Strontium Ratios Research Articles

Riverine sediment geochemistry and its dispersal pattern on the western Sunda Shelf

Understanding sediment provenance in continental shelf basins is essential for reconstructing paleoenvironmental changes, enhancing insights into sedimentary dynamics, and elucidating their contributions to the global carbon cycle. To decipher sediment provenances and enhance comprehension of the sediment dispersal patterns and the factors governing geochemical compositions on the Sunda Shelf, we conducted an exhaustive analysis of trace elemental concentrations and the isotopic ratios of strontium (87Sr/86Sr) and neodymium (εNd) in the silicate fractions of 35 surface sediment samples. These samples were collected from the western Sunda Shelf and its proximate major river end-members, namely, the Mekong, Rajang, Pahang, and Kelantan Rivers. Through the application of various statistical methodologies, including classical cluster analysis, Principal Component Analysis (PCA), the La-Sc-Th discrimination diagram, and an array of elemental ratios, we identified three distinct geochemical provinces on the Sunda Shelf. Each province is defined by unique geochemical signatures indicative of varied sediment sources or provenances. This distinction was primarily attributed to pronounced sediment heterogeneity, reflecting lithologic variances from the diverse river end-members. In pursuit of a holistic understanding of sediment provenance in the region, SrNd isotopic data was also integrated from prior studies encompassing the eastern Sunda Shelf and the southern South China Sea. By utilizing the SrNd mixing model, complemented with Monte-Carlo simulations, we estimated the sediment contributions from surrounding river end-members to the southern South China Sea basin. According to the model, the Mekong River emerges as the principal sedimentary source of the Sunda continental shelf and the southern South China Sea, attributed to its substantial sediment outputs. Additionally, the model has identified significant contributions from the Rajang, Pahang, and Kelantan rivers, particularly in offshore regions near their estuaries. Further, this study revealed the previously underappreciated influence of South China's rivers, namely the Red and Pearl Rivers, on the eastern Sunda Shelf and deeper southern South China Sea region beyond the continental shelf. This study not only delineates the dominant sediment sources influencing the Sunda Shelf and the South China Sea but also underscores the importance of considering a broad spectrum of river end-members to understand sedimentary dynamics in an active marine environment.

Interpretation and implications of high-resolution hydroclimatic records of the past 7,000 years based on Gaho paleolake sediments in South Korea

In this study, we investigated the past hydroclimate and its controlling factors over East Asia by reconstructing hydroclimate variability during the middle-to-late Holocene using rainfall-driven sedimentary features in the Gaho paleolake, Hapcheon County on the southern Korean Peninsula. Based on radiocarbon dates, median grain sizes, and elemental ratios of strontium (Sr), titanium (Ti), and zirconium (Zr) measured by high-resolution X-ray fluorescence core scanning, we tested potential indicators of past heavy rainfall. During the past 7000 years, temporal changes in median grain size and elemental ratios (Sr/Ti and Zr/Ti) were found to be similar to those in the Asian monsoonal precipitation index and sea surface temperature (SST) in the western North Pacific region, suggesting that periods with increased elemental ratios may have been influenced by intensified regional rainfall events and higher SSTs. During the past 2000 years, time series of Sr/Ti and Zr/Ti ratios in the paleolake sediments appeared to covary with a megadrought period (AD 1593–1698; 357-252 cal BP), flooding events in the 1500s, and the collapse of ancient nations in Korea and other parts of East Asia. This similarity between sedimentary records and historical events suggests considerable potential for the dating of elemental ratios in lake sediments as high-resolution analogs of past hydrological events to support historical records.

Optimizing Sr-doped CaSiO3 synthesis for enhanced bioceramic properties: A Plackett–Burman approach

Doping Sr has the potential to enhance bioceramic properties. However, controlling purity, Sr concentration, and properties is crucial. Therefore, precise evaluation of synthesis variables is essential, achieved through experimental design techniques. This study synthesized Sr-doped calcium silicate wollastonite using a Plackett–Burman design with 11 variables to identify key factors affecting synthesis yield and physical, structural, and chemical attributes for tissue engineering. Results indicate that the strontium proportion significantly impacts material properties, affecting porosity, surface area, and pore volume. Moreover, observations reveal that calcination temperature contributes to heightened crystallinity and strontium doping. Adjusting calcium and strontium precursor concentrations while reducing the silicon to calcium and strontium ratio improves efficiency crystallinity, purity, and promotes the formation of the preferred β-CaSiO3 phase. Overall, consistent and reproducible findings provide valuable insights into the variables influencing the process and facilitate optimization for future ceramic synthesis.

