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Coastal wetlands are seen as efficient coastal stabilizers and provide an optimal natural ecosystem for the sequestration and storage of carbon. Thus, it is critically important for scientists and environmental managers to understand the future dynamics of coastal wetlands. The understanding of yearly to decadal development in coastal ecosystems can assist in the coastal management activity, to sustain biodiversity. In the current study, high-resolution granulometric analysis of a back-barrier salt-marsh deposit of tropical barrier estuary environments at Chandipur, India, is utilized to provide an overview of the mesoscale geomorphic processes and history of changing sediment dynamics. The multivariate statistical examination with coefficients of probability density functions and compositional data analysis helps to determine the four lithofacies of the deposit. Granulometric analysis combined with satellite image analysis reveals that relatively coarser facies were deposited during the incipient stage of the barrier development, when the marshland vegetation was relatively less dense as suggested by the lower normalized difference vegetation index (NDVI) and the saline sea water easily drowned the area and saline sediment was deposited. After rapid marsh accretion, the flow dynamics shifted to a negligible flow component in the final stage when finer facies were deposited in vegetated marshland, and the organic carbon concentration increased up to 3.5%. As plant organic matter and sediment continuously accumulates in this marshland, elevation capital grows and the marsh continues to develop and expand, reaching a densely vegetated marsh with a considerable increase in NDVI values. The findings of this multiproxy study, in conjunction with multivariate statistical analysis, provide valuable insight into the characteristics of accretion in a tropical saltmarsh, which is unique in such a geological setting. [ABSTRACT FROM AUTHOR]

• Sediment OP and OC during the outbreak and decline of algal blooms were studied. • The changes in OC and OP in the sediment were synchronous. • Mono-P was the main component of OP during the decline of algal blooms. • The impact of the algal blooms on active OC in sediment was significant. In this study, sediment organic phosphorus (OP) and organic carbon (OC) in Lake Taihu, China, as well as their relationships, were analyzed during the outbreak and decline of algal blooms (ABs) over a five-month field study. The results showed synchronous temporal changes in the sediment OP and OC contents with the development of ABs. In addition, there was a significant positive correlation between the sediment OP and OC (p < 0.01), suggesting simultaneous deposition and consumption during the ABs outbreak. The sediment OP and OC contents decreased significantly at the early and last stages of the ABs outbreak and increased at the peak of the ABs outbreak and during the ABs decline. These temporal variation patterns suggest that the sediment OC and OP contents did not consistently increase during the ABs outbreak, even though algae are an important source of organic matter in sediments. The depletion or enrichment of OC and OP in sediments may also depend on the scale of the ABs outbreak. The obtained results revealed significant differences in the sediment OC and OP contents between the months (p < 0.05). In addition, OP in the sediments was dominated by orthophosphate diester (phospholipids and DNA-P) and orthophosphate monoester during the ABs outbreak and decline, respectively. The active OC contents and proportions in the sediments in the ABs outbreak were significantly lower than those observed in the ABs decline period, demonstrating the significant impacts of the ABs outbreak and decline on the sediment OC and OP in Lake Taihu. [ABSTRACT FROM AUTHOR]

Identifying organic carbon (OC) sources in lake sediment is essential for elucidating biogeochemical cycling processes and effectively supporting watershed management. However, the complexity of sources as well as environments in the land–river–lake continuum makes it challenging to accurately identify OC sources. Accordingly, the current study utilized a systematic approach to identify and validate OC sources in a typical land–river–lake continuum. Two tracer groups (group 1: δ13C and δ15N; group 2: fluorescence index and biotic index, respectively (where C is carbon and N is nitrogen)) and one model (MixSIAR) were eventually selected from five tracer groups and two models to identify the OC sources in a land–river–lake continuum according to a consistency evaluation and virtual mixing test. The results showed that the distribution of OC sources in lake sediment was spatially heterogeneous. Closer to the lake center (from sampling site S1 to S3), the autochthonous contributions increased while the allochthonous contributions decreased. Downstream of the inlet river (site S1) was dominated by allochthonous contributions (78.6%), especially cropland (28.7% ± 0.5%, where ± indicates a standard deviation range) and urban land (30.5% ± 2.5%). From site S1 to S2, the allochthonous contribution decreased 11.4%. Autochthonous OC gradually became the major source closer to the lake center (site S3: phragmites: 48% ± 4.5%). This distribution of OC sources in the land–river–lake system was attributed to the mixing effect of the autochthonous sources, selective transport of sediment, and human activities. The current findings may aid in validating the ability of different tracers and models to identify OC sources in complex ecosystems and also provide a theoretical basis for watershed management. • Consistency evaluation of multi-indicator facilitated the identification of OC sources. • Stable isotope and fluorescent index were more reliable than fluorescent component. • MixSIAR model was more stable than Iso Source model. • The OC source distribution showed obvious spatial heterogeneity. [ABSTRACT FROM AUTHOR]

