Groundwater Lake Interactions Research Articles

Hydraulic Relationship between Hulun Lake and Cretaceous Confined Aquifer Using Hydrochemistry and Isotopic Data

Hydraulic Relationship between Hulun Lake and Cretaceous Confined Aquifer Using Hydrochemistry and Isotopic Data

Simulation of lake-groundwater interaction under unsteady-state flow using the sloping lakebed method

Water exchange between lakes and aquifers directly affects the water balance in lakes, which is a challenging problem in groundwater numerical models. The refined characterization of the lake bottom in popular lake models often results in computational instability. In this article, a new method, namely, the groundwater-sloping lakebed method (SLM), is proposed for simulating unsteady-state flow in lakes and groundwater coupling. The SLM is based on the definition of lake units and the lake bottom setting method, which have been introduced in an article on stable flow coupling simulation. This method offers several advantages, which have been recognized in previous studies. In this article, we provide a detailed explanation of the equation to obtain the fully coupled exchange flux between lakes and groundwater for lake units with different water accumulation states. A modified calculation equation for the water storage term (confined storage coefficient and unconfined specific yield) and the hydraulic conductance of lake units is also presented based on the variation characteristics of the groundwater level. This equation can be used for unsteady-state numerical simulation of lake–groundwater coupling. Supported by the fully coupled lake–groundwater equation, the lake water level can be calculated based on strict equilibration of the lake water volume during each simulation period. Finally, the rationality of the SLM is verified through examples. The results indicate that the SLM coupled with lake–groundwater numerical simulation calculations is strict and stable. Therefore, this approach can be applied in regions with similar conditions and research requirements.

Identifying interactions of linked irrigated lake-groundwater system by combining hydrodynamic and hydrochemical method.

During the irrigation period, the interactions between the linked lake-groundwater systems are complicated and change. This is because natural and human activities are happening at the same time, which makes it harder to identify the interactions. This study uses data on water level, hydrochemistry, and hydrogen-oxygen stable isotopes to analyze the hydrodynamics, electrical conductivity (EC), isotopic characteristics, and spatial distribution of lake water and groundwater to reveal lake-groundwater interactions. The results indicate that the hydrochemical type of Chagan Lake and groundwater is dominated by the HCO3-Na type. The key hydrochemical indicator EC obtained by principal component analysis (PCA) can be used to reveal the lake-groundwater interaction, and the interaction should be identified by location according to the significant correlation between hierarchical clustering results and regional distribution. The lake body's geographic coefficient of variation for EC and δ18O is small, and irrigation return flow is one factor in the region's surface water's significant spatial variation for EC and δ18O. The three study methods indicate that the groundwater supplies the lake in the vicinity of the Huoling River-Hongzi Pool, while in other sections, the lake water leaks and replenishes the groundwater, exhibiting geographic inconsistency. The isotope method was employed as a support tool to determine that groundwater might recharge the lake at Xinmiao Pool. According to the calculations of the Mix SIAR model, the groundwater recharge contribution rate in the Xinmiao Pool section is approximately 51%, while in the remaining sections, the contribution rate of lake water to groundwater ranges from approximately 25% to 52%. Therefore, the identification of the interaction is crucial for the linked irrigated lake-groundwater system where water sources are scarce and threatened by agricultural pollution.

Spatio‐temporal patterns and quantification of lake–groundwater interaction determined in a large water transfer lake

