Water δ2H Research Articles

Investigating Induced Infiltration by Municipal Production Wells Using Stable Isotopes of Water (δ18O and δ2H), Four Mile Creek, Ohio

Many municipalities around the world place their production wells in shallow alluvial aquifers that are adjacent to streams. Pumping these wells then induces the infiltration of surface water into the aquifer, allowing the greater extraction of water without significantly depleting the aquifer. However, induced infiltration poses a risk of introducing contamination from surface water into groundwater systems. The goal of this study was to quantify the amount of induced infiltration due to municipal pumping at the Four Mile Creek well field in Oxford, Ohio, using stable isotopes of water oxygen (δ18O) and deuterium (δ2H). In areas of municipal pumping, we sampled water from the production wells, Four Mile Creek, and from monitoring wells that we hypothesized to be both influenced and not influenced by induced infiltration. Samples were collected over 10 months in 2012 and over 12 months in 2021. In 2012, surface water δ18O values ranged from −3.89 to −8.04‰, and δ2H ranged from −26.55 to −55.65‰ at sampling sites. PW1 δ18O values ranged from −4.71 to −7.39‰ with a mean of −6.61 and −32.01 to −47.86‰ with a mean of −42.74‰ for δ2H. PW2 δ18O values ranged from −5.74 to −7.34‰, with a mean of −6.45‰, and δ2H ranged from −36.29 to −47.82‰ with a mean of −42.43‰. PW3 had lower values of both δ18O and δ2H, ranging from −6.36 to −8.02‰ and −47.7 to −40.35‰, and with means of −7.08 and −45.11, respectively. In 2021/2022, surface water δ18O values ranged from −5.32 to −7.93‰, and the δ2H ranged from −36.14 to −50.56‰. PW1 δ18O values ranged from −6.15 to −7.54‰ with a mean of −7.13‰, and δ2H ranged from −43.52 to −49.01‰ with a mean of −45.99‰. PW2 δ18O values ranged from −5.72 to −7.34‰, with a mean of −6.70‰, and δ2H ranged from −36.69 to −46.14‰, with a mean of −43.61‰. Using the time averaged values of δ18O of groundwater, production wells and surface water, the percentages of surface water resulting from induced infiltration in 2012 were 57%, 59% and 15% at the three wells, respectively, while in 2021, PW1 had 35% and PW2 91%. The amount of induced infiltration was apparently related to the pumping rates of the production wells, the length of time of pumping and the distance between Four Mile Creek and production wells. Our results indicate that stable isotopes of water provide a reliable method of quantifying groundwater/surface water interaction in alluvial aquifers.

Stable Isotope Ratio and Elemental Analysis (CNS) in Mangrove Leaves in the Creek Ecosystem: An Indicator of Coastal Marine Pollution

AbstractThe stable isotopes ratio and elemental composition in the mangrove leaves are excellent indicators for coastal marine pollution. The present study investigated the composition of Carbon, Nitrogen, and Sulfur, δ13C and δ15N values in mangrove leaves to identify the source of pollution and energy to the mangroves in the creek ecosystem of Mumbai Harbour Bay. The oxygen and hydrogen stable isotope ratios (δ18O and δ2H) of leaf water were estimated to understand the relative contribution of freshwater and seawater to the mangrove's water source. The Carbon, Nitrogen and Sulfur contents were found to vary from 37.79 to 42.55% (Average: 40.06 ± 1.54%), 2.13–3.79% (Average: 2.94 ± 0.45%) and 0.37–0.81% (Average: 0.53 ± 0.14%) in the mangrove leaves, respectively. The δ13C and δ15N values were found to vary from − 30.43 to − 28.41‰ (Average: − 29.46 ± 0.74‰) and from − 2.67 to 5.54‰ (Average: 2.21 ± 3.20%), respectively. The δ18O and δ2H values were found to vary from − 2.7 to 0.83‰ and − 6.86 to 5.43‰ with an average of − 0.94 ± 0.83 and − 2.03 ± 3.52‰ respectively. According to the observed δ18O and δ2H values, mangroves in the northern part had a relatively higher contribution of freshwater input compared to southern part of the study area. The lower values of δ15N towards the northern end of the creek indicate a relatively higher contribution of nitrogen from industrial discharges. Similar values of δ13C in mangrove in the region suggest a common source of carbon. Mangroves found near discharge locations have different elemental composition and δ15N values compared to those mangroves that are not located near discharge location. These differences can be used as potential markers to identify the coastal marine pollution. The results of the present study may be used for developing rational approaches for protection and conservation of the mangrove ecosystem in the bay.

