Differences In δ13C Values Research Articles

A Stable Isotope Tracer (δ13C) Study ofEscherichia coliRetention in Two Freshwater Bivalves (Corbicula flumineaandElliptio complanata) (Corbiculidae and Unionidae)

Bacteria are ingested by suspension feeding bivalves and can be an important component of their diet. This study evaluated whether a common bacterium of vertebrate enteric origin, Escherichia coli (Migula, 1895), is retained in the stomach or gill by two different freshwater bivalve species, Corbicula fluminea (Müller, 1974) and Elliptio complanata (Lightfoot, 1786). A series of diet treatment experiments were conducted comparing each anatomical section using a δ13C label and E. coli cells grown from stock cultures. A significant difference in δ13C values was related to anatomic structure among all treatment groups during a 7-day feeding experiment (24 jars, df = 140; F = 4.88; P < 0.001). A key finding was that in gill tissue, a significant difference was observed among <δ13C-labeled and unlabeled treatment combinations for both C. fluminea and E. complanata (F = 13.57; df = 31; P < 0.0001). The results suggest that water column E. coli are likely retained on gill tissue and to a lesser degree in the stomach in both E. complanata and C. fluminea. This study serves to validate the hypothesis that E. coli may be initially more abundant in gill tissue during sorting processes before being transferred to the stomach.

Stable isotopes and fatty acids as dietary tracers of intertidal bivalves

We evaluated the potential food sources of six commercially important bivalve species (Mactra veneriformis, Mactra chinensis, Ruditapes philippinarum, Cyclina sinensis, Dosinia laminate, and Sinonovacula constricta) that coexist in intertidal areas of Zhuanghe Bay, northern China. The δ13C values of bivalves (−19.9 to −19.0 ‰) were between those of particulate organic matter (POM) (−22.5 ‰) and sedimentary organic matter (SOM) (−14.9 ‰). Based on the isotope two-source mixing model, the relative contributions of POM and SOM to the dietary regime of intertidal bivalves were 71.6 and 29.4 %, respectively. This result is consistent with the traditional view that POM is the principal food source of bivalves. The lack of significant differences in δ13C values among species suggests that they had the same primary food source. High proportions of dinoflagellate fatty acid markers in all species supported the premise that POM was their primary food source. Levels of bacterial and terrestrial organic matter (TOM) fatty acid markers were also high in all species, indicating that bacteria and TOM can be important supplemental food sources for intertidal bivalves.

Ecological influences on the difference in δ15N and δ13C values between fish tissues: implications for studies of temporal diet variation

AbstractTemporal diet changes can be detected by comparing δ13C and δ15N values between tissues with different isotopic turnover times. However, other factors contribute to disparities in δ13C and δ15N signatures between tissues and could confound the interpretation of stable isotope data. We examined the effects of ecological factors on differences in muscle and liver δ13C and δ15N signatures of Arctic charr [Salvelinus alpinus, (L.)] to determine whether their effects were large enough to influence studies of diet change. In addition, we examined whether differences in lipid content accounted for a significant portion of the differences in δ13C values between tissues. Results indicated that life history, diet, reproductive status and gender had significant effects on the differences in δ13C values between tissues, while gender and diet significantly affected differences in δ15N values. Differences in % lipid content between tissues also explained approximately 74% of the observed variation in the difference in δ13C values between tissues. The differences in δ13C values observed between muscle and liver tissues may be partially explained by physiological differences in lipid storage and use between tissues associated with ecological factor effects. These results demonstrate that ecological factors other than a change in diet can influence the differences in δ13C and δ15N signatures between muscle and liver tissues. However, the impact of ecological factors on studies of diet change depends on how the magnitude of the factor effects compared with a biologically meaningful change in diet.