AbstractThe exchange rate is often characterized by spatio‐temporal heterogeneity, but the spatio‐temporal patterns of exchange rate have rarely been quantified, especially in water transfer lakes. This study was conducted from March to July 2021. The tracer data of δ2H, δ18O (n = 121),222Rn (n = 522), Cl (n = 151), TDS (n = 155) in lake water, shallow groundwater (7–10 m), deep groundwater (25–40 m), and an improved single‐well radon model were applied in 3 (A, B and C) typical areas (~1 km2) of the Hongze lake. The results show that during the water transfer period (March to May) the rising lake level from normal water level (13 m asl) to the storage level (13.5 m asl), caused the exchange rate to increase from −6.3 × 10−7to 33.2 × 10−7 m/s. All tracers in groundwater of A and C were continuously diluted by lake water, but shown a better mixing of the lake water, shallow and deep groundwater in area B with a water transfer channel/river (~−100 m3/s). In rainstorm season (June and July), the exchange rate changed from 3.4 × 10−7to −44.8 × 10−7 m/s due to the high groundwater table (13–15 m asl) caused by flood and rainstorm. The rainstorm imposed the inflow of both shallow and deep groundwater into lake in river areas (A and B), but only shallow groundwater recharged lake in non‐river area (C). Additionally, the exchange rate of the whole lake was estimated by the water balance equation, which varied between −1011 and 458 m3/s with an average of −26 m3/s. Finally, a conceptual model of exchange rate among lake, shallow and deep groundwater under spatio‐temporal heterogeneity is proposed. The findings offer better understanding of the spatio‐temporal heterogeneity of lake–groundwater interaction and the effects on lake water balance and recharge systems.

Spatial-Temporal Characteristics and Influencing Factors of Lake Water and Groundwater Chemistry in Hulun Lake, Northeast China

Lakes in cold and arid regions are extremely vulnerable to global climate change, and the study of seasonal spatial and temporal fluctuations of lake-groundwater chemistry is of major significance for water resource management and environmental preservation. In this study, we combined hydrogeochemical, multivariate statistical, and spatial interpolation methods to assess spatial and temporal variations of lake and groundwater chemistry in Hulun Lake during the frozen and non-frozen periods. The results show that sodium (Na+) is the most abundant cation in the Hulun Lake area. Bicarbonate (HCO3−) and sulfate (SO42−) are the most predominant anions in the lake, river, and ground water during both seasons. The higher Na+ + K+ concentrations in the frozen season were related to longer circulation time and lower renewable rate. The water chemistry of the lake was of the HCO3-SO4-Cl-Na type and that of groundwater in the east and west regions was of the SO4-Cl-Na and HCO3-Na types, respectively. The chemical compositions of groundwater in the non-frozen season were mainly affected by evaporation and concentration, while rock weathering, evaporation, and human activities jointly controlled groundwater chemical component in the frozen period. Based on hierarchical cluster analysis (HCA) and principal component analysis (PCA) methods, Ca2+, NO3−, and SO42− were identified as the main controlling indicators of the chemical characteristics of groundwater and lake water. The increase of Ca2+ concentration in the center of the lake was related to groundwater discharge along the marginal tectonic fracture zone along the lake shores, which was the potential groundwater discharge area. The unconsolidated aquifer provides recharge channels for groundwater on the eastern side, which has a certain influence on the increase of nutrient concentration (NO3−) in the lake on the eastern shore. This research adds to our rough understanding of the lake-groundwater interaction in Hulun Lake, and provides a scientific foundation for the sustainable use of water resources, as well as the eco-logical integrity preservation in cold and arid regions.

Groundwater dynamics of a lake-floodplain system: Role of groundwater flux in lake water storage subject to seasonal inundation

Groundwater behaviors in lake-floodplain systems are dynamic and complex; in particular, the role of groundwater flux in regulating lake water storage subject to strong seasonal variation is not well understood. This study addresses the contribution of groundwater flux in a large floodplain system (Poyang Lake, China), with focus on quantifying the groundwater-lake interactions at multiple time scales in high rainfall (2010) and low rainfall (2011) years using a groundwater flow model (MODFLOW). Simulated results revealed that the unconfined aquifer received approximately 8 % of the annual rainfall as groundwater recharge. Fluctuations in shallow groundwater and lake water level reflected hydraulic synchronization and hysteresis. Additionally, the diurnal variability in the groundwater-lake exchange fluxes was subject to dynamic and bidirectional patterns, and a time lag between the water exchange and rainfall was also found. For 2010 and 2011, the monthly net flux of lake infiltration into groundwater was 1.5–10.0 mm and 0.1–6.0 mm and groundwater exfiltration into lake was 1.3–9.5 mm and 0.4–2.2 mm, respectively, demonstrating a significant variation of the exchange magnitude and direction. In particular, we found that groundwater exfiltration contributed up to 55 % of lake storage change in February of 2011. The outcomes from this study indicate that groundwater can be a major component of the Poyang Lake's water balance, which suggests an important role of groundwater in regulating the lake water storage and perhaps other flood pulse systems.

