Water 2H Research Articles

Water resource sources in the ancient town of Si Mahosot, Thailand

Management of available water resources has been practiced throughout human history. We examine here some aspects of water resource management in the ancient (6th to 13th century) town of Si Mahosot (Thailand). Based on isotopic measurements (2H, 18O, and 222Rn) of both surface water and groundwater samples, we confirmed that groundwater is the main source of water that feeds the town's canal network. Based on a series of shallow wells in the area, we estimated a radon endmember activity of 14,200 Bq/m3 for the groundwater that feeds the canals. We used a radon mass balance model that considers radon inputs via groundwater and losses via decay and atmospheric evasion. Applying our estimated endmember activity, we calculated a water flux into the canal domain studied of 145 ± 36 m3/day, enough to replace the water within this section of the canal within 16–26 days. A separate independent approach using a18O mass balance resulted in a very similar discharge estimate of 154 ± 39 m3/day into the studied canal. The flux may have been higher when the former town was occupied as there are indications that groundwater levels were higher here in the past.

Groundwater recharge sources and mechanisms in the Ethiopian central Afar rift: Insights from isotopic and hydrogeochemical tracers.

Groundwater flow and recharge mechanisms in the central Afar rift and the associated western marginal grabens and Northwestern Plateau (NWP) are poorly understood because of the complex geology and spatial heterogeneity in the aquifer systems. The major aquifers in the region include the Oligocene and Pliocene to recent volcanics and recent alluvio-lacustrine sediments. We employed hydrogeochemical, stable isotopes of water (18O and 2H), and geological structures insights to identify groundwater recharge sources and mechanisms, aiming to develop a representative conceptual groundwater flow model. Water samples from groundwater and surface water were collected based on lithological/aquifer variation and geomorphological setup for isotope and hydrochemical analysis. Findings reveal distinct isotopic differences between the deep (>350 m) and shallow groundwater systems of the Afar rift, with deep systems showing relative isotopic depletion, indicating varying recharge sources. The deep groundwater exhibited a similar isotopic signature to that of the marginal grabens and NWP. The distribution of major ion chemistry and electric conductivity (EC) of groundwaters from the western plateau to the Afar rift show significant spatial variability. However, in some corridors of western parts of the rift, there is a clear geochemical evolution along the flow paths inferring groundwater flow continuity between aquifers. The results revealed the existence of preferential deep groundwater recharge from the NWP through the highly fractured linking zones, interacting fault zones in between the marginal grabens, to the deeper volcanic aquifers of the central Afar rift. The proposed groundwater flow model of this study illustrates the deep groundwater flow from the NWP to the Afar rift is primarily directed by the orientations of the faulted marginal grabens and the highly fractured interacting zones. This model is pivotal for understanding groundwater dynamics in similar continental rift environments, offering insights for effective groundwater management.

Evidence for variations in cryogenic extraction deuterium biases of plant xylem water across foundational northeastern US trees

AbstractMeasurements of oxygen and hydrogen isotopes in plant xylem water (2H, 18O) have helped to redefine conceptual and numerical models of the hydrological cycle and understand how plants compete for subsurface water. Recent experiments have shown that Cryogenic Vacuum Extraction (CVE) of plant xylem water can result in a δ2H bias. We tested if CVE δ2H‐biases varied significantly across seven foundational northeastern US forest trees with a series of tree core rehydration experiments. Our analysis demonstrated that CVE δ2H‐biases were well predicted by sample gravimetric water content and varied significantly with tree species identity. We show that species‐level δ2H‐bias corrections can result in substantially different understandings of plant water uptake and transpiration versus uncorrected data or generic bias corrections. This research demonstrates an urgent need for the critical evaluation of CVE for plant water extraction. In the absence of a stronger understanding of CVE δ2H‐biases, we recommend that xylem water δ2H observations should not be used in plant water uptake studies.

