Stable Isotope Studies Research Articles

Hypogene Alteration of Base–Metal Mineralization at the Václav Vein (Březové Hory Deposit, Příbram, Czech Republic): The Result of Recurrent Infiltration of Oxidized Fluids

The Václav vein (Březové Hory deposit, Příbram ore area, Czech Republic) is a base–metal vein containing minor Cu-Zn-Pb-Ag-Sb sulfidic mineralization in a usually hematitized gangue. A detailed mineralogical study using an electron microprobe revealed a complicated multistage evolution of the vein. Early siderite and Fe-rich dolomite were strongly replaced by assemblages of hematite+rhodochrosite and hematite+kutnohorite/Mn-rich dolomite, respectively. In addition, siderite also experienced strong silicification. These changes were associated with the dissolution of associated sulfides (sphalerite, galena). The following portion of the vein contains low-Mn dolomite and calcite gangue with Zn-rich chlorite, wittichenite, tetrahedrite-group minerals, chalcopyrite, bornite, and djurleite, again showing common replacement textures in case of sulfides. The latest stage was characterized by the input of Ag and Hg, giving rise to Ag-Cu sulfides, native silver (partly Hg-rich), balkanite, and (meta)cinnabar. We explain the formation of hematite-bearing oxidized assemblages at the expense of pre-existing “normal” Příbram mineralization due to repeated episodic infiltration of oxygenated surface waters during the vein evolution. Episodic mixing of ore fluids with surface waters was suggested from previous stable isotope and fluid inclusion studies in the Příbram ore area. Our mineralogical study thus strengthens this genetic scenario, illustrates the dynamics of fluid movement during the evolution of a distinct ore vein structure, and shows that the low content of ore minerals cannot be necessarily a primary feature of a vein.

Simultaneous observation of 2H and 13C enrichment of methyl phosphonic acid via Orbitrap-IRMS with applications to nerve agent forensics

Quantification of the stable isotopes within a compound aids forensic investigations as it provides a fingerprint which can determine that compound's source substrates, synthetic route, and possible mechanisms of degradation. Previous stable isotope studies have explored 13C and 2H measurements of the sarin precursors methylphosphonic dichloride (DC) and methylphosphonic difluoride (DF) as forensic signatures. However, these measurements required different sample preparations and measurement techniques. Orbitrap isotope ratio mass spectrometry (Orbitrap-IRMS) is a developing technique which can characterize multiple stable isotopes simultaneously. Here, we apply Orbitrap-IRMS to simultaneously observe the 13C and 2H content of methylphosphonic acid (MPA), the hydrolysis product of DC and DF, which can be used as a proxy for the isotopic content of DC and DF. Our method requires 20 min analyses and consumes ≈60 nmol of sample, with precisions of ≈0.9 ‰ (13C) and ≈3.6 ‰ (2H). We apply our method to both commercially acquired MPA and MPA obtained from the hydrolysis of commercially acquired DC. We validate our methods via comparison to elemental-analyzer isotope ratio mass spectrometry (EA-IRMS). The combined 13C and 2H measurement creates a more robust forensic tool than either isotope individually. Our results demonstrate the viability of Orbitrap-IRMS for chemical forensic measurements.

Iron Absorption from an Iron-Fortified Follow-Up Formula with and without the Addition of a Synbiotic or a Human-Identical Milk Oligosaccharide: A Randomized Crossover Stable Isotope Study in Young Thai Children