Comparison of Numerical Methods in Simulating Lake–Groundwater Interactions: Lake Hampen, Western Denmark

The numerical simulation of lake–groundwater interaction dynamics is very challenging, and, thus, only few model codes are available. The present study investigated the performance of a new method, namely, the Sloping Lakebed Method (SLM), in comparison to the widely used MODFLOW lake package (LAK3). Coupled lake–groundwater models based on LAK3 and SLM were developed for Lake Hampen, Denmark. The results showed that both methods had essentially the same accuracy when simulating the lake water level, the groundwater head and the overall water balance. The SLM-based model had the potential to reproduce the change of the lake surface area in a more natural way. Moreover, the vertical discretization of a lake in the SLM is independent of the groundwater model, and, thus, the model grid at the top layers could be considerably coarsened without a loss of model accuracy. This could lead to savings in computational time of approximately 30%.

Understanding groundwater behaviors and exchange dynamics in a linked catchment-floodplain-lake system

Groundwater and surface water are hydrologically interconnected systems that exhibit dynamic water, heat and mass exchanges. In this study, a conceptual framework was used to investigate groundwater behaviors and associated hydrological exchanges by combining field measurements, digital filtering and analytical approaches, exemplified by a linked catchment-floodplain-lake system (Poyang Lake, China). The results show that the hydrological regime for both groundwater and surface water exhibit a seasonal variability in the lake catchment. Topographically, the lake catchment can be divided into the mountainous baseflow, ungauged lateral groundwater and floodplain groundwater that contribute to the lake storage changes. Although groundwater flow is generally from the mountainous catchment to the lake floodplain areas due to topographic effects, precipitation provides an additional input for the shallow groundwater and is expected to enhance the groundwater dynamics in terms of spatially heterogeneous responses. The estimation indicates that about 40 % of the catchment river discharge may be coming from the mountainous baseflow (~290 × 108 m3/yr) and discharged into the lake through a surface flow pathway. The ungauged groundwater-lake interaction shows the annual discharge volume is up to 10 × 108 m3/yr and associated exchange fluxes tend to be stronger during spring-summer months (23–45 m3/s) than those of autumn-winter months (9–22 m3/s). Additionally, the floodplain groundwater-lake exchange (~9.5 × 108 m3/yr) indicates that groundwater generally receives the lake water during summer months (mean flux = 110 m3/s) and discharges into the lake during other months (90 m3/s) through a subsurface pathway. This study highlights the importance of groundwater's contributions to the surface river-lake system in terms of the flux variability and different transport pathways. The outcomes of this work will benefit future water resources management and applications by providing a methodology for predicting the groundwater hydrology of large lake-catchment systems.

Quantifying the uncertainty of lake-groundwater interaction using the forward uncertainty propagation framework: The case of Lake Urmia

The interaction between a lake and groundwater has important implications to the quantity and quality of water in both environments. Quantification of lake-groundwater interaction (LGI) has been challenging in regions with limited in-situ data. LGI can be quantified by physically-based models, direct measurement of seepage, measurements of conservative chemical or isotopic tracers, and lake water balance. Despite the accuracy of the methods based on hydrochemical or isotopic measurements and analysis, they require extensive field data that are costly to collect in large lakes. Instead, the data required to quantify LGI by the lake water budget method can be obtained via typical ground measurements and satellite remote sensing. However, the influence on the estimated LGI imposed by the uncertainty associated with the other components of lake water budget (e.g., precipitation, evaporation, and inflow/outflow) is still poorly understood. In this study, we coupled a forward uncertainty propagation framework with the lake water budget to estimate the uncertainty of LGI using Latin-Hypercube sampling. We implemented the above framework in the hypersaline Lake Urmia (LU), located in the northwestern Iran, over five consecutive study periods between September 2017 and May 2020. The results revealed the exchange of flow from groundwater to the LU in all studied periods, ranging between 0.2 million cubic meters (MCM)/day and 7.6 MCM/day. The relative contribution of LGI in the water budget varied between 3% and 37%. The results of the uncertainty analysis further demonstrated that the cumulative probability of LGI < 0, which indicates flow direction from the LU to groundwater, was insignificant in all the study periods ranging between 0.001 and 0.35.