Simulating water balance and nutrient losses in a pastoral catchment using the SWAT+ model: added value of isotope data

ABSTRACT New Zealand’s freshwater is under increasing pressure from intensified dairy farming. This study assesses agricultural nitrogen loads from small pastoral catchments contributing to eutrophication and periodic algae blooms in a lake. Using the Soil and Water Assessment Tool (SWAT+), we simulated hydrological processes and nutrient loads, incorporating water (δ2H, δ18O) and nitrate (δ15N, δ18O) isotope data to improve model performance. The SWAT+ model was calibrated and validated with flow and nitrate data, achieving R2 values of 0.65–0.90, Nash-Sutcliffe efficiency (NSE) of 0.46–0.82, and percent bias (PBIAS) between 10.24% and 33.48%. The study demonstrates that stable isotope insights can enhance SWAT+ modelling accuracy and highlight the need for better fertilizer management to reduce nutrient loads.

Hydrochemical Characterisation of the Basement Aquifer with a Focus on the Origin of Nitrate in the Highly Urbanised Niamey Region, SW of Niger

This study investigated the basement aquifer beneath the urbanised city of Niamey and the agricultural fields of Kollo, SW of Niger. During the observation period spanning from 2021 to 2023, groundwater and surface water samples were collected for analysis of major ions and the stable isotopes oxygen-18 and deuterium (δ18O and δ2H) of water. To trace the origin of high nitrate concentrations (NO3−) found in several observation and drinking water wells in both areas, δ15N and δ18O isotope values of NO3− were analysed in groundwater and eluted soil samples. The observed hydrochemical patterns mainly reflect the heterogeneity of the weathered fringe of the basement aquifer. Decreasing concentrations of NO3− and δ18O and δ2H values were observed in relation to the distance of the Niger River and increasing thickness of the clay layer on the surface. The wells close to the river in Niamey show a dilution effect during the flood season, and the NO3− concentrations displayed a continuous increasing trend. The δ15N-NO3 and δ18O-NO3 values confirmed that septic tank water is spreading in the region of Niamey and that manure originating from livestock in Kollo is the main source of NO3−. The patterns of δ15N in the soil samples coincide with those of cattle’s manure spread in both areas. The shallow wells show significantly higher values of electric conductivity and NO3− concentrations compared to the deeper wells, which clearly indicates the influence of shallow septic tanks on water quality.

Subsurface influences on watershed nutrient concentrations and loading in a clay dominated agricultural system

Water quality issues in the Great Lakes Basin persist despite management and monitoring efforts. With changing land use and climatic conditions, the need for improved understanding of nutrient loss from agricultural field to surface water is imperative to reduce consequences on human and aquatic life, such as perpetual algal blooms and contaminated drinking water. There remains a gap in holistic rural water management studies that investigate the understanding of the water cycle in rural settings and the interconnections between different components of the water cycle, including artificial drainage. In the current study, a year-round paired investigation of subsurface and nutrient dynamics was conducted in a small, intensively managed agricultural watershed within southwestern Ontario, Canada. Nutrients (Nitrate and Phosphorus) and stable isotopes of water (δ2H and δ18O) were sampled at varying scales (i.e., field and watershed), from multiple hydrologic components (e.g., groundwater, surface water, tile flow, and soil water), from 2020 to 2022. Results indicate that nutrient concentrations in surface water were elevated during the growing season, while nutrient loading was greater during the non-growing season in surface water. Monthly nitrate loads were found to be significantly (p < 0.01) related to groundwater elevation, soil moisture and tile flow, whereas total phosphorus loading was found to be significantly (p < 0.01) related to soil moisture and tile flow. δ2H and δ18O signatures revealed that during the growing season nutrient movement was predominantly through interflow pathways (including tile drainage) comprised of event-water. In the non-growing season, there was an increased subsurface influence on nutrient transport. This study highlights the importance of including subsurface characterization in nutrient management studies. A comprehensive understanding of varying seasonal hydrologic mechanisms that control nutrient movement within an agricultural watershed is essential to sustain growing rural communities.

