Multi-tracer Approach Research Articles

Understanding complex volcanic hydrosystems using a multi-tracer approach.

Climate change affects groundwater availability and residence times, necessitating a thorough understanding of aquifer characteristics to define sustainable yields, particularly in regions where water is heavily exploited. This study focuses on the Volvic volcanic aquifer (Chaîne des Puys, France), where groundwater recharge has decreased due to climate change, raising concerns about water use sustainability. To address these challenges, this work proposes a multi-tracer approach, based on hydrogeological monitoring, including the estimation of groundwater ages, major elements chemistry and water stable isotopes to better characterise this resource decrease and more peculiarly its origin and its impact on the environment that has never been addressed. Relative fractions of ancient and modern water contributions (up to 20%) to the aquifer have been thus estimated as well as the apparent ages of groundwaters (34years). We highlight the complementarity of tracers used, allowing a better definition of recharge sources and transit times of groundwaters within the aquifer. These results led to the proposal of a hydrogeological conceptual model, highlighting a bi-modal recharge, distinguishing between a long-term recharge upon 30years, supplemented by a recent component (≃ 1year) related to annual precipitation. This study provides valuable information on groundwater circulation and the response of volcanic aquifers systems to climate change, while highlighting the importance of assessing residence times. By addressing the challenges posed by systems with contrasting permeability and recharge gradients, it improves understanding of volcanic hydrology and provides a basis for the development of (numerical) hydrological models to assess the impacts of global change.

Unravelling the magmatic and hydrothermal evolution of rare-metal granites through apatite geochemistry and geochronology: The Variscan Beauvoir granite (French Massif Central)

Peraluminous rare-metal granites (PRMGs) represent highly differentiated crustal granites characterised by extreme enrichment in metals, such as Li, Sn, Nb, Ta, W, and Be. This geochemical specificity is considered to be the result of a succession of magmatic and hydrothermal processes, the importance and individual impact of which are still debated. In this study, we investigate the magmatic and hydrothermal evolution of the Beauvoir leucogranite, a world-class PRMG from the French Paleozoic Variscan belt, through extensive characterisation of suprasolidus to subsolidus apatite. We employ a multi-tracing approach, combining in-situ elemental compositions (major, trace, and halogen elements), oxygen isotopic systematics, and U-Pb geochronology.Four major magmatic and hydrothermal stages were identified through apatite petrography and U-Pb geochronology. Magmatic apatite crystallised at 314.6 ± 4.7 (2s) Ma. Decrease in the amplitude of the Eu anomaly in magmatic apatite from the deeper to shallower granitic units record an increase in the oxygen fugacity (fO2) of the magma with differentiation, likely contributing to the crystallisation of a first and predominant cassiterite generation. Magmatic apatite REE patterns show significant tetrad effects; they reflect the exsolution of magmatic fluids involved in the precipitation of early hydrothermal apatite replacing igneous minerals or precipitating within veins during greisenisation episode dated at 314.3 ± 5.5 Ma and 311.7 ± 8.1 Ma. Early hydrothermal apatite, characterised by enrichment in Sr or S and Mn-REE depletion along with variable Br/I ratios and δ18O compositions down to negative values, record mixing dynamics between two fluid end-members: (i) magmatic fluids, and (ii) oxidising meteoric fluids partially reequilibrated with country rocks. Meteoric fluids progressively invaded the Beauvoir PRMG at temperatures ≥ 450 °C and triggered precipitation of a second generation of cassiterite during mixing with magmatic fluids. Two late, non-magmatic, hydrothermal events are dated at 268.3 ± 20.4 Ma and 148.5 ± 26.6 Ma. Related apatite is marked by specific mineralogical and geochemical features such as high As contents and heavy oxygen isotope signatures. They are proposed to be linked to extension-related regional hydrothermal fluid circulation that contributed to metal endowment (U, F-Ba-Pb-Zn) in the crystalline basement and overlying sedimentary cover of Western Europe following the Variscan Orogeny.Our results demonstrate that apatite is a key mineral to decipher the role of magmatic and hydrothermal processes leading to ore deposition and remobilisation in PRMGs, in relation with geodynamic evolution. Apatite records of external fluid incursions at near-solidus conditions highlight the open system nature of the Beauvoir PRMG, which is crucial for developing fully integrated metallogenic models applicable to similar deposits.

