Isotopic and geochemical tracers reveal similarities in transit times in contrasting mesoscale catchments

There is a need for more isotopic tracer studies at the mesoscale to extend our understanding of catchment transit times and their associated controls beyond smaller experimental sites (typically < 10 km²). This paper, therefore, examines the isotope hydrology of six mesoscale (10¹–10² km²) sub‐catchments of the 2000 km² basin of the River Dee in northern Scotland. All the catchments were upland in character (mean altitude > 400 m) with similar suites of soil coverage (predominantly regosols, gleys, peats and podzols), although the relative distribution varied, as did the presence of other landscape features such as aquifers in Quaternary drifts and lakes. Input–output relationships of δ¹⁸O in precipitation and runoff revealed contrasting responses and differential damping which were broadly consistent with catchment characteristics. The mean transit times (MTTs) were estimated using a convolution integral with a Gamma distribution as the transfer function. These varied from 528 days in the most responsive catchments to > 800 days in catchments where the tracer signature was most damped. Shorter MTTs were found in sub‐catchments with a higher percentage cover of responsive soils (i.e. regosols, gleys and peats), whilst sub‐catchments with longest MTTs had a higher coverage of free‐draining podzolic and alluvial soils, as well as significant amount of stored water either in fluvio‐glacial aquifers or large lakes. The MTT of all six catchments had the same order of magnitude; this contrasts with studies in the Scottish Highlands with smaller (<10 km²) catchments where MTT has been shown to vary between 60 and 1200 days. Copyright © 2010 John Wiley & Sons, Ltd.     

Influence of lowland aquifers and anthropogenic impacts on the isotope hydrology of contrasting mesoscale catchments

We examined the isotope hydrology of eight, contrasting mesoscale (104–488 km²) catchments characterized by a systematic change in the relative importance of upland and lowland areas that reflects the relative distribution of metamorphic and sedimentary rocks. Precipitation and stream water were monitored over a 12‐month period, and stable isotopes were used to examine spatial variations in the hydrometric and tracer dynamics of the catchments. Isotopic tracers were used to examine the temporal dynamics of different runoff sources, and geochemical tracers (alkalinity) were used to identify the geographic sources of runoff. Input–output relationships of isotopic tracers were explored using a gamma function to fit a transit time distribution, which was used to test the hypothesis that the length of mean transit times increased systematically with the cover of sandstone aquifers in the catchments. However, in three catchments, the increased influence of anthropogenic factors, notably reservoir storage, urban runoff and agricultural abstraction for irrigation, prevented reliable transit time estimation. For sites where tentative mean transit time estimates were possible, these varied from around 1.6 years in upland catchments dominated by metamorphic rocks (>75%) and responsive soils to around 4 years in catchments with 34% sandstone cover and freely draining soils. These preliminary results were consistent with inferences of geochemical tracers on the increased role of sedimentary aquifers as runoff sources in lowland areas, but observation from a larger number of sites is needed to confirm this. Copyright © 2012 John Wiley & Sons, Ltd.     

Preliminary evaluation of the runoff processes in a remote montane cloud forest basin using Mixing Model Analysis and Mean Transit Time

In this study, the Mean Transit Time and Mixing Model Analysis methods are combined to unravel the runoff generation process of the San Francisco River basin (73.5 km²) situated on the Amazonian side of the Cordillera Real in the southernmost Andes of Ecuador. The montane basin is covered with cloud forest, sub‐páramo, pasture and ferns. Nested sampling was applied for the collection of streamwater samples and discharge measurements in the main tributaries and outlet of the basin, and for the collection of soil and rock water samples. Weekly to biweekly water grab samples were taken at all stations in the period April 2007–November 2008. Hydrometric data, Mean Transit Time and Mixing Model Analysis allowed preliminary evaluation of the processes controlling the runoff in the San Francisco River basin. Results suggest that flow during dry conditions mainly consists of lateral flow through the C‐horizon and cracks in the top weathered bedrock layer, and that all subcatchments have an important contribution of this deep water to runoff, no matter whether pristine or deforested. During normal to low precipitation intensities, when antecedent soil moisture conditions favour water infiltration, vertical flow paths to deeper soil horizons with subsequent lateral subsurface flow contribute most to streamflow. Under wet conditions in forested catchments, streamflow is controlled by near surface lateral flow through the organic horizon. Exceptionally, saturation excess overland flow occurs. By absence of the litter layer in pasture, streamflow under wet conditions originates from the A horizon, and overland flow. Copyright © 2011 John Wiley & Sons, Ltd.     

