Geochemical Tracers Research Articles

Agricultural abandoned lands as emission sources of dust containing metals and pesticides in the Sonora-Arizona Desert.

This investigation examines the transport of metal- and pesticide-polluted dust emitted by one of the most relevant agricultural areas of Northwestern Mexico. In the contaminated area, an excessive water extraction of the aquifer and seawater intrusion caused the abandonment of fields, which are pollutant-loaded dust emitters. We used air mass forward trajectories (HYSPLIT) model to obtain particle trajectories in the wind and the use of banned pesticides as geochemical tracers for dust transported by wind. Fifty dust samples from 10 agriculture fields and 26 roof dust of a city close to the agricultural area were analyzed for their contents of zirconium, lead, arsenic, zinc, copper, iron, manganese, vanadium, and titanium, by portable X-ray fluorescence. Nine pesticides were analyzed in the roof dust and agricultural soil samples by gas chromatography. Results show that the distribution of metals was significantly different between active and abandoned fields. Arsenic-lead-copper was mainly concentrated in abandoned fields, while zinc-iron-manganese-titanium was dominant in active fields. Two potential sources of metal contamination were found by principal component analysis (PCA): (I) a mixture of traffic and agricultural sources and (II) a group related to agricultural activities. The occurrence of banned pesticides in dust deposited on roofs collected at nearby cities confirms the atmospheric transport from the agricultural area. The HYSPLIT results indicated that the dust emitted from agricultural fields can reach up to the neighboring states of Sonora, Mexico, and the USA. The impacts that these emissions can have on human health should be studied in future research.

Celebrating a pioneer in geochemical tracer science for groundwater and surface water research: Professor Ian Cartwright

Over a more than 35-year career Professor Ian Cartwright's research has provided advances in the understanding of a wide range of earth-science processes, from metamorphic geology to palaeo-climates, groundwater hydrology, catchment hydrology and geochemistry. His research has predominantly utilised geochemistry, stable and radioactive isotope tracers to understand links between palaeo-climate and groundwater, geochemical processes impacting on groundwater and surface water quality, and metamorphic processes. He has made outstanding contributions to scientific knowledge and training through mentoring numerous PhD and masters students, journal editorial roles – including as a long-time Associate Editor for Applied Geochemistry, and active participation in conferences, professional societies and working groups – such as the Applied Isotope Geochemistry group and the International Association of Geochemistry. As he moves into retirement, we take the opportunity to summarise his impact and contributions across many scientific disciplines and reflect on the significance of his distinguished career.

Investigating Multilayer Aquifer Dynamics by Combining Geochemistry, Isotopes and Hydrogeological Context Analysis

Geochemical tracers have the potential to provide valuable insights for constructing conceptual models of groundwater flow, especially in complex geological contexts. Nevertheless, the reliability of tracer interpretation hinges on its integration into a robust geological framework. In our research, we concentrated on delineating the groundwater flow dynamics in the Innisfil Creek watershed, located in Ontario, Canada. We amalgamated extensive hydrogeological data derived from a comprehensive 3D geological model with the analysis of 61 groundwater samples, encompassing major ions, stable water isotopes, tritium, and radiocarbon. By seamlessly incorporating regional physiographic characteristics, flow pathways, and confinement attributes, we bolstered the efficiency of these tracers, resulting in several notable findings. Firstly, we identified prominent recharge and discharge zones within the watershed. Secondly, we observed the coexistence of relatively shallow and fast-flowing paths with deeper, slower-flowing channels, responsible for transporting groundwater from ancient glacial events. Thirdly, we determined that cation exchange stands as the predominant mechanism governing the geochemical evolution of contemporary water as it migrates toward confined aquifers situated at the base of the Quaternary sequence. Fourthly, we provided evidence of the mixing of modern, low-mineralized water originating from unconfined aquifer units with deep, highly mineralized water within soil–bedrock interface aquifers. These findings not only contribute significantly to the development a conceptual flow model for the sustainable management of groundwater in the Innisfil watershed, but also offer practical insights that hold relevance for analogous geological complexities encountered in other regions.