BackgroundPrevious studies showed that pre- and probiotics may enhance iron absorption. Probiotics combined with prebiotics (synbiotics), including human-identical milk oligosaccharides (HiMOs), are commonly added to infant and follow-up formula (FUF). Whether these additions enhance iron absorption from iron-fortified commercial milk formula is uncertain. ObjectivesWe determined the effect of adding 1) a synbiotic [galacto-oligosaccharide [GOS] + Limosilactobacillus reuteri (L. reuteri)] or 2) the HiMO 2′-fucosyllactose (2′FL) to iron-fortified FUF on iron absorption in young Thai children. MethodsIn a randomized, controlled, single-blinded (participants) crossover study, 82 Thai children aged 8–14 mo were enrolled to consume single servings (235 mL) of FUF with isotopically labeled ferrous sulfate (2.2 mg iron) with 1) the synbiotic (400 mg/100 mL GOS and L. reuteri DSM 17938), 2) the HiMO 2′FL (100 mg/100 mL), and 3) without synbiotic and 2′FL (control) in random order and a 3-d washout period between administrations. Fractional iron absorption [FIA (%)] was assessed by measuring erythrocyte incorporation of isotopic labels 14 d (n = 26) and 28 d (n = 76) after consumption of the last test FUF. ResultsMedian (IQR) FIA from iron-fortified FUF with the synbiotic [8.2 (5.2, 12.9)%] and with 2′FL [8.4 (5.5, 14.1)%] did not differ from the control FUF [8.1 (4.8,14.7)%] (synbiotic compared with control, P = 0.24; 2′FL compared with control, P = 0.95). FIA from all FUF did not differ when measured after 14 and 28 d of erythrocyte incorporation (Time, P = 0.368; FUF, P = 0.435; Time × FUF, P = 0.937). Fecal pH and hemoglobin were negatively associated with FIA. ConclusionsIn young Thai children, the addition of a synbiotic (GOS + L. reuteri) or 2′FL to iron-fortified FUF did not impact FIA from a single serving.The study was registered at clinicaltrials.gov as NCT04774016.

The subsistence strategy transformation of the Yangshao culture (6900-4800BP) in the Guanzhong Area and Western Henan based on new faunal materials from the Miaodigou site

While the significance of the Yangshao culture in early China is widely recognized, systematic and detailed analysis and discussion of its subsistence strategy are lacking, especially for faunal materials. This paper examines the new and crucial faunal remains that include 3,400 identified specimens from the Miaodigou site unearthed in 2002. At that site, pig husbandry was predominant and wild animals were occasionally hunted as supplemental resources. In combination with published research including zooarchaeology, paleoethnobotany, and carbon and nitrogen stable isotope studies of 29 other sites mainly from the Guanzhong area and western Henan, we argue that subsistence strategy underwent a comprehensive and profound transformation during the middle period of Yangshao culture, namely Miaodigou period, as crop production and pig husbandry flourished in a wide range of areas. Domestic pigs accounted for over 80% of mammals, reaching an unprecedented proportion in the Neolithic age and manifesting a high level of consistency in feeding and slaughtering, and foxtail millet replaced broomcorn to become the most important crop at all sites, both of which demonstrate the breadth and depth of this transformation. The tension between the deterioration of climate, the decrease of surrounding wildlife resources due to excessive development and the continuous growth of the population may have contributed to this transformation. This study enriches our understanding of human-environment interactions in the embryonic stage of Chinese civilization and triggers further thoughts on how culture, society, the environment and subsistence were entangled in the development of civilization.

Reconstructing the social structure of kinship members in the Central Plains during the Late Shang and Western Zhou dynasties in China: A stable isotopic study on the Xisima site

AbstractKinship plays a role at the grassroots of social organization, especially in the Shang and Zhou dynasties, which is an important research topic in China. However, the relationship between diet and the social status of kinship and kinship members has been little explored in previous studies. In this article, 52 skeletal bone collagen samples from humans and buried dogs from three different kinships in the Xisima cemetery in China were analysed by stable C and N isotope analysis to reveal dietary strategies, and thus explore subsistence patterns and social structure. Overall, the mean human δ13C was −8.4‰ ± 1.3‰ (n = 44), with a range of −10.0‰ to −7.4‰, and the mean δ15N was 9.0‰ ± 0.7‰ (n = 44), with a wide range of 7.9–11.1‰, which shows that C4 food dominates people’s diet, and that their diet was varied. There are differences in diet and rank among different kinships. Similar situations exist among kinship members based on platforms. Along with previous research, this study provides unprecedented dietary details of different social stratification from martyrs, common people and small nobles to high‐ranking nobles in order to better understand the hierarchical Shang and Zhou dynasties society based on kinship.

