14C Activity Research Articles

Can we see differences between the 14C activities of urban (Zagreb) and rural (Cvetković) sites (central Croatia)?

Radiocarbon (Δ14C) was measured for four years (2019–2022) in Zagreb (Croatia) and in Cvetković village near Jastrebarsko (Zagreb County, Croatia) to see whether there are differences between the city site and the rural one because of the fossil fuel combustion. The δ13CCO2 was measured as grab samples once in a month in period December 2020–November 2022. The bomb-produced 14C has been globally distributed across the planet, but the combustion of fossil fuels that do not contain 14C causes a local effect of lowering Δ14C. Zagreb is considered to be a location with heavy fossil fuel combustion as compared to the Cvetković (rural site). Monthly 14C activity at Zagreb is constantly below the 14C activity at Cvetković. Mean 14C activity at Zagreb (Δ14CZagreb = −18.4 ± 2.6 ‰) is lower than that in Cvetković (Δ14CCve = −2.9 ± 2.1 ‰) due to fossil fuel combustion in the city of Zagreb. This is especially pronounced during winter when the mean value in Zagreb is Δ14CZagreb = −26.0 ± 4.3 ‰ and in Cvetković Δ14CCve = −5.9 ± 3.4 ‰.Natural gas consumption was used as the proxy for fossil fuel combustion, and it shows better correlation with Δ14C in Zagreb than in Cvetković. The Δ14C difference, Δ14CCve ‒ Δ14CZagreb, becomes statistically negligible when natural gas consumption is small.No difference is observed on δ13CCO2; in Zagreb mean δ13CCO2 is −11.0 ± 1.3 ‰, and in Cvetković −11.4 ± 1.4 ‰. Lower δ13CCO2 values are observed in winter (Zagreb −11.9 ± 1.1 ‰, −12.2 ± 1.5 ‰ Cvetković) than in summer (−10.1 ± 0.8 ‰ vs. −10.4 ± 1.0 ‰) at both locations. Together with higher Δ14C in Cvetković, it indicates that at the area of Cvetković biogenic samples of modern origin (biomass, wood) as energy source for heating is more pronounced.

Hydrogeochemistry of geothermal water in Huangshadong and adjacent areas of Guangdong province: Implications for water-rock interaction

Hydrogeochemical characteristics can reflect important information on the circulation processes of geothermal fluids, reservoir temperatures, etc., which are essential for exploring geothermal field evolution and the rational development of geothermal resources. 23 sets of water samples were collected from Huangshadong and adjacent geothermal fields. Major cations and anions, hydrogen and oxygen isotopes, and 14C activities were analyzed to investigate the hydrogeochemical characteristics of geothermal fluids and their formation mechanisms. Hydrogen and oxygen isotope analysis and major element chemistry indicate that the geothermal waters in the study area are mainly recharged by meteoric water. The chemical facies of the geothermal waters are mainly Na−HCO3 and Ca−HCO3, and most of the geothermal waters have high Na+ contents, which are attributed to the involvement of albite in water-rock interaction and the replacement of Na+ in rocks by Ca2+ or Mg2+ in water. Geothermometry of geothermal waters suggests that the reservoir temperatures are between 140-150 ℃, and the geothermal water circulation depths range from 2.0 to 4.3 km. The residence time of up to 17.3ka for geothermal water likely suggests the earliest precipitation recharge during the Late Pleistocene. Major element chemistry and hydrogen and oxygen isotope systematics indicate essential information on the origins of geothermal waters and water-rock interaction processes and provide a more comprehensive understanding of the geothermal system in Huangshadong and adjacent areas of Guangdong province.

