Isotope (δ13C, δ15N, δ2H) diet–tissue discrimination in African grey parrot Psittacus erithacus: implications for forensic studies

Diet–tissue isotopic relationships established under controlled conditions are informative for determining the dietary sources and geographic provenance of organisms. We analysed δ¹³C, δ¹⁵N, and non-exchangeable δ²H values of captive African grey parrot Psittacus erithacus feathers grown on a fixed mixed-diet and borehole water. Diet–feather Δ¹³C and Δ¹⁵N discrimination values were +3.8?±?0.3?‰ and +6.3?±?0.7?‰ respectively; significantly greater than expected. Non-exchangeable δ²H feather values (?62.4?±?6.4?‰) were more negative than water (?26.1?±?2.5?‰) offered during feather growth. There was no positive relationship between the δ¹³C and δ¹⁵N values of the samples along each feather with the associated samples of food offered, or the feather non-exchangeable hydrogen isotope values with δ²H values of water, emphasising the complex processes involved in carbohydrate, protein, and income water routing to feather growth. Understanding the isotopic relationship between diet and feathers may provide greater clarity in the use of stable isotopes in feathers as a tool in determining origins of captive and wild-caught African grey parrots, a species that is widespread in aviculture and faces significant threats to wild populations. We suggest that these isotopic results, determined even in controlled laboratory conditions, be used with caution.     

Field-deployable measurements of free-living individuals to determine energy balance: fuel substrate usage through δ13C in breath CO2 and diet through hair δ13C and δ15N values

Carbon isotopes of breath CO₂ vary depending on diet and fuel substrate used. This study examined if exercise-induced δ¹³C-CO₂ changes in substrate utilization were distinguishable from baseline δ¹³C-CO₂ variations in a population with uncontrolled diet, and compared hair isotope values and food logs to develop an isotope model of diet. Study participants included nine women with diverse Body Mass Index (BMI), age, ancestry, exercise history, and diet. Breath samples were collected prior to and up to 12?h after a 5- or 10?K walk/run. Indirect calorimetry was measured with a smartphone-enabled mobile colorimetric device, and a field-deployable isotope analyzer measured breath δ¹³C-CO₂ values. Diet was assessed by food logs and δ¹³C, δ¹⁵N of hair samples. Post-exercise δ¹³C-CO₂ values increased by 0.54?±?1.09‰ (1 sd, n?=?9), implying enhanced carbohydrate burning, while early morning δ¹³C-CO₂ values were lower than daily averages (p?=?0.0043), indicating lipid burning during overnight fasting. Although diurnal δ¹³C-CO₂ variation (1.90?±?0.77‰) and participant baseline range (3.06‰) exceeded exercise-induced variation, temporal patterns distinguished exercise from dietary isotope effects. Hair δ¹³C and δ¹⁵N values were consistent with a new dietary isotope model. Notwithstanding the small number of participants, this study introduces a novel combination of techniques to directly monitor energy balance in free-living individuals.     

Seasonal variation in natural abundance of δ13C and 15N in Salicornia brachiata Roxb. populations from a coastal area of India

High and fluctuating salinity is characteristic for coastal salt marshes, which strongly affect the physiology of halophytes consequently resulting in changes in stable isotope distribution. The natural abundance of stable isotopes (δ¹³C and δ¹⁵N) of the halophyte plant Salicornia brachiata and physico-chemical characteristics of soils were analysed in order to investigate the relationship of stable isotope distribution in different populations in a growing period in the coastal area of Gujarat, India. Aboveground and belowground biomass of S. brachiata was collected from six different populations at five times (September 2014, November 2014, January 2015, March 2015 and May 2015). The δ¹³C values in aboveground (?30.8 to ?23.6?‰, average: ?26.6?±?0.4?‰) and belowground biomass (?30.0 to ?23.1?‰, average: ?26.3?±?0.4?‰) were similar. The δ¹³C values were positively correlated with soil salinity and Na concentration, and negatively correlated with soil mineral nitrogen. The δ¹⁵N values of aboveground (6.7–16.1?‰, average: 9.6?±?0.4?‰) were comparatively higher than belowground biomass (5.4–13.2?‰, average: 7.8?±?0.3?‰). The δ¹⁵N values were negatively correlated with soil available P. We conclude that the variation in δ¹³C values of S. brachiata was possibly caused by soil salinity (associated Na content) and N limitation which demonstrates the potential of δ¹³C as an indicator of stress in plants.     

