Mixing Model Research Articles

Feeding habits of a latest Pleistocene megamammal community. A synecological perspective by stable isotopes analysis

The coexistence and interaction between the Pleistocene megamammals and the first human groups have been mainly addressed extrinsically, without considering the megafauna's paleoecology. This study used the stable carbon and oxygen isotopic composition of carbonate fraction of well-preserved fossils to deepen the knowledge of these latest megamammals. We focus on an Argentine Pampas area, where they are concentrated archaeological and paleontological contexts with radiocarbon ages for the final Pleistocene. We employ Bayesian mixing models, built through quantitative diet information for modern analogs, a novel methodological approximation for the study area. The results indicate that the megamammals of the final Pleistocene Pampas were in equilibrium with the ecosystem, showing signs of resource natural cycles. Those rhythms suppose differential distribution and availability of these animals.

Prehistoric human diet composition in Northwest Patagonia: Complementing isotopic analysis with zooarchaeological information

AbstractIn this work, we study diet composition of prehistoric human populations of Northwest Patagonia by exploring the combination of two different approaches frequently used in bioarchaeology, Bayesian isotope mixing models, and zooarchaeological analysis. For this purpose, we compiled a large dataset of previously published δ13C and δ15N human and resource values, as well as zooarchaeological data, corresponding to the Middle–Late Holocene and distributed throughout Northwest Patagonia. We first propose a replicable approach to divide the region into different areas comprising human individuals that shared the same available resources and perform isotope mixing models at individual level using default (i.e., uninformative) prior distributions in the Bayesian mixing models. Then, we explore a potential complementation of isotopic and zooarchaeological evidence by introducing the frequency of zooarchaeological assemblages with the different resources, as well as NISP, as priors in the Bayesian mixing models to guide diet estimations. Additionally, we use these frequencies to analyze the possible absence of some important resources in previous analyses. Based on the species distribution and geographical location of bioarchaeological sites, we divided the region into five areas (Northwest and Northeast Neuquén, South Neuquén/Rio Negro, and Southwest and Central‐east Mendoza) that differ in the resources available for potential human consumption. The results obtained show high diet variability among these areas, with individuals from Northwest and Northeast Neuquén consuming mainly large animals (i.e., guanaco and rhea, respectively) and South Neuquén/Rio Negro and Center‐east and Southwest Mendoza consuming a larger diversity of resources. Our results show that considering zooarchaeological priors in the analyses results in diet composition estimations more in line with the ecological diversity present in the region than previous estimations. We propose that approaches like this, which are common in ecological studies, should be considered in bioarchaeology to make more robust estimates of diet composition.

Influence of subducted carbonate on the composition of basalts in the Paleo-Asian Ocean domain

The fate of subducted carbonate of the Paleo-Asian Ocean and its control on the compositional variability of Cenozoic basalts to the west of the Daxing'anling–Taihang Gravity Lineament remain uncertain. Here we report major- and trace-element contents and Zn–Sr–Nd isotopic data for Cenozoic basalts from eastern Mongolia. The studied basalt samples from eastern Mongolia are classified as nephelinite, basanite, alkaline basalt, and tholeiite. They have different Zn–Sr–Nd isotopic compositions (δ66Zn = 0.38‰ ± 0.02‰ to 0.50‰ ± 0.04‰, 87Sr/86Sr = 0.704239–0.705175, εNd = 4.72–5.67) but display trace-element signatures of sedimentary marine carbonate, reflecting mantle heterogeneity and marine carbonate imprint. Compared with the high-Si tholeiites, which were erupted over thinner lithosphere, the nephelinites–basanites–alkaline basalts erupted over thicker lithosphere have higher δ66Zn values, La/Yb, Sm/Yb, and Nb/Y ratios, and Nb contents, indicating that these low-Si basalts were the product of lower-degree melting of carbonated mantle under higher pressure. By combining our data with available data for Cenozoic basalts from central Inner Mongolia, we suggest that the compositions of the nephelinite–basanite–alkaline-basalt–tholeiite suite show systematic spatial variation with respect to the northward subduction zone of the Paleo-Asian Ocean. The tholeiites, which have lower δ66Zn values, SiO2 contents, and Sm/Yb ratios, are dominant near the subduction zone, whereas the basanites and alkaline basalts, which have higher δ66Zn values, Sm/Yb ratios, and SiO2 contents, are dominant in the region far from the subduction zone. On the basis of a mixing model for Sr–Nd–Zn isotopic compositions, we suggest that the mantle source of the basanites and alkaline basalts incorporated a higher proportion of marine carbonate, whereas the tholeiite mantle source incorporated a higher proportion of siliceous sediments. We deduce that with increasing depth of slab subduction, more sedimentary carbonates and lesser siliceous sediments were released from the subducted slab.

