Riparian Buffers as a Bidirectional Filter: Hotspots for Removal of Riverine Microcystin

Microcystins (MCs), a group of highly toxic compounds produced by cyanobacteria, pose risks to both aquatic and terrestrial ecosystems. Riparian buffers are widely recognized for mitigating land-derived pollution, but their capacity to attenuate river-derived MCs remains understudied. Here, we combined field monitoring, laboratory column experiments, and microbial community analyses to assess the capacity of riparian soils to remove MCs under dynamic groundwater-river exchange conditions. Field data from a semi-diurnal tidal river revealed bidirectional vertical hydraulic gradients and elevated MC concentrations, suggesting that riverine MCs can intrude into riparian zones. 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 sequencing revealed enrichment of potential MC-degrading taxa such as Sphingomonas and Novosphingobium in riparian soils. These findings highlight the role of riparian zones as critical yet often overlooked biogeochemical filters for riverborne MCs. Understanding the fate of MCs in riparian systems can inform watershed management strategies to mitigate cyanotoxin pollution in aquatic environments.