Amino acids (AAs) including D- and L- enantiomers are a group of organic nitrogen species in ambient aerosol. Due to the low abundances of AAs (level of ng/m3) and the matrix effects by coexistent components, it is challenging to quantify AA enantiomers in ambient aerosols especially under pollution conditions. In this study, we present an optimized method for analyzing AA enantiomers in atmospheric aerosol samples including a pretreatment process and the detection by high performance liquid chromatography coupled to a fluorescence detector (HPLC-FLD). Matrix effects caused by coexistent chemicals on AA enantiomers analysis in ambient aerosol samples were investigated especially for those collected in pollution episodes. The results revealed that the determination of AA enantiomers is significantly affected by the coexistent organic carbon (as a proxy of organic matter) and water-soluble ion of NH 4 +. To remove the matrix effects, we applied a pretreatment using the solid phase extraction column coupled with alkaline adjustment to sample extract. After pretreatment, 18 AAs including 6 pairs of D- and L-enantiomers (i.e., leucine, isoleucine, valine, alanine, serine, and aspartic acid) can be successfully separated and quantified in aerosol samples by HPLC-FLD. The recoveries are in the range of 67%-106%. This method was successfully applied to the urban aerosol samples from pollution and non-pollution periods for AA enantiomers determination. We suggest that the concentrations of D-AAs and the ratio of D-AA/L-AA are indicative of the contribution of bacterial sources and the influence of biomass burning. [ABSTRACT FROM AUTHOR]

Multistep physical and biological processing of organic matter in marginal seas modifies its composition, sedimentary pathway, and burial efficiency. This study examines how organic geochemical signals pertaining to the source and transformation in surface sediments are transported and preserved in the conduit portion of source-to-sink sedimentary systems in marginal seas such as the Taiwan Strait (TS). The aim is to gain more insight in not only the total OC burial in this highly dynamic region, but also to establish a quantitative assessment of the provenance and age of this carbon. Our study revealed that terrestrial plant wax n -alkanols represent a portion of terrestrial organic matter, characterized by refractory property and strong mobility leading to efficient transfer from the river mouth to the shelf. Soil bacteria-derived branched glycerol dialkyl glycerol tetraethers (br-GDGTs) represent the portion of terrestrial OM characterized by labile properties and low transmissibility restricted within the river mouth under normal conditions, except for episodic and pulse delivery situations. Sedimentary OC in the TS is typically characterized by a large amount of ancient OC with intensive oxidation, indicated by extremely old 14C ages (<13000 ± 180 yr) and lower petrogenic OC content in marine sediments than that of rocks sourced from the land. Diverse sourced OC supply and accumulation patterns in shallow marine conduit systems mainly influenced by complex physical processes. Quantitative source apportionment of sedimentary OC using a ternary mixing model based on the bulk δ13C and Δ14C proxies combined with sediment mass accumulation rates revealed 0.01–3.44, 0.002–3.79, and 0–3.38 mg C cm−2 yr−1 of marine, terrestrial biospheric, and petrogenic OC burial loadings in the TS. Marine OC burial could only explain 30% of net air–sea CO 2 sequestration in a narrow conduit system such as the TS, which is characterized by high sediment resuspension and strong hydrodynamic processes due to strong tidal currents and wind-driven circulation. Our findings revealed the net C buried in different marginal seas varies as a function of local couplings between physical processes and biogeochemical characteristics. [ABSTRACT FROM AUTHOR]

The relationship between the proportions of multicomponent mixtures with the technological properties of ceramic granular materials (synthetic aggregates) has been studied using statistical methods. The four phases involved in the formulations have been: kaolin (K) as aluminosilicate source; cork powder (C) as organic carbon source; sodium carbonate (N) as flux and pyrite (P) as source of iron and sulfur. The Mixture Experiments - Design of Experiments (ME-DOE) has been the statistical methodology applied from the initial configuration of the 36 starting formulations to the final validation of the models and optimums. After granulation, artificial aggregates have been obtained by sintering in a rotary kiln, and their main technological properties have been determined. Bloating index (BI), particle density (ρ rd), water absorption (WA 24) and crushing strength (S) were selected as the four key characteristics to be modeled and optimized, using response surface and effect plots to assess the effect of K, C, N and P on such properties. 32 out of 36 starting varieties met the density criteria for lightweight aggregates. In the optimum formulations obtained, the minimum percentage of K was 83 wt%, so that the variations in the percentages of P, C and N were the critical variables for determining the final properties of the aggregate. The contrast between experimental and estimated data has shown that the models fit adequately, indicating that this type of approach may have enormous potential for future research on artificial aggregates and other ceramic materials. [ABSTRACT FROM AUTHOR]

The deposition of fluvially derived terrestrial organic carbon (OC) together with marine OC in marine sediments has important implications for the global carbon cycle. However, dispersal extent and fates of terrestrial soil and petrogenic OC on the continental shelf have remained unclear and debated. Here, we present OC compositions and mineral properties of marine sediments from the Gulf of Thailand and the adjacent Mekong shelf, as well as river sediments from continents surrounding them in order to determine the provenance of sedimentary OC in this tropical epicontinental sea. We find that stable carbon isotope composition (δ13C) and radiocarbon activity (Δ14C) of sedimentary OC fall between those of marine OC and of river sediments, mainly composed of C3 plant-dominated pre-aged soil and petrogenic OC. Mixing model reveals that the OC in river sediments is predominantly sourced from pre-aged deep soils, accounting for 73 ± 5%, with the remaining consisting of modern surface soil (25 ± 6%) and bedrock (2 ± 1%). The sedimentary OC on the shelf is primarily derived from marine OC, accounting for 65 ± 15%, with terrestrial soil OC and petrogenic OC contributing 24 ± 14% and 10 ± 5%, respectively. The sources, degradation, and aging of OC and mineral surface area determine the spatial pattern of sedimentary OC compositions in the Gulf of Thailand and the Mekong shelf. The contents of marine, soil, and petrogenic OC decrease with increasing distance offshore, consistent with changes in spatial patterns of sedimentation rate of terrestrial materials and of marine primary production in the overlying water column. Extensive degradation of terrestrial OC and extremely low OC burial rate in this tropical epicontinental sea suggest a minor role on OC sequestration in marine sediments, but an important CO 2 source to the atmosphere in the context of the global carbon cycle. [ABSTRACT FROM AUTHOR]