Catchment storage and residence time in a periodically irrigated watershed

Understanding anthropogenic impacts on water storage and water flow pathways in catchments is an ongoing challenge in hydrology. Here, we study the dynamics of subsurface storage and residence time of water in a catchment in Berkeley, California, that is within a regional park but contains diverse land use within its perimeter, including a periodically irrigated golf course. Our study combines several isotopic tracers with water budget data to examine sources of water in a stream draining the site. Irrigation water, applied to a small area of the watershed, is a minor component of the water budget. However, geochemical tracers reveal that irrigation water is a significant fraction of stream flow downstream of the golf course during baseflow and during precipitation events. Isotopic tracers indicate that the watershed has a preference to release young water for stream flow generation, resulting in contrasting tritium ages for stream water and groundwater of 1.3 ± 0.5 year and 8.2 ± 1.7 year, respectively. We determined that the older water is a very small component (0.7%) of the stream water in the tail of an assumed exponential distribution. We used the seasonal variation of stable water isotopes in precipitation and stream water over two water years to explain the damping of the isotopic signature of stream water, which yields information about the catchment's response to the input signal. The methods described here may be applicable to other urban or suburban headwater catchments in areas with a component of non-natural recharge from, for example, leaky infrastructure, storm water routing or dry season irrigation.     

杭嘉湖地区水化学及同位素特征初步分析

本文通过初步分析杭嘉湖地区地下水化学和同位素特征,认为地下水的水化学分布存在着一定的分带性。浅层地下水化学类型为Cl,HCO3-Ca,Na型,代表了降水或地表水补给的形成过程,且补给前受到不同程度的蒸发。深层承压水化学类型为HCO3-Ca,Na和HCO3-Na型,代表了以铝硅酸盐矿物溶解为主的形成过程,其补给源为古气候条件下的降水补给。利用氘过量参数d值判断了第承压水（120~150 m）总体流向为南西至北东,即由杭州和湖州向嘉兴方向径流。     

Does the incorporation of process conceptualization and tracer data improve the structure and performance of a simple rainfall‐runoff model in a Scottish mesoscale catchment?

A geomorphological instantaneous unit hydrograph (GIUH) rainfall‐runoff model was applied in a 31 km² montane catchment in Scotland. Modelling was based on flow path length distributions derived from a digital terrain model (DTM). The model was applied in two ways; a single landscape unit response based on the DTM alone, and a two‐landscape unit response, which incorporated the distribution of saturated areas derived from field‐validated geographic information system (GIS) analysis based on a DTM and soil maps. This was to test the hypothesis that incorporation of process‐information would enhance the model performance. The model was applied with limited multiple event calibration to produce parameter sets which could be applied to a spectrum of events with contrasting characteristics and antecedent conditions. Gran alkalinity was used as a tracer to provide an additional objective measure for assessing model performance. The models captured the hydrological response dynamics of the catchment reasonably well. In general, the single landscape unit approach produced the best individual model performance statistics, though the two‐landscape unit approach provided a range of models, which bracketed the storm hydrograph response more realistically. There was a tendency to over‐predict the rising limb of the hydrograph, underestimate large storm event peaks and anticipate the hydrograph recession too rapidly. Most of these limitations could be explained by the simplistic assumptions embedded within the GIUH approach. The modelling also gave feasible predictions of stream water chemistry, though these could not be used as a basis for model rejection. Nevertheless, the study suggested that the approach has potential for prediction of hydrological response in ungauged montane headwater basins. Copyright © 2007 John Wiley & Sons, Ltd.     