Detecting relativistic Doppler by multi-tracing a single galaxy population

New data from ongoing galaxy surveys, such as the Euclid satellite and the Dark Energy Spectroscopic Instrument (DESI), are expected to unveil physics on the largest scales of our universe. Dramatically affected by cosmic variance, these scales are of interest to large-scale structure studies as they exhibit relevant corrections due to general relativity (GR) in the n-point statistics of cosmological random fields. We focus on the relativistic, sample-dependent Doppler contribution to the observed clustering of galaxies, whose detection will further confirm the validity of GR in cosmological regimes. Sample- and scale-dependent, the Doppler term is more likely to be detected via cross-correlation measurements, where it acts as an imaginary correction to the power spectrum of fluctuations in galaxy number counts. We present a method allowing us to exploit multi-tracer benefits from a single data set, by subdividing a galaxy population into two sub-samples, according to galaxies’ luminosity/magnitude. To overcome cosmic variance we rely on a multi-tracer approach, and to maximise the detectability of the relativistic Doppler contribution in the data, we optimise sample selection. As a result, we find the optimal split and forecast the relativistic Doppler detection significance for both a DESI-like Bright Galaxy Sample and a Euclid-like Hα galaxy population.

Mechanisms of evolution and pollution source identification in groundwater quality of the Fen River Basin driven by precipitation

Groundwater pollution has attracted widespread attention as a threat to human health and aquatic ecosystems. However, the mechanisms of pollutant enrichment and migration are unclear, and the spatiotemporal distributions of human health risks are poorly understood, indicating insufficient groundwater management and monitoring. This study assessed groundwater quality, human health risks, and pollutant sources in the Fen River Basin(FRB). Groundwater quality in the FRB is good, with approximately 87 % of groundwater samples rated as “excellent” or “good” in both the dry and rainy seasons. Significant precipitation elevates groundwater levels, making it more susceptible to human activities during the rainy season, slightly deteriorating water quality. Some sampling points in the southern of Taiyuan Basin are severely contaminated by mine drainage, with water quality index values up to 533.80, over twice the limit. Human health risks are mainly from As, F, NO3−, and Cr. Drinking water is the primary pathway of risk. From 2019 to 2020, the average non-carcinogenic risk of As, F, and NO3− increased by approximately 28 %, 170 % and 8.5 %, respectively. The average carcinogenic risk of As and Cr increased by 28 % and 786 %, the overall trend of human health risks is increasing. Source tracing indicates As and F mainly originate from geological factors, while NO3− and Cr are significantly influenced by human activities. Various natural factors, such as hydrogeochemical conditions and aquifer environments, and processes like evaporation, cation exchange, and nitrification/denitrification, affect pollutant concentrations. A multi-tracer approach, integrating hydrochemical and isotopic tracers, was employed to identify the groundwater pollution in the FRB, and the response of groundwater environment to pollutant enrichment. This study provides a scientific basis for the effective control of groundwater pollution at the watershed scale, which is very important in the Loess Plateau.

Long-term impact of wastewater effluent discharge on groundwater: Identification of contaminant plume by geochemical, isotopic, and organic tracers' approach

Infiltration of effluents from wastewater treatment plants (WWTP) into groundwater can be a source of Contaminants of Emerging Concern (CECs), such as pharmaceutical compounds, that are not fully removed during the treatment processes. A multi-tracer approach, based on hydrogeochemical, isotopic, and organic tracers, is applied in the Vistrenque Aquifer (Gard, France) to assess the dispersion of such unintentional plumes and its potential implication on groundwater quality for CECs in a small catchment area. In this area, a point source of WWTP effluent causes contaminant infiltration and unintentional transfer to the aquifer. This strong impact of an urban effluent was revealed from the Br/Cl ratio, boron concentrations and δ11B isotopic signature of the groundwater in the direct vicinity of the infiltration point. With increasing distance from that point, dilution with groundwater rapidly attenuates the urban signal from these hydrogeochemical and isotopic tracers. Nevertheless, a gadolinium anomaly, resulting from discharges of urban wastewater containing the contrast agents used for magnetic resonance imaging (MRI), highlights the presence of a wastewater plume further along the flow line, that comes with a series of organic molecules, including pharmaceutical residues. Monitoring persistent or reactive molecules along the plume provides a more detailed understanding of the transfer of CECs into groundwater bodies. This highlights the relevance of pharmaceutical compounds as co-tracers for WWTP plume delineation. The present multi-tracer approach for groundwater resource vulnerability towards CECs allows a more in-depth understanding of contaminant transfer and their fate in groundwater.