The δ2H and δ18O isotopic evidence for hydraulic redistribution by Alnus acuminata in an agricultural landscape

Understanding of the process of hydraulic redistribution in agricultural landscapes is important for informing agroforestry design and agricultural management. The measurement of hydraulic lift and redistribution in the field is still a challenge. Due to the robustness of stable isotope analysis, we hypothesized that the measurement and analysis of the natural abundance of stable isotopes δ2H and δ1⁸O, in the twigs of agroforestry trees, stems of wheat intercrop, rain, and soil water coupled to an isotopic mixing modeling by IsoSource supplemented with other physiological crop parameters, would estimate the extent of hydraulic redistribution in intercropping, and inform the design of an agroforestry system. There are still many plant species that have not been investigated for their potential hydraulic redistribution yet, and Alnus acuminata is among them, therefore this study aimed to contribute to filling that gap. The field experiment was conducted in an Andic soil of the northern Rwanda highlands to address the extent of water efflux redistribution from tree roots of Alnus acuminata to the wheat intercrop across bench terraces. The study involved the measurement of the natural abundance of stable isotopes δ2H, and δ1⁸O of the tree twigs, soil and wheat stems at distances of 1, 3, 5, and 7 m from the tree lines of Alnus acuminata, and of rainwater. The isotopic mixing modeling was supplemented by measuring both specific leaf area (SLA) and carbon discrimination (Δ13C) in the wheat leaf. We noted a significant (p < 0.01) gradient in the depletion of wheat xylem water δ2H and δ18O signatures moving further away from the tree lines. Based on the wheat value of δ2H, the isoSource indicated that the trees may have contributed the wheat water up to 64.3 ± 2.6% at 5 m from the trees, and the values of both the SLA (cm2 g–1) and ∆13C (‰) of wheat leaf indicated the water use efficiency of wheat significantly improved around the trees up to 3 m away from the trees with 140.10 ± 3.74 cm2 g–1, 149.56 ± 3.43 cm2 g–1 and 20.6 ± 0.1‰, 20.8 ± 0.1‰ at 1 m and 3 m for SLA and ∆13C respectively. We concluded that Alnus acuminata exhibits significant hydraulic redistribution in the field.

Stable water isotopic composition and evaporation to inflow ratios for high-mountain tropical Ecuadorian lakes

ABSTRACT In this study, we explore the utility of stable isotopes of water (δ2H and δ18O) as integrative proxies for evaporative condition in high-mountain tropical lakes using a set of small Ecuadorian lakes in the Cajas National Park. Specifically, we (1) characterize the variability of stable water isotopic composition across several lakes of varying size and depth and (2) determine the evaporation as a fraction of inflow using stable isotopes of water for these lakes. We have used the Hydrocalculator tool for estimation of the evaporation to inflow (E/I) ratio. Results indicated that larger lakes have lower seasonal variability in isotopic composition across their depth compared with the smaller lakes. Further, there was clear seasonal variation across the monthly E/I ratios estimated in several lakes, indicating that evaporation likely plays some (albeit limited) role in the water level variability experienced within a year.

Water utilization characteristics of dominant plant species from different functional groups of desert steppe.