Effects of global and climate change on the freshwater-seawater interface movement in a Mediterranean karst aquifer of Mallorca Island

Karst aquifers are globally prized freshwater sources, posing a significant preservation challenge. These aquifers typically exhibit dual or even triple porosities, encompassing matrix, fractures-fissures and conduits, rendering them highly responsive to variations in chemical characteristics and hydraulic head. In coastal regions, these aquifers often possess extensive subsurface conduit networks intricately linked to the rock matrix, facilitating groundwater discharge into the sea. Therefore, they display acute sensitivity to seawater intrusion, swiftly reacting to changes in precipitation and pumping regimes. This makes them exceptionally vulnerable to short-term meteorological fluctuations and long-term climate change. Their high heterogeneity leads to uneven penetration of the freshwater-seawater interface, causing rapid seawater intrusion inland over significant distances. The Mediterranean region, characterized by water deficit and water stress, faces strong impacts from climate change, featuring a warming atmospheric trend exceeding the global average, along with diminished rainfall exacerbating water scarcity. Increasing water demands for agriculture, urban development, and the growing tourism industry, because of global change, are worsening water stress. Our primary research objectives were analyzing the environmental consequences of global and climate change on seawater intrusion in Mediterranean coastal karst aquifers, with a focus on the role of the double-flow model, thus contributing to the understanding of the processes involved. To achieve this, we selected a study region on Mallorca Island in the western Mediterranean, where a karst aquifer system discharges into the sea. We employed various study methods, notably hydrochemical techniques and multi-isotopic analysis, encompassing the examination of 2H and 18O isotopes in water, 87Sr/86Sr ratio, Sr and B concentrations, and δ11B in water. A key finding is the rebound effect, wherein aquifers recontaminate due to solute molecular back-diffusion following cessation of extractions and the retreat of marine intrusion, providing insight into the impact of climate and global change on Mediterranean karst aquifers.

Climatic controls on leaf wax hydrogen isotope ratios in terrestrial and marine sediments along a hyperarid-to-humid gradient

Abstract. The hydrogen isotope composition of leaf wax biomarkers (δ2Hwax) is a valuable tool for reconstructing continental paleohydrology, since it serves as a proxy for the hydrogen isotope composition of precipitation (δ2Hpre). To yield robust palaeohydrological reconstructions using δ2Hwax in marine archives, it is necessary to examine the impacts of regional climate on δ2Hwax and assess the similarity between marine sedimentary δ2Hwax and the source of continental δ2Hwax. Here, we examined an aridity gradient from hyperarid to humid along the Chilean coast. We sampled sediments at the outlets of rivers draining into the Pacific as well as soils within catchments and marine surface sediments adjacent to the outlets of the studied rivers and analyzed the relationship between climatic variables and δ2Hwax values. We found that apparent fractionation between leaf waxes and source water is relatively constant in humid and semiarid regions (average: −121 ‰). However, it becomes less negative in hyperarid regions (average: −86 ‰) as a result of evapotranspirative processes affecting soil and leaf water 2H enrichment. We also observed that along strong aridity gradients, the 2H enrichment of δ2Hwax follows a non-linear relationship with water content and water flux variables, driven by strong soil evaporation and plant transpiration. Furthermore, our results indicate that δ2Hwax values in marine surface sediments largely reflect δ2Hwax values from the continent, confirming the robustness of marine δ2Hwax records for paleohydrological reconstructions along the Chilean margin. These findings also highlight the importance of considering the effects of hyperaridity in the interpretation of δ2Hwax values and pave the way for more quantitative paleohydrological reconstructions using δ2Hwax.

