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The large amounts of organic carbon buried in mangrove wetlands are well recognized, but the lateral dissolved carbon export and greenhouse gas (GHGs) outgassing are often overlooked. In this study, we carried out seasonal observations of dissolved carbon and GHGs in an estuarine mangrove wetland with high input of riverine nitrogen in southeast China in 2019–2020. The results showed that the tidal range and season were the two main factors controlling the lateral dissolved carbon export including total alkalinity (TA), dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC). The positive correlations between the average offsets of DIC, TA, DOC and tidal range confirmed the hydrological controls on the exchange of dissolved carbon between the mangrove creek and the estuary. The seasonal variability in temperature, groundwater export and freshwater input resulted in a larger carbon offset during low tidal range in spring and a smaller offset during high tidal range in fall. The mangrove creek acted as a net source of DIC, DOC, TA and GHGs. When the emissions of GHGs were calculated as CO2-equivalents, the average emission of CO2 was four times higher than that of N2O and the average emission of N2O was six times higher than that of CH4. In contrast with pristine mangroves, denitrification in mangrove wetlands with high input of riverine nitrogen played a crucial role in mineralization processes, leading to the production of DIC, TA and N2O. These biogeochemical processes may not be conducive to the blue carbon sequestration in mangrove soils. These findings suggested that there are mutual benefits between the reduced loss of blue carbon and the mitigation of eutrophication when restoring mangrove wetlands and reducing nitrogen pollution. [ABSTRACT FROM AUTHOR]

Background: Understanding the responses of riverine dissolved carbon dynamics and chemical weathering processes to short-term climatic variabilities is important to understand the Surface-Earth processes under ongoing climate change. Temporal variations of solutes and stable carbon isotope of dissolved inorganic carbon (δ13CDIC) were analysed during a hydrological year in the Guijiang River, South China. We aimed to unravel the chemical weathering processes and carbon dynamics in karst areas under ongoing climate changes. Results: Significant positive relationships were found between weathering rates and climatic factors (i.e. temperature and discharge) over the hydrological year. The total flux of CO2 consumption (760.4 × 103 mol/km2/year) in the Guijiang River was much higher than the global mean flux, with a higher CO2 consumption capacity in the Guijiang River relative to most other global rivers. Chemical weathering fluxes in this karst area showed high sensitivity to global climate change. CO2 evasion during the warm–wet seasons was much lower than those during cold–dry seasons. Light δ13CDIC values occurred under high-flow conditions, corresponding with the high temperatures in high-flow seasons. IsoSource modelling revealed that biological carbon could account for 53% of all dissolved inorganic carbon (DIC), controlling the temporal carbon variabilities. Conclusion: This study quantitatively evaluated the temporal variations in CO2 fluxes and carbon cycling of karstic river systems and demonstrated that riverine carbon cycling will have a higher sensibility to ongoing global climate change. High discharges accelerate solutes transport, with relatively large quantities of 13C-depleted carbon being flushed into rivers. Meanwhile, high temperatures also accelerate organic carbon mineralisation, producing high content of soil CO2, whose influx can shift the 13C-depleted values in the high-flow seasons. Taken together, biological carbon influx should be responsible for the temporal carbon dynamics. [ABSTRACT FROM AUTHOR]

PM2.5 is an important global air pollution issue. PM2.5 causes various problems on the environment and human health. Even though PM2.5 of the outdoor air is eliminated by particulate air filters, the chemicals adsorbed on the filtered PM2.5 can be outgassed and introduced into the semiconductor manufacturing facilities and processes, thus causing defects on the semiconductor chips by producing particles and haze as airborne molecular contamination. Therefore, estimating the amount of the outgassing from PM2.5 is a very important factor to control gaseous contaminants in the semiconductor industry. In this paper, the PM2.5 samples at different PM2.5 mass loadings were collected in Xi’an, China and evaluated using the soft X-ray radiolysis method for determining the relation between the outgassing and the PM2.5 mass loading. The PM2.5 samples were also analyzed by several methods for quantifying organic and elemental carbons, water soluble ions, and organic compounds in the PM2.5 samples. The outgassing measured by the soft X-ray method increased linearly with the PM2.5 mass loading, and the chemical analyses explained that the organic carbon (OC) was dominantly detected by the soft X-ray method in the current study. Moreover, the sampling location of the PM2.5 affected on the organic compounds of the PM2.5. [ABSTRACT FROM AUTHOR]