A study of interaction between surface water and groundwater using environmental isotope in Huaisha River basin

The surface water and groundwater are important components of water cycle, and the interaction between surface water and groundwater is the important part in water cycle research. As the effective tracers in water cycle research, environmental isotope and hydrochemistry can reveal the interrelationships between surface water and groundwater effectively. The study area is the Huaisha River basin, which is located in Huairou district, Beijing. The field surveying and sampling for spring, river and well water were finished in 2002 and 2003. The hydrogen and oxygen isotopes and water quality were measured at the laboratory. The spatial characteristics in isotope and evolution of water quality along river lines at the different area were analyzed. The altitude effect of oxygen isotope in springs was revealed, and then using this equation, theory foundation for deducing recharge source of spring was estimated. By applying the mass balance method, the annual mean groundwater recharge rate at the catchment was estimated. Based on the groundwater recharge analysis, combining the hydrogeological condition analysis, and comparing the rainfall-runoff coefficients from the 1960s to 1990s in the Huaisha River basin and those in the Chaobai River basin, part of the runoff in the Huaisha River basin is recharged outside of this basin, in other words, this basin is an un-enclosed basin. On the basis of synthetically analyses, combining the compositions of hydrogen and oxygen isotopes and hydrochemistry, geomorphology, geology, and watershed systems characteristics, the relative contributions between surface water and groundwater flow at the different areas at the catchments were evaluated, and the interaction between surface water and groundwater was re- vealed lastly.     

Linking metrics of hydrological function and transit times to landscape controls in a heterogeneous mesoscale catchment

Long‐term river flow data and one year of isotopic tracer data in a nested 749 km² catchment were analysed conjunctively to evaluate the relationships between hydrometric statistics, transit times, and catchment characteristics. The catchment comprised two distinct geomorphic provinces; upland headwaters draining glaciated landscapes underlain by crystalline geology and lowland headwaters draining a major regional sandstone aquifer. In the uplands, flow regimes were ‘flashy’ with high runoff coefficients for storm hydrographs, steep recession curves and strong nonlinearity in event responses. In the lowlands, runoff coefficients were low, recessions less steep, and event responses more linear. Flow data from the catchment outfall showing damping of these extremes, but was most strongly influenced by the upland headwaters where precipitation was highest. The damping of variability in stable water isotopes between precipitation inputs and streamflow outputs reflected this; with upland tributaries least damped and lowland tributaries most damped. Attempts to quantify the mean transit times of the sampling points met with mixed success; partly reflecting the short run (1 year) of data, but mainly as a result of the marked damping in lowland sites. As a consequence, MTT estimates can only be said to be in the order of a few years in upland sites, but are probably decadal or greater in lowland tributaries. Again, the catchment outfall averages these extremes, but is more similar to the upland headwaters. Despite the difficulties in quantifying MTTs, it is clear that they, like the hydrological response, primarily reflect the dominant control of catchment soil cover, which in turn is determined by geology and glacial history. Copyright © 2011 John Wiley & Sons, Ltd.     

Delineating extent and magnitude of river flooding to lakes across a northern delta using water isotope tracers

Hydrological monitoring in complex, dynamic northern floodplain landscapes is challenging, but increasingly important as a consequence of multiple stressors. The Peace-Athabasca Delta in northern Alberta, Canada, is a Ramsar Wetland of International Importance reliant on episodic river ice-jam flood events to recharge abundant perched lakes and wetlands. Improved and systematic monitoring of landscape-scale hydrological connectivity among freshwater ecosystems (rivers, channels, wetlands, and lakes) is needed to guide stewardship decisions in the face of climate change and upstream industrial development. Here, we use water isotope compositions, supplemented by measurements of specific conductivity and field observations, from 68 lakes and 9 river sites in May 2018 to delineate the extent and magnitude of spring ice-jam induced flooding along the Peace and Athabasca rivers. Lake-specific estimates of input water isotope composition (δ_I) were modelled after accounting for influence of evaporative isotopic enrichment. Then, using the distinct isotopic signature of input water sources, we develop a set of binary mixing models and estimate the proportion of input to flooded lakes attributable to river floodwater and precipitation (snow or rain). This approach allowed identification of areas and magnitude of flooding that were not captured by other methods, including direct observations from flyovers, and to demarcate flow pathways in the delta. We demonstrate water isotope tracers as an efficient and effective monitoring tool for delineating spatial extent and magnitude of an important hydrological process and elucidating connectivity in the Peace-Athabasca Delta, an approach that can be readily adopted at other floodplain landscapes.     

