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In Germany, 70 % of the drinking water demand is met by groundwater, for which the quality is the product of multiple physical–chemical and biological processes. As healthy groundwater ecosystems help to provide clean drinking water, it is necessary to assess their ecological conditions. This is particularly true for densely populated urban areas, where faunistic groundwater investigations are still scarce. The aim of this study is, therefore, to provide a first assessment of the groundwater fauna in an urban area. Thus, we examine the ecological status of an anthropogenically influenced aquifer by analysing fauna in 39 groundwater monitoring wells in the city of Karlsruhe (Germany). For classification, we apply the groundwater ecosystem status index (GESI), in which a threshold of more than 70 % of crustaceans and less than 20 % of oligochaetes serves as an indication for very good and good ecological conditions. Our study reveals that only 35 % of the wells in the residential, commercial and industrial areas and 50 % of wells in the forested area fulfil these criteria. However, the study did not find clear spatial patterns with respect to land use and other anthropogenic impacts, in particular with respect to groundwater temperature. Nevertheless, there are noticeable differences in the spatial distribution of species in combination with abiotic groundwater characteristics in groundwater of the different areas of the city, which indicate that a more comprehensive assessment is required to evaluate the groundwater ecological status in more detail. In particular, more indicators, such as groundwater temperature, indicator species, delineation of site-specific characteristics and natural reference conditions should be considered. [ABSTRACT FROM AUTHOR]

• Coastal algal bloom is jointly regulated by physical and chemical controls. • Coastal phosphate is significantly originated from coastal groundwater. • The fluctuation of groundwater phosphate is governed by temperature. • Groundwater phosphate along with submarine groundwater discharge enters coasts. Algal blooms have been identified as one major threat to coastal safety and marine ecosystem functioning, but the dominant mechanism regulating the formation of algal blooms remains controversial, ranging from physical control (via water column stability), the chemical control (via coastal nutrients) to joint control. Here we leveraged the unique data collected in the Hong Kong water over the annual cycle and past three decades, including direct observations of algal blooms and coastal nutrients and process model output of water column stability, and evaluated the differential competing hypotheses in regulating algal blooms. Our results demonstrate that the joint mechanism rather than the single mechanism effectively predicts all algal blooms. Meanwhile, we observed that the adequate nutrients (phosphate, PO 4 3−) significantly originate from coastal groundwater. The production and fluctuation of PO 4 3− in beach aquifers are primarily governed by groundwater temperature, leading to a sustained and sufficient supply of PO 4 3− in a low groundwater temperature environment. Furthermore, along with submarine groundwater discharge (SGD), the ongoing release of PO 4 3− in groundwater enters coastal waters and serves as sufficient nourishment for promoting algal blooms in coastal areas. These results highlight the importance of both physical and chemical mechanisms, as well as SGD, in regulating coastal algal blooms. These findings have practical implications for the prevention of coastal algal blooms and provide insights into mariculture, water security, and the sustainability of coastal ecosystems. [Display omitted] [ABSTRACT FROM AUTHOR]

The Linta Basin, located in the Southwestern Madagascar, is a semi-arid area where groundwater in fractured media bedrock aquifer constitutes the main source of water supply. In the last two decades, highly mineralized groundwater was identified in this area; however, the origin of the salinity was not clear. The purpose of the study was to clarify the origin of salinity and to identify hotspots with groundwater unsuitable for water supply. Groundwater quality in this basin was investigated by hydrogeochemical and isotopic methods accompanied by mineralogical study. In total, 32 groundwater samples were collected and analyzed. The results showed that groundwater temperature varied from 25.2 °C to 31.7 °C. Values of pH and TDS varied from 6.55 to 8.24 and 221 to 5612 mg/L, respectively. The aquifer, which is mainly fractured, showed 7 groundwater types, namely Mg–HCO 3 ,Na–HCO 3 and also Na–C1, Mg–Cl, Na–Cl–HCO 3 , Mg–Cl–HCO 3 -, and Ca–Mg–HCO 3. Two groups of variables have been identified by factor analysis; the factor F1 comprises EC, Ca2+, Mg2+, SO 4 2−, and Cl− whereas the factor F2 comprises HCO 3 −, K+, and Na+, and they were interpreted in terms of hydrogeochemical processes. Values of saturation indices (SI) for carbonate minerals were generally positive, indicating their possible precipitation. Based on the Gibbs diagram and factor analysis, groundwater mineralization is affected by water-rock interactions and evaporation, respectively. The important role of evaporation is confirmed by enrichment of stable isotopes with δ18O values up to 1.2 ‰. Processes such as base ionic exchange process and reverse ionic exchange process may also be important locally. The main origin of groundwater mineralization is the hydrolysis of silicate minerals such as feldspars and micas coupled with evaporation. In several wells, salinity is too high for water supply and nitrate concentration is above the WHO limit for drinking water. Results of the study highlighted groundwater chemistry formation processes and are applicable in other African countries with bedrock aquifers. • Groundwater chemistry in bedrock aquifer in SW Madagascar was investigated. • Mineralization increases in flow direction and dominant groundwater types are Mg– HCO 3 and Na–HCO 3. • Principal processes affecting groundwater chemistry are dissolution of silicates and evaporation. • Hotspots with high salinity and nitrate concentration were identified. [ABSTRACT FROM AUTHOR]

[Display omitted] • Groundwater levels in the province of Quebec show a slight downward trend. • In cold and humid climates, hydrogeological systems undergo an annual reset due to the cold period, keeping droughts short. • 10- to 20-year time series are sufficient for analyses of trends and determining the role of precipitation and temperature on groundwater variability. • Standardized indexes are extremely useful to assess how groundwater levels are affected by meteorological conditions. Understanding the fluctuations in groundwater levels in response to meteorological conditions is challenging, especially given the slow transit time associated with groundwater reservoirs and the short duration of time series for groundwater levels. Nevertheless, this knowledge is crucial for water resource management, especially given that global warming will drastically impact the hydrological dynamics in cold and humid climates. The objective of this work was to quantify how standardized indexes contribute to understanding groundwater level fluctuations in response to meteorological conditions in cold and humid climates and with short time series (10 to 23 years). The relationships between the standardized precipitation index (SPI), standardized temperature index (STI), global climate indexes, and standardized groundwater index (SGI) were analyzed. The reactivity of groundwater levels was examined between 2000 and 2022 using groundwater level measurements from 152 wells located between 46 °N and 52 °N in the province of Quebec (Canada). The results showed that the available time series were sufficient to provide new insights into the role of precipitation and temperature on groundwater fluctuations, demonstrating the usefulness of the indexes. One of the main contributions of this study was that hydrogeological systems in cold and humid climates go through an annual reset due to the prolonged freezing period. This annual reset was one of the drivers isolating year-to-year hydrogeological conditions, contributing to short-duration droughts. [ABSTRACT FROM AUTHOR]

Geothermal waters are featured in many locations in Aakkar district north of Lebanon. Among which, the town of Semmaquiyeh is home to a geothermal well, drilled back in the seventies. To this date this geothermal source remains unexploited. To investigate the potential use of this site, it is imperative to define the subsurface geology and groundwater flow. The geological information of the area was reviewed, and a geophysical investigation was carried out on site with measurements of the Multi-Channel Analysis of Surface Waves (MASW). The horizontal-to-vertical spectral ratio (HVSR) method was also used to estimate the resonant frequency of sedimentary layers on top of bedrock, and the Audio-frequency Magnetotelluric probing (AMT) was applied for groundwater true resistivity. The results of the MASW investigation showed conformity with the geologic formations of fluvio-marine deposits with a thick layer of clayey limonite soil. The Audio-frequency Magnetotelluric probing profile indicated that the groundwater table is very shallow, and the gradient is flat mimicking the surface topography. The study gave insights into some potential economic exploitations. Further detailed geological studies of the subsoil from boreholes, laboratory soil testing, detailed geochemical water analysis and determination of the groundwater temperature gradient with depth are recommended to be able to determine future geothermal applications. [ABSTRACT FROM AUTHOR]