Distribution, bioaccumulation, and trace element transfer among trophic levels in the southeastern Gulf of California

Our understanding of the trophic transfer of pollutants in marine subtropical ecosystems remains limited due to the complexity of their food webs. Thus, we aimed to evaluate Cd, Cu, Mn, Pb, and Zn sources, incorporation, and trophodynamics throughout the food web of the southeastern Gulf of California by stomach content analysis, stable isotope analysis, isotope mixing models, and trace element analysis in biological and environmental matrices. The food web comprised three main trophic guilds (TG1, TG2, and TG3). The bioaccumulation of Cd and Zn from seawater was efficient (> 1000) in TG2 and TG3. Bioaccumulation factor from sediment (BSAF >1) evidenced of Cd in all trophic guilds. In addition, non-trophic Cd relationships were identified in the food web. Based on the trophic magnification factor (TMF), Mn and Pb showed biodilution (TMFMn = 0.38; TMFPb = 0.16), while Cu and Zn exhibited biomagnification (TMFCu = 2.08; TMFZn = 3.31).

An investigation of non-canonical mixing in red giant stars using APOGEE 12C/13C ratios observed in open cluster stars

ABSTRACT Standard stellar evolution theory poorly predicts the surface abundances of chemical species in low-mass, red giant branch (RGB) stars. Observations show an enhancement of p–p chain and CNO cycle products in red giant envelopes, which suggests the existence of non-canonical mixing that brings interior burning products to the surface of these stars. The 12C/13C ratio is a highly sensitive abundance metric used to probe this mixing. We investigate extra RGB mixing by examining: (1) how 12C/13C is altered along the RGB, and (2) how 12C/13C changes for stars of varying age and mass. Our sample consists of 43 red giants, spread over 15 open clusters from the Sloan Digital Sky Survey’s APOGEE DR17, that have reliable 12C/13C ratios derived from their APOGEE spectra. We vetted these 12C/13C ratios and compared them as a function of evolution and age/mass to the standard mixing model of stellar evolution, and to a model that includes prescriptions for RGB thermohaline mixing and stellar rotation. We find that the observations deviate from standard mixing models, implying the need for extra mixing. Additionally, some of the abundance patterns depart from the thermohaline model, and it is unclear whether these differences are due to incomplete observations, issues inherent to the model, our assumption of the cause of extra mixing, or any combination of these factors. Nevertheless, the surface abundances across our age/mass range clearly deviate from the standard model, agreeing with the notion of a universal mechanism for RGB extra mixing in low-mass stars.

Microplastic transport dynamics in surcharging and overflowing manholes

The transport of microplastics within urban water systems remains poorly understood, with little prior research on their behaviour within manhole configurations. This study represents the first to measure and model the transport dynamics of microplastics within circular and square manholes under different hydraulic scenarios. The transport and fate of polyethylene (PE) was quantified and compared to solutes (Rhodamine WT dye) using energy losses, residence time distributions (RTDs), and mixing models within surcharging and overflowing manholes. The bulk mass of solute and PE concentrations followed similar flow paths across all conditions except for 17.3 ± 7.9 % of PE mass that was immobilized in a dead zone above the inlet pipe for manholes with a surcharge to pipe diameter ratio ≥2. Consequently, these microplastics only exit after a significant change in hydraulic regime occurs, causing microplastics to be at risk of being contaminated over a prolonged duration. No significant mixing differences for PE and solutes were found between manhole geometries. The deconvolution method outperformed the ADZ model with goodness of fit (Rt2) values of 0.99 (0.60) and 1.00 (0.89) for PE and solute mixing, respectively. This establishes the deconvolution method as the most accurate and appropriate model to accurately predict microplastic mixing in manholes and urban drainage systems.

