Isotopic Composition Of Water Research Articles

Carbonate precipitation-derived CO2 outgassing offsets the mineral weathering sink in the orogenic regime of southwestern Taiwan: Insights from triple Sr isotopes

Secondary carbonate precipitation plays a crucial role in determining the CO2 outgassing from carbonate-saturated rivers and influences the short-term terrestrial carbon cycle. The fractionation of stable isotopes has been extensively employed to quantify post-weathering reactions in rivers and assess the quantities of metals removed by secondary carbonates. However, a major challenge is that water isotopic compositions usually reflect both lithological mixing and biogeochemical fractionation, which complicates distinguishing between these signals. In this study, we applied triple Sr isotopes (87Sr/86Sr and δ88/86Sr) to determine the “unfractionated” δ88/86Sr of water. This method allowed us to precisely quantify the precipitation-derived fractionation. Our results show that a median of 48 % of Sr was incorporated into carbonates in southwestern (SW) Taiwan, corresponding to the removal of 69 % of the originally weathered Ca. This process is closely related to a significant increase in HCO3− concentration in the water. In SW Taiwan, high river discharge during wet periods typically enhances carbonate dissolution, leading to increased carbonate precipitation along with CO2 outgassing. Thus, hydrology and river discharge constraints significantly influence CaCO3 precipitation and CO2 outgassing processes and their associated CO2 budget. Using a machine learning model, we estimated that the precipitation-derived CO2 outgassing from rivers is +7.9 × 108 mol per year. This flux is nearly twice the long-term (~10 kyr) emission flux of +4.2 ± 1.4 × 108 mol per year in this region. This indicates that precipitation-driven CO2 emissions from rivers constitute a significant carbon source within the terrestrial carbon cycle of orogenic regions.

Synthesis of a hydrological, water chemistry, and contaminants research program in the Peace-Athabasca Delta (Canada) to inform long-term monitoring of shallow lakes

In a multistressor world, evidence-based stewardship of aquatic ecosystems requires long-term monitoring data to understand the timing and magnitude of environmental change and potential causes. At the Peace-Athabasca Delta (PAD; northeastern Alberta, Canada), concern for aquatic ecosystem degradation has triggered renewed and urgent calls by Indigenous, national, and international governance bodies for implementation of a long-term lake monitoring program capable of tracking changes in hydrological conditions and contaminant deposition attributable to major energy projects located upstream, climate change, and other unnatural and natural processes. Challenges imposed by the delta's size, hydrological complexity, inaccessibility of lakes, and other factors, however, have long impeded implementation of a delta-wide lake monitoring program. To address this pressing need, here we review and synthesize results obtained during 7 years (2015–2021) of intensive, multifaceted research at 60 shallow lakes spanning the delta's broad hydroecological gradients to inform an integrated hydrology, water chemistry, and contaminants monitoring program. The research involved systematic, repeated measurements of water isotope composition, water depth variation, water chemistry and turbidity, and metal(loid) concentrations in lake surface sediment and periphytic biofilm. Results reveal marked spatial and temporal variation of hydrological processes and their affects on lake water balance and depth, strong association between hydrological processes and lake water chemistry, and that concentrations of nickel and vanadium (key oil sands indicators) remain within the range of natural variation. Correspondence of generalized additive model trendlines for isotope-derived lake evaporation-to-inflow ratios and water chemistry with climate indices (Pacific Decadal Oscillation, Oceanic Niño Index) demonstrates the sensitivity, and predictability, of lake ecosystem processes in the delta to large-scale climatic patterns. We provide recommendations for field sampling, sample analysis, data display, and integration of information for ongoing monitoring at the PAD. These approaches are readily transferable to other complex landscapes with abundant shallow waterbodies threatened by multiple stressors that may alter hydrological regimes and contaminant delivery.

