Composition δ13C Research Articles

Tree-ring δ13C of Pinus koraiensis is a better tracer of gross primary productivity than tree-ring width index in an old-growth temperate forest

Tree-ring carbon (C) isotope composition (δ13C) varies depending on photosynthetic capacity and stomatal conductance, and it is therefore intrinsically associated with vegetation productivity. Still, very little is known about the relationship between tree-ring δ13C values and forest gross primary productivity (GPP). Here, we investigated relationships between tree-ring δ13C, tree-ring width index (RWI) and ecosystem-level GPP in a Korean pine (Pinus koraiensis)-dominated old-growth temperate forest in northeastern China. Specifically, we generated chronologies of RWI and δ13C from early-wood (δ13CEW) and late-wood (δ13CLW) of Korean pines, and we built a 17-year continuous ecosystem-level GPP series using eddy covariance measurements, in which a GPP model was used for gap filling. RWI showed vague relationships with tree-ring δ13C and whole-forest GPP, and it was insensitive to interannual variations in climate at the study site. By contrast, both δ13CEW and δ13CLW showed significant relationships with climate variables and GPP. This suggests that isotopic signals of photosynthetic C uptake were imprinted on the formation of tree rings and that tree-ring δ13C of Korean pine is a better proxy for forest GPP than RWI. In addition, tree-ring δ13C of Korean pines was positively correlated with GPP, with an especially close relationship between δ13CEW and GPP of the current year. This implies that photosynthetic activity, rather than stomatal conductance, was the main driver of tree-ring δ13C signals of Korean pine and it was mainly influenced by the climate conditions of the current year, probably because of a limited use of previously fixed C during early-wood formation. Our findings demonstrate the great potential of tree-ring δ13C for reconstructing GPP timeseries at the centennial scale for forest ecosystems, and they could help to constrain parameters in terrestrial C cycle models to improve predictions of C fluxes.

Bacterial physiology highlighted by the δ13C fractionation of bacteriohopanetetrol isomers

Lipid biomarkers, such as the various bacteriohopanetetrol (BHT) isomers studied here, are useful tools in tracing bacterially mediated nitrogen and carbon cycle processes affecting greenhouse gas emissions, including the anaerobic oxidation of ammonia. Three BHT isomers occur commonly in the environment. By gas chromatography, BHT-34S elutes first; it is produced by numerous bacteria. The two later eluting isomers are more constrained in their origin. The marine anammox bacteria ‘Ca. Scalindua’ is the only known producer of a BHT isomer of unknown stereochemistry (BHT-x), making BHT-x a diagnostic biomarker in anoxic marine settings. The BHT-34R isomer is produced by three freshwater aerobic heterotrophic producers (Frankia spp., Acetobacter pasteurianus, and Komagataeibacter xylinus), a freshwater serine-cycle (Type II) methanotroph (Methylocella palustris), and the freshwater anammox ‘Ca. Brocadia’, which makes the detection of freshwater anammox using BHT-34R more complicated. We investigated whether the source of BHT-34R in freshwater environments could be ascertained via its δ13C value. We used conventional on-column gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS) (as opposed to high temperature GC-C-IRMS) to determine the δ13C composition of acetylated BHT isomers in cultured bacteria and bacterial enrichments. We combined these with bulk biomass and substrate δ13C compositions to establish carbon isotopic fractionation factors. The two anammox genera had large fractionation factors from dissolved inorganic carbon (DIC) to biomass (Δ13Cbiomass – DIC = –43.8 to –26.4 ‰) and to BHTs (Δ13CBHT – DIC = –53.8 to –38.2 ‰), which clearly distinguished them from the freshwater aerobic heterotrophic producers (Δ13Cbiomass – substrate = –2.3 to –0.1 ‰; Δ13CBHT – substrate = –12.8 to 5.2 ‰). Methylocella assimilated mainly carbon from DIC, rather than from methane, into its biomass and BHT, and previous work suggested this assimilation comes with relatively small fractionation. Thus, in peatlands, the BHT δ13C values of Methylocella would not reflect the low δ13C values of biogenic methane. Consequently, the presence of BHT-34R with low δ13C values relates to ‘Ca. Brocadia’ and presents a novel tool to trace anammox in freshwater environments.