Temporal sediment source tracing during storm events in the black soil region, Northeast China

Sediment fingerprinting technology is widely used to differentiate sediment sources. However, despite its long-recognized benefits, there it has been seldom applied to assess the variability of sediment sources during storm events. In this study, sediment fingerprinting is used for four storm events to determine the dynamic changes in sediment sources throughout them in the black soil region in Northeast China. Three potential sediment sources—cultivated land, unpaved roads, and gullies—were effectively differentiated using four geochemical tracers (As, Be, Cs, and Cu), with an accuracy of 100%. The relative sediment contribution from each source was determined using linear and Bayesian mixing models. The mean absolute fit (MAF) values of the linear mixing model (MAFmean = 0.976–0.949) were higher than those of the Bayesian mixing model (MAFmean = 0.921–0.992), indicating that the first performed better. Cultivated land was the primary source of the sediment load, accounting for 59.03% of it (load-weighted mean = 68.29%), followed by the gullies (37.15%, load-weighted mean = 28.09%), and unpaved roads (3.90%, load-weighted mean = 3.69%) for the four storm events. In addition, a high variability in sediment source contribution was observed during the storm events. Cultivated land was the dominant sediment source during storm events with higher sediment concentrations (logarithmic function, r2 = 0.878, p < 0.01), discharge (linear function, r2 = 0.452, p < 0.05), and sediment flux (logarithmic function, r2 = 0.857, p < 0.01), whereas the reverse was observed for gullies. Contrastingly, the contribution of sediment from unpaved roads remained relatively stable during rainfall events. This provides a potential means to assess dynamic changes in sediment contributions from different erosion units. Moreover, it provides data support for exploring soil erosion mechanisms and effective erosion control in the black soil region in Northeast China.

Reinterpreting the Polluted White Dwarf SDSS J122859.93+104032.9 in Light of Thermohaline Mixing Models: More Polluting Material from a Larger Orbiting Solid Body

The polluted white dwarf (WD) system SDSS J122859.93+104032.9 (SDSS J1228) shows variable emission features interpreted as originating from a solid core fragment held together against tidal forces by its own internal strength, orbiting within its surrounding debris disk. Estimating the size of this orbiting solid body requires modeling the accretion rate of the polluting material that is observed mixing into the WD surface. That material is supplied via sublimation from the surface of the orbiting solid body. The sublimation rate can be estimated as a simple function of the surface area of the solid body and the incident flux from the nearby hot WD. On the other hand, estimating the accretion rate requires detailed modeling of the surface structure and mixing in the accreting WD. In this work, we present MESA WD models for SDSS J1228 that account for the thermohaline instability and mixing in addition to heavy element sedimentation to constrain accurately the sublimation and accretion rate necessary to supply the observed pollution. We derive a total accretion rate of , several orders of magnitude higher than the estimate obtained in earlier efforts. The larger mass accretion rate implies that the minimum estimated radius of the orbiting solid body is = 72 km, which, although significantly larger than prior estimates, still lies within the upper bounds (a few hundred kilometers) for which the internal strength could no longer withstand the tidal forces from the gravity of the WD.

Iron, boron, and sulfur isotope constraints on the ore-forming process of subseafloor replacement-style volcanogenic massive sulfide systems

