Modeling and simulation with microsites on vertical concentration profiles in sediments of aquatic zones

Abstract

Modeling of reactions in sediments with microsites which have particulate organic matter (POM) in their cores as energy source for bacteria (called the M-S model) and subsequent simulation using it are executed for the explanation of vertical concentration profiles in sediment, and for the comparison with a conventional vertically one-dimensional transport-reaction model (the V-1 model). The POMs in the sediment are assumed to be sphereical with a range from 50μm to 500μm in radius and a logarithmic normal distribution. The POM size and distribution alter the concentration profiles in the sediment in the M-S model, especially NO3--N profiles, because of dependence of denitrification rate on the POM characteristics. Anoxic and anaerobic reaction rates in the sediment in the V-1 model are underestimated because of no microsite. For the practical purpose of calculating concentration profiles of substances, the M-S model has higher accuracy and controlability, and is useful for detailed explanation of reactions in the sediment.

Benthic organic carbon influences denitrification in streams with high nitrate concentration

“…, 1992; Pretty, Hildrew & Trimmer, 2006). Anoxia may additionally occur in particle‐associated microsites in an otherwise oxic environment (Sørensen, Jørgensen & Revsbech, 1979; Sakita & Kusuda, 2000). We measured denitrification on substrata (i.e.…”

“…This suggests that the active zone of denitrification begins immediately below the sediment surface, and the shallow depth to anoxia may be related to fine particles that slow penetration of oxygenated stream-water into the benthos (Vervier et al, 1992;Pretty, Hildrew & Trimmer, 2006). Anoxia may additionally occur in particle-associated microsites in an otherwise oxic environment (Sørensen, Jørgensen & Revsbech, 1979;Sakita & Kusuda, 2000). We measured denitrification on substrata (i.e.…”

Oxygen dynamics of marine sediments

“…The existence of anoxic microniches in oxic sediments has been repeatedly discussed and postulated for almost half a century in order to explain porewater profiles and organism distributions indicating anaerobic activity in otherwise presumed oxic environments (e.g. Emery & Rittenberg 1956;Jørgensen 1977;Jahnke 1985;Brandes & Devol 1995;Sakita & Kusda 2000). However, whereas reduced microniches in suboxic sediment layers are commonly observed as black enclosures or spots (e.g.…”

A physical explanation for the development of redox microzones in hyporheic flow

“…Heterogeneity of in situ carbon availability has been proposed to influence microzone formation along groundwater flow paths and within marine sediments [e.g., Sakita and Kusuda, 2000;Sawyer, 2015]. For most simulations here we assume consistent reaction rates throughout the pore network to most clearly investigate the underlying control of local hydraulic connectivity.…”

“…Decades of N 2 O and N 2 evidence collected in bulk-oxic hyporheic zones supports the hypothesis of embedded anoxic microzones [e.g., Holmes et al, 1996;Zarnetske et al, 2011;Harvey et al, 2013]; however, the mechanisms of HZ microzone formation remain speculative. The microzone concept has also been discussed for unsaturated soils [e.g., Parkin, 1987], groundwater [Sawyer, 2015], and marine sediments [e.g., Sakita and Kusuda, 2000;Lehto et al, 2014]. In each of these subsurface environments, spatial and temporal availability in particulate carbon as reaction substrate has been found to drive local anoxic conditions due to increased reaction rates.…”