Spatial and temporal variation of H and O isotopic compositions of the Xijiang River system,Southwest China

Ratios of stable isotopes of hydrogen and oxygen (²H/¹H and ¹⁸O/¹⁶O) in river waters were measured to investigate the hydrological pathway of the Xijiang River, Southwest China. The δ²H and δ¹⁸O values of river waters exhibit significant spatial and temporal variations and the isotopic compositions vary with elevation, temperature and precipitation of the recharge area. Spatially, δ¹⁸O values of river waters from high mountain areas are lower than those from the lower reaches of the Xijiang River due to lower temperature and higher elevation for the recharge area. However, both ²H and ¹⁸O are enriched differently in river waters from the middle reaches during the high flow season, depending on the season and degree of anthropogenic disturbances (e.g. water impoundments). In contrast, deuterium excess (d-excess) values of waters from the middle reaches are substantially lower than those from the upper and lower reaches, suggesting that river waters may be resided in the reservoir and evaporation increases in the middle reaches of the Xijiang River.     

Isotopic composition of atmospheric moisture from pan water evaporation measurements

A continuous and reliable time series data of the stable isotopic composition of atmospheric moisture is an important requirement for the wider applicability of isotope mass balance methods in atmospheric and water balance studies. This requires routine sampling of atmospheric moisture by an appropriate technique and analysis of moisture for its isotopic composition. We have, therefore, used a much simpler method based on an isotope mass balance approach to derive the isotopic composition of atmospheric moisture using a class-A drying evaporation pan. We have carried out the study by collecting water samples from a class-A drying evaporation pan and also by collecting atmospheric moisture using the cryogenic trap method at the National Institute of Hydrology, Roorkee, India, during a pre-monsoon period. We compared the isotopic composition of atmospheric moisture obtained by using the class-A drying evaporation pan method with the cryogenic trap method. The results obtained from the evaporation pan water compare well with the cryogenic based method. Thus, the study establishes a cost-effective means of maintaining time series data of the isotopic composition of atmospheric moisture at meteorological observatories. The conclusions drawn in the present study are based on experiments conducted at Roorkee, India, and may be examined at other regions for its general applicability.     

Spatial and temporal characteristics of stable isotopes in the Tarim River Basin

By using 233 isotope samples, we investigated the spatial and temporal variations of δ¹⁸O and δ²H in precipitation and surface water, and the contribution of different water sources in the rivers within the Tarim River Basin (TRB), which receives snow/glacier meltwater, groundwater, and rainfall. Our study revealed a similar seasonal pattern of precipitation δ¹⁸O and δ²H at both the north and south edges of the basin, indicating the dominant effect of westerly air masses in the summer and the combined influence of westerly and polar air masses during the winter, although the southern part showed more complex precipitation processes in the summer. River water in the basin has relatively large temporal variations in both δ¹⁸O and δ²H showing a distinct seasonal pattern with lower isotope values in May than in September. Higher d-excess values throughout the year in the Aksu river and the Tizinafu river suggest that water may be intensively recycled in the mountains of the TRB. Based on isotopic hydrograph separation, we found that groundwater is the main water source that discharges the entire basin although individual rivers vary.     

Isotopic composition in precipitation and groundwater in the northern mountainous region of the Central Valley of Costa Rica

The linkage between precipitation and recharge is still poorly understood in the Central America region. This study focuses on stable isotopic composition in precipitation and groundwater in the northern mountainous region of the Central Valley of Costa Rica. During the dry season, rainfall samples corresponded to enriched events with high deuterium excess. By mid-May, the Intertropical Convergence Zone poses over Costa Rica resulting in a depletion of ¹⁸O/¹⁶O and ²H/H ratios. A parsimonious four-variable regression model (r^2?=?0.52) was able to predict daily δ¹⁸O in precipitation. Air mass back trajectories indicated a combination of Caribbean Sea and Pacific Ocean sources, which is clearly depicted in groundwater isoscape. Aquifers relying on Pacific-originated recharge exhibited a more depleted pattern, whereas recharge areas relying on Caribbean parental moisture showed an enrichment trend. These results can be used to enhance modelling efforts in Central America where scarcity of long-term data limits water resources management plans.     