Integration of animal husbandry and millet agriculture in Bronze Age East-central Eurasia revealed by faunal stable isotopes at the Jirentai Goukou site, Xinjiang

How food globalization in the Bronze Age influenced the economies and societies of regions along the Eurasian continent has attracted widespread attention. As an integral part of this food globalization, previous studies have focused on the impact of the westwards spread of millet crops on the human populations of East-Central Eurasia. However, the relationship between millet crops and key subsistence economies, such as animal husbandry, which humans rely on in East-Central Eurasia, remains unclear. Here, we carry out a new stable isotope study of 68 domesticated faunal bones from Bronze Age Jirentai Goukou site, Xinjiang, and combine about 1500 published stable isotope data of human and faunal bones to explore systemically the relationship between animal husbandry and millet agriculture in Bronze Age East-Central Eurasia. Our study reveals first the integration of animal husbandry and millet agriculture in Bronze Age Xinjiang, which is indicated by the adoption of C4 millet byproducts to feed domesticated sheep/goats and cattle. Further wide-range stable isotopic analysis in Bronze Age East-Central Eurasia highlights the existence of two different patterns in the relationship between animal husbandry and millet agriculture: the Central Plains pattern and the Inner Asia pattern. These differences can be expressed clearly in several aspects, including the species of domesticated herbivores fed, the degree, method and seasonality of feeding sheep/goats and cattle, and the composition of fodder. On this basis, the possible reasons for the different patterns in the relationship between millet agriculture and animal husbandry in East-Central Eurasia are further explored, such as the different histories of agricultural and pastoral development between the Central Plains and Inner Asia, the distinct characteristics of agriculture and pastoralism (sedentary and mobile), and the specific social, economic/political and geographical environments. Our study provides important information for understanding the specific impact of the globalization of millet agriculture on the animal husbandry economy in Bronze Age Eurasia.

Invasive Ponto‐Caspian amphipods are less carnivorous outside their native range

AbstractA species' expansion beyond the native range is often assumed to be associated with an increased dietary niche breadth. However, empirical evidence remains limited due to a scarcity of studies comparing both the parental and invaded ranges. Here, we test the trophic niche expansion hypothesis by examining stable isotopes and functional morphology across native (NW Black Sea) and invaded (SE Baltic Sea) ranges of two amphipods, Dikerogammarus villosus and Pontogammarus robustoides, originating from the Ponto‐Caspian region—a major source of species invading Holarctic inland waters. Stable isotopes revealed that both species underwent a marked dietary niche contraction by becoming less carnivorous in the invaded range. This dietary shift was morphologically mirrored by an overall reduction of functional traits related to predation. The magnitude of dietary and morphological change was greater in D. villosus. Our findings indicate that previous experimental reports of aggressive predation in D. villosus reflect opportunistic foraging and align with local stable isotope studies which generally indicate a low trophic position. We conclude that Ponto‐Caspian species can undergo rapid dietary changes outside the native range, and that dietary niche expansion is not a prerequisite for successful non‐native establishment.

Experimental assessment of the impact of food processing on δ15N values in dietary meat – Implications for paleodietary reconstruction

Stable isotope studies of bone collagen are widely applied in an attempt to understand the history and range of modern human and earlier hominin diets. The nitrogen isotope system has been extensively applied to the human bioarchaeological record to predict dietary protein sources, as nitrogen isotope ratios roughly track the trophic positionality of an organism. While the ratio of nitrogen isotopes in organisms (δ15N) tends to be reflective of trophic position, nitrogen isotope fractionation is complex and subject to many sources of variation. This study explores how human behavior might influence this variation. We experimentally investigated the impact of food-related behaviors on the δ15N dietary proxy, with specific focus on selection and processing of animal food sources. In assessing putrefaction, processing, prey choice, and fuel wood, we saw that these variables generated small shifts of ∼1.5‰ or less in the δ15N values of food items. We conclude that scavenging as a frequent dietary adaptation may be isotopically visible, but the timing of carcass scavenging likely matters. We also posit that prey species and fuel wood species might matter for the patterning of δ15N shifts produced by different types of cooking. The results of this study expand the range of contributing factors to consider when utilizing the nitrogen isotope dietary proxy and open new testable questions about the use of this method in populations where complex food behavior may be common.