Geochemistry and genesis of low-grade metasediment-hosted Zn–Pb–Ag mineralization, southern Proterozoic Curnamona Province, Australia

Sediment-hosted, Paleoproterozoic low-grade Zn–Pb–Ag and Cu–Au mineralization occurs at the Polygonum, Thunderdome, Hunters Dam, and Benagerie Ridge prospects under a thick sedimentary cover in the Mulyungarie Domain (MD) of the southern Curnamona Province (SCP), Australia. Host rocks and mineralization were metamorphosed to lower greenschist facies at Benagerie Ridge, upper greenschist facies at Hunters Dam, and lower to upper amphibolite facies at Polygonum and Thunderdome. The giant Paleoproterozoic Pb–Zn–Ag Broken Hill deposit, which was metamorphosed to the granulite facies, is hosted in the Broken Hill Domain (BHD). The general lithostratigraphy for each prospect is similar and can be subdivided into four main units. Unit 1, at the base of the stratigraphic section, hosts Cu–Au mineralization and is characterized by the presence of oxidized magnetic metapsammopelites. Unit 2 consists of sulfide-rich, pyritic carbonaceous metapelites, calcareous metashales/siltstones, Mn-bearing sideritic metacarbonates, metacalc-silicates, and carbonate and feldspar lenses and layers. Syn-sedimentary sulfide mineralization occurs as laminations of fine-grained pyrite and sphalerite and resembles that at the HYC deposit, Queensland. Differences in δ13C values (δ13CVPDB=−10.2 and −0.8‰) of calcite in unit 2 from the same area suggest variable amounts of original organic C. The δ13C values of carbonates in Broken Hill ore and those obtained here from the Esmeralda deposit near Broken Hill are extremely low (δ13C=−25 to −21‰) and likely resulted from volatilization and high temperature effects during high-grade metamorphism. Barren laminated carbonaceous metapelites in unit 3 constitute a marker unit throughout the SCP. Unit 4 at the top of the stratigraphic sequence consists of psammopelitic and laminated andalusite or chiastolite phyllites that contain garnet and gahnite, laminated garnetite, quartz garnetite, Mn-bearing banded iron formation, amphibolite, and stratabound hydrothermal Pb–Zn mineralization. This unit, which is present at the Polygonum and Thunderdome prospects, is stratigraphically equivalent to the upper Broken Hill Group, which hosts the Broken Hill deposit. Base metals occur in metacarbonates and metapelites and close to redox boundaries between units 1 and 2, and units 2 and 3. Geochemical indicators of stratabound Pb–Zn mineralization in the northern part of the SCP include whole-rock values of >4ppm Tl, >25ppm Cd, and >17ppm Se in units 2 and 4, (Mn+Fe+Mg)/(Mn+Fe+Mg+Ca) ratios>0.9 for carbonates, Mn/(Mn+Fe+Mg) ratios>0.6 for garnet in garnet–quartz rocks, and Mn/(Mn+Ca+Fe) ratios>0.3 for garnet in metacalc-silicate rocks.

Stable isotopes and elements as biological markers to determine food resource use pattern by Lasioderma serricorne (Coleoptera: Anobiidae)

The cigarette beetle, Lasioderma serricorne (F.) (Coleoptera: Anobiidae) is a pest of durable grain commodities, spices, and stored tobacco. Larvae cause most feeding damage to commodities; adult L. serricorne rarely feed and are good fliers. Since L. serricorne can potentially disperse between different landscapes and may feed on different hosts, understanding insects' host use pattern may help to direct management efforts to specific commodity storages. In this study, quantitative and qualitative differences of carbon and nitrogen isotopes and five inorganic elements (Mg, Mn, Fe, Cu and Zn) present in the insect body tissue were used to identify the dietary history of L. serricorne. Adults reared on different hosts in the laboratory, including respective rearing media and insects collected from different field locations, were used in the study. The δ13C values in the laboratory, reared L. serricorne, were similar to the values of respective rearing media with an enrichment of about 1‰ in the insect body. The enrichment for δ15N value greatly increased from host to insect body and varied about +3.30 to +5.73‰ in beetles. There was a distinct difference in δ13C values for insects raised on C3-based or C4-based hosts. A majority of the field-collected beetles showed δ13C values similar to expectations for a C3 plant (−20 to −28‰); however, a few beetles showed evidence for feeding on C4 plants (<−14‰) or diet mixing between C3 and C4 plants. Of the five inorganic elements evaluated, only Mn showed distinct variation in concentrations between the rearing media and insect body. This study shows potential exists for delineating the food sources of L. serricorne, using carbon and nitrogen stable isotopes and elements like Mn.