Temporal and spatial distribution of isotopes in river water in Central Europe: 50 years experience with the Austrian network of isotopes in rivers

The Austrian network of isotopes in rivers comprises about 15 sampling locations and has been operated since 1976. The Danube isotope time series goes back to 1963. The isotopic composition of river water in Central Europe is mainly governed by the isotopic composition of precipitation in the catchment area; evaporation effects play only a minor role. Short-term and long-term isotope signals in precipitation are thus transmitted through the whole catchment. The influence of climatic changes has become observable in the long-term stable isotope time series of precipitation and surface waters. Environmental ³H values were around 8 TU in 2015, short-term ³H pulses up to about 80 TU in the rivers Danube and March were a consequence of releases from nuclear power plants. The complete isotope data series of this network will be included in the Global Network of Isotopes in Rivers database of the International Atomic Energy Agency (IAEA) in 2017. This article comprises a review of 50 years isotope monitoring on rivers and is also intended to provide base information on the (isotope-)hydrological conditions in Central Europe specifically for the end-users of these data, e.g. for modelling hydrological processes. Furthermore, this paper includes the 2006–2015 supplement adding to the Danube isotope set published earlier.     

Controls over spatial and seasonal variations on isotopic composition of the precipitation along the central and eastern portion of Brazil

Based on Global Network Isotopes in Precipitation (GNIP) isotopic data set, a review of the spatial and temporal variability of δ¹⁸O and δ²H in precipitation was conducted throughout central and eastern Brazil, indicating that dynamic interactions between Intertropical and South Atlantic Convergence Zones, Amazon rainforest, and Atlantic Ocean determine the variations on the isotopic composition of precipitation over this area. Despite the seasonality and latitude effects observed, a fair correlation with precipitation amount was found. In addition, Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) air mass back trajectories were used to quantify the factors controlling daily variability in stable isotopes in precipitation. Through a linear multiple regression analysis, it was observed that temporal variations were consistent with the meteorological parameters derived from HYSPLIT, particularly precipitation amount along the trajectory and mix depth, but are not dependent on vapour residence time in the atmosphere. These findings also indicate the importance of convective systems to control the isotopic composition of precipitation in tropical and subtropical regions.     

Analysis of isotopic signals in the Danube River water at Tulln,Austria, based on daily grab samples in 2012

Results of stable isotope measurements (δ²H, δ¹⁸O) of daily grab samples, taken from the Danube River at Tulln (river km 1963) during 2012, show seasonal and short-term variations depending on the climatic/hydrological conditions and changes in the catchment area (temperature changes, heavy rains and snow melt processes). Isotope ratios in river water clearly reflect the isotopic composition of precipitation water in the catchment area since evaporation influences play a minor role. Average δ²H and δ¹⁸O values in 2012 are?78‰ and?11.0‰, respectively, deuterium excess averages 10‰. The entire variation amounts to 1.8‰ in δ¹⁸O and 15‰ in δ²H. Quick changes of the isotopic composition within a few days emphasise the necessity of daily sampling for the investigation of hydrological events, while monthly grab sampling seems sufficient for the investigation of long-term hydro-climatic trends. ³H results show peaks (half-width 1–2 days, up to about 150 TU) exceeding the regional environmental level of about 9 TU, probably due to releases from nuclear power plants.     

First field-based observations of δ2H and δ18O values of event-based precipitation,rivers and other water bodies in the Dzungarian Gobi,SW Mongolia

For certain remote areas like Mongolia, field-based precipitation, surface and ground water isotopic data are scarce. So far no such data exist for the Mongolian Gobi desert, which hinders the understanding of isotopic fractionation processes in this extreme, arid region. We collected 26 event-based precipitation samples, 39 Bij river samples, and 75 samples from other water bodies in the Dzungarian Gobi in SW Mongolia over a period of 16 months for hydrogen and oxygen stable isotope analysis. δ²H and δ¹⁸O values in precipitation show high seasonal variation and cover an extreme range: 175?‰ for δ²H and 24?‰ for δ¹⁸O values. The calculated local meteoric water line (LMWL) shows the isotopic characteristics of precipitation in an arid region. Individual water samples fall into one of three groups: within, above or below the 95?% confidence interval of LMWL. Data presented provide a basis for future studies in this region.     