Simulated soil erosion predominantly affects fungal abundance in the rapeseed rhizosphere

Eroded agricultural soils have reduced soil organic carbon (SOC) levels that may affect the plant-microbiome interactions in the rhizosphere. We explored the impact of simulated erosion on major microbial groups in a pot experiment with rapeseed (Brassica napus L.) grown on arable soil with the potential to capture SOC. An erosion gradient was simulated by admixture (0%, 12%, 24%) of subsoil horizon (Bt) to topsoil (Ap) material. Rapeseed plants were pulse-labeled with 14CO2 at three growth stages and two soil compartments (bulk and rhizosphere soil) were sampled. Fungal ITS copy numbers were consistently higher in the rhizosphere and decreased with progressing plant growth stages. A significant increase of bacterial 16S rRNA gene copies in the rhizosphere only occurred at flowering. A response of fungal abundance to subsoil admixture was found detectable based on fungi:Bacteria and fungi:Archaea ratio at flowering. Archaea were neither affected by soil compartment nor subsoil admixture. 14C activity of microbial biomass, an indicator for relative input of freshly assimilated C into soil microbiome, was impacted by growth stage and compartment and decreased with ongoing growth stage. During the rosette growth stage, the 14C activity of the microbial biomass was elevated in the rhizosphere of the eroded soil indicating a plant response to the erosion factor. Our experiment revealed a compositional separation of the fungal community along the simulated erosion gradient and a selection of fungi for the two different soil compartments at flowering. Olpidimycetes, Fusarium and Rhizopus and putative pathogens were enriched in the rhizosphere at flowering. Fungi may have a competitive advantage in the rhizosphere of strongly eroded and nutrient diluted soils due to ecological adaptation and morphological traits i.e. hyphae that can bypass soil areas with low nutrient availability.

Leakage of old carbon dioxide from a major river system in the Canadian Arctic.

The Canadian Arctic is warming at an unprecedented rate. Warming-induced permafrost thaw can lead to mobilization of aged carbon from stores in soils and rocks. Tracking the carbon pools supplied to surrounding river networks provides insight on pathways and processes of greenhouse gas release. Here, we investigated the dual-carbon isotopic characteristics of the dissolved inorganic carbon (DIC) pool in the main stem and tributaries of the Mackenzie River system. The radiocarbon (14C) activity of DIC shows export of "old" carbon (2,380 ± 1,040 14C years BP on average) occurred during summer in sampling years. The stable isotope composition of river DIC implicates degassing of aged carbon as CO2 from riverine tributaries during transport to the delta; however, information on potential drivers and fluxes are still lacking. Accounting for stable isotope fractionation during CO2 loss, we show that a large proportion of this aged carbon (60 ± 10%) may have been sourced from biospheric organic carbon oxidation, with other inputs from carbonate weathering pathways and atmospheric exchange. The findings highlight hydrologically connected waters as viable pathways for mobilization of aged carbon pools from Arctic permafrost soils.

Improving the Methodology for Determining the Biomass/Coal Co-Combustion Ratio: Predictive Modeling of the 14C Activity of Pure Biomass

Sampling and 14C detection of biomass are now essential steps to ensure the accuracy of the 14C method, but they require additional time and economic investment. When there are multiple types of biomass fuels, it is not possible to guarantee the uniformity of sampling. The 14C activity of biomass fuels exhibits variability, and this value significantly impacts the precision of the 14C method. Therefore, this study aims to investigate the influencing factors of 14C activity in biomass fuels. It also provides predicted values of 14C activity for different types of biomass fuels for each year from 2020 to 2030. Additionally, this study discusses the potential blending ratio measurement errors that may arise due to the uncertainties of the predicted values. The reduction in the 14C activity of biomass fuels can occur due to the utilization of fossil fuels, human activities, and the photosynthesis mode of C3 plants. This study presents a prediction method for determining the reduction factor. The other component of the prediction methodology involves determining the original 14C activity of biomass fuels. The 14C activity of the annual biomass is equal to the 14CO2 activity (the 14C activity of CO2) of the surrounding environment, and it experiences a decline of 0.355 pMC/year. The 14C activity has ranges of five types of perennial biomass fuels, including wood chips and branches, bark, leaves, wasted furniture, and abandoned building wood, for the time period between 2020 and 2030, are 97.34~102.84, 96.35~106.27, 96.35~102.64, 111.00~118.60, and 111.32~129.47 pMC, respectively. Based on these, this study introduces a new formula for calculating blending ratios, which enhances the current methodology. The calculation errors of blending ratios caused by the uncertainties of the predicted values are generally negligible, with the exception of wasted furniture and construction wood. The annual decrease in the blending ratio calculation error, caused by the uncertainty associated with the predicted value, can be observed. This study aims to reduce the implementation time and economic cost of the 14C method while ensuring the accuracy of biomass blending ratio detection.