With groundwater temperature, hybrid-genetic algorithm is employed to locate multi-passage concentrated seepage underground to increase the probability of optimal global solutions, calculation efficiency and precision. The parameters of concentrated seepage passages (CSPs) indicated initially by the previous optimization and attraction basins of modified temperature residuals are evaluated again by the proposed full parameter optimization. The smaller CSP impacts on the stronger are eliminated, since all the parameters associated with all the CSPs are calculated by the last one-off optimization. In this case, three optimization steps are implemented with crossover fractions of 0.8, 0.5 and 0.45 (0.3), and the modified resultant residuals are 13.441, 2.27 and 0.7 individually. Results of this method are more effective compared to those from other methods and actual applications. [ABSTRACT FROM AUTHOR]

This work presents the results of a hydrogeochemical study conducted in two galleries on the island of Tenerife: Fuente del Valle and San Fernando, during a 2-year period with weekly sampling (July 2016 to July 2018). Groundwater temperature, pH, and electrical conductivity exhibited stable values throughout the study period, while significant temporal variations were observed in the total alkalinity, SO42−/Cl− ratio (in meq·L−1), and isotopic composition (δ18O and δD). δ13CTDIC values showed an endogenous signature for both galleries, while δ18O and δD values indicated a meteoric origin with interaction with endogenous gases, mainly CO2. Changes in isotopic ratios coincided with variations observed in alkalinity and SO42−/Cl− ratio. On October 2, 2016, a seismic swarm of long-period events was recorded on Tenerife followed by a general increase of the seismic activity in and around the island. A correlation was observed between some hydrogeochemical parameters in the groundwaters of the galleries related to observed changes of the seismic activity. [ABSTRACT FROM AUTHOR]

Hydropeaking, the alternating storage and release of water from reservoirs for hydropower generation, perturbs the thermal regime of many large rivers. While its effects on river temperature have been long studied, impacts on the thermal regime of riverbeds remain mostly unknown, despite riverbed temperature affecting rates of nutrient cycling and habitat suitability for benthic organisms. This study combines detailed field observations and flow and heat transport modeling to assess the impact of hydropeaking on riverbed temperatures in a large regulated river. The field site was 12 km downstream from a dam that induces large daily flow variations. Vertical thermistor arrays were used to collect riverbed temperature data across the entire 70 m‐wide channel. The riverbed near the left bank was highly dynamic thermally, transitioning between river and groundwater temperatures over daily hydropeaking cycles. In contrast, the rest of the riverbed, including near the right bank, was similar in temperature to the river and had relatively stable temperatures. Modeling showed that the temperatures near the banks are explained by advective heat transport driven by hydrostatic changes in river level, while the temperatures over the rest of the channel can be explained mostly by conductive heating. Gaining groundwater conditions and high sediment hydraulic conductivity favor thermally dynamic zones near banks, while low hydraulic conductivity (below 1 m/d) and neutral or losing groundwater conditions result in muted temperature fluctuations, as observed at the right bank. These spatial patterns can help predict thermally sensitive processes in the riverbeds of hydropeaked or flooding rivers. Plain Language Summary: Temperature is critical in the structure and health of aquatic environments. Temperature and flow patterns in rivers are often altered by dam releases. Ecologists have studied the effects of dam operations on aquatic environments for decades. However, many studies exclusively focused on the surface water environment. Our study instead focused on understanding how the temperature in the riverbed is affected by daily dam releases. Riverbeds are an important habitat for a diverse array of aquatic organisms, many of which are sensitive to temperature. Riverbed temperature can also affect the rates of important chemical reactions involving carbon and nutrients. We found that dam releases can cause large changes in riverbed temperatures near the bank of the river, but that temperatures in the rest of the channel remain relatively constant. The differences in the riverbed temperature near the bank suggest that these areas could ecologically function differently from one another, such as what organisms are adapted to these two different environments and in the rates of temperature‐sensitive chemical reactions in these two regions of the riverbed. Key Points: This study combines high‐resolution observations with modeling to evaluate controls on riverbed temperature dynamicsDaily stage fluctuations in large rivers can cause sizable temperature changes near banks but not the entire channelHigh hydraulic conductivities and gaining groundwater conditions favor dynamic temperature zones near banks [ABSTRACT FROM AUTHOR]

Managed aquifer recharge through bank filtration is an important method to produce sustainable drinking water. Yet, water quality related to transport of pathogens (bacteria and viruses) into groundwater systems from surface waters can be a matter of concern, especially in urbanized regions. Based on a 1‐year monitoring campaign, a reactive transport model was developed for bacteria transport at a riverbank filtration site located in Germany. The model allows simulating advective‐dispersive transport and relies on the colloid filtration theory to mimic attachment and detachment of bacteria to and from the sediment in addition to inactivation, straining and blocking of bacteria. Due to the complexity of the investigated processes, the reactive transport model is characterized by a high level of parametrization, encompassing parameters driving flow as well as solute and colloid transport. A global sensitivity analysis has been applied to identify the most relevant model parameters with respect to piezometric pressure heads, groundwater temperature, and concentrations of chloride, oxygen, coliforms, and Escherichia coli. The model has been calibrated within a stochastic framework, to provide model parameter estimates and to quantify their uncertainty. Our results suggest that bacteria transport models are highly sensitive to inactivation coefficients, straining coefficients, and bacteria size. Permeability of the colmation layer at the riverbank is a key factor for bacteria transport through its influence on residence times. Seasonal variability of boundary conditions, especially anoxic aquifer conditions in the summer and high groundwater flow velocities during flooding periods, resulted in a reduction of inactivation and increased bacteria concentrations at observation wells. Key Points: Inactivation, straining, and permeability of the colmation layer are key for bacteria transport at riverbank filtration sitesBacteria transport is markedly driven by seasonal variations of the river stage, temperature, and oxygen contentUncertainty linked to bacteria transport parameters is quantified via stochastic inverse modeling relying on a 1‐year monitoring campaign [ABSTRACT FROM AUTHOR]

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In the present work, a spatio-temporal study of arsenic (As) concentration in groundwater and its impact in barley uptake is presented. The impact of As on barley is studied through the determination of its bioaccumulation in the soil-plant system, As uptake, as well as a correlation between As concentration in water and its temperature in the groundwater. For the groundwater, spatial and temporal variability of As concentration in central Mexico was determined through a geostatistical analysis using ordinary kriging. The results show that the variability of As in the ground water is correlated with its temperature (R2 > 0.83). The As accumulation in the structures of plant follows the order root > leaf > ear in concentration. The bioaccumulation factor BAFT suggests that As is mobilized to the aerial parts of the barely for both As concentrations used in the irrigation water. However, for As concentration lower than 25 μg L−1, the BAFT is lower than 0.57, suggesting that the amount of As in root is the same as that contained in the aerial parts; whereas, for higher As concentrations (from 170 to 250 μg L−1), the BAFT is around 0.92, indicating that the As is mainly contained in root. The spatial distribution of As concentration trend in groundwaters along the time is the same, which means high As concentration areas remain in the same groundwaters and these areas are presenting the highest water temperature. These results shall contribute to understand the bioaccumulation of As in barley and the As spatial variability in central Mexico. [ABSTRACT FROM AUTHOR]

Groundwater temperature (GWT) is usually measured using screened monitoring wells (MWs). The aim of this study was to investigate whether MWs are suitable for monitoring the effects of large-scale geothermal collector systems (LSCs) on GWT, focusing on possible vertical flows within the MWs due to both natural and forced convection. Comparative temperature depth profiles were therefore recorded over a period of nine months in both shallow MWs and in small-diameter, non-screened temperature monitoring stations (TMSs), each of which was installed in a single borehole. Particularly high temperature deviations were measured in MWs in the upper part of the water column where the GWT reached up to 1.8 K warmer than in the surrounding subsurface. These deviations correlate unambiguously with the prevailing positive thermal gradients and are caused by thermal convection. Where forced convection occurred, the GWT was measured to be up to 0.8 K colder. Potential temperature deviations must be considered when monitoring very shallow GWT as thermal gradients can be particularly high in these zones. For monitoring concepts of LSCs, a combination of MW and TMS is proposed for GWT measurements decoupled by the effects of convection and in order to enable further investigations such as pumping tests.