Influence of the balance of the intertropical front on seasonal variations of the isotopic composition in rainfall at Kisiba Masoko (Rungwe Volcanic Province,SW, Tanzania)

Tropical rainfall isotopic composition results from complex processes. The climatological and environmental variability in East Africa increases this complexity. Long rainfall isotope datasets are needed to fill the lack of observations in this region. At Kisiba Masoko, Tanzania, rainfall and rain isotopic composition have been monitored during 6 years. Mean year profiles allow to analyse the seasonal variations. The mean annual rainfall is 2099?mm with a rain-weighted mean composition of ?3.2?‰ for δ¹⁸O and ?11.7?‰ for δ²H. The results are consistent with available data although they present their own specificity. Thus, if the local meteoric water line is δ²H?=?8.6 δ¹⁸O?+?14.8, two seasonal lines are observed. The seasonality of the isotopic composition in rain and deuterium excess has been compared with precipitating air masses backtracking trajectories to characterize a simple scheme of vapour histories. The three major oceanic sources have two moisture signatures with their own trajectory histories: one originated from the tropical Indian Ocean at the beginning of the rainy season and one from the Austral Ocean at its end. The presented isotopic seasonality depends on the balance of the intertropical front and provides a useful dataset to improve the knowledge about local processes.     

Use of isotopes to study floodplain wetland and river flow interaction in the White Volta River basin,Ghana

Floodplain wetlands influence the timing and magnitude of stream responses to rainfall. In managing and sustaining the level of water resource usage in any river catchment as well as when modelling hydrological processes, it is essential that the role of floodplain wetlands in stream flows is recognised and understood. Existing studies on hydrology within the Volta River basin have not adequately represented the variability of wetland hydrological processes and their contribution to the sustenance of river flow. In order to quantify the extent of floodwater storage within riparian wetlands and their contribution to subsequent river discharges, a series of complementary studies were conducted by utilising stable isotopes, physical monitoring of groundwater levels and numerical modelling. The water samples were collected near Pwalugu on the White Volta River and at three wetland sites adjacent to the river using the grab sampling technique. These were analysed for ¹⁸O and ²H. The analysis provided an estimate of the contribution of pre-event water to overall stream flow. In addition, the variation in the isotopic composition in the river and wetland water samples, respectively, revealed the pattern of flow and exchange of water between the wetlands and the main river system.     

Stable H and O isotope variations reveal sources of recharge in Dhofar,Sultanate of Oman

Due to the ability of stable water isotopes to characterize the origin of water and connected processes of groundwater recharge, we used the isotope variations of hydrogen and oxygen in different water sources for assessing the recharge process in the Dhofar region. δ¹⁸O and δ²H of precipitation, spring water, and groundwater cover a range from ?10 to +2 and from ?70 to +7?‰ (vs Vienna Standard Mean Ocean Water), respectively, and correlate in a linear relationship close to the Global Meteoric Water Line. No obvious evaporation processes are detected. A clear signal of the recent precipitation is given by the annual monsoon. The monsoon signal is confirmed by several springs existing in the south at the foot of the Dhofar mountains and sources at Gogub above 450?m and Tawi Atir at 650?m above sea level. They occur here first in the form of water intercepted by trees as stemflow and throughflow. The isotope signature of groundwater in the Dhofar mountains reflects the climatic conditions at the time of recharge and the lithological features of the limestone matrix. To the north, the isotope patterns of the groundwater are continuously depleted from the monsoon signal along the outcropping aquifer D (Lower Umm Er Radhuma). Here, a more negative signature towards the wells in the Najd desert region was observed. Cyclone water that flooded wadis in the Dhofar region occasionally, as observed in November 2011, falls isotopically into the same range as we observed in the fossil groundwater. Taking into account the different sources of precipitation and groundwater and thus a clear distinction of the isotopic composition of the water sources, we conclude a recharge process divided into a southward and a northward component in the Dhofar region.     