Fe-Si-C isotope constraints on the genesis of iron ores in Gongchangling iron deposit in northeastern China

The Gongchangling iron deposit is an oxide-facies Algoma-type banded iron formation (BIF) and one of the most representative iron deposits in northeastern China. We present new data from petrological, whole-rock geochemical, and Fe-Si-O isotope compositional data from the Gongchangling BIFs to constrain the origin of ore-forming materials and mineralization processes. The low Al2O3 and TiO2 contents in iron ores indicate that the sources of the BIFs were not contaminated by terrigenous clastic sediments. The Gongchangling BIFs are characterized by depletions in LREEs and 30Si and enrichments in HREEs, with positive Eu and Y anomalies. Given these and the Fe isotope results, we conclude that both high-temperature hydrothermal fluid and seawater contributed to the formation of the BIFs and that a mixture of seawater and ~ 0.1 % hydrothermal fluid, which percolated and dissolved the submarine volcanic rocks, provided the ore-forming materials. Combining the Ce anomalies, enrichments in heavy Fe isotopes and low δ13C compositions, we conclude that the fO2 of Archean seawater was limited. Integrated petrographic and geochemical evidence indicates that the high-grade iron ores from the Gongchangling BIFs experienced incomplete oxidation and low amounts of Fe precipitation in a marine environment and that dissimilatory iron reduction and metamorphic hydrothermal fluid played important roles.

Atmospheric CH4 and Its Isotopic Composition (δ13C) in Urban Environment in the Example of Moscow, Russia

Measurements of near-surface methane (CH4) mixing ratio and its stable isotope 13C were carried out from January 2018 to December 2020 at the A.M. Obukhov Institute of Atmospheric Physics (IAP) research site in the center of Moscow city. The data show moderate interannual variations in monthly mean CH4 with maximum values being observed predominantly in winter (2.05–2.10 ppmv on average). The most δ13C depleted CH4 (up to −56‰) is observed in summer and autumn following seasonal decrease in traffic load in the city. The highest CH4 concentrations (>2.2 ppmv) were likely to be caused by air transport from the E–SE sector where potentially large microbial CH4 sources are located (landfills and water treatment plants, Moscow River). Keeling plots of these episodes in different seasons of 2018–2020 showed δ13C isotopic signatures of about −58–−59‰ for the spring–autumn period and −67‰ for winter. A good correlation was observed between CH4 and other pollutants: CO2, CO, and benzene in daytime (10:00–19:00) hours (R > 0.7). Contribution of urban methane emissions due to vehicle exhausts (∆[CH4]auto) and microbial activity (∆[CH4]micro+) along with regional baseline mixing ratios of CH4 ([CH4]base) and CO ([CO]base) were estimated from the linear orthogonal regression analyses of the measured daytime mixing ratios. A significant role of microbial methane in the formation of CH4 maximums in Moscow was revealed. Contributions of the upwind continental CH4 and CO sources to the measured species levels were estimated through comparison with the Mace Head site data representative for the Northern Hemisphere baseline air. The study provides, for the first time, important insights into the long- and short-term variations of CH4 levels in Moscow in connection to the local (urban) emissions and long-range transport from upwind continental sources. The results will contribute to elaboration of a default emission inventory in air quality modeling and help to identify the areas for targeted mitigation efforts.

Tracking the early signals of crude oil in seawater and plankton after a major oil spill in the Red Sea

Understanding the immediate impacts of oil spills is essential to recognizing their long-term consequences on the marine environment. In this study, we traced the early (within one week) signals of crude oil in seawater and plankton after a major oil spill in October 2019 in the Red Sea. At the time of sampling, the plume had moved eastward, but we detected significant signs of incorporation of oil carbon into the dissolved organic carbon pool, resulting in a 10–20% increase in the ultraviolet (UV) absorption coefficient (a254) of chromophoric dissolved organic matter (CDOM), elevated oil fluorescence emissions, and depletion of the carbon isotope composition (δ13C) of the seawater. The abundance of the picophytoplankton Synechococcus was not affected, but the proportion of low nucleic acid (LNA) bacteria was significantly higher. Moreover, specific bacterial genera (Alcanivorax, Salinisphaera, and Oleibacter) were enriched in the seawater microbiome. Metagenome-assembled genomes (MAGs) suggested that such bacteria presented pathways for growing on oil hydrocarbons. Traces of polycyclic aromatic hydrocarbons (PAHs) were also detected in zooplankton tissues, revealing the rapid entry of oil pollutants into the pelagic food web. Our study emphasizes the early signs of short-lived spills as an important aspect of the prediction of long-term impacts of marine oil spills.