Seasonal recharge mechanism of the upper shallow groundwater in a long-term wastewater leakage and irrigation region of an alluvial aquifer

Understanding the mechanisms that control seasonal groundwater recharge at local and intermediate scales is critical for understanding contaminant transport. The recharge mechanism of seasonal precipitation and irrigation, companied with legacy wastewater in porewater in alluvial aquifer were complicated due to the seasonal variation of multiple recharge sources. In this study, a long-term wastewater leakage and irrigation region along the Tanghe Wastewater Reservoir (TWR) in the alluvial plain area of North China Plain to investigate the recharge mechanism from unsaturated zone to the upper shallow groundwater affected by multiple water sources. Water chemical ions and stable isotopes of water (2H and 18O) of 30 m deep sediment profiles and groundwater boreholes were used to trace the recharge processes. The porewater stable isotopes of the sediment profiles revealed vertical recharge rates ranging from 0.63 to 1.09 m/year for the layered unsaturated zone with silt and silty clay. Due to the matrix flow through unsaturated zone, the legacy wastewater in the unsaturated zone affected the variation of groundwater quality in long term. However, fast flow (i.e., preferential or lateral flow) occurred in sand layers of alluvial aquifers lead to significant precipitation contributions (44 to 61 %) to the upper shallow groundwater (USGW) recharge, resulting in the seasonal variation of stable isotopes and water chemical ions. Affected by the fast flow with seasonal variations and matrix flow with legacy wastewater in the unsaturated zone, the δ2H and δ18O relationship of the USGW showed two types of hysteresis loops in the dual isotope space: 1) groundwater in regions affected by the TWR wastewater leakage shows narrow loops and a nearly straight line with end-members of precipitation that recharged to groundwater by fast flow, and evaporated porewater plotting along the TWR evaporation line; and 2) groundwater in irrigated farmlands with low and high irrigation amounts and intense evaporation shows stronger hysteresis with loops overlapping with shallow porewater, suggesting the impact of legacy wastewater of the unsaturated zone on groundwater. The residual pollutants in soil and the type of fast flow determine the different seasonal variation of groundwater quality. Preferential flow in alluvial aquifer regions can increase the proportion of seasonal recharge from precipitation, resulting in the rapid introduction of contaminants from surface or shallow soils into the alluvial aquifer.

A deuterium tracer experiment for simulating accumulation and elimination of organically bound tritium in an edible flatfish, olive flounder

Tritium (3H, T) is discharged by nuclear facilities into coastal oceans as tritiated water (HTO). When the concentration of HTO in seawater increases, the accumulation of organically bound tritium (OBT) in edible fish becomes a concern because of its longer residence time than HTO. To evaluate the accumulation potential of OBT in olive flounder (Paralichthys olivaceus), a commercially important edible fish in northeast Asia, we experimentally exposed the fish to seawater enriched with deuterium (2H, D) as a substitute for tritium. Progressive increases and decreases in the concentration of organically bound deuterium (OBD) were observed in the edible part (i.e., muscle) of the fish during the period of exposure to 2H (161 days) and the subsequent period of elimination of OBD (196 days). The measured concentration of OBD was analyzed using a newly developed single-compartment model to describe the metabolism of OBD in muscle via the following three transfer pathways: formation of OBD from 2H in water, elimination of OBD by catabolism, and ingestion of feed with natural abundance of OBD. The model estimates were in good agreement with the measured muscle OBD concentrations. The formation and elimination rate constants for OBD in the muscle were estimated by fitting our model to the measured data. The biological half-life of OBT in the muscle, estimated from the elimination rate constant, was 133 days, which was far longer than that of HTO in the free water of the muscle. Our model facilitates the estimation of OBT accumulation potential in olive flounder inhabiting coastal areas near nuclear facilities, and thus, will help to assess the radiation dose that humans are exposed to from ingesting seafood.