Early diagenesis of marine organic matter dramatically impacts Earth's surface chemistry by changing the burial potential of carbon and promoting the formation of authigenic mineral phases including carbonate concretions. Marine sediment-hosted carbonate concretions tend to form as a result of microbial anaerobic diagenetic reactions that degrade organic matter and methane, some of which require an external oxidant. Thus, temporal changes in the oxidation state of Earth's oceans may impart a first-order control on concretion authigenesis mechanisms through time. Statistically significant variability in concretion carbonate carbon isotope compositions indicates changes in shallow marine sediment diagenesis associated with Earth's evolving redox landscape. This variability manifests itself as an expansion in carbon isotope composition range broadly characterized by an increase in maximum and decrease in minimum isotope values through time. Reaction transport modelling helps to constrain the potential impacts of shifting redox chemistry and highlights the importance of organic carbon delivery to the seafloor, marine sulfate concentrations, methane production and external methane influx. The first appearance of conclusively anaerobic oxidation of methane-derived concretions occurs in the Carboniferous and coincides with a Paleozoic rise in marine sulfate. The muted variability recognized in older concretions (and in particular for Precambrian concretions) likely reflects impacts of a smaller marine sulfate reservoir and perhaps elevated marine dissolved inorganic carbon concentrations. Causes of the increase in carbon isotope maximum values through time are more confounding, but may be related to isotopic equilibration of dissolved inorganic carbon with externally derived methane. Ultimately the concretion isotope record in part reflects changes in organic matter availability and marine oxidation state, highlighting connections with the subsurface biosphere and diagenesis throughout geologic time. [ABSTRACT FROM AUTHOR]

The fixation of environmentally hazardous Cr(VI) in soils is largely attributed to its retention by iron (Fe) (oxyhydr)oxides in the soil environment, which are prevailingly associated with organic carbon (OC). The effect of OC with different binding strengths on Cr(VI) adsorption and the mobility and fate of Cr(VI) during aging of Fe (oxyhydr)oxide however, are unknown. Here we investigate how OC binding strength influences Cr(VI) adsorption to ferrihydrite (Fh) organominerals, the aging of Fh organominerals and the subsequent retention or release of Cr(VI) as aging proceeds. We conduct Cr(VI) adsorption experiments onto Fh organominerals, apply surface complexation modelling to study the relative binding strengths between OC and Cr(VI), and then conduct aging experiments to track the redistribution of Cr(VI). We show based on the relative binding strength between OC and Cr(VI), that weakly-bound OC at different C loadings has almost no discernable influence on Cr(VI) adsorption, while strongly-bound OC significantly suppresses Cr(VI) adsorption via surface site blocking and/or electrostatic repulsion. The mobility and fate of Cr(VI) with Fh organominerals during the aging process is strongly influenced by the presence of OC. Weakly-bound carboxyl-poor OC not only near doubles the rate of Cr(VI) retained (i.e., Cr(VI) redistribution from a weakly-bound to a strongly-bound fraction) in neoformed Fe minerals at pH 5.0, but also increases the final proportion of Cr(VI) strongly-bound , which we attribute to the loose and porous structure of Fh organominerals and easier replacement of weakly-bound OC by Cr(VI). More strongly-bound carboxyl-rich OC and higher pH however, reduces the influence of OC, such that the rate of Cr(VI) retained is similar to or lower than that for the pure Fh system, which we attribute to the fact that the strongly-bound OC is less easily replaced by Cr(VI) and hence Cr(VI) is less able to access surface sites or surface pores and thus to be retained inside neoformed minerals. Overall we suggest that OC with higher carboxyl-richness will further suppress the rate of Cr(VI) retained and overall proportion of Cr(VI) strongly-bound , and thus that the mobility and fate of Cr(VI) in soils is strongly controlled by the carboxyl-richness of OC in Fe organominerals. [ABSTRACT FROM AUTHOR]

Carbonaceous aerosols primarily comprise organic carbon (OC) and black carbon (BC). Thermal-optical analysis (TOA) is the most commonly used method for separating carbonaceous aerosols into OC and EC (BC is referred to as elemental carbon EC, in this method). Advances in hardware design and algorithms have expanded the capabilities of TOA beyond just distinguishing OC and EC. However, a comprehensive understanding of the enhanced functionality of TOA is still lacking. This study provides the first comprehensive review of the TOA technique, highlighting expanded capabilities to measure brown carbon (BrC), mass-absorption efficiency, absorption enhancement, source contributions, and refined OC/EC split points. This review discusses the principles, advantages, and limitations of these advancements. Furthermore, the TOA system anticipates further advancements through integration with other instruments, establishing correlations between EC values obtained from different TOA instruments/protocols, correlating between BrC measurements from TOA and non-TOA methods, and developing an algorithm to quantify BrC from progressive absorption Ångström exponent (AAE) values. This review enhances the understanding of the TOA system and its implication for air quality and atmospheric radiation research. [Display omitted] • The capability of thermal/optical analysis (TOA) technique has been notably expanded. • Brown carbon can be measured by a multiwavelength TOA instrument. • New TOA instruments can measure black carbon's absorption efficiency and enhancement. • Incorporating a receptor model enables TOA technique to apportion ambient aerosol. • OC/EC split can be refined by visualizing optical attenuation during a TOA process. [ABSTRACT FROM AUTHOR]

