Isotopic Composition Of Water Research Articles

Isotopic signatures of moisture recycling and evaporation processes along the Western Ghats orography

The water isotopic composition (δ18O and δ2H) of humid tropical mountain belts is influenced by the limited isotopic elevation effect due to the narrow temperature gradient, high relative humidity, and the moisture feedback processes. The Western Ghats mountain forest ecosystem, recognized as a biological hotspot, contributes significantly to characterizing the hydrological and weather patterns over its windward and leeward sides. The Indian Summer Monsoon southwesterly winds advancing towards the Indian subcontinent through the Arabian Sea between June to September are obstructed by this mountain belt and get orographically uplifted, producing heavy rainfall. The present study intends to improve understanding of the variation of precipitation isotopic composition along multiple stations located at different elevations of the heavily regulated Periyar river basin (PRB), southern Western Ghats, and a coastal station (TRV). The δ18O variation with elevation across PRB reveals an abrupt depletion at the highland station and a pseudo-elevation effect due to the supply of evaporated local moisture from reservoirs and lakes. The contribution of recycled precipitation estimated using back trajectories suggests a maximum of 8.5% of locally recycled rainfall over midland station towards the September month, the daily contribution reaching a maximum of 50.7%. Though this approach did not show any signatures of moisture recycling in the highland station, the surface water (reservoirs and lakes) lc-excess (line-conditioned excess), and the d-excess (deuterium excess) values of precipitation suggest the higher rates of evaporation from large water bodies and their successive role in generating local rainfall. Statistically significant amount effects visible only along coastal stations with lower rates of precipitation and higher temperature indicate that precipitation along the Ghats region (midland and highland) is significantly controlled by orographic uplift of air moisture and the contribution from locally recycled moisture. This is further supported by the significant correlation of δ18O with regional convective processes along the Arabian Sea till midland station and further decrease towards the highland. The present study provides important information on the moisture feedback mechanism in the Western Ghats and the factors controlling the isotopic signatures over the region.

Multi-isotopic (O, H, C, S, Sr, B, Li) characterization of waters in a low-enthalpy geothermal system in Havza (Samsun), Turkey

In this study, multi-isotopic (O, H, C, S, Sr, B, Li) compositions were used to perform geochemical characterization, determine the source and reservoir rocks, and explain the water-rock interaction mechanisms for geothermal fluids in the low-enthalpy Havza (Samsun) geothermal field (HGF) in Turkey. The geothermal water of Na-HCO3 water type has a wellhead temperature of 53°C, pH of nearly 7.7 and an EC value of 1140 µS/cm. The geothermal springs of Ca-HCO3 water type have an EC value of nearly 667 µS/cm and a temperature of nearly 26°C. The reservoir temperatures of the HGF geothermal system were calculated as 60–90°C and 108–160°C by silica and SO4-H2O oxygen isotope geothermometers, respectively. Stable isotope compositions (δ2H and δ18O) show that the geothermal well water is mixed with deeply circulated waters fed from higher elevations (∼ 830–1260 m), while the geothermal spring water is mixed with shallow cold water. The positive δ13C value (+3.01‰) indicates that the dissolved inorganic carbon (DIC) in the geothermal well water has no contribution from the atmospheric CO2 but originates in the metamorphic CO2 and marine limestones. However, the DIC in the geothermal springs is derived from C3 plants and silicate weathering. The values of 34SCDT show that the sulfate in the geothermal waters is due to the dissolution of sulfate minerals. The values of δ11B (-1.12 to +9.37 ‰) in the geothermal well and spring waters reflect both leaching of surrounding rocks and mantle-derived B. The reservoir rock may be Late Cretaceous-Permian limestones and Jurassic sandstones considering 87Sr/86Sr ratios (0.707108–0.707688) and δ7Li values (-7.44 to +6.18 ‰), whereas it might be Jurassic sandstones based on δ11B values. The strontium isotope composition of the geothermal spring water indicates the mixing of deep geothermal waters and cold groundwaters.