Compositions and sources of sedimentary organic carbon on the tropical epicontinental sea

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 CO2 source to the atmosphere in the context of the global carbon cycle.

Assessment of soil development during rapid urbanization using the carbon and nitrogen stable isotope composition.

The proposed paper is devoted to the analysis of the urbanization effects on soil cover using physico-chemical parameters and stable isotopic signatures on the example of Tyumen. The study methods included analysis of C and N elemental and isotope (δ13C and δ15N) composition, analysis of soil physico-chemical properties and major oxides content. The results of the survey have shown that soil properties within the city limits vary significantly depending on both anthropogenic activities and geomorphological context. The urban soils of Tyumen differ from very strongly acidic with pH values down to 4.8 to strongly alkaline with pH values reaching 8.9, and from sandy loams to silty loams by texture. The study results have shown that δ13C values varied from -33.86 to -25.14‰ and δ15N values varied in range, especially, from -1.66 to 13.38‰. The range of these signatures was smaller than those reported for urbanized areas in Europe and USA. The δ13C values in our case were more related to the geological and landscape parameters of the study area, rather than with urban disturbances and development of urban ecosystems. At the same time, the δ15N values probably indicate zones with increased atmospheric N deposition in the case of Tyumen. The application δ13C and δ15N is a promising tool for analysis of urban soil disturbances and functions, though the regional context should be taken into account.

Isotopic Signatures of Carbon Transfer in a Proterozoic Analogue Microbial Mat.

Modern microbial mats are potential analogues for Proterozoic ecosystems, yet only a few studies have characterized mats under low-oxygen conditions that are relevant to Proterozoic environments. Here, we use protein-stable isotope fingerprinting (P-SIF) to determine the protein carbon isotope (δ13C) values of autotrophic, heterotrophic, and mixotrophic organisms in a benthic microbial mat from the low-oxygen Middle Island Sinkhole, Lake Huron, USA (MIS). We also measure the δ13C values of the sugar moieties of exopolysaccharides (EPS) within the mat to explore the relationships between cyanobacterial exudates and heterotrophic anabolic carbon uptake. Our results show that Cyanobacteria (autotrophs) are 13C-depleted, relative to sulfate-reducing bacteria (heterotrophs), and 13C-enriched, relative to sulfur oxidizing bacteria (autotrophs or mixotrophs). We also find that the pentose moieties of EPS are systematically enriched in 13C, relative to the hexose moieties of EPS. We hypothesize that these isotopic patterns reflect cyanobacterial metabolic pathways, particularly phosphoketolase, that are relatively more active in low-oxygen mat environments, rather than oxygenated mat environments. This results in isotopically more heterogeneous C sources in low-oxygen mats. While this might partially explain the isotopic variability observed in Proterozoic mat facies, further work is necessary to systematically characterize the isotopic fractionations that are associated with the synthesis of cyanobacterial exudates. IMPORTANCE The δ13C compositions of heterotrophic microorganisms are dictated by the δ13C compositions of their organic carbon sources. In both modern and ancient photosynthetic microbial mats, photosynthetic exudates are the most likely source of organic carbon for heterotrophs. We measured the δ13C values of autotrophic, heterotrophic, and mixotrophic bacteria as well as the δ13C value of the most abundant photosynthetic exudate (exopolysaccharide) in a modern analogue for a Proterozoic environment. Given these data, future studies will be better equipped to estimate the most likely carbon source for heterotrophs in both modern environments as well as in Proterozoic environments preserved in the rock record.