• R&D work on HHLT facility for ITER large vacuum components is successful in China. • A satisfying result (lower than 2.69×10−10 Pa*m3/s) in the 1st HHLT on the shield block full-scale prototype. • H 2 O and H 2 outgassing is the major factor impacting the performance of HHLT facility at different temperatures. • The facilities' performance was improved by at least one order of magnitude after adopting outgassing-removal measures. • HHLT results of 50 shield blocks with the improved facilities are better and stable. China Domestic Agency (DA) will provide ITER with 220 shield blocks (SB) which are important, large, and actively water-cooled components in ITER vacuum vessel, their leakage rate shall not exceed 2.69 × 10 − 10 Pa · m 3 / s in hot helium leak tests (HHLT) at 250±20 °C. The HHLT work started with developing a HHLT facility and manufacturing a SB full-scale prototype (FSP). The result showed the FSP could satisfy ITER's requirement at 235 °C. H 2 outgassing from stainless steel surfaces is the main factor that impacts both the background leakage rate and sensitivity of the testing system in hot testing cases. Hydrogen-removal measures were taken to improve the facility performance, and a new facility was built. A better facility performance came out at 250 °C rather than 235 °C, the background leakage rate decreased by one order of magnitude while the system sensitivity increased by two orders of magnitude. The background is at 10−10 Pa.m3/s and 10−9 Pa.m3/s level at room temperature (RT) and 250 °C, respectively, while the system sensitivity is at 10−12 Pa.m3/s and 10−11 Pa.m3/s level at the two temperatures. With the two facilities, series HHLTs have been carried out on 50 SBs covering two types, with all results complying with ITER requirements. [ABSTRACT FROM AUTHOR]

Rivers are an important source of CO 2 to the atmosphere, however, mountainous rivers and streams with high emission rates are not well studied particularly in China. We report the first detailed investigation on monsoonal mountainous rivers in the Three Gorges Reservoir (TGR) region, with a focus on the riverine CO 2 partial pressure ( p CO 2 ), CO 2 degassing and their potential controls. The p CO 2 levels ranged from 50 to 6019 µatm with averages of 1573 (SD. ±1060) in dry Autumn and 1276 (SD. ±1166) µatm in wet Summer seasons. 94% of samples were supersaturated with CO 2 with respect to the atmospheric equilibrium (410 µatm). Monsoonal precipitation controlled p CO 2 seasonality, with both the maximal and minimal levels occurring in the wet season, and showing the overall effects of dilution. Riverine pCO 2 could be predicted better in the dry season using pH, DO% and DTP, whereas pH and DOC were better predictors in the wet season. We conclude that in-situ respiration of allochthonous organic carbon, rather than photosynthesis, resulted in negative relationships between p CO 2 and DO and pH, and thus CO 2 supersaturation. Photosynthetic primary production was effectively limited by rapid flow velocity and short residence time. The estimated water-to-air CO 2 emission rate in the TGR rivers was 350 ± 319 in the Autumn and lower, yet more variable at 326 ± 439 mmol/m 2 /d in Summer. Our calculated CO 2 areal fluxes were in the upper-level magnitude of published data, demonstrating the importance of mountainous rivers and streams as a global greenhouse gas source, and urgency for more detailed studies on CO 2 degassing, to address a global data gap for these environments. [ABSTRACT FROM AUTHOR]

This article introduces the source and utility circumstance of off-gas in China. The utility circumstance of off-gas is discussed in detail. For example, off-gas is used to hydrogenate finely as synthesized ammonia material, alkylation of toluene and dilute ethylene in off-gas is applied to generate 1,3-dimethylethylbenzene, off- gas produceds ethyltoluene, off- gas is used to seal centrifugal compressors, and the flow chart of off-gas is concretely enumerated. According to the full utility of off- gas, its good economic and social benefit are obtained. [ABSTRACT FROM PUBLISHER]

The mining of medium- to high‑sulfur coal in karst areas has led to serious acidification problems in surface water, thus encouraging a re-evaluation of DIC transformation and CO 2 source-sink relationships in karst watersheds. The weathering of limestone and sulfide-rich coal measures jointly influence the pH of the Huatan River in karst areas in Southwest China, which is lower in the rainy season and higher in the dry season. Due to CO 2 degassing, DIC concentration tends to decrease along the flow direction, while δ 13 C-DIC gradually becomes heavier. In general, DIC transformation in the Huatan River is controlled by AMD input, CO 2 degassing, organic matter (OM) degradation, and the dissolution and precipitation balance of carbonate minerals in different seasons. In spring, the mineralization of OM from terrestrial and domestic sewage gradually enhances and replenishes DIC in the water. As the pH increases in this season, the capacity for buffering CO 2 increases. Meanwhile, OM degradation generates a large amount of CO 2 in summer, and carbonic acid begins to dissolve limestone. In autumn, the pH decreases due to the enhanced weathering of sulfide-rich coal measures and the mass input of AMD. Thus, the river shows the ability to drive CO 2 outgassing. In winter, CO 2 degassing gradually weakens, DIC concentration is at its lowest, and δ 13 C-DIC reaches the heaviest value., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022. Published by Elsevier B.V.)

