Environmental Isotopes Research Articles

Evaluating sustainability of Bhuj aquifer system, Western India using nuclear dating techniques

Abstract Increasing population, food demands and climatic stressors pose an imminent threat to groundwater sustainability in regional aquifer systems globally. Limited availability of surface water and erratic/uncertain rainfall necessitates preservation of groundwater resources, which form reliable fresh water reserves in most of the arid regions. Bhuj Sandstone aquifer is one such fresh groundwater systems in Western India catering the domestic/irrigational needs for over 2 million population. Rapid groundwater depletion in this area warranted a mandatory conservation of groundwater resources for future sustainability. Nuclear techniques using 3H and 14C provide estimates of groundwater age that help in planning sustainable groundwater management. In this study, sustainability of deep groundwater was assessed using environmental radioactive isotopes (3H, 14C). Results indicate that 14C activity of the groundwater samples varies from 26 to 73.6 pMC (percent modern carbon). Considering the various biases and uncertainties present, multiple correction models were applied to obtain representative groundwater ages by incorporating stable (13C) isotope and hydrogeochemical data. The corrected and representative ages are found to range from 5.8 to 8.6 ka BP (thousand years before present). From the study it can be inferred that central Bhuj aquifer hosts paleo-groundwater while the western part is recently recharged. Therefore, over-exploitation of deep groundwater in central Bhuj aquifer may further lower the water levels and this would have long-term impact on the socio-economic development of Kutch region.

14C MEASUREMENT OF SAMPLES FOR ENVIRONMENTAL SCIENCE APPLICATIONS AT THE NATIONAL ENVIRONMENTAL ISOTOPE FACILITY (NEIF) RADIOCARBON LABORATORY, SUERC, UK

ABSTRACT The National Environmental Isotope Facility (NEIF) Radiocarbon Laboratory at the Scottish Universities Environmental Research Centre (SUERC) performs radiocarbon measurement of a wide range of sample matrices for applications in environmental research. Radiocarbon is applied to palaeoenvironmental, palaeoceanographic, and palaeoclimatic investigations, as well as work to understand the source, fate, turnover, and age of carbon in the modern carbon cycle. The NEIF Radiocarbon Laboratory supports users in the development and deployment of novel sampling techniques and laboratory approaches. Here, we give an overview of methods and procedures used by the laboratory to support the field collection, laboratory processing, and measurement of samples. This includes in-house development of novel and/or specialized methods and approaches, such as field collection of CO2 and CH4, hydropyrolysis, and ramped oxidation. The sample types covered include organic remains (e.g., plant material, peat, wood, charcoal, proteins), carbonates (e.g., speleothems, foraminifera, mollusc shell, travertine), waters (dissolved organic and inorganic carbon), gases (CO2 and CH4), soils and sediments (including sub-fractions).

Developments and applications of the HYDRUS computer software packages since 2016

AbstractThe HYDRUS codes have become standard tools for addressing many soil, agricultural, environmental, and hydrological problems requiring the evaluation of various subsurface physical, chemical, and biological processes. There are now many thousands of HYDRUS users worldwide, with thousands of applications of the HYDRUS models appearing in the peer‐reviewed literature. In this manuscript, we provide an overview of the capabilities of the most recent Version 5 of HYDRUS, focusing primarily on features implemented since 2016. We briefly describe the standard HYDRUS model and its standard and nonstandard specialized add‐on modules that significantly expand the capabilities of the software packages. The standard add‐on modules include HPx, UNSATCHEM, Wetland, Furrow, PFAS, COSMIC, DPU, SLOPE Cube, and Particle Tracking. Recent developments of the HYDRUS Package for MODFLOW are also described, along with additional capabilities incorporated into the graphical user interface supporting HYDRUS. Also discussed are new or improved options to simulate the fate and transport of environmental isotopes, multi‐cropping systems, compensated root water uptake, and hydraulic redistribution within the rootzone, which will be implemented in upcoming add‐on modules. Another objective is to review selected applications of the HYDRUS models, such as evaluations of various irrigation, low‐impact development (LID), and managed aquifer recharge (MAR) schemes.