Source, distribution, and transformation of dissolved and particulate organic matters in Qinzhou Bay, Northern Beibu Gulf

Both dissolved and particulate organic matters (DOM and POM) provide a reduced carbon pool of considerable size in coastal ecosystems, and the two are closely linked. Currently, however, the integrated study of DOM and POM remains limited, precluding a more in-depth understanding of their interaction in coastal regions. In April 2021, 13 surface water samples were collected from Qinzhou Bay, in the northern Beibu Gulf. The DOM samples were characterized using dissolved organic carbon (DOC) analysis and UV-visible and fluorescence spectroscopy techniques. We determined the POM for the particulate organic carbon and nitrogen (POC and PN) and also isotopic composition (δ13C and δ15N). The weak to negligible relationships found between the DOC, colored and fluorescent DOM, salinity, and chlorophyll a together suggested that DOM’s distribution in Qinzhou Bay is concurrently shaped by various processes, namely, hydrological and in situ biological processes. A high C/N ratio of ~17, high POC/chlorophyll a ratio (253 ± 112), and depleted δ13C (−25.7 ± 1.6‰) confirmed that POM is highly degraded and originates mainly from allochthonous input, to which the terrigenous organic matter and freshwater phytoplankton each contributes 35%. The total organic carbon (TOC = DOC + POC) was positively correlated with the humic-like peak M, revealing the transformation of labile DOM and POM into recalcitrant DOM components. The in situ production efficiency of peak M in surface waters of Qinzhou Bay is one order of magnitude greater than that in inland waters or open oceans, indicating that not only temperature but also the activity of substrate is a key factor controlling the in situ production of recalcitrant DOM in Qinzhou Bay. High levels of TOC and humic-like fluorescent DOM suggest the mass coexistence of organic matter differing in its reactivity, highlighting the large potential for photochemical as well as microbial degradation in the future.

Differences in ecophysiological responses of Populus euphratica females and males exposed to salinity and alkali stress

Soil salinity is usually accompanied by alkalization in northwest China, and they both negatively impact plant growth and result in severe ecological problems. Some studies have reported tree responses to salinity or alkali stress alone, however, the interactive salinity and alkali effects are still unclear, especially in dioecious trees. In this study, we measured growth, morphology, leaf stomata, gas exchange, carbon isotope composition (δ13C), total soluble sugar and starch contents, Na+ accumulation and allocation, oxidative stress, and antioxidants of female and male Populus euphratica seedlings in response to salinity, alkali and their interaction. Our study showed no significant sexual differences in studied traits under control conditions. In addition, P. euphratica females showed greater inhibitory and negative effects, such as bigger decreases in growth and gas exchange, lower stomatal density and water use efficiency (as described by δ13C), and lower levels of soluble sugars and antioxidant enzyme activities compared with males under salinity, alkali and interactive stress conditions. Furthermore, P. euphratica males had a greater ability of ion exclusion and Na + transport restriction. For example, males allocated more Na+ to stems and roots than females, whereas females had higher Na+ contents in leaves under stress conditions. In conclusion, our results indicated that P. euphratica males have superior resistance and they perform better than females under salinity, alkali and their interactive stress conditions.

Evaluation of the non-climatic (age-related) trends of stable oxygen and carbon isotopes in Swiss stone pine (Pinus cembra L.) tree rings from the Eastern Carpathians, Romania

The presence, magnitude, and duration of age and/or size-related trends in the stable isotopes in tree-ring cellulose time series has been a subject of scientific debate. Where present, their evaluation and removal are key to the development of robust climate calibrations and reconstructions, especially in the low-frequency domain and where sample replication levels are low. Where reported, results suggest that the age/size/height-related trend of stable oxygen (δ18O) and carbon (δ13C) isotope compositions in tree-ring cellulose may vary according to the tree species and the individual tree location. For this reason, it is important when developing long palaeoclimate reconstructions for a new species, geographical region or ecological setting to perform studies to investigate non-climatic (age-related) trends. This study evaluates the ontogenetic pattern in the δ18O and δ13C data in Swiss stone pine trees from the Eastern Carpathians, Romania. For this, we used a new multi-centennial dataset consisting of 5 living and 10 relict Swiss stone pine samples collected from the Eastern Carpathians, which were annually resolved for δ18O and δ13C composition. Age-related trends were evaluated using the conventional “slope of the mean” approach as well as the “mean of the slope” method. The results suggest that neither the traditional “slope-of-the mean” nor the “mean-of-the-slope” approach indicates a persistent linear trend in the Swiss stone pine δ18O data, while for the δ13C data a systematic enrichment in 13C was observed over a < 40 year-long period after germination. Despite the limited sample size of this developing dataset these findings help to inform more detailed analyses and future sampling strategies in the Eastern Carpathian Swiss stone pine stands.

