Groundwater discharge tracing for a large Ice-Covered lake in the Tibetan Plateau: Integrated satellite remote sensing data, chemical components and isotopes (D, 18O, and 222Rn)
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Groundwater discharge
δ18O
Abstract. Groundwater recharge sustains groundwater discharge, including natural discharge through springs and the base flow to surface water as well as anthropogenic discharge through pumping wells. Here, for the first time, we compute long-term (1996–2015) groundwater recharge rates using data retrieved from several groundwater-level monitoring locations across India (3.3 million km2 area), the most groundwater-stressed region globally. Spatial variations in groundwater recharge rates (basin-wide mean: 17 to 960 mm yr−1) were estimated in the 22 major river basins across India. The extensive plains of the Indus–Ganges–Brahmaputra (IGB) river basins are subjected to prevalence of comparatively higher recharge. This is mainly attributed to occurrence of coarse sediments, higher rainfall, and intensive irrigation-linked groundwater-abstraction inducing recharge by increasing available groundwater storage and return flows. Lower recharge rates (<200 mm yr−1) in most of the central and southern study areas occur in cratonic, crystalline fractured aquifers. Estimated recharge rates have been compared favorably with field-scale recharge estimates (n=52) based on tracer (tritium) injection tests. Results show that precipitation rates do not significantly influence groundwater recharge in most of the river basins across India, indicating human influence in prevailing recharge rates. The spatial variability in recharge rates could provide critical input for policymakers to develop more sustainable groundwater management in India.
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Abstract. Groundwater recharge sustains groundwater discharge, including natural discharge through springs and base flow to surface water as well as anthropogenic discharge through pumping wells. Here, for the first time, we compute long-term (1996–2015) groundwater recharge rates using data retrieved from several groundwater level monitoring locations across India (3.3 million km2 area), the most groundwater-stressed region globally. Spatial variations in groundwater recharge rates (basin-wide mean: 17 to 960 mm/yr) were estimated in the 22 major river basins across India. The extensive plains of the Indus–Ganges–Brahmaputra (IGB) river basins are subjected to prevalence of comparatively higher recharge. This is mainly attributed to occurrence of coarse sediments, higher rainfall, and intensive irrigation-linked groundwater abstraction inducing recharge by increasing available groundwater storage and return flows. Lower recharge rates (
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δ18O
Carbon fibers
Isotope Analysis
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The stable isotope change in the Yamzho Lake Basin is discussed based on the observed results of stable isotope of precipitation,river and lake water in 2004 and on the stable isotope fractionation model in a closed lake.This study shows that the present-5.9‰ of Yamzho Lake δ18O is related to the eventual steady lake δ18O after evaporation enrichment under the relative humidity of around 54%~58%.It is also found that the input δ18O to the closed lake has also affected the eventual δ18O after evaporation enrichment.However,the impact of the lake water temperature has little effect on the steady lake δ18O.The lake itself has a strong adjustment to the input δ18O change.For the large change of input δ18O,the Yamzho Lake δ18O can reach another steady state in less than 50 years.
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Water cycle
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Stable isotopic composition of fossil ostracode is used as an ideal proxy for paleo-lake sedimentary environments.Over the last three decades,measurements of the δ13C and δ18O values of ostracode shells have been extensively used in lake palaeoenvironmental reconstruction.Many methods for sample preparation have been applied in stable isotope measurements of ostracode shells from lake sediments.However,for stable isotope measurements of biocarbonate samples,different methods will probably affect the resolution,reproducibility and inter-laboratory comparison of the measurement results.In this paper,previous methods of sample preparation for biocarbonate isotopic measurements are compared,with their effects on δ13C and δ18O analyses evaluated.The results suggest that different methods will not result in remarkable differences in δ13C and δ18O measurements of lake ostracode shells.Therefore,sample cleaning procedure is considered unnecessary for such analyses.
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Groundwater resources are generally evaluated by quantifying groundwater recharge and its storage into the aquifer using for example conceptual or numerical models. Recharge modelling provides a preliminary estimation of the renewable part of the groundwater resource. Moreover, results of regional groundwater recharge models may be used as input data for models on a smaller scale, i.e. at the catchment scale dedicated to water management for present and future conditions. It is thus necessary to constrain the recharge models for example by comparing their outputs to historical long-term observations of groundwater flows that can be derived from time series of groundwater levels or spring discharge.Karst systems with their high infiltration rate and preferential flow in enlarged conduit networks, react quickly to climatic events and changes. Thus, they can be used as proxies to evaluate the impact of global change on groundwater resources. Karst systems are present in different climatic regions of Europe, which allows comparing long-term trends of groundwater recharge with spring discharge (similar or opposing trends). In our study, two different regional recharge models covering entire Europe – one calculating potential groundwater recharge using simple soil water balance methods and one calculating groundwater recharge over karst areas only using 1-D physical equations for infiltration – are compared to the measured spring discharge from a large European database of more than 100 monitored karst systems. To identify and highlight changes in dominant recharge processes related to changing climatic or physiographic (land cover / land use) conditions, different variables used in the regional recharge models will be correlated to indices describing dynamics of karst spring discharge. The results of our study will help to understand the impact of climatic and groundwater recharge related influences on various geographic locations and give insights on uncertainties in the model structure of the applied regional groundwater recharge models.