Hydrogen and Oxygen Isotopic Characteristics of Different Water and Indicative Significance in Baiyangdian Lake

In order to better understand the water cycle processes in Baiyangdian Lake, samples for precipitation, river water, lake water, and groundwater were collected in 2020 via the analysis of oxygen and hydrogen isotopes and the total dissolved solids. A combined approach including correlation analysis, end-member modeling, and evaporation modeling was used to identify hydrogen and oxygen isotopic characteristics of different water types and their indicative significance to evaporation, hydrodynamics, and lake-groundwater interactions. The results showed that the compositions of hydrogen and oxygen isotopes in surface water and groundwater differed from each other. The average values of δD and δ18O were the highest in samples from lake water in June, secondary for lake water in October, and the lightest in groundwater. The slope of the lake water line was lower than that of the local meteoric water line, which could be attributed to a greater evaporative enrichment in lake water. The water loss ratio was estimated to be 18.8%-42.3% in June and 2.7%-30.3% in October by applying an evaporation model using deuterium excess. Lake water isotopes exhibited highly spatial heterogeneity, which indicated that Baiyangdian Lake was a poor-mixed lake controlled by the complex hydrodynamic conditions. The values of δD and δ18O were lighter around the estuary area and higher in the district far from the estuary. Although the main water isotopes in areas such as channels had a short residence time, the spatial differences in lake water isotopes were not remarkable, which suggested that the well-mixed conditions of the lake water contributed to reducing the heterogeneity of the lake water isotopic compositions on a spatial scale. The contribution ratios of lake leakage to groundwater were 0-91.7% and varied spatially. It had a negative relationship with the buried depth of groundwater and the distance to the lakeshore. No obvious relationship was found between lake leakage magnitude and groundwater level gradient. This study could provide a theoretical basis and technical support for the sustainable development of water resources and ecological environment protection in Baiyangdian Lake.

Partially penetrating lake-aquifer interaction in a laboratory-scale tidal setting

Freshwater lakes close to the coast are important ecotones with strong functional dependency on ocean forces. Tides are likely to create dynamic lake-groundwater interactions, which have not been previously assessed for partially penetrating lakes. This study investigates tidal lake-groundwater interaction in a laboratory-scale aquifer cross-section with and without the existence of a partially penetrating lake. Experimental observations were found to be well matched to the results of numerical modeling in terms of the amplitudes and phases of pressure fluctuations at 19 locations. The results show that the lake dampened tide-induced pressure head fluctuations, indicating that the enhanced storage capacity was more influential in modifying tidal propagation relative to the increased transmissiveness imparted by the lake. The lake also caused stronger depth-dependency in groundwater tidal fluctuations, as determined from vertical profiles of tidal amplitude and phase. Vertical profiles also reveal that the tidal amplitude and phase responded differently to the addition of the lake, in a manner that reflects previous studies of tidal propagation in layered aquifers. Tides created significant aquifer-lake fluxes, leading to strong rates of lake flushing, particularly through the seaward lake boundary. Including a clogging layer at the lake bottom (within numerical models) tended to reduce the lake’s effects on tidal propagation, although clogging layer effects were complex. This study highlights the important role of tides on partially penetrating lake-groundwater exchange dynamics and the influence of partially penetrating lakes on tidal propagation in coastal settings, albeit at the laboratory scale.

Investigating groundwater-lake interactions in the Laurentian Great Lakes with a fully-integrated surface water-groundwater model