Selective feeding in nematodes: a stable isotope analysis of bacteria and algae as food sources for free-living nematodes

Laboratory experiments with stable isotopes (13C and 15N) were conducted to determine the importance of bacteria and algae as food sources for free-living nematodes. All tested bacterivorous nematodes (Caenorhabditis elegans, Acrobeloides tricornis, Poikilolaimus sp. and Panagrolaimus sp.) were found to be depleted in δ13C (on average by −1.71 ± 0.56‰) and enriched in δ15N (on average by 3.17 ± 1.27‰) relative to their bacterial diets of Escherichia coli and Matsuebacter sp. The nematode species showed considerable differences in their stable isotope composition with respect to food sources. Moreover, they differed significantly in δ13C and δ15N values when placed on the same bacterial diet of E. coli, consistent with differences in their trophic shifts. Conversely, no differences in δ13C values were observed among nematode species placed on the same Matsuebacter sp. diet. In mixed food sources of E. coli and Matsuebacter sp., E. coli contributed 71% of the carbon to C. elegans and Matsuebacter sp. more than 90% of the carbon to A. tricornis. An enrichment experiment based on 13C-enriched NaH13CO3, 13C6-glucose and 15N-enriched Na15NO3 tracers in a freshwater periphytic community showed the importance of micro-algae and diatoms over heterotrophic bacteria as the main food sources of free-living periphytic nematodes. In this respect, direct grazing may predominate, possibly together with the use of extracellular polymeric substances (EPS) from diatoms. In general, the use of stable isotopes to study nematode feeding ecology can be useful to investigate directly the type of ingested food item(s), different bacteria and algae, and the contribution to nematode diet, in addition to the conventional feeding type scheme.

Role of body size and temporal hydrology in the dietary shifts of shortjaw tapertail anchovy Coilia brachygnathus (Actinopterygii, Engraulidae) in a large floodplain lake

Seasonal water-level changes in floodplain lakes can induce variations in primary and secondary production, thus affecting trophic interactions. In this study, we tested the latter by studying size- and temporal hydrology-related shifts in the diet of shortjaw tapertail anchovy Coilia brachygnathus (Actinopterygii, Engraulidae) from Lake Poyang. During the wet season, δ13C values ranged from −28.2‰ for small anchovies to −24.6‰ for larger individuals, but δ15N ranged from 18.9‰ for smaller fish to 12.4‰ for larger fish. Significant 13C-enrichment and 15N-depletion occurred with increasing size, revealing that different carbon sources were used as the fish grew. Given the high hydrologic fluctuation levels, significant differences in δ13C values were observed among larger anchovies between seasons, indicating a temporal dietary shift. Anchovies fed primarily on shrimp and fish during the low-water season despite the predominance of zooplankton during the two seasons studied, which indicated increased piscivorous reliance. C. brachygnathus exhibited higher δ15N values during the wet season because the food items were 15N-enriched. Human waste brought by floods could be another possible interpretation. Considering C. brachygnathus is an important link between plankton production and higher piscivorous trophic levels, changes in the species are expected to affect the functioning of lake food webs along the trophic pathway.

Stable isotopes reveal variable foraging behaviour in a colony of the Imperial Shag Phalacrocorax atriceps: differences between ages, sexes and years

Stable isotope analysis (SIA) is used in the study of trophic relationships in food webs, being also a powerful tool for the study of intraspecific diet segregation. Unlike short-term data from most conventional diet studies, SIA can also provide information about times when seabirds stay out at sea and are thus not easily accessible. Imperial Shags Phalacrocorax atriceps are resident seabirds showing sexual dimorphism in body size. Previous studies showed strong intra-species dietary segregation between male and female Imperial Shags during the breeding season. Between 2006 and 2009 at New Island in the Falkland Islands/Islas Malvinas (southwest Atlantic), we investigated if intraspecific differences were also present between age-groups, namely adults and immature males. We further tested if differences existed over the year, particularly during the non-breeding season. Finally, we tested if differences were consistent among studied years. We found no differences in δ13C values between immature and adult males. However, lower δ15N values indicated feeding at lower trophic levels for immatures. This might be explained by poorer hunting abilities of young, inexperienced birds, compared to adults. In both the breeding and non-breeding seasons, differences among years in both δ13C and δ15N suggest that the foraging behaviour of the shags differed among years in terms of spatial distribution and trophic level. Males consistently foraged on a higher trophic level than females and had lower δ13C values, which is in line with the use of foraging areas further offshore.