Effects of freeze-thaw cycles on nutrient cycling and microbial activity have been well documented in laboratory simulations; however, field evidence remains insufficient, and studies regarding their effects on soil quality index (SQI)—as evaluated by soil functions that are influenced by multiple soil properties—are scarce. Therefore, we conducted spatiotemporal paired soil profile surveys along a freeze-thaw intensity gradient covering six grassland types. Results are as follows: 1) After a seasonal freeze-thaw event, soil properties across the 0–80 cm profile changed by 0.96%–31.02% (physical), −34.29%–44.04% (chemical), and −70.46%–272.97% (biological), with change rates varying across soil layers. 2) A function-based framework was employed to assess SQI 0–30 under freeze-thaw conditions, and the reliability of the function indices and SQI 0–30 was validated. 3) Compared to pre-freezing levels, post-thawing water retention and regulation index changed negligibly (+5.31%), carbon sequestration index remained stable (+2.52%), and the primary productivity index declined noticeably (−9.43%). Conversely, the nutrient supply and cycling index increased notably (+23.89%) due to elevated total potassium, catalase activity, and urease activity. The biodiversity provision index improved substantially (+95.63%) owing to increased dissolved organic carbon. Collectively, the SQI 0–30 increased evidently by 11.78%. 4) These alterations were associated with different freeze-thaw indicators, and the daily freeze-thaw temperature difference at 0–10 cm during the "freezing→frozen→thawing" period explained 55% of the SQI 0–30 change, surpassing impacts of meteorological factors (precipitation, air temperature, and snow depth). Our study suggests that natural seasonal freeze-thaw events can raise alpine grassland soil quality, with varied functional responses. The identified soil indicators and functions sensitive to freeze-thaw cycles facilitate the research on seasonal dynamics of alpine grassland soil and its multi-objective management, and the quantitative relationships with freeze-thaw indicators provide new insights for regional soil mapping in frozen areas under climate change. • A function-based assessment was applied for alpine grassland soil quality. • Biodiversity provision index notably increased with enhanced DOC after soil thawing. • Primary productivity index declined due to rising soil pH after soil thawing. • Nutrient-related function improved due to elevated total potassium and enzyme activities. • Daily freeze-thaw temperature difference at 0–10 cm greatly influenced SQI 0–30. [ABSTRACT FROM AUTHOR]

The Jiaozhou Bay (JZB) intertidal zone is a significant carbon reservoir that plays a crucial role in transporting and accumulating organic matter; however, quantitative studies of organic matter sources are scarce. In this study, we present bulk parameters of total organic carbon (TOC), TOC/TN, δ13C, and biomarker contents in 36 surface sediment samples from the JZB intertidal zones to quantify the contribution of organic carbon (OC) derived from terrestrial/marine sources, such as C 3 plants, C 4 plants, estuarine productivity, sewage outlets, and marine productivity. The results demonstrated that a two-end-member model based on the traditional indicators of TOC/TN or δ13C is not appropriate for quantifying the OC source. The presence of C 3 plants, C 4 plants, and sewage outlets in the JZB intertidal zone could lead to errors in determining OC contribution when solely using TOC/TN or δ13C. A classical mixing diagram (three-end-member model) utilizing TOC/TN and δ13C values revealed that OC contribution was dominated by marine productivity throughout the intertidal zone. In the west, the average OC contribution from marine productivity, estuarine productivity, and C 4 plants was 73.8 %, 14.2 %, and 12.0 %, respectively. In the east, the average OC contribution from marine productivity, estuarine productivity, and sewage outlets was 57.6 %, 24.9 %, and 17.4 %, respectively. The higher OC contribution from marine productivity in the west was attributed to the occurrence of Spartina alterniflora , while the OC contribution from estuarine productivity in the east was primarily due to the presence of more rivers flowing into the JZB compared to the west. By combining biomarkers and OC contents, a significant positive relationship verified the suitability of the end-member values selected for the three-end-member mixing model in the west and east intertidal zones of JZB. This finding was further supported by principal component analysis (PCA) analyses of these proxies. This study demonstrated that OC sources in intertidal zones varied among contrasting coastal environmental conditions and addressed the knowledge gap regarding biogeochemical cycles and ecological protection in the JZB intertidal zones. • The two-end-member model was not appropriate for quantifying the OC source in the JZB. • The OC contribution was dominated by marine productivity based on TOC/TN and δ13C. • The significant positive correlation occurred between biomarkers and OC contents. [ABSTRACT FROM AUTHOR]

Thawing Arctic permafrost is releasing massive amounts of terrestrial mercury (Hg) into the Arctic shelf, which is expected to form a Hg sink in sediments. Here we analyzed the coupling roles of terrestrial input and biological processes in varying mineral/organic matrix-related Hg sequestration and deposition on the East Siberian Arctic shelf (ESAS), using Pearson and partial correlation analysis. Results show that the occurrence of Hg in the Laptev Sea under the Lena River-dominated input exhibits strong correlations with the organic carbon (OC) content and sediment specific surface area. This indicates that the prolonged riverine loading processes facilitate Hg sequestration by organic/mineral matrices and these land-derived mineral-OC-Hg complexes remain stable during cross-shelf transportation. By contrast, the comparative samples with coastal erosion-dominated Hg input in the western East Siberian Sea shows limited Hg complexation, primarily due to the absence of regulation by riverine processes and/or the high sedimentation rates. The correlations between Hg and OC source proxies (δ13C and lignin) indicate that these matrix-free Hg could be more readily sequestrated by the marine OC, which facilitates its deposition via the biological pump. While unexpectedly low Hg abundance in the Chukchi Sea may indicate that the effective biological scavenging of Hg sequestration could be constrained by insufficient terrestrial Hg input. Our findings of the matrix-related Hg sequestration by mineral and/or OC association in this study may shed light on the biogeochemical cycle of Hg in the Arctic aquatic regime, which could reduce the methylmercury formation in water column, and the methylation within sediments needs further exploration. • Rapid release of terrestrial Hg via coastal erosion limits Hg complexation with organic carbon (OC) and/or mineral matrixes. • River-dominated Hg input is exported and transported as mineral–OC–Hg complexes due to prolonged riverine loading processes. • The synergy of terrestrial input and primary productivity regulates the deposition and fate of Hg in the Arctic shelf. [ABSTRACT FROM AUTHOR]