Discriminative characteristics of hydrochemical components and sedimentary organic matter in Korean coastal aquaculture systems during summer

Understanding the spatial distribution and sources of sedimentary organic matter (OM) in coastal environments is crucial for effective water quality management and the preservation of ecosystem health. Although extensive research has been conducted on OM dynamics, there remains a gap in understanding the ongoing biogeochemical processes in Korean coastal aquaculture zones, particularly during the summer season. To address this gap, we investigated the spatial variation of water chemical properties and isotopic composition of sedimentary OM to trace the composition, source, and reactivity of mixed OM in aquaculture systems along the Korean coast during the summer season. The isotopic approach was applied to surface sediments from five sections: western (W)-1, W-2, southern (S)-1, S-2, and eastern (E)-1. With respect to increased nutrients (mainly nitrate; 1.2 ± 0.6 mg/L) by dam-water discharge near W sections, our isotopic signatures revealed that a substantial fraction of sedimentary OM might dominantly originated from autochthonous OM source (algae; 36.5%) related to the increase of terrestrial nutrients. Simultaneously, the deposition of allochthonous OM (aquacultural feces; 44%) was predominant in the S-2 sections. The 34S-depleted patterns (approximately -7.2‰) in the S-2 section was indicative of active sulfate reduction occurring at the sedimentary boundary. Therefore, together with the precise determination of ongoing OM, our isotopic results provide valuable insights for effectively managing water-sedimentary qualities under the increase of anthropogenic contamination.

Different continuous freshwater contributions to submarine groundwater discharge at a coastal peatland, southern Baltic Sea

ABSTRACT The impact of freshwater sources like surface river runoff and submarine groundwater discharge (SGD) on coastal waters is currently in focus of intense debate and investigation. One of the ongoing challenges in SGD research is the characterization and quantification of the freshwater endmember contributions to the subsurface mixing zone and their influences on element balance and biogeochemical transformations. Long-term investigations of the sediment porewater composition provide characterization and understanding of the physical, hydrological and biogeochemical processes controlling the substance exchanges. In this study, we focus on the hydrochemical and stable isotope (δ 2H, δ 18O) compositions of sediment porewaters along the coastline of a southern Baltic Sea peatland. Coastal surface water and groundwater dynamics were monitored at two coastal sites using 5-m-long stationary lances over a 5-year period. The vertical compositional gradients were used to extrapolate to zero-salinity (ZS) components applying a binary mixing model on the salinity and water isotope composition. The results characterize a subterranean estuary (STE) with three potential mixing endmembers: two fresh groundwaters and the brackish Baltic Sea. Tritium–helium (3H–3He) porewater dating gave ages of more than about 20 years for the freshwater components. The ZS components were compared with other SGD sites along the southern Baltic Sea and North Sea and highlight the importance of local SGD studies for a proper groundwater endmember characterization as basis to understand hydrological and biogeochemical developments at the land–ocean continuum in times of current climate change.

Isotopic composition of natural waters of Kuzbass in coalbed methane production areas

Relevance. In Kuzbass, a coalbed methane production project is being implemented for the first time in Russia. Formation water extracted together with coalbed methane plays an important role, since it has been in contact with the coal-bearing rocks for a long time, therefore it contains rich geochemical information. Over the period 2002–2022, new isotopic data were accumulated both on the waters of the region coal deposits and on overlying waters, including surface waters. Aim. Based on the material accumulated on the isotopic composition (δD, δ18O, δ13C, 34S, 3H, 14C) of natural waters in coal-bearing areas, create an evolutionary scheme for the formation of waters within the framework of the developed hypothesis on the interaction of water-rock-coal-methane. Objects. River, underground waters of the zone of active water exchange, upper and lower parts of the zone of slow water exchange (extracted together with coalbed methane). Methods. Studies of the isotopic composition of waters were carried out in several laboratories: in the Multielement and Isotope Research Center of the SB RAS, the Technical Branch of the Federal State Unitary Enterprise “SNIIGGIMS”, in the radiocarbon AMS laboratory based on the Center for Collective Use “Cenozoic Geochronology” and in the Pacific Oceanological Institute Far Eastern Branch Russian Academy of Sciences (POI) FEB RAS. Results and conclusions. The paper introduces the data on δD, δ18О, δ13С и δ34S for surface and groundwater in Kuzbass in coalbed methane production areas. It is shown that all the waters under consideration are infiltration based on their isotopic composition (δD and δ18О). The waters of the lower part of the slow water exchange, produced together with coalbed methane, are characterized by a positive oxygen shift and very light hydrogen. A diagram of the evolution of the isotopic composition of water-dissolved carbon in the region has been compiled according to the data obtained. It is noted that the atmospheric source of CO2 is characteristic only of river waters, and only biogenic carbon dioxide is present in groundwater. The wide range of δ13СDIC values of the latter is explained by the varying degrees of participation of light soil carbon dioxide and heavy biochemical carbon dioxide formed during methane formation in the coal seam. The heaviest values are typical for waters produced together with coalbed methane, which is associated with long-term interaction with coal and methane. The time of such interaction was determined using the radiocarbon method: 17–30 thousand years. In areas where coalbed methane is produced, an increase in δ13СDIC values for all natural waters is observed, which requires further study.

