Understanding the exchange of carbon dioxide (CO2) and methane (CH4) between the geosphere and atmosphere is essential for the management of anthropogenic emissions. Human activities such as carbon ...capture and storage and hydraulic fracturing (“fracking”) affect the natural system and pose risks to future global warming and to human health and safety if not engineered to a high standard. In this paper an innovative approach of expressing ground gas compositions is presented, using data derived from regulatory monitoring of boreholes in the unsaturated zone at infrequent intervals (typically 3 months) with data from a high frequency monitoring instrument deployed over periods of weeks. Similar highly variable trends are observed for time scales ranging from decades to hourly for boreholes located close to sanitary landfill sites. Additionally, high frequency monitoring data confirm the effect of meteorological controls on ground gas emissions; the maximum observed CH4 and CO2 concentrations in a borehole monitored over two weeks were 40.1% v/v and 8.5% v/v respectively, but for 70% of the monitoring period only air was present. There is a clear weakness in current point monitoring strategies that may miss emission events and this needs to be considered along with obtaining baseline data prior to starting any engineering activity.
We used thermal analysis to compare the proportions of active and more stable components in soil organic matter (SOM) fractions and whole soil under contrasting agricultural land-uses. The fractions ...(free light, intra-aggregate, and organomineral fractions) were isolated using density fractionation. Exothermic weight loss between 300 and 350 degrees C was attributed to a relatively labile portion comprising carboxyl and aliphatic C, and that between 400 and 450 degrees C to the decomposition of material rich in aromatic components. Under arable cultivation, free light SOM showed much greater weight loss in the first exothermic range than intra-aggregate SOM. In soil receiving very small inputs of organic matter (a long-term bare fallow) the free light and intra-aggregate fractions displayed similar characteristics and resembled the intra-aggregate fraction from the arable soil. The difference between the free light and intra-aggregate fractions was also small for the grassland soil but the fractions resembled the free light fraction from the arable soil. Small total weight loss for whole soil and organomineral fractions demonstrated the value of physical fractionation techniques in establishing the effect of land-use on SOM with greater precision than is possible whole (unfractionated) soil.
As part of a programme of finding new uses for industrial wastes, a trial of PFA (pulverized fuel ash) as a thermal grout for borehole heat exchangers has been tested experimentally. Several mixes of ...PFA-based grouts were developed by blending PFA with different solid materials by weight in different mix proportions with a constant percentage of cement. The materials used in these mixes are: fine sand, coarse sand, ground glass, and fluorspar. The thermal conductivity of seven different groups of grouts has been measured at dry and saturated conditions. A new thermal cell that utilizes the steady state technique developed by Newcastle University was used for these measurements. The results show poor enhancement of thermal conductivity using fine sand or medium ground glass, with maximum value of 1.15 W/m K at saturation. Results obtained using coarse or mixed ground glass gave a maximum value of 1.39 W/m K. The highest thermal conductivity values were achieved using fluorspar or coarse sand where the thermal conductivity reached 2.88 and 2.47 W/m K respectively at 20% of PFA. It was also observed that the combination of fluorspar with coarse ground glass can offer relatively high thermal conductivity at both dry and saturated conditions. Moreover, this combination of materials comprises a practical amount of low-cost material (PFA and ground glass).
► Experimental programme is conducted to investigate the thermal conductivity of PFA as thermal grouts. ► A developed new thermal cell that utilizes the steady state technique is used for the measurements. ► Low thermal enhancement has been achieved using fine sand or ground glass. ► Good thermal enhancement achieved using coarse sand or fluorspar. ► The practical amount of PFA should not exceed 40% by weight.