Channel cross-section heterogeneity of particulate organic carbon transport in the Huanghe

Abstract. The Huanghe (Yellow River), one of the largest turbid river systems in the world, has long been recognized as a major contributor of suspended particulate matter (SPM) to the ocean. However, over the last few decades, the SPM export flux of the Huanghe has decreased over 90 % due to the high management, impacting the global export of particulate organic carbon (POC). To better constrain sources and modes of transport of POC beyond the previously investigated transportation of POC near the channel surface, SPM samples were for the first time collected over a whole channel cross-section in the lower Huanghe. Riverine SPM samples were analyzed for particle size and major element contents, as well as for POC content and dual carbon isotopes (13C and 14C). Clear vertical and lateral heterogeneities of the physical and chemical properties of SPM are observed within the river cross-section. For instance, finer SPM carry more POC in general with higher 14C activity near the surface of the right bank. Notably, we discuss how bank erosion in the alluvial plain is likely to generate lateral heterogeneity in POC composition. The Huanghe POC is millennial-aged (4020 ± 500 radiocarbon years) and dominated by organic carbon (OC) from the biosphere, while the lithospheric fraction is ca. 12 %. The mobilization of aged and refractory OC, including radiocarbon-dead biospheric OC, from deeper soil horizons of the loess–paleosol sequence through erosion in the Chinese Loess Plateau is an important mechanism contributing to fluvial POC in the Huanghe drainage basin. Altogether, anthropogenic activities can drastically change the compositions and transport dynamics of fluvial POC, consequentially altering the feedback of the source-to-sink trajectory of a river system to regional and global carbon cycles.

Evaluating sustainability of Bhuj aquifer system, Western India using nuclear dating techniques

Abstract Increasing population, food demands and climatic stressors pose an imminent threat to groundwater sustainability in regional aquifer systems globally. Limited availability of surface water and erratic/uncertain rainfall necessitates preservation of groundwater resources, which form reliable fresh water reserves in most of the arid regions. Bhuj Sandstone aquifer is one such fresh groundwater systems in Western India catering the domestic/irrigational needs for over 2 million population. Rapid groundwater depletion in this area warranted a mandatory conservation of groundwater resources for future sustainability. Nuclear techniques using 3H and 14C provide estimates of groundwater age that help in planning sustainable groundwater management. In this study, sustainability of deep groundwater was assessed using environmental radioactive isotopes (3H, 14C). Results indicate that 14C activity of the groundwater samples varies from 26 to 73.6 pMC (percent modern carbon). Considering the various biases and uncertainties present, multiple correction models were applied to obtain representative groundwater ages by incorporating stable (13C) isotope and hydrogeochemical data. The corrected and representative ages are found to range from 5.8 to 8.6 ka BP (thousand years before present). From the study it can be inferred that central Bhuj aquifer hosts paleo-groundwater while the western part is recently recharged. Therefore, over-exploitation of deep groundwater in central Bhuj aquifer may further lower the water levels and this would have long-term impact on the socio-economic development of Kutch region.

14C and 14C‐10Be terrestrial age dating system for meteorites—New data for four recently fallen meteorites

AbstractWe perform a systematic and detailed study of the 14C and 14C‐10Be dating systems for meteorite terrestrial ages. Physical model calculations indicate that neither the 14C production rates nor the 14C/10Be production rate ratios are constant enough to be reasonably approximated by average values. By using simple averages, one introduces a significant size‐dependent bias into the database for meteorite terrestrial ages. By combining modeled 14C production rates and 14C/10Be production rate ratios with (22Ne/21Ne)cos ratios and assuming ~80% ablation losses, relatively easy to use correlations of 14C production rates and 14C/10Be production rate ratios as a function of (22Ne/21Ne)cos are established. The new correlations enable the determination of terrestrial ages that are more accurate than ages based solely on average values for 14C and/or 14C/10Be. We validate the model predictions by measuring 14C activity concentrations, 14C/10Be production rate ratios, 21Necos concentrations, and (22Ne/21Ne)cos ratios in four recently fallen meteorites: Mt. Tazerzait, Boumdeid (2011), Bensour, and SaU 606. The experimental data confirmed the model predictions, although the available data are insufficient to be conclusive. More data from freshly fallen meteorites are needed for validating the model predictions for different chondrite sizes and chondrite types.