Nitrate transformation and source tracking of Yarlung Tsangpo River using a multi-tracer approach combined with Bayesian stable isotope mixing model

Excessive levels of nitrate nitrogen (NO3−-N) could lead to ecological issues, particularly in the Yarlung Tsangpo River (YTR) region located on the Qinghai Tibet Plateau. Therefore, it is crucial to understand the fate and sources of nitrogen to facilitate pollution mitigation efforts. Herein, multiple isotopes and source resolution models were applied to analyze key transformation processes and quantify the sources of NO3−. The δ15N–NO3- and δ18O–NO3- isotopic compositions in the YTR varied between 1.23‰ and 13.64‰ and −7.88‰–11.19‰, respectively. The NO3−-N concentrations varied from 0.08 to 0.86 mg/L in the dry season and 0.20–1.19 mg/L during the wet season. Nitrification remained the primary process for nitrogen transformation in both seasons. However, the wet season had a widespread effect on increasing nitrate levels, while denitrification had a limited ability to reduce nitrate. The elevated nitrate concentrations during the flood season were caused by increased release of NO3− from manure & sewage (M&S) and chemical fertilizers (CF). Future endeavors should prioritize enhancing management strategies to improve the utilization efficiency of CF and hinder the direct entry of untreated sewage into the water system.

Using natural gas content of groundwater to improve the understanding of complex thermo-mineral spring systems

The varied gaseous composition of thermo-mineral waters emerging in a non-active zone reflects the diversity and complexity of groundwater pathways and provides important insights into their hydrogeological behaviours. The investigated geochemical content of complex thermo-mineral springs revealed the need to use dissolved gas contents as part of a multi-tracer approach to discriminate processes, geogenic (water–gas-rock interactions), abiotic (geological confinement, flow paths) and biotic activity influencing geochemical of groundwater along regional pathways. Irrespective of the dissolved element content or the water type, examining the overall concentration of dissolved gases enables an effective delineation of regional groundwater flow paths. Using dissolved gas content further contributed to the circumvention of some analytical challenges associated with conventional isotopic or geochemical techniques, often linked to the high concentration of elements such as iron, sulfate, sulfide or other naturally occurring elements content. The primary objectives are to analyse the gas composition of individual springs, to identify the origin of these gases in the groundwater, and to use this gas composition to improve the understanding of the flow patterns contributing to the geochemical diversity observed at the surface. From field investigations in a geologically and structurally complex area of Eastern Corsica (France), three types of gas contents are identified: (type 1) CH4 & H2S-rich, (type 2) N2-rich and (type 3) CO2-rich. The study of these dissolved gases highlights that the wide geochemical diversity of thermo-mineral waters observed here is not only related to the mineralogical composition of the local aquifer but also involves strong and cumulative interactions along deep regional circulation pathways. This approach also reveals a common deep crustal gaseous influence characterised by N2 production, which interacts during up flow with groundwater and then with the local metamorphic or sedimentary rock matrix. The groundwater’s isotopic and geochemical contents are then altered by local lithologies encountered through both abiotic and biotic interactions. Finally, at shallow depths, phreatic groundwater can add its geochemical and isotopic footprint and dilute this complex mixture before groundwater emerges as mineral spring. This paper answers the primary objectives yet further demonstrates that using dissolved gas as a tracer of groundwater flow paths allows a deeper interpretation of surface geochemical and isotopic observations, distinguishes local from regional flow paths, and provides information about processes at the origin of groundwater diversity.The combination of tools presented in this paper (i.e., geochemical, dissolved gas, and isotopic tools) allows the establishment of a reliable regional groundwater flow scheme for thermo-mineral waters in a non-active zone. This scheme is essential to improve thermo-mineral water management, and protection to ensure their sustainable quality in front of increasing anthropogenic and climatic pressures.

