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Intertidal groundwater springs provide thermally stable, nutrient‐rich freshwater that causes fine‐scale variability in water temperature and salinity and promotes biodiversity in coastal estuaries and lagoons. In this study, we combined three thermal sensing techniques to elucidate summer water temperature patterns at the mouths of intertidal groundwater springs and the ambient coastal lagoon in Prince Edward Island, Canada. Thermal infrared imagery captured the spatiotemporal variability in relative temperatures of the lagoon channel and cold‐water plumes from the springs. Thermal anomalies due to the springs were detected at the surface throughout a tidal cycle, suggesting that the thermal plumes were buoyant. Fiber‐optic distributed temperature sensing paired with temperature loggers near the spring outlets recorded groundwater temperatures at low tide (~ 7°C) but ambient lagoon temperatures (up to 26°C) at high tide due to the vertical thermal gradient in the stratified water column. Calculated estuarine Richardson numbers throughout the study confirm intertidal spring buoyancy due to salinity differences. The fiber‐optic distributed temperature sensing results revealed pronounced variations in temperature as evidenced by spatial (3.7°C) and temporal (5.5°C) standard deviations over the cable length during the study and lower mean lagoon bed water temperatures at high tide (22.5°C) than low tide (24.3°C) due to heat advection from tidal pumping. Lagoon temperatures fluctuate at diurnal (solar) and semi‐diurnal (tidal) frequencies. The findings emphasize the efficacy of a multi‐technology approach to reveal fine‐scale and dynamic thermal processes that drive temperature patterns and habitat distribution in coastal lagoon ecosystems and highlight the thermal influence of intertidal springs. [ABSTRACT FROM AUTHOR]

Objective: In a changing climate, the effects of air temperature, precipitation, and groundwater on water temperature and thermal habitat suitability for Gulf Sturgeon Acipenser desotoi, listed as threatened under the U.S. Endangered Species Act, are not well understood. Hence, we incorporated these factors into thermal habitat models to forecast how Gulf Sturgeon may be affected by wide‐ranging climate change scenarios in 2024–2074. Methods: Using data from the Choctawhatchee River, Florida, we developed precipitation‐ and groundwater‐corrected air–water temperature models, compared their accuracy with that of conventional air–water temperature models used in fisheries management, and projected future Gulf Sturgeon thermal habitat suitability for normal physiological functioning and fieldwork (i.e., population sampling and telemetry surgeries) in summer (May–August) under 16 climate change scenarios. Result: Precipitation‐ and groundwater‐corrected models were more accurate than conventional air–water temperature models (mean improvement in adjusted R2 = +0.45; range = +0.09 to +0.75). Water temperature was projected to warm at widely variable rates across climate change scenarios encompassing different air temperature, precipitation, and groundwater regimes. Importantly, Gulf Sturgeon summer aggregation areas were cooler and influenced more by precipitation and groundwater and less by air temperature than were non‐aggregation areas. If precipitation and groundwater—as drivers of cooling—become warm in a changing climate, summer aggregation areas were projected to exhibit thermal habitat degradation equivalent to or greater than that of non‐aggregation areas. Conclusion: Our results add hydrological context to the premise that aggregation areas provide cool water and energetic savings for Gulf Sturgeon during summer, underscoring the importance of protecting these habitats through groundwater conservation, water quality monitoring, and riparian/watershed habitat management. Our findings indicate that identifying thermally appropriate times for fieldwork activities will be increasingly important and time‐restricted as climate change intensifies. However, our research provides managers with a portfolio of water temperature models and an accurate, cost‐effective, management‐relevant approach to forecasting thermal habitat conditions for Gulf Sturgeon and other species in a changing climate. Impact StatementWater temperature models with precipitation and groundwater are accurate and useful, allowing managers to locate key thermal habitats, forecast temperatures, and decide when and where to safely target, capture, tag, and monitor Gulf Sturgeon and other species amid climate change. [ABSTRACT FROM AUTHOR]