Integrating major ion geochemistry, stable isotopes (18O, 2H) and radioactive isotopes (222Rn, 14C, 36Cl, 3H) to understand the interaction between catchment waters and an intermittent river

Determining the locations and sources of baseflow and the transit times of water is important for understanding catchment behaviour and functioning. Major ion geochemistry, stable isotopes (18O and 2H), and radioisotopes (222Rn, 3H, 14C, and 36Cl) were used to investigate the sources and transit times of water in the upper catchment of the intermittent Avoca River in southeast Australia. 222Rn activities and Cl concentrations implied the presence of baseflow inputs and the distribution was mainly controlled by local topography. Fluctuation of Cl concentrations implied that low-salinity near-river water was an important component of baseflow. The 3H activities of laterally disconnected pool waters during the summer months were 1.64 to 5.11 TU. The higher of these values exceed those of average annual rainfall (2.8–3.2 TU), probably due to the input of later winter to spring rainfall. The stream water had 3H activities ranging from 2.21 to 2.40 TU in July and 2.39 to 2.77 TU in August, which yield mean transit times of 4.0 to 7.0 years and 1.4 to 4.8 years respectively. These 3H activities were significantly higher than those of regional groundwater (3H activities <0.1 TU), implying that the river is largely sustained by young near-river stores at all flow conditions. Regional groundwater had 14C activities of 34.0 to 98.1 pMC, which yield mean residence times of up to 12,900 years. R36Cl values of regional groundwater (50.9–61.9 × 10−15) were higher than those of modern rainfall, probably reflecting the R36Cl values of recharge. Similar R36Cl values of the pool and stream water (33.3–58.7 × 10−15) implied that some Cl is derived from the regional groundwater influx. As with other intermittent streams in southeast Australia, the upper Avoca River was mainly sustained by relatively small water stores, and it will be vulnerable to short-term changes in climate and land use.

THE POTENTIAL OF BIOGENIC FRACTION ANALYSIS BY RADIOCARBON IN FOOD, DRUG, AND COSMETIC PRODUCTS

ABSTRACTBiobased content analysis is a well-established, analytically independent, standardized method to determine the biobased content of fuels and plastics, based on differences of the specific radiocarbon (14C) activity of fossil and recent biogenic compounds. This biogenic content analysis can be useful for the producers as a quality assurance tool, for the customers as feedback about the truly biobased products and for the control organizations as an independent analytical tool to prove the biological origin. More than 100 commercially available foods, cosmetics, and drug samples have been used for biobased carbon content analysis by accelerator mass spectrometry (AMS) 14C measurement to demonstrate the potential of this technique. Our results show that this measurement technique is a unique tool for the determination of biocontent in foodstuff and medical products. Most of the tested materials were nearly or completely biobased (≥ 98 pMC), and no completely fossil-based final product was detected. The lowest biogenic compound was measured in a vanilla aroma flavor. In 45 of the 102 samples selected a wide range (2–98%) presented fossil-based carbon content. The method can be applied for monitoring raw materials and final products for biobased content in the industry and consumer protection as well.