Understanding water use characteristics of plants and their interrelations is essential for achieving sustainable vegetation restoration of desert steppe. This study focused on five dominant plant species inhabiting two habitats: sierozem (Populus euphratica, Caragana liouana, and Stipa breviflora) and aeolian sandy soil (P. euphratica, Salix psammophila, and Leymus secalinus). We analyzed δ2H and δ18O isotopes in xylem, soil water, groundwater, and precipitation. By integrating soil water content and root data at various depths, we employed the MixSIAR model to quantitatively assess water utilization characteristics. Results revealed that these plants primarily relied on soil water during the growing season, with variations in water uptake depths at different growth stages. In the sierozem habitat, Populus exhibited significant variations in water source throughout the growing season. Early in the growing season (May to June), P. euphratica primarily extracted soil water from depths of 60-100 cm. During the peak growth period (July to August), water source shifted to depths of 100-200 cm, and returned to the depth of 0-20 cm by the end of the season (September). C. liouana initially utilized soil water at 60-100 cm but shifted to 0-20 cm during and after peak growth. S. breviflora predominantly tapped into soil water at 20-60 cm early and late in the growing season, but shifted to 0-20 cm during peak growth. In the aeolian sandy soil habitat, P. euphratica initially utilized soil water at 60-100 cm but shifted to 0-20 cm during and after peak growth. S. psammophila primarily utilized soil water at 60-100 cm early and during peak growth, shifting to 100-200 cm by the end of the season. L. secalinus mainly relied on soil water at 20-60 cm throughout the growing season. Soil moisture, seasonal precipitation variation, and root distribution influenced vegetation water use patterns. Throughout the growing season, trees, shrubs, and herbs in the sierozem habitat exhibited hydrological niche partitioning, which facilitated their water distribution and utilization. Conversely, dominant plants in the aeolian sandy soil habitat showed hydrological niche overlap, which intensified water competition, particularly between trees and shrubs. Therefore, species traits and soil properties should be given full consideration when selecting species combinations for vegetation restoration. Introducing species combinations with complementary water use characteristics is essential for fostering species diversity and sustainable vegetation restoration in desert steppe.

Water uptake patterns and rooting depths of Tamarix ramosissima in the coppice dunes of the Gurbantünggüt Desert, China: a stable isotope analysis.

Tamarix ramosissima has an important role in stabilizing sand dunes in desert ecosystems. Understanding the water use strategies of T. ramosissima is essential to understand its adaptations on coppice dunes. We utilized the stable isotopes δ2H and δ18O in soil water, groundwater, and xylem water to identify monthly differences in water sources. Additionally. we explored rooting depth using 2H2O as an artificial tracer. In May, T. ramosissima derived 75% of its water from shallow and middle soil layers. In July, it absorbed 90% water from middle and deep soil layers. In August and September, it acquired approximately 80% of its water from deep soil layers. The labelling using 2H as an artificial tracer indicated that the root system of T. ramosissima could reach depths >500 cm in the coppice dunes. 2H absorption was observed at depths of 100, 200, 300 and 400 cm. Soil water is the dominant water source for T. ramosissima in the coppice dunes because groundwater is at depths >30 m. The flexible water-use strategies of T. ramosissima enable it to effectively utilize different available water sources to adapt to the arid environment. These findings improve our understanding of water uptake patterns and drought adaptation strategies of T. ramosissima in the coppice dunes of desert ecosystems.

The preservation of photosynthetic and hydrological signals in the carbon and hydrogen isotope compositions of n-fatty acids in the seasonal wetland soils of the Okavango Delta (Botswana)

The Okavango wetland (Botswana) is the world’s largest inland delta. A strong seasonality in water input leads to the contraction and extension of wetlands in the floodplains. The extreme evapotranspiration and little precipitation lead to a difference in the hydrogen isotope signature of rain, soil and river water. Biomarkers, such as plant waxes, are stored in the soils and preserved on geological timescales. To understand which signal is preserved in the stable isotope signatures of plant waxes, soils along a 250 m-long transect spanning waterlogged to dry soils were collected over several seasons and three years. In addition, plants, and plant and soil water were collected along this transect. First, carbon isotope ratios (δ13C) of plant waxes (i.e, n-fatty acids) were used to classify their metabolism. δ13C of bulk organic matter and individual n-fatty acids analyzed in the soils show a strong dependance on the type of vegetation found along the transect (C3 versus C4 plants). Hydrogen isotope ratios (δ2H) of water present in soil showed that shallow-rooted C4 grasses use superficial soil water, whereas the xylem water δ2H content in trees growing near the flooded channel indicated the use of river water. In addition, plant hydrogen fractionation between lipids and rain showed a strong influence of carbon metabolisms with larger fractionation for C3 plants compared with C4 grasses. n-fatty acid δ2H ratios in surface soils followed the hydrological variation in the Delta with its floods and dry periods. Hence δ2H of long-chain fatty acids seems to track the river-level variation rather than precipitation.