Heterotrophic origin and diverse sources of branched glycerol monoalkyl glycerol tetraethers (brGMGTs) in peats and lignites

The branched glycerol monoalkyl glycerol tetraether lipids of bacteria (brGMGTs, sometimes referred to as H-brGDGTs) are found in marine, lacustrine, and terrestrial mesophilic environments. The abundance of brGMGTs relative to their dialkyl analogues (brGDGTs) has been proposed as a proxy for past continental air and lake water temperature. However, the source(s) of brGMGTs remain unknown. brGDGT production has been described in multiple cultivated Acidobacteria, but so far no brGMGT producer has been identified. We hypothesize that the stable carbon isotopic composition (δ13C) of brGMGTs, as a tracer of carbon source and metabolic pathway, could be used to elucidate the source(s) of brGMGTs relative to brGDGTs. However, the large monoalkyl moiety of these compounds impedes carbon isotopic analysis using conventional techniques based on gas chromatography. Here, we used spooling-wire microcombustion to analyse the stable carbon isotopic composition of brGMGTs and brGDGTs found in peats and lignites. We show that the δ13C of brGMGTs is within ∼2‰ similar to that of brGDGTs from the same samples, as well as the δ13C of the total organic carbon. This suggests that the source organisms use heterotrophic metabolism. However, offsets in the δ13C of brGDGTs and brGMGTs in some samples suggest that not all brGDGT producers also produce brGMGTs. Further, in modern peats we observe downcore increases in brGMGT relative abundance and decreases in the carbon isotopic offsets with brGDGTs, which indicates that brGMGT producers occur throughout the oxic-anoxic continuum and may metabolize different organic carbon pools. Based on this indirect evidence for diverse brGMGT sources, we suggest that in addition to homeostatic responses to temperature, brGMGT relative abundances may be influenced by changes in bacterial community composition in response to additional environmental and biogeochemical parameters.

A tool for Zn-Pb MVT exploration by combining C and O isotopes and REE geochemistry of dolomite

An exploration guide for Mississippi Valley-type (MVT) deposits is proposed and illustrated in the Riópar area (SE Spain), where extensive dolostone geobodies hosting Zn-(Fe-Pb) MVT mineralization occur. These base metal deposits are found within stratabound and patchy dolostones replacing Upper Jurassic to Lower Cretaceous limestones. However widespread stratabound dolostones, with no Zn-(Fe-Pb) mineralization associated, are also found in the same area replacing Lower Jurassic to Upper Cretaceous carbonates. A detailed sampling of both, Zn-(Fe-Pb) mineralized dolostones (fertile), as well as unmineralized ones (barren), has been performed in an area of ∼106 km2 to characterize their rare earth element (REE) and isotopic (C, O, Sr) compositions. Barren Lower and Middle Jurassic and Upper Cretaceous dolostones show C, O and Sr isotopic characteristics (δ13C = +2.1 to +3.8‰ VPDB, δ18O = +27.6 to +29.8 ‰ VSMOW, 87Sr/86Sr = 0.70736 to 0.70764) like the Jurassic-Cretaceous undolomitized limestones and marine carbonates, and consistent with dolostones produced by low temperature seawater. On the contrary, barren and fertile Upper Jurassic to Lower Cretaceous stratabound and patchy dolomitized limestones are depleted in δ13C and δ18O and relatively enriched in 87Sr/86Sr compared to the host limestones. This δ13C and δ18O composition can be explained by an interaction of warm fluids with regional carbonates (2–3% of fluid/rock interaction at 190–230 °C). The hydrothermal character for the dolomitizing fluid is supported by REE geochemical data (e.g., (Pr/Pr*)PAASN and (Ce/Ce*)PAASN anomalies). Thus, C and O isotopes, as well as (Ce/Ce*)PAASN and (Pr/Pr*)PAASN ratios, can be used to discriminate between low temperature dolostones, formed from cold seawater that do not contain Zn-(Fe-Pb) mineralization (barren), from hydrothermal dolomites (HTDs), which may host Zn-(Fe-Pb) mineralization. Furthermore, most barren HTDs show more restricted and higher δ13C (+0.4 to +0.9 ‰ VPDB) and δ18O values (+26.4 to +27.1 ‰ VSMOW), as well as lower ∑REE contents (5.41 to 7.38 mg kg−1), compared to Zn-(Fe-Pb) mineralized HTDs (δ13C: −2.3 to +0.6 ‰ VPDB; δ18O: +25.1 to +27.1 ‰ VSMOW; ∑REE 14.10 to 54.79 mg kg−1). Therefore, the obtained REE contents, and partially the δ13C values, can be used to discriminate between HTDs associated with Zn-(Fe-Pb) mineralization (fertile dolostones) and barren HTDs, revealing their potential as a new geochemical tool for MVT exploration in dolomitized terrains.