Atmospheric methane's rapid growth from late 2006 is unprecedented in the observational record. Assessment of atmospheric methane data attributes a large fraction of this atmospheric growth to ...increased natural emissions over the tropics, which appear to be responding to changes in anthropogenic climate forcing. Isotopically lighter measurements of δ13CCH4 ${\delta }^{13}{\mathrm{C}}_{\mathrm{C}\mathrm{H}4}$ are consistent with the recent atmospheric methane growth being mainly driven by an increase in emissions from microbial sources, particularly wetlands. The global methane budget is currently in disequilibrium and new inputs are as yet poorly quantified. Although microbial emissions from agriculture and waste sources have increased between 2006 and 2022 by perhaps 35 Tg/yr, with wide uncertainty, approximately another 35–45 Tg/yr of the recent net growth in methane emissions may have been driven by natural biogenic processes, especially wetland feedbacks to climate change. A model comparison shows that recent changes may be comparable or greater in scale and speed than methane's growth and isotopic shift during past glacial/interglacial termination events. It remains possible that methane's current growth is within the range of Holocene variability, but it is also possible that methane's recent growth and isotopic shift may indicate a large‐scale reorganization of the natural climate and biosphere is under way.
Plain Language Summary
Atmospheric methane's unprecedented current growth, which in part may be driven by surging wetland emissions, has strong similarities to ice core methane records during glacial‐interglacial “termination” events marking global reorganizations of the planetary climate system. Here we compare current and termination‐event methane records to test the hypothesis that a termination‐scale change may currently be in progress.
Key Points
The rapid growth in the atmospheric methane burden that began in late 2006 is very different from methane's past observational record
Recent studies point to strongly increased emissions from wetlands, especially in the tropics
This increase is comparable in scale and speed to glacial/interglacial terminations when the global climate system suddenly reorganized
The amount and compositional characteristics of black carbon in soils (mollisol and vertisol), charred biomass (laboratory produced; rice, chestnut), and soils (southern Spain) affected by forest ...fire have been determined using a combination of thermogravimetry (TG), TG coupled with isotope ratio mass spectrometry (IRMS), solid state 13C nuclear magnetic resonance (NMR) spectroscopy, and pyrolysis‐gas chromatography/mass spectrometry (Py‐GC/MS). Samples affected by fire had higher total organic matter content, and this was enriched in aromatic components. Good agreement was observed between the content of refractory organic matter (ROM) determined by TG analysis and the aromatic content measured by 13C NMR. Py‐GC/MS demonstrated the presence of aromatic compounds in samples rich in black carbon, the absence of furans (derived from carbohydrates) in soils affected by fire, and the detection of methoxyphenols (derived from lignin) in artificially charred grass and wood. Some of the characteristic peaks obtained by analytical pyrolysis in combination with TG analysis and NMR 13C spectra could be used as markers in the detection of black carbon. This is the first study in which TG‐differential scanning calorimetry (DSC)‐IRMS has been used to detect black carbon formed during artificial smoldering and natural combustion processes.
The role of clay minerals in crude oil saturated hydrocarbon removal during biodegradation was investigated in aqueous clay/saturated hydrocarbon microcosm experiments with a hydrocarbon degrading ...microorganism community. The clay minerals used for this study were montmorillonite, palygorskite, saponite and kaolinite. The clay mineral samples were treated with hydrochloric acid and didecyldimethylammonium bromide to produce acid activated- and organoclays respectively which were used in this study. The production of organoclay was restricted to only montmorillonite and saponite because of their relative high CEC. The study indicated that acid activated clays, organoclays and unmodified kaolinite, were inhibitory to biodegradation of the hydrocarbon saturates. Unmodified saponite was neutral to biodegradation of the hydrocarbon saturates. However, unmodified palygorskite and montmorillonite were stimulatory to biodegradation of the hydrocarbon saturated fraction and appears to do so as a result of the clays’ ability to provide high surface area for the accumulation of microbes and nutrients such that the nutrients were within the ‘vicinity’ of the microbes. Adsorption of the saturated hydrocarbons was not significant during biodegradation.