The 14C dose assessment model chain – 14C source term definition and uncertainty quantification

Abstract. Carbon-14 (14C) is an important, dose-determining contributing radionuclide in a deep geological repository for low and intermediate level radioactive waste (L/ILW). 14C is relevant for safety assessments as it can be present both as dissolved and gaseous species in the disposal facility and the host rock, and 14C-organic compounds migrate in the near field and the geosphere due to weak interaction with mineral surfaces in alkaline to near-neutral conditions. Thus, the chemical form of the 14C-bearing carbon species dictates the routes of 14C migration in the engineered barrier system of a deep geological repository and the surrounding host rock and therefore determines the long-term contribution of 14C to dose release from a repository for radioactive waste. Furthermore, 14C released from a deep repository would be subject to a certain accumulation in the biosphere, given the role of carbon as main building block of any life form on earth. The contribution will illustrate Nagra's recent progress within the 14C dose assessment model chain for a L/ILW deep geological repository to address the quantification of uncertainties. The systematic approach began by incorporating a realistic best-estimate plus uncertainty description of 14C activities within the Swiss model inventory of radioactive materials assembled specifically for the purpose of the general licence application. In this context state-of-the-art activation calculations for expected reactor and decommissioning wastes as well as extensive inquiries into origin and use of 14C within medicine, research, and industry played a key role. Uncertainties were screened for relevance and main contributing factors taken into account, differentiating between the characterisation methods of the relevant waste streams. Based on detailed knowledge of the expected activity and material inventory, release rates for the release pathways through congruent and instantaneous release processes as well as resulting chemical species could be defined with confidence. Key findings and characteristics of the 14C source term will be highlighted and discussed.

Characterizing the water–rock interactions and groundwater flow processes in the Paleozoic to Cenozoic strata aquifer systems with contrasting mineralogy at basin scale: Qingyi river, east China

This study aims to identify water–rock interaction and groundwater flow processes in aquifer systems with contrasting mineralogy at the basin scale. Investigations have been carried out using major ion geochemistry and environmental isotopes (δ2H and δ18O of water, δ13C values, 87Sr/86Sr ratios, and 14C activities) within aquifers with contrasting mineralogy in the Qingyi river basin (QRB, east China) composed of marine carbonate and continental granitic sediments with successive strata during Paleozoic, Mesozoic and Cenozoic. Analysis of 95 rain, surface and groundwater, and 12 solid rock samples found that dissolution of limestone, silicate minerals, and evapotranspiration dominated the hydrogeochemical process in the lower, upper, and middle basin, respectively. The various major ion and 87Sr/86Sr ratios of groundwater in each aquifer suggest that local lithology minerals dissolution controls the water–rock equilibria in the groundwater system. The 87Sr/86Sr ratios are correlated with both major ion geochemistry and δ13C values, constraining the process of varying proportions of silicate and carbonate minerals dissolution. Percolating water from soils carrying dissolved CO2 plays an important role in controlling the hydrogeochemical processes in the groundwater system throughout the QRB. Inter-aquifer flow has been proved by the well correlated relations between 87Sr/86Sr ratios and δ13C values or/and Sr/Na and Ca/Na ratios, as well as the irregular groundwater apparent 14C ages (1.78 to 8.52 kyr) with respect to position in the basin. Admixture ratios of 9–50% are derived from the groundwater in limestone aquifer. The rapid decrease in carbonate groundwater mixing ratio is accompanied by an increase in 87Sr/86Sr ratios, indicating that groundwater is derived Sr from silicate weathering and abundant carbon from the soils. Regional inter-aquifer flow occurs in the buried carbonate aquifers based on isotopic evidence, which could result in karstic groundwater leakage in the Wuhu cityside and should be given special attention.

A speleothem record of seasonality and moisture transport around the 8.2 ka event in Central Europe (Vacska Cave, Hungary)

AbstractA stalagmite was collected in northern Hungary from the Vacska Cave, where monitoring and ventilation-based site selection had been conducted. The stalagmite covers the 10–8 ka (relative to AD 1950) period, including the so-called 8.2 ka event, and showed preceding signs of climate change that were evaluated by petrographic observations, 14C activities, Sr concentrations, and stable isotope compositions of calcite and inclusion-hosted water. Comparisons of speleothem records show that isotope peaks at ca. 8.5 ka are related to a regional climate anomaly, rather than to a continental-scale event. In accordance with regional proxy records, the 8.2 ka event was associated with a series of temperature and precipitation amount changes, starting with cooling and a reduction in the winter-to-summer precipitation ratio, and then becoming a humid and warm phase at 8.15 ka. X-ray diffraction-based crystallinity parameter (FWHM) values provided evidence for diagenetic alteration of the stable oxygen isotope compositions of inclusion waters. Nevertheless, the stable hydrogen isotope compositions of inclusion waters and the oxygen isotope values of the host calcite revealed elevated d-excess values, and therefore increased Mediterranean moisture contribution during the 8.2 ka event, which indirectly indicate the southward displacement of moisture transport from the Atlantic Ocean.