The relative isotopic abundance (δ13C, δ15N) during composting of agricultural wastes in relation to compost quality and feedstock

Variations in the relative isotopic abundance of C and N (δ¹³C and δ¹⁵N) were measured during the composting of different agricultural wastes using bench-scale bioreactors. Different mixtures of agricultural wastes (horse bedding manure?+?legume residues; dairy manure?+?jatropha mill cake; dairy manure?+?sugarcane residues; dairy manure alone) were used for aerobic–thermophilic composting. No significant differences were found between the δ¹³C values of the feedstock and the final compost, except for dairy manure?+?sugarcane residues (from initial ratio of ?13.6?±?0.2?‰ to final ratio of ?14.4?±?0.2?‰). δ¹⁵N values increased significantly in composts of horse bedding manure?+?legumes residues (from initial ratio of +5.9?±?0.1?‰ to final ratio of +8.2?±?0.5?‰) and dairy manure?+?jatropha mill cake (from initial ratio of +9.5?±?0.2?‰ to final ratio of +12.8?±?0.7?‰) and was related to the total N loss (mass balance). δ¹³C can be used to differentiate composts from different feedstock (e.g. C₃ or C₄ sources). The quantitative relationship between N loss and δ¹⁵N variation should be determined.     

Using the 13C/12C carbon isotope ratio to characterise the emission sources of airborne particulate matter: a review of literature

ABSTRACT

Particulate matter (PM) from atmospheric aerosols contains carbons that are harmful for living organisms and the environment. PM can originate from vehicle emissions, wearing of vehicle components, and dust. Size and composition determine PM transport and penetration depth into the respiratory system. Understanding PM emission characteristics is essential for developing strategies to improve air quality. The number of studies on carbon isotope composition (¹³C/¹²C) of PM samples to characterise emission factors has increased. The goal of this review is to integrate and interpret the findings from ¹³C/¹²C carbon isotope ratio (δ¹³C, ‰) analyses for the most common types of emission sources. The review integrates data from 25 studies in 13 countries. The range of δ¹³C of PM from vehicle emissions was from ?28.3 to ?24.5?‰ and for non-vehicle anthropogenic emissions from ?27.4 to ?23.3?‰. In contrast, PM ranges for δ¹³C from biomass burning sources differed markedly. For C₃ plants, δ¹³C ranged from ?34.7 to ?25.4?‰ and for C₄ plants from ?22.2 to ?13.0?‰. The ¹³C/¹²C isotope analysis of PM is valuable for understanding the sources of pollutants and distinguishing vehicle emissions from biomass burning. However, additional markers are needed to further distinguish other anthropogenic sources.     

Oxygen and nitrogen isotopic composition of nitrate in commercial fertilizers,nitric acid,and reagent salts

Nitrate is a key component of synthetic fertilizers that can be beneficial to crop production in agro-ecosystems, but can also cause damage to natural ecosystems if it is exported in large amounts. Stable isotopes, both oxygen and nitrogen, have been used to trace the sources and fate of nitrate in various ecosystems. However, the oxygen isotope composition of synthetic and organic nitrates is poorly constrained. Here, we present a study on the N and O isotope composition of nitrate-based fertilizers. The δ¹⁵N values of synthetic and natural nitrates were 0?±?2?‰ similar to the air N₂ from which they are derived. The δ¹⁸O values of synthetic nitrates were 23?±?3?‰, similar to air O₂, and natural nitrate fertilizer δ¹⁸O values (55?±?5?‰) were similar to those observed in atmospheric nitrate. The Δ¹⁷O values of synthetic fertilizer nitrate were approximately zero following a mass-dependent isotope relationship, while natural nitrate fertilizers had Δ¹⁷O values of 18?±?2?‰ similar to nitrate produced photochemically in the atmosphere. These narrow ranges of values can be used to assess the amount of nitrate arising from fertilizers in mixed systems where more than one nitrate source exists (soil, rivers, and lakes) using simple isotope mixing models.     

Comparison of δ13C and δ18O from cellulose,whole wood,and resin-free whole wood from an old high elevation Pinus uncinata in the Spanish central Pyrenees*

δ¹³C and δ¹⁸O values from sapwood of a single Pinus uncinata tree, from a high elevation site in the Spanish Pyrenees, were determined to evaluate the differences between whole wood and resin-free whole wood. This issue is addressed for the first time with P. uncinata over a 38-year long period. Results are also compared with published isotope values of α-cellulose samples from the same tree. The differences in δ¹³C and δ¹⁸O between whole wood and resin-free whole wood vary within the analytical uncertainty of 0.3 and 0.5?‰, respectively, indicating that resin extraction is not necessary for sapwood of P. uncinata. Mean differences between cellulose and whole wood are 0.9?‰ (δ¹³C) and 5.0?‰ (δ¹⁸O), respectively. However, further analyses of different species and other sites are needed to evaluate whether the findings reported here are coherent more generally.     