Modelling groundwater-surface water (GW-SW) interactions at scales of large river basins is a difficult challenge. In this study, a fully-integrated surface water-groundwater model accounting for hydrologic seasonality is developed for the 766,000 km2 Laurentian Great Lakes basin, and applied towards the characterization of groundwater-lake (GW-lake) interactions in the five Great Lakes under monthly normal climatology. The simulated annual average rates of direct groundwater discharge to Lakes Superior, Michigan, Huron, Erie and Ontario through the combined lakebed and 8 km wide band of shoreline surrounding each lake are 29.0, 38.6, 24.5, 11.9, and 11.6 m3/s, respectively. Thus, direct groundwater discharge accounts for a small component of positive basin supply; ranging from 0.6% for Lake Ontario to 1.3% for Lake Michigan, with an overall average of 0.8% for all lakes combined. Simulation results demonstrate that GW-lake interactions are strongest nearshore, and vary temporally in response to seasonal fluctuations in both lake levels and terrestrial groundwater levels in nearshore regions. In winter, direct groundwater discharge dominates the GW-lake interactions in both the distal and nearshore lakebed areas. In summer, the combined effects of rising lake levels and lowering terrestrial groundwater levels lead to notable reductions in direct groundwater discharge through nearshore areas. Direct groundwater discharge is also shown to vary spatially, with highest rates associated with areas containing thick Phanerozoic hydrostratigraphy, as opposed to Precambrian basement rock. The results from this study indicate that the Great Lakes primarily act as groundwater receivers, gaining considerable amounts of water directly from the basin’s groundwater system.

Simulation of Lake-Groundwater Interaction under Steady-State Flow.

MODFLOW is one of the most popular groundwater simulation tools available; however, the development of lake modules that can be coupled with MODFLOW is lacking apart from the LAK3 package. This study proposes a new approach for simulating lake‐groundwater interaction under steady‐state flow, referred to as the sloping lakebed method (SLM). In this new approach, discretization of the lakebed in the vertical direction is independent of the spatial discretization of the aquifer system, which can potentially solve the problem that the lake and groundwater are usually simulated at different scales. The lakebed is generalized by a slant at the bottom of each lake grid cell, which can be classified as fully submerged, dry, and partly submerged. The SLM method accounts for all lake sources and sinks, establishing a governing equation that can be solved using Newton's method. A benchmarking case study was conducted using a modified model setup in the LAK3 user manual. It was found that when there is a sufficient number of layers at the top of the groundwater model, SLM simulates an almost identical groundwater head as the LAK3‐based model; when the number of layers decreases, SLM is unaffected while LAK3 may be at a risk of giving unrealistic results. Additionally, the SLM can reflect the relationship between the simulated lake surface area and lake water depth more accurately. Therefore, the SLM method is a promising alternative to the LAK3 package when simulating lake‐groundwater interaction.

Interaction of lake-groundwater levels using cross-correlation analysis: A case study of Lake Urmia Basin, Iran

Lake Urmia (LU) is the second largest hypersaline lake in the world. Lake Urmia's water level has dropped drastically from 1277.85 m to 1270.08 m a.s.l (equal to 7.77 m) during the last 20 years, equivalent to a loss of 70% of the lake area. The likelihood of lake-groundwater connection on the basin-scale is uncertain and understudied because of lack of basic data and precise information required for physically-based modeling. In this study, cross-correlation analysis is applied on a various time-frames of water level of the lake and groundwater levels (2001–2018) recorded in 797 observation wells across 17 adjacent aquifers. This provides insightful information on the lake-groundwater interaction. The cross-correlation coefficient between the monthly water level of lake and observations wells (rGW−L) and the difference of these two variables (Hf) was calculated for different time-frames. The values of rGW−L (ranged −0.69 to 0.97) and Hf (ranged −53 m to 293 m) indicated the significant role of time-frames of observed dataset on dynamic behavior of lake-groundwater interaction, and exchange fluxes in the study setting. Results suggested two opposing behaviors in lake-groundwater interaction of the study system mainly arise from anthropogenic activity (overexploitation of groundwater for irrigation) and aquifer type (unconfined/pressurized): three out of 17 adjacent aquifers are feeding by the LU and act as “gaining aquifers” (located in northern half of LU) and others discharging into the LU and act as “losing aquifers”. This study aimed to provide easy-to-obtain insights into LGWI in the complex setting of LU Basin. It can be considered a preliminary step towards a deeper understanding of the interaction through physically-based analysis and modeling.

