Intact Core Research Articles

Use of carbon-14 labeled trichloroethene to assess degradation potential in rock core microcosms

In fractured rock aquifers contaminated with trichloroethene (TCE), the extent of groundwater plumes is impacted by degradation occurring within the rock matrix. The objective of this study was to evaluate TCE degradation in rock samples from three sites where in situ conditions may favor natural or enhanced attenuation. Intact rock core microcosms (94 total) were used to assess in situ conditions and enhancement by addition of lactate or lactate + sulfate. A key advance for this study was inclusion of carbon-14 (14C) labeled TCE in the experimental design, which enables monitoring of 14C-labeled products in addition to more readily detectable compounds associated with TCE degradation (i.e., cis-1,2-dichloroethene (cDCE), vinyl chloride, acetylene, ethene, and ethane). 14C-labeled products comprised 35–95 % of the total degradation products recovered over 9–21 months of monitoring, indicating that inclusion of 14C-TCE was essential to capturing the full potential for abiotic and biotic degradation of TCE. Microcosms infused with TCE but not 14C-TCE exhibited enrichment in δ13C-TCE, and enrichment in δ13C-cDCE in microcosms that underwent reductive dechlorination of TCE to cDCE. The results demonstrate the advantages of using diffusion-transport microcosms and 14C-TCE to document degradation of chlorinated ethenes in fractured rock aquifers.

Subsurface Sediment Transport in the Shallow Vadose Zone of Fine‐Textured Soils With Heterogenous Preferential Flows

ABSTRACTSubsurface sediment transport in tile‐drained landscapes occurs through macropores; however, little is known regarding how heterogeneous preferential flows influence fluxes. We performed laboratory rainfall simulations on 10 intact core lysimeters from a tile‐drained field in Indiana, USA to study the impacts of surface and subsurface erosion on sediment leachate in heterogeneous preferential flow paths. Seven rainfall simulations were conducted to assess the impact of rainfall intensity on the leachate of surface eroded sediments (three events), and the impact of antecedent conditions on subsurface eroded sediments (four events). Cumulative sediment yield, linear mixed effects modelling, and hysteresis analyses were performed for all events. Results were presented in a series of four case studies. Results showed that surface sediment leachate concentration and yield were tightly linked to the filtration capacity of lysimeters, with more than 2/3rd of sediment originating from a single lysimeter, despite similar flow leachate volumes from each. Rainfall intensity significantly impacted the transport of surface eroded sediment at the highest intensity. Subsurface sediment erosion from undisturbed macropores was low compared to surface soils, but we found contrasting controls on sediment concentrations at low and high antecedent moistures that were equally important to sediment leachate yields. Disturbed macropores produced comparable sediment yields to surface erosion and behaved similarly to soil pipes in terms of erosion mechanics. Hysteresis results generally highlighted contrasting results for surface and subsurface sources but suggest that the prominence of slow flow, low‐concentration leachate sources can alter the interpretation of results in field‐scale applications. Our findings underscore an array of processes and pathways for sediment transport in the shallow vadose zone, and results will be useful for evaluating new model formulations.

Adynamic spoken language in corpus callosum dysgenesis

Corpus callosum dysgenesis (CCD) is a congenital brain malformation that occurs when the development of the corpus callosum is disrupted, either partially or completely. The cognitive outcomes in individuals with CCD vary greatly, but generally the neuropsychological profile is characterised by slow processing speed, poor transfer of interhemispheric sensory-motor information, and impaired complex problem solving. Core language skills are often preserved in CCD, but there is some evidence that complex language may be impaired. Thus, the current study sought to examine whether spontaneous speech output was reduced in a cohort of individuals with CCD compared to age-matched controls. We further explored a series of factors that may be contributing to poor spontaneous speech in CCD, such as difficulties generating, selecting, and sequencing ideas for expression, as well as apathy and slowed processing speed. A cohort of 25 individuals with CCD and 39 neurotypical controls were enrolled in this study. Participants completed a picture description task to measure spontaneous speech output, alongside a series of cognitive and language baseline tests. Verbal and nonverbal fluency tasks gauged idea generation and sequencing, and sentence-level selection tasks measured idea selection. We found that, despite having largely intact core language skills, individuals with CCD produced significantly less spontaneous speech on the picture description task than controls. This language profile may be described as “adynamic”. Further, we found that poor spontaneous speech output in CCD was related to problems generating ideas for expression, as individuals with CCD performed below controls on the verbal and nonverbal fluency tasks. Exploratory analyses revealed that apathy and slowed processing speed may be contributing factors. Adynamia in CCD is a novel finding that may be an intervention target for improving communication skills in this population.

