Changes In Stable Isotope Composition Research Articles

Stable isotope composition of pesticides in commercial formulations: The ISOTOPEST database

By assessing the changes in stable isotope compositions within individual pesticide molecules, Compound Specific Isotope Analysis (CSIA) holds the potential to identify and differentiate sources and quantify pesticide degradation in the environment. However, the environmental application of pesticide CSIA is limited by the general lack of knowledge regarding the initial isotopic composition of active substances in commercially available formulations used by farmers. To address this limitation, we established a database aimed at cataloguing and disseminating isotopic signatures in commercial formulations to expand the use of pesticide CSIA. Our study involved the collection of 25 analytical standards and 120 commercial pesticide formulations from 23 manufacturers. Subsequently, 59 commercial formulations and 25 standards were extracted, and each of their active substance was analyzed for both δ13C (n = 84) and δ15N CSIA (n = 43). The extraction of pesticides did not cause significant isotope fractionation (Δ13C and Δ15N < 1‰). Incorporating existing literature data, stable carbon and nitrogen isotope signatures varied in a relatively narrow range among pesticide formulations for different pesticides (Δ13C and Δ15N < 10‰) and within different formulations for a single substance (Δ13C and Δ15N < 2‰). Overall, this suggests that pesticide CSIA is more suited for identifying pesticide transformation processes rather than differentiating pesticide sources. Moreover, an inter-laboratory comparison showed similar δ13C (Δ13C ≤ 1.2 ‰) for the targeted substances albeit varying GC-IRMS instruments. Insignificant carbon isotopic fractionation (Δ13C < 0.5‰) was observed after 4 years of storing the same pesticide formulations, confirming their viability for long-term storage at 4 °C and future inter-laboratory comparison exercises. Altogether, the ISOTOPEST database, in open access for public use and additional contributions, marks a significant advancement in establishing an environmentally relevant pesticide CSIA approach.

Effects of ethanol storage and lipid extraction on stable isotope compositions of twelve pelagic predators

Stable isotope analysis (SIA) has proven to be a powerful tool in reconstructing diets and characterizing trophic relationships for pelagic predators. Ethanol has been a common preservative solution for biopsy samples from remote areas and archived collections. It is still under debate whether the effects of ethanol (ET) would bias the trophic interpretation of the stable isotope values. Further, lipid extraction (LE) is becoming more popular as a general treatment for standardization prior to SIA, particularly for investigating intra and interspecific variation of sympatric species, because lipids have lower δ13C values. In this study, the long-term (up to 448 days) effects of treatment ET and combined treatments ET and LE (ET+LE) on stable carbon and nitrogen isotope values (δ13C and δ15N, respectively) of twelve pelagic predators from the open ocean were evaluated. Results showed that compared with control values, δ15N values displayed a positive change (δ15Nmean offset was 0.71 ± 0.56‰) but δ13C values had variable results (δ13Cmean offset was 0.42 ± 0.64‰) among all species following treatment with ET during the first 28 days and then remained stable throughout the experiment. Compared with treatment LE results, no difference was observed in δ13C, δ15N values, and C/N ratios through time following treatment ET+LE. These results indicated that treatment ET may have species-specific effects on stable isotope values, and the shifts from treatment LE could counter the changes caused by treatment ET. In addition, after 28 days of preservation, the values following treatment ET were similar to those following treatment LE in low C/N species (C/N&amp;lt;3.5), which suggested ethanol may also affect some of lipid contents from muscle tissues. Nevertheless, further research is needed to focus on the mechanisms that control changes in stable isotope composition in tissues stored in ethanol. Given the effects on pelagic predators, muscle tissue samples stored in ethanol from the open ocean or a museum after LE treatment could be used to develop SIA.