Use of 222Rn and δ18O-δ2H Isotopes in Detecting the Origin of Water and in Quantifying Groundwater Inflow Rates in an Alarmingly Growing Lake, Ethiopia

Dual Radon (222Rn) and δ18O-δ2H isotopes were utilized to (a) detect the origin of water, (b) pinpoint groundwater inflow zones and (c) determine rates of groundwater inflows in an expanding lake in central Ethiopia. The lake area expanded from 2 km2 to 50 km2 over the last 60 years, causing serious engineering and socio-economic challenge (inundation of urban utilities, irrigation farms, railways and roads; ecological changes in the lake; and threatening water salinization for water users downstream). Commensurate with the changes in volume, there was a change in salinity of the lake from a hypersaline (TDS 50 g/L) to a near freshwater (3 g/L) condition. 222Rn is powerful in pinpointing sites of groundwater inflows and determining groundwater inflow rates in lake systems with non-hydrologic steady-state conditions. The 222Rn method is complemented by the use of the stable isotopes of water (δ18O-δ2H pair). The δ18O-δ2H isotopes were used to discriminate the source of the water responsible for the expansion of the lake. The results show that the main source of water responsible for the expansion of the lake is the irrigation of excess water joining the lake through subsurface flow paths. The fast and voluminous flow is aided by a dense network of faults and by seismically induced modern ground-cracks that enhance the transmissivity of the aquifers to as high as 15,000 m2/day. The 222Rn mass balance shows the groundwater inflow rate is estimated at 4.6 m3/s. This is comparable with the 4.9 m3/s annual seepage loss from three large farms in the area. This work adds to the meager literature in the use of 222Rn in lake-groundwater interaction studies by demonstrating the capability of the method in addressing a practical engineering and socio-economic challenges.

Development of a spreadsheet-based model for transient groundwater modelling

Understanding and modelling the passage of groundwater is important for a wide range of environmental and earth science disciplines. The science of groundwater modelling is mature, and advanced modelling algorithms are routinely implemented, for example via the widely used MODFLOW software. However, for the non-specialist scientist or student, the fundamentals of such software can be difficult to comprehend, whilst the algorithms are arguably too complex to be easily applied for many applications which require integration of a groundwater model with climate, surface-water, soil or ecological data. In this context, a spreadsheet-based groundwater model (A2016), capable of solving transient groundwater behaviour in multiple spatial dimensions, was developed. Inter-comparison tests investigating nine transient groundwater scenarios were performed between MODFLOW, A2016 and the Time-dependent Groundwater Modeling using Spreadsheet Simulation (TGMSS) model. Results demonstrated that A2016 is directly comparable to MODFLOW, with identical hydraulic heads in all model experiments. TGMSS was not able to accurately simulate hydraulic heads for any of the model experiments. A groundwater–lake interaction scenario was identified for which MODFLOW will produce unrealistic results, due to the way conductance beneath lakes is determined. Applying a specified saturated thickness approximation for the region beneath the lake resulted in improved lake–groundwater interactions. A2016 is potentially useful for educational purposes and as a tool for groundwater experiments by non-specialists, as it is modular in nature and incorporates MODFLOW terminology and techniques.

The influence of slope collapse on water exchange between a pit lake and a heterogeneous aquifer

Due to the increase in open pit mining, pit lakes have become common surface water features, posing a potential risk to subsurface aquifer. In this study, a pit lake–groundwater interaction model is built based on the general program MODFLOW with the LAK3 package. For the first time, the effects of lake-slope collapse and aquifer heterogeneity on pit lake–groundwater interactions are analyzed by dividing the lake into six water exchange zones based on the aquifer lithology and groundwater level. Our investigation and simulations reveal a total water exchange from groundwater to the lake of 349000 m3/a without collapse of the pit lake slope, while the total net water exchange under slope collapse conditions is 248000 m3/a (i.e., a reduction of 1.40-fold). The monthly net water exchange per unit width from groundwater to the lake reaches the largest in April, shifting to negative values in zone IV from June to August and in zone Vin June and July. Moreover, the monthly net water exchange per unit width decreases from north to south, and the direction and magnitude of water exchange are found to depend on the hydraulic gradients between the lake and groundwater and the hydraulic conductivity of the slope collapse.