Elemental and isotopic carbon and nitrogen records of organic matter accumulation in a Holocene permafrost peat sequence in the East European Russian Arctic

AbstractA peat deposit from the East European Russian Arctic, spanning nearly 10 000 years, was investigated to study soil organic matter degradation using analyses of bulk elemental and stable isotopic compositions and plant macrofossil remains. The peat accumulated initially in a wet fen that was transformed into a peat plateau bog following aggradation of permafrost in the late Holocene (∼2500 cal a BP). Total organic carbon and total nitrogen (N) concentrations are higher in the fen peat than in the moss‐dominated bog peat layers. Layers in the sequence that have lower concentrations of total hydrogen (H) are associated with degraded vascular plant residues. C/N and H/C atomic ratios indicate better preservation of organic matter in peat material dominated by bryophytes as opposed to vascular plants. The presence of permafrost in the peat plateau stage and water‐saturated conditions at the bottom of the fen stage appear to lead to better preservation of organic plant material. δ15N values suggest N isotopic fractionation was driven primarily by microbial decomposition whereas differences in δ13C values appear to reflect mainly changes in plant assemblages. Positive shifts in both δ15N and δ13C values coincide with a local change to drier conditions as a result of the onset of permafrost and frost heave of the peat surface. This pattern suggests that permafrost aggradation not only resulted in changes in vegetation but also aerated the underlying fen peat, which enhanced microbial denitrification, causing the observed 15N‐enrichment. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Response of Mallorca shelf ecosystems to an early Holocene humid phase

Benthic foraminiferal data as well as stable oxygen and carbon isotope records of different planktonic and benthic foraminifera from a shelf sediment core off southwest Mallorca document major sedimentological, hydrological and trophic changes during the Holocene. The Holocene relative sea-level rise resulted in the progradation of different sediment facies types characterized by specific benthic foraminiferal assemblages. This succession reflects the evolution from an unstable shelf ecosystem with high-energy conditions at the sea-floor in the earlier Holocene to a more stable shelf ecosystem in the middle and late Holocene. Between approximately 10.3 and 5.5 kyr BP, low δ13C values of the surface dweller Globigerinoides ruber (white) and high difference in δ13C values between the epifaunal Cibicides lobatulus and the infaunal Bulimina aculeata document enhanced input of nutrients in surface waters and high remineralization rates at the sea floor. The trophic change is associated with a change in sediment facies and can be attributed to higher precipitation and consequently, higher nutrient supply via riverine runoff from the island, mainly during the late summer/early fall season. This early Holocene humid interval is nearly contemporaneous to the formation of sapropel S1 in the eastern Mediterranean Sea and the African Humid Period. Highlights ► Isotope records and foraminiferal data from the western Mediterranean are presented. ► Benthic shelf ecosystem adaption is related to the Holocene sea-level rise. ► In the early–mid Holocene more humid conditions were established on Mallorca shelf. ► The humid interval is nearly contemporaneous to the sapropel S1 formation. ► Its end is synchronous to the end of the African Humid Period.

Diet segregation between two colonies of little penguins Eudyptula minor in southeast Australia

AbstractWe studied foraging segregation between two different sized colonies of little penguins Eudyptula minor with overlapping foraging areas in pre‐laying and incubation. We used stomach contents and stable isotope measurements of nitrogen (δ15N) and carbon (δ13C) in blood to examine differences in trophic position, prey‐size and nutritional values between the two colonies. Diet of little penguins at St Kilda (small colony) relied heavily on anchovy while at Phillip Island (large colony), the diet was more diverse and anchovies were larger than those consumed by St Kilda penguins. Higher δ15N values at St Kilda, differences in δ13C values and the prey composition provided further evidence of diet segregation between colonies. Penguins from each colony took anchovies from different cohorts and probably different stocks, although these sites are only 70 km apart. Differences in diet were not reflected in protein levels in the blood of penguins, suggesting that variation in prey between colonies was not related to differences in nutritional value of the diet. Anchovy is currently the only available prey to penguins throughout the year and its absence could have a negative impact on penguin food supply, particularly at St Kilda where the diet is dominated by this species. While it is difficult to establish whether diet segregation is caused by inter‐ or intra‐colony competition or spatial differences in foraging areas, we have shown that colonies with broadly overlapping foraging ranges could have significant differences in trophic position, diet composition and prey size while maintaining a diet of similar nutritional value.