Shell beaches to beachrock: Diagenetic stable isotopic trends

Modern shell accumulations on Padre Island, Texas Gulf Coast, are composed of pristine aragonite whereas laterally adjacent Pleistocene beachrock on the mainland shores of Laguna Madre are made up of the same taxa but display a range of mixtures of aragonite and diagenetic low-Mg calcite. Cements and pedogenic crusts associated with the beachrock are 100% low-Mg calcite. Stable isotopic values for shells composed of 0, 15, 20, 45, 75 and 90% calcite display high correlations between the δ18O values and mineralogy (R2 = 0.95) and δ13C values and mineralogy (R2 = 0.87). The highly correlated changes in the stable isotopic compositions and mineralogy of the skeletal material are also evident in the data from the analyses of the pure calcite cements and pedogenic crusts. Changes in stable isotopic composition of the shells are the result of the early diagenetic alteration of the original aragonitic composition to low Mg-calcite.

Effects of ethanol storage and lipids on stable isotope values in a large mammalian omnivore

Ethanol storage and lipid extraction can alter the isotopic composition of animal tissues, which can bias dietary estimates calculated by stable isotope mixing models (SIMMs). We examined the effects of ethanol storage and lipid extraction on [delta]13C, [delta]15N, and [delta]34S values measured in brown bear (Ursus arctos) muscles and livers. We also used isotopic data from our experiment to understand the effect of ethanol storage and lipid extraction on dietary contributions calculated by SIMMs. We found that ethanol storage and lipid extraction caused small increases in [delta]13C values for both muscles (ethanol storage: +0.4 - 0.5 prom., lipid extraction: +0.4 - 0.4 prom.) and liver (ethanol storage: +0.6 - 0.3prom., lipid extraction: +0.8 - 0.5 prom.). In contrast, [delta]15N and [delta]34S values did not change when stored in ethanol or when lipids were extracted from tissues. Ethanol storage and lipid extraction had negligible effects on estimated dietary contributions. We show that a relatively high lipid content in the muscles and livers of some large-bodied terrestrial omnivores do not necessarily have an effect on dietary estimates that rely on carbon stable isotopes. Our results suggest that ethanol storage could be a valuable alternative method for preserving animal tissue prior to stable isotope analysis when freezing or drying is impractical. Nevertheless, further research is needed on the mechanisms that control changes in stable isotope composition in tissues stored in ethanol. We recommend investigating the effects of ethanol on stable isotope values in species and tissues of interest before storing samples in ethanol.

Changes in stable isotope compositions during fasting in phocid seals.

RationaleThe grey seal, Halichoerus grypus (GS), and the northern elephant seal, Mirounga angustirostris (NES), come ashore for reproduction. This period involves intense physiological processes such as lactation in females and a developmental post‐weaning fast in juveniles. Previous studies have shown that δ13C and δ15N values are affected by starvation, but the precise effects of fasting associated with lactation and post‐weaning fast in seals remain poorly understood.MethodsTo examine the effect of lactation and post‐weaning fast on stable isotope ratios in GS and NES, blood and hair were sampled from 21 GS mother‐pup pairs on the Isle of May and on 22 weaned NES pups at Año Nuevo State Reserve during their respective breeding seasons. Milk samples were also collected from GS mothers. Stable isotope measurements were performed with an isotope ratio mass spectrometer coupled to an N‐C elemental analyser.ResultsChanges in stable isotope ratios in blood components during fasting were similar and weak between GS and NES mothers especially in blood cells (GS: Δ15N = 0.05‰, Δ13C = 0.02‰; NES: Δ15N = 0.1‰, Δ13C = 0.1‰). GS showed a 15N discrimination factor between maternal and pup blood cells and milk, but not for 13C. The strongest relationship between the isotopic compositions of the mother and the pup was observed in the blood cells.ConclusionsIsotopic consequences of lactation, fasting, and growth seem limited in NES and GS, especially in medium‐term integrator tissues of feeding activity such as blood cells. Stable isotope ratios in the blood of pups and mothers are correlated. We observed a subtle mother‐to‐pup fractionation factor. Our results suggest that pup blood cells are mostly relevant for exploring the ecology of female seals.