Stable carbon isotope composition (δC) of carbonate sediments and the molecular (biomarker) characteristics of a continuous Permian-Triassic (PT) layer in southern China were studied to obtain geochemical signals of global change at the Permian-Triassic boundary (PTB). Carbonate carbon isotope values shifted toward positive before the end of the Permian period and then shifted negative above the PTB into the Triassic period. Molecular carbon isotope values of biomarkers followed the same trend at and below the PTB and remained negative in the Triassic layer. These biomarkers were acyclic isoprenoids, ranging from C to C, steranes (C dominates) and terpenoids that were all significantly more abundant in samples from the Permian layer than those from the Triassic layer. The Triassic layer was distinguished by the dominance of higher molecular weight (waxy) n-alkanes. Stable carbon isotope values of individual components, including n-alkanes and acyclic isoprenoids such as phytane, isop-C, and squalane, are depleted in δC by up to 8-10‰ in the Triassic samples as compared to the Permian. Measured molecular and isotopic variations of organic matter in the PT layers support the generally accepted view of Permian oceanic stagnation followed by a massive upwelling of toxic deep waters at the PTB. A series of large-scale (global) outgassing events may be associated with the carbon isotope shift we measured. This is also consistent with the lithological evidence we observed of white thin-clay layers in this region. Our findings, in context with a generally accepted stagnant Permian ocean, followed by massive upwelling of toxic deep waters might be the major causes of the largest global mass extinction event that occurred at the Permian-Triassic boundary. [ABSTRACT FROM AUTHOR]

Rivers have been under sampled to establish them as sinks or sources of the atmospheric carbon oxide (CO2). Such poor coverage is well known for tropical and sub-tropical, particularly monsoon driven rivers. An unprecedented high-temporal-resolution (daily) sampling during July 2008-August 2009 were conducted from the Longchuanjiang River of the upper Yangtze basin, a subtropical monsoon river in China to reveal the daily-to-seasonal dynamics of the partial pressure of CO2 (pCO2) and CO2 degassing flux from the river. The pCO2 levels were supersaturated in CO2 with respect to atmospheric equilibrium (380 µatm) during the entire survey period with obvious daily and seasonal variations, ranging from 450 to 63000 µatm with an average of 3900 µatm. pCO2 values in the surface water in the wet season were relatively low, except flooding period in November, due to a dilution effect by heavy rainfall. However, both daily and monthly minimal and maximal pCO2 also occurred in this period. In contrast, the pCO2 levels in the dry season were much higher, mainly resulted from lower pH by anthropogenic activities. Net CO2 flux and pCO2 were strongly correlated with pH, but weakly with water temperature, dissolved inorganic carbon and water discharge, and uncorrelated with particulate nutrients and biogenic elements. The estimated water-to-air CO2 degassing flux in the Longchuanjiang River was about 110 mol m-2 yr-1, with the upper limit of 460 mol m-2 yr-1. Our study also indicated that among the total organic carbon remobilized through soil erosion, around 17% (11 400tC yr-1) of was emitted to the atmosphere, 52% (35 000tC yr-1) deposited in the river-reservoirs system and 31 % (21 000tC yr-1) exported further downstream. High spatial and temporal resolution of estimates of CO2 emission from the world large rivers is required due to that catchment characteristics and anthropogenic activities are extremely heterogeneous in space and time. [ABSTRACT FROM AUTHOR]

Abstract: We examined the carbonate system, mainly the partial pressure of CO2 (pCO2), dissolved inorganic carbon (DIC) and total alkalinity (TAlk) in the Changjiang (Yangtze) River Estuary based on four field surveys conducted in Sep.–Oct. 2005, Dec. 2005, Jan. 2006 and Apr. 2006. Together with our reported pCO2 data collected in Aug.–Sep. 2003, this study provides, for the first time, a full seasonal coverage with regards to CO2 outgassing fluxes in this world major river–estuarine system. Surface pCO2 ranged 650–1440 μatm in the upper reach of the Changjiang River Estuary, 1000–4600 μatm in the Huangpujiang River, an urbanized and major tributary of the Changjiang downstream which was characterized by a very high respiration rate, and 200–1000 μatm in the estuarine mixing zone. Both DIC and TAlk overall behaved conservatively during the estuarine mixing, and the seasonal coverage of these carbonate parameters allowed us to estimate the annual DIC export flux from the Changjiang River as ∼1.54×1012 mol. The highly polluted Huangpujiang River appeared to have a significant impact on DIC, TAlk and pCO2 in the lower reaches of the inner estuary. CO2 emission flux from the main stream of the Changjiang Estuary was at a low level of 15.5–34.2 mol m−2 yr−1. Including the Huangpujiang River and the adjacent Shanghai inland waters, CO2 degassing flux from the Changjiang Estuary may have represented only 2.0%–4.6% of the DIC exported from the Changjiang River into the East China Sea. [Copyright &y& Elsevier]