Insights on long-term ecosystem changes from stable isotopes in historical squid beaks

BackgroundAssessing the historical dynamics of key food web components is crucial to understand how climate change impacts the structure of Arctic marine ecosystems. Most retrospective stable isotopic studies to date assessed potential ecosystem shifts in the Arctic using vertebrate top predators and filter-feeding invertebrates as proxies. However, due to long life histories and specific ecologies, ecosystem shifts are not always detectable when using these taxa. Moreover, there are currently no retrospective stable isotopic studies on various other ecological and taxonomic groups of Arctic biota. To test whether climate-driven shifts in marine ecosystems are reflected in the ecology of short-living mesopredators, ontogenetic changes in stable isotope signatures in chitinous hard body structures were analysed in two abundant squids (Gonatus fabricii and Todarodes sagittatus) from the low latitude Arctic and adjacent waters, collected between 1844 and 2023.ResultsWe detected a temporal increase in diet and habitat-use generalism (= opportunistic choice rather than specialization), trophic position and niche width in G. fabricii from the low latitude Arctic waters. These shifts in trophic ecology matched with the Atlantification of the Arctic ecosystems, which includes increased generalization of food webs and higher primary production, and the influx of boreal species from the North Atlantic as a result of climate change. The Atlantification is especially marked since the late 1990s/early 2000s. The temporal patterns we found in G. fabricii’s trophic ecology were largely unreported in previous Arctic retrospective isotopic ecology studies. Accordingly, T. sagittatus that occur nowadays in the high latitude North Atlantic have a more generalist diet than in the XIXth century.ConclusionsOur results suggest that abundant opportunistic mesopredators with short life cycles (such as squids) are good candidates for retrospective ecology studies in the marine ecosystems, and to identify ecosystem shifts driven by climate change. Enhanced generalization of Arctic food webs is reflected in increased diet generalism and niche width in squids, while increased abundance of boreal piscivorous fishes is reflected in squids’ increased trophic position. These findings support opportunism and adaptability in squids, which renders them as potential winners of short-term shifts in Arctic ecosystems.

Differences in Non-heme Iron Absorption Between Healthy Adults of East Asian and Northern European Ancestry: A Stable Iron Isotope Study

Differences in Non-heme Iron Absorption Between Healthy Adults of East Asian and Northern European Ancestry: A Stable Iron Isotope Study

Toward mending the marine mass balance model for nickel: Experimentally determined isotope fractionation during Ni sorption to birnessite

In fewer than fifteen years, the study of Ni stable isotopes has advanced from early method development to application of a powerful tool for resolving a long-standing question: why does it appear that output fluxes of Ni from the global oceans far exceed input fluxes? The seawater concentration of Ni, a bioessential trace metal, is almost certainly at steady state on timescales comparable to its residence time of ∼20 kyr, so some of the current flux estimates must be inaccurate. Just as the input and output fluxes should balance, so should the flux-weighted isotopic compositions of the inputs and outputs. Thus, isotopic characterization of inputs and outputs provide an additional constraint on a balanced model of the marine Ni budget. Here, we report on experiments designed to elucidate fractionation mechanisms and magnitudes for sorption of Ni to Mn oxyhydroxide (birnessite), because Mn-rich sediments accumulating on abyssal plains represent the largest sink flux of Ni from seawater to marine sediments. Our results show remarkably large fractionations at low ionic strength (average Δ60/58Nidissolved-sorbed = +1.38 ‰). Neither closed-system equilibrium trends nor Rayleigh curves fit the data well. Fractionations are even larger at high ionic strength (Δ60/58Nidissolved-sorbed ranging from +2.0 to +4.0 ‰), and they decrease with experimental duration from 2 d (49 h) to 27 d. The high ionic strength data fit Rayleigh trends well. Here, we use X-ray absorption fine-structure spectroscopy (EXAFS) and results from previous studies to support interpretation of our data as combinations of kinetic and equilibrium isotope effects that vary in their proportional contributions to the total fractionation with time and with surface loading. One important consequence of this study is that none of the experimental results reported thus far, including ours, are directly applicable to building steady-state models of the Ni cycle. Even our longest duration experiments did not achieve equilibrium, which is likely to be manifest in the very slowly accumulating sediments on abyssal plains. Our work constrains further the mechanisms of Ni sorption to birnessite and clearly indicates that determination of equilibrium fractionation in this system, although challenging, will be a crucial step toward resolving the apparent marine Ni imbalance.