Study of Environmental Isotopes and Hydrochemical Characteristics of Groundwater from Springs at Archaeological Sites in Dompu Regency, West Nusa Tenggara, Indonesia

The existence of groundwater sources in several springs at archaeological sites in Dompu Regency, West Nusa Tenggara, Indonesia, has been widely used by the surrounding community for various needs. However, from a number of the springs, there are springs whose water discharge has decreased. Meanwhile, from a number of existing springs, there is one spring whose groundwater is used every day even though it tastes a bit brackish. For this reason, it is important to conduct a groundwater study in the area with the aim of knowing the characteristics, preliminary identification of recharge areas and quality of groundwater in the study area through an environmental isotope and hydrochemical. The study was conducted by taking a number of groundwater samples from several archaeological sites in Dompu Regency. The results of environmental isotope and hydrochemical analysis show that there are 2 springs (2 archaeological sites), namely the Riwo and Ncona springs, because these two areas are part of the recharge area, which must be preserved by not clearing forest land. Meanwhile, for the quality of groundwater, of the 5 springs located at the archaeological sites, only the Hodo spring is of “poor quality” with the Na–Cl water type; it is unfit for drinking water.

Understanding hydrological processes of glacierized catchments in the western Himalayas by a multi‐year tracer‐based hydrograph separation analysis

AbstractSnow and glacier melt are significant contributors to streamflow in Himalayan catchments, and their increasing contributions serve as key indicators of climate change. Consequently, the quantification of these streamflow components holds significant importance for effective water resource management. In this study, we utilized the spatio‐temporal variability of isotopic signatures in stream water, rainfall, winter fresh snow, snowpack, glaciers, springs, and wells, in conjunction with hydrometeorological observations and Snow Cover Area (SCA) data, to identify water sources and develop a conceptual understanding of streamflow dynamics in three catchments (Lidder, Sindh, and Vishow) within the western Himalayas. The following results were obtained: (a) endmember contributions to the streamflow exhibit significant spatial and seasonal variability across the three catchments during 2018–2020; (b) snowmelt dominates streamflow, with average contributions across the entire catchment varying: 59% ± 9%, 55% ± 4%, 56% ± 6%, and 55% ± 9% in Lidder, 43% ± 6%, 38% ± 6%, 32% ± 4%, and 33% ± 5% in Sindh and 45% ± 8%, 40% ± 6%, 39% ± 6%, and 32% ± 5% in Vishow during spring, summer, autumn, and winter seasons, respectively; (c) glacier melt contributions can reach ~30% to streamflow near the source regions during peak summer; (d) The primary uncertainties in streamflow components are attributed to the spatiotemporal variability of tracer signatures of winter fresh snow/snowpack (±1.9% to ±20%); (e)regarding future streamflow components, if the glacier contribution were to disappear completely, the annual average streamflow in Lidder and Sindh could decrease up to ~20%. The depletion of the cryosphere in the region has led to a rapid increase in runoff (1980–1900), but it has also resulted in a significant streamflow reduction due to glacier mass loss and changes in peak streamflow over the past three decades (1990–2020). The findings highlight the significance of environmental isotope analysis, which provides insights into water resources and offers a critical indication of the streamflow response to glacier loss under a changing climate.

Multienvironmental tracers in coastal aquifer (Morocco): A window into groundwater mixing and risk to contamination.

In many coastal areas in Morocco, groundwater (GW) constitutes an important water supply for human activities. Intensive pumping makes GW highly susceptible to contamination, affecting its quality and then human health. This work aims to assess and improve the application of environmental isotopes in exploring the connections between GW recharge and discharge, as well as to identify the direction, age, and speed of GW flow, in the coastal aquifer system of the Akermoud plain. A total of 23 boreholes and wells were sampled during two sampling campaigns in 2017 and 2018, including 11 samples from the shallow aquifer and 12 samples from the deep aquifer. A set of chemical and isotopic tracers (δ18 O, δ2 H, 3 H, δ13 C, 14 C, and 3 He) is used to track water and solute from input to output of the investigated system. Stable isotopes distinguish recharge at different altitudes for the shallow and deep aquifers. Both aquifers reveal consistently low values of 3 H (between 0.3 and 0.9 tritium units) and from 28% to 64% of modern carbon for six boreholes. According to 14 C correction models, GW has ages ranging from 3300 to 11,000 years before present. GW flows from SSE to NNW and discharge along the Atlantic coast of Akermoud plain with a velocity ranging from 0.41 to 1.8m/year. PRACTITIONER POINTS: The use of environmental tracers helps determine the origin of salinity and identify the recharge area. Investigating the MRT of groundwater resources is essential, especially in arid regions. Evaluating the efficiency of isotopic tracing is crucial in assessing the risk of groundwater contamination. The findings provide insights for stakeholders to promote more sustainable groundwater management in coastal areas.