Geochemical evolution along regional groundwater flow in a semi-arid closed basin using a multi-tracing approach

Groundwater is the main source for domestic drinking water supply, irrigation, and industrial activities in Zacatecas in central Mexico, a good example for numerous semiarid regions worldwide, however, there is insufficient information about characterization and evolution of the baseline water quality to create hydrogeological conceptual models, fundamentals for the future planning of new sources of groundwater supply for the population, especially under ongoing global climate change conditions. By a multi-method analysis that included geological, geophysical, hydrochemical and isotopic tools this investigation allowed the identification of: a) local flows, represented by shallow groundwater and shallow wells, hosted over basin fill sediments with low average temperatures (≈ 23.3 °C), variation in water types related to anthropogenic activities, low trace elements concentrations, δ18O and δ2H signatures indicating surface water and tritium being present in this system, b) intermediate flows (25 °C), identified in wells with depths of 100 to 200 m, water circulating through the basin fill sediments and the sequence of volcanic rocks characterized by intermediate concentrations of trace elements, and groundwater ages calculated for this system vary from 1,000 to 6,000 years, c) regional flows in volcanic rocks, characterized by groundwater from wells with depths of more than 200 m, high temperatures (up to 31.5 °C) and elevated concentrations of trace elements. The δ18O and δ2H signals are more homogenous and the 14C residence times for this flow system are greater than 8,000 years, and d) regional flows in Cretaceous rocks, with depths greater than 400 m, the highest temperatures (≈ 43.7 °C) and intermediate concentrations of trace elements. The δ18O and δ2H signals are homogenous and δ13C can widely be associated with carbonate shales. The hydrogeochemical evolution has been documented along a 62 km flow line to develop a robust conceptual model, reflecting the water–rock interaction in the system. Physicochemical parameters, as well as major and trace element concentrations, reflect a distinct evolution according to the flow paths and their increase is generally proportional to the residence time. Likewise, processes of dissolution of feldspars and some clay minerals from initial weathering in the basin fill sediments, as well as devitrification of the glassy matrix in the volcanic rocks are taking place in the evolution of the system.The results obtained through the analysis of water–rock interaction in this research can be applied to other semi-arid regions with geogenically impacted aquifers, due to the geological and climatic similarity with numerous volcano-sedimentary basins around the world.

Nitrate dynamics in the streamwater-groundwater interaction system: Sources, fate, and controls

Nitrate (NO3−) pollution has attracted widespread attention as a threat to human health and aquatic ecosystems; however, elucidating the controlling factors behind nitrate dynamics under the context of changeable hydrological processes, particularly the interactions between streamwater and groundwater (SW-GW), presents significant challenges. A multi-tracer approach, integrating physicochemical and isotopic tracers (Cl−, δ2H-H2O, δ18O-H2O, δ15N-NO3− and δ18O-NO3−), was employed to identify the response of nitrate dynamics to SW-GW interaction in the Fen River Basin. The streamwater and groundwater NO3− concentrations varied greatly with space and time. Sewage and manure (28 %–73 %), fertilizer (14 %–36 %) and soil organic nitrogen (12 %–28 %) were the main NO3− sources in water bodies. Despite the control of land use type on streamwater nitrate dynamics in losing sections, SW-GW interactions drove NO3− dynamics in both streamwater and groundwater under most circumstances. In gaining streams, streamwater nitrate dynamics were influenced either by groundwater dilution or microbial nitrification, depending on whether groundwater discharge ratios exceeded or fell below 25 %, respectively. In losing streams, groundwater nitrate content increased with streamwater infiltration time, but the influence was mainly limited within 3 km from the river channel. This study provides a scientific basis for the effective management of water nitrate pollution at the watershed scale.