Geochemical fingerprinting to determine sediment source contribution and improve contamination assessment in mining-impacted floodplains in the Philippines

Constraining the main sediment sources and pathways across landscapes impacted by anthropogenic activity is essential to limit the dispersal of sediment-borne contaminants, especially in global conservation priority areas. This study examined the provenance, partitioning, and enrichment of metals in the floodplain of the mining-affected Santa Cruz catchment, The Philippines. Composite geochemical fingerprinting of fine sediment samples (n = 36) was performed using a stepwise statistical screening procedure (range test, Kruskal-Wallis H test, discriminant function analysis) to derive the optimum set of tracers. Using a standard unmixing model, flood deposits downstream of the mining areas were shown to be predominantly mining-induced (71.9 ± 7.7 %), followed by natural erosion from gullies and stream banks (15.1 ± 11.0 %) and agricultural sediment (13.0 ± 5.1 %). Element partitioning data (Log Kd = 1.3–6.6) during a high flow event indicated that metals are dominantly associated and transported via suspended particulate matter. Background concentrations of Ni and Cr were found to be orders of magnitude higher than the threshold values set by international sediment quality guidelines (SQGs), emphasizing the need for site-specific SQGs in mineralised areas. Enrichment factor values indicated low to significant contamination of flood deposits relative to natural and agricultural sediment (EF 1.0–5.5). Furthermore, it was demonstrated that using different conservative elements could considerably influence the enrichment factor calculation. Based on tracer screening tests, Th was shown to be the most suitable reference element. The findings provide new insights on the application of geochemical tracers in a mining setting and integrating fingerprinting approaches with traditional assessment techniques to improve the reliability of contamination risk assessment in other areas facing similar sediment pollution problems.

Novel Methods for Concomitant Determination of the Stable Zr Isotope Composition, Lu‐Hf Isotope Systematics and U‐Pb Age of Individual Zircons

The stable Zr isotope ratios in zircon yield a novel geochemical tracer that, together with the Lu‐Hf and U‐Pb radiogenic isotope systems, allows for a better understanding of the magmatic evolution of silicate melts. We present a solution‐based procedure for coupled stable Zr, Lu‐Hf and U‐Pb isotope ratio determinations for individual zircons using a 91Zr‐96Zr tracer purified from Hf and a late‐spiking protocol for Zr. This method yields high‐precision Zr and Hf isotope results while maintaining low blank levels for U‐Pb isotope and Lu/Hf ratio determinations. With a two‐fold improvement on the precision relative to previous solution‐based work, we report δ94ZrIPGP‐Zr values (deviation of the 94Zr/90Zr ratio in the sample relative to the IPGP‐Zr reference material) and associated intermediate precisions (2s) for the zircon reference materials 91500, Mud Tank, Plešovice and Penglai of ‐0.041 ± 0.015‰, 0.018 ± 0.013‰, 0.089 ± 0.020‰ and ‐0.117 ± 0.021‰, respectively. Furthermore, this method yields un‐biased δ94ZrIPGP‐Zr and 176Hf/177Hf results for 25‐ng Zr and 0.56‐ng Hf aliquots of the Mud Tank zircon with intermediate precisions (2s) of 0.027‰ and 1.7 ε (parts per ten thousand), respectively. Thus, the presented method is applicable for the analysis of extremely small and rare zircon grains.

Understanding the origins of and influences on precipitation major ion chemistry on the Island of O'ahu, Hawai'i.