Bank filtration is considered to improve water quality through microbially mediated degradation of pollutants and is suitable for waterworks to increase their production. In particular, aquifer temperatures and oxygen supply have a great impact on many microbial processes. To investigate the temporal and spatial behavior of selected organic micropollutants during bank filtration in dependence of relevant biogeochemical conditions, we have set up a 2D reactive transport model using MODFLOW and PHT3D under the user interface ORTI3D. The considered 160-m-long transect ranges from the surface water to a groundwater extraction well of the adjacent waterworks. For this purpose, water levels, temperatures, and chemical parameters were regularly measured in the surface water and groundwater observation wells over one and a half years. To simulate the effect of seasonal temperature variations on microbial mediated degradation, we applied an empirical temperature factor, which yields a strong reduction of the degradation rate at groundwater temperatures below 11 °C. Except for acesulfame, the considered organic micropollutants are substantially degraded along their subsurface flow paths with maximum degradation rates in the range of 10−6 mol L−1 s−1. Preferential biodegradation of phenazone, diclofenac, and valsartan was found under oxic conditions, whereas carbamazepine and sulfamethoxazole were degraded under anoxic conditions. This study highlights the influence of seasonal variations in oxygen supply and temperature on the fate of organic micropollutants in surface water infiltrating into an aquifer. [ABSTRACT FROM AUTHOR]

The understanding of hydro systems is of great importance in monitoring quantitative and qualitative changes in water resources. The Essaouira region at the edge of the Moroccan Atlantic Ocean is subject to a semi-arid climate. The decrease in rainfall as a result of climate change and the increase in the exploitation of surface and groundwater have disrupted the stability of these resources and threaten the socio-economic and environmental balance in the area under investigation. Climate scenarios estimate that precipitation will decrease by 10–20% while warming increases by 3 °C over the next 30 years. The physico-chemical parameters studied show that the evolution of the pH and temperature of the groundwater remained stable with a neutral (pH ≈ 7) and a hypothermal character (T < 30 °C). For the electrical conductivity, it showed an increasing trend from 2017 to 2020. A hydrochemical approach showed that the groundwater mineralization was controlled by the dissolution of evaporites and carbonates, by cation exchange processes, and by seawater contamination. A groundwater assessment for drinking use was made by comparing the concentrations of the chemical elements with the standards set by the World Health Organization. The results obtained show that the groundwater from the aquifers studied requires treatment before being consumed, in particular for Cl− and SO42−. Furthermore, the groundwater quality for irrigation was evaluated based on the parameters Na% and Sodium Adsorption Ratio (SAR). The results showed that the groundwater was adequate for agricultural purposes, especially for the plants that adapt to high salinity. The monitoring of surface water by processing the satellite images via the calculation of the normalized difference water index (NDWI) showed an increase in water surface areas in the region following the commissioning of two large dams (Zerrar and Igouzoullene). Despite the installation of these hydraulic structures, a drop of 4.85 km2 in water surface area was observed beyond 2016. This situation requires intervention in order to preserve this vital resource. [ABSTRACT FROM AUTHOR]

Compacted bentonite–sand mixtures are commonly considered as the key materials for the construction of engineered barrier systems (EBSs) in deep geological repositories (DGRs) in Canada and other countries. These bentonite-based barriers can be simultaneously exposed to a wide range of chemical and thermal (nuclear waste heat decay) conditions of underground water. Thus, an understanding of the effects of groundwater chemistry and temperature and their interactions on the changes in the swelling properties as well as the microstructure of bentonite-based barriers is essential for assessing the durability and safety of an EBS in a DGR. This study experimentally investigates the impact of a Canadian deep underground water chemistry (C; total dissolved solids up to 300 g/L), temperature (T; 23 °C, 40 °C, and 80 °C), and the coupled effects of C and T on the swelling properties and microstructure of bentonite–sand barrier mixtures (30 to 70% by weight). The results show that the groundwater chemistry of southwestern Ontario (Canada) has a significant impact on the swelling characteristics of the examined bentonite–sand material. The swelling ability significantly decreases with respect to the groundwater chemistry. The mineralogical composition of the bentonite changes. Most of the Na-montmorillonite is mainly transformed to Ca-montmorillonite and traces of illite with a lower swelling capacity when the bentonite–sand barrier material is exposed mixed to saline water solutions. The temperature (alone) has a limited effect. However, the temperature–groundwater chemistry interactions significantly affect the swelling capacity of the studied bentonite–sand material. Future safety assessments and the final engineering design of engineered barriers for DGRs in Ontario should take into consideration the possibility of the long-term deterioration of bentonite–sand barriers from chemical attacks and/or thermochemical attacks induced by the high salinity of the groundwater and by simultaneous impact of the chemistry of the groundwater and the heat generated by the nuclear wastes, respectively. [ABSTRACT FROM AUTHOR]

High-temperature aquifer thermal energy storage (HT-ATES) is a promising technique to reduce the CO2 footprint of heat supply in the frame of transitioning to renewable energies. However, HT-ATES causes temperature fluctuations in groundwater ecosystems potentially affecting important microbial-mediated ecosystem services. Hence, assessing the impact of increasing temperatures on the structure and functioning of aquifer microbiomes is crucial to evaluate potential environmental risks associated with HT-ATES. In this study, we investigated the effects of temperature variations (12–80°C) on microbial communities and their capacity to mineralize acetate in aerobically incubated sediment sampled from a pristine aquifer. Compared to natural conditions (12°C), increased acetate mineralization rates were observed at 25°C, 37°C and 45°C, whereas mineralization was decelerated at 60°C and absent at 80°C. Sequencing of 16S rRNA genes revealed that the bacterial diversity in acetate-amended and non-acetate-amended sediments decreased with rising temperatures. Distinct communities dominated by bacterial groups affiliated with meso- and thermophilic bacteria established at 45°C and 60°C, respectively, while the number of archaeal phylotypes decreased. The changes in microbial diversity observed at 45°C and 60°C indicate a potential loss of ecosystem functioning, functional redundancy and resilience, while heat storage at 80°C bears the risk of ecological collapse. [ABSTRACT FROM AUTHOR]

The presence of permafrost influences the flow paths of water through Arctic landscapes and thereby has the potential to impact stream discharge and thermal regimes. Observations from 11 headwater streams in Alaska showed that July water temperatures were higher in catchments with more near‐surface permafrost. We apply a fully coupled cryohydrology model to investigate if the impact of permafrost on flow path depth could cause the same pattern in temperatures of groundwater discharging from hillslopes to streams. The model simulates surface energy and water balances, snow, and subsurface water and energy balances for two‐dimensional hillslope model cases with varying permafrost extent. We find that hillslopes with continuous permafrost have more shallow flow paths and twice as high rates of evapotranspiration, compared to hillslopes with no permafrost. For our simulated cases, 6.7% of the horizontal water flux moves through the top organic soil layers when there is continuous permafrost, while only 0.5% moves through organic layers without permafrost. The deeper flow paths in permafrost‐free simulations buffer seasonal temperature extremes, so that summer groundwater discharge temperatures are highest with continuous permafrost. Our results suggest that permafrost thawing alters groundwater flow paths and can lead to decreases in summer stream temperatures and reductions in evapotranspiration in headwater catchments. These changes are of potential importance for stream biotic components of ecosystems, however, the full impact remains unknown. Key Points: Models of hillslope permafrost show that groundwater flow paths deepen as permafrost thickness and extent decreasesLess permafrost, and therefore deeper flow paths, result in reduced evapotranspiration and increased groundwater dischargeModel and observations show that shallow permafrost leads to higher July stream temperatures, suggesting streams will cool as soils warm [ABSTRACT FROM AUTHOR]

Investigation of the effect of horizontal groundwater seepage in a rock mass subjected to artificial freezing on the parameters of a frozen wall formed around a projected shaft is carried out. For this purpose, a mathematical model of coupled heat and mass transfer in a watered rock mass subjected to freezing is formulated, and numerical multiparametric simulation of the formation of frozen wall under the conditions of groundwater seepage with variable rate has been made. A sandstone layer for the conditions of Petrikovo deposit of potash and rock salts is predominantly considered in the work. An analysis of the results has shown that the influence of groundwater flow on the frozen wall thickness begins at seepage rates of about 50 mm/day. In this case, the influence of the groundwater flow on the temperature field of the rock mass begins earlier, at seepage rates 10–25 mm/day. Three mechanisms of the frozen wall dynamics on increase in the rate of groundwater seepage rate are determined: shift, deformation, and loss of continuity. Corrections for the frozen wall thickness in the presence of groundwater flow for a sandstone layer for the interval of seepage rates from 50 to 150 mm/day have also been established. [ABSTRACT FROM AUTHOR]