A pilot bioavailable strontium isotope baseline map of Southern British Columbia, Canada

Strontium isotopes are used for provenience and mobility studies in archaeology, ecology, and forensic studies, and rely on accurate baseline maps that are used to compare and interpret human and animal strontium ratios. Here, we present a bioavailable 87Sr/86Sr map, also called an isoscape, for southern British Columbia derived from modern plant samples’ 87Sr/86Sr ratios. We sampled 67 medium root depth plants over a 900 km transect from the southern BC coast to inland BC to capture the natural 87Sr/86Sr ratios of plants along the four major geological belts in British Columbia. Non-parametric Kruskal–Wallis and pairwise Wilcox tests were used to examine whether the geological belts had statistically significant mean differences. It was found that the province could be effectively divided into east and west, with the Coastal–Intermontane and Omineca–Foreland regions having statistically different means from each other. 87Sr/86Sr ratios had statistically significant relationships with salt deposition, volcanic deposition, and mean age of the underlying lithology. Generally, 87Sr/86Sr ratios increased with distance from the coast as the atmospheric input of radiogenic strontium from marine-derived rainwater decreased and the input of radiogenic strontium isotopes from the underlying geology of the Rockies in the far east of the province increased.

Perovskite Oxide as A New Platform for Efficient Electrocatalytic Nitrogen Oxidation

AbstractElectrocatalytic nitrogen oxidation reaction (NOR) offers an efficient and sustainable approach for conversion of widespread nitrogen (N2) into high‐value‐added nitrate (NO3−) under mild conditions, representing a promising alternative to the traditional approach that involves harsh Haber–Bosch and Ostwald oxidation processes. Unfortunately, due to the weak absorption/activation of N2 and the competitive oxygen evolution reaction, the kinetics of NOR process is extremely sluggish accompanied with low Faradaic efficiencies and NO3− yield rates. In this work, an oxygen‐vacancy‐enriched perovskite oxide with nonstoichiometric ratio of strontium and ruthenium (denoted as Sr0.9RuO3) was synthesized and explored as NOR electrocatalyst, which can exhibit a high Faradaic efficiency (38.6 %) with a high NO3− yield rate (17.9 μmol mg−1 h−1). The experimental results show that the amount of oxygen vacancies in Sr0.9RuO3 is greatly higher than that of SrRuO3, following the same trend as their NOR performance. Theoretical simulations unravel that the presence of oxygen vacancies in the Sr0.9RuO3 can render a decreased thermodynamic barrier toward the oxidation of *N2 to *N2OH at the rate‐determining step, leading to its enhanced NOR performance.

Perovskite Oxide as A New Platform for Efficient Electrocatalytic Nitrogen Oxidation.

Electrocatalytic nitrogen oxidation reaction (NOR) offers an efficient and sustainable approach for conversion of widespread nitrogen (N2 ) into high-value-added nitrate (NO3 - ) under mild conditions, representing a promising alternative to the traditional approach that involves harsh Haber-Bosch and Ostwald oxidation processes. Unfortunately, due to the weak absorption/activation of N2 and the competitive oxygen evolution reaction, the kinetics of NOR process is extremely sluggish accompanied with low Faradaic efficiencies and NO3 - yield rates. In this work, an oxygen-vacancy-enriched perovskite oxide with nonstoichiometric ratio of strontium and ruthenium (denoted as Sr0.9 RuO3 ) was synthesized and explored as NOR electrocatalyst, which can exhibit a high Faradaic efficiency (38.6 %) with a high NO3 - yield rate (17.9 μmol mg-1 h-1 ). The experimental results show that the amount of oxygen vacancies in Sr0.9 RuO3 is greatly higher than that of SrRuO3 , following the same trend as their NOR performance. Theoretical simulations unravel that the presence of oxygen vacancies in the Sr0.9 RuO3 can render a decreased thermodynamic barrier toward the oxidation of *N2 to *N2 OH at the rate-determining step, leading to its enhanced NOR performance.

Human mobility on Cancun Island during the Late Postclassic: Intra- and inter-site demographic interactions.