Carbon isotopic signature reveals the geographical trend in methane consumption and production pathways in alpine ecosystems over the Qinghai–Tibetan Plateau

On the Qinghai–Tibetan Plateau, isotopic signatures in soil–atmosphere CH₄ fluxes were investigated in nine grasslands and three wetlands. In the grasslands, the fractionation factor for soil CH₄ uptake, α_soil, was much smaller than the usually reported value of 0.9975–1.0095. Stepwise multiple variation analysis indicates that α_soil is higher for higher soil water contents but is lower for higher C/N ratios of soil surface biomass. In the three wetlands, the soil-emitted δ¹³C–CH₄ was similar (?55.3?±?5.5?‰ and ?53.0?±?5.5?‰) in two bogs separated by >1000?km but was lower (?63.4?±?6.3?‰) in a marsh. Environmental factors related to intrasite variations in soil-emitted δ¹³C–CH₄ include the soil C/N ratio, oxidation–reduction potential, soil C concentration and soil water contents. Geographical isotopic surveys revealed environmental constraints on the CH₄ consumption pathways in grasslands and the biome type-specific consistency in CH₄ production pathways in wetlands.     

13C discriminations of Pinus sylvestris vs. Pinus ponderosa at a dry site in Brandenburg (eastern Germany): 100-year growth comparison

The carbon isotope composition (δ¹³C, ‰) and discrimination (Δ, ‰) of old grown North American Pinus ponderosa Dougl. Ex P. et C. Laws. and European Pinus sylvestris L. were determined using trees grown under almost identical growing conditions in a mixed stand in Bralitz, Northeast Germany. Single-tree δ¹³C analyses of tree-ring cellulose of both species were carried out at a yearly resolution for the period 1901–2001 and the results compared with growth (basal area increment). Annual mean δ¹³C values for P. ponderosa ranged from?21.6 ‰ to?25.2 ‰ and for P. sylvestris from?21.4 ‰ to?24.4 ‰. Accordingly, ¹³C discrimination (Δ) showed higher values for P. ponderosa throughout the investigation period. Five characteristic periods of Δ were identified for both the tree species, reflecting positive and negative influences of environmental factors. Good growing conditions such as after-thinning events had a positive effect on Δ, reflecting higher values, while poor conditions like aridity and air pollution had a negative influence, reflecting lower values. The dynamics of Δ were likewise reflected in the growth (basal area increment, BAI). Higher ¹³C discrimination values of P. ponderosa led to higher BAIs of P. ponderosa in comparison with P. sylvestris. Correlation function analyses confirmed that P. sylvestris was more dependent on precipitation than P. ponderosa, which showed a closer relationship with temperature. The results confirm that under predominantly dry growing conditions, P. ponderosa showed better growth performance than P. sylvestris, indicating better common intrinsic water-use efficiency and, therefore, higher rates of net photosynthesis at a given transpiration. In view of the prospect of climate change, the results are very significant for assessing both trees’ physiological properties and, hence, their potential for coping with future growing conditions.     

Isotopic characteristics of meteoric waters in the Belgrade region

Abstract

The stable isotope composition of hydrogen (δ²H) and oxygen (δ¹⁸O) in monthly precipitation and river water (Sava River and Danube) samples in the Belgrade area gathered between 1992 and 2005 are determined. The local meteoric water line δ²H=7.8 (±0.2) δ¹⁸O+7.3(±1.6) (r ²=0.98, n=60, σ=0.52) for the whole period of observation is close to the global meteoric water line. The amount-weighted mean δ²H and δ¹⁸O values of precipitation were?65±27 ‰ and?9.4±3.4 ‰, respectively. Good correlation between δ¹⁸O values (r>rsim0.67) and ambient temperature and relative humidity was obtained. Stream-water data ranged from?94 to?60 ‰ for δ²H and from?11.0 to ～5.7 ‰ for δ¹⁸O with highly statistically significant difference (p>0.01) between the Sava River and the Danube. In addition, the isotopic compositions of local precipitation and adjacent river water at monitoring sites were compared. Obtained data will give an opportunity to improve the knowledge of mixing stream water and local groundwater, and assessment of potential groundwater risks and pressures in the Belgrade basin.     