Assessing surface water–groundwater interactions in a complex river‐floodplain wetland‐isolated lake system

AbstractFloodplain systems are most often hydrologically complex settings characterized by highly variable surface water–groundwater interactions that are subjected to wide‐ranging wetting and drying over seasonal timeframes. This study used field methods, statistical analysis, and the Darcy's law approach to explore surface water–groundwater dynamics, interactions, and fluxes in a geographically complex river‐floodplain wetland‐isolated lake system (Poyang Lake, China). The floodplain system of Poyang Lake is affected by strongly seasonal shifts between dry and wet processes that cause marked changes in surface water and groundwater flow regimes. Results indicate that wetland groundwater is more sensitive to variations in river levels than the seasonal isolated lakes. In general, groundwater levels are lower than those of the isolated lakes but slightly higher than river levels. Statistical analysis indicates that the river hydrology plays a more significant role than the isolated lakes in controlling floodplain groundwater dynamics. Overall, the river shows gaining conditions and occasionally losing conditions with highly variable Darcy fluxes of up to +0.4 and −0.2 m/day, respectively, whereas the isolated lakes are more likely to show slightly losing conditions (less than −0.1 m/day). Although seasonal flux rates range from 7.5 to 48.2 m/day for surface water–groundwater interactions in the floodplain, the flux rates for river–groundwater interactions were around four to seven times higher than that of the isolated lake–groundwater interactions. The outcomes of this study have important implications for improving the understanding of the water resources, water quality, and ecosystem functioning for both the river and the lake.

Investigating the mysteries of groundwater in the Badain Jaran Desert, China

The Badain Jaran Desert (BJD) in China is a desert with impressive sand dunes and a groundwater situation that has attracted numerous researchers. This paper gives an overview of the mysteries of groundwater in the BJD that are exhibited as five key problems identified in previous studies. These problems relate to the origin of the groundwater, the hydrological connection between the BJD and the Heihe River Basin (HRB), the infiltration recharge, the lake–groundwater interactions, and the features of stable isotope analyses. The existing controversial analyses and hypotheses have caused debate and have hindered effective water resources management in the region. In recent years, these problems have been partly addressed by additional surveys. It has been revealed that the Quaternary sandy sediments and Neogene-Cretaceous sandstones form a thick aquifer system in the BJD. Groundwater flow at the regional scale is dominated by a significant difference in water levels between the surrounding mountains and lowlands at the western and northern edges. Discharge of groundwater from the BJD to the downstream HRB occurs according to the regional flow. Seasonal fluctuations of the water level in lakes are less than 0.5 m due to the quasi-steady groundwater discharge. The magnitude of infiltration recharge is still highly uncertain because significant limitations existed in previous studies. The evaporation effect may be the key to interpreting the anomalous negative deuterium-excess in the BJD groundwater. Further investigations are expected to reveal the hydrogeological conditions in more detail.

Determination of groundwater discharge rates and water residence time of groundwater‐fed lakes by stable isotopes of water (18O, 2H) and radon (222Rn) mass balances

AbstractLacustrine groundwater discharge (LGD) and the related water residence time are crucial parameters for quantifying lake matter budgets and assessing its vulnerability to contaminant input. Our approach utilizes the stable isotopes of water (δ18O, δ2H) and the radioisotope radon (222Rn) for determining long‐term average and short‐term snapshots in LGD. We conducted isotope balances for the 0.5‐km2 Lake Ammelshainer See (Germany) based on measurements of lake isotope inventories and groundwater composition accompanied by good quality and comprehensive long‐term meteorological and isotopic data (precipitation) from nearby monitoring stations. The results from the steady‐state annual isotope balances that rely on only two sampling campaigns are consistent for both δ18O and δ2H and suggested an overall long‐term average LGD rate that was used to infer the water residence time of the lake. These findings were supported by the good agreement of the simulated LGD‐driven annual cycles of δ18O and δ2H lake inventories with the observed lake isotope inventories. However, radon mass balances revealed lower values that might be the result of seasonal LGD variability. For obtaining further insights into possible seasonal variability of groundwater–lake interaction, stable water isotope and radon mass balances could be conducted more frequently (e.g., monthly) in order to use the derived groundwater discharge rates as input for time‐variant isotope balances.