly toxic compounds produced by cyanobacteria, pose risks to both aquatic and terrestrial ecosystems. Though riparian buffers are widely recognized for their role in mitigating land-sourced pollution, their capacity to attenuate riverborne MCs remains understudied. In this study, we combined field monitoring, laboratory column experiments, and microbial community analyses to evaluate the capacity of riparian soils to remove MCs under dynamic river-groundwater exchange. Field data collected from a tidal river revealed bidirectional hydraulic gradients and elevated MC concentrations in groundwater wells during the river infiltration phase, suggesting that riverine MCs can intrude into riparian zones. Meanwhile, the flow-through column experiment demonstrated 90% MC mass retention relative to chloride, with first-order degradation rate constants ranging from 1.02 to 1.15 day⁻¹. Microbial analyses revealed that riparian soils harbored Sphingomonas, Novosphingobium, and other taxa with MC-degrading potential. Furthermore, key genes associated with MC degradation were identified in the samples. These findings highlight the role of riparian buffers as overlooked filters for riverborne MCs. Understanding the fate of MCs in riparian systems can further inform watershed management strategies to mitigate cyanotoxin pollution in aquatic environments.