Stable Isotope Hydrology Research Articles

Stable isotope hydrology of a polymictic lake: Capturing transience of groundwater interactions

Although there have been many studies of groundwater inflow to small lakes, no systematic attention has been paid to the role of the time interval in the reliability of transient flow analysis. We addressed this issue in a two-year study of the isotope hydrology and water budget of a small lake in eastern Washington State (USA) that has been subject to limited management over several decades. The weighted local meteoric water line is δ2H = 7.14 δ18O – 5.22, reflecting the impact of convective recycling in this semi-arid region of inland northwestern North America. Groundwater inflow to the lake was quantified over two years using a short-interval isotopic transient mass balance approach. Calculated inflow was less than a fifth of the lake’s total water budget. Unrealistic temporal fluctuation of the calculated inflow was apparently correlated with fluctuation of the observed isotopic ratio of lake water (δL). We obtained realistic lake fluctuation and groundwater–lake exchange estimates by experimenting with the time interval of the isotope mass balance. It is crucial to acknowledge that each lake possesses unique characteristics that influence hydrologic and isotopic variations. Therefore, the optimal time interval for sampling and calculating mass balance may vary among different small lakes. Our findings have implications for long-term studies with frequent interval sampling.

Stable Isotope Hydrology of Karst Groundwaters in Romania

In this article we present the first investigation of the stable isotope composition of groundwater in Romania, East-Central Europe, with a focus on the karst areas. Our aim is twofold: (1) to provide a countrywide map with the distribution of stable oxygen and hydrogen isotope ratios in groundwater, and (2) to assess the recharge patterns of karst water. We collected more than 600 water samples from springs and wells across Romania for stable isotope analyses and monitored in detail the stable isotope composition of the waters as they pass through five cave systems. Our data show a spatial distribution of the stable isotope composition of the groundwater with low values in the mountainous area and high values in the surrounding lowlands and the central Transylvanian Depression. However, waters in karst areas induce departures from this distribution, resulting from the fast (hours to days) transfer of waters from high (ponor) to low (spring) altitudes. Water emerging from the karst springs has generally lower δ values than before sinking through the ponors, thus indicating a substantial contribution of winter recharge through diffuse infiltration and seepage. This contribution results in overall dilution of the water entering through ponors, likely resulting in changes in the chemical composition of the water and diluting potential pollutants. Our data call for careful separation between karst and non-karst spring/well waters, as indiscriminate common treatment might lead to erroneous interpretations.

The stable isotope hydrology of Sable Island, Nova Scotia, Canada with implications for evaluating the water budget of wild horses

ABSTRACT We investigated the stable isotope hydrology of Sable Island, Nova Scotia, Canada over a five year period from September, 2017 to August, 2022. The δ 2H and δ 18O values of integrated monthly precipitation were weakly seasonal and ranged from –66 to –15 ‰ and from –9.7 to –1.9 ‰, respectively. Fitting these monthly precipitation data resulted in a local meteoric water line (LMWL) defined by: δ 2H = 7.22 ± 0.21 · δ 18O + 7.50 ± 1.22 ‰. Amount-weighted annual precipitation had δ 2H and δ 18O values of –36 ± 11 ‰ and –6.1 ± 1.4 ‰, respectively. Deep groundwater had more negative δ 2H and δ 18O values than mean annual precipitation, suggesting recharge occurs mainly in the winter, while shallow groundwater had δ 2H and δ 18O values more consistent with mean annual precipitation or mixing of freshwater with local seawater. Surface waters had more positive values and showed evidence of isolation from the groundwater system. The stable isotopic compositions of plant (leaf) water, on the other hand, indicate plants use groundwater as their source. Fog had δ 2H and δ 18O values that were significantly more positive than those of local precipitation, yet had similar 17O-excess values. δ 2H values of horsehair from 4 individuals lacked seasonality, but had variations typical to those of precipitation on the island. Differences in mean δ 2H values of horsehair were statistically significant and suggest variations in water use may exist between spatially disparate horse communities. Our results establish an important initial framework for ongoing isotope studies of feral horses and other wildlife on Sable Island.