Development of a secondary reference material for application in carbon-14 specific activity determination by thermal oxidation and liquid scintillation counting method

Abstract Carbon-14 (14C) is a pure beta-emitting radionuclide with a half-life of 5730 ± 30 y. Considering the long half-life and its biological importance, significant attention is given to monitoring 14C in the vicinity of nuclear facilities. The 14C measurement technique employed by the majority of environmental monitoring laboratories for impact assessments in the vicinity of nuclear facilities is based on the thermal oxidization of the samples and the determination of activity by liquid scintillation counting. One of the difficulties faced by these laboratories is the nonavailability of a suitable matrix-matching reference material which is truly representative of the type of sample being analyzed. In this study, an effort has been made to develop a reference material that is representative and has a similar thermal oxidation/combustion property as that of a typical terrestrial plant biota observed in the vicinity of the nuclear power plants of India for quality assurance programs. A prebomb era wood (~150 years old) was identified as a potential secondary reference material. The stable carbon ratio (d13C) of the sample was determined by isotopic ratio mass spectrometer (IRMS), and the mean value was −26.33 ± 0.47 ‰. The 14C specific activity of the sample was determined by accelerator mass spectrometry and a mean value of 221.6 ± 0.6 Bq kg−1 C was assigned as the reference value to the prebomb wood. In addition, measurements were performed by thermal oxidation in a tube furnace and by analysis of the 14C activity in a liquid scintillation counter.

Identification and characterization of CYP71 subclade cytochrome P450 enzymes involved in the biosynthesis of bitterness compounds in Cichorium intybus.

Industrial chicory (Cichorium intybus var. sativum) and witloof (C. intybus var. foliosum) are crops with an important economic value, mainly cultivated for inulin production and as a leafy vegetable, respectively. Both crops are rich in nutritionally relevant specialized metabolites with beneficial effects for human health. However, their bitter taste, caused by the sesquiterpene lactones (SLs) produced in leaves and taproot, limits wider applications in the food industry. Changing the bitterness would thus create new opportunities with a great economic impact. Known genes encoding enzymes involved in the SL biosynthetic pathway are GERMACRENE A SYNTHASE (GAS), GERMACRENE A OXIDASE (GAO), COSTUNOLIDE SYNTHASE (COS) and KAUNIOLIDE SYNTHASE (KLS). In this study, we integrated genome and transcriptome mining to further unravel SL biosynthesis. We found that C. intybus SL biosynthesis is controlled by the phytohormone methyl jasmonate (MeJA). Gene family annotation and MeJA inducibility enabled the pinpointing of candidate genes related with the SL biosynthetic pathway. We specifically focused on members of subclade CYP71 of the cytochrome P450 family. We verified the biochemical activity of 14C. intybus CYP71 enzymes transiently produced in Nicotiana benthamiana and identified several functional paralogs for each of the GAO, COS and KLS genes, pointing to redundancy in and robustness of the SL biosynthetic pathway. Gene functionality was further analyzed using CRISPR/Cas9 genome editing in C. intybus. Metabolite profiling of mutant C. intybus lines demonstrated a successful reduction in SL metabolite production. Together, this study increases our insights into the C. intybus SL biosynthetic pathway and paves the way for the engineering of C. intybus bitterness.