Precipitation is the primary groundwater source for the Island of O'ahu, Hawai'i, USA, and is an important source of terrestrial nutrients. Since Pacific Islands are particularly vulnerable to the impacts of climate change, they are important venues for studying the controls on and fluctuations in precipitation chemistry. Spatial variations in some of the dissolved rainfall ions can also be of value as natural geochemical tracers in examining surface and groundwater flow. This study collected and chemically analyzed bulk precipitation from 20 sites across the Island of O'ahu approximately quarterly between April 2018 and August 2021. The new precipitation chemistry data were integrated with previously published precipitation data to characterize major ion composition and examine the atmospheric processes controlling inorganic ion deposition. Linear regression and multivariate analysis were used to quantify the relationships among major ions and to assess the impacts of various environmental and meteorological factors on precipitation chemistry. Ordinary kriging and inverse distance weighted interpolations were conducted to help visualize spatial variations in major ion deposition. The results clearly indicate that ocean sea spray is the primary driver of precipitation inorganic chemistry, with marine sea salt aerosols accounting for more than 90% of the measured ion load. However, they also show that various weather patterns and nutrient sources impact inorganic deposition. Most notably, upper atmospheric transport of Asian continental dust during Hawaiian wet seasons, Ca2+ from local sedimentary deposits, and anthropogenic K+ from agricultural activity appear to be substantial non-marine deposition sources. This study synthesizes data from multiple sources into the most spatially and topographically diverse precipitation collector network on O'ahu to date. The findings from this effort help establish a baseline for assessing future fluctuations in inorganic ion deposition and lay important groundwork for examining connections between precipitation and groundwater chemistry within the study area.

Natural ilmenite reference material for trace elemental in situ microanalysis

Ilmenite is a commonly occurring mineral in both igneous and metamorphic rocks and its major and trace elements have various applications in geology, including as a geothermometer, oxygen barometer, and geochemical tracer. In this study, a 500 g ilmenite megacryst sample (LY) was developed as a reference material for in situ element microanalysis. Twenty-two ilmenite fragments, with grain sizes ranging from 1 to 8 mm, were subjected to major and trace element analysis using electron microprobe analysis (EMPA) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) in four different laboratories. The results indicate that the ilmenite sample is homogeneous with respect to TiO2, FeO, Mg, Sc, V, Cr and Mn, whereas Co and Nb are minor inhomogeneous. Consequently, this sample can be used as a reliable reference material for in situ microanalysis.

Karst Groundwater Vulnerability Determined by Modeled Age and Residence Time Tracers

AbstractKarst aquifers are a vital groundwater resource globally, but features such as rapid recharge and conduit flow make them highly vulnerable to land‐surface contamination. We apply environmental age tracers to the south‐central Texas Edwards aquifer, a karst resource in a rapidly urbanizing and drought‐prone region, to assess vulnerability to land‐surface contamination and risks unique to karst aquifers. We show that vulnerability of Edwards aquifer groundwater follows similar spatial and depth patterns common to porous‐media type aquifers, despite complicated karst hydrogeologic features. Shallow and unconfined parts are more vulnerable to land‐surface contamination than the deeper and confined parts, although even the oldest groundwater is mixed with some recent recharge. When modeled age‐tracer results are coupled with other independent geochemical tracers of water‐rock interaction specific to karst settings, they can yield insight into residence time and associated vulnerability.

Fe–Mg Isotopes Trace the Mechanism of Crustal Recycling and Arc Magmatic Processes in the Neo‐Tethys Subduction Zone

AbstractThere has been intense debate on the mechanism of crustal recycling in subduction zones, and Fe–Mg isotopes may provide new constraints on this issue. This study reports Fe–Mg isotope data for mafic plutonic rocks from the eastern and central Gangdese arc, along with their associated trench sediments in southern Tibet. The δ26Mg values of the eastern Gangdese arc rocks show negative correlations with (87Sr/86Sr)i and (206Pb/204Pb)i values, but positive correlations with εNd(t) and εHf(t) values. Conversely, the δ56Fe values of the eastern Gangdese arc rocks show positive correlations with (87Sr/86Sr)i and (206Pb/204Pb)i values, but negative correlations with εNd(t) and εHf(t) values. The Mg and Fe isotopic compositions of the central Gangdese arc rocks are comparable with those of the eastern ones, but they do not correlate with Sr–Pb–Nd–Hf isotopic compositions. Notably, the Fe–Mg isotopic compositions of most arc rocks fall between those of local trench sediments and the mantle wedge. Combined qualitative analyses and quantitative simulations suggest that: (a) the Fe–Mg isotope variations observed in the eastern Gangdese arc rocks highlight the important role of source mixing between sediment‐derived melts and peridotite, whereas (b) the Fe–Mg isotope variations observed in the central Gangdese arc rocks reflect the superposition of carbonated serpentinite‐derived Mg‐rich fluids‐peridotite source mixing and source melting. The strong correlations between Fe–Mg isotope ratios and traditional geochemical tracers provide further evidence for the recycling of crustal materials in subduction zones via various types of slab‐derived fluids and melts.

