Stable Nitrogen Isotope Analysis Research Articles

Isotopic diversity and niche patterns reveal contrasting resource use among co-occurring non-native fishes within a flow-altered African river system

AbstractClassic and contemporary trophic ecology-based studies have shown that most non-native freshwater fish species (NNS) that integrate into novel environments have the potential to influence the recipient ecosystems’ structure and function. However, the interspecific trophic interactions amongst co-occurring NNS within invaded systems remain poorly studied. Here, we used carbon (δ13C) and nitrogen (δ15N) stable isotope analyses to examine general fish trophic diversity patterns (native and non-native fishes) and to explore trophic niche patterns amongst co-occurring NNS within a flow-modified river system, the Great Fish River (South Africa). The system was characterised by isotopic variation, which revealed spatial differences in trophic complexity from uninvaded headwater tributaries to invaded mainstem and downstream sections. Two of the invaded sections, the upper mainstem of the Great Fish River (UGFR) and the Koonap River, had low isotopic overlaps between NNS and the native fish assemblages. Furthermore, co-occurring NNS in these two invaded sections had variable isotopic niche sizes and low interspecific isotopic niche overlaps, suggesting the potential for trophic differentiation. By comparison, there was evidence of high resource use patterns among NNS within the lower mainstem section of the Great Fish River (LGFR), which likely reflected trophic plasticity. Overall, results of this study provided evidence of both trophic niche differentiation (UGFR and Koonap River) and niche overlap (LGFR) as probable mechanisms of co-occurrences of the non-native fishes within different invaded sections of the Great Fish River system, and underscores the difficulties associated with predicting their trophic impacts.

Trophic ecology and small‐scale differentiation of ecological groups of franciscana dolphin, Pontoporia blainvillei, in southeastern Brazil, revealed by carbon and nitrogen stable isotopes

AbstractThe franciscana, Pontoporia blainvillei, is an endemic dolphin off the east coast of South America and is considered the most endangered cetacean in the western South Atlantic. In the present study, we analyzed the muscle tissue of 24 franciscana dolphins found on the coast of Espírito Santo (ES) between 2010 and 2019 to investigate trophic ecology using carbon and nitrogen stable isotope analysis. In addition, 127 prey were analyzed to identify the preferred prey. The most important prey species in the diet of the franciscana dolphins were Trichiurus lepturus, Chirocentrodon bleekerianus, and Pellona harroweri. The franciscana dolphins were grouped into three subareas according to where they were collected throughout the distribution: 1 (North), 2 (Center), and 3 (South). In subarea 1, the preferred prey were Stellifer spp., Isopisthus parvipinnis, and P. harroweri, while in subareas 2 and 3, the prey were similar, changing the order of preference among them (Stellifer spp., T. lepturus, and C. bleekerianus). Finally, we identify two possible ecological groups of franciscana dolphins on the coast of ES, influenced by different carbon sources. Our results improve our understanding of the franciscana dolphin's trophic ecology and habitat use, providing new information and guidelines for species conservation in the region.

Evaluating the suitability of sedimentological, geochemical, and biological proxies for reconstructing floodplain palaeohydrology

Fundamental insight into the long-term ‘geoecohydrological’ dynamics of rivers and floodplains is required for their sustainable management. To study these dynamics, a multi-proxy approach is essential. While suitable proxies are available for reconstructing floodplain geomorphology and past vegetation, the suitability of the available proxies for past hydrology to reconstruct floodplain wetness has not yet been evaluated. In this study, we apply a multi-proxy analysis combining testate amoebae and several geochemical proxies for decomposition (humification, carbon and nitrogen stable isotopes), in comparison to sedimentological (stratigraphy, loss on ignition) and palaeobotanical records, to obtain independent hydrological reconstructions of alluvial floodplains in contrasting environmental settings to explore the suitability of the available proxies for past hydrology to reconstruct floodplain wetness.This study concludes that testate amoebae cannot provide a continuous and reliable hydrological reconstruction, as they are insufficiently preserved in alluvial peat deposits. In addition, mineral particles within the tests size range hamper the analysis in mineral-dominated sediment units. As organic matter decomposition is low when water tables are high and vice versa, we expected the decomposition proxies to reflect the hydrological conditions. While the amount of humic acids appears to depend mainly on the substrate rather than the decomposition of the organic matter in it, the analyses of carbon and nitrogen stable isotopes provide promising results, for both peat and non-peat deposits.