Assessing a standardized method to identify optimal baselines for trophic position estimation in stable isotope studies of stream ecosystems

Assessing a standardized method to identify optimal baselines for trophic position estimation in stable isotope studies of stream ecosystems

Camelids in the hyperarid core of the Atacama desert 12,000–11,000 years ago? A stable isotope study and its consequences for early human settlement

How did hunter-gatherers initially settle and move across extreme environments? We conducted a multi-disciplinary study to tackle this question, focusing on how Paleoindigenous populations inhabited the hyperarid core of the Atacama Desert. Particularly, we examined the stable isotopic values of ∼12,000–11,200-year-old camelid and rodent bones and hair samples retrieved from low-elevation archaeological sites (Pampa del Tamarugal basin - PdT, 800–1200 masl). By integrating novel and existing data into a regional stable isotope ecology, we offer a baseline for interpreting our results. δ13C and δ15N values on archaeological remains show animals with different geographical origins. A first group includes camelids and rodents with lower δ15N values and δ13C values indicating a dominantly C3 diet, corresponding to animals either local to the PdT or from the Andean Steppe, at least ∼80 km away and between 4000 and 4500 masl. Most of these remains, however, come from residential sites and belong to young camelids, indicating a local origin. A second group presents a higher δ15N signal and δ13C values indicative of a mixed C3–C4 based diet. These animals were not local but source to the Puna at least ∼60 km away between 3200 - 4000 masl. We hypothesize that the first would correspond to animals associated with hunter-gatherer bands settled around a wetland and grove environment in the PdT. The second group could correspond to remains brought by humans from the Puna to the PdT. Our results demonstrate that during the Late Pleistocene/Early Holocene the Atacama was very different than today, supporting life that included large and mid-size game. These results also show that the core of the Atacama attracted animals and people and counters the notion of this ecosystem as a barren passageway from the Andes to the coast.

The Importance of PET Imaging to Understanding Whole-Body Cortisol Metabolism in Alzheimer's Disease.

Excess cortisol is associated with more severe cognitive decline, Alzheimer's disease, and related dementia phenotypes. The intracellular enzyme 11β-HSD1 regenerates active cortisol from inactive cortisone. In this current issue, high regional brain occupancy of Xanamemtrademark, determined by [11C]TARACT PET imaging of 11β-HSD1, in cognitively normal individuals and mild cognitive impartment/Alzheimer's disease (AD) patients is presented. In the future, comprehensive kinetic modeling using arterial sampling for occupancy studies, and whole-body PET imaging of 11β-HSD1 enzyme levels, in combination with stable isotope studies of cortisol metabolism, can provide broad insight into enzyme levels and activity in AD and other relevant diseases.

Metabolic activity of Planktothrix rubescens and its consequences on oxygen dynamics in laboratory experiment: A stable isotope study.

Fluctuations in dissolved oxygen (DO) contents in natural waters can become intense during cyanobacteria blooms. In a reconnaissance study, we investigated DO concentrations and stable isotope dynamics during a laboratory experiment with the cyanobacterium Planktothrix rubescens in order to obtain insights into primary production under specific conditions. This observation was extended to sub-daily timescales with alternating light and dark phases. Dissolved oxygen concentrations and its isotopes (δ18ODO) ranged from 0.02 to 0.06 mmol · L-1 and from +9.6‰ to +23.4‰. The δ18ODO proved to be more sensitive than concentration measurements in response to metabolic variation and registered earlier shifts to dominance by respiration. Oxygen (O2) contents in the headspace and its isotopes (δ18OO2) ranged from 2.62 to 3.20 mmol · L-1 and from +9.8‰ to +21.9‰. Headspace samples showed less fluctuations in concentration and isotope trends because aquatic processes were hardly able to alter signals once the gas had reached the headspace. Headspace δ18OO2 values were corrected for gas-water equilibration and were determinedto be higher than the mean δ18OH2O of -8.7‰. This finding suggests that counteracting respiration was important even during the highest photosynthetic activity. Additionally, headspace analyses led to the definition of a fractionation factor for respiration (αR) of this cyanobacterium with a value of 0.980. This value confirms the one commonly used for cyanobacteria. Our findings may become important for the management of water bodies where decreases in DO are caused by cyanobacteria.