LA–ICP–MS analysis of sulfides from the Jianzhupo deposit, Guangxi Province, China: Insights into element incorporation mechanisms and ore genesis

The Jianzhupo deposit, the largest Zn-Sb deposit in the Wuxu orefield in China, contains abundant sphalerite and jamesonite, contrasting with typical Sb deposits elsewhere. Whether the Sb and Zn in the deposit derived from similar parental sources is not clearly resolved. Here, trace-element compositions of sulfides from the deposit were determined by laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS). Results indicate that jamesonite is an important Cd-bearing sulfide with Cd contents of 523–764 ppm and minor or no significant Cd variations were observed within jamesonite crystals. Trace-element compositions of jamesonite indicates that Cd enters the lattice by coupled substitution as 2Fe2+ ↔ Zn2+ + Cd2+. Due to similar geochemical behaviors between Zn and Cd in hydrothermal systems, Zn/Cd ratio of sphalerite was suggested as a robust geochemical tracer to distinguish metal sources in such systems. Here, we summarized the Zn/Cd ratios of sphalerite from various hydrothermal systems and the results show that values between 169 and 233, and lower than 44 are from high- and low-temperature temperature fluid conditions, respectively. Due to different Zn/Cd ratios between sediments and igneous rocks, we conclude that metals in sphalerite from the Jianzhupo deposit were likely derived from granite; in contrast, metals in jamesonite were related to sedimentary rocks. These conclusions are consistent with previous studies on the deposit. Overall, our results indicate that ore-forming fluids of the Jianzhupo deposit were derived from magmatic–hydrothermal and basin water. This study extends the application of trace-element compositions in resolving the sources of sulfides in hydrothermal systems.

Fe–Cu Isotope Characteristics and Geological Significance of the Yushui Seafloor Massive Sulfide Deposit in the Late Paleozoic Marine Depression, Eastern Guangdong Province

The Yong’an-Meixian Late Paleozoic Hercynian depression, located in western Fujian-eastern Guangdong, is an important metallogenic belt in China. The Yushui copper-polymetallic massive sulfide deposit from the middle part of the depression, with extremely high copper grades, has attracted considerable attention and research interest from geologists for years. In most previous research, the ore-forming material source and metallogenic process were inferred from indirect evidence (i.e., using H-O-C-S isotopic systematics as geochemical tracers). In this paper, the ore-forming process of the Yushui deposit has been studied directly by using nontraditional stable (Fe–Cu) isotopes for the first time, providing new evidence for the genesis of this deposit. The results show that there is a relatively negative Fe-Cu isotopic composition in the Yushui deposit, with δ56Fe values ranging from −0.519 to −1.063‰ and δ65Cu values ranging from −1.539 to −1.609‰, respectively. The fractionation of Fe isotopes is primarily attributed to hydrothermal leaching of the basement strata by ore-forming fluids, along with rapid precipitation of sulfides during the ore-forming process. On the other hand, the fractionation of Cu isotopes is probably controlled by the relatively low temperature of ore formation, sulfide precipitation and the involvement of organic matter in mineralization. Combining our findings with previous studies, the ore-forming materials of the Yushui deposit are likely derived from the basement ore-bearing strata (pre-Devonian strata) through leaching by hydrothermal fluids. Moreover, some of the ore bodies might have been locally overprinted by late-stage hydrothermal reworking and alteration.