Distribution of Environmental Isotopes 18O and 2H in Water Resources in the Al-Taji Area, Northern Baghdad, Iraq

In this study, the stable isotop 18O and 2H has been used to investigate the interaction of surface water (SW), and groundwater (GW) in Al-Taji district/ Northern Baghdad for two seasons (March and August 2022). 16 Samples were collected from water resources in the Al-Taji district (Tigris channel, Tigris River, and groundwater), in each season water samples from 8 Tigris channel, 5 drilled wells, and 3 Tigris River were taken for the analysis of the isotopes 18O and 2H. The average analysis results of 18O and 2H in the Tigris channel, Tigris River, and groundwater were found to be -3.435‰ and -18.6094‰, -2.07167‰ and -17.81‰, -4.125‰ and -34.707‰ respectively. The results, generally, show a comparable range of isotope content on the Tigris Channel and groundwater (W1 about 1 km from the Tigris Channel). This indicates a mixing/interconnection between groundwater and the Tigris River, and it could be concluded that the wells (W1 and Ch1 and Ch2) near the Tigris channel have been recharged or mixed from them.

Hydrochemical and Environmental Isotope of Groundwater Samples in Al- Khassa Sub-Basin, Kirkuk, Northeastern Iraq

Hydrochemical study of groundwater has carried out for the Al-Khassa Sub-Basin during the October 2020 and May 2021 seasons for estimating the impacts of seasonal variation and human activity on water quality and using the isotope to determine the main source of recharge. It was found that Biological Oxygen Demand (BOD), Chemical Oxygen Demand (COD), and Dissolved Oxygen (DO) were out of the standard indicating that the groundwater environment was reduced and difficult to recover from pollution. Physical and chemical properties that were high (Total Dissolved Solid (TDS), Total Suspended Solid (TSS), Electrical conductivity (EC), Total Hydrocarbon (THC)). Partial pollution by nitrate and phosphorous due to the use of fertilizers for these elements. The contamination by manganese, molybdenum and boron was present in all samples of the two seasons, and partly for lead and mercury due to fertilizers, agricultural activities, the presence of animal and poultry ranches, besides the poor sewage system in the basin based on a septic tank. Washing polluted agricultural soil by rain lead to polluting groundwater. From the environmental isotope analysis (δ2H and δ18O), the isotopic compositions of precipitation were used to construct a local meteoric water line for the study area. The isotopic compositions of groundwater samples were situated to the left of the Global meteoric water line (GMWL), suggesting input of local rainfall that derives from weather front originating from the Mediterranean Sea. Comparing the isotope composition of groundwater and precipitation showed that the infiltrated precipitation that was the main source of recharge to the aquifer system in the study area.

Investigating the enigma of an irregular groundwater age pattern in a confined, presumed “fossil” complex aquifer through mixing cell flow modeling

