Permeable Biofilms Can Support Persistent Hyporheic Anoxic Microzones

Abstract

Experimental observations reveal the existence of anoxic microzones within oxygen‐rich aquatic sediments. The microzones are hotspots of enhanced removal of nitrate and production of greenhouse gas nitrous oxide. Here we established a new microscale flow, reactive transport and biofilm growth model and explore how anoxic microzones form and evolve within hyporheic zones under dynamic interactions among pore‐scale flow, reactive transport and biofilm growth. The microzones can form and evolve by two patterns as streambeds are progressively clogged due to biofilm growth: (a) physical and biogeochemical conditions‐dependent perennial microzones for permeable biofilms, and (b) physical and biogeochemical conditions‐independent ephemeral microzones for low permeability biofilms. During biofilm growth, persistent transport‐dominated systems sustain for the former, whereas the transformation of transport‐dominated to reaction‐dominated systems occurs for the latter. These findings are significantly different from previous single pattern of ephemeral microzones.

Effect of Particulate Organic Carbon Deposition on Nitrate Reduction in the Hyporheic Zone

“…Thus, it is very difficult to implement because of the huge data and computational resource requirements. Conceptually, in heterogeneous streambed sediments, POC would also be deposited in the shallow streambed, reduce sediment permeability, block nutrient intrusion, and stimulate microbial growth, resulting in the shallow portion of streambeds with low permeability and high rates of biogeochemical reactions (Mendoza‐Lera et al., 2019; Sunjidmaa et al., 2022; Xian et al., 2022). In the deep streambed, biogeochemical reactions are relatively weak due to the scarcity of nutrients and microbial communities caused by sediment clogging (Caruso et al., 2017; Ping et al., 2020).…”