Fast dehydration reduces bundle sheath conductance in C4 maize and sorghum.

In the face of anthropogenic warming, drought poses an escalating threat to food production. C4 plants offer promise in addressing this threat. C4 leaves operate a biochemical CO2 concentrating mechanism that exchanges metabolites between two partially isolated compartments (mesophyll and bundle sheath), which confers high-productivity potential in hot climates boosting water use efficiency. However, when C4 leaves experience dehydration, photosynthesis plummets. This paper explores the physiological mechanisms behind this decline. In a fast dehydration experiment, we measured the fluxes and isotopic composition of water and CO2 in the gas exchanged by leaves, and we interpreted results using a novel biochemical model and analysis of elasticity. Our findings show that, while CO2 supply to the mesophyll and to the bundle sheath persisted during dehydration, there was a decrease in CO2 conductance at the bundle sheath-mesophyll interface. We interpret this as causing a slowdown of intercellular metabolite exchange - an essential feature of C4 photosynthesis. This would impede the supply of reducing power to the bundle sheath, leading to phosphoglycerate accumulation and feedback inhibition of Rubisco carboxylation. The interplay between this rapid sensitivity and the effectiveness of coping strategies that C4 plants deploy may be an overlooked driver of their competitive performance.

Produced water geochemistry from hydraulically stimulated Niobrara Formation petroleum wells: Origin of salinity and temporal perspectives on treatment and reuse

Produced water (i.e., a mixture of returned injection fluids and geologic formation brines) represents the largest volumetric waste stream associated with petroleum production in the United States. As such, produced water has been the focus of intense study with emphasis on understanding the geologic origin of the fluids, environmental impacts of unintended or intentional release, disposal concerns, and their commodity (e.g., lithium) potential. However, produced water geochemistry from many active petroleum plays remain poorly understood leading to knowledge gaps associated with the origin of brine salinity and parameters (e.g., radium levels) that can impact treatment, disposal, and possible reuse. Here we evaluate the major ion geochemistry, radium concentrations, and stable water isotope composition of ~120 produced water samples collected from 17 producing unconventional petroleum wells in Weld County, Colorado from the Late Cretaceous Niobrara Formation. This sample set encompasses eight produced water time series from four new wells across production days 0 to ~365 and from four established wells across production days ~1000 to ~1700. Additionally, produced water from nine other established Niobrara Formation wells were sampled at discrete time points ranging from day 458 to day 2256, as well as hydraulic fracturing input fluids. These results expand the available Niobrara Formation produced water geochemical data, previously limited to a few wells sampled within the first year of production, allowing for the heterogeneity of major ions and radium to be evaluated. Specific highlights include: (i) observations that boron and bromide concentrations are higher in produced waters from new wells compared to older, established wells, suggesting the role of input fluids contributing to fluid geochemistry; and (ii) barium and radium concentrations vary between the producing benches of the Niobrara Formation with implications for treating radiological hazards in produced waters from this formation. Furthermore, we explore the geochemical relationships between major ion ratios and stable water isotope composition to understand the origin of salinity in Niobrara Formation brines from the Denver-Julesburg Basin. These findings are discussed with perspective toward potential treatment and reuse of Niobrara produced water prior to disposal.

Soil moisture and water redistribution patterns in white oak (Quercus alba) saplings and trees in fragmented urban woodlands