Significant fluctuations in the groundwater (GW) age along the eastern flow path of the Nubian Sandstone Aquifer's (NSA), as derived from Krypton-81 groundwater dating, have suggested that this aquifer, located in Israel's Negev Desert and previously presumed to be a fossil, is not entirely isolated but mixes with younger and even recent water. The intermittent rejuvenation and drastic increases in the GW age across short distances most likely imply hydraulic connectivity with the surrounding aquifers, which contribute both younger and more ancient water to the NSA. The current study aims at modeling the GW flow system to locate and quantify its water sources despite the aquifer's hydrogeological complexity and the scarcity of hydrological data. We implemented the Mixing Cell Modeling (MCM) approach, understanding that the alternating rejuvenations and increases in the GW age downstream of the NSA's eastern flow trajectory reflect the mixing of the NSA's groundwater with young and old GW bodies, respectively. Thus, prompted by the 81Kr water age distribution, yet independent of the Kr radioisotope data, a multi-tracer mixing cell flow model was adopted based on a set of balance equations of water, dissolved minerals, and stable environmental isotopes. The findings indicate that (1) there is a small, yet substantial, intrusion of old brackish GW from a deep-seated, highly pressurized aquifer into the NSA in the northeastern Negev; (2) the rejuvenation of GW in the NSA is due to significant mixing with water from nearby overlying carbonate and chert aquifers, and (3) the NSA is substantially replenished through the Nubian Sandstone (NS) outcrops along the Negev Desert anticlines. Most GW intrusions into the NSA occur near the intersections of the eastern flow path with some of the Negev's major faults and synclines, such as the Paran and Ramon Fault zones and the Zin Syncline. In light of the relatively young GW age at the end of the NSA's western flow path in the northern Negev, and based on the similarities in the hydrogeological structures in the Negev and northern Sinai Deserts, we propose that similar mixing processes with GW from the overlying carbonate aquifers and direct GW recharge through the NS outcrops also occur in the northern Sinai Peninsula. The approach presented in this study might apply to examining recharge processes and hydraulic connectivity in other aquifers that were formerly classified as “fossil,” such as the immense NSA found in the Arabian (Jordan & Saudi Arabia) and the Western (Egypt) Deserts.

Focused recharge enhances soil carbon leakage and carbonate weathering in groundwater: Implications for subsurface carbon sinks

Soil carbon leakage into groundwater is a crucial and natural carbon sink process in the subsurface carbon cycling. However, the primary driving force for soil carbon downward leakage and the following fate of the carbon in groundwater remains elusive. Here, we investigated multi-seasonal hydrodynamics, hydrogeochemistry and environmental isotopes (δ13C, δ2H and δ18O) in groundwater wells in a humid region. Frequent water-table rise (1 ∼ 3 m) and isotopic signature fluctuation after the concentrated rainfall supported evidence for the occurrence of focused groundwater recharge. We found that focused recharge during the shorter and wetter season induced the increase of groundwater DOC (306.5 ± 231 μmol/L) and CO2 (2154 ± 726.6 μmol/L), the dilution of CH4 (1.75 ± 1.2 μmol/L) and DIC (4486 ± 790.8 μmol/L) as well as depleted δ13C signatures (−17‰ ∼ −18‰). These variations jointly elucidated accelerated soil carbon downward leakage and hydrodynamic mixing driven by focused recharge. Saturation index calculation and PHREEQC simulations confirmed that massive groundwater CO2 from soil carbon leakage during focused recharge exerted positive perturbations on carbonate weathering, and ultimately stored in a more stable form by transforming into HCO3−. Carbon isotope analysis further identified carbonate weathering accounted for approximately one third of DIC dynamics compared to biogenic sources. This study highlights that focused recharge has a disproportional contribution to flushing soil-derived carbon into groundwater and activating carbonate weathering in the groundwater, with important implications for temporal variability of non-negligible subsurface carbon sinks in the global carbon budget.

Mechanism of denitrification in subsurface-dammed Ryukyu limestone aquifer, southern Okinawa Island, Japan

Denitrification crucially regulates the attenuation of groundwater nitrate and is unlikely to occur in a fast-flowing aquifer such as the Ryukyu limestone aquifer in southern Okinawa Island, Japan. However, evidences of denitrification have been observed in several wells within this region. This study analyzed environmental isotopes (δ15NNO3 and ẟ18ONO3) to derive the rationale for denitrification at this site. Additionally, the presence of two subsurface dams in the study area may influence the processes involved in nitrate attenuation. Herein, we analyzed 150 groundwater samples collected spatially and seasonally to characterize the variations in the groundwater chemistry and stable isotopes during denitrification. The values of δ15NNO3 and δ18ONO3 displayed a progressive trend up to +59.7 ‰ and + 21 ‰, respectively, whereas the concentrations of NO3−–N decreased to 0.1 mg L−1. In several wells, the enrichment factors of δ15NNO3 ranged from −6.6 to −2.1, indicating rapid denitrification, and the δ15NNO3 to δ18ONO3 ratios varied from 1.3:1 to 2:1, confirming the occurrence of denitrification. Denitrification intensively proceeds under conditions of depleted dissolved oxygen concentrations (<2 mg L−1), sluggish groundwater flow with longer residence times, high concentrations of dissolved organic carbon (>1.2 mg L−1), and low groundwater levels during the dry season with precipitation rates of <100 mm per month (Jun–Sep). SF6 analysis indicated the exclusive occurrence of denitrification in specific wells with groundwater residence times exceeding 30 years. These wells are located in close proximity to the major NE–SW fault system in the Komesu area, where the hydraulic gradient was below 0.005. Detailed geological and lithological investigations based on borehole data revealed that subsurface dams did not cause denitrification while the major NE–SW fault system uplifted the impermeable basement rock of the Shimajiri Group, creating a lithological gap at an equivalent depth that ultimately formed a sluggish groundwater area, promoting denitrification.