The well-preserved Ashele subseafloor replacement-style volcanogenic massive sulfide (VMS) deposit in the Central Asian Orogenic Belt comprises two stages of Cu mineralization, i.e., early massive sulfides dominated by colloform and euhedral pyrite intergrown with chalcopyrite and sphalerite, which were replaced by late vein-dominated chlorite-chalcopyrite assemblages. In this study, a combined systematic Fe, B, and S isotope investigation was first applied to investigate the sulfide precipitation processes and the relative proportion of fluid sources in different alteration and mineralization stages of the Ashele deposit. Boron isotopes of Mg-rich tourmaline (δ11B from −5.57‰ to −2.73‰, average (avg.) −4.23‰) indicate significant seawater (∼19%) participated during the formation of massive sulfides. A two-component mixing model is used to estimate the contribution of seawater and igneous sulfur to the total sulfur budget, and the results show the increasing contribution of magmatic sulfur from the early (35%) to late (76%) stages. In addition, δ56Fe values of pyrite gradually increase from the massive ore (−0.46‰ to −0.02‰, avg. −0.24‰), quartz-pyrite (−0.09‰ to 0.07‰, avg. −0.01‰), chlorite-chalcopyrite-quartz-pyrite (0‰ to 0.21‰, avg. 0.08‰) to the quartz-sericite zone (−0.02‰ to 0.29‰, avg. 0.14‰), which is likely related to the different extent of isotopic exchange and formation temperature, and could be used in the exploration of VMS systems. The new two-stage ore-forming model shows that in the early stage, rapid mixing of hydrothermal fluid from underlying magma chamber with abundant cold seawater led to rapid deposition of pyrite and associated Cu mineralization under relatively oxidized condition, and long-term hydrothermal activities in relatively closed systems would promote the formation of upper massive ores, which resulted in an equilibrium system between pyrite, chalcopyrite, and associated fluid with wide ranges of δ56Fe in pyrite (−0.46‰ to −0.02‰) and chalcopyrite (−1.56‰ to −0.49‰). The late hydrothermal activities in relatively open system would contribute to stringer sulfides or stockworks underlying the massive ore in relatively reduced conditions with heavier Fe isotope compositions in pyrite (−0.09‰ to 0.29‰) and chalcopyrite (−0.60‰ to −0.04‰). Overall, our study demonstrates that the coupling of B, Fe, and S isotopes could be a useful tool to indicate long-term subseafloor infilling and replacement processes for subseafloor replacement-type VMS deposits, which are the prerequisite to form large-tonnage VMS deposits.

Nitrogen uptake by methanotrophic consortia in deep-water gas hydrate-bearing sediments

Methane-consuming microbes inhabiting marine methane seeps have recently been found to have the capacity to assimilate inorganic nitrogen, suggesting a previously unaccounted role in the global nitrogen cycle. Despite ex-situ experimental observations, definitive evidence of this process under in-situ conditions remains elusive, hindering the complete understanding of the controlling factors and magnitude of this process. We present the isotopic variations of organic carbon δ13Corg and total nitrogen δ15N values in two sediment cores collected from the gas hydrate-bearing Håkon Mosby Mud Volcano, SW Barents Sea (72°N, ∼1260 m water depth). We identified a stratigraphic interval containing methane-derived carbonates directly overlying a gas hydrate layer at 67 cm and typified by δ13Corg and δ15N as low as −42.0‰ and 1.2‰, respectively. Stable isotope mixing models confirm in-situ nitrogen uptake by methanotrophic consortia, contributing to up to 49.1 wt% of the local bulk sedimentary organic matter – a finding calling for reevaluation of the role of methane seeps in the oceanic nitrogen cycle.

Quantitative comparison of the performance of vapor compression cycles with compressor vapor or liquid injection

Increasing the Coefficient of Performance (COP) of vapor compression cycles has been a major focus for decades. Significant improvements can be brought by modifying multistage compressor to flooded single-stage compressor to approach isothermal compression. This work presents the comparative analysis of the cycle performance of a flash tank economized system (FTES), multiple refrigerant injection system (MRIS) and an oil flooded system (OFS). Thermodynamic models of each of these systems using ideal mixing models of refrigerants with the flooding agents are presented. Additionally, mixing effectiveness is introduced as a metric to evaluate the non-ideal mixing of the OFS. Results show that in MRIS, an increase in the number of injection ports significantly increases the COP of the cycle between 18% and 51% for air conditioning and refrigeration applications. The OFS shows that increasing the oil mass flow rate increases the COP significantly above the baseline cycle, benefiting higher temperature lift applications. At evaporating temperature of -40 ℃, relative COP for MRIS with 2 injection points is 7.5% higher than FTES and 5.0% higher than OFS. Further, quantification of the influence of the non-ideal mixing model for OFS showed that a mixing effectiveness of 80% results in 21% degradation of system COP suggesting the ideal mixing assumption has significant influence on the potential for an OFS.