Measuring δ13C values of atmospheric acetaldehyde via sodium bisulfite adsorption and cysteamine derivatisation

δ¹³C values of gaseous acetaldehyde were measured by gas chromatograph–combustion–isotope ratio mass spectrometer (GC–C–IRMS) via sodium bisulfite (NaHSO₃) adsorption and cysteamine derivatisation. Gaseous acetaldehyde was collected via NaHSO₃-coated Sep-Pak^® silica gel cartridge, then derivatised with cysteamine, and then the δ¹³C value of the acetaldehyde–cysteamine derivative was measured by GC–C–IRMS. Using two acetaldehydes with different δ¹³C values, derivatisation experiments were carried out to cover concentrations between 0.009×10^?3 and 1.96×10^?3 mg·l^?1) of atmospheric acetaldehyde, and then δ¹³C fractionation was evaluated in the derivatisation of acetaldehyde based on stoichiometric mass balance after measuring the δ¹³C values of acetaldehyde, cysteamine and the acetaldehyde–cysteamine derivative. δ¹³C measurements in the derivertisation process showed good reproducibility (<0.5 ‰) for gaseous acetaldehyde. The differences between predicted and measured δ¹³C values were 0.04–0.31 ‰ for acetaldehyde–cysteamine derivative, indicating that the derivatisation introduces no isotope fractionation for gaseous acetaldehyde, and obtained δ¹³C values of acetaldehyde in ambient air at the two sites were distinct (?34.00 ‰ at an urban site versus?31.00 ‰ at a forest site), implying potential application of the method to study atmospheric acetaldehyde.     

Methane-Derived Carbonates in a Native Sulfur Deposit: Stable Isotope and Trace Element Discriminations Related to the Transformation of Aragonite to Calcite

Abstract

Stable isotope (¹³C, ¹⁸O, ³⁴S) and trace element (Sr²⁺, Mg²⁺, Mn²⁺, Ba²⁺, Na⁺) investigations of elemental sulfur, primary calcites and mixtures of aragonite with secondary, post-aragonitic calcite from sulfur-bearing limestones have provided new insights into the geochemistry of the mineral forming environment of the native sulfur deposit at Machów (SE-Poland). The carbon isotopic composition of carbonates (δ¹³C = ?41 to ?47‰ vs. PDB) associated with native sulfur (δ³⁴S = + 10 to + 15‰ vs. V-CDT) relates their formation to the microbiological anaerobic oxidation of methane and the reduction of sulfate derived from Miocene gypsum. From a comparison with experimentally derived fractionation factors the element ratios of the aqueous fluids responsible for carbonate formation are estimated. In agreement with field and laboratory observations, ratios near seawater composition are obtained for primary aragonite, whereas the fluids were relatively enriched in dissolved calcium during the formation of primary and secondary calcites. Based on the oxygen isotope composition of the carbonates (δ¹⁸O = ?3.9 to ?5.9‰ vs. PDB) and a secondary SrSO₄ (δ¹⁸O = + 20‰ vs. SMOW; δ³⁴S = + 59‰ vs. V-CDT), maximum formation temperatures of 35°C (carbonates) and 47°C (celestite) are obtained, in agreement with estimates for West Ukraine sulfur ores. The sulfur isotopic composition of elemental sulfur associated with carbonates points to intense microbial reduction of sulfate derived from Miocene gypsum (δ³⁴S ≈ + 23‰) prior to the re-oxidation of dissolved reduced sulfur species.     

First field-based observations of δ2H and δ18O values of event-based precipitation,rivers and other water bodies in the Dzungarian Gobi,SW Mongolia

For certain remote areas like Mongolia, field-based precipitation, surface and ground water isotopic data are scarce. So far no such data exist for the Mongolian Gobi desert, which hinders the understanding of isotopic fractionation processes in this extreme, arid region. We collected 26 event-based precipitation samples, 39 Bij river samples, and 75 samples from other water bodies in the Dzungarian Gobi in SW Mongolia over a period of 16 months for hydrogen and oxygen stable isotope analysis. δ²H and δ¹⁸O values in precipitation show high seasonal variation and cover an extreme range: 175?‰ for δ²H and 24?‰ for δ¹⁸O values. The calculated local meteoric water line (LMWL) shows the isotopic characteristics of precipitation in an arid region. Individual water samples fall into one of three groups: within, above or below the 95?% confidence interval of LMWL. Data presented provide a basis for future studies in this region.     