Impact and implications of hydrothermal fluids migration in the Frolov hydrocarbon province in West Siberia

Both the prolific source rocks of the Bazhenov Formation and the reservoir-prone units of the Abalak Formation cover most of the West Siberian region. Hydrothermal fluids circulation has been suggested to affect hydrocarbon potential and reservoir properties at some localities of this vast hydrocarbon province. However, integrated studies are currently lacking. Here we present an extensive multidisciplinary study combining regional studies with core logging properties and sample analyses (i.e. geochemistry, petrography, organic geochemistry) to reveal processes related to the hydrothermal activity that affected both formations. We also focus on the factors and implications for secondary unconventional reservoir formation within the deposits from the Kamennaya summit of the Frolov oil and gas region. Three boreholes corresponding to type sections located in different parts of the study area (elevated, transitional and deep) were investigated. The elevated and transitional parts of the basin are adjacent to the weakened contact zones of a granite massif. These tectonic discontinuities acted as conductors for hydrothermal fluids circulation on the area. Lithological and stable isotope studies revealed the presence of intensive hydrothermal secondary alterations in various types in rocks, including massive metasomatic carbonatization, sulfatization, sulfide mineralization and leaching processes. This hydrothermal fluid activity resulted in reservoir formation within siliceous radiolarite layers, while in the deep part of the basin potential reservoirs were completely healed. Organic matter maturity varies in different parts of the basin. We identify several mechanisms related to the various hydrothermal processes that influenced rocks composition, structure and organic matter maturity: (1) A weakened zone located on the periphery of the granite massif in the basin basement is characterized by extensive fault damage zones facilitating the migration of high temperature fluids along deposits during post-sedimentation stages; (2) The thickness, mineral composition of the rocks overlying the basement control fault attenuation and fluid workflow; (3) The fluids composition, their acidity/alkalinity, prompted various changes in rock structure, especially in secondary porosity formation. The identification of various hydrothermal processes and their influence on pore space allowed to determine the approach for the spatial distribution prediction of unconventional reservoirs in the studied formations, and subsequently improve the efficiency and effectivity of the exploration process not only at the Kamennaya summit, but also on the other similar West Siberian basin areas.

Changes in protein requirements of elderly people over 5 years assessed using the indicator amino acid oxidation method

To evaluate the changes in protein requirements of the elderly during the past five years. Based on the previous study of protein requirements of 14 elderly in 2017, 4 of these elderly(70-80 y) were included as study participants and protein requirements were re-evaluated using the indicator amino acid oxidation method. There were seven protein levels: 0.1, 0.3, 0.6, 0.9, 1.2, 1.5 and 1.8 g/(kg·d). Maintenance diets were given for the first two days of each protein level. A stable isotope study was conducted on the day 3, using L-~(13)C-phenylalanine as an indicator on the basis of an amino acid rationed diet, which was orally ingested into the body along with the amino acid rationed diet, and breath and urine samples were collected when the metabolism of L-~(13)C-phenylalanine reached steady state in the body. By measuring the kinetic parameters of labeled amino acids in the samples, a nonlinear mixed-effects model was constructed for the protein intake to be tested and the oxidation rate of labeled amino acids. The mean protein requirement of the study population was determined by the protein intake corresponding to the inflection point of the curve. Based on the production rate of ~(13)CO_2 in exhaled breath of four elderly people at different protein levels, the mean protein requirement was 1.05(95%CI 0.51-1.60) g/(kg·d). The protein recommended nutrient intake was 1.31(95%CI 0.64-2.00) g/(kg·d) was estimated by applying the coefficient of variation of the mean protein requirement to derive the recommended nutrient intake. Protein requirements in the elderly have increased over a five-year period and sarcopenia may be the main cause of increased protein requirements.