Temporal variations of mangrove-derived organic carbon storage in two tropical estuaries in Hainan, China since 1960 CE

Mangrove wetlands are important sites of carbon burial amounting to 15% of the global total for coastal environments even though they comprise only 0.5% of the coastal area. Carbon fixation and burial in mangrove wetlands are sensitive to environmental changes but difficult to quantify. In this paper, records of mangrove-derived organic carbon (OC) burial were analyzed for two mangrove wetlands, Bamen Bay estuary (BMB) and Danzhou Bay estuary (DZB), in Hainan Province, China, over timescales of the last few decades. The mangrove-specific biomarker taraxerol and the more established proxies of C/N ratio and δ13C of bulk OC were used to investigate OC sources and burial history. A mixing model based on C/N ratios, bulk OC δ13C values and taraxerol concentrations indicates that mangrove-derived OC accounts for 25 ± 14% (mean ± SD) of sedimentary OC burial in (BMB and 16 ± 7% in DZB since 1960 CE. The estimated top 100 cm organic carbon storage was 242 Mg/ha in BMB and 89 Mg/ha in DZB. The carbon sequestration rate in BMB increased from 0.29 Mg/ha/yr to 6.54 Mg/ha/yr after 2012 CE, likely as a response to local mangrove protection since 1981 CE. Compared to the less-protected DZB, mangroves in BMB contributed 31% more to the sedimentary OC pool after mangrove protection, suggesting that mangrove protection has the potential to increase ecosystem health and to increase carbon burial in coastal wetlands.

Transformation of dissolved organic matter and related arsenic mobility at a surface water-groundwater interface in the Hetao Basin, China

Porewater arsenic mobility above the groundwater table has been recognized as a potential cause of arsenic-rich groundwater, but the processing pathways of dissolved organic matter (DOM) in that hyporheic zone and their effect on porewater arsenic release remain poorly understood. To address these issues, two porewater profiles were sampled in a surface water-groundwater interaction zone from the Hetao Basin, China, to monitor the porewater geochemistry and DOM molecular characteristics. The results show that the porewater arsenic, Fe(II), and DOC concentrations were all significantly higher than those of the intruding pond water, and were located above the conservative mixing model lines. This indicates a net release of these solutes from the sediment. By comparing the porewater with pond water DOM, we found that the carboxyl-rich alicyclic molecules (CRAM) were selectively preserved, carbohydrates and aliphatics/proteins were preferentially consumed, and low O/C-ratio compounds with high bioproduction index (I_bioprod) and terrestrial index (I_terr) were produced. The transformation of CHO to CHOS compounds also represented a pathway of recalcitrant DOM production. The produced recalcitrant organic compounds mostly contributed to the elevated porewater DOC concentrations, but their contribution decreased along the filtration path. The consumption of labile DOM compounds would be responsible for Fe(III) hydroxide reduction and arsenic release. The generated recalcitrant DOM may also be a driver of porewater arsenic mobility by acting as electron shuttles. This study highlights the importance of the hyporheic zone in shaping shallow groundwater DOM composition and the potential contribution to arsenic enrichment.

Modeling mixing kinetics for large-scale production of Ultra-High-Performance Concrete: effects of temperature, volume, and mixing method

The mixing of ultra-high-performance concrete (UHPC) featuring low water-to-binder ratios involves different evolution of microstructures and mixing torques from conventional concrete. This paper investigates the mixing kinetics of UHPC in the mixing process, presents a mixing kinetics model to predict the mixing torque at an arbitrary time instant, and develops a multi-batching method to reduce the mixing torque for large-volume production of UHPC. The presented mixing kinetics model considers the effects of mixing temperature, mixing volume, and mixing methods. The mixing kinetics model is calibrated using experimental data, and the calibrated model shows high prediction accuracy. The multi-batching method enables large-volume mixing of UHPC by reducing the mixing torque while retaining desired flowability and hardened properties of UHPC. Specifically, when the number of sub-batches is two, the peak mixing torque of the multi-batching method was approximately reduced to half of the peak mixing torque of the mono-batching method. Besides, the differences in workability, compressive strength, and autogenous shrinkage by using the multi-batching method and mono-batching method are within 5%. Finally, the reliability and repeatability of the presented mixing kinetics model are verified through the validation tests with different UHPC mixture designs and mixing methods. This study will advance understandings of the mixing kinetics for UHPC and promote large-volume UHPC production.

Assessing the contribution of atmospheric transport to phosphorus in the East China Sea using the oxygen isotope in phosphate

Phosphorus is an important nutrient for the growth of marine organisms. External inputs of phosphorus can lead to changes in the primary productivity and may trigger harmful algal blooms. However, few studies have focused on the atmospheric transport of phosphorus to the ocean. We measured the oxygen isotopes in phosphate (δ18Op) and quantitatively determined the contribution of phosphate from atmosphere sources using seawater samples from the East China Sea, a two-component mixing model and a Bayesian isotope mixing model. Our results showed that the δ18Op value retains the signal of the original source and can be used to trace the source of phosphate. The main sources of phosphate in the northeastern East China Sea were from atmospheric inputs, with the contribution of terrigenous phosphate accounting for 56 – 78% of the total. Our findings highlight the importance of the atmospheric transport of phosphate to the ocean, which is important for exploring the mechanisms of harmful algal blooms and in disaster prevention and mitigation.