Groundwater Circulation in the Shallow Crystalline Aquifer of Tharisa Mine, South Africa: Evidence from Environmental Isotopes and Near-Surface Geophysics

For underground mining, efficient groundwater management is one of the critical mining economics components. The region of interest, known as Tharisa Mine, is situated on the western limb of the Bushveld Igneous Complex, which is home to South Africa’s premier platinum-group metal resources. This work aimed to provide the findings from the investigation and imaging of the near-subsurface hydrogeological architecture in a shallow profile using stable isotopes of water (18O and 2H) and radioactive water isotopes (3H). Regarding isotope data, 18O varied from −3.5 to 1.5‰; 2H from −24 to 4.7‰; and 3H from 2.0 to 3.4 T.U. Utilizing combined geophysical techniques, the results were verified. Additionally, the geophysical methods, including seismic refraction tomography, multichannel analysis of surface waves, electrical resistivity tomography, and magnetics, helped identify the fluid’s pathways and lineaments during migration to verify the isotope results. The groundwater inflow volumes into the open pit were initially determined by integrating the following findings: the delineation of fracture systems/zones and fluid migration pathways; mining activities enhance the storage and transmission ability of the aquifer; and the main sources of water in the mine include mixing of surface and deep water sources, recycling of water possibly via lineaments, and tailings dam seepages.

Summer-autumn variability of isotopes (2H and 18O) in water at small mountain catchments in South Sikhote-Alin (Pacific Russia)

Summer-autumn variability of isotopes (2H and 18O) in water at small mountain catchments in South Sikhote-Alin (Pacific Russia)

The Spatiotemporal Variability of Snowpack and Snowmelt Water 18O and 2H Isotopes in a Subarctic Catchment

AbstractThis study provides a detailed characterization of spatiotemporal variations of stable water 18O and 2H isotopes in both snowpack and meltwater in a subarctic catchment. We performed extensive sampling and analysis of snowpack and meltwater isotopic compositions at 11 locations in 2019 and 2020 across three different landscape features: (a) forest hillslope, (b) mixed forest, and (c) open mires. The vertical isotope profiles in the snowpack's layered stratigraphy presented a consistent pattern in all locations before snowmelt, and isotope profiles homogenized during the peak melt period; represented by a 1–2‰ higher 18O value than prior to melting. Our data indicated that the liquid‐ice fractionation was the prime reason that caused the depletion of heavy isotopes in initial meltwater samples prior to the peak melt period. The liquid‐ice fractionation was influenced by snowmelt rate, with higher fractionation during slow melt. The kinetic liquid‐ice fractionation was evident only in close examination of meltwater lc‐excess values, not 18O values alone. Meltwater was isotopically heavier and more variable than the depth‐integrated snowpack; the weighted mean of meltwater isotope values was higher by 0.62–1.33‰ 18O than the weighted mean of snowpack isotope values in forest hillslope and mixed forest areas, and 1.51–6.37‰ 18O in open mires. Our results reveal close to 3.1‰ 18O disparity between the meltwater and depth‐integrated snowpack isotope values prior to the peak melt period, suggesting that proper characterization of meltwater 18O and 2H values is vital for tracer‐based ecohydrological studies and models.

Spatial and Temporal Variations of Stable Isotopes in Precipitation in the Mountainous Region, North Hesse

Patterns of stable isotopes of water (18O and 2H) in precipitation have been used as tracers for analyzing environmental processes which can be changed by factors such as the topography or meteorological variables. In this study, we investigated the isotopic data in precipitation for one year in the low mountain range of North Hesse, Germany, and analyzed mainly for altitude, rainfall amount, and air temperature effects on a regional scale. The results indicate that the isotopic composition expressed an altitude effect with a gradient of −0.14‰/100 m for δ18O, −0.28‰/100 m for δ2H and 0.83‰/100 m for Deuterium excess. Patterns of enrichment during warmer months and depletion during colder months were detected. Seasonal correlations were not consistent because the altitude effect was superimposed by other processes such as amount and temperature effects, vapor origins, orographic rainout processes, moisture recycling, and sub-cloud secondary evaporation. Precipitation was mostly affected by secondary evaporation and mixing processes during the summer while depleted moisture-bearing fronts and condensation were more responsible for isotope depletion during winter. In autumn and spring, the amount effect was more prominent in combination with moisture recycling, and large-scale convective processes. The altitude effect was also detected in surface water. The investigated elevation transect with multiple stations provided unique insights into hydrological and climatic processes of North Hesse on a regional scale. The spatial heterogeneity and mixing of different processes suggest that multiple rainfall stations are required when rainfall isotopes serve as forcing data for hydrological applications such as transit time assessments in complex terrains.