Early Jurassic carbon and oxygen isotope records and seawater temperature variations: Insights from marine carbonate and belemnite rostra (Pieniny Klippen Belt, Carpathians)

New carbon and oxygen isotope records and discussion of the main variations in seawater temperature through the Sinemurian–Aalenian of the Pieniny Klippen Basin (northern Tethys Ocean) are presented herein. Comparison of the recorded changes in stable-isotope compositions of bulk carbonate and belemnite rostra from an open-marine environment with previously documented, predominantly restricted epicontinental data enables determination of major climatic events that were most likely of worldwide extent. A slight positive δ13C shift is recorded in the lowermost Upper Pliensbachian. A significant positive excursion in carbonate carbon isotope values is documented in the Lower Toarcian Serpentinum Zone. Furthermore, the δ13C values display a falling trend in the Lower–Upper Toarcian and relatively constant values in the Aalenian. Temperatures inferred from the δ18O values of well-preserved belemnite rostra suggest rather cool seawater conditions (10–13 °C) in the Pieniny Klippen Basin during the Late Sinemurian, warming by 4 °C in the Early Pliensbachian and then cooling by 8 °C in the Late Pliensbachian. The seawater temperature rose once more in the Early Toarcian and began to fall again during the Middle Toarcian. In the Middle–?Late Aalenian, seawater temperatures oscillated between 10 and 13 °C.

Effect of in-stream physicochemical processes on the seasonal variations in δ13C and δ18O values in laminated travertine deposits in a mountain stream channel

Travertines are potential archives of continental paleoclimate. Records of stable carbon and oxygen isotopic composition (δ13C and δ18O) in laminated travertine deposits from endogene spring waters show regular cyclic patterns which may be due to seasonal change in climate determinants such as temperature and rainfall. In this study, δ13C and δ18O measurements of three travertine specimens that grew naturally over the eight years, 2004–2011, at upstream, middle and downstream sites in a canal at Baishuitai, SW China, are presented. They exhibit clear seasonal variations that generally correlate with biannual laminations. Specifically, δ13C and δ18O values show significant positive correlation with each other for the three travertine specimens, with the correlation coefficients increasing downstream along the canal. To reveal the factors governing the seasonal and spatial variations in δ13C and δ18O values, newly formed travertines precipitated on Plexiglas substrates are also examined. Both δ13C and δ18O of the substrate travertines are low in the summer/rainy season and high in the winter/dry season, showing a great consistency with the patterns in the natural travertines. Spatially, isotope values increase downstream in both seasons, with higher increase rates in winter that are related to removal of larger fractions of dissolved inorganic carbon (DIC) from the solution and stronger kinetic isotopic fractionation in winter. Due to in-stream physicochemical processes, including CaCO3 precipitation and the associated degassing of CO2, seasonal changes in δ13C and δ18O in the travertines are amplified by two times between the upstream and downstream sites: this is opposite to trends for epigene (meteogene) tufas whose seasonal changes in stable isotope compositions are reduced downstream. We suggest in-stream physicochemical processes are a potential reason for underestimation of annual temperature ranges that are inferred from epigene tufa δ18O data.

Hydrothermal alteration of kimberlite by convective flows of external water.

Kimberlite volcanism involves the emplacement of olivine-rich volcaniclastic deposits into volcanic vents or pipes. Kimberlite deposits are typically pervasively serpentinised as a result of the reaction of olivine and water within a temperature range of 130–400 °C or less. We present a model for the influx of ground water into hot kimberlite deposits coupled with progressive cooling and serpentisation. Large-pressure gradients cause influx and heating of water within the pipe with horizontal convergent flow in the host rock and along pipe margins, and upward flow within the pipe centre. Complete serpentisation is predicted for wide ranges of permeability of the host rocks and kimberlite deposits. For typical pipe dimensions, cooling times are centuries to a few millennia. Excess volume of serpentine results in filling of pore spaces, eventually inhibiting fluid flow. Fresh olivine is preserved in lithofacies with initial low porosity, and at the base of the pipe where deeper-level host rocks have low permeability, and the pipe is narrower leading to faster cooling. These predictions are consistent with fresh olivine and serpentine distribution in the Diavik A418 kimberlite pipe, (NWT, Canada) and with features of kimberlites of the Yakutian province in Russia affected by influx of ground water brines. Fast reactions and increases in the volume of solid products compared to the reactants result in self-sealing and low water–rock ratios (estimated at <0.2). Such low water–rock ratios result in only small changes in stable isotope compositions; for example, δO18 is predicted only to change slightly from mantle values. The model supports alteration of kimberlites predominantly by interactions with external non-magmatic fluids.