Ecosystems adapt differently to global warming through microclimatic factors. Mires are sensitive wetland habitats that strongly rely on local soil properties, making them a good model to understand how local climatic parameters counteract the effects of climate change. We quantified the temperature buffering effect in waterlogged mire soils as compared with adjacent dry soils. We buried dataloggers at 5 cm depth in waterlogged and dry points in eight mires of the Cantabrian Mountains (Spain, southwestern Europe) and recorded soil temperatures for ca. 5 years. We also compared our local measures with air temperatures predicted by the CHELSA model. Waterlogged soils had less diurnal thermal amplitude (−2.3°C), less annual thermal amplitude (−5.1°C), cooler summer maxima (−4.3°C) and warmer winter minima (+0.8°C). CHELSA air temperatures only correlated significantly (p <.05) with winter minimum soil temperatures (Pearson's r >.83), and CHELSA predictions were less accurate (higher root‐mean‐square error [RMSE]) for waterlogged soils, except for the summer maxima. We conclude that mire soils show a thermal buffer effect that insulates them from the surrounding landscape. This effect is stronger at the warm end of the climatic spectrum, that is, during summer and at lower elevations. These results highlight the potential refugial character of mires under global warming, and the need to integrate microclimate measurements into climate change models. [ABSTRACT FROM AUTHOR]

The anomalies associated with the 12 May, 2008 Ms8.0 Wenchuan earthquake have been widely reported. Nevertheless, so far, these anomalies have not been synergically analyzed to interpret or prove the potential geosphere physical coupling process. Moreover, the 14 April, 2010 Ms7.1 Yushu earthquake with similar active tectonic background is less studied. In this paper, we present a reanalysis of the groundwater temperature and radon measurements from the same stations for both the Wenchuan and Yushu earthquakes. Finnaly, a statistical analysis on published literatures and our reanalysis, reveals quasi-synchronous multi-parameter anomalies from all Earth spheres of lithosphere, coversphere, atmosphere and ionosphere, within a quasi-synchronous time window of five and seven days before the Wenchuan and Yushu earthquakes respectively. The p-hole theory is expected to explain why anomalies travel so fast between different Earth spheres. [ABSTRACT FROM AUTHOR]

Groundwater (GW) is sensitive to climate change (CC), and the effects have become progressively more evident in recent years. Many studies have examined the effects of CC on GW quantity. Still, there is growing interest in assessing the qualitative impacts of CC, especially on GW temperature (GWT), and the consequences of these impacts. This study aimed to systematically review recently published papers on CC and GWT, determine the impacts of CC on GWT, and highlight the possible consequences. The Scopus and Web of Science databases were consulted, from which 144 papers were obtained. After an initial screening for duplicate papers, a second screening based on the titles and abstracts, and following an analysis of topic applicability to this subject after examining the full text, 44 studies were included in this review. The analysed scientific literature, published in 29 different journals, covered all five continents from 1995 to 2023. This review indicated that the subject of GWT variations due to CC is of global interest and has attracted significant attention, especially over the past two decades, with many studies adopting a multidisciplinary approach. A general increase in GWT was noted as a primary effect of CC (especially in urban areas); furthermore, the implications of this temperature increase for contaminants and GW-dependent ecosystems were analysed, and various applications for this increase (e.g. geothermal) were evaluated. This review highlights that GWT is vulnerable to CC and that the consequences can be serious and worthy of further investigation., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2024 The Authors.)

Subterranean soil erosion is a common form of soil failure that is caused by groundwater seepage. In this paper, we present a subterranean soil erosion model ideally supposed as pipe flow with four conditions. By using the theories of pipe flow, its critical expressions are derived, including the critical flow quantity (Qcr), the critical velocity (Vcr), and the hydraulic gradient (Icr). A simulating experiment is designed to test Qcr to calculate the other critical values. In a case study, 14 clay samples from Guiyang, Guizhou, China, are tested via a simulation experiment. As a result, the critical shear stress of samples is found to be 32.01 Pa. Furthermore, three critical values of suffusion, including Qcr, Vcr and Icr, are calculated with different diameters of soil pores by using the critical expressions. Analyzing the relationship among the values shows that the pore diameter and groundwater temperature influence the critical hydraulic condition of subterranean soil erosion. [ABSTRACT FROM AUTHOR]

Thermodynamic coupling between atmosphere and ground yields increasing aquifer temperatures as a consequence of global warming. While this is expected to manifest as a gradual warming in groundwater temperature time series, such continuous long-term recordings are scarce. As an alternative, the present work examines the use of repeated temperature-depth profiles of 32 wells in southern Germany, that were logged during campaigns in the early 1990s and in 2019. It is revealed that the temperatures have increased in nearly all cases. We find a moderate to good depth-dependent correlation to trends in air temperature, which however is strongly influenced by local hydrogeological and climate conditions. While during the last three decades, air temperatures have increased by a rate of 0.35 K (10a)−1 on average, the temperature increase in the subsurface is decreasing with depth, with median values of 0.28 K (10a)−1 in 20 m and only of 0.09 K (10a)−1 in 60 m depth. Still, the slow and damped warming of the groundwater bodies are remarkable, especially considering naturally very minor temperature changes in pristine groundwater bodies and predictions of atmospheric temperatures. This entails implications for temperature-dependent ecological and hydro-chemical processes, and also for the heat stored in the shallow ground. Moreover, it is demonstrated that the annual heat gain in the groundwater bodies below 15 m due to climate change is in the range of one third of the state’s heat demand, which underlines the geothermal potential associated with the change in natural heat fluxes at the ground surface.

Based on the statistical analysis of the time series of data, the influence of the change of Sava River temperature and geothermal anomalies on the changes of the groundwater temperature of the Zagreb and Samobor-Zaprešić aquifers is described. In the analysis, data were used from daily measurements of the Sava River temperature and from the quarterly measurements of the groundwater temperature. Statistical methods of correlation, cross-correlation and linear regression were applied and the maximum, mean and minimum groundwater temperatures were analysed. Obtained results are presented in the form of statistical parameters, diagrams and maps of isotherms. This data is indispensable for development of shallow geothermal applications related to open loop groundwater heat pump systems. Since efficiency of the heat pump is directly dependent source temperature, presented analyses is necessary for prefeasibility study of geothermal projects and comparison between different designs. Furthermore, currently operating projects in the Zagreb and Samobor-Zaprešić are systematically elaborated, giving first approximation of energy consummation from this renewable energy resource.

In semiarid areas, precipitations usually appear in the form of big and brief floods, which affect the aquifer through water infiltration, causing groundwater temperature changes. These changes may have an impact on the physical, chemical and biological processes of the aquifer and, thus, modeling the groundwater temperature variations associated with stormy precipitation episodes is essential, especially since this kind of precipitation is becoming increasingly frequent in semiarid regions. In this paper, we compare the predictive performance of two popular tools in statistics and machine learning, namely Bayesian networks (BNs) and artificial neural networks (ANNs), in modeling groundwater temperature variation associated with precipitation events. More specifically, we trained a total of 2145 ANNs with different node configurations, from one to five layers. On the other hand, we trained three different BNs using different structure learning algorithms. We conclude that, while both tools are equivalent in terms of accuracy for predicting groundwater temperature drops, the computational cost associated with the estimation of Bayesian networks is significantly lower, and the resulting BN models are more versatile and allow a more detailed analysis.