How do precipitation events modify the stable isotope ratios in leaf water at Lhasa on the southern Tibetan Plateau?

ABSTRACT Serving as a medium between source water and cellulose, leaf water contributes to the isotope ratios (δ 18O, δ 2H) of plant organic matter, which can be used for paleoclimate reconstruction. This study is the first to examine the diurnal variations in the δ 18O and δ 2H of leaf water on the southern Tibetan Plateau. The δ 18O and δ 2H of leaf water were relatively low when precipitation events occurred. In particular, 18O and 2H of leaf water became extremely depleted 5 h after the precipitation event. Our findings demonstrate that precipitation can modify the isotope ratios of leaf water from external and internal causes. First, precipitation events affect meteorological elements, lead to decreases in leaf transpiration, and immediately weaken the isotope enrichment of leaf water (‘rapid effect’ of precipitation). Second, precipitation events affect the internal plant–soil water cycle process, causing the plant to preferentially use deeper soil water, and the corresponding isotope ratios of leaf water exhibit extremely low values 5 h after precipitation events (‘delay effect’ of precipitation). This study suggests that researchers need to be cautious in separating the signals of precipitation and hydrological processes when interpreting isotope records preserved in tree-ring cellulose archives from the Tibetan Plateau.

Do 2 H and 18 O in leaf water reflect environmental drivers differently?

SummaryWe compiled hydrogen and oxygen stable isotope compositions (δ2H and δ18O) of leaf water from multiple biomes to examine variations with environmental drivers. Leaf water δ2H was more closely correlated with δ2H of xylem water or atmospheric vapour, whereas leaf water δ18O was more closely correlated with air relative humidity. This resulted from the larger proportional range for δ2H of meteoric waters relative to the extent of leaf water evaporative enrichment compared with δ18O. We next expressed leaf water as isotopic enrichment above xylem water (Δ2H and Δ18O) to remove the impact of xylem water isotopic variation. For Δ2H, leaf water still correlated with atmospheric vapour, whereas Δ18O showed no such correlation. This was explained by covariance between air relative humidity and the Δ18O of atmospheric vapour. This is consistent with a previously observed diurnal correlation between air relative humidity and the deuterium excess of atmospheric vapour across a range of ecosystems. We conclude that 2H and 18O in leaf water do indeed reflect the balance of environmental drivers differently; our results have implications for understanding isotopic effects associated with water cycling in terrestrial ecosystems and for inferring environmental change from isotopic biomarkers that act as proxies for leaf water.

Appraising the factors favouring uranium mobilization and associated health risk assessment in groundwaters of north-western India

An attempt has been made in this study to evaluate the factors favoring the uranium mobilization into the groundwater of Northwest India using uranium isotope activity ratio (234U/238U), radon (222Rn) and environmental isotopes of water (2H, 18O and 3H). The values range from 23 - 597 µg/L for total uranium and 634–3210 Bq/m3 for radon and the corresponding annual effective dose is estimated to be 18.9–490 µSv/a and 6.2–31.5 μSv/a respectively. Uranium activity ratio (UAR) varies from 0.68 - 1.17 and maximum samples indicate secular equilibrium. Environmental isotopic data indicates that the source to groundwater is vertical percolation of rainwater in the case of shallow zone while regional flows from outcrop areas recharge the deep groundwater. A wide scatter is noticed in environmental 3H content (0.23–6.62 TU) indicating both fast and sluggish water flows. The UAR phase diagram suggests that leaching process controls the uranium mobilization into the groundwater. The correlations among UAR, uranium and Uexcess further indicate oxidative nature of leaching process. Statistical treatment of the obtained data along with available geochemical and isotope evidences suggest that source of uranium is common but the driving processes are different for shallow and deep zone. Influences of root zone CO2, oxic species from irrigation return flows and water level fluctuations are also evaluated. Low uranium, low UAR, low 3H and high 222Rn activity in deep zone suggest uranium being released from the roll front as well as transported from outcrop regions. This study highlights the application of uranium isotope ratio, radon and environmental isotopes in assessing vulnerability of alluvial aquifers towards uranium contamination.