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Infiltration (HVAC)
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Conjunctive use of surface water and groundwater for irrigation plays an important role in the hydrology of alluvial fans, both as a source of recharge to the groundwater and as a cause of discharge by pumping. Therefore, reliable estimates of distributed groundwater recharge and discharge are critical in analyzing groundwater budgets in alluvial fans. Nasunogahara basin, Tochigi Prefecture, Japan, is an alluvial fan with abundant shallow groundwater, which is extracted and used for irrigation. In this study an integrated surface water- groundwater model, which combined a modified tank model with a finite difference model, was used to evaluate quantitatively groundwater recharge and discharge capacities of each recharge source and discharge route and to assess the effect of conjunctive use of surface water and groundwater for paddy field irrigation on the water balance of the shallow aquifer of Nasunogahara. The tank model calculated recharge by different recharge sources to the shallow aquifer and also calculated the amount of groundwater pumped for irrigation. Distributed groundwater recharge and discharge were estimated at each node in the groundwater flow model based on the paddy field area around the node. Results of the model indicate that the calculated water table elevations were able to describe the actual behavior of the shallow aquifer adequately. From the model simulation runs, it was found that although paddy fields are big users of groundwater by pumping, the irrigation water applied is used in a cyclic manner to recharge the shallow aquifer. The percentage of the recharge from paddy fields to the total net recharge is 21 %, which is mainly provided from paddy fields irrigated by canal water. These facts indicate the importance of the conjunctive use of surface water and groundwater for irrigation in maintaining the hydrologic system of the basin.
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The δ2H and δ18O values in water bodies are essential to the management of water resources because of the ability to insight into hydrological processes. In this study, we have measured and analyzed the major ions (Na+, K+, Ca2+, Mg2+, Cl–, SO24– and HCO–3 ) and stable H-O isotopes (δ2H and δ18O) for fifteen surface water samples collected from the Xinbian River in Suzhou, northern Anhui Province, China. The results show that all of the water samples are classified to be Na-HCO3 type, and the mean values of δ2H and δ18O are –42.93‰ and –5.36‰, respectively. Gibbs diagram and the relationship between δ2H and δ18O indicate that both water chemistry and stable isotopes in river water are mainly controlled by evaporation. Correlation analysis reveals that a significant correlation between major ions and δ18O. Predictors (K+, SO24– and HCO–3 ) have been selected by optimal subset regression analysis were used to model the δ18O values in the river water. Moreover, the residuals of the model were normally distributed and values between –0.2‰ to 0.2‰ for most water samples, suggesting a strong relationship between the observed and predicted δ18O values.
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Hydrological studies have been done in the Lake Tana basin to determine the groundwater recharge rate based on different methods, groundwater inflow to and outflow from the Tana Lake, and to understand the groundwater and surface waters interaction. Recharge rates of 195.6, 284.0 and 285.4 mm/year have been estimated based on base flow analysis, chloride mass balance (CMB) and soil water balance (SWB) methods, respectively. Base flow separation method shows mean shallow aquifer recharge that feeds the streams. The recharge estimates from CMB and SWB are nearly similar and the average of the two (284.7 mm/year) can be taken as the mean basin recharge rate. The difference between the basin recharge and the base flow (89.1 mm/year or 31.3% of the recharge) contributes to deep aquifers recharge.Tana Lake balance study has also showed leakage underflow of 954.8 hm 3 /year, which mixes with groundwater mainly in the Beles basin and to some extent in Tis Abay area. Groundwater inflow directly to the lake is found to be negligible. Keywords: groundwater recharge, water balance, base flow, groundwater and surface waters interaction, Lake Tana, Blue Nile River, Ethiopia
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Abstract. Knowledge of groundwater residence times and recharge locations is vital to the sustainable management of groundwater resources. Here we investigate groundwater residence times and patterns of recharge in the Gellibrand Valley, southeast Australia, where outcropping aquifer sediments of the Eastern View Formation form an "aquifer window" that may receive diffuse recharge from rainfall and recharge from the Gellibrand River. To determine recharge patterns and groundwater flow paths, environmental isotopes (3H, 14C, δ13C, δ18O, δ2H) are used in conjunction with groundwater geochemistry and continuous monitoring of groundwater elevation and electrical conductivity. The water table fluctuates by 0.9 to 3.7 m annually, implying recharge rates of 90 and 372 mm yr−1. However, residence times of shallow (11 to 29 m) groundwater determined by 14C are between 100 and 10 000 years, 3H activities are negligible in most of the groundwater, and groundwater electrical conductivity remains constant over the period of study. Deeper groundwater with older 14C ages has lower δ18O values than younger, shallower groundwater, which is consistent with it being derived from greater altitudes. The combined geochemistry data indicate that local recharge from precipitation within the valley occurs through the aquifer window, however much of the groundwater in the Gellibrand Valley predominantly originates from the regional recharge zone, the Barongarook High. The Gellibrand Valley is a regional discharge zone with upward head gradients that limits local recharge to the upper 10 m of the aquifer. Additionally, the groundwater head gradients adjacent to the Gellibrand River are generally upwards, implying that it does not recharge the surrounding groundwater and has limited bank storage. 14C ages and Cl concentrations are well correlated and Cl concentrations may be used to provide a first-order estimate of groundwater residence times. Progressively lower chloride concentrations from 10 000 years BP to the present day are interpreted to indicate an increase in recharge rates on the Barongarook High.
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