This study aims to elucidate the environmental changes signified by biogenic components, assess fluctuations in upwelling over the past century, and evaluate the potential risks associated with variations in coastal upwelling intensity on the degradation of fisheries within the Zhoushan Fishing Ground. High-resolution sediment records were established to reveal long-term variations in Zhoushan coastal upwelling. Results showed a significant reduction in nutrient components between 1900s and 1950s, suggesting a decline in upwelling strength. Since the 1960s, lightened δ15N and the incline of nutrients suggests an increase in anthropogenic nutrients influx, and increased OP and CUI SST (SST-based coastal upwelling index) indicates strengthening of upwelling during the 1950s to 1980s. A positive correlation between organic phosphorus (OP) and δ13C has been observed since the 1960s, implying that P is a limiting nutrient due to increasing anthropogenic N influx, and the change in CUI SST coincides well with our OP records. OP is a potential indicator of upwelling strength because upwelling contributes to over 90 % of the P on the East China Sea shelf. A prominent decline in the nutrient composition occurred from the 1980s to 2010s, despite substantially increased anthropogenic nutrients influx and eutrophication in adjoining Changjiang delta regions in the past decades. Weakening upwelling and the consequent decreasing nutrients influx has presumably hindered recovery and thus contributed to the degradation of fishery resources in recent decades. [Display omitted] • Nutrient and organic carbon changes have occurred on the Zhoushan coast since 1900. • The correspondence between OP and δ13C suggestsP limitation since 1960s. • Changes in OP and the SST-based coastal upwelling index indicating correspond. • OP is determined as an indicator of upwelling. • Weakening upwelling has hindered the recovery of fishery resources since the 1980s. [ABSTRACT FROM AUTHOR]

Air pollution in upper Southeast Asia (SEA) has become critical particularly regarding atmospheric particles. This study aims to investigate the sources and formation of fine size-fractionated particulate matters (FSPMs), as well as their potential impact on climate. Particulate matter in three size ranges (2.1–1.1 μm, 1.1–0.65 μm, and 0.65–0.43 μm) was collected using cascade impactors in rural Chiang Dao (CD) and urban Chiang Mai (CM) during the smoke haze period (March–April 2019) in Chiang Mai, Thailand. The average concentration of FSPM was approximately 1.3 times higher in rural CD (88 ± 34 μg/m³) than in urban CM (66 ± 26 μg/m³). Both areas showed significantly higher concentrations of finer particles, with rural CD detecting 41 ± 17 μg/m³ (46% of FSPM) and urban CM presenting 27 ± 11 μg/m³ (41% of FSPM). Total carbon (TC) concentrations, including organic carbon (OC) and elemental carbon (EC), showed the same pattern as PMs. The most abundant fractions, including OC3 (32–45% of total OC) and EC1 (91–100% of total EC) in FSPM samples, particularly in fine particles (PM1), suggest that biomass burning was the primary source. Source classification based on diagnostic ratios of polycyclic aromatic hydrocarbons (PAHs), OC/EC ratios, combined with primary and secondary formations, revealed that PM 2.1-1.1 was influenced by biomass burning and secondary organic carbon (SOC), while PM 0.65-0.43 originated from both SOC and vehicular emissions. PM 1.1-0.65 in the rural area was probably caused by SOC and other mixed sources, whereas SOC and vehicular emissions were the main source in urban CM. With respect to the effective carbon ratio (ECR), lower values were observed in finer particles (0.37 ± 0.15 in rural CD and 0.36 ± 0.38 in urban CM), suggesting enhanced light-absorbing properties of fine particulate matter during the haze period in the upper SEA region. [ABSTRACT FROM AUTHOR]

• Aliphatic carbon compounds were found in a martian meteorite via in-situ techniques. • Catalytic surfaces of titano-magnetite could have driven Fischer–Tropsch synthesis. • Organics likely formed in hydrothermal conditions after an impact cratering event. • Our sample approximates the martian regolith as a case study for mars sample return. The martian meteorite Northwest Africa (NWA) 11220 and paired stones (notably NWA 7034) are the only group of meteorites that sample a clastic near-surface lithology from Mars. The stones have been recognized as an impact-reworked lithology subjected to an impact-induced hydrothermal system — comparable to the postulated history of Jezero Crater, currently being explored by the NASA Perseverance rover. By applying Mössbauer spectroscopy in combination with several in situ analytical techniques including Raman spectroscopy, FTIR spectroscopy, and NanoSIMS, we show that aliphatic carbon compounds dominate the inventory of insoluble indigenous carbon compounds within NWA 11220. Disordered carbon — present in ∼5 μm heterogeneous masses — is preferentially found within porosity where it adjoins the mineral surface of titano-magnetite. This relationship suggests catalytic surfaces have enabled Fischer–Tropsch (FT) synthesis of hydrocarbons. Our in situ micron-scale analytical study indicates that such methods can help determine the origin of organic material that exists in the near-surface martian regolith. Such multimodal approaches will be a key methodology for searching for traces of past life in future samples returned from Mars. [ABSTRACT FROM AUTHOR]