Water Isotopic Signature of Surface Snow Metamorphism in Antarctica

AbstractWater isotope ratios of ice cores are a key source of information on past temperatures. Through fractionation within the hydrological cycle, temperature is imprinted in the water isotopic composition of snowfalls. However, this signal of climatic interest is modified after deposition when snow remains at the surface exposed to the atmosphere. Comparing time series of surface snow isotopic composition at Dome C with satellite observations of surface snow metamorphism, we found that long summer periods without precipitation favor surface snow metamorphism altering the surface snow isotopic composition. Using excess parameters (combining D,17O, and18O fractions) allow the identification of this alteration caused by sublimation and condensation of surface hoar. The combined measurement of all three isotopic compositions could help identifying ice core sections influenced by snow metamorphism in sites with very low snow accumulation.

Event-Based Stable Isotope Analysis of Precipitation Along a High Resolution Transect on the South Face of O‘ahu, Hawai‘i

While the influence of elevation and seasonal variation on isotopic composition has been studied on Maui, Hawai‘i Island, and O‘ahu (Scholl et al. 1996, Scholl et al. 2002, Scholl et al. 2007, Dores et al. 2020, Fackrell et al. 2020, Tachera et al. 2021), this work is the first to investigate event-based precipitation in detail on the island of O‘ahu. The stable isotopic composition of water has been used to track the movement of water within the hydrosphere, to investigate the type and origin of a rainfall event, and elevation of collection, among other characteristics. Here, we present a high-resolution study of the stable isotopes δ2H and δ18O of precipitation along a compact land-to-sea transect in Waikīkī, a southwest facing region on O‘ahu. The study provides a unique, in-depth investigation into the nature of individual storm events, and how they contribute to a larger seasonal climatic pattern. Monthly precipitation samples were collected at three sites along the transect from December 2017 to March 2019 and event-based samples were collected at the Makai site from October 2018 to February 2019. Storm direction, temperature, and relative humidity were recorded for each event-based sample. Results suggest that evaporative conditions at different elevations influence the isotopic composition of precipitation, either through net addition as moisture recycling, or net loss of evaporated water. The spatial distribution of these patterns from site to site illustrates the extreme heterogeneity of Hawaiian watersheds.

Variations in human body water isotope composition across the United States

Accurate human provenancing using stable isotopes depends directly on solid understandings of the geographic and individual factors affecting isotope variability and incorporation into human tissues. Transfer of isotopic, and therefore spatial, information between environmental water and biological tissues is mediated by the isotopic composition of body water. Thus, there is a need to study body water isotope ratios at a population level and over a large isotopic and geographic range. We evaluated oxygen (δ18Obw) and hydrogen (δ2Hbw) isotope values of body water from 72 volunteers in 10 different cities across the US, and over a 5–10-day period. We analyzed covariates (e.g., water intake, physical activity, biometrics, gender) that might explain individual stable isotope ratio variations and tested a predictive model that incorporates the δ-values of drinking water, food, and O2 as well as individual variables to predict the δ-values of body water. The individual variability in body water isotope values overtime (mean 0.3‰ for δ18Obw and 2.3‰ for δ2Hbw) was lower than the intra-city variability (mean 0.9‰ for δ18Obw and 6.9‰ for δ2Hbw). Body water isotope values differed among cities (ANOVA: δ18ObwF = 97.2, p < 0.001; δ2HbwF = 176.2, p < 0.001). However, significant overlap among some cities with different drinking water was discovered. We detected significant covariation of measured drinking water and human body water isotope values (both isotope systems R2 ≥ 0.89, p < 0.001) and small but significant effects of the average daily exercise and amount of fluid intake. The differences between measured and model-predicted body water values (mean 0.12 ± 1.2‰ for Δδ18O and −1.2 ± 8.2‰ for Δδ2H) were statistically indistinguishable from zero (Δδ18O t = −0.751, p = 0.45; Δδ2H t = 1.133, p = 0.26). Here we show that community level variation exists in the δ18Obw and δ2Hbw values and the primary drivers are the regional differences in drinking water isotopes. Consistency of the body water isotope composition over the study period suggests that tissues would incorporate a stable isotope signal over time. The amount of drinking water and physical activity influence body water values, while the variation in the isotopic values of food may contribute to regional level variability, but that still remains to be assessed further. The human body water model provides accurate estimates for measured values, capturing and reproducing the main features of the body water isotope variation across space.