Assessing the isotopic biases of soil water from cryogenic water extraction in different soil types in China

AbstractThe utilization of deuterium (δ2H) and oxygen (δ18O) isotope ratios in cryogenically extracted water from soil samples is a widely employed method in hydrological and ecological research. Nevertheless, an increasing body of research indicates that cryogenic water extraction (CWE) leads to δ2H depletion in soil water. To investigate the widespread existence of this phenomenon, samples from eight physicochemically distinct soils in China underwent rehydration with a reference water at five different water contents and were subsequently extracted using CWE. In comparison to the reference water, significant and inconsistent δ2H depletion was observed in all eight soil samples. The δ18O bias also exhibited variation, ranging from enrichment to depletion. Generally, Z score assessments indicated unacceptable results for all soils. Water content emerged as the most influential variable affecting both δ2H and δ18O biases, while soil properties had different impacts on these biases. Source water, as calculated by a linear regression model, revealed that the isotopic composition of extracted soil water differed from that of the reference water. The cryogenic extraction error in soil water could not solely attributed to fractionation processes during the extraction but resulted from the release of tightly bound soil water into the reference water. Using the influencing factors, correction models for δ2H and δ18O biases by CWE were developed. By these models, the δ2H and δ18O biases were mostly successful corrected. High soil water extraction efficiency (e.g., 99%) was recommended to minimize isotopic biases. These efforts necessitate further testing, particularly in ecohydrological studies involving isotope measurements of soil water through CWE.

Increasing effect of biocrusts on evaporation is evidenced by simulating evaporation and diffusion experiments and water stable isotope analysis

Evaporation, one of the main components of the water and energy balance between soil and atmosphere, plays a key role in hydrological processes particularly in semi-arid and arid climate regions. As critical living organism communities inhabiting the soil-atmosphere boundary, biocrusts are capable of modifying near-surface soil properties and structure in drylands. However, the roles of biocrusts in mediating soil evaporation still remain greatly controversial, and the literature yet lacks in a systematic assessment. In this study, evaporation experiments were conducted under simulated isothermal and non-isothermal conditions for bare soil and three types of biocrusts (cyanobacterial, moss, and their mixture) sampled from a semi-arid climate region of the Chinese Loess Plateau. During the evaporation, soil temperature and moisture were measured at depths 2, 5, 10, and 15 cm for those biocrusts and bare soil. Their water vapor diffusion process and stable isotopic composition were also analyzed in the laboratory. We found that the measured evaporation yielded 4.9%, 17.5%, and 31.6% higher average evaporation rate for cyanobacterial, cyano-moss, and moss crusts, respectively, when compared to the bare soil. In comparison to bare soil, all types of biocrusts markedly reduced the rate of temperature rise, prolonged the duration of wetting time, and delayed the formation of dry surface layer. The largest regulating effects on soil temperature and moisture were found in the moss crusts instead of cyanobacterial or cyano-moss crusts. The increasing evaporation in biocrusts was attributed to their higher fine particle content, lower bulk density, and greater water holding capacity. Moreover, the water vapor diffusion rate and diffusivity of biocrusts were 18.2% and 16.4% higher than those of bare soil, respectively, which is attributable to the increased total porosity and better soil structure. Additionally, the isotopic composition of soil water (0–50 cm) in bare soil and moss crusts was distributed below the local meteoric water line. The mean δ18O and δ2H in soil water gradually decreased with increasing soil depth, and the moss crusts were more isotopically enriched than bare soil. Based on the enhanced soil evaporation rate, improved vapor diffusivity, and enriched isotopic composition of biocrusts in contrast to bare soil, we conclude that biocrusts exacerbate vapor transport and evaporative loss, and consequently they are crucial surface cover in rebalancing surface ecohydrological and biochemical processes in global drylands. These findings improve our understanding of the complexity of dryland hydrology, and a full consideration should be given in future biocrust studies.