The Jizhong Depression is located in the western Bohai Bay Basin, eastern China. The deep strata are mainly composed of carbonate buried hill, and the shallow strata are a mainly siliciclastic deposition. In the present work, the Na-K-Mg triangle diagram and geothermometers were used to investigate the geochemical characteristics of shallow groundwater and reservoir temperature features of three geothermal reservoirs in the depression, including the Ordovician, the Cambrian, and the Precambrian Wumishan Formation. The results showed that the geothermal water in the depression could be divided into three groups: group I, Cl· HCO 3 -Na type; group II, Cl-Na type; and group III, Cl-Na·Ca type. By using the Na-K-Mg triangle diagram, group II and group III geothermal water samples were identified as the partially equilibrated water, whose temperature of the geothermal reservoir can be calculated based on the cation geothermometers. The ranges of the calculated temperature of the shallow strata and the deep strata are 91~146°C and 147~176°C, respectively. It has the good results obtained with some cation geothermometers in a geothermal system hosted in carbonate rocks like the studied area. The analysis workflow and calculation data obtained in this work contribute to the evaluation of the temperature field and the exploration and development of the geothermal resources in the Bohai Bay Basin. [ABSTRACT FROM AUTHOR]

Marine tracer studies indicate that large volumes of saline groundwater discharge to the ocean in passive margin settings. These results have not found widespread recognition because the location and cause(s) of this submarine groundwater discharge (SGD) are unclear. Here we report observations from a new long‐term seafloor monitoring network in the South Atlantic Bight that support large‐scale SGD far from shore. In the study area near Charleston, South Carolina, we determined hydrostratigraphy via vibracoring and chirp seismic surveys, collected water samples from seafloor wells, and used heat as a tracer to monitor SGD. We detected significant pulses of saline SGD issuing from the seafloor 10–15 km from shore. These pulses coincided with abrupt sea level declines of up to 30 cm. Based on an analysis of marine conditions at the time, we propose that upwelling‐favorable winds depressed sea level in the region, causing saline groundwater to discharge from confined coastal aquifers that connect land and ocean. The combination of stacked confined aquifers and variations in sea level are nearly ubiquitous in passive coastal margins. This previously overlooked combination can explain a wide range of other published observations and promotes more dynamic flows than simple tidal fluctuations. This new mechanism may explain Ra tracer signals in the coastal Atlantic Ocean and supports significant nutrient inputs to the ocean. These large natural geochemical fluxes may be sensitive to groundwater usage on land. Plain Language Summary: Previous studies based on the chemistry of coastal ocean water show that saline groundwater must discharge to the ocean. In the Atlantic Ocean, the rate of groundwater discharge roughly equals river discharge, and the groundwater delivers more nutrients to the ocean than rivers. Studies of marine ecosystems largely ignore these inputs because it is not clear where or why these flows occur. We installed wells in the seafloor 10–20 km offshore to monitor the composition of groundwater and the temperature of the sediments below the seafloor. We used heat as a tracer to calculate groundwater flow rates. We found that groundwater discharged to the ocean in response to anomalous changes in sea level, likely associated with wind events. This can only happen if permeable sediment layers (aquifers) form a hydraulic connection between the land and the seafloor. Aquifers like this are extremely common in coastal regions, and wind‐related variations in sea level are equally common. The combination of stacked coastal aquifers and variations in sea level can explain many different observations. These large groundwater pulses probably occur widely, far beyond the southeastern United States. Groundwater pumping could affect this discharge, which could in turn alter coastal ecosystems. Key Points: We detected significant pulses of submarine groundwater discharge 10–15 km offshore, caused by wind‐driven variations in sea levelThe groundwater must issue from confined aquifers, common in coastal areas, that promote groundwater‐seawater exchange far offshoreThis mechanism explains prior observations and likely drives major fluxes of groundwater and nutrients in passive continental margins [ABSTRACT FROM AUTHOR]

Coastal aquifers provide an important hydrologic connection between terrestrial freshwater and oceanic seawater. Understanding the water flow and salinity distributions in those aquifers is essential to manage seawater intrusion and regional groundwater resources. For the last 50 yr, these processes have been extensively examined; however, previous studies typically assumed isothermal conditions and overlooked groundwater‐seawater temperature contrasts, as commonly found along the global coastline. Here, we validated a solute and heat transport model against laboratory experiments and then revisited the classical Henry problem for coastal confined aquifers. We found that as the seawater temperature increases or freshwater temperature decreases, the freshwater‐seawater interface retreats seaward and thus the freshwater storage increases. This occurs as a result of temperature‐induced changes to the fluid density and aquifer hydraulic conductivity. Furthermore, double diffusion of salt and heat can induce two circulation cells in opposing directions in the saltwater wedge once the seawater temperature exceeds that of groundwater by a certain extent. Consequently, the circulating seawater flux and associated travel time change dramatically compared with isotheral conditions. Overall, the effect of thermal forcing can be significant, as demonstrated by a sensitivity analysis considering a large range of groundwater‐seawater temperature contrasts. These results highlight the impact of changing thermal regimes on the flow and salinity distributions in coastal confined aquifers and provide guidance for better assessment of water resources in coastal zones. Plain Language Summary: Coastal zones are often densely populated with associated significant economic activity. Groundwater in coastal aquifers provides an essential freshwater resource for domestic and industrial use as well as food production. Intensive human activities and climate change cause water regime shifts and thus threaten water security in coastal areas. Coastal water resource assessments often overlook groundwater‐seawater temperature contrasts, even though such contrasts are globally ubiquitous. Here, we show those assessments could be improved with thermal effects considered as temperature contrasts can markedly influence salinity distributions and water circulations in coastal aquifers. The results provide guidance for better assessment of water resources in coastal zones. Water temperature affects ocean‐land exchange and various biogeochemical processes, which should be considered in future studies including climate change evaluations. Key Points: Freshwater‐seawater interface is affected by both groundwater and seawater temperaturesDouble diffusion of salt and heat can induce two circulation cells in opposing directionsCirculating seawater flux is affected by both groundwater and seawater temperatures [ABSTRACT FROM AUTHOR]

Continuous rock core was collected for 1764 m (5786′) on the Pohakuloa Army Training base near the center of the big island of Hawaii. The core traverses basaltic lava flows from the volcano's shield-building phase, and perched aquifers and higher temperature groundwaters were encountered. The collected samples record water-rock interactions of basaltic materials in a setting that may be a model for groundwater interactions on Mars. We collected visible and infrared point spectra of materials in the lowest portion of the core, where alteration was noted to become more prominent. We identified three types of phyllosilicate spectral signatures and three types of zeolites. The phyllosilicates show similarity to those identified on Mars using data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM). Based on the field survey, 25 depths were selected for sampling and petrographic analysis of thin sections. The spectral data and thin section work have a strong agreement in the types of materials identified by the two different techniques. Both the spectral and petrographic data indicate low to moderate temperature geothermal alteration occurred in the lower half of the core. The field spectra are a useful reconnaissance tool for selecting mineralogic diversity for subsequent higher resolution and more time-consuming laboratory analysis. [ABSTRACT FROM AUTHOR]

We hypothesized that Cholera (Vibrio cholerae) that appeared along Lake Kivu in the African Rift in the seventies, might be controlled by volcano-tectonic activity, which, by increasing surface water and groundwater salinity and temperature, may partly rule the water characteristics of Lake Kivu and promote V. cholerae proliferation. Volcanic activity (assessed weekly by the SO2 flux of Nyiragongo volcano plume over the 2007–2012 period) is highly positively correlated with the water conductivity, salinity and temperature of the Kivu lake. Over the 2007–2012 period, these three parameters were highly positively correlated with the temporal dynamics of cholera cases in the Katana health zone that border the lake. Meteorological variables (air temperature and rainfall), and the other water characteristics (namely pH and dissolved oxygen concentration in lake water) were unrelated to cholera dynamics over the same period. Over the 2016–2018 period, we sampled weekly lake water salinity and conductivity, and twice a month vibrio occurrence in lake water and fish. The abundance of V. cholerae in the lake was positively correlated with lake salinity, temperature, and the number of cholera cases in the population of the Katana health zone. V. cholerae abundance in fishes was positively correlated with V. cholerae abundance in lake water, suggesting that their consumption directly contaminate humans. The activity of the volcano, by controlling the physico-chemical characteristics of Lake Kivu, is therefore a major determinant of the presence of the bacillus in the lake. SO2 fluxes in the volcano plume can be used as a tool to predict epidemic risks. Author summary: The area of the African Great Lakes has been an endemic area for cholera since the late 1970s. We focused on the Katana health zone, bordering Lake Kivu, as during outbreaks, this is, (together with the Kalemie health zone located along the west coast of the Tanganyika lake) the health zone in which the first cases of Cholera are usually observed, and the highest number of cases are also usually reached in this area. The persistence of this aquatic bacillus, usually associated with warm and salty waters, led us to formulate the hypothesis that the geothermal springs supplying Lake Kivu, mainly from the Nyiragongo volcano, should control the physico-chemical characteristics of the lake and promote the persistence of the bacillus. The lake would thus be a reservoir of the pathogen, which could contaminate local residents through the consumption of water and fish. Over the 2007–2012 period, we demonstrated a long-term unidirectional relationship between volcanic activity and cholera cases in the Katana health Zone. Contamination of the lake's water and fish was also correlated to the lake characteristics. The activity of the volcano can thus be used for predicting epidemic risks. [ABSTRACT FROM AUTHOR]