In the midwestern United States, models predict extended summer heatwaves and increasingly frequent and prolonged drought conditions. In the Chicago region, the potential for large-scale mortality of white oak trees (Quercus alba) coupled with the ongoing decline of white oak sapling recruitment are major concerns for researchers and practitioners. In this study, we determined the sources of water used by mature white oak trees and saplings in three qualitatively different sites within a remnant oak forest in Chicago during the 2021 drought. We investigated soil moisture dynamics (volumetric water content, VWC) and water isotope composition of leaf tissues (δD, δ18O), rainwater, and groundwater. These data were linked to sapling height (proxy for biomass) and ectomycorrhizal (ECM) functional types. We predicted that: (i) mature oak trees use deeper water sources and conducted hydraulic redistribution (HR), and (ii) mature trees shared water with saplings during dry periods via long-distance ECM functional types. Soil moisture decreased progressively from June to October (spring to fall), with August and September having the lowest moisture (<20 % VWC). Following rainfall recharge, temporal patterns of soil moisture showed gravity drainage and then ongoing stair-stepwise drawdown consistent with plant evapotranspiration. Leaf δD and δ18O values in mature trees and saplings were consistent with water uptake from rainfall and subsequent enrichment via evapotranspiration. In two sites, mature trees and saplings demonstrated distinct δD: δ18O slopes, with mature trees more enriched than saplings. In the third site, mature trees and saplings δD: δ18O slopes overlapped but here, the ECM community was dominated by contact-type ECM and sapling height increased with distance from the mature oak. Our findings indicate that HR was not a component of site ecohydrology, and future climate conditions may present increasing challenges for white oak recruitment as both mature trees and saplings compete for limited rainfall-derived soil moisture.

Isotopic steady state or non-steady state transpiration? Insights from whole-tree chambers.

Unravelling the complexities of transpiration can be assisted by understanding the oxygen isotope composition of transpired water vapour (δE). It is often assumed that δE is at steady state, thereby mirroring the oxygen isotope composition of source water (δsource), but this assumption has never been tested at the whole-tree scale. This study utilized the unique infrastructure of 12 whole-tree chambers enclosing Eucalyptus parramattensis E.C.Hall trees to measure δE along with concurrent temperature and gas exchange data. Six chambers tracked ambient air temperature and six were exposed to an ambient +3°C warming treatment. Day time means for δE were within 1.2‰ of δsource (-3.3‰) but varied considerably throughout the day. Our observations show that E. parramattensis trees are seldom transpiring at isotopic steady state over a diel period, but transpiration approaches source water isotopic composition over longer time periods.

Effects of Short‐Term Climate Variations on Young Water Fraction in a Small Pre‐Alpine Catchment

AbstractContinuous and extended observations of hydrometeorological parameters, alongside the analysis of the isotopic composition across diverse waters within catchments, can significantly enhance our understanding of the potential ramifications of climate change on the hydrological response. In this study, a comprehensive analysis of hydrometeorological and isotopic data was conducted over 10 hydrological years (October 2012–September 2022) within a small, forested catchment in the Italian pre‐Alps, aiming to investigate the impacts of short‐term climatic changes on the isotopic composition of waters and the young water fraction (Fyw). The results showed that the catchment experienced climate conditions with rapid warming and drying trends. Significant isotopic enrichments were observed in all sampled water sources, driven primarily by air temperature. Fyw was estimated to be 0.64 ± 0.06, 0.45 ± 0.07, and 0.16 ± 0.03 for stream water, soil water, and shallow groundwater based on the whole‐period sinusoidal fittings, respectively. Comparative analyses comprising different approaches for the estimation of Fyw showed that time‐windows scenarios and detrending corrections yielded smaller Fyw than approaches based on the whole‐period fitting and discharge‐sensitivity modeling. Such differences can be attributed to an uneven temporal distribution of stream water isotopic data, the difficulties in capturing high flows in a humid catchment characterized by a fast runoff response during rainfall‐runoff events, and the presence of isotopic trends. Our findings underscore the imperative of integrating interannual isotopic trends and adopting appropriate sampling strategy and methodological approaches to ensure a robust Fyw estimation.

ИЗУЧЕНИЕ ФИЗИКО-ХИМИЧЕСКИХ СВОЙСТВ «ЛЕГКОЙ» ВОДЫ И ЕГО ВЛИЯНИЕ НА РОСТ И РАЗВИТИЕ РАСТЕНИЙ

The article is devoted to the study of the physico-chemical properties of light water and its effect on plant growth and development. The author focuses on the fact that water does not occur in nature in its pure form, since it always contains various chemical elements. The types of water are considered: chemically and physically bound, as well as free water. Special attention is paid to the isotopic composition of water, including heavy water, and its physical characteristics such as density, boiling point and melting point. An experiment on the effect of light water depleted with deuterium on the growth of indoor roses is described. The study showed that plants watered with light water develop better compared to control groups watered with ordinary water. The author provides data on the results of plant growth for 12 weeks, which confirms the unique properties of light water, which helps to improve the condition of plants. In addition, an analysis of the chemical composition of drinking water and a phytochemical analysis of the content of flavonoids in plants watered with various types of water is provided. In conclusion, it is emphasized that light water has significant advantages over conventional water, which makes it promising for use in agriculture.