Multi-tracer approach to constrain groundwater flow and geochemical baseline assessments for CO2 sequestration in deep sedimentary basins

Geological storage of gases will be necessary in the push to net zero and the energy transition to reduce carbon emissions to atmosphere. These include CO2 geological storage in suitable sandstone reservoirs. Understanding groundwater flow, connectivity and hydrogeochemical processes in aquifer and storage systems is vital to prevent risk and protect important water resources, such as the Great Artesian Basin. Here, we provide a ‘tool-box’ of geochemical assessment methods to provide information on flow patterns through the basin's aquifers (changes in chemistry along flow path), stagnant versus flowing conditions (cosmogenic isotopes and noble gases), inter-aquifer connectivity and seal properties (major ions, Sr and stable isotopes), water quality (major ions and metals) and general assessments on residence times of groundwater (cosmogenic isotopes and noble gases). This information can be used with reservoir and groundwater models to inform on possible changes in the above-mentioned processes and serve as input parameters for CO2 injection impact modelling. We demonstrate the use and interpretation on an example of a potential CO2 storage geological sequestration site in the Surat Basin, part of the Great Artesian Basin, and the aquifers that overly the reservoir. The stable water isotopes are depleted compared to average rainfall and most likely indicate greater contributions from monsoonal rain events from the northern monsoonal troughs, where amount and rainout effects lead to the depletion rather than colder recharge climates. This is supported by the modern recharge temperatures from noble gases. Inter-aquifer mixing between the Precipice Sandstone reservoir and the Hutton Sandstone aquifer seems unlikely as the Sr isotope ratios are distinctly different suggesting that the Evergreen Formation is a seal in the locations sampled. Mixing, however, occurs on the edges of the basin, especially in the south-east and east where the Surat Basin transitions into the Clarence-Moreton Basin. Groundwater flow appears to be to the south in the Precipice Sandstone, with a component of flow east to the Clarence-Morton Basin. The cosmogenic isotopes and noble gases strongly indicate very long residence times of groundwater in the central south Precipice Sandstone around a proposed storage site. 14C values below analytical uncertainty, R36Cl ratios at secular equilibrium as well as high He concentrations and high 40Ar/36Ar ratios support the argument that groundwater flow in this area is extremely slow or groundwater is stagnant. The results of this study reflect the geological and hydrogeological complexities of sedimentary basins and that baseline studies, such as this one, are paramount for management strategies.

Radio-optical synergies at high redshift to constrain primordial non-Gaussianity

We apply the multi-tracer technique to test the possibility of improved constraints on the amplitude of local primordial non-Gaussianity, f_NL, in the cosmic large-scale structure. A precise measurement of f_NL is difficult because the effects of non-Gaussianity mostly arise on the largest scales, which are heavily affected by the low statistical sampling commonly referred to as cosmic variance. The multi-tracer approach suppresses cosmic variance and we implement it by combining the information from next-generation galaxy surveys in the optical/near-infrared band and neutral hydrogen (Hi) intensity mapping surveys in the radio band. High-redshift surveys enhance the precision on f_NL, due to the larger available volume, and Hi intensity mapping surveys can naturally reach high redshifts. In order to extend the redshift coverage of a galaxy survey, we consider different emission-line galaxy populations, focusing on the Hα line at low redshift and on oxygen lines at higher redshift. By doing so, we cover a wide redshift range 1≲ z≲4. To assess the capability of our approach, we implement a synthetic-data analysis by means of Markov chain Monte Carlo sampling of the (cosmological+nuisance) parameter posterior, to evaluate the constraints on f_NL obtained in different survey configurations. We find significant improvements from the multi-tracer technique: the full data set leads to a precision of σ(f_NL)<1.

The Value of Going To Sea on Big Ships and the Advantage of Multiple Tracers for GEOTRACES Style Programs

Following a brief description of a typical GEOTRACES oceanographic cruise, this article illustrates the benefits of the multidisciplinary and multi-tracer approach that has characterized GEOTRACES. The value and organization of this type of research cruise—which requires many people and large vessels—are discussed in relation to the resulting carbon footprint and the potential alternatives.

Multitracer Approach to Understanding the Complexity of Reactive Astrogliosis in Alzheimer's Brains.