Seasonal isotope hydrology of three Appalachian forest catchments

Seasonal oxygen-18 variations in precipitation, throughfall, soil water, spring flow and stream baseflow were analysed to compare the hydrology of two forested basins in West Virginia (WV) (34 and 39 ha) and one in Pennsylvania (PA) (1134 ha). Precipitation and throughfall were measured with funnel/bottle samplers, soil water with ceramic-cup suction lysimeters and spring flow/baseflows by grab and automatic sampling during the period March 1989 to March 1990. Isotopic damping depths, or depths required to reduce the amplitude of subsurface oxygen-18 fluctuations to 37% of the surface amplitude, were generally similar for soil water on the larger PA basin, and baseflows and headwater spring flows on the smaller WV basins. Computed annual isotopic damping depths for these water sources averaged 49 cm using soil depth as the flow path length. The equivalent annual mean hydraulic diffusivity for the soil flow paths was 21 cm² d⁻¹. Mean transit times, based upon an assumed exponential distribution of transit times, ranged from 0·2 y for soil water at a depth of 30 cm on the larger catchment, to 1·1–1·3 y for most spring flows and 1·4–1·6 y for baseflows on the smaller catchments. Baseflow on the larger PA basin and flow of one spring on a small WV basin showed no detectable seasonal fluctuations in oxygen-18, indicating flow emanated from sources with mean transit times greater than about 5 y. Based upon this soil flow path approach, it was concluded that seasonal oxygen-18 variations can be used to infer mean annual isotopic damping depths and diffusivities for soil depths up to approximately 170 cm. © 1997 John Wiley & Sons, Ltd.     

Water age in stormwater management ponds and stormwater management pond-treated catchments

Expansion of impervious surface cover results in “flashy” hydrologic response, elevated flood risk, and degraded water quality in urban watersheds. Stormwater management ponds (SWMPs) are often engineered into stream networks to mitigate these issues. A clearer understanding of how water is stored and released from SWMPs and SWMP-treated catchments is required to better represent these engineered systems in hydrological and water quality models of urban and urbanizing watersheds. Stable water isotopes were used to compare water age in SWMPs and SWMP-treated catchments in an urbanizing watershed. We sampled water biweekly from two SWMPs and five stream sites with varying land cover and stormwater control in their catchments. Two inverse transit time proxies (damping ratio and young water fraction) were computed along with the mean transit time (MTT) by sine–wave fitting for each SWMP and stream site using the δ¹⁸O and δ²H data. Water entering the SWMPs was consistently older (224 and 177 days) than water in or exiting the ponds (ranging from 46 to 91 days and 39 to 67 days, respectively). This finding is likely due to a combination of groundwater infiltration into broken sewer pipes that transport water into the ponds and a bias toward baseflow sampling. At the catchment scale, detention provided by SWMPs was not found to be more significant than the interactive effects of impervious cover, surficial geology, land use proportions, and catchment size in determining MTT. Overall, surficial geology explained the most variation in MTT among the seven sites. This study illustrates the potential for isotope-based approaches of water age to provide information on individual SWMP functioning and the influence of SWMPs on catchment-scale water movement.     