Hydrochemical dynamics of stream following rainfall events at agricultural catchments in New Zealand

One of the prerequisites for efficiently managing lake water quality is reliable data regarding the quantity and quality of inflows water, mainly the export of nutrients from the catchment area during rainfall events. We investigated the dynamic characteristics of hydrochemicals concerning rainfall events in agricultural stream waters flowing into eutrophic lakes situated on the North Island’s central plateau of New Zealand. We utilized isotopic composition of water (δ2H-H2O and δ18O-H2O) and nitrate (δ15N-NO3- and δ18O-NO3-) along with high-frequency hydrochemical data for source identification of water and nitrate during a drought period (2020). Our findings indicate that it is essential to initially grasp the fundamental mechanisms associated with rainfall events to formulate effective strategies for minimizing nutrient losses. The methodology outlined in this research integrates stable isotope hydrology with water quality monitoring initiatives, facilitating the understanding and managing the primary governing mechanisms behind diverse contaminant losses from land to adjacent water bodies, explicitly focusing on nitrates. This approach establishes a framework that can assist in devising measures for water quality improvement capable of anticipating the repercussions of substantial rainfall events more effectively.

The contemporary stable isotope hydrology of Lake Suigetsu and surrounding catchment (Japan) and its implications for sediment-derived palaeoclimate records

The Lake Suigetsu sediment cores exemplify a high-quality archive of palaeoclimatic change in East Asia during the past 150 ka. Robust interpretation of stable isotope-based proxy reconstructions from the Suigetsu cores can be aided by a greater understanding of the factors affecting the isotope composition of the lake and how it relates to that of precipitation. Here we use extended contemporary monitoring to establish the factors affecting the stable isotope composition (δ18O, δ2H and d-excess) of precipitation, river water and lake water in the catchment surrounding Lake Suigetsu, central Japan. We show that the composition of precipitation is influenced by the dual East Asian Monsoon system, producing minima in δ18O and δ2H and semi-annually varying d-excess values across the year. These signals are then transferred to the lake system, where they are combined with secondary local influences on lake water composition: homogenisation with existing catchment waters, a catchment transit lag, the interaction with saline water from the nearby Sea of Japan, and evaporative enrichment during summer. Our observations suggest that the palaeo-isotope composition of Lake Suigetsu was closely related to the behaviour of the East Asian Monsoon. We highlight lake stratification and proxy seasonality as critical components of signal interpretation.

Stable isotope hydrology of surface and ground waters in King George Island, Antarctica

ABSTRACT The region around the tip of the Antarctic Peninsula is warming fast, a situation that will lead to widespread changes in local hydrological cycles. King George Island (KGI) hosts a complex network of lakes and rivers, fed by glaciers, snow and rain, and underlain by thick permafrost. We present here the first study of the stable isotope composition of the surface waters in the ice-free southern peninsulas of KGI. Permafrost samples had the highest δ 18O and δ 2H values (–6.7 and –50 ‰, respectively), and river waters the lowest (–9.1 and –70 ‰, respectively), with groundwater (–8.2 and –62.7 ‰, respectively), lakes (–8.6 and –66.8 ‰, respectively) and (summer) meltwater (–9 and –69.5 ‰, respectively) having intermediary values. Our results suggest that a clear separation of the various water bodies (permafrost, snow, meltwater, lakes) based on the δ 18Owater and δ 2Hwater is possible. Further, water in lakes on a W–E transect (i.e. with increased distance from the Bellingshausen Sea) have a general tendency towards lower δ 18O (and δ 2H) values. The results allow for the establishment of a baseline against which ongoing and future changes of the hydrological cycle could be analysed, and past climate changes be reconstructed.

Stable isotope hydrology of surface and groundwater from the Doon Valley: geometeorological processes and hydraulic linkages

ABSTRACT Effective management of water resources requires an understanding of local hydrology and its links to precipitation. This study provides insights into geometeorological controls on precipitation and the hydraulic relationship between the water sources in the Doon Valley of the Indian Himalaya. Results suggest that inherent variance in isotopic characteristics of precipitation is closely associated with the evolution of different sources of moisture and topographic features. Back trajectories and d-excess suggest that precipitation is transported from the Arabian Sea, the Bay of Bengal, and the Mediterranean Sea. The differences in slopes and intercepts of δ18O–δ2H regressions with space reveal that evaporation and local recycling regulate the compositional variation of precipitation. The study suggests a strong hydraulic connection between surface water and groundwater and recharge through flowpaths with higher permeability, where the Indian summer monsoon acts as the dominant replenishment input. Using the vertical isotopic gradient of precipitation, the groundwater feeding zones were also determined.