Stable carbon isotope characteristics of desert plants in the Junggar Basin, China

AbstractDesert plants have unique strategies for survival and growth to cope with the limited water availability in arid regions. The stable carbon isotope (δ13C) provides an integrated measurement of internal plant physiological and external environmental properties affecting photosynthetic gas exchange and water use efficiency. The δ13C values of 84 species in the Junggar Basin were categorized into two groups (ranged from −30.1 to −23.3‰ for C3 and −14.9 to −9.9‰ for C4 species, respectively). No life form differences in δ13C values were detected in C3 (p = 0.78) and C4 plants (p = 0.63). Small differences among life forms were observed in δ13C values in C4 species with shrubs slightly depleted (−13.3‰) relative to perennials (−13.1‰) and annuals (−12.5‰). These differences suggested that δ13C value could not represent a plant functional group classification based on life forms in C4 plants in extremely arid regions. Ephemerals are all using C3 photosynthetic pathway and no significant differences (p = 0.92) in δ13C values were observed between annuals (−26.5‰) and perennials (−26.4‰). The δ13C values of Tulipa iliensis (an important ephemeral species distributed widely in the Junggar Basin) among nine natural populations were positively correlated with leaf (r2 = 0.46, p = 0.046) and soil (r2 = 0.67, p = 0.007) total nitrogen content, and negatively correlated with leaf (r2 = 0.48, p = 0.039) and soil (r2 = 0.79, p = 0.001) water content. This indicated that the variation in δ13C values of T. iliensis was probably caused by both water availability associated stomatal openness and nitrogen availability associated photosynthetic capacity. T. iliensis is very sensitive to water and nitrogen availability in soil.

Challenges using stable isotopes for estimating trophic levels in marine amphipods

In marine food web studies, stable isotopes of nitrogen (δ15N) and carbon (δ13C) are widely used to estimate organisms’ trophic levels (TL) and carbon sources, respectively. For smaller organisms, whole specimens are commonly analyzed. However, this “bulk method” involves several pitfalls since different tissues may fractionate stable isotopes differently. We compared the δ15N and δ13C values of exoskeleton versus soft tissue, in relation to whole specimens, of three common Arctic amphipods in Svalbard waters: the benthic Anonyx nugax, the sympagic (ice-associated) Gammarus wilkitzkii and the pelagic Themisto libellula. The δ15N values of the exoskeletons were significantly lower than those of the soft tissues for A. nugax (10.5 ± 0.7‰ vs. 15.7 ± 0.7‰), G. wilkitzkii (3.3 ± 0.3‰ vs. 8.3 ± 0.4‰) and T. libellula (8.6 ± 0.3‰ vs.10.8 ± 0.3‰). The differences in δ13C values between exoskeletons and soft tissues were insignificant, except for A. nugax (−21.2 ± 0.2‰ vs. −20.3 ± 0.2‰, respectively). The δ15N values of whole organisms were between those of the exoskeletons and the soft tissues, being similarly enriched in 15N as the exoskeletons (except G. wilkitzkii) and depleted in 15N by 1.2–3.7‰ compared to the soft tissues. The δ15N-derived TLs of the soft tissues agreed best with the known feeding preferences of the three amphipods, which suggest a potential underestimation of 0.5–1.0 TL when stable isotope analyses are performed on whole crustaceans with thick exoskeletons. The insignificant or small differences in δ13C values among exoskeletons, soft tissues and whole specimens, however, suggest low probability for misinterpretations of crustaceans’ primary carbon source in marine ecosystems with distinctly different δ13C-carbon sources.

Variation in δ13C among species and sexes in the family Restionaceae along a fine‐scale hydrological gradient

AbstractConsistent, repeatable segregation of plant species along hydrological gradients is an established phenomenon that must in some way reflect a trade‐off between plants' abilities to tolerate the opposing constraints of drought and waterlogging. In C3 species tissue carbon isotope discrimination (δ13C) is known to vary sensitively in response to stomatal behaviour, reflecting stomatal limitation of photosynthesis during the period of active growth. However, this has not been studied at fine‐spatial scale in natural communities. We tested how δ13C varied between species and sexes of individuals in the family Restionaceae growing along a monitored hydrological gradient. Twenty Restionaceae species were investigated using species‐level phylogeny at two sites in the Cape Floristic Region, a biodiversity hotspot. A spatial overlap analysis showed the Restionaceae species segregated significantly (P &lt; 0.001) at both sites. Moreover, there were significant differences in δ13C values among the Restionaceae species (P &lt; 0.001) and between male and female individuals of each species (P &lt; 0.01). However, after accounting for phylogeny, species δ13C values did not show any significant correlation with the hydrological gradient. We suggest that some other variable (e.g. plant phenology) could be responsible for masking a simple response to water availability.