Preparing Environmental Isotopes Databases for Determining Groundwater and Surface Water Relationships in Iraq

This study is prepared to constitute an isotopic database of Deuterium (δ2H) and Oxygen 18 (δ18O) for groundwater and its relationship with the isotopic footprint for surface water The 311 samples of groundwater were collected between 2013 and 2021 and analyzed using a Liquid-Water Isotope Analyzer (LWIA). The study covered different regions of Iraq, including the Western region (Al-Anbar), Northern region (Kirkuk), Central Region (Samarra, Shirqat, Khanaqin, Baghdad, Karbala, Najaf, Diyala), and Southern region (Samawah، Nasiriya, Diwaniyah, Basra). In addition, the 208 surface water samples were collected from different sources including (the Tigris, Euphrates, Diyala, and Shatt Al-Arab) rivers during the same period. The isotopic measurements showed a linear relationship between the two stable isotopes (δ18O, δ2H) with a slope of 7.38 and an excessive deuterium reach to (-9.4597) compared with the excessive value of the domestic rain line of (14.15). It is defined according to the local meteoric water line equation (LMWL δ2H = 7.7035 * δ18O + 14.158), which characterized a fingerprint of groundwater and showed the impact of the climate on it. The study showed a significant interaction between groundwater and surface water of the Tigris and Euphrates Rivers in the Southern region of Iraq, due to the aquifers in these areas being close to the surface, with depth ranges between (6 – 40 m), and high porosity that simulative of the sedimentary plain characterization. The samples of these areas calculated the highest and the lowest value for δ2H of (12.04‰) and (-36.14‰) respectively. A similar result was found in the western regain. This region recorded the highest value of δ2H (-4.42‰) and the lowest value (-42.2‰), the depth of the wells ranged between (2 – 22 m), which explains the relationship between the groundwater and the Euphrates River. However, the study indicated that the wells in Diyala Governorate, have depth ranges between (10 – 70 m) and were not affected by rainwater or Diyala River, with the highest and lowest value for δ2H of (4.66‰), (-38.54‰), respectively. On the other hand, the highest and lowest values of δ2H were recorded in the Khanaqin area with a value of (-13.48‰) and (-32.67‰) respectively.

Using multiple isotopes to determine groundwater source, age, and renewal rate in the Beishan preselected area for geological disposal of high-level radioactive waste in China

Understanding hydrogeological conditions is crucial for selecting and assessing the long-term safety performance of a high-level radioactive waste (HLW) disposal repository. Utilizing environmental isotopes as effective markers for analysing groundwater movement, this study investigates groundwater recharge sources, age, and renewal rates using multiple isotopes in China's potential HLW repository site, the Beishan area. The results indicated deep bedrock groundwater primarily derives from ancient precipitation infiltration under cold climatic conditions. A noteworthy distinction is that loose sedimentary groundwater exhibits higher tritium content (>10 TU) compared to bedrock groundwater (<3.2 TU). Groundwater within the recharge area, especially within gullies and piedmont slope deposits, is relatively youthful, with an age of less than 30 years and an annual renewal rate exceeding 5 %. In contrast, the shallow groundwater age in the intermountain basins and depressions of the discharge area generally exceeds 50 years, with an annual renewal rate often falling below 0.5 %. At the Beishan underground research laboratory site, deep groundwater at the disposal repository depth displays a corrected 14C age exceeding 8,000 years, indicating an extremely slow movement and alteration rate. As a result, the hydrogeological conditions in the Beishan area are expected to be relatively beneficial for ensuring the safety of HLW repository.