Restoration Strategies in the Heidaigou Open-Pit Mine Dump Based on Water Sources and Plant Water Utilization

In this study, three typical plants capable of restoring in the Heidaigou open-pit mine dump, namely, Pinus sylvestris var. mongolica, Caragana korshinskii, and Medicago sativa, were taken as the research objects. The δ2H and δ18O values of atmospheric precipitation, soil water, stem water, and leaf water were measured using the stable isotope technique, and the distribution characteristics of the δ2H and δ18O values of different water sources were identified. The IsoSource model (version1.3.1) was used to calculate the contribution rate of different water sources to the plants, and the differences and dynamic changes in the water sources for P. sylvestris var. mongolica, C. korshinskii, and M. sativa during the rainy season were examined. Results showed that the water source of the three plants was found to be mainly soil water, and the utilization of each potential water source varied in different periods of the rainy season. In June, when SWC was sufficient, P. sylvestris var. mongolica and M. sativa primarily absorbed and utilized shallow and middle soil water, with relative utilization ratios of 55.5% and 59%, respectively, while C. korshinskii has a more balanced utilization ratio of soil water in each layer, with shallow soil water utilization at 33.7%, middle soil water at 34.2%, and deep soil water at 32.2%. In August, when SWC decreased, P. sylvestris var. mongolica, C. korshinskii, and M. sativa were all transferred to deep soil water, with utilization ratios of 75.8%, 78.8%, and 71.1%, respectively. The values showed that these three typical plants are capable of restoring can respond to external water changes through the plastic transformation of water absorption sources. Among them, C. korshinskii can flexibly use soil water in each layer, has stronger survival competitiveness in drought, and can better adapt to the fragile ecological environment of a mining dump.

Leaf wax n-alkane distribution and hydrogen isotopic fractionation in fen plant communities of two Mediterranean wetlands (Tenaghi Philippon, Nisí fen—Greece)

Many continental paleoclimate archives originate from wetland sedimentary sequences. While several studies have investigated biomarkers derived from peat-generating vegetation typical of temperate/boreal bogs (e.g., Sphagnum), only scant information is available on emergent plants predominant in temperate/subtropical coastal marshlands, peri-lacustrine and fen environments. Here, we address this gap, focusing on two wetlands in the Mediterranean (Nisí fen and Tenaghi Philippon, Greece). We examined the concentration, homologue distribution, and hydrogen stable isotopic composition (δ2H) of leaf wax n-alkanes in 13 fen plant species, their surrounding soil, and surface water during the wet growing season (spring) and the declining water table period (summer). Our findings indicate that local graminoid species primarily contribute to the soil n-alkane signal, with a lesser influence from forbs, likely owing to differences in morphology and vegetation structure. The δ2H values of surface and soil water align with local average annual precipitation δ2H, reflecting winter-spring precipitation. Consistently, the average δ2H of local surface, soil, and lower stem water showed negligible evaporative enrichment, confirming minimal 2H-fractionation during water uptake. We find that δ2H values of source water for wax compound synthesis in local fen plants accurately mirror local annual precipitation. Furthermore, despite differences between leaves and lower stems in n-alkane production rates, their δ2H values exhibit remarkable similarity, indicating a shared metabolic substrate, likely originating in leaves. Our net 2H-fractionation values (i.e., precipitation to leaf n-alkanes) align with those in Chinese highlands and other similar environments, suggesting consistency across diverse climatic zones. Notably, our data reveal a seasonal decrease in the carbon preference index (CPI) in plant samples, indicating wax lipid synthesis changes associated with increased aridity. Additionally, we introduce a new parity isotopic difference index (PID) based on the consistent δ2H difference between odd and even n-alkane homologues. The PID demonstrates a strong anticorrelation with plant CPI, suggesting a potential avenue to trace long-term aridity shifts through δ2H analysis of odd and even n-alkane homologues in sedimentary archives. While further development of the PID is necessary for broad application, these findings highlight the intricate interplay between plant physiology, environmental parameters, and sedimentary n-alkanes in unravelling past climatic conditions.