Demystifying the decadal shift in the extent of groundwater in the coastal aquifers of Gujarat, India: A case of reduced extent but increased magnitude of seawater intrusion

Catastrophic increase in urbanisation and industrialisation along the coastal region leads to increased stress on groundwater reservoirs worldwide. As a growing economy, India faces extreme water crises due to rising water demand and escalating salinisation, specifically in the coastal districts. Therefore, this study shows the implication of a comprehensive modelling approach to assess the spatiotemporal changes in hydrogeochemical processes in the coastal aquifer of the Surat district. Using a multi-model assessment approach, the present study focuses on the decadal evolution in groundwater quality of the coastal aquifers of Surat, Gujarat. Fifty-one groundwater samples were collected for 2008, 2012, and 2018 to assess the spatio-temporal shift in groundwater quality. Piper diagram revealed a shift of hydrogeochemical facies from Mg2+-HCO3− type to Ca2+-Mg2+-Cl− type, indicating the increased salinisation over a decade. The result suggests that rock-water interaction, seawater intrusion mechanism, and anthropogenic activities (intensive agricultural activities and improper waste management) govern the hydrogeochemical processes in the coastal aquifer. A shift of dominance of carbonate weathering to silicate weathering with the dissolution of calcite, dolomite, and gypsum, changing the hydrogeochemistry, was observed over the last decades. This shift leads to the increasing hardness of groundwater. The enrichment of nutrients in groundwater during 2018 (NO3− = 2 to 85 mg. L−1) compared to 2008 (NO3− = 1 to 36 mg.L−1) indicates the increasing imprints of agricultural fertilizer application and human organic waste through sewage contamination on the coastal aquifer. The seawater mixing index model demonstrates that extent of seawater intrusion reduced in 2018 compared to 2012, but the magnitude increased near the coastal talukas (SMI =9.5). The present study helps to understand the increasing anthropogenic activities over a decade leading to increased salinisation and groundwater contamination in the aquifer system. This work can help local stakeholders, water resource managers, and the state government manage the groundwater resources and the future potential threat of aquifer contamination.

Deconvolving mechanisms of particle flux attenuation using nitrogen isotope analyses of amino acids

AbstractParticulate organic matter settling out of the euphotic zone is a major sink for atmospheric carbon dioxide and serves as a primary food source to mesopelagic food webs. Degradation of this organic matter encompasses a suite of mechanisms that attenuate flux, including heterotrophic metabolic processes of microbes and metazoans. The relative contributions of microbial and metazoan heterotrophy to flux attenuation, however, have been difficult to determine. We present results of compound specific nitrogen isotope analysis of amino acids of sinking particles from sediment traps and size‐fractionated particles from in situ filtration between the surface and 500 m at Ocean Station Papa, collected during NASA EXPORTS (EXport Processes in the Ocean from RemoTe Sensing). With increasing depth, we observe: (1) that, based on the δ15N values of threonine, fecal pellets dominate the sinking particle flux and that attenuation of downward particle flux occurs largely via disaggregation in the upper mesopelagic; (2) an increasing trophic position of particles in the upper water column, reflecting increasing heterotrophic contributions to the nitrogen pool and the loss of particles via remineralization; and (3) increasing δ15N values of source amino acids in submicron and small (1–6 μm) particles, reflecting microbial particle solubilization. We further employ a Bayesian mixing model to estimate the relative proportions of fecal pellets, phytodetritus, and microbially degraded material in particles and compare these results and our interpretations of flux attenuation mechanisms to other, independent methods used during EXPORTS.