Marginal sea sediments offer one of the most stable and critical carbon repositories of sequestered organic carbon (OC). Quantification of the magnitude and the potential of OC sequestration in marginal sea sediments could provide data supporting the formulation of coastal carbon management strategies in the future. Nonetheless, controversies and difficulties still exist given the lack of integrity on statistical data, the incomplete understanding of the complex OC sources and the dynamic processes in the marginal seas. This work presents a systematic and holistic analysis of the OC stock and carbon stock accumulation rate (CSAR) in surface sediments (0–5 cm) of the Eastern China Marginal Seas (ECMS). The estimated total OC stock in the top 5 cm sediments in the ECMS (9.57 × 105 km2) was 201.48 ± 15.98 Tg and the sequestration rate was 24.24 ± 9.93 Tg per year. Because only the preservation of fresh terrestrial OC and the marine OC is regarded as a valid CO 2 sink on modern timescale, we further elucidated the magnitude and the potential of the valid OC stocks and CSAR with different sources and ages based on the δ13C and Δ14C. This study quantifies high resolution OC stock and CSAR and presents the magnitude and potential of the valid sedimentary carbon sink in the ECMS. • The total OC stock of the Eastern China Marginal Seas (ECMS) was 201.48 ± 15.98 Tg. • The total CSAR in the ECMS was estimated as 24.24 ± 9.93 Tg yr−1. • The sources and ages of OC stock and CSAR were distinguished basing δ13C and Δ14C. [ABSTRACT FROM AUTHOR]

Mercury (Hg) concentrations normalized to their dominant hosts have been widely used to identify geological events such as massive volcanic eruptions. However, the modern Hg cycle has significantly changed, and the implications of host-normalized Hg concentrations for the Hg dynamics in contemporary coastal environments (e.g., sources, delivery mechanisms, and Hg fluxes) remain poorly understood. In this study, 66 surface sediment samples from the continental shelf of the East China Sea (ECS) were analyzed, and the total organic carbon (TOC), aluminum (Al), total sulfur (TS), and Hg concentrations were determined. Our results support that organic matter predominantly hosts Hg in these sediments. Factors such as the Hg source and abundances of organic fractions influence Hg distributions, with notable enrichment in the Changjiang River estuary and the inner shelf of the ECS, especially near the mud depocenter located off the Oujiang River estuary. The oxic to suboxic redox state and the lack of significant sulfide accumulation in surface sediments suggest that sulfides are not the primary Hg hosts. The Hg/TOC ratios, ranging from 3.0 to 169.6 (ppb/%), are particularly high in the Changjiang River estuary and exhibit an exponential correlation with the Hg accumulation rates (Hg-AR). These findings suggest that the host-normalized Hg concentration could serve as a valuable tool for assessing Hg dynamics where the accumulation rates are uncertain. • Organic matter is the dominant host for Hg in the East China Sea continental shelf. • The extremely low TS content does not support its role as a host phase for mercury. • The abundance of TOC controls the variations of Hg in spatial. • The Hg/TOC ratio indicates that the Changjiang serves as the primary source of Hg inputs in the East China Sea. [ABSTRACT FROM AUTHOR]

Approximately 220 million hectares of former croplands are abandoned worldwide, with a quarter of this area located in Russia. In these areas, natural zonal vegetation is developing, and the soils, including soil carbon (C) stocks, are recovering. Accumulated organic C serves as a structural and energetic source for soil microorganisms. Postagricultural soil restoration affects organic matter stability, microbial organic carbon decomposition, and C cycling. We studied a chronosequence of abandoned croplands in the Eastern Siberian forest steppe zone (Haplic Luvisol) to assess the effects of cropland natural restoration on the stability of soil organic matter (SOM) and energy stocks. The energy content and thermal stability of C in the bulk soil, in free and occluded particulate organic matter (fPOM and oPOM), and in mineral-associated organic matter (MAOM) were analysed by thermogravimetry and differential scanning calorimetry as proxies for С available for microbial decomposition. The soils sequestered 0.85 Mg C ha−1 y−1 (0–30 cm) during the first 25 years after abandonment. In abandoned soils, thermally labile C with an activation energy of 69±0.6 kJ·mol⁻¹ accumulated 2.8 times faster than did stable C with a higher energy barrier to combustion (80±0.5 kJ·mol⁻¹). This increased energy availability and microbial activity led to faster C and nutrient cycling in the abandoned soils than in soils of current croplands. MAOM stored 1.7 times more energy per unit of C (42 kJ·g⁻¹ C) than did the free and occluded POM fractions (25 kJ·g⁻¹ C). fPOM was the dominant energy pool for labile C in the restored soil and increased microbial activity. Due to the preferential accumulation of C with lower thermal stability and with greater susceptibility to microbial decomposition in the restored soils, greater CO 2 release could occur if these lands are tilled again. The content of thermally stable C also increased in abandoned soils; therefore, we must account for the ecological balance between C sequestration and release after the natural restoration of croplands. [Display omitted] • Haplic Luvisol accumulated 0.85 Mg C ha−1 annually after cropland abandonment. • Thermally labile SOM accumulated 2.8 times faster than stable SOM. • Cropland abandonment increased energy content in SOM for 1.8 times over 25 years. • Ratio of labile to stable C in SOM increases during the cropland restoration. • MAOM stored 1.7 times more energy compared to free and occluded POM. [ABSTRACT FROM AUTHOR]