Geochemical Study on the Annual Variation of Oxygen Isotope and Chemical Composition of Groundwater in the Sho River Alluvium Fan, Toyama, Japan, as an Investigation of Selected Qualitative Aspects of Efficient Utilization of Groundwater Heat

Seasonal variations of water temperature, electric conductivity, and oxygen isotope and chemical composition of shallow groundwaters and river waters were determined in the Sho River alluvial fan, western Toyama Prefecture, Japan, to examine groundwater heat utilization for indoor climate control. Samples were collected at 31 sites every 2 months for 1 year and at 11 representative sites monthly. In addition, the results of monthly precipitation amount and oxygen isotope composition of precipitation collected within the region during the same period were also taken into account. The sources of the shallow groundwaters are a mixture of river water and precipitation. The contribution of precipitation to groundwater is generally small along the Sho River but reaches as much as 80% along the Oyabe River and in the south and west of the alluvial fan. Though the origin of the groundwater differs regionally, water temperature is fixed at around 15 °C throughout the year in the northern part of the alluvial fan, and open-type ground source heat pump systems can be used for cooling and heating there, if adequate quantitative aquifer properties (exploitable groundwater amounts) are present.

Geochemical Features of the Thermal and Mineral Waters From the Apuseni Mountains (Romania)

The Apuseni Mountains are located between the large geothermal area of the Pannonian Basin and the low thermal flux Transylvanian Basin. Thermal and mineral waters have been sampled from 42 points along a NW-SE transect. The general chemistry and the water isotope (deuterium and oxygen-18) composition were analyzed. Most of the thermal aquifers are located in carbonate reservoirs. The waters mainly belong to the Ca-HCO3 hydrochemical type, excepting the western side, towards the Pannonian Basin, where the Na-HCO3 type may occur. The isotope composition indicates aquifer recharge from precipitation. The geochemical characteristics and the structural position of the study area suggest two distinct geothermal contexts. The Southern Apuseni area geothermal features are likely connected to the Neogene—Early Quaternary magmatic activity from the Mureş Valley and Zarand Depression. The geothermal manifestations in the north-western part of the study area, at the border between the Northern Apuseni and the Pannonian Depression, share features of the latter one.

Differentiation of Hydrogen and Oxygen Isotopes in the Water Source Treatment Wetlands of Stream Networks

To explore the isotopic distribution and differentiation of water along the hydraulic flow gradients and plant-bed/ditch systems in constructed root-channel wetlands, surface and subsurface water samples were collected from four ecological wetlands, namely Shijiuyang and Guanjinggang in Jiaxing, as well as Changshuitang and Taishangang in Haining. All samples were collected along water flow pathways during the wet and rainy summer season in August 2019, except for those from Taishangang, which were collected within the plant-bed/ditch system during the dry and cold winter season in January 2020. The abundance of deuterium (δD) and δ18 O was determined in each functional area of the wetlands to assess the influence of wetlands on water differentiation. Stable isotope technology and mathematical statistics were used to analyze the distribution of δD and δ18 O in constructed root-channel wetlands and to reveal the influence of plant-bed/ditch systems on stable isotopes of water. A variety of data mining methods were used to examine the differentiation of stable isotopes of water, at various dimensions and scales, including nonparametric Kendall's tau-b correlation, stepwise regression, gray relational analysis, and machine learning (random forest) combined with scatter diagrams and model hypothesis diagnosis analysis. The main results were as follows:① The spatiotemporal variations in water isotopes of stream networks were largely affected by different water supply and evaporation enrichment effects. The slope and intercept of the wetland water line in Jiaxing were both significantly lower than the regional precipitation line of the adjacent Changshu Station (CHNIP). This showed that the wetlands area had undergone hydrogen and oxygen isotope enrichment. The δD values in Shijiuyang wetland water ranged from -52.2‰ to -49.4‰, and δ18 O values ranged from -7.6‰ to -6.9‰. In Guanjinggang wetland water samples, δD ranged from -48.1‰ to -45.1‰, and δ18 O ranged from -6.8‰ to -5.8‰. The δD values in Changshuitang wetland water ranged from -49.8‰ to -48.4‰, and δ18 O ranged from -7.2‰ to -6.6‰. The δD values in Taishangang wetland water ranged from -55.3‰ to -51.6‰, and δ18 O ranged from -7.8‰ to -7.2‰. ② Hydrogen and oxygen isotope abundance and composition of water showed complex nonlinear changes in the vertical and horizontal dimensions at different scales. At the regional scale, water level elevation in the vertical dimension had a greater impact on water isotope distribution than the length of the hydraulic flow pathway in the horizontal dimension. Water isotopes tended to be enriched in low-lying areas with low water levels. At the local scale, the influence of hydraulic process often played a greater role in determining water isotope distributions. The spatial variations of water isotopes were comprehensively determined by the evaporation of regional water and meandering hydraulic processes inside the wetland. ③ Compared with other wetland functional areas, the central constructed root-channel area (middle treatment zone) was more enriched in water isotopes. ④ The underground macropore network formed by plants with developed rhizomes or roots (e.g., Phragmites communis Trin. and Typha orientalis Presl), mineral-rich substrate soil, and aquatic plants in the plant bed had a significant influence on the abundance of hydrogen and oxygen isotopes in the plant-bed/ditch system. Therefore, when water passed through the plant-bed/ditch system, the values of δD and δ18 O in the lower ditch (outlet) were lower than those in the higher ditch (inlet). ⑤ The abrupt change in isotopic contents of the plant-bed/ditch system might indicate an inflection point in water quality purification. ⑥ The deuterium excess (d-excess) in subsurface water of the plant-bed/ditch system was significantly higher than that in ditch water, and the coefficient of variation in subsurface water was considerably greater than that in ditch water. The d-excess in the wetland root-channel ecological purification zone showed significant temporal differences and was negative in the summer and positive in the winter, which reflected the seasonal variation in water vapor sources and the spatial variation in isotope fractionation behavior in wetlands. These results provide some understanding of the distribution of water isotopes in constructed wetlands, which will strengthen their operation and management. This study also provides some ideas regarding new technologies for water quality improvement and shows that water isotope technology may be a reliable method for analyzing wetland hydrology.