Copyright of Hydrogeology Journal is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Featured Application: This study can reveal the hydraulic characteristics of deep groundwater in sedimentary and volcanic rocks. The geothermal characteristics of specific areas on Earth can be identified using geophysical and lithological logs based on deep boreholes, such as those more than 1000 m in depth. Based on the combined analyses of geophysical logs (temperature, caliper, electrical conductivity (EC), and natural gamma-ray logs) and lithological logs, as well as 1D steady-state heat transfer model, the deep groundwater flow and temperature were characterized in four deep boreholes (BH-1–BH-4) roughly 2000 m deep in the area of Heunghae-eup, Pohang, South Korea. The estimated thermal gradients from the temperature profiles are as follows: 22.37–30.77 °C/km for BH-1, 35.67–64.52 °C/km for BH-2, 40.85–46.44 °C/km for BH-3, and 33.33–35.71 °C/km for BH-4. According to the geophysical logs and lithology profiles, the groundwater mainly flows into and out of the boreholes through the basic dyke, rhyolite, and sandstone/mudstone. Evidently, the groundwater flows moving through the fractures and faults induce nonlinear temperature changes. The upward and downward groundwater flows passing through fractures and faults can be estimated using a 1D steady-state heat-transfer equation, by considering a fracture angle based on the lithological and geophysical profiles. To determine the direction (up/down) and rate of groundwater flow, the values for the parameter β were estimated as follows: −1.95 to 5.40 for BH-1, −13.48 to 4.87 for BH-2, −1.76 for BH-3, and −3.39 to 14.15 for BH-4. [ABSTRACT FROM AUTHOR]

Nowadays, heat transport in an aquifer is a widely discussed topic. Groundwater temperature rise is the result of a variety of factors and a common phenomenon, especially in larger cities. Heating and cooling in buildings, infrastructure, even paved surfaces can accumulate solar energy and further emit heat into the subsurface, leading to an increase in temperature. The research of the issue of increased groundwater temperature is related to the potential use of heat as an energy source. Numerical modelling, which is based on the solution of partial differential equations, can be used to evaluate the given phenomenon. The Aupark shopping centre in Bratislava was selected for the model area, where the temperature in hydrogeological boreholes is monitored, and at the same time, multilevel monitoring of the rock environment temperature takes place. The evaluation of monitoring data was realised through the Groundwater Vistas 7 programme, where a hydraulic and transport model was compiled using MODFLOW and MT3DMS. The MT3DMS code is intended for the transport of dissolved substances; however, with the appropriate substitution of input parameters, it is also applicable for the transport of heat. The sensitivity of the input data and calibration of the model was evaluated through the PEST programme, where the goal was to achieve the highest possible correlation between the measured and modelled results. By analyzing the data from monitoring, it was possible to quantify the areal and depth impact of the Aupark shopping centre. Last but not least, the energy input from Aupark to the rock environment was determined, and ranges from 0.1 W·m-2 at a distance of 100 m to 12 W·m-2 immediately next to the building. [ABSTRACT FROM AUTHOR]

Evaluating temporal variability of CO2 efflux from the tree trunks of Scots pine (Pinus sylvestris L.) are presented. The field measurements were performed by the chamber method in a swampy cotton grassy–sphagnum pine forest in Yaroslavl region and in a highly productive grassy–bilberry pine forest on well drained sandy soils in the Serebryaniy Bor forest service area in Moscow region. Tree trunk respiration was measured during several growing seasons under different weather conditions and groundwater level depths. The results showed that the CO2 emission of living tree trunks in the southern European taiga forests exhibited clear seasonal and diurnal variation and it was a highly sensitive to changing ambient conditions (air temperature and groundwater level). The differences in the trunk respiration rate of trees of various growth classes for a swampy pine forest were also revealed. [ABSTRACT FROM AUTHOR]

Understanding how changes in stream temperature affect survival and growth of coldwater fishes, including brown trout (Salmo trutta) and rainbow trout (Oncorhynchus mykiss), is important for conserving coldwater stream fisheries in a changing climate. However, some contemporary stream temperature models assume spatially uniform (i.e. unrealistic) air–stream temperature relationships or demand hydrometeorological predictors (e.g. solar radiation and convection) that are expensive and often impractical for fisheries managers to measure. As such, we produced a relatively cost‐effective, management‐relevant modelling approach for predicting effects of changes in air temperature, precipitation and groundwater inputs on stream temperature and, consequently, the survival and growth of brown trout and rainbow trout in Michigan, USA. We found that precipitation‐ and groundwater‐corrected stream temperature models (mean adjusted R2 =.77, range = 0.65–0.88) performed better than linear air–stream temperature models (mean adjusted R2 =.59, range = 0.21–0.80). Stream temperature was projected to increase by 0.07–3.88°C (1%–22%) with simulated changes in air temperature, precipitation and groundwater inputs. The greatest warming was predicted for surface runoff‐dominated sites with limited groundwater‐driven thermal buffering, where thermal habitat suitability for salmonid survival and growth declined 20%–40%. However, groundwater‐dominated sites may not be immune to temperature warming, especially if groundwater temperature increases or groundwater inputs decline in a changing climate. Our modelling approach provides a reliable, cost‐effective method for predicting effects of climate change on brown trout and rainbow trout survival and growth, allowing for strategic management actions to increase the thermal resilience and sustainability of salmonid populations (e.g. groundwater conservation and riparian/watershed rehabilitation). [ABSTRACT FROM AUTHOR]

A new significant aspect in the utilization of hydrothermal energy in China is the large-scale exploitation using multiwells from a single geothermal site. This requires detailed hydrogeochemical investigations to gain insight about deep groundwater circulation. At the Xiongxian karst geothermal site in North China, where the demonstration project of large-scale utilization was conducted, 40 boreholes with depths from 1000 to 1800 m were drilled in a region of 50 km2. A total of 25 water samples were collected, and temperature loggings were conducted in 16 of these wells. At the site scale, the hydraulic head was observed to decline from SW to NE, i.e., orthogonal to that at the regional scale. Moreover, the geothermal groundwater temperature, borehole temperature gradient, and heat flow in the caprock all exhibited the same spatial trend with the groundwater head. Based on the hydrogeochemical and temperature logging data, this was explained by mixing of lateral recharging groundwater with ascending thermal fluids through the Xiongxian Fault, after excluding the causes of pumping activities and geologic structure. In addition, geothermal groundwater 81Kr age was estimated to be approximately 760 k yr, which is much older than the 14C age of 20 to 30 k yr. The older 81Kr age implies a low renewability of deep groundwater circulation, which should be considered in terms of sustainable management in relation to the large-scale utilization of geothermal resources. [ABSTRACT FROM AUTHOR]

The initial premises of using a heat pump are that in winter (a cold period of a year) it is used to heat a farmhouse and in summer (a warm period), when heating the house is not required, it is used as part of a grain dryer. Analysis of the operation of a batch fluidized-bed grain dryer for maize seed grains (loading 75 kg), equipped with a heat pump for heating the drying agent, is performed. It is assumed that the source of low-potential heat in the heat pump is groundwater with a temperature of 6°C at the inlet of the heat exchanger and 8°C at the outlet, and the drying agent (air) is heated in the condenser of the heat pump up to 60°C. Freon R600a was chosen as the working body in the heat pump. It is shown that, under these conditions, the heat pump operated at the refrigeranttemperature in the evaporator of 3°C and its temperature in the condenser of 70°C makes it possible to reduce the consumption of heat for heating the drying agent by ~66% (the energy conversion coefficient is 2,98), and the use of partial recycling of the spent drying agent saves another 25% of energy. The analysis provides evidence for good perspectives of using a heat pump dryer in farms. A technique is developed for kinetic calculation of a batch fluidized-bed dryer for a granular material, taking into account the non-steady-state nature of the drying process. The technique is based on an analytical solution of the problem of mass conductivity for individual grains, makes use of the zonal method of calculation, and takes into account changes in the parameters of the drying agent during the process, both over the height of the fluidized bed and in time. The adequacy of the mathematical model for calculating the drying kinetics to the real process is demonstrated. [ABSTRACT FROM AUTHOR]