The Sympatric Coexistence Mechanism: A Case Study of Two Penahia Species in the Beibu Gulf, South China Sea.

The study of trophic relationships among closely related species plays an important role in deepening our understanding of the resource utilization characteristics, differentiation patterns, and population dynamics of co-occurring species in the same habitat. This research uses two congeneric fish species, Pennahia pawak and Pennahia anea, as examples. Based on a stomach content analysis and a carbon-nitrogen stable isotope analysis, a comparative analysis of their feeding habits and trophic niches is conducted. Additionally, a spatial niche analysis is employed to explore the coexistence and competitive mechanisms between these two closely related fish species. The results show that specialized feeding habits mitigate intraspecific competition as the population densities increase. The carbon and nitrogen stable isotope analysis reveals variations in the feeding habits and trophic levels with body length, indicating adaptive shifts in prey selection. Despite similar food resources, niche differentiation arises due to differences in dominant prey, facilitating coexistence. Differences in spatial niche further contribute to niche separation and coexistence. In resource-limited environments, species such as Pennahia utilize trophic and spatial niche differentiation to collectively exploit resources and achieve coexistence, with implications for fishery management favoring Pennahia resource occupancy capabilities.

Food web structures of irrigated rice fields estimated from carbon and nitrogen stable isotopes: Special reference to the role of filamentous green algae as a food resource of aquatic consumers

AbstractRice fields are characterized by high algal production and dense mats of filamentous green algae, and they function as habitats for various aquatic organisms. However, how algal production supports the secondary production of aquatic consumers in rice fields has not been assessed. Herein, aquatic food web structures in two adjacent rice fields in northeastern Japan were examined using carbon and nitrogen stable isotope analyses. Filamentous algae often showed higher δ13C values (mean, −23.1‰ to −21.4‰) than other organic matter sources, including particulate organic matter, benthic microalgae, and soil organic matter (−30.1‰ to −25.4‰). A δ13C‐based isotopic mixing model estimated that among 19 taxa of herbivores and omnivores, most taxa depended on filamentous algae‐derived carbon (ca. >30%). Particularly, Peltodytes intermedius larvae, a specialist feeder for filamentous algae, showed the highest reliance (mean, 66.7%–80.0%). The microcrustacean, Ostracoda sp. also utilized a diet consisting of a substantial proportion of filamentous algae‐derived carbon (57.6%). Seven out of 10 carnivorous taxa showed reliance on filamentous algae‐derived carbon by >30%. Particularly, larvae of beetles (Berosus sp., Enochrus sp., and Hydrochara affinis) showed the highest reliance (40.2%–44.3%). They could assimilate filamentous algae‐based carbon by consuming herbivores, such as P. intermedius. Because fresh filamentous green algae were eaten less by aquatic consumers, the herbivores could consume decomposed filamentous algae rather than fresh ones. Our results suggest that filamentous algae are one of the major organic matter sources supporting secondary production in rice field food webs.

Stable isotope analyses of carbon and nitrogen in hair keratin of suspected man-eating wolves from 1880s

The so-called man-eating wolves of Turku, a pack of three wolves, reportedly killed 22 children in South-Western Finland in 1880–1881. Enormous efforts were carried out to eradicate them. In January 1882 the last remaining wolf was killed. Since then, there has been considerable debate regarding the validity and extent of the man-eating behaviour. This study aims to clarify whether man-eating behaviour can be observed from the remains of these wolves. One of the wolves was mounted in 1882 and is on display at St. Olaf’s school in Turku, enabling us to collect hair keratin samples. Additionally, hair keratin was collected from two other suspected man-eaters. We analysed carbon (δ13C) and nitrogen (δ15N) stable isotope values to study the wolf’s diet during the last months of its life. Samples from seven temporally concurrent wolves were used to construct reference values. Our analyses indicated that δ15N values of suspected man-eaters were relatively low compared to the reference sample. We could not detect clear trends in isotope ratios associated with potential man-eating behavior. We believe that this lack of distinctive patterns can be explained by the relatively minor role that man-eating played in their overall diet.