Chirripó hydrological research site: Advancing stable isotope hydrology in the Central American Páramo

AbstractThe Chirripó hydrological research site (CHRS) is located within the Chirripó National Park, Costa Rica (between 3100 and 3820 m asl) whereby ~100 km2 are covered by Páramo, a high‐elevation tropical grassland ecosystem. A lake district with approximately 30 lakes of glacial origin is also protected in this area. The CHRS has been monitored since April 2015 with the aim of establishing the first water isotope baseline for the Central American Páramo. At a regional scale, the water isotope ratios (δ2H and δ18O) in precipitation and surface water at CHRS are useful for describing the governing moisture transport from the Caribbean Sea and Pacific Ocean and the complex rainfall producing systems across the N–S mountain range of Central America. These data are also providing unique information about the evaporation and water balance conditions of tropical glacial lakes and the formation of orographic and convective precipitation in high‐elevation tropical ecosystems. Current data sets from CHRS include continuous lake water temperature and meteorological conditions (i.e., precipitation amount, air temperature and relative humidity), as well as water stable isotopes in precipitation, stream water, and lake water (daily to biweekly sampling frequency). Stream water is collected at several locations across the topographic gradient whereas lake water is sampled in the three main lake systems of CHRS. CHRS serves as a reference site for conducting pilot isotopic research in high‐elevation ecosystems to advance the atmospheric, hydrogeological and ecohydrological studies in these understudied biomes. All data from April 2015 to November 2020 are publicly available.

Can δ18O help indicate the causes of recent lake area expansion on the western Tibetan Plateau? A case study from Aweng Co

Glacier-fed lakes on the Tibetan Plateau (TP) have undergone rapid expansions since the late 1990s, concurrent with the changing climate. However, the dominant cause(s) of lake area increases is still debated. To identify the drivers of lake expansion, we studied Aweng Co, a glacier-fed lake in the western TP, where surface area has increased (0.74 km2 year−1) since the late 1970s and most rapidly (0.998 km2 year−1) since the late 1990s. A water balance model was used to clarify the reasons for increased lake water volume, supported by stable isotope hydrology and the δ18O change recorded in recent sediments. Results showed that glacial meltwater probably had the biggest impact on changes in Aweng Co lake level in recent decades, but that precipitation was also an important contributor. Our study shows that δ18O of carbonate (δ18Ocarb) has great potential for indicating source changes of water supply in such lakes, but there is a need to be cautious when interpreting δ18Ocarb due to the influence of multiple hydrological factors, which can change in dominance over time.

Stable Isotope Hydrology of Cave Groundwater and Its Relevance for Speleothem-Based Paleoenvironmental Reconstruction in Croatia

Speleothems deposited from cave drip waters retain, in their calcite lattice, isotopic records of past environmental changes. Among other proxies, δ18O is recognized as very useful for this purpose, but its accurate interpretation depends on understanding the relationship between precipitation and drip water δ18O, a relationship controlled by climatic settings. We analyzed water isotope data of 17 caves from different latitudes and altitudes in relatively small but diverse Croatian karst regions in order to distinguish the dominant influences. Drip water δ18O in colder caves generally shows a greater resemblance to the amount-weighted mean of precipitation δ18O compared to warmer sites, where evaporation plays an important role. However, during glacial periods, today’s ‘warm’ sites were cold, changing the cave characteristics and precipitation δ18O transmission patterns. Superimposed on these settings, each cave has site-specific features, such as morphology (descending or ascending passages), altitude and infiltration elevation, (micro) location (rain shadow or seaward orientation), aquifer architecture (responsible for the drip water homogenization) and cave atmosphere (governing equilibrium or kinetic fractionation). This necessitates an individual approach and thorough monitoring for best comprehension.