Residential mobility in Prehispanic Mesoamerica is of paramount importance in bioarchaeology to determine the "how, where and why" people established biological, political and economic networks. The goal of this paper is to assess the presence of non-local people on the East Coast of the Yucatan Peninsula during the Late Postclassic (AD 1200-1540), and how they might have been perceived by the local Maya people. We analyze the presence, origin and mortuary distribution of 50 individuals based on their dental and bone 87Sr/86Sr signatures in the "urban" assemblage constituted by the archaeological sites known as El Rey and San Miguelito on Isla Cancun. Both sites present a strontium ratio "plateau" between 0.7091 and 0.7092, which is considered the local signature. Seven individuals, ranging in age from 5 years old to adulthood, were detected as potentially non-local, and originating from a wide range of regions both near and distant to Isla Cancun. Funerary patterns, burial location, and dietary data do not indicate these people were treated differently from the rest of the population, at least at the moment of death. This suggests that these non-locals might not have been perceived as "foreigners" and that they had integrated into the local community. Such mobility and cultural integration could have motivated by multiple factors, including economic and trade connections, or kinship relationships.

Образ жизни детей и взрослых варварской округи Херсонеса (по материалам могильников Фронтовое 3 и Киль-Дере 1)

The necropolises Frontovoe 3 and Kil-Dere 1 from the environ of Chersonesos are interesting and important for the reconstruction of the cultural and historical situation on the borders of the Roman Empire. Data on the isotopic composition of bone collagen and tooth enamel provide new opportunities to discuss the nutrition, economy, and mobility of societies. The isotope composition of carbon and nitrogen informs about the average dietary intake of an individual over the last few years of life (7—10), while the ratio of strontium isotopes in tooth enamel characterizes the habitat of the child during the formation of the crown of the teeth (in this case, from 1 to 6 years). Thus, we obtain information about local natives and migrants of the first generation, whose childhood, probably, passed outside the environ of Chersonesos. The isotopic composition of carbon and nitrogen in 67 samples of bone tissue and the composition of strontium in 35 samples of tooth enamel were studied. The life support system of these societies was based on the use of local terrestrial food resources. Few individuals have been found who can be named first-generation migrants. The low variability of the isotope ratios of strontium and carbon indicates a clear localization of this population group on the given territory. We also discuss the factors behind the differences in the isotopic markers of groups from Kil-Dere 1 and Frontovoye 3. These can be both environmental factors and cultural differences. The questions addressed here can be answered by studying a broader base of the compared materials.

Lithium isotope composition of Ediacaran dolostones from the Nuccaleena and Doushantuo formations

The end of the Cryogenian glaciations undoubtedly affected the chemistry of the Neoproterozoic oceans, with potential consequences for the evolution of life; the duration and extent of this influence are poorly constrained. Lithium (Li) isotopes in carbonates can be used to investigate past weathering events and riverine input into the oceans. Here, we report the Li isotope (δ7Li) composition of the Ediacaran cap dolostones (Marinoan) from the Nuccaleena Formation, South Australia and the Doushantuo Formation, South China to investigate changes in weathering during the aftermath of the Marinoan glaciation. The origin of dolomite formation is still hotly debated, and the inability to precipitate dolomite at ambient temperatures (the ‘dolomite problem’) has not yet been resolved. The dominant hypothesis for the presence of marine dolomite is that it is of secondary origin, owing to diagenetic replacement of calcium carbonate, but a second hypothesis is that it forms as a result of primary marine deposition; both are plausible hypotheses. Using carbon isotopes (δ13C) and ratios of manganese and strontium (Mn/Sr), we suggest that diagenesis may not have significantly altered the δ7Li composition of the primary dolomite, but this cannot be discounted without further diagenetic modelling. As a result, we cannot infer the δ7Li composition of the Ediacaran oceans, as further work must be done to address the impact of diagenesis on the δ7Li values. Nevertheless, this dataset contributes to a Li isotope chemostratigraphic record of the Proterozoic, which is a key element to understanding the emergence of complex life.

Changes in the quality parameters of Cephalaria syriaca L. seed oil after the refining process

The present study has determined that the crude-oil refining process from the Cephalaria syriaca (CS) seed, which could be a new vegetable oilseed source, changed its physical and chemical quality properties (except specific gravity and refractive index). It was also determined that the dominant saturated and unsaturated fatty acids in the crude and refined oils were myristic (21.06-11.80%), palmitic (10.8-8.91%), stearic (2.26-2.70%), oleic (29.17-34.24%) and linoleic (35.56-40.57%). The vitamin E values of the crude and refined CS seed oils were 51.95-50.90 mg/kg, respectively. The oxidative stability values for crude and refined CS seed oils were 2.32-2.69 h, respectively. β-sitosterol and campesterol were the predominant sterols. As a result of the refining process, although magnesium, potassium, iron and copper decreased, the ratios of sodium, aluminum, calcium, chromium, strontium, rubidium, and barium increased. The results provide preliminary data for the future consumption of CS oil in particular for refined CS seed oil.