Nondestructive flash cathode recycling

Effective recycling of end-of-life Li-ion batteries (LIBs) is essential due to continuous accumulation of battery waste and gradual depletion of battery metal resources. The present closed-loop solutions include destructive conversion to metal compounds, by destroying the entire three-dimensional morphology of the cathode through continuous thermal treatment or harsh wet extraction methods, and direct regeneration by lithium replenishment. Here, we report a solvent- and water-free flash Joule heating (FJH) method combined with magnetic separation to restore fresh cathodes from waste cathodes, followed by solid-state relithiation. The entire process is called flash recycling. This FJH method exhibits the merits of milliseconds of duration and high battery metal recovery yields of ~98%. After FJH, the cathodes reveal intact core structures with hierarchical features, implying the feasibility of their reconstituting into new cathodes. Relithiated cathodes are further used in LIBs, and show good electrochemical performance, comparable to new commercial counterparts. Life-cycle-analysis highlights that flash recycling has higher environmental and economic benefits over traditional destructive recycling processes.

Catalytic hairpin-assembled and DNAzyme-driven DNA walker integrated hybridization chain reaction to construct a label-free electrochemical aptasensor for the detection of acetamiprid

As a new type of nicotine pesticide, the excessive residue of acetamiprid (ACE) in food and the environment seriously poses human health. Hence, this article developed an electrochemical aptasensor for detecting ACE based on a cascaded amplification circuit composed of catalytic hairpin-assembled and DNAzyme-driven DNA walker and hybridization chain reaction. Through the target triggered catalytic hairpin assembly (CHA), the free travelling strand of DNA walker and intact catalytic core of DNAzyme were formed, and with the assistance of Mg2+, DNAzyme was activated, driving the travelling strand to walk autonomously, repeatedly cutting hairpin DNA substrates on the electrode surface, and obtaining abundant DNA fragments. These fragments contained the initiators of hybridization chain reaction (HCR) could trigger HCR and produce the long double-strand DNA (dsDNA) for loading methylene blue (MB). Owing to the fact that Ce(Ⅲ, Ⅳ)-MOF material with electrocatalytic activity, the electrochemical reduction of MB could be effectively catalyzed, obtain significantly enhanced current signals, and ultimately achieve label-free and sensitive detection of ACE, with a detection limit of 16.38 fM (S/N = 3). Moreover, the aptasensor demonstrated excellent selectivity, stability, and reproducibility, and exhibited good reliability for detecting ACE in the vegetable soil and tomato samples, providing a new idea for the detection of pesticide residues in the fields of food and environment.

Comparative diagnostic performance of endoscopic ultrasound-guided fine-needle aspiration (EUS-FNA) versus endoscopic ultrasound-guided fine-needle biopsy (EUS-FNB) for tissue sampling of solid pancreatic and non-pancreatic lesions without ROSE: a prospective multicenter study