Between boreal Siberia and arid Central Asia – Stable isotope hydrology and water budget of Burabay National Nature Park ecotone (Northern Kazakhstan)

Study regionBurabay National Nature Park (BNNP) of North Kazakhstan is located between humid boreal forests and an arid steppe of Central Asia. Study focusThe stable hydrogen and oxygen isotope analyses of precipitation, stream, lake and ground waters were used for water budget calculations of the BNNP endorheic lake system to assess the impact of increasing aridity on lakes in this most continental part of the Earth. New hydrological insights for the regionThe stable isotope results confirmed two different types of lakes in BNNP: Burabay and Shortandy Lakes are more similar to higher latitude lakes (e.g. South Siberia), while Kishi and Ulken Shabakty Lakes are more comparable to the steppe lakes of Central Asia. The slopes of evaporation lines for this region, obtained by regression analysis of lake water samples, ranged from 4.57 (steppe lakes) to 6.21 (forest lakes). The evaporation over inflow ratios (0.34 Burabay, 0.69 Ulken Shabakty, and 0.53 Shortandy) are in good agreement with catchment water budget calculations reflecting different groundwater inputs and water retention times. The recent water level rise in the Ulken Shabakty Lake terminal basin was observed for the first time in a decade. This increase can be explained by the ‘fill and spill’ hypothesis and suggest that a single unusually wet year may significantly replenish water resources despite long-term increasing aridity of the region.

Stable isotope constraints on hydrostratigraphy and aquifer connectivity in the Table Mountain Group

Abstract The Table Mountain Group is a folded, faulted, quartzite-dominated sedimentary sequence, metamorphosed to lower greenschist facies, that forms steep mountains dominating the topography of the Western Cape and causing orographic rainfall in an otherwise semi-arid region. These quartzites are highly fractured to depths of kilometres and act as a complex aquifer system that supplies groundwater directly and indirectly, through baseflow, essential for sustaining the natural environment and human activity in the region. Hydrogen and oxygen isotope data for rain, rivers and groundwater (boreholes and springs) in the region give typical altitude effects of -1.8‰ δD/100 m and -0.33‰ δ18O/100 m, and a very strong continental effect of -30‰ δD/100 km and -4.7‰ δ18O/100 km. This allows for application of stable isotopes as natural hydrological tracers. Groundwater at several locations had stable isotope compositions different from ambient rainfall, but similar to rainfall at high altitudes in adjacent mountains, indicating recharge at high altitude. The groundwater flow is through the Skurweberg Aquifer, here defined as all three formations of the Nardouw Subgroup. Observations on the Peninsula Aquifer suggest a very well mixed aquifer, due to extensive fracturing. Potential exists to delineate groundwater protection zones, detect overabstraction and understand aquifer connectivity better by applying stable isotope hydrology to the Table Mountain Group.

An abrupt decrease in Southern Hemisphere terrestrial temperature during the Eocene–Oligocene transition

Earth's climate transitioned from the greenhouse conditions of the Eocene to the icehouse of the Oligocene ∼34 million years ago. Global cooling was triggered by a decrease in atmospheric pCO2 and is associated with the first appearance of large, permanent ice-sheets on Antarctica. The Eocene–Oligocene transition (EOT) is marked by a large two-step increase in the δ18O of benthic foraminifera, reflecting a combination of cooler global temperatures and continental ice growth. We measured the hydrogen isotope composition of hydrated volcanic glasses deposited in Patagonia during the EOT to reconstruct stable isotope hydrology and associated changes in temperature during this critical climate transition. These data show changes in stable hydrogen isotope ratios that are consistent with Patagonian terrestrial mean annual temperature decreasing by ∼5°C during the EOT before returning to 2°C below pre-EOT values by the Early Oligocene. This is approximately synchronous with Northern Hemisphere cooling during the EOT, and indicates close coupling of temperature and atmospheric pCO2.

Use of isotope hydrology in groundwater conceptualization for modeling flow and contaminant transport at northwestern Sinai, Egypt.