Simple bulk pigment analysis suggests microphytobenthos contributions to food webs may be underestimated due to isotopic contamination by remineralized wetland carbon

Stable isotope studies have revealed the importance of microphytobenthos (MPB) in coastal food webs. Microalgae typically have δ13C values between depleted C3 wetland/terrestrial macrophytes, and enriched C4 macrophytes and seagrasses. However, the challenges of obtaining clean samples of microalgae from sediments means they are often represented by limited sampling in many food web studies; consequently, we have a limited understanding of spatial and temporal variation in their δ13C values. We tested a simple technique to measure the δ13C of bulk pigments extracted from surficial sediments to represent MPB and applied it to quantify fine scale spatial variation in MPB δ13C around salt marshes. The bulk extraction method is logistically simple, and drives substantial but relatively consistent fractionation in δ13C of −3.5 ± 0.13 ‰ (mean ± 1 S.E., range = 2.3–4.4 ‰, n = 18 paired comparisons) compared to whole cell values. The consistency in fractionation suggests that spatial and temporal δ13C patterns measured in field samples should reflect real variation in source values, and that measured values could be corrected and incorporated into isotope mixing models. In 88 MPB samples among four marsh sites over two summers, MPB δ13C in marsh creeks was lower by an average of 4.4 ± 0.72 ‰ and up to 8.4 ‰ compared to sites along the outer marsh-open water fringe 10's of m away. Few food web studies incorporate this magnitude of variation in their MPB source estimates into mixing models. Over three weekly samplings at one marsh creek site, low tide dissolved inorganic carbon (DIC) δ13C was similarly lower by 4.8 ± 0.36 ‰ and up to 6.2 ‰ compared to high tide and adjacent open water DIC values. The significant small-scale variability in MPB δ13C appears to be driven by remineralized marsh carbon which depletes the DIC δ13C in the marsh creeks, a phenomenon that has long been recognized but is rarely considered in food web studies. Mixing models that assume a narrower range in MPB source values will erroneously attribute isotopically variable MPB contributions to end-member production sources thereby clouding our understanding of energy flows through coastal seascapes.

Dietary change of North Patagonian guanacos: A historical ecology perspective through the study of stable isotopes

This paper presents the results of a study on the isotopic ecology of guanacos in central western Argentina. We examine the historical population ecology of guanacos using stable isotope analysis of bone collagen from pre-Hispanic and modern guanaco populations ( n = 129), considering variability in two ecoregions: the Monte hot desert and the Andean-Patagonian cold desert. Our study addresses the consistency of guanaco diets over time, evaluating palaeoecology to provide information for conservation of this taxon. We found significant differences in isotopic niche size between modern and archaeological guanacos. When analyzed by ecoregion, there were significant differences in niche size through time, indicating that guanacos had distinctive dietary habits and occupied different ecological niches across the ecoregions. Comparing Standard Ellipse Areas (SEA) through time and across space, we observed that the archaeological SEA for guanacos is smaller than its modern counterpart in the Andean-Patagonia ecoregion. Conversely, in Monte, the archaeological SEA is larger than the one established for modern samples. The contrast between pre-Hispanic and modern populations highlight the impact of human activity and conservation efforts on the distribution and ecology of guanacos. These findings have important implications for understanding guanaco ecology with consequences for conservation policies.

Unravelling the sources contributing to the urban water supply: An isotope perspective from Ljubljana, Slovenia

In cities experiencing rapid urbanization, we must continually update our understanding of the partitioning of drinking water sources concerning its supply if it is to be managed sustainably. This need is especially crucial given the pressure on water resources arising from evolving land use patterns and climate change. For this reason, a city-wide study of stable water isotopes (δ2H and δ18O) in precipitation, surface water and groundwater across Ljubljana, Slovenia, was undertaken. The goal was to characterise the temporal dynamics of urban water cycling and trace the various sources contributing to the city’s drinking water supply. Monthly water sampling, combined with hydrogeochemical and in-situ data, permitted the identification of local precipitation and surface water contributions to its two groundwater supply aquifers. In addition, a re-examination of the mean residence times (MRT) of surface waters revealed an MRT of 3–4 years, which is much longer than previously reported. Also, changes in the contributions of surface water and precipitation to groundwater were observed compared to previous studies. These findings improve our understanding of local water partitioning and provide valuable insights for water managers addressing future urban water resource management.