Chlorine isotopic compositions of deep saline fluids in Ibusuki coastal geothermal region,Japan: using B–Cl isotopes to interpret fluid sources

We report chlorine stable isotopic compositions (δ³⁷Cl, expressed in ‰ relative to the standard mean ocean chloride) as well as δ²H and δ¹⁸O values of deep saline fluids taken at eight drill-holes reaching from 73 to 780?m below sea level in the Ibusuki coastal geothermal region, Japan. Analytical results show that the δ³⁷Cl values narrowly range between ?0.26 and +0.21?‰ with an analytical precision of ±0.06?‰. Except for one sample, the samples examined are negative in δ³⁷Cl value with varying Cl/B molar ratios from 117 to 1265. A correlation study between the Cl/B molar ratio and the δ³⁷Cl/δ¹¹B ratio indicates a hyperbola-type mixing of at least two Cl sources in the Ibusuki region. One of them depletes in ³⁷Cl with a higher value of Cl/B molar ratio; and the other one enriches in ³⁷Cl with a lower Cl/B molar ratio. The former is chemically identical to that of the deep brine, which is altered seawater through the seawater–hot rock interaction. The latter is chemically similar to gas condensate derived from the high-temperature (890?°C) vent of an island-arc volcano near the Ibusuki region.     

Assessing the authenticity of commercial deep-sea drinking water by chemical and isotopic approaches

This study combines stable isotopes and chemical elements with statistical principal component analysis (PCA) to assess the authenticity of bottled commercial drinking water desalinized from deep seawater in the Taiwan market. Isotopic results indicate that true bottled deep-sea drinking water (DSDW) exhibits about 0?‰ for both δ²H and δ¹⁸O values, which are values similar to those of open seawater. By comparison, suspected counterfeit DSDW products display δ²H and δ¹⁸O values of around ?51?‰ and ?8?‰, respectively. These values are representative of terrestrial freshwater. In addition, suspected counterfeit DSDWs have δ and electrical conductivity values similar to a mixed water (MW) product that was manufactured by purifying terrestrial freshwater and adulterating this with small amounts of brine. Furthermore, PCA results indicate the chemical constitution of suspected DSDW products to be similar to the MW product which falls between purified terrestrial freshwater and desalinized open seawater. These similarities imply that suspected counterfeit DSDW products are manufactured in a similar manner to the declared MW product. This study demonstrates how combining knowledge of stable water isotopes and PCA can be used in assessing the authenticity of commercial DSDW products. The method should be of great interest to similar investigations elsewhere.     

Carbon isotope analysis of dissolved organic carbon in fresh and saline (NaCl) water via continuous flow cavity ring-down spectroscopy following wet chemical oxidation

This work examines the performance and limitations of a wet chemical oxidation carbon analyser interfaced with a cavity ring-down spectrometer (WCO-CRDS) in a continuous flow (CF) configuration for measuring δ¹³C of dissolved organic carbon (δ¹³C-DOC) in natural water samples. Low-chloride matrix (<5?g Cl/L) DOC solutions were analysed with as little as 2.5?mg C/L in a 9?mL aliquot with a precision of 0.5?‰. In high-chloride matrix (10–100?g Cl/L) DOC solutions, bias towards lighter δ¹³C-DOC was observed because of incomplete oxidation despite using high-concentration oxidant, extended reaction time, or post-wet chemical oxidation gas-phase combustion. However, through a combination of dilution, chloride removal, and increasing the oxidant:sample ratio, high-salinity samples with sufficient DOC (>22.5?µg C/aliquot) may be analysed. The WCO-CRDS approach requires more total carbon (µg C/aliquot) than conventional CF-isotope ratio mass spectrometer, but is nonetheless applicable to a wide range of DOC concentration and water types, including brackish water, produced water, and basinal brines.     