• Coastal vegetation type and rhizosphere effect jointly drove soil SOC and HFOC accumulation. • Higher soil alkalinity exerted significant inhibitory effects on SOC, ROC, MAOC and HFOC. • Phosphorus acquisition capacity contributed significantly to coastal SOC fractions and their accumulation. • The construction of coastal protection forests improved soil carbon sequestration in saline-alkali soils. Rhizosphere processes are key pathways through which plants influence the carbon cycling of diverse ecosystems and are closely associated with vegetation types. However, the environmental responses of rhizospheric soil organic carbon (SOC) mediated by the interaction between rhizosphere effect and vegetation type remain uncertain, severely limiting our assessment of the carbon sequestration potential of different coastal vegetation. Here, we identified the core factors driving changes in various soil carbon fractions in the rhizosphere of four coastal vegetation types by testing the contents of the reactive, dissolved, particulate, mineral-associated, heavy and light fractions of SOC and their relationships with physicochemical properties and enzyme activities. It was found that the rhizosphere effect significantly influenced SOC, with rhizospheric SOC contents varying significantly among vegetation types, ranging from 2.12 to 9.04 g/kg. Besides, rhizospheric soil pH was found to contribute significantly to SOC fractions (except for light organic carbon) and exert significant inhibitory effects on SOC, reactive organic carbon, mineral-associated organic carbon and heavy organic carbon. Despite the different responses of various SOC fractions to physicochemical properties and enzyme activities, soil available phosphorus and alkaline phosphatase activity emerged as core environmental factors influencing rhizospheric SOC accumulation across different coastal vegetation types. This study presents a promising framework for understanding the determinants of SOC fractions in rhizospheric soil, and their accumulation in the vegetation of coastal saline-alkali soils. In addition to alkalinity, phosphorus acquisition capacity can be a key predictor of coastal SOC fractions and their accumulation. [ABSTRACT FROM AUTHOR]

[Display omitted] • Applies a novel approach based on the check dam deposit of an individual event. • Establishes the inter-gully areas as the main source of the sediment-associated TOC. • The main sources of the two organic C fractions (POC and MOC) were different. • Approximately 10% of the TOC mobilized by erosion was lost during delivery to the dam. • The lost carbon was dominated by POC, while MOC accounted for ca. 13% of the loss. Information on the sources and fate of organic carbon mobilized by soil erosion is crucial for understanding the impact of erosion on carbon (C) cycling. However, few studies have evaluated this in low-order stream systems. In this study, we adopted a novel approach, that used the sediment deposited behind a check dam constructed at the outlet of the Fengzigou catchment (0.91 km2) on the Chinese Loess Plateau by a single high magnitude storm event, to simplify the field sampling requirements. The total sediment-associated organic carbon (TOC) was fractionated into particulate organic carbon (POC) and mineral associated organic carbon (MOC). These results were combined with those from a sediment source tracing exercise. This made it possible to explore further the source and loss of the sediment-associated organic carbon. The results showed that the inter-gully areas contributed the most eroded TOC (52.3 ± 7.6 %) and, together with the gully walls, represented the main TOC source. The primary contributor of the POC fraction in the deposited sediment was the inter-gully areas (80.5 ± 12.6 %), whereas the gully walls were the main contributor of the MOC fraction (54.9 ± 10.2 %). The total output of sediment produced by the event was 1304 ± 48 t and the equivalent value for sediment-associated TOC was 2.94 ± 0.26 t, of which the POC fraction accounted for 27.6 ± 3.6 % and the MOC fraction 72.4 ± 9.8 %. The TOC lost (0.3 ± 0.02 t) through the mobilization and delivery processes was 10.2 ± 1.2 % of the TOC mobilized by erosion, and the lost carbon was dominated by the POC fraction (86.7 ± 8.8 %). The specific TOC output from the catchment associated with the event documented was 0.3 t km−2. This work demonstrates the potential for erosion-induced carbon redistribution to provide a source for atmospheric CO 2 in the study area. [ABSTRACT FROM AUTHOR]

• Earthworm increased plant biomass, particularly in infertile soils. • The impacts of root and earthworm on aggregate varied with soil moisture and types. • Root and earthworm jointly promoted carbon accumulation associated in aggregates. Soil's potential as a carbon sink is uncertain due to biotic and abiotic interactions. Soil aggregates are important carriers of organic carbon (OC), and clarifying the response of aggregates and their associated OC to plant roots and earthworms can better understand the carbon cycle in terrestrial ecosystems. Herein, we determined the regulatory role of plant roots (Lolium perenne) and earthworms (Metaphire tschiliensis) in isolation and in combination on aggregate size distribution and their associated OC and readily oxidizable OC (ROOC) under contrasting soil types (Phaeozems and Anthrosols) and soil moisture conditions (constant wetting, CW; wetting–drying cycle repeated four times, 4WD) by a laboratory microcosm experiment. Results showed that earthworm presence significantly increased plant biomass by 30 % and 221 % in Phaeozems and Anthrosols, respectively (p < 0.05). For Phaeozems, plant alone (P) and plant and earthworm in combination (PE) had lower proportion of large aggregate (5–8 and 2–5 mm) than bare soil (CK) under 4WD condition (p < 0.05). For Anthrosols, the PE treatment decreased the proportion of 5–8 and 2–5 mm aggregate by 45 % and 25 %, respectively, under CW condition, and decreased the proportion of 5–8 mm aggregate by 37 % under 4WD condition (p < 0.05). Moreover, the proportion of 5–8 and 2–5 mm aggregate in P treatment was lower under CW condition (6.92 % and 22.13 %) but was higher under 4WD condition (11.49 % and 32.55 %) than those in CK (14.69 % and 29.91 %; 8.85 % and 20.56 %) (p < 0.05). Our results further indicated that the PE treatment had relatively higher OC and ROOC contents, especially for small aggregates in Anthrosols. The study indicates that plant roots and earthworms significantly influence aggregate turnover and the carbon cycle, with soil type and moisture playing a crucial role. [ABSTRACT FROM AUTHOR]

