Variability Of Stable Isotope Ratios Research Articles

Stable Isotopic Analysis of Long-whiskered Catfish (Sperata aor) Otoliths for Characterization of their Habitat and Relationship with Water Temperature in the Ganges River

Background: Spatial variability of stable isotope ratios in water from River Ganges is preserved in aragonite or calcite present in otoliths and formed at equilibrium with ambient water. This technique is used for a set of long-whiskered catfish aragonite otoliths from four different locations along the course of the River Ganges Methods: Acid digestion of otolith and the analysis of δ13C and δ18O in these carbonates using an isotope ratio mass spectrometer allowed the distinction of fish habitat and provided an idea about environmental conditions of water along the Ganges River. Results: The δ18O signature of otolith carbonate revealed a distinct compositional trend denoting glacial water input in the upstream segment of the Ganges, close to the water reservoir at Narora. However, the δ13C values remained constant, suggesting similar bicarbonate composition and food intake along the stream length. The δ18O signature in otolith from Varanasi was unexpectedly lighter and showed a tendency of the catfish population to migrate upstream segment of the river. The fish from the Narora location showed the lowest δ18O values, denoting the signature of water derived from the melting of a glacier. The heavier δ18O values were seen in the population from Kanpur. The upstream migration of fish population is indicated from the δ18O values of a fish otolith from Varanasi and Bhagalpur. The Varanasi location shows aberration in δ18O signature in otoliths, and this exists because this catfish moves to other places to avoid anthropogenic stress at this location Conclusion: The δ18O of otolith carbonate covaries with average environmental temperature recorded at the individual location and serves as an important thermometric measurement for marking environmental conditions and stress in changing climatic parameters along the stream length of River Ganges and its tributaries.

Importance of estuary morphology for ecological connectivity with their adjacent coast: A case study in Brazilian tropical estuaries

Coastal habitats are interlinked by ecological connectivity, defined as the exchange of organic matter or organisms between habitats. The degree of this connectivity will depend in particular on the geometric properties of the landscape. The increasing anthropogenic alterations in estuaries therefore raises the need to understand how their morphological characteristics influence fluxes between habitats. We used stable isotopes to investigate the variability of ecological connectivity between three estuaries and their adjacent coastal areas by tracking the origin of the organic matter (estuarine vs coastal) underlying the diet of the migrant species Eucinostomus argenteus. The chosen estuaries were geomorphologically distinct, exhibiting, in particular, differences in their degree of connection to the sea, corresponding to the morphological features (shape, mouth width) controlling key physico-chemical variables in this habitat (e.g. salinity). The sampling of the basal food sources contributing to the food web was performed in the three estuaries and in their adjacent coasts. The variability in stable isotope ratios between estuaries was examined for both fish and sources of organic matter. In the three estuaries, Bayesian models were applied for each season (dry and rainy) to quantify the relative contribution of sources from estuarine and coastal environments supporting the diet of the silver mojarra. The share of coastal organic matter increased with the degree of sea connection, indicating that the properties of the seascape can regulate the intensity of interactions between ecosystems. Variations in ecological connectivity are likely to affect the functioning of ecosystems as they influence trophic pathways and energy flows between adjacent habitats. Morphological modifications could thus significantly disturb ecosystems by altering the structure of food web, thereby affecting certain ecosystem services such as the availability of living marine resources.

Intraskeletal variability in stable isotope ratios of C and N among pinnipeds and cetaceans

Fil: Bas, Maria. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Austral de Investigaciones Cientificas; Argentina. Universidad de Barcelona; Espana

Characterizing stable isotope relationships between green turtle (Chelonia mydas) skin and unhatched eggs.

Stable isotope analysis is used to understand the foraging habits and movements of a diverse set of organisms. Variability in stable isotope ratios among tissues derived from the same animal makes it difficult to compare data among study results in which different tissue types are evaluated. Isotopic relationships between two green turtle (Chelonia mydas) tissue types, skin and unhatched egg contents are unknown. Similarly, few data exist to evaluate the influence of time elapsed after oviposition (as a proxy for decomposition) on isotopic variability among unhatched eggs within the same nest. Skin and unhatched egg contents were collected from 69 adult female green turtles and associated nests at the Archie Carr National Wildlife Refuge in Florida, USA. Values of δ13 C, δ15 N, and δ34 S were measured for both tissue types using a continuous flow isotope ratio mass spectrometer. Standardized major-axis (SMA) regression was used to generate conversion equations of carbon, nitrogen, and sulfur isotope ratios between the two tissue types. Model selection frameworks consisting of single-factor linear models were employed per isotope ratio to assess how egg time-in-nest affected intraclutch isotopic variability. Conversion equations for all three isotope ratios indicated significant relationships between skin and unhatched egg values, although model fits were lower than found in some studies examining similar patterns in other marine turtle species. The probability of increased intraclutch variability was significantly higher among eggs collected at longer intervals after deposition. This study reports the first-ever δ13 C and δ15 N conversion equations between skin and unhatched eggs for green turtles, and the first δ34 S conversion equation for any marine turtle species. SMA regression was used to directly convert tissue values bidirectionally, unlike equations generated using ordinary least-squares regression. Issues with increased intraclutch variability at later excavation dates highlight the importance of collecting unhatched eggs as soon as possible after hatchling emergence.