Lithium partition and isotopic fractionation for cation exchange in clay: Insights from molecular simulations

Chemical weathering is one of the most important processes on the Earth’s surface, and lithium isotopes have been used as a promising tracer of silicate weathering, as the secondary clay minerals precipitated during silicate weathering are thought to preferentially incorporate the lighter 6Li isotope. However, to utilize lithium isotopes as a geochemical tracer, it is essential to quantitatively understand the partitioning of Li in clay minerals, including structurally bound Li and exchangeable interlayer ions, as well as the associated isotope fractionation. With classical molecular dynamic simulations and thermodynamic calculations, the cation exchange between Na-/K-montmorillonite and solvated Li in environmental solution are disclosed under different aqueous activity conditions. The Li+ ion, whose hydration ability is stronger than Na+ and K+ ions, is easier to swell the montmorillonite and shows less affinity for the clay. And the calculated cationic selectivity coefficients between Na+/K+ and Li+ ions are Kc (Li → Na) = 2.0, Kc (Li → K) = 10.0 for Arizona-type montmorillonite and Kc (Li → Na) = 1.0, Kc (Li → K) = 4.0 for Wyoming-type montmorillonite, which are comparable to reported experiments. The cationic partition of Li in the clay interlayer decreases when the hydration states of montmorillonite transform from triple-layer to bilayer and then to monolayer. Based on the density functional theory, the Li isotope fractionations for Li in clay interlayer sites and structural octahedral sites are further derived by thermodynamic calculations with path integral molecular dynamic simulation, which deals with the quantum anharmonicity. The behaviors of Li isotope in the bilayer hydration state closely resembles that in the aqueous solution, and only a slight Li isotope fractionation is found between the monolayer hydrated octahedral-substituted clay and solution phase (Δ7Limonolayer-aq = −2.0‰). While Li isotope fractionation between aqueous solution and mica structural sites is significant (Δ7Listructural-aq = −10.4‰) and shows an obvious quantum anharmonicity, which indicates the importance of the anharmonic treatment for Li isotope fractionation calculations. The newly calculated Li equilibrium isotope fractionation between clay and aqueous solution deviates from the experimentally determined fractionation factor, which can be attributed to the kinetic effects. Moreover, on the basis of the surface kinetic reaction model, the Li isotope fractionation becomes more pronounced with higher clay growth rate. By integrating the cationic selectivity coefficient and Li isotope fractionation, it is possible to constrain the fluid composition during Li-clay deposit and diagenesis, and to evaluate the intensity of chemical weathering processes as well as the related carbon cycle.

The Role of Submarine Groundwater Discharge to the Input of Macronutrients Within a Macrotidal Subpolar Estuary

The major sources of macronutrients (nitrate, ammonium, phosphate, and silicic acid) in Jakolof Bay, Alaska are submarine groundwater discharge (SGD), rivers, and offshore water. We estimated SGD using natural geochemical tracers (radon and radium), a salt mass balance, and a two-component salinity mixing equation based on the change in groundwater salinity on falling lower low tide. Previous studies have hypothesized that the major macronutrient input into Jakolof Bay is offshore water. This study challenges that assumption by determining the relative contribution of macronutrients from SGD relative to offshore water and rivers. Here, SGD is tidally driven and, as the Northern Gulf of Alaska experiences some of the largest tidal ranges in the world, the SGD fluxes from this region are high relative to the global average regardless of local sediment type. The fluxes ranged from 596 ± 85 cm day−1 at low tide to 97 ± 83 cm day−1 at high tide and are predominantly composed of recirculated seawater (89%) rather than freshwater (11%). The major macronutrients in seawater had different input mechanisms into the semi-enclosed bay. SGD and offshore waters contend as the primary sources of nitrate, which is shown to be the limiting nutrient in this coastal area, while SGD dominates the input of silicic acid. Conversely, the aquifer is found to be a sink for phosphate, indicating that the nutrient is primarily sourced from offshore water.

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.