Identification of recharge processes and mixing patterns by using CFC's and isotopic multi-tracing (δ18O, δ2H) of groundwater in a stratified volcanoclastic aquifer of the semiarid Amazcala Basin in Central Mexico

Understanding groundwater flow is essential for quantifying recharge and identifying relevant processes in an aquifer. Hydrogeochemical models have proven to be successful in identifying origin and processes during water recharge. We integrated the hydrogeochemistry, environmental isotopes and CFC technique to develop a conceptual and a groundwater mixing model of the Amazcala aquifer in Central Mexico. Results demonstrate that groundwater recharge consists of local meteoric recharge and a regional geothermal input. The local resident groundwater component represents the primary source of groundwater contributing with an average of 56% (σ = 0.07). The second crucial component of groundwater is the contribution of the local meteoric component contribution with averages to 23% (σ = 0.05). The third component is the regional geothermal component, which on average contributes to 21% (σ = 0.03). Regional geothermal influence has been reported in several aquifers in volcanic regions. This geothermal input influences volcanic aquifers located in the Trans-Mexican Volcanic Belt and should be considered in the water balance budget. Excessive groundwater extraction raises the vulnerability of the aquifer to natural and/or anthropogenic pollution, affecting the quality of water. Understanding the hydrogeological system offers a useful framework for developing and executing Managed Aquifer Recharge strategies (MAR).

Spatial characteristics of hydrochemistry and stable isotopes in river and groundwater, and runoff components in the Shule River Basin, Northeastern of Tibet Plateau

Water resources play a crucial role in constraining the high-quality development of the arid, necessitating an in-depth investigation and understanding of hydrological processes, hydrochemical characteristics, and their influencing factors amidst climate change. This study meticulously examined and analyzed the hydrochemistry and stable isotope composition (δ18O and δD) of river and groundwater within the Shule River Basin (SRB). Results showed that both river (mean: 8.01) and groundwater (mean: 7.92) had alkaline pH values, while average total dissolved solids were measured at 709.25 mg/L in river and 861.88 mg/L in groundwater, indicating predominance of fresh water sources. HCO3−, SO42−, Na+ and Ca2+ were the most abundant ions, influenced by evaporation-crystallization processes and rock weathering. The dominated hydrochemical facies in both river and groundwater were Ca–HCO3 type in the upper (UR) and the middle reaches (MR), while Ca–Mg–Cl type in the lower reaches (LR). The local meteoric water line (LMWL) was defined as δD = 8.01δ18O + 18.48 (R2 = 0.98, n = 163; P < 0 0.001). The more negative δ18O and δD values in river and groundwater were plotted nearby and lower right of the LMWL, implying that the important recharge source of those waters is from precipitation. The relationship between river δ18O and elevation showed an increase of 0.14‰/100 m in the UR, but a negative correlation with a rate of −0.47‰/100 m in the MR and LR. Precipitation, groundwater, baseflow and meltwater accounted for 62.5%, 19.8%, 11.9% and 5.8% of the UR river, respectively, during the observed period, according to the end-member mixing analysis. These runoff components displayed distinct seasonal variations, primarily driven by precipitation during the early and groundwater/baseflow during the rapid and end-stage ablation periods. The observed alterations in hydrological elements present both opportunities and challenges for water resource management across the SRB, and adaptive measures have been proposed based on our study. These findings provide valuable insights into efficient utilization of water resources from water chemistry and environmental isotopes.

Tracing nitrate pollution sources of karst groundwater in water resources using environmental isotopes

Tracing nitrate pollution sources of karst groundwater in water resources using environmental isotopes

Assessment of Water Quality Changes Using Physical Parameter and Stable Isotope in Ciliwung River

The Ciliwung River is the potential water source for the people of Jakarta and Bogor. Rapid urbanization and industrial development have sparked severe problems in the water resources of the Ciliwung River. The potential pollutants increase as the river flows through residential, business, and industrial areas, where drainage and sanitation infrastructure are worse. Water is naturally tagged with natural tracers, such as temperature, electrical conductivity, chemical constituents, and environmental water isotopes (δ2H and δ18O). These proved valuable tracers to identify the origin of the water. This research aims to trace the origin of the Ciliwung River water using a stable isotope approach and physical parameters. Research methods are field surveys, laboratory analysis, and analytical studies—sampling at 12 points of river water for a physical parameter and 5 points for stable isotopes. The research results show that the water origin of Ciliwung’s is rainwater. The stable isotopes in the upstream area are smaller than those in the upstream area experiencing enrichment. Factors leading to enrichment are inputs from anthropogenic activities to water bodies from household, agricultural, and industrial pollution. The results of this research are helpful for the government and academics in designing Ciliwung River conservation policies.