Less is more? A novel method for identifying and evaluating non-informative tracers in sediment source mixing models

PurposeAccelerated soil erosion poses a global hazard to soil health. Understanding soil and sediment behaviour through sediment fingerprinting enables the monitoring and identification of areas with high sediment delivery. Land-use specific sediment source apportionment is increasingly determined using the Bayesian mixing model MixSIAR with compound-specific stable isotopes (CSSI). Here, we investigate CSSIs of fatty acid (FA) tracer selection with a novel method to identify and investigate the effect of non-informative tracers on model performance.MethodsTo evaluate CSSI tracer selection, mathematical mixtures were generated using source soils (n = 28) from the Rhine catchment upstream of Basel (Switzerland). Using the continuous ranked probability (CRP) skill score, MixSIAR’s performance was evaluated for 11 combinations of FAs and 15 combinations of FAs with δ15N as a mixing line offset tracer. A novel scaling and discrimination analysis (SDA) was also developed to identify tracers with non-unique mixing spaces.ResultsFA only tracer combinations overestimated pasture contributions while underestimating arable contributions. When compared to models with only FA tracers, utilizing δ15N to offset the mixing line resulted in a 28% improvement in the CRP skill score. δ15N + δ13C FA26 was the optimal tracer set resulting in a 62% model improvement relative to δ15N + all δ13C FAs. The novel SDA method demonstrated how δ13C FA tracers have a non-unique mixing space and thus behave as non-informative tracers. Importantly, the inclusion of non-informative tracers decreased model performance.ConclusionsThese results indicate that MixSIAR did not handle non-informative CSSI tracers effectively. Accordingly, it may be advantageous to remove non-informative tracers, and where feasible, all combinations and permutations of tracers should be assessed to optimize tracer selection. Application of these tracer selection steps can help improve and advance the performance of sediment fingerprinting models and ultimately aid in improving erosion mitigation and management strategies.

Transit time estimation of drying springs in Uttarakhand region using environmental tritium concentration

Many parts of the Uttarakhand state, situated in the hilly terrain of the Himalayan region of India are facing acute water crisis due to the drying up of the perennial springs which are the only source of potable water in those regions. Tritium (3H), the radioactive isotope of hydrogen (half-life of 12.32 years) and also a part of water molecule (in the form of HTO) acts as a very useful tracer in estimating the transit time of the hydrological systems. Tritium concentrations of three springs (S-1, S-2 and S-3) were monitored consecutively for three years (2017–2019) to better constrain the transit time estimation. The tritium concentrations of the springs are found to vary between 3.66 and 4.15 TU. All the springs show gradual decrease in tritium concentration with the passage of time indicating the diminishing percentage of freshly recharged modern water component. Among various lumped parameter models, the piston-flow model (PFM), exponential mixing model (EMM), exponential piston-flow model (EPM) and partial exponential mixing model (PEM) have been employed in this study. The historical record of weighted mean concentration of tritium in precipitation available for the Uttarakhand region is taken as input function in the modelling procedure. The application of various LPMs (PFM, EMM, EPM and PEM) indicates that the transit time of the S-1 spring ranges from 1.26 to 1.46 years whereas for S-2 spring, the transit time is found to vary from 5 months to 1.1 years. The MTT of S-3 spring ranges from 5 months to 11 months. The relatively short residence time of these springs indicates the actively recharged system. The estimation of accurate transit time is thus very crucial for understanding the renewability of the spring water systems.

Using mixing models to study human paleodiets in central‐western Santa Cruz (Argentina) during Late Holocene

AbstractDuring the final Late Holocene, there was a socio‐economic reorganization among the people in the central‐western of Santa Cruz, Argentina. Analysis of bone collagen revealed that hunter–gatherer groups maintained a consistent diet rich in steppe animal protein for the past 3000 years. However, there was a change in bioapatite δ13C values in the last 1000 years, indicating a shift in the whole diet that was not reflected in the protein component. This article seeks to evaluate the differential consumption of resources over time and between sexes among hunter–gatherer populations in the region. A total of 39 adult individuals of both sexes, recovered from stone burial structures with different chronologies, were analyzed. Quantitative diet reconstruction was achieved through the use of the Bayesian mixing model known as Food Reconstruction Using Isotopic Transferred Signals (FRUITS). The results show that the guanaco (Lama guanicoe) was the most consumed animal throughout the studied period, considering both temporal and sex differences. Additionally, there is an increased importance of plant consumption in the last millennium, particularly among females. However, this can be the result of overrepresentation of this resource in our food web samples, due to the impossibility of resolving the origin of the carbon for the formation of bioapatite values.