Neolithisation through bone: Stable isotope analysis of human and faunal remains from Syltholm II, Lolland, Denmark

Despite an increasing number of studies, the application of stable sulfur (δ34S) isotope analysis to prehistoric bone collagen remains in its infancy. Conventionally, stable sulfur isotope compositions reflect coastal proximity and the interaction between humans and animals. Here, we undertook stable carbon (δ13C), nitrogen (δ15N) and sulfur (δ34S) isotope analysis of human and faunal bone collagen. To understand the local environmental conditions as well as the husbandry regime employed by the first farmers, and investigate where the animals were raised or hunted in non-specific terms, we sampled 50 faunal, including wild and domestic taxa, and human remains from the Late Mesolithic to Early-Middle Neolithic (c. 4860–2310 cal BC) site of Syltholm II on the island of Lolland, Denmark. We show that the wild animals were obtained from multiple locations surrounding the prehistoric Syltholm Fjord, including forested and open landscapes, areas impacted by sea spray and saltmarshes. In contrast, the domestic taxa, especially cattle, were tightly managed for the majority of their lives based on their δ13C and δ15N isotope compositions, though were likely raised in multiple locations, including sea spray-affected areas, saltmarshes and wetlands, based on their δ34S values. The domestic dogs had a broad range of δ13C, δ15N and δ34S values, reflecting the consumption of varying degrees of marine foodstuffs, including animals that were sulfide-derived. Overall, our results contribute to a growing body of evidence for possible cultural and animal husbandry duality during the earliest Neolithic in southern Scandinavia.

Assessment of nursery areas for the scalloped hammerhead shark (Sphyrna lewini) across the Eastern Tropical Pacific using a stable isotopes approach

The scalloped hammerhead shark (Sphyrna lewini) is one of the most iconic marine species across the Eastern Tropical Pacific (ETP), yet little is still known about its reproductive biology and the origin of their nursery areas, despite a continuous global decline in their populations. Understanding the origin of shark nurseries is a complex task; however, it is known that the obtention of resources in the first stages of life of placental sharks occurs through maternal reminiscence, thus it is possible to infer the origin of the energy that neonates accumulate during their gestation. In this study we assessed the ecological connectivity and nursery ground use by undertaking a stable isotope analysis of carbon (δ13C) and nitrogen (δ15N) in skin samples of neonates S. lewini across much of their distribution in the ETP, including the Galapagos Marine Reserve (GMR). Our isotopic mixing models revealed that the S. lewini neonates found in the GMR, have isotopic information similar to adult females inhabit in the Galapagos archipelago, suggesting that they are direct descendants of the females that inhabit the GMR. While neonates found off the continental coasts of Ecuador and Panama have isotopic signatures like those of adult females inhabiting several locations across the ETP. This work provides insight into the origin of nursery areas used by adult S. lewini that aggregate in large numbers across oceanic islands of the ETP, highlighting the value of isotopic models to generate useful information for the conservation of sharks.