Background and aimsEndoscopic ultrasound-guided tissue acquisition, including both fine-needle aspiration (EUS-FNA) and fine-needle biopsy (EUS-FNB), has been frequently performed to acquire samples from both pancreatic and non-pancreatic lesions. Still, the impact of the diagnostic yield between FNA and FNB is uncertain. We conducted this study to compare the diagnostic performance and accuracy of the 22-gauge FNA needles with the 22-gauge FNB needles in sampling solid pancreatic and non-pancreatic lesions.MethodsThis is a prospective multicenter study conducted on 465 cases presented with solid pancreatic or non-pancreatic lesions.ResultsPatients were 275 male and 190 females with a mean age of 59 years. Three-hundred twenty-seven patients had solid pancreatic lesions, while 138 had non-pancreatic lesions; 245 cases underwent EUS-FNA, and the remaining 211 cases underwent EUS-FNB. The presence of intact tissue core and sample adequacy was significantly higher in the FNB cases in solid pancreatic and non-pancreatic lesions. Blood contamination was significantly more in cell blocks and smears of EUS-FNA compared to that of EUS-FNB in solid pancreatic and non-pancreatic lesions. Based on histologic assessment of cell block only, EUS-FNB had more diagnostic accuracy (99%) than FNA (61%) (P-value < 0.005). However, cytological diagnosis by smears only showed no significant difference. The combined cytological and histological evaluation had 100% sensitivity, specificity, and accuracy.ConclusionEUS-FNA and EUS-FNB have comparable accuracy in diagnosing solid pancreatic and non-pancreatic lesions without ROSE. EUS-FNB is superior to EUS-FNA in acquiring intact tissue core and adequate samples with little blood contamination. Based on histological assessment (cell block/tissue core) only, EUS-FNA has less accuracy than EUS-FNB in diagnosing solid pancreatic lesions.

HIV-1 uncoating requires long double-stranded reverse transcription products.

HIV-1 cores, which contain the viral genome and replication machinery, must disassemble (uncoat) during viral replication. However, the viral and host factors that trigger uncoating remain unidentified. Recent studies show that infectious cores enter the nucleus and uncoat near the site of integration. Here, we show that efficient uncoating of nuclear cores requires synthesis of a double-stranded DNA (dsDNA) genome >3.5 kb and that the efficiency of uncoating correlates with genome size. Core disruption by capsid inhibitors releases viral DNA, some of which integrates. However, most of the viral DNA is degraded, indicating that the intact core safeguards viral DNA. Atomic force microscopy and core content estimation reveal that synthesis of full-length genomic dsDNA induces substantial internal strain on the core to promote uncoating. We conclude that HIV-1 cores protect viral DNA from degradation by host factors and that synthesis of long double-stranded reverse transcription products is required to trigger efficient HIV-1 uncoating.

Altered circadian gene expression in primary human airway epithelial cells in asthma.

Primary human airway epithelial cells demonstrate altered rhythmic gene expression in cytokine-related pathways in asthma with intact core circadian gene expression https://bit.ly/3v9lOC6.

Comprehensive molecular-isotopic characterization of archaeal lipids in the Black Sea water column and underlying sediments.

The Black Sea is a permanently anoxic, marine basin serving as model system for the deposition of organic-rich sediments in a highly stratified ocean. In such systems, archaeal lipids are widely used as paleoceanographic and biogeochemical proxies; however, the diverse planktonic and benthic sources as well as their potentially distinct diagenetic fate may complicate their application. To track the flux of archaeal lipids and to constrain their sources and turnover, we quantitatively examined the distributions and stable carbon isotopic compositions (δ13 C) of intact polar lipids (IPLs) and core lipids (CLs) from the upper oxic water column into the underlying sediments, reaching deposits from the last glacial. The distribution of IPLs responded more sensitively to the geochemical zonation than the CLs, with the latter being governed by the deposition from the chemocline. The isotopic composition of archaeal lipids indicates CLs and IPLs in the deep anoxic water column have negligible influence on the sedimentary pool. Archaeol substitutes tetraether lipids as the most abundant IPL in the deep anoxic water column and the lacustrine methanic zone. Its elevated IPL/CL ratios and negative δ13 C values indicate active methane metabolism. Sedimentary CL- and IPL-crenarchaeol were exclusively derived from the water column, as indicated by non-variable δ13 C values that are identical to those in the chemocline and by the low BIT (branched isoprenoid tetraether index). By contrast, insitu production accounts on average for 22% of the sedimentary IPL-GDGT-0 (glycerol dibiphytanyl glycerol tetraether) based on isotopic mass balance using the fermentation product lactate as an endmember for the dissolved substrate pool. Despite the structural similarity, glycosidic crenarchaeol appears to be more recalcitrant in comparison to its non-cycloalkylated counterpart GDGT-0, as indicated by its consistently higher IPL/CL ratio in sediments. The higher TEX86 , CCaT, and GDGT-2/-3 values in glacial sediments could plausibly result from selective turnover of archaeal lipids and/or an archaeal ecology shift during the transition from the glacial lacustrine to the Holocene marine setting. Our in-depth molecular-isotopic examination of archaeal core and intact polar lipids provided new constraints on the sources and fate of archaeal lipids and their applicability in paleoceanographic and biogeochemical studies.