Combining spectral analysis and geochemical tracers to investigate surface water–groundwater interactions: A case study in an intensive agricultural setting (southern Guatemala)

An increase in the frequency of severe hydrological events has highlighted the importance of sustainable water management in intensive agricultural regions. In a warming climate, improved understanding and stewardship of water resources are needed to guarantee water supply, ensure food security, and build resilience against extreme events. In this study, we evaluate a framework that combines spectral analysis and geochemical tracers as a potential tool for (1) gaining valuable insights into surface water (SW)–groundwater (GW) interactions, and (2) providing guidance for improved water management in an intensive agricultural basin in southern Guatemala. The framework proves to be useful in revealing important water dynamics, exposing key feedback mechanisms for water availability and quality. With the use of power density functions and hydrochemistry (T, pH, EC, and major ions), two specific interaction regimes (influent and effluent) were identified and delimited for the main watercourse. These segments are estimated to interact at high rates with the shallow aquifer in the river channel proximities and would lose influence towards the basin flanks. Furthermore, the δ2H and δ18O values indicate that regional groundwater flow systems play an essential role in the basin groundwater recharge. Lastly, we established three influence zones that depict the spatial extent of the SW-GW interactions within the basin. With these zones, we provide recommendations that will allow for further investigation and application into better water management strategies regulating groundwater development and land use activities within the agricultural context of the area.

A method to produce low lead blank silicon dioxide gel as an emitter for isotopic analysis of sub-nanogram lead sample

Lead (Pb) isotopes have been widely used in isotopic dating and geochemical tracing. The rapid development in Earth sciences requires high precision and accuracy of isotopic measurements of low Pb contents or small amounts of samples. However, low ionization efficiency can significantly affect the sensitivity and precision of the measurement. Emitters, such as silicon dioxide (SiO2) gel used in the thermal ionization mass spectrometer (TIMS) measurement of Pb isotopes, can reduce Pb loss at the low-temperature stage and improve Pb ionization efficiency at the high-temperature stage, but they inevitably introduce Pb blank and affect the quality of the results. Therefore, the emitters should possess the features of both high ionization efficiency and low Pb blank. In the present study, a SiO2 gel solution was produced via a double-bottle method and then purified by the Sr-spec® resin. We further measured Pb blank value of this emitter using the isotopic dilution method and examined its ionization efficiency via measuring isotopic composition of standard reference materials of Pb solution and rock powders using different amounts of Pb. Analytical data show that Pb blank values of the twice-purified SiO2 gel solution are lower than 1 pg/μL (lowest value of ∼0.3 pg/μL). Moreover, it can effectively improve Pb ionization, and maintain high and stable ion signal intensity during the measurement runs. Analytical results of Pb isotopic compositions, obtained from nano- to subnano-gram Pb amounts of reference materials, all fall in the ranges of their reference values, meeting the requirements in precision and accuracy for the measurements on micro-samples. This emitter is useful for Pb isotopic measurement of micro-samples and predictable to promote the application of Pb isotopic geochemistry.

Geochemical fingerprint and heavy metals assimilation on grapes from south Lessini (Italy)

ABSTRACT Geochemical fingerprints of grape samples have been defined for 10 cultivars grown in two sampling areas characterized by homogeneous pedological and climate systems in the province of Treviso (northeast Italy). The choice of lithologies was based on the fact that vineyards in Italy frequently grow in both sedimentary soils with various terrigenous carbonate contents and basic volcanic soils. The latter may have high concentrations of heavy metals that are essential for a balanced human diet but can be toxic or harmful if assimilated in excess. To identify possible geochemical tracers within the soil that can be passed to the grapes and possible bioaccumulation of soil-derived elements within the grapes, major and trace elements of the soils, sampled at depths of greater root development, were determined by X-ray fluorescence, and metal concentrations in grape juice were determined by inductively coupled plasma-mass spectrometry. All samples were compared with samples collected at two other sites located in the Euganean Hills, in the southern part of the Veneto region, considering that the wines produced in these areas are exported all over the world.

Utilizing anthropogenic compounds and geochemical tracers to identify preferential structurally controlled groundwater pathways influencing springs in Grand Canyon National Park, Arizona, USA