Copyright of Hydrogeology Journal is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Reliably quantifying groundwater fluxes to and from confined aquifers in sedimentary basins is increasingly recognized as a critical challenge that impedes sustainable groundwater management. One approach to quantify such fluxes is through the analysis of deep (e.g., >50 m) borehole thermal profiles penetrating through aquifer‐acquitard systems. Recently developed methods to interpret such data exploit the relationship between vertical groundwater flow and the downward propagation of surface temperature disturbances resulting from climate warming. In this note, we advance beyond prior studies that assumed steady‐state groundwater flow by demonstrating how hydrogeological regime shifts on decadal time scales can be quantitatively inferred from temperature‐depth profiles (TDPs). We use a set of repeated temperature‐depth profiles from one site in an unconsolidated sedimentary aquifer system, recorded in 1980 and 2016/2018 to tentatively infer a minimum of a threefold increase in groundwater downwelling to deeper aquifers (i.e., from 100 to 350 mm/year). The enhanced flux likely results from intensified, deep groundwater abstraction in the vicinity since the mid‐1980s. We reach this conclusion through analyzing the occurrence and downward propagation of the minimum temperature in the profiles as well as the temporal trend in deeper groundwater temperatures. We conclude that repeated temperature‐depth profiles can be suitable to archive hydrogeological changes. Our results provide the impetus for more systematic collection of present‐day TDPs to provide a historical benchmark from which to assess future groundwater flow alterations, especially in areas that lack traditional aquifer monitoring via hydraulic head measurements. Key Points: Changes to long‐term groundwater recharge or discharge fluxes are challenging to recordRepeated deep temperature profiles archive groundwater flow information over timeChanges in temperature profiles at depth can reveal hydrogeological regime shifts [ABSTRACT FROM AUTHOR]

Over a hundred sizable lakes, some even larger than ~1 km2, are distributed across the lowlands between megadunes in the southeastern Badain Jaran Desert (BJD), northwest China. With rather limited precipitation and hardly any surface runoff, these lakes are fed mainly by groundwater. However, the source of the groundwater and the groundwater discharge rates to these lakes are poorly understood. Water level and temperature of four representative lakes in the southeastern BJD were monitored continuously between 2013 and 2017. Water surface evaporation and rainfall in this area were also measured. Combining these acquired data, groundwater discharge rates were estimated using water balance models. The results show that the four lakes have similar recharge and discharge patterns, but at different average net groundwater discharge rates ranging from 1.79 to 3.09 mm d−1. The lake level variation mainly depends on groundwater discharge and lake surface evaporation. We found that diurnal lake level variation may be controlled by earth tide and atmospheric pressure change, and is five times greater than the evaporation. The desert precipitation and deep confined groundwater with high temperature were found also recharging the desert lakes. An Empirical Mode Decomposition (EMD) method was used to identify the lake level trend. All lake levels increased over the last four years, except one decreased in 2015 and 2016. The lake levels' increasing trend is synchronously similar with the precipitation in north China. This study analyzes annual and seasonal lake level variations, and also finds the diurnal water cycle between the groundwater and lake water for the first time. [ABSTRACT FROM AUTHOR]

Groundwater temperature is a useful hydrogeological parameter that is easy to measure and can provide much insight into groundwater flow systems, but can be difficult to interpret. For measuring temperature directly in the ground, dedicated specifically designed monitoring wells are recommended since conventional groundwater wells are not optimal for temperature monitoring. Multilevel monitoring of groundwater temperature is required to identify contributions of different possible heat inputs (sources) on measured temperature signals. Interpreting temperature data as a cosine function, including period, average temperature, amplitude, and phase offset, is helpful. Amplitude dampening and increasing phase shift with distance from a boundary can be used for estimation of transport parameters. Temperature measurements at different depths can be used for evaluation of unknown parameters of analytical functions by optimization of regression fits in Python. These estimated parameters can be used to calculate temperatures at known water table depths which can be applied as a fixed transient boundary condition in MT3DMS to overcome the limitations of MT3DMS heat transport modeling in the unsaturated zone. In this study, temperature monitoring and modeling was used to evaluate the influence of a department store's heated basement foundation on groundwater temperature within a green space (city park), with the main outcome that 17 years after construction, the department store foundation has increased the mean groundwater temperature by 3.2 °C. Heat input evaluated by the MT3DMS model varied from 0.1 W/m2 at a distance of 100 m up to 12 W/m2 next to the building. Article impact statement: Multilevel temperature monitoring is needed for realistic heat transport modeling in aquifers. [ABSTRACT FROM AUTHOR]

This study is aimed to analyse the impacts of Land Use/Land Cover (LULC) to Land Surface Temperature (LST) and water level fluctuation in Raipur city, for which pre- & post-monsoon data for four years 2000, 2008, 2014 and 2018 have been analysed. By this study, it has been observed that changing LULC has its direct impact on surface temperature as it is increasing with rapid urbanization. Also due to the modern agricultural practices and increasing urbanization as the major factor responsible for changing LULC, and the declining water level. [ABSTRACT FROM AUTHOR]

Outbreaks of viral gastroenteritis are often connected to contaminated drinking water. The assessment of the water quality relies on the cultivation of indicator bacteria, and little is known of the fate of viruses in groundwater, especially in arctic regions. In Iceland, the groundwater temperature is between 3 and 6°C. The aim of this study was to determine virus inactivation at low temperature in a groundwater microcosm and in a borehole in a postglacial lava field. Two phage species that are commonly used as surrogates for norovirus were used, MS2 and PhiX174. Dialysis bags were used for the samples, and a device was constructed to hold many samples at a time and protect the samples in the borehole. No significant decrease of infective PhiX174 phages in the borehole or of the MS2 phages in the microcosm was observed. A slightly significant decrease of PhiX174 in the microcosm was noticed, with one log reduction time of 476 days. On the other hand, a significant reduction in MS2 was found in the field test, where the time needed for 90% reduction was 12·5 days. The results showed that an infective virus can exist in groundwater for months or years in arctic regions and a great difference may exist between results from microcosm and field tests. Significance and Impact of the Study: This study reveals that arctic regions are highly sensitive to virus contamination as an infective virus may exist in groundwater for years at low temperature. The results also show that the virus inactivation observed in field tests may differ considerably from the inactivation observed in laboratory microcosms. The results emphasize the importance of large protection zones around drinking water intakes as well as good wastewater treatment so that the likelihood of faecal contamination of groundwater is reduced. [ABSTRACT FROM AUTHOR]

The study proposes a methodology for the construction of a thematic map of the suitability of the Quaternary shallow alluvial sediments for heat pumps. This map was compiled on the basis of the minimum groundwater temperature, specific capacity of a well, the aquifer thickness, the groundwater temperature range (amplitude), and ranking of the months according to the lowest groundwater temperature. A second methodology allows the creation of a thematic map of the groundwater energy potential. This map is based on two criteria: 1. the specific capacity (l s−1 m−1) of the borehole and 2. the temperature change due to the consumption of heat energy. The calculated energy in kW was classified into one of seven usability categories. The highest rated categories in both maps coincided with areas with the largest sediment volumes (the widest alluvia and the highest sediment thickness) coinciding with the highest river flows. Suitability decreases considerably at higher elevations (mountainous) river catchments with a small volume of sediment as characterized by narrow valleys and low sediment thicknesses. There is a logical link between these factors in relation to the potential for heat pumps exploitation. [ABSTRACT FROM AUTHOR]