Use of Formalin-Preserved Collections to Infer Trophic Indicators of Marine Zooplankton from Stable Isotopes

Formalin preservation affects the stable isotope composition of zooplankton samples, thus limiting the analysis of valuable collections covering large time intervals. Here, we compare different procedures for correcting the bias caused by formalin in δ13C and δ15N of zooplankton community samples. Zooplankton samples representative of seasonal variations in the period 2000–2009 were collected off A Coruña (NW Spain). Part of the sample was immediately dried and analysed for δ13C, δ15N, and elemental composition within 3 years of collection. These values were used as the unpreserved reference. The remaining sample was preserved in 4% formaldehyde and aliquots obtained after a period ranging from 3 years to more than 10 years of storage were analysed as the originally dried samples. Additionally, the copepod fraction of total biomass was determined in the preserved samples. Corrections of formalin effects based on ordinary least squares regression had large uncertainties, while mass balance corrections based on the change in C:N ratio (only possible for δ13C) overestimated reference values. However, either simple corrections based on the mean difference between values in dry and preserved samples or more complex generalised additive models considering seasonality, copepod biomass, and time of sample storage, produced estimations with relatively low uncertainty. Our results highlight the importance of determining specific correction solutions for each preserved collection before reconstructing stable isotope time series. Furthermore, the uncertainties associated with the estimates can be used in sensitivity analysis to assess their potential impact on the interpretation of the series.

Investigation of sources and atmospheric transformation of carbonaceous aerosols from Shyamnagar, eastern Indo-Gangetic Plains: Insights from δ13C and carbon fractions

This study reports the chemical characterization of the carbonaceous component of PM2.5 (particulate matter with aerodynamic diameter ≤2.5 μm) collected over a year-long campaign from a regional site in Shyamnagar, West Bengal, in the Indo-Gangetic Plains (IGP), India. The carbonaceous fractions (elemental and organic carbon), mass concentrations, and stable carbon isotopic composition (δ13C value) of aerosols were measured and utilized to characterize the sources and understand the atmospheric processing of aerosols. Cluster analysis, Potential Source Contribution Function (PSCF) modeling, and fire count data were analyzed to decipher the pattern of air masses, source contributions, and extent of burning activities. The PM2.5 mass concentrations were significantly higher during winter (168.3 ± 56.3 μg m−3) and post-monsoon (109.8 ± 59.1 μg m−3) compared to the monsoon (29.8 ± 10.7 μg m−3) and pre-monsoon (55.1 ± 23.0 μg m−3). Organic carbon (OC), elemental carbon (EC), and total carbon (TC) concentrations were also several factors higher during winter and post-monsoon compared to monsoon and pre-monsoon. The winter and post-monsoon experienced the impact of air masses from upwind IGP. On the other hand, long-range transported air masses from the South-West direction dominated during monsoon and pre-monsoon, which are also relatively cleaner periods. The average δ13C during post-monsoon and winter was ∼1‰ higher compared to monsoon and pre-monsoon. The vehicular exhaust and biomass/biofuel burning contributed dominantly in winter and post-monsoon. In comparison, lower δ13C in pre-monsoon and monsoon might be attributed to the dominance of biomass/biofuel combustion. Photochemical-induced aging of the anthropogenic aerosols resulted in a higher δ13C of TC in winter and post-monsoon, whereas the mixing of different local sources in pre-monsoon and monsoon resulted in lower δ13C values. These findings benefit policymakers in strategizing proper and effective management of biomass/biofuel burning in the IGP to minimize air pollution.