A monoamine oxidase B (MAO-B) selective positron emission tomography (PET) tracer [11C]-deuterium-l-deprenyl holds promise for imaging reactive astrogliosis in neurodegenerative diseases, such as Alzheimer's disease (AD). Two novel PET tracers ([11C]-BU99008 and [18F]-SMBT-1) have recently been developed to assess the complexity of reactive astrogliosis in the AD continuum. We have investigated the binding properties of SMBT-1, l-deprenyl, and BU99008 in AD and cognitively normal control (CN) brains. Competition binding assays with [3H]-l-deprenyl and [3H]-BU99008 versus unlabeled SMBT-1 in postmortem AD and CN temporal and frontal cortex brains demonstrated that SMBT-1 interacted with [3H]-deprenyl at a single binding site (nM range) and with [3H]-BU99008 at multiple binding sites (from nM to μM). Autoradiography studies on large frozen postmortem AD and CN hemisphere brain sections demonstrated that 1 μM SMBT-1 almost completely displaced the [3H]-l-deprenyl binding (>90%), while SMBT-1 only partly displaced the [3H]-BU99008 binding (50-60% displacement) in cortical regions. In conclusion, SMBT-1, l-deprenyl, and BU99008 interact at the same MAO-B binding site, while BU99008 shows an additional independent binding site in AD and CN brains. The high translational power of our studies in human AD and CN brains suggests that the multitracer approach with SMBT-1, l-deprenyl, and BU99008 could be useful for imaging reactive astrogliosis.

Groundwater Resources of the Transboundary Quaternary Aquifer of the Lake Chad Basin: Towards a Better Management via Isotope Hydrology

A multi-tracer approach has been implemented in the southwestern part of the Lake Chad Basin to depict the functioning of aquifers in terms of recharge, relationship with surface water bodies, flow paths and contamination. The results are of interest for sustainable water management in the region. The multi-layered structure of the regional aquifer was highlighted with shallower and intermediate to deep flow paths. The shallower aquifer is recharged with rainwater and interconnected with surface water. The groundwater chemistry indicates geogenic influences in addition to a strong anthropogenic fingerprint. The intermediate to deep aquifer shows a longer residence time of groundwater, less connection with the surface and no to only a little anthropogenic influence. Ambient Background Levels (ABLs) and Threshold Values (TVs) show the qualitative status of the groundwater bodies and provide helpful information for water resources protection and the implementation of new directives for efficient and more sustainable groundwater exploitation.

Nitrate transformation and source tracking of rivers draining into the Bohai Sea using a multi-tracer approach combined with an optimized Bayesian stable isotope mixing model

Excessive levels of NO3- can result in multiple eco-environmental issues due to potential toxicity, especially in coastal areas. Accurate source tracing is crucial for effective pollutant control and policy development. Bayesian models have been widely employed to trace NO3- sources, while limited studies have utilized optimized Bayesian models for NO3- tracing in the coastal rivers. The Bohai Rim is highly susceptible to ecological disturbances, particularly N pollution, and has emerged as a critical area. Therefore, identification the N fate and understanding their sources contribution is urgent for pollution mitigation efforts. In addition, understanding the influenced key driven factors to source dynamic in the past ten years is also implication to environmental management. In this study, water samples were collected from 36 major river estuaries that drain into the Bohai Sea of North China. The main transformation processes were analyzed and quantified the sources of NO3- using a Bayesian stable isotope mixing model (MixSIAR) with isotopic approach (δ15N-NO3- and δ18O-NO3-). The overall isotopic composition of δ15N-NO3- and δ18O-NO3- in estuary waters ranged from −0.8–19.3‰ (9.3 ± 4.6‰) and from −7.1–10.5‰ (5.0 ± 4.3‰), respectively. The main sources of nitrate in most river estuaries were manure & sewage, and chemical fertilizer, while weak denitrification and mixed processes were observed in Bohai Rim region. A temporal decrease in the nitrogen load entering the Bohai Sea indicates an improvement in water quality in recent years. By incorporating informative priors and utilizing the calculated coefficients, the accuracy of sourcing results was significantly improved. This study highlighted the optimized MixSIAR model enhanced its accuracy for sourcing analysis and providing valuable insights for policy formulation. Future efforts should focus on improving management strategies to reduce nitrogen into the bay.