Applied current on the suppression of strontium segregation in Sr2Fe1.5Mo0.5O6-δ electrode for improved oxygen evolution reaction

Strontium surface segregation is the main issue that causes long-term performance degradation in strontium-containing electrodes for solid oxide electrolysis cells. In this research, we effectively suppress strontium segregation by applying an anodic current that drives the segregated strontium back to the perovskite lattice and mitigate electrode performance degradation. By monitoring the impedance of Sr2Fe1.5Mo0.5O6-δ (SFM) air electrode under open circuit voltage at high temperature with changing current densities over time, the degradation caused by strontium segregation is verified. The applied current successfully prevent the polarization resistance from increasing is observed. The cell with 0.8 A/cm2 of the applied current increase only 3% of polarization resistance as compared to the cell without applied current after testing at 800 ℃ for 24 h. The atomic ratio of strontium on the SFM electrode surface shows lower strontium content after undergoing applied current, which means that the strontium is indeed migrated back to perovskite lattice under the applied current and result in slower degradation of the SFM electrode.

Diachronic forager mobility: untangling the Stone Age movement patterns at the sites Norje Sunnansund, Skateholm and Västerbjers through strontium isotope ratio analysis by laser ablation

Strontium isotope ratios in human teeth from the three Swedish prehistoric Stone Age hunter-fisher-gathering societies Norje Sunnansund (Maglemose), Skateholm (Ertebølle) and Västerbjers (Pitted Ware Culture) were analysed with laser ablation to produce data on both individual movement patterns and societal mobility trends. The analyses of teeth from both Skateholm and Västerbjers displayed homogeneous ratios and corresponding mobility patterns, while the data from Norje Sunnansund showed larger variances with heterogenous strontium ratios and varied inter-individual mobility patterns. Correlation with the bioavailable baseline suggests that the size of the geographical areas, where human strontium ratios could have originated, was roughly comparable for all three sites. The teeth measurements were reflected within a 50-km radius of the surrounding landscape and the 25–75% data quartile matched with distances between 3 and 30 km from the sites, suggesting limited mobility ranges among aquatically dependent foragers from southernmost Sweden. By applying ethnographic analogies and site-specific contextual inferences, the results suggest that mobility ranges at Norje Sunnansund were likely not delimited by neighbouring group territories. This changed over time and an increasing territorialisation of the landscape may have influenced movement patterns and caused restrictions to the foraging activities at both Skateholm and Västerbjers.

<sup>87</sup>87Sr/<sup>86</sup>Sr ISOTOPE RATIOS IN THE RIVER WATERS OF THE SOUTHERN URALS

87Sr/86Sr isotopic ratios are widely used to identify strontium sources and study strontium behaviour in(bio)geochemical cycles. 87Sr/86Sr in surface waters can reflect the average composition of bioavailable (i.e. available forfurther absorption by plants and animals) strontium in the catchment specific area. Based on those 87Sr/86Sr ratios, theregional maps of the bioavailable strontium distribution (strontium isoscapes) can be compiled. A complex block structurecharacterizes the Ural mountain system. Individual parts (blocks) are composed of rocks of various ages, genesis andgeochemical characteristics, which can radically change at a distance of several tens of kilometres. Such variability wouldbe reflected in strontium isotopic ratios, thus making it possible to determine the local isotopic signatures of bioavailablestrontium.This work aimed to study 87Sr/86Sr in the water in the rivers of the Southern Urals. We determined the contents andisotopic ratios of strontium in river water samples collected from the territories of the Orenburg and Chelyabinsk regionsand the Republic of Bashkortostan in 2019–2020.For the first time in the surface water of the rivers in the Southern Urals (Ural, Belaya, Tobol, Karagaily-Ayat, Sim, andothers), the 87Sr/86Sr isotopic ratios have been determined, and their variations have been analyzed. 87Sr/86Sr values varyin the range 0.70666–0.71063 (average 0.70908) for the rivers of the Urals basin, 0.70749–0.71058 (average 0.70924)for the Kama-Volga basin, 0.70946–0.71176 (average 0.71071) for the Tobol basin. Such features of the strontium isotopiccomposition may be due to the influence of underlying rocks of the catchment area drained by river water. The dataobtained can be used to identify the sources of strontium input into the water system during hydrological and environmentalstudies; to confirm the authenticity of food products of plant and animal origin; to carry out comparisons in thestudies of the migration of ancient people and animals, as well as to determine the raw material areas for the productionof vegetable and woollen textiles and wooden products in antiquity.

