Hydrodynamically Controlled Abiotic Recycling of Organic Phosphorus in Riparian Sediments

Abstract

Organic phosphorus (OP), a major phosphorus pool in sediments, can be converted into bioavailable phosphate. Although biological activity is considered the primary driver of OP dephosphorylation, the abiotic mechanism under redox oscillations remains unexplained. Here, we show that hydrological perturbation-driven redox fluctuations can mediate abiotic phosphate release from OP. Through laboratory simulations and analyses of natural riparian sediments, we demonstrate that the dark production of reactive oxygen species (ROS) is essential for this process. Hydroxyl radical (^•OH)-mediated oxidation emerges as the dominant dephosphorylation pathway, with superoxide (O₂^•-) and hydrogen peroxide (H₂O₂) acting as key intermediates. Redox oscillations enhance the mobilization of sedimentary OP into the dissolved phase, thereby accelerating its ROS-mediated dephosphorylation. Investigations of natural sediments confirm that ROS produced during redox oscillations drive abiotic OP mineralization, with reaction rates controlled by sediment electron-exchange capacity and iron speciation. These results reveal a previously unrecognized abiotic pathway for OP transformation that operates alongside enzymatic hydrolysis, photodegradation, and mineral-catalyzed degradation.