The Inca child of the Quehuar volcano: Stable isotopes clue to geographic origin and seasonal diet, with putative seaweed consumption

The Incas occupied the west coast of South America between 1438 and 1532 CE. Among the many rites they practised was the Capacocha, which involved the offering of children. Here we studied the mummy of a child found on the Quehuar volcano, Salta, Argentina. In order to determine the geographical origin of the child and to understand the living habits prior to its presentation as an offering, we incrementally measured the δ13C, δ15N, δ34S and δ2H values of keratin from a hair strand and the δ18O value of apatite phosphate from a rib bone. Although the origin of the child remains uncertain, the oxygen isotope composition of the drinking water deduced from the rib composition argues for an origin between 2,500 and 3,000 m.a.s.l. bordering the Andes. Furthermore, the sinusoidal δ2H signal measured in hair is compatible with the recording of local seasonal precipitation variations. The results indicate that the child did not move or moved only briefly prior to death. This offering may have occurred at the onset of the wet season (summer), as suggested by the hair δ2H values. By combining δ13C, δ15N and δ34S measurements in hair, we also proposed as the most parsimonious hypothesis that seaweed constituted a proportion (16.2 ± 12.9 %) of the diet, with a peak of consumption during the wet season (summer).

Coupled sulfur and nitrogen cycling at a catchment scale: insights from isotopic and molecular techniques

The biogeochemical cycles of nitrogen (N) and sulfur (S) play important roles in sustaining the Earth's ecosystem. However, their potential coupling process and underlying mechanisms in the nature remain unclear. Through joint applications of river water's isotopic compositions, isotope-pairing experiments, and molecular techniques, this study revealed the coupled N-S cycling processes at a catchment scale from both geochemical and biological perspectives. The river water's natural abundance isotopic compositions indicated that sulfide oxidation was an important source (67.0 ± 5.5 % in summer and 72.0 ± 5.5 % in winter) of riverine sulfate (SO42−). In addition, sulfide oxidation and NOx reduction (especially denitrification) were tightly coupled in summer but less significantly so in winter. However, the coupling of sulfide oxidation and dissimilatory nitrate reduction to ammonium (DNRA) could not be overlooked in winter. The 15N pairing experiments quantitatively showed that the high sulfide oxidation rates in summer (4.7 ± 2.3 mol/km2/h) were significantly associated with the denitrification. Metagenomics and qPCR analyses of the soils supported the isotopic interpretations, substantiating the metabolic potential and coexistence of bacterial denitrification, DNRA, and sulfide oxidation, which was more prevalent in summer. This study reveals comprehensive evidence that sulfide oxidation and NOx reduction are tightly coupled at the catchment scale, which provides a new perspective towards a better understanding of N-S cycling.

Isotope‐Tracing for Conceptual Model Formation During the Holocene of Eletsky Palsa, Bolshezemelskaya Tundra

ABSTRACTStudies of permafrost agradation within peat mires leading to palsa growth and palsa dynamics during the Holocene are important for predicting the future of permafrost in a changing climate. The radiocarbon age of peat cover and stable isotope composition of the ice cores of palsas near Eletsky settlement, north‐east of the European part of Russia, were studied. Palsa growth was the most active between 8 and 5 cal ka BP. The main sources for ice core formation were precipitation‐fed surface and suprapermafrost waters. It is assumed that the isotope composition of the initial water was isotopically depleted compared with modern surface waters, which may be explained by general climate cooling during earlier stages of palsa growth (response to the 8.2 ka cooling event). The ice cores of the studied palsas were formed during the freezing of water in semi‐closed conditions, mainly by the segregation mechanism during permafrost agradation, thickness of the ice lenses and ice volume could depend on freezing rates and water supply. The upper part of the palsa ice core experienced deep thawing and could be saturated with meteoric water; repeated freezing of this part of the ice core likely occurred in closed system conditions.