Impact of landscape dams on river water cycle in urban and peri-urban areas in the Shiyang River Basin: Evidence obtained from hydrogen and oxygen isotopes

To meet the needs of human recreation and provide community amenities, landscape dams (i.e., water retaining structures for intercepting river water in cities and surrounding areas, which are mainly used to create an urban landscape environment) are built in urban and peri-urban areas worldwide. The construction of these dams, however, may adversely affect the local and regional water cycle. We collected water samples from 2015 to 2019 from different water bodies in urban and peri-urban areas traversing the middle and upper reaches of Shiyang River Basin in the arid area of Central Asia to analyze their isotopic characteristics. Meanwhile, field surveys as well as meteorological, hydrological, and remote-sensing data were added to evaluate the hydrologic effects of urban landscape dams on a watershed scale in an arid region with scarce water resources and fragile ecosystems. Isotopic values of landscape water were more enriched than that of natural river. The result of the evaporation loss ratio showed that the landscape water was 0–5% higher. Moreover, the cumulative effect of multiple landscape dams leads to a great loss of water resources in arid areas. The study also demonstrated that evaporation is a vital factor in causing change in the isotope composition of the landscape water in the Shiyang River Basin. The interaction between surface water and groundwater was frequent within the landscape dam area wherein groundwater was mainly recharged by surface water leakage. Sufficient attention should be given to the evaporation, leakage, local precipitation, and groundwater changes caused by the impoundment of landscape dams. Thus, the potentially adverse effects of urban landscape dams in arid regions should be highly considered in long-term water-resources sustainability planning.

Using fin ray chemistry to discriminate hatchery reared juvenile age-0 Persian sturgeons by their origin in the Southern Caspian Sea region using split stream ICP-MS/MC ICP-MS