To investigate the influences of land surface temperatures (LSTs) on suprapermafrost groundwater discharge, a river valley was selected in a typical permafrost region of Fenghuoshan (FHS) watershed on the central Qinghai‐Tibet Plateau. We developed a two‐dimensional model to simulate the suprapermafrost groundwater seasonal dynamics controlled by LSTs and the changing trends under a warming climate scenario (3°C/100 year). We calibrated key parameters of our model by the field observations at FHS watershed and analysed the relationship between the different LSTs and the suprapermafrost groundwater discharge dynamics in the active layer. The results show that (a) by changing the permeability of the active layer, the LSTs have a significant effect on the suprapermafrost groundwater discharge. A higher LST causes more suprapermafrost groundwater discharge, resulting in a different discharge pattern and affecting the ability to replenish the nearby river in the permafrost area. (b) Under a warming climate, the most obvious change in the suprapermafrost groundwater occurs in the freeze initiation period (from October to December), and there is a significant increase in the suprapermafrost groundwater discharge rate. This study reveals that the LST has a controlling effect on the seasonal dynamics of shallow groundwater systems in permafrost regions, indicating that the impact of local topography on the suprapermafrost groundwater should not be ignored in suprapermafrost groundwater simulations. Moreover, the warming simulation results demonstrate that the freezing season is the significant transformation period of suprapermafrost groundwater dynamics under future climate change, which can be used to better understand hydrological and ecological process changes in permafrost regions under climate warming. [ABSTRACT FROM AUTHOR]

The adsorption–desorption processes of pymetrozine were investigated in three cultivated soils in China through a batch method. Pymetrozine was determined by high-performance liquid chromatography (HPLC). At a relatively low temperature, the adsorption of pymetrozine improved with increasing organic matter content, and the Freundlich model precisely illustrates the adsorption isotherms. The adsorption of pymetrozine was classified as physical, considering that the Gibbs free energy change values of this process in the three soils ranged from –21.195 kJ/mol to –23.956 kJ/mol. The ΔH value was –37.236 kJ/mol for soil A, –13.723 kJ/mol for soil B, and –9.154 kJ/mol for soil C, suggesting that the major interaction in the adsorption involved hydrogen bonds and that the adsorption of pymtrozine in the three soils was exothermic. Soil C was shown to have the highest hysteresis among the samples. The hysteresis was enhanced at high temperatures for soil B and soil C but reduced for soil A. Pymetrozine adsorption increased with decreasing temperature, suggesting that pymetrozine may infiltrate groundwater at high temperatures. [ABSTRACT FROM AUTHOR]

Thermal performance of the ground source heat pump (GSHP) system can be significantly affected by the complex geological substructures (such as ground stratification and groundwater advection). This study installed a seepage box inside the two-layered laboratory device to investigate the heat transfer processes of the unsaturated, saturated and infiltrated ground. Various operational and geological conditions were designed to study the temperature distributions at various locations and time experimentally and numerically. The groundwater effect on ground heat exchanger (GHE) thermal performance depends on the thermal properties, flow advection and the relationship between temperatures of the groundwater and ground. If the ground was partially saturated during the heat injection period, the cooling seepage will efficiently remove the heat of GHEs in upper-stream rather than those located in the bottom-stream. Meanwhile, the heat transfer can be enhanced if two legs of the U-tube vertical to the direction of groundwater seepage. The groundwater flow can redistribute the heat within the ground and showed a better recovery performance which advance an even temperature distribution by 3 h. The temperature and carried heat load of the cooler groundwater will increase during the heat injection experiment, and further contributed to various temperature distributions of ground at different locations and time. • A laboratory box with two-layered subsurface and groundwater was introduced. • Experiments with various operational and geological conditions were conducted. • Detailed thermal distributions of partially saturated ground were analysed. • Cooling seepage can only efficiently remove the heat accumulated in upper stream. • Heat redistribution brought by groundwater flow gave a better recovery performance. [ABSTRACT FROM AUTHOR]

Upward discharge to surface water bodies can be quantified using analytical models based on temperature–depth (T‐z) profiles. The use of sediment T‐z profiles is attractive as discharge estimates can be obtained using point‐in‐time data that are collected inexpensively and rapidly. Previous studies have identified that T‐z methods can only be applied at times of the year when there is significant difference between the streambed–water interface and deeper sediment temperatures (e.g., winter and summer). However, surface water temperatures also vary diurnally, and the influence of these variations on discharge estimates from T‐z methods is poorly understood. For this study, synthetic T‐z profiles were generated numerically using measured streambed interface temperature data to assess the influence of diurnal temperature variations on discharge estimation and provide insight into the suitable application of T‐z methods. Results show that the time of day of data collection can have a substantial influence on vertical flux estimates using T‐z methods. For low groundwater discharge fluxes (e.g., 0.1 m d−1), daily transience in streambed temperatures led to relatively large errors in estimated flow magnitude and direction. For higher discharge fluxes (1.5 m d−1), the influence of transient streambed temperatures on discharge estimates was strongly reduced. Discharge estimates from point‐in‐time T‐z profiles were most accurate when the uppermost point in the T‐z profile was near the bed interface daily mean (two time periods daily). Where temperature time series data are available, daily averaged T‐z profiles can produce accurate discharge estimates across a wide range of discharge rates. Seasonality in shallow groundwater temperature generally had a negligible influence on vertical flow estimates. These findings can be used to plan field campaigns and provide guidance on the optimal application of T‐z methods to quantify vertical groundwater discharge to surface water bodies. [ABSTRACT FROM AUTHOR]

Groundwater heat pump (GWHP) system directly uses a stable temperature of groundwater for cooling and heating of buildings or districts. In this study, a simulation-optimization model for the sustainable operation of GWHP system was developed. The simulation model computed the coupled groundwater flow and heat transport with considering thermal recycling. As an optimization technique, genetic algorithm was linked with the simulation model. The developed model can determine the optimal extraction and injection rates of GWHP system to maximize system performance and efficiency, to maintain stable operation, and to minimize costs and environmental impacts. Assuming a 2D hypothetical aquifer, it was demonstrated how the optimal operation of GWHP system obtained from the model can be changed according to several operational and hydrogeological conditions, including well distance, regulation on injection water temperature, hydraulic conductivity, and regional hydraulic gradient. The results highlighted a necessity to determine an operational strategy of GWHP system through the optimization able to consider site-specific condition. In addition, the performance and capability of the developed model were demonstrated by obtaining the optimal strategy for the cooling operation of a research-oriented GWHP facility installed in Korea. • A simulation-optimization model for optimal operation of GWHP system is developed. • It can consider operational efficiency, stability, cost, and environmental impacts. • Results show that the optimum can be different depending on site-specific condition. • It implies the usefulness of this model that can consider site-specific condition. • The applicability of this model is shown on a real-scale GWHP facility in Korea. [ABSTRACT FROM AUTHOR]

Various physical, geophysical, geochemical, electrical and hydrological parameters are measured on the surface and in shallow/deep boreholes throughout mainland China to obtain early warning signals of impending earthquakes. Numerous wells are equipped with water level and temperature sensors for continuous observations of the water level and groundwater temperature. An analysis of water temperature data from boreholes equipped with water temperature sensors reveals that nearly half of the boreholes show coseismic response associated with the Wenchuan earthquake (Mw 7.9, 12 May, 2008). The coseismic response of the groundwater temperature cannot be differentiated from the groundwater flow or movement when the earthquake occurred, but there is no fixed relationship between the temperature variation and the water flow. At the same time, we observed that the rock temperature in dry wells can record the seismic events and even the pre-seismic abnormal information. The spatial distribution of the coseismic groundwater temperature response is random and irregular, which does not support the dislocation model of seismic faults at the regional or larger scale. Changes in the groundwater temperature are closely related to the borehole temperature gradient, lithology profile and geological environment of the borehole and depths of the aquifers. The mechanism of the coseismic groundwater temperature response can be explained by an enhanced permeability induced by an earthquake. The groundwater temperature increases if the temperature sensor in the borehole is located near the deep-circulating aquifer and decreases if the sensor is near the shallow-circulating aquifer when seismic waves arrive. The groundwater temperature may be slightly affected or even unchanged if the temperature sensor is far from the aquifer during the propagation of seismic waves. However, it was hard to conclude the changes of rock temperature observed in six dry wells. [ABSTRACT FROM AUTHOR]