Synergic effect of additives on the structure and properties of nano strontium hexaferrite synthesized via the gel combustion method

Strontium hexaferrite (SrFe12O19) is a ferrimagnetic oxide that is widely used as a permanent magnetic material due to its excellent magnetic properties and low production cost. Modification of chemical composition and nanoscale structural refinement can improve its properties. In the present study, the synthesis process of strontium hexaferrite by the gel combustion method was investigated. SrFe12O19 was synthesized with the iron to strontium ratio of 10-12. The calcination temperature was also optimized by modifying this ratio. The effect of adding cobalt, manganese, zirconium, and zinc cations to the composition of SrFe12-2x(Mn Co Zn)x/3ZrxO19 (x = 0.0–1.0) was investigated. The samples were characterized by X-ray diffraction (XRD), thermal analysis (TGA/DTA), field emission scanning electron microscopy (FE-SEM), vibrating sample magnetometer (VSM), and vector network analyzer (VNA). The results showed that, in the free-additive samples, the pure strontium hexaferrite phase was formed only under the optimal conditions where the iron to strontium ratio and heat-treatment temperature were about 11 and 900 °C, respectively. In this case, clustered particles with the size of 64-145 nm were observed in the structure. In addition, partial substitution of different amounts of manganese, cobalt, zinc, and zirconium cations for Fe3+ in the hexaferrite structure affected its magnetic properties, such as saturation magnetization (Ms), remnant magnetization (Mr), coercivity (Hr), and Mr/Ms ratio. The dielectric constant, reflectance, transmittance, and absorption of electromagnetic waves were also changed. The sample with x = 0.8 showed the maximum reflectance (36.20%) and minimum transmittance (54.10%). The sample with x = 0.4 showed the desired reflectance loss of −9.24 dB at the frequency of 12.15 GHz.

Influence of migratory route on early maturation of swordtip squid, Uroteuthis edulis, caught off western Kyushu Island, Japan

Mature female Swordtip squid (Uroteuthis edulis) of ca. 100 mm mantle length are found in Tachibana Bay (western Kyushu, Japan) from June to August, although many mature females caught in the eastern Tsushima Straits (the entrance to the Japan Sea) are over ca. 150 mm. To reveal the cause for the difference, statolith analyses and Lagrangian tracer experiments were conducted. The results show that the small mature female squid would have hatched in the southern East China Sea in winter and migrated to the Sea of Amakusa via the Kuroshio Current, as also would many squid caught in the eastern Tsushima Straits. The two major differences between them were found to be the history of their empirical water temperature (estimated from the ratio of Strontium to Calcium in the statoliths) and the depth of the waters where they were caught. The small mature females would have experienced water temperatures rising from 18° to 20°C in the coastal waters off Kyushu, probably over 16 °C even at the bottom layer, for one month or more before being caught. Considering also the results from previous research, a hypothesis is proposed that, after reaching the minimum age of maturity, the squid could begin (and continue) to mature when the water temperature in the bottom layer (or in the deepest zone to which this species can dive) exceeds ca. 16 °C, and take about one month to reach full maturity. The method used here to explain the size differences detected among siblings born in the same locality but following migratory paths with very different temperature conditions is a useful and the results also suggest another small mature squid that appear in the southern East China Sea in spring may migrate from the warmer waters, which can be contributed to the stock management of this species.