Trace elements integrated into fish fin rays from the ambient environment may represent a permanent record of the environmental conditions that an individual has experienced throughout its lifetime. Fish from hatcheries used for stocking may therefore carry a natural intrinsic tag of their origin, which can be then later used for assessing the efficiency of stocking measures. This study investigated the potential of the elemental and strontium isotope (n(87Sr)/n(86Sr)) composition of fin rays of juvenile Persian sturgeons (Acipenser persicus) to determine their origin. Water and pectoral fin ray samples of twenty age-0 juvenile Persian sturgeons were collected from the largest hatcheries in the east and west of the Southern Caspian Sea region. The elemental content and the Sr isotope ratio in water were determined by (multi collector) inductively coupled plasma mass spectrometry ((MC) ICP-MS), while the elemental content in fin rays (Ba, K, Mg, Mn, Na, Sr) together with the Sr isotope ratio were determined using laser ablation split stream ICP-MS/MC ICP-MS. The elemental composition of Al, B, Ba, Ca, Cu, Fe, Ga, Li, Mg, Mn, Mo, Na, Pb, Rb, Sr, Tl, U and Zn and the Sr isotope ratio of water differed between the investigated hatcheries from the east and west of the Southern Caspian Sea region. Fin rays reflected the elemental (Sr, Ba and Mn) and the Sr isotope composition of pool water of their hatchery of origin. A factor analysis yielded one main factor (high in Sr content and in the n(87Sr)/n(86Sr) ratio and low in Ba and Mn content) discriminating fin ray samples between sites explaining 86 % of the variation. A discrimination analysis by cross-validated classification yielded 100 % correct assignments of fin ray samples to the hatchery sites using all different parameter combinations. These results suggested that the Sr, Ba Mn elemental and Sr isotope composition of fin rays can be used for the determination of the source hatchery of stocked fish. This represents a valuable tool for evaluation restocking measures of Persian sturgeons in the Southern Caspian Sea region.

Seawater‐Particle Interactions of Rare Earth Elements and Neodymium Isotopes in the Deep Central Arctic Ocean

AbstractIn the central Arctic Ocean, dissolved rare earth element concentrations ([dREE]) and the neodymium (Nd) isotope compositions are constant throughout the deep water column (&gt;1,000 m water depth), indicating unique conditions among the ocean basins and therefore requiring an investigation of seawater‐particle interactions. Here, we present the first high‐resolution particulate REE and Nd isotope data from the Arctic Ocean and discuss the possible seawater‐particle processes affecting the Arctic Ocean. Our results show that particulate [REE] are on the same order of magnitude as in other ocean basins, suggesting that particle composition is the main cause for a lack of pREE release to the dissolved pool. The lithogenic fraction dominates throughout the water column while the biogenic material contribution is very small. This paucity of biogenic material results in reduced particle‐seawater exchanges of REEs and Nd isotopes. Moreover, we note only slight differences in the dissolved Nd isotope composition between the Eurasian and Canadian Basins. This is due to the different source regions supplying different dissolved and particulate Nd isotope signatures to both basins. The dissolved [REE] and Nd isotope composition of Atlantic waters are modified during their flow paths through contributions from the Kara Sea, lowering the salinity and increasing [dREE] and dNd isotope compositions. Hydrothermal influence from the Gakkel Ridge on dissolved and particulate [REE] and Nd isotopes could not be detected.

Hydrological Connectivity in a Permafrost Tundra Landscape near Vorkuta, North-European Arctic Russia

Hydrochemical and geophysical data collected during a hydrological survey in September 2017, reveal patterns of small-scale hydrological connectivity in a small water track catchment in the north-European Arctic. The stable isotopic composition of water in different compartments was used as a tracer of hydrological processes and connectivity at the water track catchment scale. Elevated tundra patches underlain by sandy loams were disconnected from the stream and stored precipitation water from previous months in saturated soil horizons with low hydraulic conductivity. At the catchment surface and in the water track thalweg, some circular hollows, from 0.2 to 0.4 m in diameter, acted as evaporative basins with low deuterium excess (d-excess) values, from 2‰ to 4‰. Observed evaporative loss suggests that these hollows were disconnected from the surface and shallow subsurface runoff. Other hollows were connected to shallow subsurface runoff, yielding d-excess values between 12‰ and 14‰, close to summer precipitation. ‘Connected’ hollows yielded a 50% higher dissolved organic carbon (DOC) content, 17.5 ± 5.3 mg/L, than the ‘disconnected’ hollows, 11.8 ± 1.7 mg/L. Permafrost distribution across the landscape is continuous but highly variable. Open taliks exist under fens and hummocky depressions, as revealed by electric resistivity tomography surveys. Isotopic evidence supports upward subpermafrost groundwater migration through open taliks under water tracks and fens/bogs/depressions and its supply to streams via shallow subsurface compartment. Temporal variability of isotopic composition and DOC in water track and a major river system, the Vorkuta River, evidence the widespread occurrence of the described processes in the large river basin. Water tracks effectively drain the tundra terrain and maintain xeric vegetation over the elevated intertrack tundra patches.