Distribution of 222Rn and CO2 across faults and its origin in Wayang Windu geothermal area, West Java - Indonesia

As a geogenic gas, 222Rn (radon) has been widely utilized to infer permeability zones in some geological settings such as fault zones, volcanic and geothermal areas. In this study, soil 222Rn was measured in Wayang Windu geothermal area to infer the relation between fault and permeability. In addition, measurement of soil CO2 and its δ13C composition were also performed to infer transport mechanism and the origin of soil CO2. The high and anomaly soil 222Rn, i.e., above 8,500 Bq/m3, were found in the south - southwest area and related to Pejaten Fault, Banjarsari Fault and Cibitung Fault. In contrast, low soil 222Rn was found in the northern area, where several highly productive geothermal wells are located. The high and anomaly soil CO2 concentrations were also found in a relatively similar area with high 222Rn, but not closely related to the fault structures. Furthermore, the δ13C composition showed that the origin of soil CO2 in the area was magmatic, biogenic and atmospheric. Based on the 222Rn/CO2 values and its δ13C compositions, the mechanism of 222Rn transport was interpreted as independent from CO2 as carrier gas.

STABLE ISOTOPES (δ13C AND δ15N) ANALYSIS INDICATE RESOURCE PARTITIONING BY ELASMOBRANCHS FROM THE TROPICAL COASTAL WATERS OF KUALA PAHANG, MALAYSIA

Nearshore habitats support high levels of biodiversity and important ecological processes such as trophic dynamics. This study aims to determine the trophic dynamics of elasmobranchs and other marine species from the coastal waters of Kuala Pahang, using stable isotope analysis. Samples of invertebrates, teleosts, and juvenile elasmobranchs were collected at the coastal waters of Kuala Pahang, and the composition of stable isotopes δ13C and δ15N were determined. Of all species, teleosts had the narrowest range of δ13C values, of between -17.5‰ and -16.7‰, indicating their reliance on similar types of food resources. On the contrary, elasmobranchs had the widest range of food sources as indicated by the δ13C values, of between -26.8‰ and-16.8‰. The banded sicklefish (Drepane longimana) occupied the highest trophic level as indicated by a δ15N value of 12.4‰, whereas the red stingray (Hemitrygon akajei) had the lowest trophic level with a δ15N value of 4.9‰. The depleted δ13C values indicated resource partitioning among elasmobranchs, presumably due to the utilisation on estuarine-based carbon resources. This study highlights the potential importance of the estuary of Kuala Pahang as a feeding ground for juvenile elasmobranchs.

Temporal variability in soil organic matter accretion rates in coastal deltaic wetlands under changing depositional environments

AbstractThe Mississippi River Deltaic Plain experiences high relative sea level rise, limited sediment supply, and high marsh edge erosion, leading to the substantial coastal wetland and stored soil organic matter (SOM) loss. The objective of this study was to understand the SOM accumulation rates over the past 1000 years related to the changes in the depositional environment in these highly eroding coastal wetlands. Soil cores (2 m) were collected from four sites in Barataria Basin, LA and analyzed for proportion of organic and mineral matter, total C, N, P, particle size, and stable isotopic composition (δ13C and δ15N), as well as 14C and 137Cs dating. The soil carbon stock in the 2 m depth (62.4 ± 2 kg m−2) was approximately 88% greater than the carbon stock in just the 1 m depth (33.1 ± 0.6 kg m−2) indicating a need for considering deeper soil profiles (up to 2 m) to estimate blue carbon stock in deltaic environments. The average vertical accretion rate for Barataria Basin was 8.1 ± 0.6 mm year−1 over 50 years. The long‐term (1000‐year time scale) C accumulation rate (39 g C m−2 year−1) was ∼14% of the short‐term accumulation rate (254 ± 19 g C m−2 year−1). Wetlands in Barataria Basin started as fresh marsh and transitioned over time to intermediate to brackish. These marshes were able to maintain relative elevation through the accumulation of organic matter and mud despite high relative rates of sea‐level rise. However, the high rates of edge erosion may limit these marshes to continue to sequester atmospheric carbon under accelerating sea level in the absence of restoration efforts.