Diet or mobility? Multi-isotopic (C, N, and Sr) dietary modeling at Shamanka II, Cis-Baikal, Siberia

Dietary reconstructions increasingly rely on Bayesian techniques such as Food Reconstruction Using Isotopic Transferred Signals (FRUITS). These models benefit from the use of additional isotopic proxies (13C, 15N, and 87Sr/86Sr), which help refine proportional contributions of potentially overlapping reference groups. However, each new isotope comes with additional considerations and uncertainties. Strontium isotopes are typically discussed as recording primarily geographic information (place of origin) that can be used to infer the movements of individuals through different phases of their lives. Yet, strontium is incorporated into the body through the foods consume, as are 13C and 15N, raising the question of whether strontium ratios are informing primarily about movement of the individual or changes in the diet. Inferring human movement across landscape thus relies on demonstration that observed values could not have come from local sources and required inputs from other geographic regions. Contemporary biogeochemical records are necessary to resolve these possibilities. Refinements in the developmental age estimates for the specific sampling locations on human teeth enable the integration of additional isotopic data through matching of biochemical signatures obtained from dentin and enamel micro-samples. Using multi-isotopic dietary modeling allows better assessment of relative contributions to overall diet of food groups such as terrestrial large game, lake or riverine fish, seal, and plants (inner bark, willow shoots, mushrooms). Notable variability between human molars and adult bone strontium isotopic ratios has been inferred as representing the presence of non-locals at the Shamanka II cemetery. Dietary reconstruction suggests that plants are the primary variable responsible for this “mobility” indicator.

Strontium sintered calcium sulfate bone graft for enhancing osteogenesis in a rat femoral defect model

Strontium-containing calcium sulfate hemihydrate has been widely investigated in bone tissue engineering in recent years. The sensitive dose-dependent effect of strontium ions limits the clinical applications due to the uncontrollable release property of fabricated bone substitutes. The purpose of our study was to design a novel strontium sintered calcium sulfate anhydrate scaffold possessing a tailored released concentration and further in vivo bone regeneration. The in vitro biocompatibility, toxicity and differentiation of MC3T3E1 cells were evaluated by using different concentrations of SrCl2 and various weight ratios of strontium sintered calcium sulfate scaffolds. For the in vivo studies, we designed a critical-sized femoral defect model of rats transplanted with different weight ratios of strontium-substituted scaffolds to study new bone regeneration. In vitro data suggested that a Sr2+ concentration below 10−4 M had a positive effect on the osteogenic differentiation of MC3T3E1 cells. The enhanced cell viability, osteogenic profiles, bone mineralization and promising cellular proliferation were measured in 1% and 5% weight ratios of strontium-substituted scaffolds. Runt-related transcription factor 2 (RUNX2)-mediated osteogenesis was associated with the activation of extracellular signal-related kinase (ERK) signaling pathways in MC3T3E1 cells cultured in scaffold extracts. The in vivo experiments revealed that these sintered scaffolds showed acceptable biodegradability in X-ray and micro-CT images at the 12th week. Histological analysis showed intact surrounding bone regeneration, more osteoid formation, neovascularization and less fibrotic tissue in the 1% weight ratio of strontium sintered calcium sulfate scaffolds, suggesting that this sintered scaffolds weight ratio possesses potential for application in bone tissue engineering.

The determination of the isotopic composition of strontium

If the process of instrumental isotopic fractionation in thermal-ionization mass spectrometry is modeled in terms of Rayleigh's distillation, the values of the isotopic ratios of strontium in a sample material can be calculated by distributions of measured ratios obtained by instrumental runs in which the process of isotopic fractionation in the sample reservoir more closely fitted the modeled behavior. Such runs can be recognized because are known, in the modeled conditions, the values of the slopes of distributions of measured values of isotopic ratios which are characterized by an equivalent difference in nominal mass between the isotope at the numerator and the isotope at the denominator (distributions 88Sr/87Sr vs. 87Sr/86Sr, and 88Sr/86Sr vs. 86Sr/84Sr). The instrumental runs that more closely fitted the theoretical conditions are characterized by the lowest deviations between the observed value of the slope of the distribution and the respective theoretical value. This model of calculation was used to determine the true/initial values of the isotopic ratios of strontium in the NIST SRM 987 by two independent sets of instrumental runs. In the first set the 86Sr, 87Sr and 88Sr peaks were sampled, and the 87Sr/86Sr ratio and the 88Sr/87Sr ratio were the ratios characterized by an equivalent difference in nominal mass between the isotope at the numerator and the isotope at the denominator. In the second set, the 84Sr, 86Sr and 88Sr peaks were sampled, and the 86Sr/84Sr ratio and the 88Sr/86Sr ratio were the ratios characterized by an equivalent difference in nominal mass. The first set of instrumental runs gives calculated true/initial 88Sr/86Sr values in the range 8.275 ± 0.019, and 87Sr/86Sr values in the range 0.7060 ± 0.0008 (errors are 1σ). The second set gives 88Sr/86Sr values in the range 8.249 ± 0.019 and 84Sr/86Sr in the range 0.05734 ± 0.00017 (1σ).