For four decades, cordgrass (Spartina alterniflora) has invaded salt marshes in the Yellow Sea, altering physical, biogeochemical, and biological processes. Here, we investigated the ecological effects of S. alterniflora invasion on benthic environments compared to native halophytes. S. alterniflora contributed to higher carbon accumulation rates compared with bare tidal flat in sediments (3.4 times), through greater primary production and root biomass, compared to Suaeda japonica (2.5 times) and Phragmites australis (2.4 times) over the given period. The results showed that S. alterniflora eradication treatments inhibited its growth but did not significantly affect the benthic communities. Compared to P. australis and bare tidal flats, S. alterniflora invasion resulted in lower greenhouse gas emission and higher contributions to macrobenthos nutrition, and increased sediment stability and carbon burial. Overall, these multiple lines of evidence provide new insights on S. alterniflora invasion, suggesting that the current eradication policy would be carefully reviewed. [Display omitted] • Elevated temperature was identified as a key correlate of Spartina expansion. • Spartina significantly contributed to C burial, compared to native halophytes. • Spartina eradication treatments did not significantly affect benthic communities. • Spartina offers advantages such as GHGs emission, food supply, sediment stability. [ABSTRACT FROM AUTHOR]

The application of manure and earthworms are frequently used in fertilization practices to improve C, N, and P cycling in soil, which may be adversely affected by roxarsone (ROX), as an organoarsenical pollutant. To effectively address this issue, in this work, the interactive impacts of ROX and earthworm Eisenia foetida on the aggregate formation, input of organic carbon (OC), and changes in the available N and P following 56-day cultivation were systematically investigated. Compared to the control, earthworms increased the mean weight diameter (MWD) of the soil aggregates from 0.6 to 1.1 mm. Thereby, they activated soil enzymes including catalase (CAT), sucrase (SC), urease (UE), and neutral phosphatase (NP), with the soil's pH decreased to 7.1. Consequently, the values of OC, soluble nitrite (NO 3 -N), and Olsen-P content were respectively increased by 0.78-, 1.69-, and 0.87- folds in the E treatment (14.3 vs. 25.5 g/kg, 12.8 vs. 33.3 mg/kg, and 7.8 vs. 14.6 mg/kg). Although the changes in the R treatment were slight, ROX reduced the earthworm-mediated improvements of soil fertility during the application of the RE treatment compared to the E treatment, i.e., the values of MWD, OC, NO 3 -N, and Olsen-P were reduced to 0.9 mm, 20.4 g/kg, 25.4 mg/kg, and 11.6 mg/kg, respectively. From the well-fitted structural equation models, it was demonstrated that earthworms enhanced the aggregate formation and nutrient cycling of OC, NO 3 -N, and Olsen-P, which were inhibited by ROX. Overall, these adverse effects can be offset by earthworm addition, which can play the dual role of monitor and driver for the soil properties. Our work provides insightful strategies for ROX-bearing manure management. [Display omitted] • Earthworm facilitated the manure mineralization by forming soil aggregate. • ROX interfered the earthworm-enhanced soil enzymatic activities. • ROX inhibited the fertilization effect of manure by suppressing earthworm activity. [ABSTRACT FROM AUTHOR]

Fluorescence lifetimes and quantum yields featuring polycyclic aromatic hydrocarbons (PAHs) and other organics constituting pyrogenic carbon particulate matter (PM) are seldom measured. In this work, PM sampled in a fuel-rich ethylene flame was firstly separated in organic carbon (OC), soluble in dichloromethane, and refractory organic carbon (ROC), soluble in N -methyl pyrrolidinone, and then analyzed by size exclusion chromatography (SEC) coupled with online UV and fluorescence detection, and by offline fluorescence spectroscopy and mass spectrometry. It was found that three classes of differently light emitting carbon dots (CDs) could be bottom-up synthesized in the same flame system by selecting appropriately the residence time. Actually, OC presented blue fluorescence regardless the residence time, whereas ROC sampled at low and high residence time emitted fluorescence in the green (green CDs) and in the yellow (yellow CDs) region, respectively. The SEC molecular weight of all CDs presented similar trimodal distributions, centered around 300, 1000 and 10,000 u. For the first time fluorescence lifetimes and quantum yields of pyrogenic CD fractions were measured as additional parameters useful for discriminating the fluorescent components and inferring their structural properties, with the support of mass spectrometry. The different spectroscopic features of CDs could be associated to different compositional characteristics as the polydispersity of molecular components featuring blue CDs, opposed to the oligomer-like nature of green and yellow CDs. Pyrogenic CDs showed different fluorescence emission ranges, quantum yield and lifetimes, appealing for their possible applications in the fields of imaging, electronics and sensors. [Display omitted] [ABSTRACT FROM AUTHOR]