Depth variation in isotopic composition of benthic resources and assessment of sculpin feeding patterns in an oligotrophic Alaskan lake

Stable isotopes of carbon (C) and nitrogen (N) are commonly used to track resource flows through lake food webs. However, there remains a weak understanding of the spatial variation in isotopic composition of benthic resources and how this variation affects inference about energy flows among species. Boundary layers at the interface between benthic substrates and the overlying water column restrict diffusion of nutrients and carbon from the water column to benthic algae and may affect the isotopic composition of benthic algae as nutrient and CO2 concentrations can become locally depleted in the benthic boundary layer. We quantified the variation in C and N stable isotope composition of benthic resources along a depth gradient in a large oligotrophic lake to assess the magnitude of change in stable isotope composition. Snails were increasingly depleted in 13C with depth, by about 10 ‰ from 0 to 20 m, while 15N in snails showed only subtle enrichment over this depth range. Sculpin (Cottas aleuticus) δ 13C and δ 15N signatures did not significantly change with depth and were more enriched in 15N than would be expected from consumption of snails alone. A comparison of δ 13C and δ 15N values from sculpins relative to shallow and deep snails, and alternative prey (marine-derived salmon resources), within a mixing model suggested sculpins feed selectively on deep grazers in this system in addition to marine-derived resources provided by migrating sockeye salmon. This study illustrates the importance of accounting for depth-related variation in isotope patterns when assessing benthic resource contributions to food webs using stable isotope data.

Modelling changes in stable isotope compositions of minerals during net transfer reactions in a contact aureole: Wollastonite growth at the northern Hunter Mountain Batholith (Death Valley National Park, USA)

One of the world's largest wollastonite deposits was formed at the contact of the northern Hunter Mountain Batholith (California, USA) in Paleozoic sediments. Wollastonite occurs as zones of variable thickness surrounding layers or nodules of quartzite in limestones. A minimum formation temperature of 650 °C is estimated from isolated periclase-bearing lenses in that area. Contact metamorphism of siliceous carbonates has produced mineral assemblages that are consistent with heterogeneous, and partly limited infiltration of water-rich fluids, compatible with 18O/ 16O and 13C/ 12C isotopic patterns recorded in carbonates. Oxygen isotope compositions of wollastonites in the study area may also not require infiltration of large quantities of externally-derived fluids that were out of equilibrium with the rocks. δ 18O values of wollastonite are high (14.8‰ to 25.0‰; median: 19.7‰) and close to those of the host limestone (19.7‰ to 28‰; median: 24.9‰) and quartz (18.0‰ to 29.1‰; median: 22.6‰). Isotopic disequilibrium exists at quartz/wollastonite and wollastonite/calcite boundaries. Therefore, classical batch/Rayleigh fractionation models based on reactant and product equilibrium are not applicable to the wollastonite rims. An approach that relies on local instantaneous mass balance for the reactants, based on the wollastonite-forming reaction is suggested as an alternative way to model wollastonite reaction rims. This model reproduces many of the measured δ 18O values of wollastonite reaction rims of the current study to within ± 1‰, even though the wollastonite compositions vary by almost 10‰.