Hydrological characteristics of the Bay of Bengal water column using δ18O during the Indian summer monsoon

The Bay of Bengal, the eastern part of the northern Indian Ocean, experiences a reversal of monsoonal winds that control its surface and subsurface hydrological characteristics. Due to the limited number of studies, many aspects of the Bay of Bengal water column, particularly its deep hydrodynamic characteristics, are not thoroughly understood. For this purpose, oxygen isotopic compositions of water (δ18O), a potential tracer of oceanographic study, were measured at twelve discrete depths at eight locations in the central Bay of Bengal during the summer monsoon. The water columns were sampled to include surface (≤ 10 m), subsurface zone (25, depth of Deep Chlorophyll Maxima, 75, and 100 m), intermediate zone (150, 200, 300, and 500 m) and deep zone (1000, 1500, and 2000 m). Slopes of δ18O-salinity relationships at the surface and subsurface zones were similar. The δ18O and salinity showed an increasing southward trend at the surface, subsurface, and intermediate zones, which could be attributed to the influx of relatively saline and 18O enriched water from the Arabian Sea through Southwest Monsoon Current. The TS characteristics along with the negative slope of δ18O-salinity in the intermediate zone (− 0.51 ± 0.14) indicated the presence of Indonesian Throughflow water in the Bay of Bengal. Temporal variation in δ18O and slope of δ18O-salinity relationship in the intermediate zone was also observed, possibly indicating variable contribution of Indonesian Throughflow water mass through time. The δ18O of the deeper water showed the signature of existence of North Atlantic Deep Water in the Bay. Mesoscale eddies, a frequent phenomenon in the Bay of Bengal, also seem to modulate the δ18O-salinity relationship in the basin.

Robust Estimation of Absorbing Root Surface Distributions From Xylem Water Isotope Compositions With an Inverse Plant Hydraulic Model

The vertical distribution of absorbing roots is one of the most influential plant traits determining plant strategy to access below ground resources. Yet little is known of natural variability in root distribution since collecting field data is challenging and labor-intensive. Studying stable water isotope compositions in plants could offer a cost-effective and practical solution to estimate the absorbing root surfaces distribution. However, such an approach requires developing realistic inverse modeling techniques that enable robust estimation of rooting distributions and associated uncertainty from xylem water isotopic composition observations. This study introduces an inverse modeling method that supports the assessment of the root allocation parameter (β) that defines the exponential vertical decay of a plants’ absorbing root surfaces distribution with soil depth. The method requires measurements obtained from xylem and soil water isotope composition, soil water potentials, and sap flow velocities when plants’ xylem water is sampled at a certain height above the rooting point. In a simulation study, we show that the approach can provide unbiased estimates of β and its associated uncertainty due to measuring errors and unmeasured environmental factors that can impact the xylem water isotopic data. We also recommend improving the accuracy and power of β estimation, highlighting the need for considering accurate soil water potential and sap flow monitoring. Finally, we apply the inverse modeling method to xylem water isotope data of lianas and trees collected in French Guiana. Our work shows that the inverse modeling procedure provides a robust analytical and statistical framework to estimate β. The method accounts for potential bias due to extraction errors and unmeasured environmental factors, which improves the viability of using stable water isotope compositions to estimate the distribution of absorbing root surfaces complementary to the assessment of relative root water uptake profiles.

Estimation of seasonal base flow contribution to a tropical river using stable isotope analysis

Increase in water demand within the Cauvery River Basin is a cause of serious concern over sustainable utilization and managment of water resources. Sustainable, efficent and equitable managment of Cauvery riverwater requires a thorough understanding of the contributing sources and hydrological processes influencing avaliability of water resources. The study investigates the seasonal contribution of surface runoff and baseflow to the Cauvery streamflow using isotope mass balance approach. Stable Isotope measurements (δ2H, δ18O) of Cauvery river water along with groundwater are carried during seasonal time intervals spanning from 2014 − 2016, covering pre-monsoon (PM), south-west monsoon (SWM) and north-east monsoon (NEM) seasons. Field campaigns yielded seasonal datasets of Cauvery riverwater and groundwater isotopic composition. Stable isotope analysis showed a seasonal shift in the river water isotopic composition (δ2H 8‰, δ18O 0.95‰) between pre- monsoon (PM) and south-west monsoon (SWM) seasons. Isotopically heavier values are recorded during the pre-monsoon season; coinciding with the period of low flow condition, whereas the monsoon season is characterized by high discharge and recorded isotopically lighter values. The Krishna Raja Sagar (KRS) Reservoir controls the isotopic composition of riverwater by evaporative process, during the pre-monsoon season resulting in river water becoming isotopically lighter. We utilized two-component mixing model to estimate the seasonal base flow contribution to the Cauvery River, for which the river is segmented into three sectors. The average base flow contribution to river flow during pre-monsoon season in sector I is 85 ± 5%, whereas in sector II and III the average groundwater contribution drops to 59 ± 3% and 39 ± 3% respectively. Similarly, the average base flow contribution to the river flow during south-west monsoon season drops to 32 ± 7% in sector I, whereas in sector II and III the average base flow contribution is estimated at 42 ± 7% and 47 ± 7% respectively. The base flow contribution is appreciably high in the upper Cauvery Basin comprising the Western Ghats, which plays a crucial role in sustaining stream flow during the pre-monsoon season. Assessment of spatial and temporal variability of surface water and groundwater isotopic composition within the Cauvery River Basin provides an important dataset for developing a sustainable river management plan in this tropical mesoscale riverine system.