Big data and environmental sustainability based integrated framework for isotope hydrology applications in India

Water contains environmental isotopes, which can act as tracers to study the source, origin, and distribution of water in the hydrological cycle. Recently, the environmental isotopes have been widely applied in hydrological investigations and it is established that the spatio-temporal variations in isotopic abundance provide valuable information to enhance the qualitative and quantitative understanding of hydrological processes such as mixing of different flow components and recharge rate, identify origin of water, delineation of groundwater recharge zones, geothermal dynamics, paleo-recharge and many others. Here, a review of case studies is presented to highlight the impact of isotope applications in water resource management in India. Along with a review of studies across India, a study is carried out for the assessment of groundwater interactions using isotopes of water (18O, 2H and 3H) in dry/semi-arid region (Jaipur) and wet/humid region (Guwahati). The major outcome of the study is the formulation of groundwater baseline for Guwahati (post-monsoon in 2017 and 2018: δD= 4.98 δ18O + 7.50) and Jaipur (post-monsoon and pre-monsoon in 2018: δD= 4.85 δ18O – 9.49). The results indicate that tritium has strong negative correlation (R2 = 0.59) with depth in Jaipur, indicating increasing groundwater age with depth. In Guwahati, the tritium shows weak positive (R2= 0.25) relationship which might be because of the presence of sandyclay layers in the shallow zone limiting vertical recharge to aquifer. Moreover, based upon the review and isotope results of the two study sites, a novel integrated framework for isotope hydrology application for India is proposed, incorporating the principles of environmental sustainability, economic efficiency and social equity. The isotopic techniques in hydrological investigations not only complements the traditional methods used in water resource management but also provides new insights and an enhanced understanding of the hydrological systems.

Oral hydration as a safe prophylactic measure to prevent post-contrast acute kidney injury in oncologic patients with chronic kidney disease (IIIb) referred for contrast-enhanced computed tomography: subanalysis of the oncological group of the NICIR study.

T he objective of this study is to evaluate oral hydration compared to intravenous (i.v.) hydration in the prevention of post-contrast acute kidney injury (PC-AKI) in the oncologic subgroup of patients with stage IIIb chronic kidney disease (CKD) included in the NICIR study referred for elective contrast-enhanced computed tomography (CE-CT). We performed a retrospective subanalysis of the oncological subgroup (174/228 patients, 74%) from a continuous prospective database of patients included in the recently published non-inferiority NICIR study. Patients received prophylaxis against PC-AKI with either oral hydration (500mL of water 2h before and 2000mL during the 24h after CE-CT) or i.v. hydration (sodium bicarbonate (166mmol/L) 3mL/kg/h starting 1h before and 1mL/kg/h during the first hour after CE-CT). The primary outcome was to compare the proportion of PC-AKI in the first 48 to 72h after CE-CT in the two hydration groups. Secondary outcomes were to compare persistent PC-AKI, the need for haemodialysis, and the occurrence of adverse events related to prophylaxis in each group. Of 174 patients included in the subanalysis, 82 received oral hydration and 92 received i.v. hydration. There were no significant differences in clinical characteristics or risk factors between the two study arms. Overall the PC-AKI rate was 4.6% (8/174 patients), being 3.7% in the oral hydration arm (3/82 patients) and 5.4% (5/92 patients) in the i.v. hydration arm. The persistent PC-AKI rate was 1.2% (1/82 patients) in the oral hydration arm and 3.3% (3/92 patients) in the i.v. hydration arm. No patient required dialysis during the first month after CE-CT or had adverse effects related to the hydration regime. In oncological patients with stage IIIb CKD referred for elective CE-CT, the rate of PC-AKI in those receiving oral hydration did not significantly differ from that of patients receiving i.v. hydration.

