- Mineral Protection and Resource Limitations Combine to Explain Profile-Scale Soil Carbon Persistence JOURNAL OF GEOPHYSICAL RESEARCH-BIOGEOSCIENCES 2022; 127 (4)
Export of Organic Carbon from Reduced Fine-Grained Zones Governs Biogeochemical Reactivity in a Simulated Aquifer.
Environmental science & technology
Sediment interfaces in alluvial aquifers have a disproportionately large influence on biogeochemical activity and, therefore, on groundwater quality. Previous work showed that exports from fine-grained, organic-rich zones sustain reducing conditions in downstream coarse-grained aquifers beyond the influence of reduced aqueous products alone. Here, we show that sustained anaerobic activity can be attributed to the export of organic carbon, including live microorganisms, from fine-grained zones. We used a dual-domain column system with ferrihydrite-coated sand and embedded reduced, fine-grained lenses from Slate River (Crested Butte, CO) and Wind River (Riverton, WY) floodplains. After 50 d of groundwater flow, 8.8 ± 0.7% and 14.8 ± 3.1% of the total organic carbon exported from the Slate and Wind River lenses, respectively, had accumulated in the sand downstream. Furthermore, higher concentrations of dissolved Fe(II) and lower concentrations of dissolved organic carbon in the sand compared to total aqueous transport from the lenses suggest that Fe(II) was produced in situ by microbial oxidation of organic carbon coupled to iron reduction. This was further supported by an elevated abundance of 16S rRNA and iron-reducing (gltA) gene copies. These findings suggest that organic carbon transport across interfaces contributes to downstream biogeochemical reactions in natural alluvial aquifers.
View details for DOI 10.1021/acs.est.1c04664
View details for PubMedID 35072465
Effects of moisture and physical disturbance on pore-scale oxygen content and anaerobic metabolisms in upland soils.
The Science of the total environment
2021; 780: 146572
Soils are the largest dynamic stock of carbon (C) on Earth, and microbial respiration of soil organic C accounts for over 25% of global carbon dioxide (CO2) emissions. Zones of oxygen depletion in upland soils (anaerobic microsites) are increasingly recognized as an important control on soil microbial respiration rates, but the factors governing the volume and distribution of anaerobic microsites are relatively unknown. We measured the dissolved oxygen (DO) content of porewater from incubated soil cores of varying moisture contents (<80% and >80% water saturation) and degrees of disturbance (undisturbed, conventionally tilled, and physically disturbed). Porewater was extracted sequentially from pores constrained by three effective pore diameters, ≥3.0mum, 3.0-1.0mum, and 1.0-0.6mum, from cores incubated for 7, 14, or 28days, using a modified Tempe cell extraction system. We observed a parabolic pattern in mean dissolved oxygen (DO) concentrations across pore sizes, independent of soil moisture and degree of disturbance. Specifically, DO values within the largest and smallest pore domains were relatively depleted (155±10muM and 160±11muM, respectively), while DO values within medium pores were closer to saturation (214±8muM). The observed DO pattern provides insight into the balance of microbial oxygen demand versus oxygen supply across pore domains within upland soils. Additionally, we observed iron and manganese reduction in all soils except samples subjected to disturbance and incubated at <80% water saturation, suggesting that disturbance enhances aeration and diminishes anaerobic metabolisms within upland soils. Our findings highlight the influence of soil moisture and management on soil redox and CO2 efflux rates.
View details for DOI 10.1016/j.scitotenv.2021.146572
View details for PubMedID 33774307