Stable isotope values (δ 13C, δ 15N) of macroalgal communities at Loch Creran and its relevance for elucidating sources of macroalgal organic carbon in fjordic sedimentary systems

Abstract Here, macroalgal isotopic values from Loch Creran, Western Scotland, were documented to determine the suitability of paired stable isotope analysis for identifying macroalgal-derived organic carbon sources in a fjordic sea loch. Variability in isotopic values (δ 13C and δ 15N) was evident within individual thalli of fucoid and kelp species, at the replicate level and between sampling localities. There were few consistent phylogenetic correlates in the isotopic values of macroalgae. The δ 13C ranges did, however, provide insight into differentiating between carbon sources more broadly, such as terrestrial from marine and between macrophyte lineages. As such, δ 13C could be indicative of the presence of macroalgal carbon sources within pools of organic matter but will likely be ineffective at separating these sources to lower taxonomic levels. Consequently, if these data are used alone to discriminate between macroalgal carbon sources and their relative contribution to a sedimentary pool of organic matter, the development of accurate conclusions will be challenging. The findings presented here demonstrate the need for complementary techniques or multi-tracer approaches to aid in the differentiation between macroalgal carbon sources to lower taxonomic levels rather than relying on stable isotopes as a biomarker alone.

A multi-tracer approach to quantifying groundwater discharge in flat areas

Identifying of groundwater discharge in surface waters is of outstanding interest in order to complete water balance models, understand the dynamics of surface hydrology, or quantify solute contribution, including nutrients and pollutants. This study aims to evaluate groundwater discharge into two small streams in the Atlantic coastal area of the Argentine Pampa Plain and ascertaining the relationship between groundwater age and 222Rn as a discharge indicator. In August 2017, samples were collected from two streams, La Ballenera and Vivoratá, and 222Rn activities, CFCs concentration, ionic composition, EC, and stable isotopes (δ18O, δ2H) were measured. The chemical composition and EC of the two streams was similar. The isotopic composition showed some difference in the Vivoratá stream among the samples close to the headwaters, which are more depleted and have a deuterium excess value similar to the ordinate of the local meteoric line. This behavior is consistent with the dominance of baseflow, with values most depleted appearing upstream and the most enriched being downstream as a result of slight evaporation from the course. The three samples in La Ballenera stream are closer to the global meteoric line, although greater enrichment is observed upstream. 222Rn concentrations were in the range of 1–2.5 Bq.L−1 in both. In the Vivoratá stream, 222Rn showed a tendency to increase in the downstream direction of the flow, while in the La Ballenera stream this trend was observed in the first two sections. CFCs values were significantly homogeneous at all sites. For most of the samples, the recharge year was set between 1987 and 1990, resulting in transit times in the order of 30 years. Combining field measurements of streamflow and EC, laboratory analyses of stable isotopes, CFCs and 222Rn, provides an efficient method for estimating groundwater discharge rates, which is ascertained by water apparent ages.

Hydrochemistry and strontium isotope fingerprints of solute sources and CO2 consumption in Changbai Mountain area, Northeast China.

As one of the most representative forms of groundwater, mineral water provides a critical understanding of regional hydrogeochemical features and rock weathering processes. However, current studies have mostly focused on the quality of mineral water and have rarely addressed the weathering process during its formation. Therefore, a multi-tracer approach combines chemical parameters, major ions, selected trace elements, and 87Sr/86Sr ratios for mineral water samples in Changbai Mountain during 2020-2021. First, we determined the hydrogeochemical characteristics of different types of mineral water. Secondly, the water-rock interaction processes governing the water mineralization were described to fix the hydrogeochemical background. Thirdly, the chemical weathering rate was calculated. The total dissolved load generated by rock weathering was around 6.76 tons/km2/year in the mineral water catchment area; 44.6% and 36.9% of the dissolved load were derived from silicate and carbonate weathering, respectively. The trace carbonates also played an important role in the overall rock weathering. Finally, after fully considering various influencing factors, we concluded that lithological characteristics and the soil environment rich in organic acids were the most important factors affecting rock weathering in the Changbai Mountain area. Overall, this study highlights the mineral water's role in the fluxes of CO2 in local area and reveals possible influence of the unique ecological and geological environment on rock weathering in Changbai Mountain. It can provide a reference for the subsequent assessment of environmental stability for basalt areas and the possibility of sustainable water resources development.