The study area extends along northwestern Sinai coastal plain, which is considered an integral part of the Mediterranean Sea. It depends mainly on the groundwater resource for different type of human activities such as agricultural and drinking. Many programs and policies should be implemented in this area to concurrently improve the sustainability of groundwater use and manage the risks of its degradation. Leakage from some factories in Bir El-Abd might be a contamination source that would threaten groundwater. In this paper, an attempt was made using an integrated approach of the hydrogeological setting and the conjugation of the hydrogeochemical data with the stable isotope hydrology for representation of the conceptual model of the study area. Those tools give more insights on the characterization of the groundwater system with all relevant boundaries and main recharge sources of the aquifer; which is considered to be the key components of a groundwater modeling. A particular focus is placed on modeling a hypothetical accident for contaminant transport in the groundwater system, using both lead and chromium as a typical contaminant component. Further predication of the concentration of those elements has been estimated, and the safety distances of their plume have been determined. This study would be helpful in dealing with water management issues related to contaminant hydrogeology. As well, it introduces some finding for reducing the environmental risk form the industrial development at the study area.

Every apple has a voice: using stable isotopes to teach about food sourcing and the water cycle

Abstract. Agricultural crops such as fruits take up irrigation and meteoric water and incorporate it into their tissue (fruit water) during growth, and the geographic origin of a fruit may be traced by comparing the H and O stable isotope composition (δ2H and δ18O values) of fruit water to the global geospatial distribution of H and O stable isotopes in precipitation. This connection between common fruits and the global water cycle provides an access point to connect with a variety of demographic groups to educate about isotope hydrology and the water cycle. Within the context of a 1-day outreach activity designed for a wide spectrum of participants (high school students, undergraduate students, high school science teachers) we developed introductory lecture materials, in-class participatory demonstrations of fruit water isotopic measurement in real time, and a computer lab exercise to couple actual fruit water isotope data with open-source online geospatial analysis software. We assessed learning outcomes with pre- and post-tests tied to learning objectives, as well as participant feedback surveys. Results indicate that this outreach activity provided effective lessons on the basics of stable isotope hydrology and the water cycle. However, the computer lab exercise needs to be more specifically tailored to the abilities of each participant group. This pilot study provides a foundation for further development of outreach materials that can effectively engage a range of participant groups in learning about the water cycle and the ways in which humans modify the water cycle through agricultural activity.

Kobresia meadow degradation and its impact on water status

AbstractAlpine Kobresia meadows are valuable pasture resources on the central and eastern Qinghai‐Tibetan Plateau that are also important in preserving local and regional water. Kobresia pygmaea is the dominant species forming a typical turf layer resistant to disturbance; however, overgrazing may have exceeded that resistance. An integrated approach, including field monitoring, soil sampling, stable isotope hydrology, and physical modelling, was used to evaluate the hydrological consequences of meadow degradation with respect to normal meadow, degraded crust, and bare soil. Multiple evidence confirms that the soil moisture condition worsens when the meadow degrades. Bare soil has the coarsest soil texture, rapid infiltration, and low soil moisture in the root zone, and soil evaporation rate is high compared to normal meadow especially in dry periods. Crusted meadow soil has the lowest surface infiltration and a larger exposure of the leaf surface because of low plant cover over a dark surface, which favours high transpiration. Crusted meadow also has a drier condition in the root zone. These suggest that degradation is a positive feedback process in which leaf and soil exposure to radiation strengthen water demand for transpiration and facilitate non‐productive water loss, leaving the root zone (0–20 cm) dry and subject to further soil erosion. This positive process suggests that recovery of the Kobresia meadow is a long‐term task which has to consider the different levels of degradation and the effects of local climate change, in order to adapt the rangeland management practices, to the needs of meadow conservation and restoration.

Stable isotope hydrology in fractured and detritic aquifers at both sides of the South Atlantic Ocean: Mar del Plata (Argentina) and the Rawsonville and Sandspruit river catchment areas (South Africa)