Sustained use of marine subsidies promotes niche expansion in a wild felid

The use of marine subsidies by terrestrial predators can facilitate substantial transfer of nutrients between marine and terrestrial ecosystems. Marine resource subsidies may have profound effects on predator ecology, influencing population and niche dynamics. Expanding niches of top consumers can impact ecosystem resilience and interspecific interactions, affecting predator-prey dynamics and competition. We investigate the occurrence, importance, and impact of marine resources on trophic ecology and niche dynamics in a highly generalist predator, the caracal (Caracal caracal), on the Cape Peninsula, South Africa. Caracals have flexible diets, feeding across a wide range of terrestrial and aquatic prey. We use carbon and nitrogen stable isotope analysis of fur samples (n = 75) to understand trophic position and niche shifts in coastal and inland foragers, as well as the implications of a diet rich in marine resources. We found significant differences in isotope signatures between these groups, with higher δ13C (P < 0.05) and δ15N values (P < 0.01) in coastal foragers. Isotope mixing models reveal that these elevated signatures were due to non-terrestrial food subsidies, where approximately a third of coastal foraging caracal diet comprised marine prey. The addition of marine prey species to diet increased both the trophic level and isotope niche size of coastal foraging caracals, with potential impacts on prey populations and competition. Our results suggest that marine prey are an important dietary resource for coastal foraging caracals, where seabirds, including two endangered species, are a major component of their diet. However, there are likely risks associated with these resource benefits, as routine consumption of seabirds is linked with higher pollutant burdens, particularly metals. Increased encounters between this terrestrial predator and seabirds may be a result of increased mainland colonies due to changes in habitat availability and the highly opportunistic and generalist foraging behaviour of a native predator.

Dominant contribution of combustion-related ammonium during haze pollution in Beijing

Aerosol ammonium (NH4+), mainly produced from the reactions of ammonia (NH3) with acids in the atmosphere, has significant impacts on air pollution, radiative forcing, and human health. Understanding the source and formation mechanism of NH4+ can provide scientific insights into air quality improvements. However, the sources of NH3 in urban areas are not well understood, and few studies focus on NH3/NH4+ at different heights within the atmospheric boundary layer, which hinders a comprehensive understanding of aerosol NH4+. In this study, we perform both field observation and modeling studies (the Community Multiscale Air Quality, CMAQ) to investigate regional NH3 emission sources and vertically resolved NH4+ formation mechanisms during the winter in Beijing. Both stable nitrogen isotope analyses and CMAQ model suggest that combustion-related NH3 emissions, including fossil fuel sources, NH3 slip, and biomass burning, are important sources of aerosol NH4+ with more than 60% contribution occurring on heavily polluted days. In contrast, volatilization-related NH3 sources (livestock breeding, N-fertilizer application, and human waste) are dominant on clean days. Combustion-related NH3 is mostly local from Beijing, and biomass burning is likely an important NH3 source (∼15%–20%) that was previously overlooked. More effective control strategies such as the two-product (e.g., reducing both SO2 and NH3) control policy should be considered to improve air quality.

A novel ontogeny-related sampling of dental tissues for stable isotopes interpretation of the paleobiology of the cave bear

In cave bear studies, stable isotope analysis of carbon and nitrogen is typically conducted on bone collagen. However, challenges arise due to biases in the classification of bones into age groups, which can be influenced by various factors that affect bone size. To overcome such issues, we present and evaluate a novel approach that involves sampling dental collagen from different ontogenetic stages of 45 fossil teeth, where only a portion of each tooth formed during the periods of interest was sampled. This approach enabled us to obtain a carbon and nitrogen fingerprint specific to a particular period in a cave bear’s life without interference from earlier stages. Stable isotopic analysis revealed a rapid decrease in δ15N values from 3 to 15 months of age. After that, the δ15N values remain stable. Based on the nitrogen isotope composition (15N/14N), cubs aged 0–3 months exclusively consumed milk, while the gradual introduction of solid plant food occurs at 5–10 months, resulting in a shift in δ15N values. Based on similar δ15N values in older age groups, it can be assumed that juveniles did not resume milk suckling after the first hibernation. The δ13C values increase until 15 months, followed by a gradual decrease until adulthood, potentially attributable to hibernation. The δ13C values also seems to indicate isotopic differences between yearlings with low δ13C values that successfully established hibernation and those with high δ13C values that failed to hibernate and starved. This novel observation, i.e., decreasing δ13C values from the second year of life onward, agrees with predicted isotopic skeletal collagen δ13C values calculated from modern brown bear blood plasma. In summary, the ontogenetic sampling strategy facilitated the acquisition of further paleobiological insights into the distinct life periods of cave bears.