Isotopic composition of bottled water in Saudi Arabia

The ¹⁸O/¹⁶O and ²H/¹H ratios of 18 water brands representing the most popular bottled water brands in the Saudi market were measured using a system based on the latest advancements in tunable off-axis integrated cavity output diode laser spectroscopy (OA-ICOS) in the near-infrared spectral region. Utilizing δ¹⁸O and the δ²H values of locally produced water samples, a meteoric water line (δ²H?=?7.84 δ¹⁸O?+?2.11) was extracted and found to be consistent with the slope of the global meteoric water line (GMWL) and the geographic location of Saudi Arabia.     

Identifying local and regional groundwater in basins: chemical and stable isotopic attributes of multivariate classification of hydrochemical data,the Lower Virgin River Basin,Nevada, Arizona and Utah,U.S.A

In the Basin and Range Province of the Southwestern U.S.A., deep carbonate groundwater has been suggested as a significant source to many overlying basin-fill alluvial aquifer systems. Notwithstanding, testing this hypothesis is limited by obtaining data from such considerable depths and complex geology.

This study uses δ²H and δ¹⁸O data from springs, rivers, and wells tapping shallow basin-fill groundwater to test the hydrochemical interpretation of deep regional carbonate groundwater flow into the basin-fill aquifers. Stable isotopic and major ion attributes of hydrochemical facies suggest basin-fill alluvial groundwater of the Lower Virgin River Basin is a mixture of precipitation recharge within the Lower Virgin River Basin or the Clover and Escalante Desert Basin northwards, and the deep carbonate flow. The data support the conclusions that in the Lower Virgin River Basin, deep carbonate groundwater is an important source to the alluvial aquifer system and likely accounts for approximately 50% of the alluvial aquifer groundwater. Na⁺, K⁺, and SO₄^2– increase in the basin-fill alluvial groundwaters outside the Virgin River floodplain appears to be related with upwelling of deep regional groundwater, and indicating that the chemical character of the basin-fill alluvial groundwaters are related to the deeper flow systems.     

Studies on stable isotopic composition of daily rainfall from Kozhikode,Kerala, India

The stable isotopic compositions of all major daily rain fall samples (n?=?113) collected from Kozhikode station in Kerala, India, for the year 2010 representing the pre-monsoon, southwest and northeast monsoon seasons are examined. The isotopic variations δ¹⁸O, δ²H and d-excess in daily rainfall ranged from δ¹⁸O: ?4.4 to 2?‰, δ²H: ?25.3 to 13.8?‰, and d-excess: ?2.4 to 15.3?‰; δ¹⁸O: ?9.7 to ?0.6?‰, δ²H: ?61.7 to 5.3?‰, and d-excess 5.8 to 17.4?‰; δ¹⁸O ?11.3 to ?1.4?‰, δ²H: ?75.3 to 0.9?‰, and d-excess: 8.8 to 21.3?‰ during the pre-, southwest and northeast monsoon periods, respectively. Thus, daily rainfall events during two monsoon periods had a distinct range of isotopic variations. The daily rain events within the two monsoon seasons also exhibited periodic variations. The isotopic composition of rain events during pre-monsoon and a few low-intensity events during the southwest monsoon period had imprints of secondary evaporation. This study analysing the stable isotopic characteristics of individual rain events in southern India, which is influenced by dual monsoon rainfall, will aid in a better understanding of its mechanism.     

Hydrology of the lakes in Central Wohlthat Massif,East Antarctica: new results

In 1983/1984, in the course of the 28th Soviet Antarctic Expedition, waterbody, ice cover, and surrounding glaciers of the lakes Untersee and Obersee were sampled along some depth profiles. The geochemical data of those samples, now available, show the homogeneity of both large lakes in vertical (down to the maximum depth) as well as in lateral directions. The comparison of isotope and chemical composition of lake water and adjoining glacier ice suggests strong differences in the long-term evolution between the lakes Untersee and Obersee. First data from a lakelet, embedded in the large morainic area to the west of Lake Untersee, are of special interest: the δ²H values of the lakelet water are lower than those of recent regional glacier ice by 50‰ SMOW. This fact indicates that the lakelet is fed episodically by Pleistocene dead ice, covered by the morainic material.     