Laboratory Hydraulic Tensile Strength Correlation with Strength-Based Brittleness Indices for Carbonate Reservoirs

Hydraulic fracturing (HF) is the primary choice for stimulating petroleum reservoirs. Rock tensile strength and brittleness are crucial parameters required for screening candidate reservoirs and in designing successful HF operations. However, in situ and laboratory determinations of the hydraulic tensile strength (HTS) of rock can prove problematic. Alternatively, the HTS could be estimated from the rock brittleness once a reliable relationship has been established between them. Accordingly, this paper investigates the correlations between the HTS, as measured using laboratory hydraulic fracture tests, and ten strength-based brittleness indices (BIs) selected from the research literature. The primary inputs for computing these BIs are uniaxial compressive strength (UCS) and the Brazilian tensile strength (BTS), which are typically measured for most projects using standard laboratory rock mechanics tests or obtained from log data. For the purposes of this experimental investigation, intact rock core samples were obtained from a carbonate–dolomite formation in Iran, comprising eight distinct geomechanical units, with measured values of UCS, BTS, and HTS ranging 29.7–162.2, 1.93–12.23, and 7.20–20.63 MPa, respectively. The measured HTS was found to directly correlate with the UCS, BTS, and Young’s modulus, and inversely correlated with the rock porosity. Seven of the ten investigated BIs correlated with the measured HTS over 69% (R2 ≥ 0.69). In particular, the BI expressions developed by Yagiz and Gokceoglu, Ghadernejad et al., and Khandelwal et al. exhibited relatively strong correlations with the measured HTS (producing R2 values of 0.94, 0.87, and 0.86, respectively), suggesting that these three HTS–BI correlations could be used to provide preliminary HTS estimates for the investigated carbonate–dolomite formation in Iran. This work adds to a database that can be expanded to include other geographical regions for providing useful information about the selection of a suitable site or reserve for conducting HF operations.

Comparison of diagnostic outcomes, safety, and cost of Franseen-tip 19G versus 22G needles for endoscopic ultrasound-guided liver biopsies.

Background and study aims Favorable outcomes were noted with refinement in newer endoscopic ultrasound-guided liver biopsy (EUS-LB) needle tips. Still, the overall usefulness and benefit are yet to be well explored. Patients and methods This was a retrospective analysis of patients with EUS-LB (Franseen-tip 19G versus 22G FNB needle) over 2 years. EUS-LB was obtained in a one-pass, two-actuation, modified wet suction technique. Diagnostic yield, fragmentation rate, aggregate specimen length (AL), number of complete portal tracts (CPT), length of longest intact core (LIC), adverse events (AEs) (early), and cost of the procedure (1USD = 82 INR) were compared. Results Fifty-four patients (33 [61.1%], female) successfully underwent EUS-LB with a median age of 46 years (interquartile range [IQR] 34-54); the majority 32 (59.2%) underwent 19G biopsies. There was a significantly increased median (IQR) AL in the 19G compared with 22G (20 mm [19-21] vs. 15 [14-15], P < 0.001), respectively. Similarly, significantly lengthier median LIC and CPT were seen, respectively. A nonsignificant diagnostic yield was noted (100% vs. 90.9%, P = 0.082), respectively. The fragmentation rate was higher in 22G FNB needles (36.4% [95% CI 16-56] vs. 12.5% [95% CI 1-24], respectively; P = 0.038). Seven patients (12.9%) had mild AEs with no difference between groups. The average procedure cost with 19G was INR 63000 (768$), and with 22G needle was INR 54500 (664$). Conclusions The Franseen-tip 19G outperforms 22G with a significantly lower fragmentation rate, longer AL, LIC, and a higher number of CPT with a marginal increase in the procedure cost, without any difference in diagnostic yield and safety.