Avian embryonic development does not change the stable isotope composition of the calcite eggshell

The avian embryo resorbs most of the calcium for bone formation from the calcite eggshell but the exact mechanisms of the resorption are unknown. The present study tested whether this process results in variable fractionation of the oxygen and carbon isotopes in shell calcium carbonate, which could provide a detailed insight into the temporal and spatial use of the eggshell by the developing embryo. Despite the uncertainty regarding changes in stable isotope composition of the eggshell across developmental stages or regions of the shell, eggshells are a popular resource for the analysis of historic and extant trophic relationships. To clarify how the stable isotope composition varies with embryonic development, the δ(13)C and δ(18)O content of the carbonate fraction in shells of black-headed gull (Larus ridibundus) eggs were sampled at four different stages of embryonic development and at five eggshell regions. No consistent relationship between the stable isotope composition of the eggshell and embryonic development, shell region or maculation was observed, although shell thickness decreased with development in all shell regions. By contrast, individual eggs differed significantly in isotope composition. These results establish that eggshells can be used to investigate a species' carbon and oxygen sources, regardless of the egg's developmental stage.

SHORT-TERM MEASUREMENT OF CARBON STABLE ISOTOPE DISCRIMINATION IN PHOTOSYNTHESIS AND RESPIRATION BY AQUATIC MACROPHYTES, WITH MARINE MACROALGAL EXAMPLES(1).

Progress in the study of stable isotope discrimination in carbon assimilation by aquatic macrophytes has been slower than for other groups of primary producers, such as phytoplankton and terrestrial plants. A probable reason has been the methodologies employed for such a study: field collections or long-term incubations, both relying on the observation of changes in carbon isotope composition of plant tissue. Here, we present a short-term incubation method based on the change in carbon stable isotope composition in water. Its fundamental advantage over the other approaches is that the change in stable isotope composition in water in a closed system is much faster than in the plant tissue. We applied the method to investigate the relationship between carbon assimilation intensity and isotope discrimination. The results included a relatively small discrimination in respiration, a significant influence of carbon assimilation rate on discrimination, and the suggestion of HCO3 (-) or CO2 uptake in photosynthesis. The information gathered using this method would be difficult to obtain in other ways, and so we believe that it should contribute to a better understanding of the physiology and ecology of aquatic macrophytes.

Chemical and isotopic composition of high-molecular-weight dissolved organic matter from the Mississippi River plume

In order to examine the source and transformation of high-molecular-weight dissolved organic matter (HMW-DOM) in the mixing zone of the Mississippi River plume, HMW-DOM with sizes between 1 kDa and 0.2 μm was collected along a salinity gradient using cross-flow ultrafiltration. Isolated OM samples were desalted, freeze-dried and characterized for elemental (C and N) and biochemical composition (proteins, carbohydrates and uronic acids), stable isotopic ( δ 13C and δ 15N) and radiocarbon (Δ 14C) signatures, and relative molecular composition using pyrolysis-gas chromatography/mass spectrometry. The organic carbon content of HMW-DOM samples ranged from 31 to 36 wt.%, indicating that isolated colloids are mostly organic in nature. Contents of N ranged from 1.9% to 3.3%, resulting in a C/N ratio of 19–20 at lower salinity stations with a strong influence by terrestrial DOM and 12–15 at higher salinity stations with more freshly photosynthesized marine DOM. While OC-normalized protein contents decreased with increasing salinity, both carbohydrate and uronic acid contents increased with increasing salinity. Variations of pyrograms demonstrated that the proportion of furfural (an indicator of polysaccharides) in HMW-DOM also increased with increasing salinity, while the proportion of phenols decreased with increasing salinity. Changes in carbohydrate, (acid) polysaccharide and phenol contents of HMW-DOM samples reflect the variation in DOM sources along the salinity gradient, with higher phenol and low polysaccharide contents in lower salinity areas but higher polysaccharide and low phenol contents in coastal waters. Values of δ 13C increased from − 25.24‰ at the Mississippi River fresh water end-member station to − 21.86‰ at an offshore station in the Gulf of Mexico. Changes in stable isotope composition resemble the changes in molecular composition from freshwater to coastal waters. Values of δ 15N, on the other hand, varied little, from 3.5‰ to 4.9‰ without a consistent trend, indicating that δ 15N is a less sensitive source tracer. Measured radiocarbon signatures (Δ 14C) expressed as apparent 14C ages ranged from > modern at lower salinity stations to 400–800 y BP at coastal stations. Results of isotopic mass balance revealed that, in addition to end-member organic matter from river and marine sources, at least 10–25% of the HMW-DOM could derive from reworked or regenerated DOM in the Mississippi River plume, most likely through sediment–water interactions and lateral transport. Thus, reworking processes are important in governing the chemical and isotopic composition of DOM in the estuarine mixing zone.