Temporal variability in stable isotope ratios of C and N in the vibrissa of captive and wild adult South American sea lions Otaria byronia : More than just diet shifts

We analyzed the δ13C and δ15N values in the vibrissae of captive adult breeding South American sea lions (Otaria byronia) fed at a constant diet and then used this information to analyze the change in stable isotope values along the vibrissae from wild individuals. The overall diet-to-vibrissa discrimination factor of the captive animals was 3.0‰ ± 0.1‰ for δ13C and 3.6‰ ± 0.1‰ for δ15N, but the stable isotope ratios fluctuated periodically despite constant diet. The δ13C and δ15N values of the captive male declined at the end of the breeding season, whereas the δ13C values of the female increased during the central part of pregnancy and the δ15N values peaked during lactation. The δ13C and δ15N values of adult wild specimens also fluctuated periodically and vibrissae growth rate (0.15 mm/d in both sexes) was slightly lower than in captivity (0.17 mm/d), assuming an annual periodicity for oscillations. Similarities in the amplitude of the cycles of captive and wild males suggested that fasting was probably the main source of periodic variability in the δ15N of wild males, whereas pregnancy and lactation were probably the main source of periodic variability for the δ13C of wild females.

Multi‐isotopic signatures of organic and conventional Italian pasta along the production chain

The variability of stable isotope ratios (δ(2) H, δ(13) C, δ(15) N, δ(18) O and δ(34) S) along the production chain of pasta (durum wheat, flour and pasta) produced by using both conventional and organic farming systems in four Italian regions in 2 years was investigated. The aim was to evaluate if and how the farming system and geographical origin affect stable isotope ratios determined along the production chain. Irrespective of the processing technology, 65% of the samples were correctly classified according to the farming system and 98% were correctly classified regarding the geographical region. When considering both farming system and geographical region simultaneously, 80% of the samples were correctly classified. The measured isotope parameters were thus primarily affected by the geographical origin. In conclusion, it is expected that the use of these parameters will allow the development of analytical control procedures that can be used to check the geographical origin of Italian organic and conventional pasta and its raw materials. Copyright © 2016 John Wiley & Sons, Ltd.

Spatial, ontogenetic and interspecific variability in stable isotope ratios of nitrogen and carbon of Merluccius capensis and Merluccius paradoxus off South Africa.

General linear models (GLMs) were used to determine the relative importance of interspecific, ontogenetic and spatial effects in explaining variability in stable isotope ratios of nitrogen (δ(15) N) and carbon (δ(13) C) of the co-occurring Cape hakes Merluccius capensis and Merluccius paradoxus off South Africa. Significant GLMs were derived for both isotopes, explaining 74 and 56% of observed variance in Merluccius spp. δ(15) N and δ(13) C, respectively. Spatial effects (west or south coast) contributed most towards explaining variability in the δ(15) N model, with Merluccius spp. off the west coast having higher (by c. 1.4‰) δ(15) N levels than Merluccius spp. off the south coast. Fish size and species were also significant in explaining variability in δ(15) N, with both species showing significant linear increases in δ(15) N with size and M. capensis having higher (by c. 0.7‰) δ(15) N values than M. paradoxus. Species and coast explained most and similar amounts of variability in the δ(13) C model, with M. capensis having higher (by c. 0.8‰) δ(13) C values than M. paradoxus, and values being lower (by c. 0.7‰) for fishes off the west coast compared with the south coast. These results not only corroborate the knowledge of Merluccius spp. feeding ecology gained from dietary studies, in particular the ontogenetic change in trophic level corresponding to a changing diet, but also that M. capensis feeds at a slightly higher trophic level than M. paradoxus. The spatial difference in Merluccius spp. δ(15) N appears due to a difference in isotopic baseline, and not as a result of Merluccius spp. feeding higher in the food web off the west than the south coast, and provides new evidence that corroborates previous observations of biogeographic differences in isotopic baselines around the South African coast. This study also provides quantitative data on the relative trophic level and trophic width of Cape hakes over a large size range that can be used in ecosystem models of the southern Benguela.