Parametric study of depth to maximum bending moment for prestressed concrete piles resisting lateral load

Seismic design of prestressed concrete piles requires transverse spiral reinforcement to be proportioned to confine and thus retain an intact concrete core during inelastic rotation cycles. Prescriptive provisions of the International Building Code require a prescriptive minimum volumetric ratio of confinement reinforcement relative to the pile cross section and a minimum in-ground depth to which the confinement reinforcement must extend. This study seeks to determine a practical maximum depth to maximum in-ground bending moment for 12, 14, and 16 in. (300, 360, and 410 mm) prestressed concrete piles subjected to displacement consistent with lateral seismic loads. A commercially available lateral analysis software was used to conduct a parametric analytical study of square and octagonal piles embedded in substantially varied soil conditions. Piles were modeled to remain elastic. Depth to maximum in-ground moment was recorded. Maximum depth values for each pile type were reported. Analysis of results indicates that prescriptive depth requirements may be overly conservative for 12 and 14 in. square piles in nonliquefiable soils. It was concluded that a reduction could be made to the code-prescribed depth of ductile reinforcement for some pile types in nonliquefiable conditions.

Development and validation of an in situ high-resolution technique for measuring antibiotics in sediments

Important biogeochemical processes occur in sediments at fine scales. Sampling techniques capable of yielding information with high resolution are therefore needed to investigate chemical distributions and fluxes and to elucidate key processes affecting chemical fates. In this study, a high-resolution diffusive gradients in thin-films (DGT) technique was systematically developed and tested in a controlled sediment system to measure organic contaminants, antibiotics, for the first time. The DGT probe was used to resolve compound distributions at the mm scale. It also reflected the fluxes from the sediment pore-water and remobilization from the solid phase, providing more dynamic information. Through the fine scale detection, a reduction of re-supply was observed over time, which was concentration and location dependent. Compared to the Rhizon sampling method, antibiotic concentrations obtained by DGT probes were less than the pore-water concentrations, as DGT measures the labile fraction of the compounds. The DGT probe was also tested on an intact sediment core sampled from a lake in China and used to measure the distribution of labile antibiotics with depth in the core at the mm scale. Environmental ImplicationThe abuse of antibiotics and widespread of their residues influences the ecosystem, induces the generation of super-bacteria, and finally poses threat to human health. Sediments adsorbs pollutants from the aquatic environment, while may also release them back to the environment. We systematically developed DGT probe approach for measuring antibiotics in sediment in situ in high resolving power, it provides information at fine scale to help us investigate biogeochemical processes take place in sediment and sediment-water interface.

Determination of soil water retention curves from thermal conductivity curves, texture, bulk density, and field capacity

The soil water retention curve (SWRC) is frequently expressed using the van Genuchten (VG) model, which has four parameters: saturated water content (θs), residual water content (θr), α, and m (1–1/n). Soil thermal conductivity (λ), which is linked to the hydraulic properties of unsaturated soil, has been a proxy variable used to estimate SWRC. In this study, we present a new approach to estimate the VG model parameters. Parameters θs, α and m are calculated from the information of soil texture, bulk density (ρb), and a measured water content at field capacity (θfc, at −33 kPa or −10 kPa), and θr is estimated from the thermal conductivity versus water content curve, λ(θ), based on similarities between SWRCs and λ(θ) curves. The new approach was evaluated with laboratory and field measurements on 23 soils of various textures, ρb values, and θ values. Results showed that for repacked core samples, intact core samples, and in situ field soils, the new approach estimated SWRCs with average root mean square errors (RMSEs) of 0.042, 0.030, and 0.049 m3 m‐3, respectively. The new approach offers a quick and effective way to estimate SWRCs accurately with measured λ(θ) curves, texture, bulk density, and θ at field capacity.