Tritium hydrology of the Mississippi River basin

In the early 1960s, the US Geological Survey began routinely analysing river water samples for tritium concentrations at locations within the Mississippi River basin. The sites included the main stem of the Mississippi River (at Luling Ferry, Louisiana), and three of its major tributaries, the Ohio River (at Markland Dam, Kentucky), the upper Missouri River (at Nebraska City, Nebraska) and the Arkansas River (near Van Buren, Arkansas). The measurements cover the period during the peak of the bomb‐produced tritium transient when tritium concentrations in precipitation rose above natural levels by two to three orders of magnitude. Using measurements of tritium concentrations in precipitation, a tritium input function was established for the river basins above the Ohio River, Missouri River and Arkansas River sampling locations. Owing to the extent of the basin above the Luling Ferry site, no input function was developed for that location. The input functions for the Ohio and Missouri Rivers were then used in a two‐component mixing model to estimate residence times of water within these two basins. (The Arkansas River was not modelled because of extremely large yearly variations in flow during the peak of the tritium transient.) The two components used were: (i) recent precipitation (prompt outflow) and (ii) waters derived from the long‐term groundwater reservoir of the basin. The tritium concentration of the second component is a function of the atmospheric input and the residence times of the groundwaters within the basin. Using yearly time periods, the parameters of the model were varied until a best fit was obtained between modelled and measured tritium data. The results from the model indicate that about 40% of the flow in the Ohio River was from prompt outflow, as compared with 10% for the Missouri River. Mean residence times of 10 years were calculated for the groundwater component of the Ohio River versus 4 years for the Missouri River. The mass flux of tritium through the Mississippi Basin and its tributaries was calculated during the years that tritium measurements were made. The cumulative fluxes, calculated in grams of ³H were: (i) 160 g for the Ohio (1961–1986), (ii) 98 g for the upper Missouri (1963–1997), (iii) 30 g for the Arkansas (1961–1997) and (iv) 780 g for the Mississippi (1961–1997). Copyright © 2004 John Wiley & Sons, Ltd.     

Modelling the effects of spatial and temporal resolution of rainfall and basin model on extreme river discharge

Abstract

Important characteristics of an appropriate river basin model, intended to study the effect of climate change on basin response, are the spatial and temporal resolution of the model and the rainfall input. The effects of input and model resolution on extreme discharge of a large river basin are assessed to give some indication on appropriate resolutions. A simple stochastic rainfall model and a river basin model with uniform parameters and multiple rainfall input have been developed and applied to the River Meuse basin in northwestern Europe. The results show that the effect of model resolution on extreme river discharge is much greater than that of input resolution. The highest model resolution seems to be quite accurate in determining extreme discharge. Although the results should be interpreted with caution, they may give some indication of appropriate input and model resolutions for the determination of extreme discharge of a large river basin.     

Stable isotope tracers as diagnostic tools in upscaling flow path understanding and residence time estimates in a mountainous mesoscale catchment

δ¹⁸O measurements of precipitation and stream waters were used as a natural tracer to investigate hydrological pathways and residence times in the River Feshie, a complex mesoscale (231 km²) catchment in the Cairngorm Mountains of Scotland. Precipitation δ¹⁸O exhibited strong seasonal variation over the 2001–02 hydrological year, ranging from −6·9‰ in the summer, to −12·0‰ during winter snowfalls (mean δ¹⁸O −9·59‰). Although damped, this seasonality was reflected in stream water outputs at seven sampling sites in the catchment, allowing δ¹⁸O variations to be used to infer hydrological source areas. Thus, stream water δ¹⁸O was generally controlled by a seasonally variable storm flow end member, mixing with groundwater of more constant isotopic composition. Periodic regression analysis allowed the differences in this mixing process between monitoring subcatchments to be assessed more quantitatively to provide a preliminary estimate of mean stream water residence time. This demonstrated the importance of responsive hydrological pathways associated with peat and shallow alpine soils in the headwater subcatchments in producing seasonally variable runoff with short mean residence times (33–113 days). In contrast, other tributaries with more freely draining soils and larger groundwater storage in shallow aquifers provided more effective mixing of variable precipitation inputs, resulting in longer residence time estimates (178–445 days). The mean residence time of runoff leaving the Feshie catchment reflected an integration of these contrasting influences (110–200 days). These insights from δ¹⁸O measurements extend the hydrological understanding of the Feshie catchment gained from other hydrochemical tracers, and demonstrate the utility of isotope tracers in investigating hydrological processes at the mesoscale. Copyright © 2005 John Wiley & Sons, Ltd.     