Effects of large dams on the aquatic food web along a coastal stream with high sediment loads

The contribution of two basal energy sources – detrital organic matter and primary producers – as part of aquatic food webs varies typically along river continua. A host of barriers to river flow increase the water residence time and sediment and nutrient retention in reservoirs worldwide, and potentially alter the balance between detritus-based and algae-based energy pathways in the downstream food webs. We explored this issue on the Sélune River (Normandy, France), a small coastal stream that drains an agricultural catchment with high sediment runoff. Seasonal measurements of the following parameters were compared upstream and downstream of the reservoirs of two large dams (16 m and 36 m high): sediment fluxes, nutrient and chlorophyll a concentrations, algal communities in the epilithic biofilm (taxonomic composition, biomass and growth), and benthic invertebrate communities (abundance and trophic guild structure). As anticipated, annual sediment fluxes were much lower downstream of the reservoirs, where significant decreases in water turbidity, phosphate and silicate concentrations were recorded. A higher chlorophyll a concentration in water and a higher contribution of pelagic algae taxa to the photosynthetic biofilm suggested drifting and deposition of reservoir-borne phytoplankton downriver. Photosynthetic biofilm growth was higher downstream of the reservoirs in spring and fall, and so was the abundance of herbivores in the invertebrate community, notably scrapers and algae eaters. Energy pathways within riverine food webs were traced using stable isotope analyses of carbon (C) and nitrogen in the tissues of aquatic consumers (invertebrates and fish). Mixing models revealed a discontinuity in the origin of the C entering the food webs along the river continuum, confirming a greater contribution of algal C to aquatic consumers downstream of the reservoirs. These results illustrate mechanisms whereby large reservoirs can modulate C flow in food webs along a small coastal river with high sediment loads, and make it possible to anticipate the effects of dam removal on the future river ecosystem.

Trophic positions of soil microarthropods in forests increase with elevation, but energy channels remain unchanged

AbstractMountain forests are at risk as the consequences of climate change will likely lead to altered tree species boundaries. Characterizing food webs along elevation gradients in primary forests may help to predict the potential consequences of such changes, for example with regard to the decomposition of dead organic matter. Here, for the first time, we studied trophic variations in two species‐rich microarthropod taxa, Collembola and Oribatida, along an elevation gradient of primary forest at Changbai Mountain, China. Samples were taken at seven elevations of 150‐m elevational difference between 800 and 1700 m. At each elevation, Collembola and Oribatida were extracted from litter samples of eight subplots. We applied three state‐of‐the‐art methods to elucidate trophic positions and basal resource use at community level: Bulk stable isotope analysis of nitrogen (Δ15Nbulk) and carbon (Δ13Cbulk), compound‐specific stable isotope analysis of amino acids (CSIA‐AA), and dietary routing of neutral lipid fatty acids (NLFAs). Trophic positions calculated using Δ15Nbulk and CSIA‐AA (TPCSIA) in both taxa increased similarly with elevation by about half and one third of a trophic position, respectively. Stable isotope mixing models and linear discriminant analysis bootstrapping using δ13C of essential amino acids indicated fungi as the most important resource at all elevations for both taxa. Also, proportions of marker NLFAs changed little across elevations in both taxa; overall high proportions of linoleic acid indicated high fungal contributions, but in Collembola the contribution of bacterial markers was generally higher than in Oribatida. Δ13Cbulk did not respond linearly to the elevation gradient; however, changes in elevation differed between Collembola and Oribatida. A strong linear relationship between δ15N of phenylalanine and δ15N of litter indicated litter as the basis of energy channels in both taxa. Overall, food web functioning likely changes with changing forest types along elevation gradients, with microarthropods switching from feeding closer to the base of the food web at lower elevations to feeding at higher trophic levels at higher elevations, potentially compromising their role in litter decomposition and nutrient cycling.