Comparison of methods for stable isotope ratio (δ13C, δ15N, δ2H, δ18O) measurements of feathers

Summary Natural variations in the stable isotope ratios of bioelements in bird feathers are being increasingly used by animal ecologists to investigate different aspects of bird life. However, to ensure reliability of the data, a critical and very delicate aspect is the preparatory phase (cleaning, drying and subsampling) and the proper analysis, mainly in relation to δ2H and δ18O, respectively, for the presence of exchangeable Hs and of nitrogen and sulphur in keratin. With respect to determination of the isotope ratios of C, N, O and H, in this work, we compare the cleaning mixture most commonly used in the literature (chloroform : methanol 2 : 1) with diethylether : methanol 2 : 1, which avoids the use of the carcinogenic solvent chloroform. We also compared oven‐drying with air‐drying of samples, as well as subsampling of feathers by cutting with surgical scissors or cryogenic pulverization. Finally, we investigated whether stable isotope ratios varied along the vane and between the rachis and vane. The different methods compared in the three preparatory stages showed no differences performance‐wise and can therefore be used interchangeably. Variability in stable isotope ratios can be considerable, both along the vane and between rachis and vane, which is because their compositions register changes in diet, area and climate. However, in this specific study, when the parts of the feather closest to the calamus were removed, the delta values were clearly more homogeneous. Finally, we demonstrate that a casein with a known δ2H value, although probably differing from keratin in the number of exchangeable Hs, can be used to normalize the δ2H values of feathers, although only in the range of values close to that of the reference material. In determining δ18O, the use of a longer gas chromatography‐GC column, its frequent change and the use of a linear equation built with matrix match equivalent reference materials seems to reduce the drift of GC column performance due to the presence of nitrogen and the accumulation of sulphur.

Spatial Variability of Stable Isotope Ratios in Oysters (Crassostrea gigas) and Primary Producers Along an Estuarine Gradient (Bay of Brest, France)

This study aimed at characterizing the diet of the oyster Crassostrea gigas along an estuarine gradient in the Bay of Brest (France), through stable isotope (δ13C and δ15N) measurements in primary producers and wild oysters. The contribution of different potential food sources to the diet of C. gigas was estimated at high spatial resolution (over a gradient of 40 km with samplings every 2 km) to identify ecological transition zones and highlighted the dominance of resuspended biofilm in oysters diet. Although the different primary producers did not display any obvious pattern along the estuarine gradient, the stable isotope signatures of C. gigas differed among estuarine, inner Bay, and open sea sites. In particular, a striking 15N depletion pattern was found along the gradient which allowed to identify seven homogeneous groups. Moreover, some unexpected values found at two stations within the estuary revealed localized anthropogenic disturbances. Overall, our results suggest that suspension feeders might be better indicators of ecosystem functioning than primary producers and reflect the different ecological processes occurring along estuarine gradients, including localized anthropogenic inputs. We suggest that the usefulness of suspension feeders as indicators of ecosystem functional typology lies in the dominance of benthic material in their diet, which results in locally occurring processes being reflected in oysters’ stable isotope ratios.

Fish scale δ15N and δ13C values provide biogeochemical tags of fish comparable in performance to element concentrations in scales and otoliths

Natural variability in stable isotope ratios and element concentrations in calcified structures of fish (e.g. scales and otoliths) has provided biogeochemical ‘tags’ for studying origins and movements of marine species, but has been little used in freshwater studies. We examine whether variability in scale δ15N and δ13C values of Salmo trutta L., could provide a tag of fish over small spatial scales in a small river catchment (River Dee, U.K.) and compared their performance as tags with that of scale/otolith element concentrations. Whole scale δ15N and δ13C values differed among six study sites and fish could be classified to their site of origin with a high degree of accuracy. Classifying fish to their site of capture was marginally superior using scale δ15N and δ13C values compared to that achieved using Sr, Mn, Ba and Mg in scale hydroxyapatite or otolith aragonite. Scale δ15N and δ13C values could therefore provide non-lethally collectable biogeochemical tags superior in performance to element concentrations in otoliths and scales. A comprehensive study of δ15N and δ13C values within freshwater systems would develop our understanding of factors influencing geographical variability in baseline δ15N and δ13C signatures.