The aim of this work is to characterize the isotope composition of water (2H and 18O) in order to establish the relationship between fractured and detritic aquifers in similar hydrological environments located at both sides of the Atlantic Ocean. The Mar del Plata zone, placed in the Argentine Buenos Aires province in South America, and the Rawsonville and Sandspruit river catchment areas, situated in the Western Cape province in South Africa were compared. Rainwater and groundwater samples from fractured and detritic aquifers were analyzed through laser spectroscopy. In both Argentina and South African study sites, stable isotopes data demonstrate an aquifers recharge source from rainfall. For the Mar del Plata region, two different groups of detritic aquifer's samples with distinct recharge processes can be identified due to the close relationship existing between the present hydrogeological environments, the aquifer's grain size sediments and the isotopes contents: one representing rapid infiltration in aquifer sediments of the creeks' palaeobeds and hills zones (sandy or silt sandy sediments) and the other with slow infiltration of evaporated water in plain zones with an aquitard behavior. In the last group, the evaporation process occurs previous infiltration or in the aquifer's non-saturated zone, because of the existence of very low topographic gradients and fine-grained sediments. The evaporation phenomenon is not evident in the Sandspruit river catchment site's detritic aquifer, because its sandy composition allows a faster infiltration rate than in the loess that compounds the Pampeano aquifer in the interfluves zones of the Argentinian study area.

Isotope hydrology and baseflow geochemistry in natural and human-altered watersheds in the Inland Pacific Northwest, USA

This study presents a stable isotope hydrology and geochemical analysis in the inland Pacific Northwest (PNW) of the USA. Isotope ratios were used to estimate mean transit times (MTTs) in natural and human-altered watersheds using the FLOWPC program. Isotope ratios in precipitation resulted in a regional meteoric water line of δ2H = 7.42·δ18O + 0.88 (n = 316; r2 = 0.97). Isotope compositions exhibited a strong temperature-dependent seasonality. Despite this seasonal variation, the stream δ18O variation was small. A significant regression (τ = 0.11D−1.09; r2 = 0.83) between baseflow MTTs and the damping ratio was found. Baseflow MTTs ranged from 0.4 to 0.6 years (human-altered), 0.7 to 1.7 years (mining-altered), and 0.7 to 3.2 years (forested). Greater MTTs were represented by more homogenous aqueous chemistry whereas smaller MTTs resulted in more dynamic compositions. The isotope and geochemical data presented provide a baseline for future hydrological modelling in the inland PNW.

Global prediction of δA and δ2H‐δ18O evaporation slopes for lakes and soil water accounting for seasonality

Global trends in the δ2H‐δ18O enrichment slope of continental lakes and shallow soil water undergoing natural evaporation are predicted on the basis of a steady state isotope balance model using basic monthly climate data (i.e., temperature and humidity), isotopes in precipitation data, and a simple equilibrium liquid‐vapor model to estimate isotopes in atmospheric moisture. The approach, which demonstrates the extension of well‐known conceptual models in stable isotope hydrology to the global scale, is intended to serve as a baseline reference for evaluating field‐based isotope measurements of vapor, surface water, and soil water and as a diagnostic tool for more complex ecosystem models, including isotope‐equipped climate models. Our simulations reproduce the observed local evaporation line slopes (4–5 range for lakes and 2–3 range for soil water) for South America, Africa, Australia, and Europe. A systematic increase in slopes (5–8 range for lakes) toward the high latitudes is also predicted for lakes and soil water in northern North America, Asia, and Antarctica illustrating a latitudinal (mainly seasonality‐related) control on the evaporation signals that has not been widely reported. The over‐riding control on the poleward steepening of the local evaporation lines is found to be the isotopic separation between evaporation‐flux‐weighted atmospheric moisture and annual precipitation, and to lesser extents temperature and humidity, all of which are influenced by enhanced seasonality in cold regions.

A model-based determination of spatial variation of precipitation δ18O over China

Many works show the dependence of precipitation δ 18O on altitude and latitude as a result of air temperature change. The assumption that these quantitative relations can hold across a large geographical region can be used to give a rough estimation of local precipitation δ 18O where there is on direct observation of precipitation δ 18O. Although there truly exists uncertainty in the estimation, an effect was made in this paper to establish the precipitation δ 18O pattern over the whole China. Based on regional topography and the δ 18O of meteoric precipitation, this paper established a quantitative relationship between δ 18O in precipitation and latitude and altitude using the existing δ 18O data from 55 sites over China. The model describes as δ 18O ppt = − 0.0073LAT2 +0.3261LAT − 0.0015ALT − 9.7776, and was used to generate a higher-resolution map of mean annual δ 18O for precipitation over China using geographic information system software, integrating with latitude, altitude and the moisture cycle. This determination of the spatial distribution of δ 18O in modern precipitation of China provides important information for ancient climate and stable isotope hydrology studies.