Identifying the foraging grounds of the new loggerhead turtle nesters in the western Mediterranean

Abstract The western Mediterranean Sea has traditionally served as a primary foraging ground for juvenile loggerhead turtles from three distinct regional management units: the North‐western Atlantic, the Mediterranean and Cape Verde. Nesting activities were sporadic. Recently, nesting activity on the beaches of eastern Spain has increased, due to warmer sand and water temperatures during the summer months. The study has integrated stable isotope analysis of carbon (C), nitrogen (N) and sulphur (S) with satellite telemetry to identify the foraging grounds of these new colonizers nesting on Spanish beaches. Results indicate that the majority of these adult females forage oceanically in the Algerian Basin, with a few exhibiting distinct stable isotope signals, tentatively associated with foraging in shallow coastal areas in the central Mediterranean Sea. The dominance of oceanic foragers in this new population is noteworthy, given the Algerian Basin's oligotrophic nature. This contrasts with the prevalence of neritic foraging in adult females nesting in the central and eastern Mediterranean Sea. The use of the Algerian Basin as a foraging ground for adult loggerhead turtles exposes them to bycatch from drifting longlines. The authorities should refrain from increasing bluefin quotas imposed on longliners in the Algerian Basin unless the fishery avoids using squid as bait and agrees to deploy hooks deeper than 25 m to reduce loggerhead turtle bycatch.

Introduction of a New Method for Total Organic Carbon and Total Nitrogen Stable Isotope Analysis of Dissolved Organic Matter in Aquatic Environments

Introduction of a New Method for Total Organic Carbon and Total Nitrogen Stable Isotope Analysis of Dissolved Organic Matter in Aquatic Environments

Seasonal stratification leads to changes within the benthic food web of the Gulf of Lions (northwestern Mediterranean)

Due to its extensive continental shelf, the Gulf of Lions, situated in the northwestern Mediterranean Sea, plays a crucial role in providing ecological services amidst various natural and anthropogenic pressures. Exposed to the impacts of climate change and suitable for marine energy development projects, the conservation of marine biodiversity in this environment raises significant concerns. To detect any potential disturbances in the functioning of the terrigenous mud community on the continental shelf, we conducted stable carbon and nitrogen isotope analyses on suspended particulate organic matter, sediments, and benthic fauna. Since seasonality is a structuring factor for the functioning of such an oligotrophic ecosystem, we conducted two sampling campaigns in 2018 to capture contrasting scenarios of water column stratification — one in April during well-mixed conditions and high phytoplankton production, and another in September at the end of the summer thermal stratification period characterized by low primary productivity. Stable isotope analysis revealed changes in the structure of the benthic food web in response to seasonal stratification of the water column. While isotopic niches of taxa remained evenly distributed, the total niche space contracted between sampling dates, primarily affecting low trophic level consumers. The observed contraction aligns with that reported at the base of the pelagic food web. These results enhance our understanding of the functioning of the continental shelf of the Gulf of Lions. The intense trawling pressure on the study site affected sampling. In this context, this research contributes not only to the knowledge of seasonal trophic variations but also provides a reference state to understand the future of this Mediterranean continental shelf.

Human diet in Lithuania during the Late Roman and Migration periods ( ca. 200–700 AD) based on stable carbon and nitrogen isotope data

In this study, 71 human individuals were subjected to stable carbon (δ13C) and nitrogen (δ15N) isotope analysis of bone collagen samples for the purpose of determining human dietary patterns in Lithuania during the Late Roman and Migration periods. More specifically, based on the isotopic data, the aim was to determine and evaluate any potential dietary differences between individuals on the basis of their sex, age, social status and place of residence during the periods in question. The results of this study suggest that there were isotopically clearly distinguishable dietary differences between individuals from different parts/regions of Lithuania. Also, statistically significant dietary differences (on the basis of δ15N values) between males and females were observed (although, when making the same sex-based isotopic comparisons at an individual site level, the same result was observed only among those from Marvelė cemetery). However, no statistically significant isotopic differences were detected between different social or age groups. Overall, these results give us one of the first glimpses into the types of dietary habits practiced by people in various parts of Lithuania during the Roman and Migration periods, which could also serve as a good starting point for future investigations into other dietary aspects in the territories and periods in question that still remain unknown.