Quantifying Gas Storage and Transport in an Intact Core Sample Using Low-Field NMR and Pressure Measurements

Quantifying Gas Storage and Transport in an Intact Core Sample Using Low-Field NMR and Pressure Measurements

Experimental investigation of CO2-CH4 core flooding in large intact bituminous coal cores using bespoke hydrostatic core holder

This paper presents the CO2-CH4 core flooding and permeability studies conducted with large intact coal core samples. A bespoke core holder was designed and commissioned to conduct the core flooding experiments. The CO2 and CH4 core flooding experiments were performed to understand the CH4 displacement efficiency of CO2 from the coal cores and the permeabilities of CO2 and CH4 during the core flooding. The CO2-CH4 gas displacement experiments were performed on intact coal cores of 9.9 cm in diameter with varying lengths to make up 60 cm-long cores that were extracted from coal blocks using a diamond core-drilling machine. The CO2 and CH4 core flooding experiments were conducted using the core holder at maximum of 1450 psi confining pressures and at 298.15 K. A constant gas flow rate of 1 mL/min was maintained to flood the core with an outlet backpressure set at 25 to 30 ± 2 psi. The core holder is equipped with two differential pressure taps to measure the pressure change along the core length to measure the differing permeability along the core lengths which is difficult to observe in the smaller size intact samples. Both coals, EMB and ZM, showed favourable CH4 displacement efficiencies of CO2 about 96.5% and 99.7%, respectively. The dependency of the core lengths on the permeability measurements is more pronounced in the results obtained in the current study. The results indicated a decreasing trend in CO2 permeability and increasing CH4 permeability during CO2 injection. The observation indicated CO2 adsorption and CH4 displacement. Overall, the core flooding experiments improved the current understanding of CO2-CH4 core flooding by showing the core size dependence in permeability measurement experiments. In contrast to the single species CO2 flow experiments, the permeability variation during the CO2-CH4 flooding and the CH4 sweeping efficiency of CO2 provided insights into the CO2-ECBM operational design.

Fine root decomposition and macronutrient release in temperate forests: Examining the litter bag and intact soil core approaches and their relationship with fungal community composition

Accurate measurement of decomposition of fine roots in forests is important for understanding nutrient cycling, carbon dynamics and biotic responses; however, various sources of error or bias interfere with commonly used approaches. Most studies of fine root decomposition have used the buried root litter bag method, but this method may underestimate decay rates based on comparisons with the less disruptive, intact soil core approach. We compared these two methods for one year for seven temperate forest trees growing in twelve monospecific plantations in central New York. The experimental design included four species that form arbuscular mycorrhizae (sugar maple, red maple, cherry, tulip poplar) and three with ectomycorrhizae (pine, spruce, oak). We also examined macronutrients (N, P) release and fungal community composition of decaying fine roots using Illumina sequencing. Across the seven species and 12 plots, fine root decay rate was significantly higher for intact cores than litter bags, with the difference being approximately 12 %, a smaller disparity than that observed in previous comparisons. However, one species (Norway spruce) showed the opposite trend. Similarly, N and P release from decaying roots was significantly greater for the intact core method, but again with an exception (red oak). No consistent effects of mycorrhizal type on the method effect or decay rate and nutrient release were detected. Fungal communities in decaying roots differed between the two methods; nevertheless, Mycena spp. dominated most plots for both methods. These results further emphasize the notion that decay rates and nutrient mobilization of fine roots in forests are usually underestimated by the litter bag approach.

The effect of antecedent soil moisture conditions on soil nitrous oxide and dinitrogen dynamics after wetting: An intact soil core study