Iraqi Meteoric Water Line and its Application in Groundwater-Surface Water Connection

The LMWL was re-plotted from the isotopic analysis data (δ2H and δ18O) for rainwater samples collected from three stations in Baghdad city in the current study and data from previous studies. Four samples of shallow groundwater and five samples from the Tigris River were isotopically analyzed for 2H and 18O using a Liquid-Water Stable Isotope Analyzer (LWSIA). The samples were collected from the Al-Jaderia area within the University of Baghdad. The analysis was done against Vienna Standard Main Oceanic Water (VSMOW). The isotopic composition of groundwater ranges between -43.91‰ and -37.57 ‰ for 2H with an average of -40.06±2.7 ‰, while it ranges between -6.28‰ and -6.01‰ for 18O with an average of -6.14±0.1‰. These values are slightly more depleted compared to the isotopic composition of the Tigris River water (-38.79 ‰ to -37.87 ‰) for 2H with an average of -38.05±0.9‰ and between -6.23‰ to -5.11 ‰ for 18O with an average of -5.74±0.4 ‰. This is a logical result since the river is usually fed with fresh new rainwater, which isotopically is relatively more enriched. The current study confirms that the Local Meteoric Water Line (LMWL) has a formula of δ 2H‰ = 7.5 δ 18O‰ + 13. The LMWL is located above the Global MWL by +13.9‰ toward the Eastern Mediterranean (EMMWL δ2H‰ = 8 δ 18O‰ + 22), indicating the origin rainwater from the Mediterranean Sea and the Atlantic Ocean. The groundwater and surface water isotopic compositions were below the LMWL due to the evaporation of shallow groundwater. There is interconnection between river water and groundwater, directly or by recharge from irrigation water. Iraq may have two different MWLs, one for the northeastern region and the other for the middle, western and southern Iraq. The MWL for the northern eastern region of Iraq is close to that of the EMMWL, indicating Mediterranean climate and vapor source, while the rest of the areas of Iraq have MWL with various isotopic compositions affected by more hot climate in these regions and by the continental tropical air masses.

Deep desert aquifers as an archive for Mid- to Late Pleistocene hydroclimate: An example from the southeastern Mediterranean

Many efforts have been made to illuminate the nature of past hydroclimates in semi-arid and arid regions, where current and future shifts in water availability have enormous consequences on human subsistence. Deep desert aquifers, where groundwater is stored for prolonged periods, might serve as a direct record of major paleo-recharge events. To date, groundwater-based paleoclimate reconstructions have mainly focused on a relatively narrow timescale (up to ∼40 kyr), limited by the relatively short half-life of the widely used radiocarbon (5.73 kyr). Here we demonstrate the usage of deep regional aquifers in the arid southeastern Mediterranean as a hydroclimate archive for earlier Mid-to-Late Pleistocene epochs. State-of-the-art dating tools, primarily the 81Kr radioisotope (t1/2 = 229 kyr), were combined with other atmosphere-derived tracers to illuminate the impact of four distinguishable wetter episodes over the past 400 kyr, with differences in climatic conditions and paleo-recharge locations. Variations in stable water isotope composition suggest moisture transport from more proximal (Mediterranean) and distal (Atlantic) sources to different parts of the region at distinct times. Large variability in the computed noble gas-based recharge temperature (NGT), ranging ~15–30 °C, cannot be explained by climate variations solely, and points to different recharge pathways, including geothermal heating in the deep unsaturated zone and recharge from high-elevation (colder) regions. The obtained groundwater record complements and enhances the interpretation of other terrestrial archives in the arid region, including a contribution of valuable information regarding the moisture source origin as reflected in the deuterium-excess values, which is unattainable from the common practice analysis of calcitic cave deposits. We conclude that similar applications in other deep (hundred-m-order) regional groundwater systems (e.g., the Sahara desert aquifers) can significantly advance our understanding of long-term (up to 1 Myr) paleo-hydroclimate in arid regions, including places where no terrestrial remnants, such as cave, lake, and spring sediments, are available.