Traceability along the production chain of Italian tomato products on the basis of stable isotopes and mineral composition

The paper shows the variability of stable isotope ratios and mineral composition in tomato and derivatives along the production chain (juice, passata and paste) in order to evaluate the possibility of tracing their geographical origin. The ratios (13)C/(12)C, (15)N/(14)N, (18)O/(16)O, D/H, (34)S/(32)S and the content of Li, Be, B, Na, Mg, Al, P, K, Ca, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Se, Rb, Sr, Y, Mo, Ag, Cd, Sn, Sb, Cs, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Tm, Yb, Ir, Tl, Pb, U and of nitrates, chlorides, sulphates and phosphates were measured by Isotope Ratio Mass Spectrometry, Inductively Coupled Plasma Mass Spectrometry and Ion Chromatography, respectively. The tomato products were from three Italian regions - Piedmont, Emilia Romagna, and Apulia. By applying linear discriminant analysis on 17 of these parameters (Gd, La, Tl, Eu, Cs, Ni, Cr, Co, δ(34)S, δ(15)N, Cd, K, Mg, δ(13)C, Mo, Rb and U) excellent discrimination among products from the three regions was achieved. Irrespective of the processing technology, over 95% of the samples were correctly reclassified in cross-validation into the production site. The use of these parameters will allow the development of analytical control procedures that can be used to check the geographical provenance of Italian tomatoes and products derived from them.

Variability of Stable Isotope Ratios of Glassfish (Ambassis jacksoniensis) from Mangrove/Saltmarsh Environments in Southeast Australia and Implications for Choosing Sample Size

Stable isotopes offer an accurate and cost-effective way to understand critical pathways of energy, and their use has application where aquatic habitats have been degraded. Isotope ratios can offer insights into appropriate conservation and rehabilitation techniques to manage these valuable resources. To date, the literature shows little attention to spatial and temporal variation in isotope signatures of samples taken from estuarine environments. This study reports on an investigation of sample size by which to determine isotopic signatures within a single species of fish, Ambassis jacksoniensis. Provided are two ways by which to determine how many samples are needed, and the results imply that care may be needed in interpreting previous studies based on small sample size. A minimum of five individuals would appear necessary in some cases.

Temporal and spatial variability in stable isotope ratios of SPM link to local hydrography and longer term SPM averages suggest heavy dependence of mussels on nearshore production

Temporal changes in hydrography affect suspended particulate matter (SPM) composition and distribution in coastal systems, potentially influencing the diets of suspension feeders. Temporal variation in SPM and in the diet of the mussel Perna perna, were investigated using stable isotope analysis. The δ13C and δ15 N ratios of SPM, mussels and macroalgae were determined monthly, with SPM samples collected along a 10 km onshore–offshore transect, over 14 months at Kenton-on-Sea, on the south coast of South Africa. Clear nearshore (0 km) to offshore (10 km) carbon depletion gradients were seen in SPM during all months and extended for 50 km offshore on one occasion. Carbon enrichment of coastal SPM in winter (June–August 2004 and May 2005) indicated temporal changes in the nearshore detrital pool, presumably reflecting changes in macroalgal detritus, linked to local changes in coastal hydrography and algal seasonality. Nitrogen patterns were less clear, with SPM enrichment seen between July and October 2004 from 0 to 10 km. Nearshore SPM demonstrated cyclical patterns in carbon over 24-h periods that correlated closely with tidal cycles and mussel carbon signatures, sampled monthly, demonstrated fluctuations that could not be correlated to seasonal or monthly changes in SPM. Macroalgae showed extreme variability in isotopic signatures, with no discernable patterns. IsoSource mixing models indicated over 50% reliance of mussel tissue on nearshore carbon, highlighting the importance of nearshore SPM in mussel diet. Overall, carbon variation in SPM at both large and small temporal scales can be related to hydrographic processes, but is masked in mussels by long-term isotope integration.