Leaf Carbon and Water Isotopes Correlate with Leaf Hydraulic Traits in Three Solanum Species (S. peruvianum, S. lycopersicum and S. chilense)

Leaf hydraulic conductance (KLeaf) is a measure of the efficiency of water transport through the leaf, which determines physiological parameters such as stomatal conductance, photosynthesis and transpiration rates. One key anatomical structure that supports KLeaf is leaf venation, which could be subject to evolutionary pressure in dry environments. In this context, it is useful to assess these traits in species from arid climates such as S. peruvianum and S. chilense, in order to determine their hydraulic strategy and potential aptitude for the improvement of domestic tomato (S. lycopersicum). In this work, we measured KLeaf, vein density, together with leaf water isotope composition (δ18O, δ2H) and leaf carbon isotope composition (δ13C), from which we derived proxies for outside-vein hydraulic resistance (Rox) and intrinsic water use efficiency (WUEi), respectively. The two wild species showed contrasting hydraulic strategies, with S. chilense performing as a water-spender, whereas S. peruvianum showed a water-saving strategy. Interestingly, S. lycopersicum was rather conservative, and showed the highest WUEi. The low water transport capacity of S. peruvianum was not explained by vein density traits, but was related with the effective pathlength L, an isotope-derived proxy for Rox. The low WUEi of S. peruvianum suggest strong photosynthetic limitations. Our results show a wide diversity in water-use strategies in the genus, encouraging a detailed characterization of wild relatives. From a methodological point of view, we provide evidence supporting the use of water isotopes to assess changes in mesophyll hydraulic conductance, not attributable to vein density.

Metric, kilometric and large-scale coherence of metamorphic conditions from graphitic phyllite in the Upper Lesser Himalaya of Nepal: Contribution to the estimation of carbon stored during Himalayan orogeny

Besides carbonates, carbonaceous material in meta-sediments represents an important carbon reservoir on Earth. In orogenic belts, carbon can be stored as graphite, a contribution to the global carbon cycle that remains insufficiently constrained. Here, we focus on the Himalayan belt where moderately crystalline graphite is found at the footwall of the Main Central Thrust. Using various analytical methods, we investigate metamorphic conditions of graphite at increasing spatial scales in the Upper Lesser Himalayan Sequence (upper-LHS) phyllites of Nepal. First, we develop and validate a new SEM-BSE technique to measure total organic carbon (TOC) content. Graphite shows mostly inter- and intra-granular flaky crystals associated with carbonates. Elemental carbon analyses yield large range of TOC content in phyllites with a mean of 3.7 ± 0.4 vol.%. Inferred from micro-Raman spectroscopy, peak metamorphic temperature (peak-T) ranges from 519 ± 9 to 590 ± 8 °C. We observe a significant coherence of metamorphic conditions of graphitic phyllites at metric, decametric and kilometric scales using extensive data obtained in the Upper Trisuli valley, Central Nepal (n = 77), and, at larger spatial scales, using data from Far-Western to Eastern Nepal (n = 67). Mean carbon isotopic composition (δ13C) of −26.3 ± 0.1 ‰ indicates biogenic source. Less negative δ13C values, also reported in other orogenic belts, suggest interaction with pre-existing sedimentary carbonates, probably related to metamorphic isotopic re-equilibration. First-order extrapolations at the upper-LHS scale suggest meta-sediment organic carbon may represent up to 20 % of the total amount of carbon stored in orogens. Central Nepal segment, with higher TOC content and peak-T, is also characterized by the largest current metamorphic carbon dioxide (CO2) emissions of the chain. This hardly coincidental association, at the scale of the Himalayan belt, between organic carbon stored as graphite and mobile inorganic carbon released as CO2, represents an important clue to investigate further for global carbon budget estimations.