Hydrologic and water isotope characterization of a regulated Canadian Shield river basin

Stable water isotope surveys have increasingly been integrated into river basins studies, but fewer have used them to evaluate impact of hydropower regulation. This study applies hydrologic and water isotope survey approaches to a Canadian Shield river basin with both regulated and natural flows. Historical streamflow records were used to evaluate the influence of three hydroelectric reservoirs and unregulated portions of the basin on downstream flows and changes in water level management implemented after an extreme flood year (1979). In 2013, water isotope surveys of surface and source waters (e.g., rainfall, groundwater, snowmelt) were conducted to examine spatial and temporal variation in contributions to river flow. Seasonal changes in relative groundwater contribution were assessed using a water‐isotope mass balance approach. Within the basin, two regulated reservoirs exhibited inverted hydrographs with augmented winter flows, whereas a third exhibited a hydrograph dominated by spring snowmelt. In 2013, spatial variation in rain‐on‐snow and air temperatures resulted in a critical lag in snowmelt initiation in the southern and northern portions of the basin resulting in a dispersed, double peak spring hydrograph, contrasting with 1979 when a combination of rain‐on‐snow and coincident snowmelt led to the highest flood on record. Although eastern basin reservoirs become seasonally enriched in δ¹⁸O and δ²H values, unregulated western basin flows remain less variable due to groundwater driven baseflow with increasing influence downstream. Combined analysis of historical streamflow (e.g., flood of 1979, drought of 2010) and the 2013 water isotope surveys illustrate extreme meteorological conditions that current management activities are unable to prevent. In this study, the influence of evaporative fractionation on large surface water reservoirs provides important evidence of streamflow partitioning, illustrating the value of stable water isotope tracers for study of larger catchments.     

Power spectral characteristics of drought indices in the Ebro river basin at different temporal scales

A deep spectral investigation of the monthly time series of Standardized Precipitation Index (SPI) and Standardized Precipitation Evapotranspiration Index (SPEI) in 45 meteorological stations in the Ebro basin (Spain) from 1950 to 2006 for timescales ranging from 1 to 48 months was performed. In order to summarize the results for the whole basin, the spectral analysis was also carried out on the four principal components of SPI and SPEI. Results confirm that SPI and SPEI presents very similar spectral characteristics. At the shorter time scales, the signal of SPI and SPEI is characterized by purely random temporal fluctuations. The longer time scales tend to feature the signal as a smoothly varying time series or persistent, mostly due to the aggregated nature of the indices calculation. The comparative analysis of the spectral properties of the drought indices for all the 45 sites in the Ebro basin lead to the identification of global or regional effects discriminated by local effects. It was found that some periodical signals are common to almost all the sites, while others where only identified in specific meteorological stations.     

Significance of isotopic and geochemical methods to determine the evolution of inland brackish and bitter water: An example from the Zuli river in the upper reaches of the Yellow River,China

With the increasing demand for water resources, the utilization of marginal water resources of poor-quality has become a focus of attention. The brackish water developed in the Loess Plateau is not only salty but also famous for its ‘bitterness’. In the present work, multi-isotope analysis (Sr, B) was combined with geochemical analysis to gain insight into the hydrogeochemical evolution and formation mechanisms of brackish water. These results demonstrate that groundwater in the headwater is influenced by carbonate weathering. After the confluence of several tributaries in the headwater, the total dissolved solids (TDS) of water is significantly increased. The dissolution of evaporates is shown to be the main source of salinity in brackish water, which also greatly affects the strontium isotopic composition of water. This includes the dissolution of Mg-rich minerals, which is the main cause of the bitterness. Furthermore, the release of calcium from the dissolution of gypsum may induce calcite precipitation and incongruent dissolution of dolomite, which also contributes to the enrichment of magnesium. The highly fractionated boron isotopic values observed in the upstream groundwater were explained by the absorption with clay minerals. The inflow of brackish groundwater is the source of river water. Then evaporation further aggravates the salinization of river water, with water quality evolving to saline conditions in the lower reach. When the river reaches the valley plain, the ⁸⁷Sr/⁸⁶Sr ratios decreases significantly, which is primarily related to erosion of the riverbanks during runoff. These results indicate that water resource sustainability could be enhanced by directing focus to mitigating salinization in the source area of the catchment.     