Diamond formation in the deep mantle: the record of mineral inclusions and their distribution in relation to mantle dehydration zones

AbstractStudies of the inclusions contained in natural diamonds have shown the occurrence of minerals which must have formed at depths below the lithosphere and which may be closely matched with the silicate mineral assemblages determined by high pressure and temperature experimental studies for depths of 300 to 800 km in the Earth's mantle. The inclusions come principally from two main depth zones: (1) the lower asthenosphere and upper transition zone; (2) the Upper Mantle/Lower Mantle (UM/LM) boundary region and the uppermost LM. The inclusions from zone 1 are very largely majoritic garnets (with or without clinopyroxene) which indicate bulk compositions of eclogitic/metabasic affinity. The minerals from zone 2 include Ca-Si and Mg-Si perovskites and ferropericlase and are dominantly of metaperidotitic bulk composition, but include some possible metabasite assemblages. In many of these natural assemblages, the tetragonal almandine pyrope phase occurs rather than the garnet found in experiments.As natural diamonds are believed to crystallize in fluids/melts, the hypothesis is developed that the restriction of diamonds and inclusions of particular compositions to the above two depth intervals is because they are controlled by loci of fluid/melt occurrence. Attention is focused on subduction zones because both suites of inclusions show some evidence of subducted protoliths. The lower zone (600–800 km) coincides with the region where dehydration may be expected for hydrous ringwoodite and dense hydrous Mg-silicates formed in subducted peridotites. The dehydration of lawsonite in subducted metabasites provides a particular location for melt formation and the inclusion of the shallower (~ 300 km) majoritic inclusions. For the deeper majoritic inclusions in the region of the upper transition zone, melt development may occur as a consequence of the hydrous wadsleyite-to-olivine transformation, and such melt may then interact with the upper crustal portion of a subducting slab. These suggestions offer an explanation of the depth restrictions and the compositional restrictions of the inclusions. The differences in δ13C values in the host diamonds for the two suites of inclusions may also be explained on this basis.

Isotopic composition of gas hydrates in subsurface sediments from offshore Sakhalin Island, Sea of Okhotsk

Hydrate-bearing sediment cores were retrieved from recently discovered seepage sites located offshore Sakhalin Island in the Sea of Okhotsk. We obtained samples of natural gas hydrates and dissolved gas in pore water using a headspace gas method for determining their molecular and isotopic compositions. Molecular composition ratios C1/C2+ from all the seepage sites were in the range of 1,500–50,000, while δ13C and δD values of methane ranged from −66.0 to −63.2‰ VPDB and −204.6 to −196.7‰ VSMOW, respectively. These results indicate that the methane was produced by microbial reduction of CO2. δ13C values of ethane and propane (i.e., −40.8 to −27.4‰ VPDB and −41.3 to −30.6‰ VPDB, respectively) showed that small amounts of thermogenic gas were mixed with microbial methane. We also analyzed the isotopic difference between hydrate-bound and dissolved gases, and discovered that the magnitude by which the δD hydrate gas was smaller than that of dissolved gas was in the range 4.3–16.6‰, while there were no differences in δ13C values. Based on isotopic fractionation of guest gas during the formation of gas hydrate, we conclude that the current gas in the pore water is the source of the gas hydrate at the VNIIOkeangeologia and Giselle Flare sites, but not the source of the gas hydrate at the Hieroglyph and KOPRI sites.