Water use characteristics of coexisting sand‐binding vegetation in two typical soil habitats in the desert steppe of China

AbstractUnderstanding the water use characteristics and water relationship of coexisting vegetation in a mixed‐species plantation of trees and shrubs is crucial for the sustainable restoration of degraded arid areas. This study investigated the water use characteristic of coexisting sand‐binding vegetation combinations in the sierozem habitat (Populus przewalskii Maxim namely Populus‐S and Caragana liouana) and aeolian sandy soil habitats (Populus przewalskii Maxim namely Populus‐A and Salix psammophila) of the desert steppe. By analysing the δ2H and δ18O isotopes in xylem, soil water, groundwater and precipitation, a Bayesian MixSIAR model was employed to quantitatively assess the water utilization characteristics of plants. Throughout the growing season, in the sierozem habitat, C. liouana exhibits the highest efficiency in utilizing soil moisture above 60 cm (53.45%) and displays adaptable water use strategies. In contrast, Populus‐A predominantly relies on deep soil moisture below 60 cm plus groundwater (63.89%). In the aeolian sandy soil habitat, both Populus‐A and S. psammophila similarly favour deep soil moisture below the 60 cm soil plus groundwater (66.77% and 67.60%, respectively). During the transition period from the dry to the wet seasons, although both Populus‐A and S. psammophila in the aeolian sandy soil habitat shifted their water sources from deeper to shallower ones, there was considerable overlap in the water sources used by Populus‐A and S. psammophila. This overlap led to competition for water resources and exacerbated the depletion of deep soil moisture in both seasons. Conversely, in the sierozem habitat, the partitioning of water sources between Populus‐S and C. liouana facilitated the allocation and utilization of water resources between the two species. The findings highlight the need for species‐specific consideration in water resource allocation within mixed‐species plantations of trees and shrubs, which is crucial for sustainable vegetation restoration in sand‐binding ecosystems.

δ2H isotopic offsets in xylem water measurements under cryogenic vacuum distillation: Quantifying and correcting wood‐water hydrogen exchange influences

AbstractStable isotopes δ18O and δ2H are used to infer vegetation water sources. In some studies, significant xylem water δ2H offsets from potential source waters have been observed. The offsets appear to be more prevalent with cryogenic vacuum distillation (CVD) of plant water. Hypothesized mechanisms for these offsets include changes during plant water uptake and transport, and methodological problems. We propose that a large portion of the offsets are due to hydrogen isotope exchange between xylem water and non‐crystalline hydroxyl groups of wood cellulose and hemicellulose during CVD. We present a method for estimating the hypothesized isotopic exchange between wood tissues and water, which is the result of Rayleigh and equilibrium fractionation. To estimate the exchange, we use published wood properties for North American tree species and isotope chemical relationships as a function of moisture content, CVD temperature and water extraction efficiency. A simple model of exchange between xylem water and hydroxyl groups captures the range of observations in studies in which CVD and non‐CVD methods were compared. To evaluate the model, we compared observed δ2H offsets (sw‐excess) values from two field datasets (90°C, n = 364, and 170°C, n = 43) to δ2H offsets estimated with our chemical model. We found good agreement between observed and estimated δ2H offsets for samples extracted at 90°C (r2 = 0.69) but not for samples extracted at 170°C (r2 = 0.20). The offset may be eliminated by increasing the extraction temperature to 229°C or by adding a standard sufficient to raise the moisture content to &gt;150%. A correction can also be approximated by applying a theoretical calculation based on the extraction temperature, moisture content and water extraction efficiency.

Seasonality of hydrogeochemical evolutions and isotopic variabilities (δ18O, δ2H and d-excess) in the surface water as well as groundwater from tropical central-south Mexico

Due to adverse impact of the global warming on hydrological resources, we intended to document the hydrogeochemical evolutions of surface and groundwater at tropical central-south Mexico in terms of seasonality of rock-water interaction, precipitation/evaporation variation and moisture source by evaluating the major ion chemistry in Piper and Gibbs plots, Durov diagram and through estimation of the chloro-alkaline indices as well as assessing the stable isotope compositions (δ18O and δ2H) in samples from different seasons of a year. Surface water of the Lake Coatetelco shifted from mostly Ca–Mg–HCO3 facies in wet summer-autumn to Na–HCO3–Cl facies in the dry spring due to elevated Na, Cl and HCO3. Greater evaporation in spring led to a maximum δ18O enrichment of ca.7‰ compared to the other seasons, and much depleted deuterium excess (−40.92‰ to −39.20‰). Interaction of the lake water with subsurface carbonate lithologies, and comparable isotopic compositions reflected the enhanced interaction between the surface water body and aquifers in the wet autumn. Effect of seasonality, however, was unclear on the groundwater facies, and its heterogenous composition (Ca–Mg–HCO3, Na–HCO3–Cl and Na–HCO3) reflected the interactions with different lithologies. Fractionations in isotope compositions of the groundwater were caused from recharge at different elevations, seasonality of moisture sources and moisture recycling. The water-mineral saturation index was an efficient proxy of seasonality as the lake water and groundwater (avg SIcalcite > 0.5) of the dry autumn were saturated with calcite. This vital information about carbonate precipitation, pCO2 and chemical facies would be useful for the better interpretation of paleoclimate archives in this region.