Study regionThis study focuses on the Colorado River watershed in the area along the South Rim of the Grand Canyon. Study focusThis study utilizes anthropogenic chemical tracers to investigate the fate of treated wastewater effluent discharged within Grand Canyon National Park. Anthropogenic chemical tracers were used to discern preferential structurally controlled pathways in a complex regional network of faults and fractures in which some are conduits and others barriers to flow. New hydrological insights for the regionPrevious investigations on water resources of Grand Canyon have suggested two different discharge locations (Garden Springs versus Monument Spring) for the treated wastewater discharged on the South Rim of Grand Canyon yet the presence of wastewater at the springs remained unstudied for decades. The treated wastewater from Grand Canyon Village is released into Bright Angel Wash that flows along the surface expression of the Bright Angel Fault and past the inferred intersection with the perpendicular Monument Fault. Multiple anthropogenic compounds (pharmaceuticals, per- and polyfluoroalkyl substances (PFAS), and elevated nitrate) were found in Bright Angel Wash and Monument Spring. Stable isotopic measurements at Monument Spring show depletion over time also suggesting contribution from a depleted stable isotopic source found in the treated wastewater. The anthropogenic tracers utilized in this study provide good insight to which geologic structures are conduits versus barriers to flow and can be useful in other fracture flow and karst settings.

Groundwater and pore water inputs to the Bay of Bengal supported by geochemical tracers: Example from Tamil Nadu and Pondicherry, East Coast of India

Submarine groundwater discharge (SGD) and Saline water intrusion (SWI) are the two major processes that influence coastal aquifers resulting in severe water stress. It is essential to characterize groundwater dynamics and discriminate geochemical characterization to understand both approaches. The present study investigates the zones influenced by SGD and SWI along the coastal aquifers of Tamil Nadu and Pondicherry. Pore water (PW) and groundwater (GW) samples were collected during the monsoon season at low tide and analyzed for major ions adopting standard procedures. Hydrogeochemical characterization of water samples revealed by the piper, ionic ratio, ionic delta (Δmi), and seawater fraction (fSea) plots suggest that the PW samples, irrespective of location and GW samples in specific areas, were attributed to SWI, while the remaining samples suggested SGD. The average chloride-attributed SGD flux calculated for PW was 23.45 × 10−7 L cm−2 S−1 and for GW, 0.58 × 10−7 L cm−S−1. Higher fluxes observed in PW suggest seawater recirculation as the primary mechanism, and GW samples were found to be influenced by fresh, recirculated, and saline intrusions. Overall, the northern parts of the study region were influenced by freshwater discharge. However, the central and southern parts of the study regions were influenced by mixed RSGD and SWI water types. The present work suggests locations influenced by fresh, recirculated, and saline water zones that can benefit the stakeholders in planning strategies to identify proper aquifer recharge and suggest ideal pumping scenarios to sustain groundwater resources.

Cadmium isotope fractionation during sorption to soil minerals: Lab evidence and field implication

Stable isotope is a potent geochemical tracer unveiling the dynamic sources of cadmium (Cd) in the environment. However, the sorption process of aqueous Cd onto solid surfaces (e.g., soil) fractionates isotopic signatures, which makes it difficult to interpret its sources and migration processes. Understanding how Cd fractionates during sorption to soil minerals, therefore, provides necessary data to open the isotope fractionation black box of liquid-solid phase partition of Cd. In this study, we explored isotopic fractionation characteristics during Cd sorption to typical soil minerals. Distinct Cd isotope fractionation was observed during sorption, including goethite (∆114/110Cdsolid−solution=−0.51∼−0.47‰), montmorillonite (−0.34∼−0.32‰), quartz (−0.34∼−0.30‰), gibbsite (−0.29∼−0.25‰), and kaolinite (−0.09∼−0.07‰), where lighter isotopes tended to be preferentially sorbed to the solid phase in a reversible manner. We've also conducted a field survey in a historical flooding-affected region to explore Cd isotopic compositions of soil samples adjacent to a polluted creek. Distinct isotopic signatures for surficial soils and deep soils were observed, which was depicted by a binary mixing mode. Leaching of Cd from mine tailings to the creek, as well as its re-adsorption to soil during historical flooding events both led to preferential enrichment of light isotopes in the solid phase, which was consistent with findings from lab sorption experiments. Mineralogical analyses including EPMA, TOF-SIMS, Mössbauer spectra, XRD, and chemical extraction tests, were applied to unveil how Cd was bound to soil minerals at field. Possible linkage between lab and field data were discussed on the basis of these findings. Results from this study are encouraging for future application of Cd isotopes for source tracing.