Isotopic evidence of dietary variations and weaning practices in the Gaya cemetery at Yeanri, Gimhae, South Korea

Stable carbon and nitrogen isotope analyses were conducted to investigate dietary variation in human skeletons (n = 109) from the Gaya cemetery at Yeanri located near Gimhae City, South Korea. The cemetery contained three distinct grave types dating to 4th-7th century AD. The main purposes of this research were to reconstruct palaeodiet in the Gaya population and to explore correlations between stable isotope compositions and burial types, inferred age, and sex of these individuals. The isotopic data indicate that the people at Yeanri consumed a predominantly C(3)-based terrestrial diet supplemented with freshwater and/or marine resources. The comparison of isotopic results reveals significant differences in delta(13)C values among three adult burial types (wood-cist coffin: -18.5 +/- 0.5 per thousand, stone-cist coffin: -18.1 +/- 0.6 per thousand, mausoleum: -17.8 +/- 0.9 per thousand). Males in wood-cist and stone-cist coffins have relatively more elevated mean delta(13)C and delta(15)N values than females. The isotopic ratios from the two adult age groups (21-40 years and 40-60 years) indicate that there was no significant dietary change in individuals with age. The isotope data from the infants and children suggest the weaning was a gradual process that was completed between 3 and 4 years of age in the Gaya population. This evidence indicates that the dietary variations within the cemetery reflect social status, sex, and childhood consumption patterns.

How does acid treatment to remove carbonates affect the isotopic and elemental composition of soils and sediments?

Environmental context. The ability to accurately determine the elemental and isotopic composition of soils and sediments has important implications to our quantitative understanding of global biogeochemical cycles. However, the analysis of organic carbon in solid matrices is a time-consuming task that requires the selective removal of carbonates, a treatment that has the potential to significantly alter the composition of the original sample. In the present work, we compare three of the most common acid treatments used for carbonate removal, and critically evaluate their effect on the content and isotopic signature of organic carbon and nitrogen in both soils and sediments. Abstract. In the present work, we compared the efficacy of three acid treatments in removing carbonates from soils and sediments for elemental and isotopic analysis. The methods tested were (1) refluxing with H2SO3; (2) in situ treatment with H2SO3 in silver capsules; and (3) treatment with HCl followed by rinsing with water. Refluxing with H2SO3 led to substantial losses of organic carbon and nitrogen, but comparatively small nitrogen isotopic shifts. The in situ treatment was inadequate for carbonate-rich samples (contents ≥30%) as a consequence of the formation of a mineral precipitate. Treatment with HCl led to substantial losses of nitrogen from carbonate-rich samples, and deviations in nitrogen isotopic signatures (δ15N) of up to 3.7‰. δ15N values showed no significant difference between acid-treated and untreated samples or between treatments, although variability was high and influenced by sample composition. Carbonate-poor samples showed no statistical difference in δ13C values between treatments, whereas carbonate-rich samples tended to be more 13C-depleted when treated with HCl, potentially suggesting the preferential preservation of 13C-depleted compounds (e.g. lipids or lignin).

Bias of ostracod stable isotope data caused by drying of sieve residues from water

Stable isotope analysis of ostracod shells is used routinely for palaeoenvironmental studies of ostracod-bearing records. Sample treatment usually involves the disaggregation of sediments and sieving; before the sieving residues were washed with water onto petri dishes and oven-dried. In our study, we compared δ18O and δ13C values of shells that were oven-dried from water and from ethanol alternatively. Large isotopic differences of up to 3‰ were determined for δ18O values, whereas differences in δ13C values were less pronounced with differences of up to 1.6‰. Stable isotope values of shells dried from water were lower for both oxygen and carbon as a result of calcite crystals precipitated on the shell surfaces during the drying process. Therefore, ostracod shells for stable isotope analysis should not be prepared by drying from water. Instead, shells should be dried from ethanol to obtain reliable stable isotope data; likewise freeze-drying is expected to provide trustworthy results.

Possible Mechanisms Leading to a Delay in Carbon Stock Recovery after Land Use Change

Changes in land use sometimes lead to soil C loss, and a long time may be required for the C stock to recover to initial levels. Thus, it is important to evaluate the mechanisms related to accumulation of newly input C following land use changes. In this study, we sought to determine the signature of newly input C in the soil profile after land use change. We used stable and radioactive C isotopes with soil fractionation methods in a C3 coniferous plantation converted from C4 grassland in Japan. The difference in δ13C values between the surface litter and the soil organic carbon (SOC) below the litter was 5‰ or greater; this large isotopic difference was attributed to rapid decomposition in the litter layer and preservation of C derived from the previous C4 vegetation. Most SOC Δ14C values were negative throughout the soil profile, suggesting that most of the SOC in the soil profile was recalcitrant and had been preserved for a long time. Only the surface sand values were slightly positive. These results suggest that most newly input C is consumed at the soil surface. The low ability of these soils to preserve newly input C is one factor in the slow recovery of soil C.