Relationship between isotope ratios in precipitation and stream water across watersheds of the National Ecological Observation Network

AbstractThe timescales associated with precipitation moving through watersheds reveal processes that are critical to understanding many hydrologic systems. Measurements of environmental stable water isotope ratios (δ2H and δ18O) have been used as tracers to study hydrologic timescales by examining how long it takes for incoming precipitation tracers become stream discharge, yet limited measurements both spatially and temporally have bounded macroscale evaluations so far. In this observation driven study across North American biomes within the National Ecological Observation Network (NEON), we examined δ18O and δ2H stable water isotope in precipitation (δP) and stream water (δQ) at 26 co‐located sites. With an average 54 precipitation samples and 139 stream water samples per site collected over 2014–2022, assessment of local meteoric water lines and local stream water lines showed geographic variation across North America. Taking the ratio of estimated seasonal amplitudes of δP and δQ to calculate young water fractions (Fyw), showed a Fyw range from 1% to 93% with most sites having Fyw below 20%. Calculated mean transit times (MTT) based on a gamma convolution model showed a MTT range from 0.10 to 13.2 years, with half of the sites having MTT estimates lower than 2 years. Significant correlations were found between the Fyw and watershed area, longest flow length, and the longest flow length/slope. Significant correlations were found between MTT and site latitude, longitude, slope, clay fraction, temperature, precipitation magnitude, and precipitation frequency. The significant correlations between water timescale metrics and the environmental characteristics we report share some similarities with those reported in prior studies, demonstrating that these quantities are primarily driven by site or area specific factors. The analysis of isotope data presented here provides important constraints on isotope variation in North American biomes and the timescales of water movement through NEON study sites.

Environmental Isotopes of Water as Potential Tool to Distinguish the Sources of Groundwater Recharge in a Semi-arid Region: A Case Study Around Veeranam Tank, Tamil Nadu, India

Environmental Isotopes of Water as Potential Tool to Distinguish the Sources of Groundwater Recharge in a Semi-arid Region: A Case Study Around Veeranam Tank, Tamil Nadu, India

Establishing a water baseline for the unconventional gas industry: A multiple environmental isotopes assessment (18O, 2H, 3H, 13C, and 14C) of surface and groundwater in the São Francisco Basin, Brazil

Unconventional hydrocarbon production has become the target of an intensive environmental debate due to the risks it poses to water resources. Fracking, while enabling the extraction of oil and gas from ultra-low permeability reservoirs, also possesses the risk of polluting water systems through failures from hydraulic fracturing and its associated procedures. The need to foster national industrial development with a transitional energy matrix has led Brazil to discuss the environmental suitability before producing its large unconventional reserves. Many studies have highlighted the need for a robust environmental characterization before the development of the unconventional industry. In this sense, multiple environmental isotopes may work as a proxy for identifying water contamination right from the early stages. Environmental isotopes may also be applied to enhance the understanding of the natural geochemical processes intrinsic to a given area. This study presents an environmental isotopes baseline for the groundwater and riverine water systems within the São Francisco Basin, a proven tight gas reservoir in Brazil, in a pre-operational context. δ18O, δ2H, 3H, δ13C, and Δ14C were evaluated in three different seasons in groundwater and surface water samples, along with other auxiliary parameters such as physical-chemical parameters (in situ), major ions, and d-excess. The δ2H and δ18O in surface water shows an upstream → downstream enrichment trend, with some variations suggesting baseflow interactions in the surface water systems. An evaporation line for the study area was defined as δ2H = 4.6903 δ18O + 10.362. δ13C indicates a mutual dissolution of silicates and carbonates in the groundwater system and suggests a group of samples highly related to the recharge areas. Groundwater dating denotes the Serra da Saudade Formation as a modern fractured aquifer with a strong recharge capacity. These findings support stakeholders in environmental monitoring and management of the unconventional gas industry.