Evaluation of the impact of the intensive exploitation of groundwater and the mega-drought based on the hydrochemical and isotopic composition of the waters of the Chacabuco-Polpaico basin in central Chile

A hydrogeochemical and isotopic study has been carried out to understand the hydrogeological functioning of a small alluvial aquifer in central Chile in a context of mega-drought and intensive exploitation of its waters. Additionally, two mine tailings dams from porphyry copper mining are situated in the area. The prolonged mega-drought, which has lasted for over thirteen years, has resulted in a significant decrease in rainfall recharge and a drop of up to 50 m in piezometric levels, although no serious groundwater contamination problems have yet been detected, except for a rise in nitrate contents (ranging between 23 and 45 mg/L NO3) attributed to return irrigation. Groundwaters are calcium-bicarbonate and calcium-sodium-bicarbonate in composition. The values of δ18O and δ2H of the alluvial aquifer indicate fractionation by evaporation that would be explained by the recirculation of water that occurs in the agricultural areas of the basin, where the excess irrigation water that go back to the aquifer presents fractionation by evaporation. The δ34S and δ18O of dissolved sulfate point to pyrite oxidation, which could be related to the pyrite present in the copper porphyry and recognized in the Andes Cordillera. The 87Sr/86Sr isotopic values of the alluvial aquifer waters are close to the isotopic fingerprint of the volcanic rocks of the Abanico Formation. However, the water from the wells located further downstream in the basin and close to the tailing dams show δ34S and δ18O of dissolved sulfate and 87Sr/86Sr consistent with Miocene intrusive mineralogies of the copper porphyry type. The groundwater chemistry does not show water seepage from the tailings dam. Therefore, a minor contribution of minerals related to the intrusive rocks is proposed, which would originate from the movement of fine particles by the wind from the dams to the valley floor. The 14C activities indicate that groundwater is recent.

Dynamic stability of mineral-associated organic matter: enhanced stability and turnover through organic fertilization in a temperate agricultural topsoil

Soil organic matter (SOM) plays a vital role for soil quality, sustainable food production and climate change mitigation. It is common knowledge that SOM consists of different pools with varying qualities, quantities, and turnover times. However, it is still poorly understood how mineral and organic fertilization affects the formation and stabilization of mineral-associated organic matter (MAOM) and how long it can remain there. Here, we report on the long-term effects of different farming systems on the stability and turnover of the fine silt and clay-sized MAOM fraction (<6.3 μm) of a Haplic Luvisol (0–20 cm) in the DOK long-term trial (Switzerland). We compared three farming systems with contrasting fertilization (CONMIN = pure mineral, CONFYM = mineral + organic, BIODYN = pure organic) with an unfertilized control (NOFERT) between 1982 and 2017. We performed specific surface area (SSA) measurements on fractionated MAOM samples (<6.3 μm) from 1982 to 2017, before and after removal of OM, measured the 14C activity of all samples during the entire period and estimated the mean residence time (MRT) with a model taking into account ‘bomb 14C’ and radioactive decay. We found constant MAOM-C contents under organic fertilization. Results of SSA analysis indicate best conditions for MAOM-C stabilization under organic fertilization and different sorption mechanisms in MAOM between farming systems with and without organic fertilization. The modelled MRTs were significantly higher in NOFERT (238 ± 40 yrs) and CONMIN (195 ± 27 yrs), compared to CONFYM (138 ± 18 yrs) and BIODYN (140 ± 19 yrs), implying a high C turnover (i.e. more active MAOM) at high C contents under organic fertilization. Our findings show that MAOM is not the dead OM but corroborates the concept of ‘dynamic stability’. Continuous OM inputs from organic fertilizers and their rapid and constant turnover are needed to stabilize the “stable” MAOM-C fraction.

Organic and inorganic carbon-14 in discharges of JSC Institute of Nuclear Materials

The aim of the study is the activity concentration measurements of organic and inorganic 14C in the discharges of JSC “Institute of Nuclear Materials” (INM). In INM the research water-water reactor “IVV-2M” is operating. Collecting of 14C species was performed using a 14C sampler with a chromium oxide and platinum catalysts at different temperatures: 400, 550 and 700 °C. The measurements of 14C activity were performed using a liquid scintillation counter. The share of organic 14C in emissions ranged from 0.30 to 0.84 and depends on the temperature of the catalyst, core structure and reactor operating mode.