Evaluating organic geochemical proxies for application to coastal lake sediments along the Gulf Coast of Florida for paleotempestology

Organic geochemical proxies (OGPs) preserved in coastal lake sediments have recently been used to reconstruct millennia-long hurricane records. Although OGPs (δ13C, δ15N and C/N) appear to be a more sensitive indicator of past storm events than traditional proxies used in paleotempestology, the method has not been tested in many lakes with modern data. In this study, we measured the δ13C, δ15N and C/N values of particulate organic matter (POM), along with the salinities and stable isotopic compositions of water (δ18O and δD), in two coastal lakes on seasonal or much shorter time scales throughout a 3-year period. This work was intended to develop a better understanding of the dynamics of OGPs in these lakes. The time-series data not only show that geochemical properties of these lakes varied seasonally, reflecting variations in lake biological and environmental conditions, but displayed unique variation patterns in response to storms that caused either seawater flooding or freshwater flooding of the lakes. The data show that seawater flooding led to higher δ13C and δ15N values, with either lower or no change in the C/N ratios of the POM, generally consistent with a previously proposed conceptual model for detecting seawater flooding events. The data also show that freshwater flooding reduces δ15N and increases the C/N values of POM, in addition to lowering the salinity, δ18O and δD of lake water. These time-series modern data demonstrate the feasibility of detecting past storm events that were large enough to cause either seawater or freshwater flooding by examining variation patterns of multiple OGPs in coastal lake sediments. Applying this understanding to a sediment core from one of the study lakes (Mullet Pond, Florida), we reconstructed a centuries-long record of storms based on the variation patterns in OGPs together with 210Pb ages. The OGP-based storm record suggests that 30 flooding events, including 15 seawater flooding and 15 freshwater flooding incidents, occurred over the last 165 years. Almost all of these flooding events can be matched (within the dating uncertainty) to the historic hurricanes that are known to have passed within 150 km of the study site. This further confirms that OGPs preserved in sediments in coastal lakes of Florida or similar regions may be used as reliable recorders of past storm activity.

Insights into the isotopic mismatch between bulk soil water and &amp;lt;i&amp;gt;Salix matsudana&amp;lt;/i&amp;gt; Koidz trunk water from root water stable isotope measurements

Abstract. Increasing numbers of field studies have detected isotopic mismatches between plant trunk water and its potential sources. However, the cause of these isotopic offsets is not clear, and it is uncertain whether they occur during root water uptake or during water transmission from root to trunk. Thus, we measured the specific isotopic composition (δ2H and δ18O) of each component (e.g. bulk soil water, mobile water, groundwater, trunk water and root water of Salix matsudana Koidz trees) in the soil–root–trunk continuum with a resolution of about 3 days. We report three main findings. First, we detected a clear separation between the isotopic compositions of mobile water and bulk soil water, but the distinction between mobile water and bulk soil water gradually decreased with increasing soil depth. Second, root water composition deviated from bulk soil water isotopic composition but overlapped with the composition derived for less mobile water. The maximum differences in δ2H and δ18O between bulk soil water and root water were −8.6 ‰ and −1.8 ‰, respectively. Third, trunk water was only isotopically similar to root water at 100–160 cm depths, and it remained stable during the experimental period, suggesting that the trees consistently used the stable deep water source. In conclusion, the isotopic offset between bulk soil water and trunk water of S. matsudana reflected an isotopic mismatch between root water and bulk soil water associated with the heterogeneity of the soil water. Our results illuminate relationships between the isotopic compositions of soil waters of various mobilities, root water and trunk water that may be useful for advancing our understanding of root water uptake and transport.