A 6.5-year continuous record of sea surface salinity and seawater isotopic composition at Harbour of Ishigaki Island,southwest Japan

We produced continuous records of sea surface salinity and isotopic composition from 1998 to 2004 at Ishigaki Island, southwest Japan, and found clear seasonal variations in salinity and oxygen isotopic composition and increasing trends of them after 1999. These increasing trends could be principally due to the decreasing difference between local precipitation (P) and evaporation (E), as a result of the reduction of horizontal vapour transport from adjacent oceans. When samples collected in heavy rainfall events were excluded, the average Δδ¹⁸O/Δ salinity slope was obtained as 0.31, 0.35 in summer and 0.28 in winter. Estimated E/P ratios based on the isotopic box model are in good agreement with the ratios of independently estimated E to observed P.     

Editor change

Beaver Lake and Radok Lake, the largest known epishelf lake and the deepest freshwater lake on the Antarctic continent, respectively, were isotopically (δ²H, δ¹⁸O) and hydrogeochemically studied. Radok Lake is an isothermal and non-stratified, i.e. homogeneous water body, while Beaver Lake is stratified with respect to temperature, salinity, and isotopic composition. The results for the latter attest to freshwater (derived from snow and glacier melt) overlying seawater.     

Hydrology of the North Klondike River: carbon export,water balance and inter-annual climate influences within a sub-alpine permafrost catchment

Arctic and sub-arctic watersheds are undergoing significant changes due to recent climate warming and degrading permafrost, engendering enhanced monitoring of arctic rivers. Smaller catchments provide understanding of discharge, solute flux and groundwater recharge at the process level that contributes to an understanding of how larger arctic watersheds are responding to climate change. The North Klondike River, located in west central Yukon, is a sub-alpine permafrost catchment, which maintains an active hydrological monitoring station with a record of >40 years. In addition to being able to monitor intra-annual variability, this data set allows for more complex analysis of streamflow records. Streamflow data, geochemistry and stable isotope data for 2014 show a groundwater-dominated system, predominantly recharged during periods of snowmelt. Radiocarbon is shown to be a valuable tracer of soil zone recharge processes and carbon sources. Winter groundwater baseflow contributes 20?% of total annual discharge, and accounts for up to 50?% of total river discharge during the spring and summer months. Although total stream discharge remains unchanged, mean annual groundwater baseflow has increased over the 40-year monitoring period. Wavelet analysis reveals a catchment that responds to El Niño and longer solar cycles, as well as climatic shifts such as the Pacific Decadal Oscillation.

Dedicated to Professor Peter Fritz on the occasion of his 80th birthday     

Combined approach of isotope mass balance and hydrological water balance methods to constrain the sources of lake water as exemplified on the small dimictic lake Silbersee,northern Germany

Stable isotopes of hydrogen and oxygen are often used for water balance calculations of lakes. We present an approach combining the lake water balance with an isotope mass balance to constrain the sources and sinks of the water of a small dimictic lake subjected to eutrophication. Meteorological and hydraulic data in combination with measured isotope signatures of the different water compartments enabled to assess the degree of surface water/groundwater interaction and the amount of overland flow into the lake. Groundwater could be excluded as a lake water source, as its water level was always below the lake water level. In the absence of a channelled inflow, precipitation and overland flow were the remaining options, whereby the latter was only active during periods of exceptionally high rainfall. While the groundwater signatures adjacent to the lake showed an influence of lake water, the lake water balance itself indicated that the associated volumetric water loss to groundwater is rather negligible. In the present case, only a combined assessment of hydrological and isotopic data allowed for an accurate characterization of the studied lake and a quantification of its water sources and sinks, highlighting the importance of using more than one methodological approach for such a purpose.