Molecular links between whitesand ecosystems and blackwater formation in the Rio Negro watershed

Tropical rivers such as the Rio Negro constitute a major portion of the global aquatic flux of dissolved organic carbon (DOC) entering the ocean, but the exact amount, source contributions and fate of terrestrial DOC remain unknown. We investigated the role of valley and upland whitesand ecosystems (WSEs) and terra firme plateaus in forming blackwater tributaries in the Rio Negro basin to develop novel constraints for the terrestrial export of carbon. 5709 molecular markers from ground- and surface waters of two contrasting valley and upland sites feeding Rio Negro tributaries were identified by ultrahigh resolution mass spectrometry (FT-MS), analyzed by multivariate statistics and compared to known Rio Negro markers. In a Principal Coordinates Analysis, valley and upland DOC molecular composition differed by 78% from plateau DOC, which was characterized by reworked, aliphatic and unsaturated N- and S-containing molecules, while valley and upland DOC contained mainly condensed aromatics, aromatics and oxidized unsaturated structures. Valley and upland samples differed by 10% in molecular DOC composition and by their isotopic content (14C of SPE-DOC, 18O and 2H of water) which indicated differences in hydrology and C turnover. Against expectation, markers of widespread whitesand valleys did not emerge as a major source of Rio Negro markers, but specific upland markers did. Pubchem suggested chromene and benzofuran structures as promising candidates for further study. Our findings indicate that the export of molecular markers diverges from expected transport-limited DOC behavior, and thereby opens new avenues for source annotation beyond DOC quantity. Terrestrial DOC from upland whitesand areas is a major source of specific blackwater molecules missing in the regional ecosystem C balance, whereas C export from the whitesand valleys and especially from terra firme plateaus represents mainly recycled and transformed carbon not directly affecting the ecosystem C balance and possibly, the watersheds downstream molecular signature. Our study highlights the potential of high-resolution techniques to constrain carbon balances of ecosystems and landscapes by novel molecular markers. A comparison with other terrestrial DOM datasets indicated molecular similarities with temperate acidic soils and tropical rivers that warrant further analysis of common DOM markers. Implications, limitations, and future challenges are discussed in the light of potential applications of diagnostic molecular links for DOC source annotation and estimation of terrestrial DOM export in the land-to-ocean continuum.

Temporal and spatial variations of runoff composition revealed by isotopic signals in Nianchu River catchment, Tibet

Understanding the hydrology of glaciated catchments is an important step in assessing the vulnerability of water resources to a changing climate. Based on multi-isotopes of water (2H, 18O and 3H) and dissolved radon (222Rn), the temporal and spatial variabilities of major hydrological processes along the main flow and tributaries in the Nianchu River catchment were examined and the isotopic response to climate variation was identified. Geographic variation in changes of isotopic composition that differ from other rivers in the Nianchu River catchment was apparent. Along the direction of runoff, river δ18O exhibited more depletion, which was closely related to water mixing and groundwater discharge. End-member mixing analysis using isotopic tracers suggested that annual recharge from summer rainfall and glacial meltwater maintained the surface water resources (their respective contributions rate were 65.9% and 26.5%); groundwater had a significant contribution on runoff in the dry season (about 46.6%). Summer rainfall and meltwater rapidly infiltrated through a series of faults and fissures and were, stored in underground reservoirs and released to runoff in the dry season, thereby ensuring rapid circulation and renewal of water resources (annual renewal proportion was about 40%). It was concluded that rainfall infiltration, meltwater and groundwater storage play important roles in the hydrology of this alpine-cold catchment. Similar to a general alpine-cold catchment, the stable isotopes (δ2H, δ18O) of river runoff will gradually be enriched, while groundwater reserves will increase in the Nianchu River catchment as a result of climate warming and an acceleration of glacial-melting.