Effect of intensive seasonal pumping and recharge on sulfur biogeochemistry in groundwater of agricultural riparian zones

Physico-chemical characteristics of groundwater are often impacted by agricultural practices such as land use, fertilizer types, and groundwater pumping. This study aimed to identify contaminant sources and redox processes controlling the hydrogeochemistry of groundwater in riparian zones influenced by intensive agricultural activities, focusing on sulfur species. Groundwater samples were collected bimonthly from March 2014 to March 2015 from groundwater wells in two zones in South Korea with different agricultural systems. The water isotopic compositions of the groundwater indicated that all groundwater originated from the same meteoric water. Groundwater samples affected by periodic groundwater pumping exhibited wide variations in Mn2+ (47.8 ± 18.2 μM) and Fe2+ (123 ± 61.0 μM) and elevated SO42−, while NO3− was below the detection limit. Groundwater chemistry was affected by fertilizer and manure, and denitrification. The oxidation of reduced sulfur compounds by oxygen and nitrate did not fully account for the elevated SO42− concentrations and isotopic composition of sulfate (δ34S and δ18O) in the investigated aquifers. Therefore, we postulate that water level change due to periodic groundwater pumping and recharge enabled oxidants (MnO2 and Fe3+) to also contribute to oxidation of reduced sulfur. Additionally, fertilizers with distinct δ34S values and bacterial sulfate reduction (BSR) affected groundwater chemistry and its sulfur species, including δ34SSO4 and δ18OSO4. Removal of sulfate from the aquifer during pumping limited BSR. Consequently, the agricultural practices may further increase sulfate concentrations in the groundwater. This environmental impact should be thoroughly managed because high sulfate concentrations in drinking water cause ingestion problems in humans.

Paleoclimate, paleoenvironment, and human impact over the last 400 years based on lipid biomarkers from Lake Höglwörth, Germany

Lipid biomarkers are valuable proxies for reconstructing paleoclimate and paleoenvironmental changes as well as human impact. However, little attention has been paid on evaluating how the combination of biomarkers can be used to reconstruct various aspects of local paleoenvironmental conditions. This study presents a suite of lipid biomarker records from a sediment core from Lake Höglwörth, southern Germany, covering the past 400 years. Compound-specific hydrogen isotopic compositions (δD) of terrestrial n-alkanes (n-C29-alkane) and n-alkanoic acids (n-C30-acid) indicate minor changes in isotopic composition of precipitation. The δD of n-C22-acid is interpreted to record the isotopic composition of the lake water and evaporative enrichment, which drops after 1700 CE, coinciding with the construction of a mill and the related rerouting of a creek into Lake Höglwörth. The δD of n-C25-alkane is also enriched but decoupled from the reconstructed isotopic composition of precipitation and lake water. Therefore, we suggest that δD of n-C25-alkane reflects the leaf water isotopic composition of Sphagnum, which is present in the catchment and undergoes transpirative enrichment. Both short-chain compounds have become more enriched over the last century, maybe related to increasing temperature associated with anthropogenic climate warming. The faecal biomarkers record the changes in human population, partly related to the history of the local Monastery, the World Wars I and II as well as the intensive farming after the mid-20th century. Polycyclic aromatic hydrocarbons (PAHs) reveal a significant change in combustion activities associated with human activities such as the industrial revolution, biomass burning, and environmental cleanup as well as the implementation of emission standards. Our study demonstrates that the combination of plant wax compounds, faecal biomarkers, and PAHs from lacustrine sediment serves as a valuable tool to reconstruct and distinguish various aspects of paleoclimate and paleoenvironmental changes including human impacts.

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.

A Continuous Root Water Uptake Isotope Mixing Model

AbstractThe depth‐wise distribution of root water uptake is typically inferred through linear mixing models that utilize knowledge of stable water isotopes in soil and plants. However, these existing models often represent the water uptake profile in discrete segments, potentially introducing significant uncertainty and bias into results. In this study, we introduced a novel root water uptake mixing model that combines a Bayesian linear mixing framework with a continuous root water uptake pattern, named CrisPy. To evaluate the performance of CrisPy, we conducted virtual and field‐based tests under several types of prior information. CrisPy showed accurate and robust reconstruction of the true root water uptake profile under various prior information settings in the virtual test. By contrast, the discrete mixing model, MixSIAR was greatly influenced by the prior information and deviated from the true profile. The root mean squared error of the uptake proportions from CrisPy ranged from 3.6% to 7.4%, while MixSIAR exhibited values of 6.3%–15.2%. Furthermore, posterior predictive checking indicated that CrisPy effectively reconstructed the mean and standard deviations of plant water isotopic compositions in both virtual and field‐based tests. MixSIAR, however, underestimated the mean and overestimated the standard deviation of these compositions. These findings collectively support the enhanced accuracy, greater robustness, and reduced uncertainty of CrisPy in comparison to MixSIAR. Therefore, CrisPy provides a powerful tool for partitioning plant water sources.