Comparative Analysis of Water Isotopic Compositions: Evaluating Isotope Analyzer for Soil and Extraction Method for Stem Water

Stable isotopes of water (δ2H and δ18O) are reliable tracers for the investigation of plant–soil–water interactions in forest ecosystems. However, variations in isotopic compositions may arise due to differences in analytical instruments and water extraction methods. In this study, we conducted three different experiments to identify isotopic differences caused by analytical and methodological variations. First, we analyzed soil water by using the two most commonly applied methods: isotope ratio mass spectrometry (IRMS) and cavity ring-down spectroscopy (CRDS). Second, we compared the isotopes in xylem water extracted from the stems of nine tree species using cryogenic vacuum distillation (CVD) with different heating times. Third, we compared the compositions in xylem water extracted with three different methods: mechanical squeezing using a pressure chamber (PC), an induction module (IM), and CVD. The differences in isotopic composition between IRMS and CRDS were significant but minimal. Soil properties were not significant factors contributing to differences between the two instruments. For the xylem water extraction with CVD, each of the nine tree species required heating for more than three hours. Significant differences were observed in δ2H among the three extraction methods for xylem water. Xylem water extracted by CVD showed more depleted values compared to those obtained by PC and IM. Our results highlight the importance of considering analytical and methodological variations in stable isotope analysis.

Unravelling the sources contributing to the urban water supply: An isotope perspective from Ljubljana, Slovenia

In cities experiencing rapid urbanization, we must continually update our understanding of the partitioning of drinking water sources concerning its supply if it is to be managed sustainably. This need is especially crucial given the pressure on water resources arising from evolving land use patterns and climate change. For this reason, a city-wide study of stable water isotopes (δ2H and δ18O) in precipitation, surface water and groundwater across Ljubljana, Slovenia, was undertaken. The goal was to characterise the temporal dynamics of urban water cycling and trace the various sources contributing to the city’s drinking water supply. Monthly water sampling, combined with hydrogeochemical and in-situ data, permitted the identification of local precipitation and surface water contributions to its two groundwater supply aquifers. In addition, a re-examination of the mean residence times (MRT) of surface waters revealed an MRT of 3–4 years, which is much longer than previously reported. Also, changes in the contributions of surface water and precipitation to groundwater were observed compared to previous studies. These findings improve our understanding of local water partitioning and provide valuable insights for water managers addressing future urban water resource management.

Water isotopic composition traces source and dynamics of water supply in a semi‐arid agricultural landscape

AbstractChanges in seasonality and form of precipitation alter the structure and function of grassland and steppe ecosystems and pose challenges for land management and crop production in regions like the Northern Great Plains, North America. This research uses isotopic composition of water (δ18O and δ2H) to explore the sources and fate of soil water in lower‐elevation agricultural areas of the Judith River watershed, in the headwaters of the Missouri River, USA. Extensive non‐irrigated cereal crop production in this area occurs on well‐drained soils and depends on careful water management. Our observations indicate that colder precipitation contributes isotopically distinct water to cultivated terrace soils relative to downgradient groundwaters and streams. Riparian waters also exhibit a higher fraction of contributions from colder precipitation relative to terrace groundwaters and streams. Apparent contributions from colder precipitation in terrace and riparian soil waters suggest that snowmelt is a key component of the water supply to these systems. Riparian waters also show evidence of evaporation suggesting that water spends sufficient time in some ponds and open channels in the riparian corridor to reflect fractionation by evaporation. The evolution of water isotopic composition from soils to shallow aquifers to stream corridors indicates source water partitioning as precipitation moves through this semi‐arid agricultural landscape. The apparent mixing processes evident in this evolution reveal source water dynamics that are necessary to understand plant transpiration, solute processing, and contaminant leaching processes.