Bedrock geology controls on catchment storage,mixing, and release: A comparative analysis of 16 nested catchments

The bedrock controls on catchment mixing, storage, and release have been actively studied in recent years. However, it has been difficult to find neighbouring catchments with sufficiently different and clean expressions of geology to do comparative analysis. Here, we present new data for 16 nested catchments (0.45 to 410 km²) in the Alzette River basin (Luxembourg) that span a range of clean and mixed expressions of schists, phyllites, sandstones, and quartzites to quantify the relationships between bedrock permeability and metrics of water storage and release. We examined 9 years' worth of precipitation and discharge data, and 6 years of fortnightly stable isotope data in streamflow, to explore how bedrock permeability controls (a) streamflow regime metrics, (b) catchment storage, and (c) isotope response and catchment mean transit time (MTT). We used annual and winter precipitation–run‐off ratios, as well as average summer and winter precipitation–run‐off ratios to characterise the streamflow regime in our 16 study catchments. Catchment storage was then used as a metric for catchment comparison. Water mixing potential of 11 catchments was quantified via the standard deviation in streamflow δD (σδD) and the amplitude ratio (A_S/A_P) of annual cycles of δ¹⁸O in streamflow and precipitation. Catchment MTT values were estimated via both stable isotope signature damping and hydraulic turnover calculations. In our 16 nested catchments, the variance in ratios of summer versus winter average run‐off was best explained by bedrock permeability. Whereas active storage (defined here as a measure of the observed maximum interannual variability in catchment storage) ranged from 107 to 373 mm, total catchment storage (defined as the maximum catchment storage connected to the stream network) extended up to ~1700 mm (±200 mm). Catchment bedrock permeability was strongly correlated with mixing proxies of σδD in streamflow and δ¹⁸O A_S/A_P ratios. Catchment MTT values ranged from 0.5 to 2 years, based on stable isotope signature damping, and from 0.5 to 10 years, based on hydraulic turnover.     

Evolution study of a regional groundwater system using hydrochemistry and stable isotopes in Songnen Plain,northeast China

Groundwater is often a critical source of water for municipal, industrial and agricultural uses, especially in arid and semi‐arid environments. Songnen Plain, located in the central part of northeast China, is such a region, it being an important productive base of commodity grain in this country. In the past two decades, groundwater quality in the region, especially salinization, has deteriorated under natural changes and human activities, and has become a crucial factor restricting sustainable eco‐environmental and socio‐economic development. In this paper, The Taoer River catchment, situated in the middle of the region, was selected as the study area for the groundwater quality evolution study using hydrochemistry and stable isotopes to obtain a better understanding of the system. Fifty‐two groundwater samples were collected with systematic design during the low‐water and high‐water periods in 2003. A series of comprehensive quality data interpretations, e.g. statistics, ratios of ions and Piper diagrams, together with stable isotope data, have been used to gain an insight into the spatial and temporal variations and evolution laws of groundwater hydrochemistry. The following main hydrochemical processes were identified as controlling the water quality of the groundwater system: weathering–dissolution, evaporation–condensation, ion‐exchange reactions and groundwater salinization. This latter process, salinization, is the most important process and is caused by the leaching of superficial or near‐surface salts from the saline–alkaline soil into shallow groundwater. Copyright © 2006 John Wiley & Sons, Ltd.     

Ionic and stable isotope chemistry as indicators of water sources to the Upper Mendoza River basin,Central Andes of Argentina

The Mendoza River is mainly dependent on the melting of snow and ice in the Upper Andes. Since predicted changes in climate would modify snow accumulation and glacial melting, it is important to understand the relative contributions of various water sources to river discharge. The two main mountain ranges in the basin, Cordillera Principal and Cordillera Frontal, present differences in geology and receive differing proportions of precipitation from Atlantic and Pacific moisture sources. We propose that differences in the origin of precipitation, geology and sediment contact times across the basin generate ionic and stable isotopic signatures in the water, allowing the differentiation of water sources. Waters from the Cordillera Principal had higher salinity and were more isotopically depleted than those from the Cordillera Frontal. Stable isotope composition and salinity differed among different water sources. The chemical temporal evolution of rivers and streams indicated changes in the relative contributions of different sources, pointing to the importance of glacier melting and groundwater in the river discharge.