Conceptual Hydrodynamic Model with Hydrochemical and Isotopic Signatures of the Triassic and Silurian-Devonian Groundwater Systems in Northwestern Saudi Arabia

Groundwaters from an Upper Silurian-Lower Devonian sandstone-siltstone aquifer and an Upper Triassic calcareous unit in the northwestern part of Saudi Arabia were geochemically assessed to define their provenances, lateral migration pathways, secondary alteration processes, and potential connectivity between both aquifers. The water samples were analysed for their hydrochemical properties (n = 74), 87Sr/86Sr ratios (n = 14), 14C activities and noble gases (n = 5). The Devonian aquifer is of NaCl and Na-Cl-HCO3 water type, while the Triassic aquifer is of NaCl and Ca-Cl-SO4 type. A general increase in water salinity from 189 mg/L toward maximum concentrations of 5546 mg/L in the NW confirms potential recharge from Devonian outcrop areas with a lateral fluid migration from SE to NW. Principal component analysis (PCA) with nine variables (Na+, Ca2+, Mg2+, K+, Cl−, and SO42−, alkalinity, TDS, pH) revealed variations in TDS reflecting the observed lateral groundwater migration. A positive correlation between SO42− and Ca2+ loadings on PC2 illustrates the presence of gypsiferous water. An inverse correlation between Ca2+ and Na+ loadings on PC2 indicates cation exchange processes for both aquifers. The sandstone/siltstone-composed Silurian-Devonian aquifer groundwater was found to be dominantly undersaturated in terms of aragonite, calcite, and dolomite. Overlapping Ca/HCO3 and Na/Cl ratios for some Devonian and Triassic samples indicates mixing between both aquifers along the Hercynian Unconformity in the northwestern part of the study area. A depth-related increase in 87Sr/86Sr ratios (from 0.708611 to 0.711577) suggests the presence of water-rock exchange processes between the infiltrating groundwater and 87Sr/86Sr-enriched underlying units, likely by vertical segregating fluids. The general lack of measured 14C activities suggest the occurrence of recharge prior to Late Pleistocene Pluvial period or, more likely, a complete 14C decay during groundwater flow from recharge to the present discharge area. Elevated 4He/20Ne and depleted R/Ra ratios (0.01 to 0.05) of the groundwater indicate crustal radiogenic influence from the interaction with crustal fluids. 4He is produced in-situ with negligible contribution from the mantle. Evidence of noble gas isotopic fractionation was reflected in one water sample, indicating a preferential loss of some of the lighter isotopes of Ne and Ar.

Long-range transport and deposition on the Arctic snowpack of nuclear contaminated particulate matter

The primary environmental concern related to nuclear power is the production of radioactive waste hazardous to humans and the environment. The main scientific and technological problems to address this are related to the storage and disposal of the nuclear waste and monitoring the dispersion of radioactive species into the environment. In this work, we determined an anomalously high 14C activity, well above the modern natural background, on surface and seasonal snow sampled in early May 2019 on glaciers in the Hornsund fjord area (Svalbard). Due to the lack of local sources, the high snow concentrations of 14C suggest long-range atmospheric transport of nuclear waste particles from lower latitudes, where nuclear power plants and treatment stations are located. The analysis of the synoptic and local meteorological data allowed us to associate the long-range transport of this anomalous 14C concentration to an intrusion event of a warm and humid air mass that likely brought pollutants from Central Europe to the Arctic in late April 2019. Elemental and organic carbon, trace element concentration data, and scanning electron microscopy morphological analysis were performed on the same snow samples to better constrain the transport process that might have led to the high 14C radionuclide concentrations in Svalbard. In particular, the highest 14C values found in the snowpack (> 200 percent of Modern Carbon, pMC) were associated with the lowest OC/EC ratios (< 4), an indication of an anthropogenic industrial source, and with the presence of spherical particles rich in iron, zirconium, and titanium which, altogether, suggest an origin related to nuclear waste reprocessing plants. This study highlights the role of long-range transport in exposing Arctic environments to human pollution. Given that the frequency and intensity of these atmospheric warming events are predicted to increase due to ongoing climate change, improving our knowledge of their possible impact to Arctic pollution is becoming urgent.