The role of vegetation in setting strontium stable isotope ratios in the Critical Zone

At Earth9s surface the stable isotope ratio of strontium (⁸⁸Sr/⁸⁶Sr) is predominantly set by biological uptake of Sr and its storage in plant litter. This conclusion was reached from a stable isotope mass balance that was independently validated by direct determination of elemental fluxes between the Critical Zone compartments (rock, soil, vegetation, and stream water) of three field sites located in the Swiss Alps, the US Sierra Nevada, and the tropical highlands of Sri Lanka. These sites cover a gradient in erosion rates, which is inversely related to the residence time of solids in the Critical Zone thereby constituting an “erodosequence”. For eroding landscapes, previous stable isotope models predicted that isotope ratios are set by the rate at which secondary solids form during the conversion of rock to regolith. Counter to this expectation we found that, after release from primary minerals, Sr is partitioned into one fraction taken up by plants and the remainder into dissolved Sr flux. The formation of secondary weathering products such as clays and oxides plays a subordinate role in determining the Sr budget. A Sr isotope fractionation factor for biological uptake was determined for each of the three ecosystems from the average Sr stable isotope composition in bulk plants and its dissolved counterpart in stream water. This fractionation factors range from <i>ca</i>. −0.3 ‰ for the Alps and Sierra Nevada to ∼0 ‰ for the tropical Sri Lanka site. That these isotope fingerprints caused by biologic uptake are preserved means that more Sr was physically removed in plant litter than recycled. Such Sr removal in plant litter appears to be strongest at the slowly-eroding site, whereas the dissolved Sr export by streams is highest at the site with the fastest erosion rate. There, all Sr taken up by plants is returned from litter back into solution. The site with short residence time of solids is the only one at which parent material and dissolved export differ in their Sr isotope composition. Our study shows that the behavior of Sr in the Critical Zone is in stark contrast to that of metals of which the isotope fractionation is not affected by biological uptake (for example lithium, mostly set by formation of secondary solids) or affected by both secondary solid formation and biological uptake (for example silicon). Strontium stable isotope signatures offer the new opportunity to quantify nutrient cycling in the Critical Zone as a function of environmental and ecological parameters.

Dissolved rubidium to strontium ratio as a conservative tracer for wastewater effluent-sourced contaminant inputs near a major urban wastewater treatment plant

Municipal wastewater (MWW) effluent discharges can introduce contaminants to receiving waters which may have adverse impacts on local ecosystems and human health. Conservative chemical constituents specific to the MWW effluent stream can be used to quantify and trace wastewater effluent-sourced contaminant inputs. Gadolinium (Gd), a rare earth element used as a contrasting agent in medical magnetic resonance imaging, can be found in urban MWW streams. Dissolved anthropogenic Gd has been shown to be an indicator and potential conservative tracer for MWW effluent in receiving waters. Like other known MWW tracers, it can be difficult and expensive to measure. Dissolved rubidium (Rb) to strontium (Sr) ratio enrichment in biological materials such as blood and urine can lead to enriched Rb/Sr values in MWW effluent relative to natural waters. This ratio is relatively easy and inexpensive to measure and represents a promising additional indicator for MWW effluent in receiving waters in urbanized freshwater systems. In July 2015 and 2016 surface water samples were collected from sites in the tidal-fresh Potomac River in the vicinity of the Blue Plains Advanced Wastewater Treatment Plant (BPAWWTP) outfall near Washington, DC USA along with treated MWW effluent samples from the BPAWWTP. Dissolved Rb/Sr ratios were measured in these waters and compared to dissolved Gd concentrations in order to demonstrate the potential of the dissolved Rb/Sr ratio as a conservative indicator for MWW effluent. Results suggest the dissolved Rb/Sr ratio represents a simple and cost-effective indicator and conservative tracer for MWW effluent. It can be used with, or in place of, other proven tracers to investigate wastewater impacts in highly-urbanized, anthropogenically-impacted freshwater systems like the tidal fresh Potomac River and perhaps in a wider range of geologic settings than previously thought. A case study is presented as an example to demonstrate the potential of using dissolved Rb/Sr ratios to trace MWW-sourced nutrient inputs from a major WWTP like BPAWWTP to the receiving waters of tidal-fresh Potomac River.