Nitrogen input by cyanobacterial biofilms of an inselberg into a tropical rainforest in French Guiana

Inselbergs are isolated rock outcrops displaying high heterogeneity in both soil formation and microclimatic condition with high variation in plant biodiversity. Vegetation patterns on inselbergs in the humid tropics range from rocks covered with dense biofilms predominated by cyanobacteria to high forest on deep soils. Along a similar transect, we investigated N supply to the vegetation using element and isotopic analyses of soil and biofilm samples from an inselberg in French Guiana. An increase in N content related to total dry weight (N%) in soils from the inselberg peak to surrounding habitats was related to changes in stable isotope composition (δ 15N). At the inselberg peak cyanobacterial biofilms on bare rocks and soils within small vegetation islands had similar δ 15N values of −1.9‰ and −1.3‰ while δ 15N of soils progressively increased towards the primary rainforest up to 6‰. From the peak towards the base of the inselberg, the density of higher plants and soil depth increased. Hence, soil N cycling and N losses to the environment resulted in a progressive increase of soil δ 15N. The distribution of N%, δ 15N and δ 13C values suggest that the main N supply for soils at and nearby the inselberg is derived from cyanobacterial N 2 fixation through leaching processes.

Warming mineralises young and old soil carbon equally

Abstract. The temperature sensitivity of soil organic carbon decomposition is critical for predicting future climate change because soils store 2-3 times the amount of atmospheric carbon. Of particular controversy is the question, whether temperature sensitivity differs between young or labile and old or more stable carbon pools. Ambiguities in experimental methodology have so far limited corroboration of any particular hypothesis. Here, we show in a clear-cut approach that differences in temperature sensitivity between young and old carbon are negligible. Using the change in stable isotope composition in transitional systems from C3 to C4 vegetation, we were able to directly distinguish the temperature sensitivity of carbon differing several decades in age. This method had several advantages over previously followed approaches. It allowed to identify release of much older carbon, avoided un-natural conditions of long-term incubations and did not require arguable curve-fitting. Our results demonstrate that feedbacks of the carbon cycle on climate change are driven equally by young and old soil organic carbon.

Temporal changes in stable isotope composition of spring waters: Implications for recent changes in climate and atmospheric circulation

Stable isotope values of shallow groundwater emerging from springs in a high-elevation basin in the central Sierra Nevada of California decrease with increasing geochemical groundwater ages. From water recharged in 1960 to water recharged in 1990, a 1.2‰ and 11‰ increase occurs in δ 18 O and δD, respectively. Historic temperature records from surrounding areas show a 1.3 °C increase in mean annual air temperature over the same time period. This temperature change alone is not great enough to explain the observed increase in δ 18 O. We suggest that changes in atmospheric circulation patterns, which have been documented in this region, account for the remaining increase in δ 18 O. The time scale of these climatic changes, recorded in both the historical and the hydrological records, is extremely short (decadal scale) and suggests that the δ 18 O of groundwater can be a useful tool for studying climatic and atmospheric circulation changes over very short time intervals. It also suggests that circulation changes must be considered along with temperature when interpreting paleoclimate data.

Isotope hydrology of inland sabkhas in the Bardawil area, Sinai

The changes in stable isotope composition of inland sabkhas can throw light on the hydrologic mechanisms which operate in these systems. Inflow waters were found to be of meteoric origin. Immediately after local rain, water drains from surrounding sand dunes onto the top of the salt crust, dissolving it. Further inflow of waters keeps the sabkhas inundated for weeks, but the different sabkhas were found to be open to varying degrees to the inflow of groundwaters and to outflow of brines into bottom sediments.