Ruminant excreta urinary‑nitrogen (N) deposited onto pasture soil generates inorganic-N concentrations in excess of the pasture's immediate requirements. Consequently, nitrous oxide (N2O) and dinitrogen (N2) may be emitted from the urine-affected soil via denitrification. Soil moisture plays a key role in determining the end-product of denitrification. Although the effects of soil moisture and drying-wetting cycles on soil N2O production have been widely studied using sieved soils in a controlled environment, these experiments may not reflect the actual conditions in the field due to the lack of plant cover and the disturbed soil structure. To address this an experiment was performed using intact soil cores (7.5 cm depth), with pasture plants present, under controlled environmental conditions (20 °C, 8 h of light per day). The 15N flux method was used to investigate how antecedent soil moisture affected soil N2O production and consumption in a pasture soil after wetting with a nitrate (NO3−) solution. The results showed that the antecedent dry condition (25 % WFPS, Dp/Do = 0.1783) increased the magnitude of the N2O flux peak after the soil was wetted (75 % WFPS, Dp/Do = 0.006) when compared to antecedent wet conditions (50 % WFPS, Dp/Do = 0.0503). There were no differences in the denitrification and nitrification related functional gene abundances between the two antecedent conditions post-wetting, indicating that the effect was not regulated by microbial changes but by the intensity of the “Birch effect” induced by soil wetting. The N2O reduction related gene (nosZII) abundance decreased after wetting with the NO3− solution, indicating a suppression effect on N2O consumption from the NO3− applied that overrode the potential “Birch effect” on N2 emission. The results of the study indicate that rewetting of antecedent dry soil increase N2O emissions but not N2 emissions when the soil NO3− concentration is high.

Permeability decides the effect of antibiotics on sedimentary nitrogen removal in Jiulong River Estuary.

Sedimentary denitrification takes place beneath the oxic layer at the sediment-water interface, where nitrate and antibiotics need to diffuse through the overlying water. However, the antibiotics' effect on sedimentary N removal and associated N2O production has not been adequately investigated under in situ conditions. Here, isotope pairing techniques, including slurry incubations (potential) and intact core incubations (in situ), combined with metagenomic analysis were applied to investigate the impacts of two protein-inhibiting antibiotics (oxytetracycline and thiamphenicol) on sediment nitrogen removal in a subtropical estuary. Slurry incubations showed that the two antibiotics significantly inhibited denitrification (67-98%) and anammox (49-99%), while intact core incubations presented no antibiotic effect at upstream but significant inhibition (23%-52%) at downstream. Meanwhile, N2O yields were stimulated up to 20 folds in slurry incubations yet showing insignificant response in intact cores. Such contrasting results between up- and down-stream and between slurry and intact core incubations strongly indicated that permeability, which determines diffusion of antibiotics to microbes, is the key to exert the effect of antibiotics on in situ sedimentary nitrogen removal processes regardless the existence of antibiotics resistance genes. This diffusive obstruction may mitigate the toxic effect of antibiotics on nitrogen removal related microbes in natural environments.

Light grazing reduces gaseous nitrogen emissions from temperate grassland soils during freeze‒thaw cycles: An intact core incubation study

Livestock grazing and soil freeze‒thaw cycles (FTCs) can affect the biogeochemical processes of nitrogen (N) and gaseous N (N2O, NO, and N2) emissions from grassland soils. However, the effect of grazing intensity on soil gaseous N emissions during FTCs and the underlying mechanisms are not clearly understood. In this intact core incubation study, soil gaseous N emissions during two FTCs were simultaneously quantified from temperate grasslands that included grazing exclusion (GE), light grazing (LG), and heavy grazing (HG) in Inner Mongolia. Additionally, the abundance of N cycle-related functional genes and the main soil characteristics were determined to better understand the drivers of gaseous N emissions. The results showed that N2 emissions dominate the gaseous N loss from all investigated soils during FTCs, with cumulative N2 exceeding NO and N2O emissions by factors of 47–135 and 71–161, respectively. Increased soil moisture during thawing promoted N2 and N2O emissions from all three sites, except for N2O at the LG site. However, no obvious NO emission peak was observed from all investigated soils during FTCs. Soil C and N availability and aeration changed by grazing regulated soil N2O fluxes, while the abundances of key functional genes generally did not show significant correlations with gaseous N emissions. Moreover, compared to the GE and HG sites, LG substantially decreased the soil N2O and total gaseous N emissions during FTCs, suggesting that light grazing rather than long-term grazing exclusion could be a promising measure to reduce gaseous N losses during spring thaw. Our results highlighted the importance of the simultaneous determination of all kinds of gaseous N emissions during FTCs for closing the ecosystem N balance and developing appropriate strategies for grassland management.