Amino acid‐specific nitrogen stable isotope analysis reveals the trophic behavior of Icelandic fin whales in winter and suggests variable feeding strategies

AbstractFin whales (Balaenoptera physalus) aggregate west of Iceland during summer, where they feed mostly on krill, but their winter distribution is poorly known. This study investigates the winter behavior of fin whales that summer off Iceland by analyzing amino acid‐specific nitrogen isotope ratios in the baleen plates. This technique is increasingly used in large marine vertebrates to discriminate between changes in trophic position and changes in isotopic baseline levels, while ruling out the effect of fasting on these patterns. Analyses were conducted on samples extracted from two baleen plate segments: one corresponding to winter, another to summer. The trophic position was higher and slightly more variable in winter (3.6 ± 0.7) than in summer (3.0 ± 0.4), which indicates that during winter fin whales tend to feed on fish and are more generalist in feeding habits. Interestingly, the δ15NPhe values were not lower in winter than in summer (winter: 5.2‰ ± 2.4‰; summer: 4.0‰ ± 2.1‰). This was unexpected because baseline δ15N values (e.g., zooplankton) tend to be lower at low latitudes, where fin whales are believed to spend the winter. Fin whales may remain in relatively high latitudes during winter or visit low‐latitude areas with locally higher than average δ15N values, such as upwelling areas.

Preservation of bone organic fraction is not predictive of the preservation of bone inorganic fraction when assessing stable isotope analysis sample quality control measures

Stable isotope analysis of carbon (C), nitrogen (N), hydrogen (H), and oxygen (O) of archaeological bone has become an increasingly common research method for interpreting human behavior in the past. However, diagenesis of skeletal material can invalidate stable isotope ratios, thereby compromising interpretations. We examine patterns of bone diagenesis using infrared spectroscopy of bone bioapatite samples in relation to indicators of organic preservation quality indicators. We assess crystallinity, an indicator of bioapatite preservation, using the infrared splitting factor (IR-SF) and carbonate content (carbonate to phosphate ratio, C/P) calculated from infrared spectra. We then test the assumption that if the organic fraction of bone is preserved, the mineral fraction will also be unaffected by postmortem chemical alteration. We analyzed 454 bone bioapatite and extracted bone organic sample pairs from modern, historic, and prehistoric humans. Consistent with previous studies, we observed a strong, statistically significant negative linear relationship between IR-SF and C/P (r = −0.855, p < 0.001). Modern bone bioapatite samples unaltered by diagenesis have low IR-SF and high C/P values. There was no significant association between the collagen yield or atomic C:N ratio and IR-SF or C/P values. The range of variation in IR-SF and C/P values for samples with organic yields between 0 and >20 percent spanned the range of modern bone bioapatite unaltered by diagenesis as well as bone bioapatite significantly affected by diagenesis. The lack of predictive patterning between bone inorganic and organic diagenesis suggests that the depositional context and site formation history play critical and independent roles in the organic and mineral fraction of bone. Thus, the preservation of the organic fraction of bone is not predictive of the preservation of the inorganic fraction (e.g., bioapatite).

Sex Determination and Isotopic Analysis of the Nivåfjord Mesolithic Burials, Zealand, Denmark

Since 1992 the prehistoric Nivåfjord in northeast Zealand, Denmark, has yielded an appreciable number of inhumation burials and cremations dating to the Mesolithic, especially the sites of Nivå 10 and Nivågård. Unfortunately, the micro-region is characterised by poor organic preservation, restricting the successful application of biomolecular techniques to human remains, including large-scale radiocarbon dating programmes as well as both stable isotope and ancient DNA analyses. Here, we apply an alternative technique, an acid etch peptide-based method, to determine the sex of eight individuals from Nivå 10 as well as the Nivågård child. Moreover, we revisit the utility of stable carbon (δ13C), nitrogen (δ15N) and sulfur (δ34S) isotope analysis of human tissues to reconstruct the life histories and diets of 10 individuals from Nivå 10 as well as the Nivågård child. To contextualise further, we sampled 14 Capreolus capreolus and three Sus scrofa from the Nivågård site for stable isotope analysis. We demonstrate that sex can successfully be determined from contexts susceptible to poor organic preservation, and show that the Nivågård child spent a proportion of its life outside a sea spray-influenced environment, and consumed significant quantities of marine protein as demonstrated by its δ13C and δ34S values.