Reactive oxygen species affect the potential for mineralization processes in permeable intertidal flats

Marine permeable sediments are important sites for organic matter turnover in the coastal ocean. However, little is known about their role in trapping dissolved organic matter (DOM). Here, we examined DOM abundance and molecular compositions (9804 formulas identified) in subtidal permeable sediments along a near- to offshore gradient in the German North Sea. With the salinity increasing from 30.1 to 34.6 PSU, the DOM composition in bottom water shifts from relatively higher abundances of aromatic compounds to more highly unsaturated compounds. In the bulk sediment, DOM leached by ultrapure water (UPW) from the solid phase is 54 ± 20 times more abundant than DOM in porewater, with higher H/C ratios and a more terrigenous signature. With 0.5 M HCl, the amount of leached DOM (enriched in aromatic and oxygen-rich compounds) is doubled compared to UPW, mainly due to the dissolution of poorly crystalline Fe phases (e.g., ferrihydrite and Fe monosulfides). This suggests that poorly crystalline Fe phases promote DOM retention in permeable sediments, preferentially terrigenous, and aromatic fractions. Given the intense filtration of seawater through the permeable sediments, we posit that Fe can serve as an important intermediate storage for terrigenous organic matter and potentially accelerate organic matter burial in the coastal ocean.

Section: Discussionmentioning

confidence: 69%

Section: Introductionmentioning

confidence: 99%

Iron Promotes the Retention of Terrigenous Dissolved Organic Matter in Subtidal Permeable Sediments

Zhou,

Waska,

Henkel

et al. 2024

“…6,11 One such possibility involves the intermittent redox cycle, during which ROS can be produced through the transfer of electrons from reduced species [e.g., Fe(II) and organic matter] to molecular oxygen. 12,13 Given the widespread occurrence of redox interfaces in the soil environment, such as riparian zones, 14 intertidal flats, 1 rhizosphere, and detritusphere, 7,15 ROS production in these zones might be prevalent and plays a crucial role in pollutant remediation, carbon emission, and biological activities. 1,16,17 Riparian zones, usually recognized as transitional areas between aquatic and terrestrial ecosystems, are intermittently inundated or water logged along with the temporal and spatial changes, which further induce the oxic−anoxic fluctuations.…”

Section: ■ Introductionmentioning

confidence: 99%

Seasonal and Spatial Fluctuations of Reactive Oxygen Species in Riparian Soils and Their Contributions on Organic Carbon Mineralization

Liu,

Wang,

Liu

et al. 2024

Reactive oxygen species (ROS) are ubiquitous in the natural environment and play a pivotal role in biogeochemical processes. However, the spatiotemporal distribution and production mechanisms of ROS in riparian soil remain unknown. Herein, we performed uninterrupted monitoring to investigate the variation of ROS at different soil sites of the Weihe River riparian zone throughout the year. Fluorescence imaging and quantitative analysis clearly showed the production and spatiotemporal variation of ROS in riparian soils. The concentration of superoxide (O 2•− ) was 300% higher in summer and autumn compared to that in other seasons, while the highest concentrations of 539.7 and 20.12 μmol kg −1 were observed in winter for hydrogen peroxide (H 2 O 2 ) and hydroxyl radicals ( • OH), respectively. Spatially, ROS production in riparian soils gradually decreased along with the stream. The results of the structural equation and random forest model indicated that meteorological conditions and soil physicochemical properties were primary drivers mediating the seasonal and spatial variations in ROS production, respectively. The generated • OH significantly induced the abiotic mineralization of organic carbon, contributing to 17.5−26.4% of CO 2 efflux. The obtained information highlighted riparian zones as pervasive yet previously underestimated hotspots for ROS production, which may have non-negligible implications for carbon turnover and other elemental cycles in riparian soils.

“…1−3 In subsurface settings, oxygen (O 2 ) fluctuation occurs frequently due to the decline in the water table, leading to the oxygenation of reduced substances like Fe(II)-bearing minerals and the consequent production of reactive oxygen species (ROS). 4−6 Intense ROS production has been documented in various natural systems, such as river aquifers, 4 marine sediments, 7 and coastal soils. 8 The important roles of ROS in biogeochemical processes, like nutrient cycling, redox-active metals transformation, and organic contaminants degradation, have gained increasing attention.…”

Section: ■ Introductionmentioning

confidence: 99%

“…Redox-fluctuating zones are critical for element cycling [e.g., carbon (C) and iron (Fe)] and contaminants transformation (e.g., cadmium and polycyclic aromatic hydrocarbons). − In subsurface settings, oxygen (O 2 ) fluctuation occurs frequently due to the decline in the water table, leading to the oxygenation of reduced substances like Fe(II)-bearing minerals and the consequent production of reactive oxygen species (ROS). − Intense ROS production has been documented in various natural systems, such as river aquifers, marine sediments, and coastal soils . The important roles of ROS in biogeochemical processes, like nutrient cycling, redox-active metals transformation, and organic contaminants degradation, have gained increasing attention. ,,, For instance, previously overlooked ROS production triggered by flooding–drainage cycles in surface paddy soils have been shown to contribute to greenhouse gas emissions like carbon dioxide (CO 2 ) and nitrous oxide (N 2 O). ,, …”

Section: Introductionmentioning

confidence: 99%

Dynamic Production of Hydroxyl Radicals during the Flooding–Drainage Process of Paddy Soil: An In Situ Column Study

Huang,

Chen,

Zhu

et al. 2023

Frequent cycles of flooding and drainage in paddy soils lead to the reductive dissolution of iron (Fe) minerals and the reoxidation of Fe(II) species, all while generating a robust and consistent output of reactive oxygen species (ROS). In this study, we present a comprehensive assessment of the temporal and spatial variations in Fe species and ROS during the flooding–drainage process in a representative paddy soil. Our laboratory column experiments showed that a decrease in dissolved O2 concentration led to rapid Fe reduction below the water–soil interface, and aqueous Fe(II) was transformed into solid Fe(II) phases over an extended flooding time. As a result, the •OH production capacity of liquid phases was reduced while that of solid phases improved. The •OH production capacity of solid phases increased from 227–271 μmol kg–1 (within 1–11 cm depth) to 500–577 to 499–902 μmol kg–1 after 50 day, 3 month, and 1 year incubation, respectively. During drainage, dynamic •OH production was triggered by O2 consumption and Fe(II) oxidation. ROS-trapping film and in situ capture revealed that the soil surface was the active zone for intense H2O2 and •OH production, while limited ROS production was observed in the deeper soil layers (>5 cm) due to the limited oxygen penetration. These findings provide more insights into the complex interplay between dynamic Fe cycling and ROS production in the redox transition zones of paddy fields.