The impact of modified montmorillonites on adsorption and biodegradation of crude oil C1-phenanthrenes, C1-dibenzothiophenes, C2-phenanthrenes and C2-dibenzothiophenes was investigated in aqueous ...clay/oil microcosm experiments with a hydrocarbon degrading microorganism community. Consequently, the effect on C1-dibenzothiophenes/C1-phenanthrenes, C2-dibenzothiophenes/C2-phenanthrenes, 2+3-methyldibenzothiophene/4-methyldibenzothiophene and 1-methyldibenzothiophene/4-methyldibenzothiophene ratios commonly used as diagnostic ratios for oil forensic studies was evaluated. The clay mineral samples were treated to produce acid activated montmorillonite, organomontmorillonite and homoionic montmorillonite which were used in this study. The different clay minerals (modified and unmodified) showed varied degrees of biodegradation and adsorption of the C1-phenanthrenes, C1-dibenzothiophenes, C2-phenanthrenes and C2-dibenzothiophenes. The study indicated that as opposed to biodegradation, adsorption has no effect on the diagnostic ratios. Among the diagnostic ratios reviewed, only C2-dibenzothiophenes/C2-phenanthrenes ratio was neither affected by adsorption nor biodegradation making this ratio very useful in forensic studies of oil spills and oil–oil correlation.
Adaptations in crop rotation with the inclusion of temporary grass-clover leys and organic amendments, have been promoted as effective ways to improve soil carbon (C) sequestration and mitigate ...climate change in agricultural systems. However, there are still a lot of uncertainties related to i) the combined effects of different crop rotations and different fertilisation sources, e.g., organic amendments, on soil C stocks; and ii) their potential effect on C stabilisation. The objective of this study was to evaluate the effect of different arable crop rotations with varying degrees of diversity in crop type and lengths of grass-clover ley periods and fertilisation sources on soil C stocks and C stabilisation down to 0.60 m soil depth. This was investigated in a long-term factorial field experiment-combining different crop rotation (cereal-intensive conventional
vs.
diversified legume-intensive organic) with different lengths of grass-clover ley periods (2
vs.
3 years), fertilisation sources (mineral
vs.
compost), and years (samples taken at the beginning and at the last year of one complete cycle of rotation; 8 years apart)-to explore their individual and interactive effect on soil C stock and C stabilisation at two soil depths (0–0.30 and 0.30–0.60 m). Soil C stabilisation was assessed using a unique combination of three different techniques: physical fractionation for separation of C associated to organic and mineral fractions, thermal analysis combined with differential scanning calorimetry and a quadrupole mass spectrometry (TG-DSC-QMS) for physical-chemical aspects, and pyrolysis coupled with gas chromatography-mass spectrometry (Py-GC/MS) for molecular structural information. The findings showed higher soil C stocks under the diversified organic rotation with 3 years of grass-clover ley period at both soil depths, regardless of the fertilisation source or sampling year. However, the organic rotation seemed to deliver stable soil C stocks only in the subsoil layer. Compost fertilisation, in turn, increased topsoil C stocks between the two sample dates under both rotations, and it appears to be stable. These results suggested that combining a diversified organic rotation with 3 years grass-clover ley with compost fertilisation could be one way for agricultural systems to deliver stable soil C sequestration.
Studies that used conflict paradigms such as the Eriksen Flanker task show that many individuals with Parkinson's disease (PD) have pronounced difficulty resolving the conflict that arises from the ...simultaneous activation of mutually exclusive responses. This finding fits well with contemporary views that postulate a key role for the basal ganglia in action selection. The present experiment aims to specify the cognitive processes that underlie action selection deficits among PD patients in the context of variations in speed-accuracy strategy. PD patients (n=28) and healthy controls (n=17) performed an arrow version of the flanker task under task instructions that either emphasized speed or accuracy of responses. Reaction time (RT) and accuracy rates decreased with speed compared to accuracy instructions, although to a lesser extent for the PD group. Differences in flanker interference effects among PD and healthy controls depended on speed-accuracy strategy. Compared to the healthy controls, PD patients showed larger flanker interference effects under speed stress. RT distribution analyses suggested that PD patients have greater difficulty suppressing incorrect response activation when pressing for speed. These initial findings point to an important interaction between strategic and computational aspects of interference control in accounting for cognitive impairments of PD. The results are also compatible with recent brain imaging studies that demonstrate basal ganglia activity to co-vary with speed-accuracy adjustments.
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