Spring response to precipitation events using δ18O and δ2H in the Tanour catchment,NW Jordan

The Tanour spring is one of the several karst springs located in the northern part of Jordan. Water samples from the Tanour spring and precipitation were collected in the area of Ajloun in NW Jordan for the analysis of stable oxygen and hydrogen isotopes to evaluate the spring response to precipitation events. Rainwater and snow samples were collected from different elevations during winters of 2013–2014 and 2014–2015. In addition, spring samples were collected between December 2014 and March 2015. δ¹⁸O values in rainwater vary from ?3.26 to ?17.34?‰ (average: ?7.84?±?3.23?‰), while δ²H values range between ?4.4 and ?110.4?‰ (average: ?35.7?±?25.0?‰). Deuterium excess ranges from 17.8 to 34.1?‰ (average: 27.1?±?4.0?‰). The Local Meteoric Water Line for the study area was calculated to be δ²H?=?7.66*δ¹⁸O?+?24.43 (R²?=?0.98). Pre-event spring discharge showed variation in δ¹⁸O (range ?6.29 to ?7.17?‰; average ?6.58?±?0.19?‰) and δ²H values (range ?28.8 to ?32.7?‰; average: ?30.5?±?1.0?‰). In contrast, δ¹⁸O and δ²H rapidly changed to more negative values during rainfall and snowmelt events and persisted for several days before returning to background values. Spring water temperature, spring discharge, and turbidity followed the trend in isotopic composition during and after the precipitation events. The rapid change in the isotopic composition, spring discharge, water temperature, and turbidity in response to recharge events is related to fast water travel times and low storage capacity in the conduit system of the karst aquifer. Based on the changes in the isotopic composition of spring water after the precipitation events, the water travel time in the aquifer is in the order of 5–11 days.     

Sauna,sweat and science II – do we sweat what we drink?

ABSTRACT

Inspired by a previous ‘Sauna, sweat and science’ study [Zech et al. Isot Environ Health Stud. 2015;51(3):439–447] and out of curiosity and enthusiasm for stable isotope and sauna research we aimed at answering the question ‘do we sweat (isotopically) what we drink’? We, therefore, pulse-labelled five test persons in a sauna experiment with beverages that were ²H-enriched at about +25,600?‰. Sweat samples were collected during six sauna rounds and the hydrogen isotope composition δ²H_sweat was determined using an isotope ratio mass spectrometer. Before pulse labelling, δ²H_sweat – reflecting by approximation body water – ranged from –32 to –22?‰. This is ～35?‰ enriched compared to usual mid-European drinking water and can be explained with hydrogen-bearing food as well as with the respiratory loss of ²H-depleted vapour. The absence of a clearly detectable ²H pulse in sweat after pulse labelling and δ²H_sweat results of ≤+250?‰ due to a fast ²H equilibration with body water are moreover a clearly negative answer to our research question also in a short-term consideration. Given that the recovery of the tracer based on an isotope mass balance calculation is clearly below 100?%, we finally answer the question ‘where did the rest of the tracer go?’     

Stable carbon isotopic composition of peat columns,subsoil and vegetation on natural and forestry-drained boreal peatlands

ABSTRACT

We studied natural and forestry-drained peatlands to examine the effect of over 34 years lowered water table on the δ¹³C values of vegetation, bulk peat and subsoil. In the seven studied sites, δ¹³C in the basal peat layer was 1.1 and 1.2?‰ lower than that of the middle-layer and surface layer, respectively. Furthermore, there was a positive correlation between the δ¹³C values of the basal and surface peat layers, possibly due to carbon (C) recycling within the peat column. In the same mire complex, natural fen peat δ¹³C values were lower than those of the nearby bog, possibly due to the dominance of vascular plants on fen and the generally larger share of recycled C in the fens than in the bogs. Furthermore, natural and 51 years previously drained fen and bog, on the opposite sides of a ditch on the same mire complex, showed no significant differences in δ¹³C values. Plant δ¹³C values were lower, while δ¹³C values of subsoil were higher in the drained than in the natural site of the fen.     

C and O stable isotopic signatures of fast-growing dripstones on alkaline substrates: reflection of growth mechanism,carbonate sources and environmental conditions

Secondary carbonate precipitates (dripstones) formed on concrete surfaces in four different environments – Mediterranean and continental open-space and indoor environments (inside a building and in a karstic cave) – were studied. The fabric of dripstones depends upon water supply, pH of mother solution and carbonate-resulting precipitation rate. Very low δ¹³C (average?28.2‰) and δ¹⁸O (average?18.4‰) values showed a strong positive correlation, typical for carbonate precipitated by rapid dissolution of CO₂ in a highly alkaline solution and consequent disequilibrium precipitation of CaCO₃. The main source of carbon is atmospheric or biogenic CO₂ in the poorly ventilated karstic cave, which is reflected in even lower δ¹³C values. Statistical analysis of δ¹³C and δ¹⁸O values of the four groups of samples showed that the governing factor of isotope fractionation is not the temperature, but rather the precipitation rate.