Prevalence of intra-patient inter-metastatic heterogeneity in mCRPC patients based on triple-tracer PET imaging: The 3TMPO study.

5033 Background: Intra-patient inter-metastatic heterogeneity (IIH) has been demonstrated in metastatic castration resistant prostate cancer (mCRPC) patients based on genomic and imaging studies, most often after several lines of therapies. IIH is of utmost importance for PSMA radioligand therapy (RLT) eligibility, biopsy-based precision medicine and/or treatment intensification decision-making. The Triple-Tracer strategy against Metastatic PrOstate cancer (3TMPO) study (NCT04000776) is a prospective multicenter PET imaging study that was designed to determine the prevalence of IIH in mCRPC patients and to determine candidacy for RLT. Methods: 3TMPO is a PET-imaging trial including mCRPC patients showing at least 3 metastases on conventional imaging with evidence of biochemical or radiographic progression, at least 3 months after initiation of the last systemic therapy. 68Ga-PSMA-617 and 18F-FDG PET/CT scans were performed within 10 days and analyzed quantitatively. A third scan with 68Ga-Octreotate was done when a PSMA-/FDG+ lesion was found. For all tracers, positivity of a lesion was defined as its SUVpeak being 1.5 times higher than the SUVmean of the liver. Lesions smaller than 1 cc and likely benign foci of uptake were excluded. IIH prevalence was the primary outcome, defined as the percentage of patients having at least two lesions with discordant features on PET imaging. Results: We included 98 patients in the final analysis. Patients had a mean age of 69 years and a median PSA of 51.1 ng/mL. Number of metastases were &lt;5 in 46.9% and ≥10 in 33.7% of patients and 10.2, 20.4, 18.4 and 51.0% had received 0, 1, 2 or &gt;2 lines of systemic therapies for mCRPC, respectively. Prevalence of IIH was 83.7% based on pre-specified PET criteria. Overall, seven different combinations of lesion phenotypes were found among patients based on FDG and PSMA PETs, and at least one PSMA-/FDG+ lesion was found in 46 patients (46.9%). Of the 44 patients who underwent Octreotate PET, six (13.6%) had at least one Octreotate-positive lesion. In this FDG/PSMA/Octreotate-imaged subgroup, 11 different combinations of phenotypes were observed between metastases of individual patients. Overall, 52.0% (IC95: 41.7-62.2) of patients were found to be candidate for PSMA RLT, but none for Octreotate RLT. Conclusions: The majority of mCRPC patients showed IIH. Based on a multi-tracer approach, up to 11 lesion phenotype combinations were found amongst patients. Correlation of these imaging phenotypes with genomics and treatment response will be highly relevant for optimized precision medicine, especially with respect to PSMA-RLT. Clinical trial information: NCT04000776 . [Table: see text]

Astrocyte Signature in Alzheimer's Disease Continuum through a Multi-PET Tracer Imaging Perspective.

Reactive astrogliosis is an early event in the continuum of Alzheimer's disease (AD). Current advances in positron emission tomography (PET) imaging provide ways of assessing reactive astrogliosis in the living brain. In this review, we revisit clinical PET imaging and in vitro findings using the multi-tracer approach, and point out that reactive astrogliosis precedes the deposition of Aβ plaques, tau pathology, and neurodegeneration in AD. Furthermore, considering the current view of reactive astrogliosis heterogeneity-more than one subtype of astrocyte involved-in AD, we discuss how astrocytic body fluid biomarkers might fit into trajectories different from that of astrocytic PET imaging. Future research focusing on the development of innovative astrocytic PET radiotracers and fluid biomarkers may provide further insights into the heterogeneity of reactive astrogliosis and improve the detection of AD in its early stages.