Dual labelling by 2H and 15N revealed differences in uptake potential by deep roots of chicory

AimsDeep-rooted crops have been widely used in agricultural systems to access deep resources such as water and nitrogen (N). However, the potential of deep roots to take water and N at various depths have not been well studied. Here we used chicory (Cichorium intybus L.) to study the potential and dynamics of water and nitrogen uptake in deep soil layers (below 1 m). MethodsChicory plants grown in outdoor rhizotrons were labelled by injecting a 2H2O and Ca(15NO3)2 mixture into the soil column at 1.1, 2.3 and 3.5 m depth. Five, ten and twenty days after injection, 2H and 15N were traced in transpiration water and leaves. ResultsWe found enriched 2H and 15N in water and plant samples, and both water and N uptake were observed down to 3.5 m. The 2H enrichment after injection at 1.1 m depth was 1552‰, almost 10 times higher than after injection at 2.3 m depth, which was 156‰. In contrast, injection at 1.1 and 2.3 m depth resulted in similar 15N enrichment of leaf samples. ConclusionDeep water uptake was found to be more sensitive to increased depth and reduced root intensity than N uptake, and labelled N was used more rapidly than labelled water. We propose several possible explanations for the discrepancies between deep water and N uptake, and further discuss the challenges of using isotopes and models in deep root studies.

ANALYZING DECELLULARIZED AND RECELLULARIZED LIVER SCAFFOLDS USING PROTEOMICS

<h3>Background</h3> Bioengineered livers are a promising approach for treating end-stage liver disease. One of the most used techniques involves decellularization, generating scaffolds that consist primarily of extracellular matrix (ECM). This ECM can be recellularized to obtain a bioartificial organ intended to mimic the native liver. Few studies focus on how cells interact with the scaffold, and therefore the goal of this study was to evaluate the interaction between HepG2 cells and rat liver scaffolds. <h3>Methods</h3> Livers, from ten female Wistar rats, weighing ∼250 g, were harvested and decellularized through portal vein (PV) perfusion with water (2h), 1% Triton X-100 (2h), and 1% SDS (18h). Decellularization was confirmed by H&E and DNA quantification. Scaffolds were perfused with HepG2 cells cultured in DMEM supplemented with 10% fetal bovine serum and 1% penicillin and streptomycin for seven days. Albumin secretion and glucose consumption were measured in the media every other day by ELISA and glucometer. DAPI staining was used to determine the number of nuclei along with H&E to characterize tissue morphology. Immunohistochemistry for collagens I, III, and IV, laminin, fibronectin, and Ki-67 were performed. Proteins from livers and decellularized and recellularized scaffolds were analyzed using label-free proteomics. <h3>Results</h3> DNA quantification showed that decellularization removed 95% of the DNA content (p < 0.0001) and H&E confirmed the absence of nuclear content in scaffolds while preserving its structural integrity. The proteins in native livers and scaffolds were analyzed by proteomics and revealed that decellularization greatly enriches structural ECM proteins (collagens I, II, III, V and XI, and fibronectin) and also some cytoskeleton components (such as several isoforms of tubulin, actnin, keratin, and myosin). As to recellularization, H&E and DAPI staining showed that HepG2 cells were evenly distributed throughout the parenchyma. The recellularized liver secreted albumin and consumed glucose. Immunohistochemistry revealed the presence of KI67 positive cells, indicating that cell division still occurred after seven days and detected ECM proteins (collagens I, III, and IV, laminin and fibronectin) which were also observed in proteomic analysis. <h3>Conclusion</h3> Liver recellularization with HepG2 cells resembles some aspects of liver histology, function, and composition, supporting the use of this strategy in future hepatic tissue engineering strategies.