Variability in stable isotope ratios in two Late-Final Jomon communities in the Tokai coastal region and its relationship with sex and ritual tooth ablation

We analyzed stable carbon and nitrogen isotope ratios in a sample of human and nonhuman mammal bones excavated from the Yoshigo and Inariyama shell mounds of the Late–Final Jomon periods in Aichi Prefecture, Japan, with a view to determining individual dietary differences. To investigate possible reasons for the dietary variations identified, we related isotope ratios to sex and tooth ablation patterns. At both sites, large intra-site variations in δ13C and δ15N values were found, compared with other Jomon populations previously studied, suggesting higher than usual levels of dietary variability, and at both sites there was a positive correlation between δ13C and δ15N values. The diet of the Jomon people at both these sites had two main protein sources: marine (marine finfish and shellfish) and terrestrial (C3 plants and terrestrial mammals) protein. The intra-site variability is probably explained by consumption of these resources in different proportions. Analysis of the Yoshigo shell mound data indicated that sex is one of the factors determining dietary difference. It was also found that individual differences in diet in Yoshigo males are greater than in females. This pattern was repeated in the Inariyama shell mound data. Dietary differences were found to be related to ritual tooth ablation characteristics, particularly in males. At Inariyama, type 4I ritual tooth ablation was associated with comparatively greater dependency on terrestrial resources, while type 2C tooth ablation was associated with greater dependency on marine resources. This may indicate that type 4I males engaged predominantly in hunting, and type 2C males in fishing, as a means of food acquisition. These results are possibly the earliest evidence of occupational differentiation in the Jomon people.

Factors Influencing Stable Isotope Ratios in CH4 and CO2 Within Subenvironments of Freshwater Wetlands: Implications for δ-Signatures of Emissions

Much uncertainty still exists regarding spatial and temporal variability of stable isotope ratios (13C/12C and D/H) in different CH4-emission sources. Such variability is especially prevalent in freshwater wetlands where a range of processes can influence stable isotope compositions, resulting in variations of up to ∼50‰ for δ13C-CH4 and ∼150‰ for δD-CH4 values. Within a temperate-zone bog and marsh situated in southwestern Ontario, Canada, gas bubbles in pond sediments exhibit only minor seasonal and spatial variation in δ13C-CH4, δD-CH4 and δ13C-CO2 values. In pond sediments, CO2 appears to be the main source of carbon during methanogenesis either directly via CO2 reduction or indirectly through dissimilation of autotrophic acetate. In contrast, CH4 production occurs primarily via acetate fermentation at shallow depths in peat soils adjacent to ponds at each wetland. At greater depths within soils, σCO2 and H2O increasingly exert an influence on δ13C- and δD-CH4 values. Secondary alteration processes (e.g., methanotrophy or diffusive transport) are unlikely to be responsible for depth-related changes in stable isotope values of CH4. Recent models that attempt to predict δD-CH4 values in freshwater environments from D/H ratios in local precipitation do not adequately account for such changes with depth. Subenvironments (i.e., soil-forming and open water areas) in wetlands should be considered separately with respect to stable isotope signatures in CH4 emission models.

Origin, Accumulation and Production of Natural Gases in the Carpathian Foredeep, Poland: ABSTRACT

The Carpathian Foredeep is the largest gas basin among all the foredeeps of the Alpine orogenic system in Europe. The Carpathian Foredeep consists of two structural complexes: Paleozoic-Mesozoic and Miocene. Up to the end of 1994, 53 gas fields in Miocene complex and 11 gas fields in the Paleozoic basement have been discovered. Cumulative gas production between 1945 and 1994 has yielded about 75 billion cubic meters from the Miocene strata, and about 7 billion cubic meters from the Paleozoic-Mesozoic basement. Gases in the Paleozoic-Mesozoic basement are variable in both molecular and stable isotope composition [[delta][sup 13]C(CH[sub 4]), [delta]D(CH[sub 4]), [delta][sup 13]C(C[sub 2]H[sub 6]), [delta][sup 13]C(C[sub 3]H[sub 8]), [delta][sup 34]S(H[sub 2]S)]. Variability of stable isotope ratios and molecular indices suggests complex origin of microbial and thermogenic gaseous hydrocarbons involving migration and mixing. The thermogenic generation of hydrocarbons was a multiphase process and in all the deposits traps were supplied at various times with new portions of hydrocarbons. The hydrogen sulfide was generated during thermochemical reduction of Jurassic sulphates. Methane which dominates gas deposits in Miocene strata originated from microbial reduction of carbon dioxide. Insignificant quantities of ethane and propane were generated during diagenetic and/or early thermogenic processes. The hydrogen sulfidemore » was generated during microbial reduction of Badenian sulphates. Accumulation of microbial methane was facilitated by high sedimentation rate of alternating clay and sand beds and the presence of methane hydrate formed in the thermodynamic regime of the Miocene basin. Uplift of the Carpathian orogen at the break of Lower and Upper Sarmatian destructed the methane hydrate zone.« less