The partial pressure of carbon dioxide (pCO2) in surface water was surveyed monthly at 6 sampling sites along the entire length of the lower reaches of the Xijiang River, a subtropical monsoon river in China, and at the mouths of its major tributaries, over a whole hydrological year from April 2005 to March 2006, to reveal the seasonal and spatial dynamics of pCO2. Intensive sampling and measurements were also conducted at Wuzhou gauge station in June and July to investigate the impact of floodwater on pCO2 and to further explore the relationship between river discharge and pCO2. The pCO2 levels were well above atmospheric equilibrium (380 μatm) during the entire survey period with obvious seasonal and spatial variations, ranging from 600 μatm to 7200 μatm for the mainstream and from 700 to 11000 μatm for tributaries, respectively. The pattern of pCO2 seasonal variation across 6 sites was almost consistent with each other with little difference. The pCO2 levels in the dry season were relatively low, with relatively slight temporal and spatial fluctuations that were predominantly controlled by in situ biogenic activities. While the pCO2 in the wet season greatly varied with river discharge, both annual maximum and minimum pCO2 levels occurring in this period. The much higher pCO2 in the early wet season were mainly induced by increasing baseflow and interflow that flushed significant soil CO2 into the streams, whereas the lower pCO2 observed after floods from July to September, some even lower than pCO2 levels in the dry season, potentially resulted from in situ plankton blooms. The annual minima pCO2 levels occurring in this period were caused by the dilution effect of floodwater. There was no obvious downstream trend in pCO2 variation during the whole survey period, probably a consequence of disturbance from tributaries or spatially distinct channel characteristics and water environments. Based on measurements, we estimate that the water-to-air CO2 flux in the lower reaches of the Xijiang River is about 8. 3–15. 6 Mg C ha−1y−1. The role of the Xijiang River as a net source of atmospheric CO2 is undoubted. [Copyright &y& Elsevier]

• The process of CO 2 outgassing from water in a karst spring-fed creek was explored. • Two distinguishable types of CO 2 outgassing exist along the flow path of stream. • The flux of CO 2 outgassing is affected by flow discharge and streambed morphology. • Calcite precipitation causes ~ 4–20% return of CO 2 to the atmosphere at Changliushui. • Limited precipitation-associated CO 2 outgassing would occur in low-order streams. Whether carbonate weathering on land represents an important terrestrial carbon sink has long been debated as the CO 2 sequestered by the dissolution of carbonate may return to the atmosphere through CO 2 outgassing from groundwater-feeding surface waters. In headwater area of karst terrain, the CO 2 outgassing frequently happens in spring-fed streams, but its flux and influencing factors still remain under-researched. In this study, we conducted a monthly monitoring of hydrochemical and isotopic compositions of stream water along a karst spring-fed creek at Changliushui, SW China that has a steep gradient and in which tufa deposition occurs, in order to explore the process of CO 2 outgassing and elucidate the outgassing flux across space and time and its influencing factors. The analyses of downstream geochemical evolution have revealed that two distinguishable types of CO 2 outgassing exist along the flow path: (i) outgassing of physically dissolved soil CO 2 during the process of carbonate dissolution, as the primary CO 2 outgassing, and (ii) an additional outgassing of the CO 2 arising from the precipitation of calcite. At a short distance from the spring, the aqueous CO 2 escapes from water to a large degree through molecular diffusion driven by high gradient of partial pressure of CO 2 (P CO 2) between the water and the atmosphere. Such CO 2 outgassing concomitantly causes the saturation index with respect to calcite (SI c) to rise, resulting in subsequent calcite precipitation and thus more CO 2 outgassing. Spatiotemporal variations in the mass transfer of CO 2 and CO 2 outgassing flux show that the rates of both types of CO 2 outgassing are significantly influenced by hydrodynamic conditions, such as flow discharge and streambed morphology. In particular, lower rates of CO 2 outgassing are observed at higher flow discharge, and vice versa. In the studied reach of stream, the primary and additional CO 2 outgassing have caused about 21%–35% and 4%–20% of the total soil CO 2 sequestered in DIC of the feeding spring water to be released back to the atmosphere, respectively and the higher flow discharge, the less CO 2 return. Based on these findings, we postulate that the CO 2 outgassing, especially that induced by calcite precipitation should be relatively smaller in streams which have a lower gradient and elevated discharge rate and where the mixing or dilution of tributaries and increased in-stream metabolism occur. This provides more evidence for the previous conclusion that the H 2 O-carbonate-CO 2 -aquatic phototroph interaction could represent a net carbon sink at least over short timescales. [ABSTRACT FROM AUTHOR]