Spatiotemporal Evolution of Riparian Redox Zonation in Response to River Stage Fluctuation and Dynamic Biofilm Growth

Abstract

AbstractRiparian zones are one of the most complex redox‐dynamic systems, where sequential redox zones of dissolved oxygen, nitrate, manganese dioxide, ferric hydroxide and sulfate reduction commonly form. River stage dynamics and microbes are two key controls on nutrient transformation in the riparian zone. Microbial growth, on one hand, increases the biogeochemical reaction rate by altering the microbial population. On the other hand, decreases the permeability of the media due to clogging effects, thereby increasing the residence time of solutes. However, previous studies have often concentrated on steady‐state flow systems and overlooked the impacts of river stage fluctuations and dynamic microbial growth on redox zonation. In this study, we investigated the interactions among river fluctuations, nutrient supplies, microbial metabolisms, and sediment physical properties in a dynamic riparian system. A column experiment was conducted, and a one‐dimensional modeling framework that coupled flow, reactive solute transport, dynamic microbial growth and bioclogging processes was developed to study the spatiotemporal evolution of redox zonation in response to river stage fluctuations and microbial growth. Our results showed that two redox zonation patterns, including a typical sequence and an interlaced sequence, could form in the dynamic riparian zone. Increasing exogenous dissolved organic carbon concentration facilitates the occurrence of anomalous sequence redox zonation. Modeling results also indicated that ignoring microbial growth leads to a significant difference in the spatiotemporal characterization of the redox zonation, especially for a more permeable sediment. Our results implicate the occurrence of more complicated redox zonation in a dynamic riparian system than previously reported.