Hydrogeochemical evolution and groundwater recharge processes in arsenic enriched area in central Gangetic plain, India

The present study dealt with understanding hydrogeochemical evolution, ascertaining distribution, fate and spatio-temporal variation of arsenic along with comprehending recharge processes and quantification of recharge rate in the central Gangetic plain, India. The arsenic enriched area was observed mostly in the fluvial deposits with younger alluvium. The depth to water levels maps for 1996 and 2016 showed marked spatio-temporal variation and the groundwater recharge rate was estimated to be varied between 0.05 m/year and 0.07 m/year in the study area. The elevated arsenic concentration was noticed in the region, having declined groundwater recharge. A total of 147 water samples were collected from hand pumps (n = 141) and rivers (n = 6) during the pre-monsoon period (May 2016). In addition, about 81 groundwater samples were collected from 27 locations during the pre-monsoon, monsoon and winter 2019 for studying seasonal variability in the hydrogeochemical parameters and isotopic composition of water. Arsenic concentration was found more in the area where deposits of coarser sediment of the Quaternary period was present along the rivers Ganga and Ghaghra. The arsenic concentration was observed higher in the pre-monsoon (maxm. As 641 μg/L), followed by the post-monsoon (425 μg/L) and monsoon season (375 μg/L). The depleted isotopic value and higher D-excess values in groundwater suggested active recharge conditions with precipitation as the major source of recharge in the study area. It is hypothesized that rainwater induced oxygenated water into the aquifer by the process of recharge, which may prompted various biogeochemical reactions due to change in redox conditions and endorsed arsenic sorption in the monsoon season. Thereafter, anoxic conditions prevailed in the post-monsoon season, and finally, in the pre-monsoon season, reducing conditions continued and arsenic released at a rapid rate, which was justified with the seasonal variation of arsenic concentration.

Sr Isotope Composition of Mud Volcanic Waters in the Kerch–Taman Province

Sr Isotope Composition of Mud Volcanic Waters in the Kerch–Taman Province

Isotopic fractionation from deep roots to tall shoots: A forensic analysis of xylem water isotope composition in mature tropical savanna trees

Studies of plant water sources generally assume that xylem water integrates the isotopic composition (δ2H and δ18O) of water sources and does not fractionate during uptake or transport along the transpiration pathway. However, woody xerophytes, halophytes, and trees in mesic environments can show isotopic fractionation from source waters. Isotopic fractionation and variation in isotope composition can affect the interpretation of tree water sources, but most studies to date have been greenhouse experiments. Here we present a field-based forensic analysis of xylem water isotope composition for 12 Eucalyptus tetrodonta and Corymbia nesophila trees. We used a 25-tonne excavator to access materials from the trees' maximum rooting depth of 3 m to their highest canopies at 38 m. Substantial within-tree variation occurred in δ2H (−91.1‰ to −35.7‰ E. tetrodonta; −88.8‰ to −24.5‰ C. nesophila) and δ18O (−12.3‰ to −5.0‰ E. tetrodonta; −10.9‰ to −0.3‰ C. nesophila), with different root-to-branch isotope patterns in each species. Soil water δ2H and δ18O dual isotope slopes (7.26 E. tetrodonta, 6.66 C. nesophila) were closest to the Local Meteoric Water Line (8.4). The dual isotope slopes of the trees decreased progressively from roots (6.45 E. tetrodonta, 6.07 C. nesophila), to stems (4.61 E. tetrodonta, 5.97 C. nesophila) and branches (4.68 E. tetrodonta, 5.67 C. nesophila), indicative of fractionation along the xylem stream. Roots of both species were more enriched in 2H and 18O than soil water at all sampled depths. Bayesian mixing model analysis showed that estimated proportions of water sourced from different depths reflected the contrasting root systems of these species. Our study adds evidence of isotopic fractionation from water uptake and along the transpiration stream in mature trees in monsoonal environments, affecting the interpretation of water sources. We discuss the findings with view of interpreting aboveground xylem water isotopic composition, incorporating knowledge of root systems.