Multiscale Investigation on Biofilm Distribution and Its Impact on Macroscopic Biogeochemical Reaction Rates

Abstract

Biofilms are critical locations for biogeochemical reactions in the subsurface environment. The occurrence and distribution of biofilms at microscale as well as their impacts on macroscopic biogeochemical reaction rates are still poorly understood. This paper investigated the formation and distributions of biofilms in heterogeneous sediments using multiscale models and evaluated the effects of biofilm heterogeneity on local and macroscopic biogeochemical reaction rates. Sediment pore structures derived from X‐ray computed tomography were used to simulate the microscale flow dynamics and biofilm distribution in the sediment column. The response of biofilm formation and distribution to the variations in hydraulic and chemical properties was first examined. One representative biofilm distribution was then utilized to evaluate its effects on macroscopic reaction rates using nitrate reduction as an example. The results revealed that microorganisms primarily grew on the surfaces of grains and aggregates near preferential flow paths where both electron donor and acceptor were readily accessible, leading to the heterogeneous distribution of biofilms in the sediments. The heterogeneous biofilm distribution decreased the macroscopic rate of biogeochemical reactions as compared with those in homogeneous cases. Operationally considering the heterogeneous biofilm distribution in macroscopic reactive transport models such as using dual porosity domain concept can significantly improve the prediction of biogeochemical reaction rates. Overall, this study provided important insights into the biofilm formation and distribution in soils and sediments as well as their impacts on the macroscopic manifestation of reaction rates.

Inferring Subsurface Preferential Flow Features From a Wavelet Analysis of Hydrological Signals in the Shale Hills Catchment

“…While the role of a catchment as a hydrologic filter has been relatively well explored in different contexts (Dwivedi et al, 2020; Guan et al, 2011), and it has been widely accepted that the properties of filtering in a catchment could be linked more explicitly to the underlying mechanistic processes of rainfall‐runoff response (Kirchner, 2009), few studies have investigated the potentials of such a perspective in characterizing subsurface processes (e.g., PF) leading to runoff (Labat et al, 2005). PF‐dominated soil structure is often considered a dual‐pore network: a “primary” network of large (macro) pores overlapped by a “secondary” network of small (micro) pores (Frey et al, 2012; Kodesova et al, 2010; Tsakiroglou & Ioannidis, 2008; Yan et al, 2017). Accordingly, a soil system is supposed to provide dual‐pore filtering, through which the smoothing effects are likely to be stronger for matrix flows and weaker for PF via macropores (Guan et al, 2011).…”

More than Meets the Dye: Evaluating Preferential Flow Paths as Microbial Hotspots

“…Modeling results for a heterogenous aquifer system has also suggested that zones of higher conductivity result in hotspots of chemical reactivity due to enhanced mixing (Pool and Dentz, 2018). Microscale modeling work has again suggested that biofilm distribution and biogeochemical activity are increased along preferential flow paths (Yan et al, 2017).…”

Radiolysis via radioactivity is not responsible for rapid methane oxidation in subterranean air

“…In the two experiments with moist soils, we documented a CH 4 loss of of ~0.09 ppmv h -1 within the common window of CH 4 concentration decline ( Fig 3A ), as determined by subtracting the diffusive CH 4 loss in blank experiments from the bulk CH 4 loss in experiments #10 and #11 with soils ( Table 1 ). It is well established that heterogeneously distributed methanotrophic biofilms in the subsurface [ 28 ] are capable of scavenging CH 4 from the atmosphere (e.g., [ 29 , 30 ]). Soil gas can often reach 222 Rn radiation levels of many thousand Bq m -3 , depending on local geology [ 31 , 32 ].…”