The circulation depth of geothermal water providing the geothermal system framework significantly dominates the evaluation of renewal capacity and geothermal resources. The traditional evaluation of circulation depth is based on the groundwater temperature variation in the recharge section and the average geothermal heating rate of geothermal system. However, misunderstanding groundwater temperature distribution in geothermal systems will lead to overestimating groundwater circulation depth based on the recharge section. Temperature measurement in a 1000 m geothermal scientific borehole from the Xinzhou geothermal field of south China is discussed as a case study to reassess the circulation depth of geothermal water. For Xinzhou geothermal system, the recharge and discharge temperatures are from 26.2 °C to 32.6 °C and from 67.0 °C to 98.0 °C, respectively. And the heat exchange temperature at the deepest point is from 121 ℃ to 154 ℃. This indicates that the temperature gradient in the recharge section should be greater than that in the discharge section. But the actual observation is opposite that the temperature gradient in the recharge section and in the discharge section is 3.04 ℃/100 m and 4.97 ℃/100 m, respectively. We proposed that the depth of geothermal water circulation evaluated by the temperature change and the geothermal heating rate in the discharge section represents the top depth of convection in the heat exchange zone, and the depth evaluated by the recharge section represents the advection depth of groundwater in the recharge section. The top depth of convection in the heat exchange zone estimated by the discharge Sect. (0.75–1.49 km) is much shallower than the advection depth of groundwater in the recharge Sect. (3.25–4.34 km). In the convective heat exchange zone (between 4.34 km and 1.49 km), the fault zone at a certain depth is the ideal location for geothermal development to extract water and heat. [ABSTRACT FROM AUTHOR]

The thermal conditions of transitional (ranging from warm to cold) coldwater streams impact the ranges and resource availabilities for biota inhabiting these lotic systems. With ongoing climate change and increasing land modifications, thermal boundaries may shift, altering thermal transition zones and their biotic communities. The objective of this study was to investigate the condition of trout across three forks of the Whitewater River catchment, located in southeastern Minnesota, and to investigate factors influencing fish community composition and distribution. Each fork was characterized into three separate sections: headwater (coolwater), middle (warmwater), and lower (coldwater). Springs were identified throughout each fork, with greatest concentrations in the lower sections of each fork. Using single-pass electrofishing, we sampled 61 sites across the three forks in the Whitewater River system (North = 21 sites, Middle = 19, South = 21), and catch statistics were used to calculate diversity, trout abundance, and trout condition. In general, diversity increased, and trout were healthier but less abundant in middle and headwater sections, whereas diversity decreased slightly, trout condition decreased, and trout abundance increased in lower reaches, with changes differing somewhat among forks. Canonical correlation analysis highlighted strong significant correlations showing that Simpson diversity and trout condition increase going upstream, with high non-trout abundance, while trout catch rates decrease and width narrows. The Whitewater River is a catchment exhibiting transitional temperature-pattern characteristics with generally low fish community diversity and trout conditions that range from thin, normal, and robust. Dominated by a changing landscape (agriculture) and intensifying climate change, we may begin to see stream temperatures increase along with species diversity. Understanding how spring temperature influences species composition and distribution can bring potential stressors to light, increasing our understanding of thermal conditions and helping to mitigate the negative impacts from land use and climate change. [ABSTRACT FROM AUTHOR]

Investigating the repercussions of climate change and irrigation timing on groundwater contamination necessitates thorough examination of the fluctuations in seawater and groundwater recharge temperature. This study introduces an innovative numerical approach to analyze groundwater salinity and temperature dynamics across three distinct scenarios using the SEAWAT code based on Henry's problem. The first scenario delves into the impact of seawater temperature, the second focuses on the consequences of aquifer freshwater recharge temperature, and the third amalgamates the effects of both scenarios. Remarkably, the study reveals that saltwater intrusion (SWI) experiences a decline attributable to the aquifer's heightened seawater temperature and the diminished inland freshwater temperature. Furthermore, combining these two scenarios has a more pronounced effect on aquifer pollution; the temperature-induced changes in SWI for this third scanrio reach + 8.10%, + 12.70%, + 16.20%, + 24.90%, + 28.30%, and + 31.80% compared to the case without considering the temperature effect. Notably, our results propose a potential strategy to mitigate SWI by introducing cold freshwater recharge into aquifers, such as irrigation at night time when water temperature is low. This innovative approach underscores the interconnectedness of various environmental factors. It provides a practical avenue for proactive intervention in safeguarding groundwater quality against the adverse impacts of climate change and irrigation practices. [ABSTRACT FROM AUTHOR]

Hydrothermal geothermal energy, as a widely distributed, large reserve and easily exploitable renewable source, can be used for both power generation and building heating. In this study, a numerical simulation of heat extraction performance is conducted based on monitoring well temperature data in a geothermal field in Xiong'an New Area. The effects of the reinjection temperature, injection flow rate, and reinjection rate on the outlet temperature and the reservoir temperature during a long-term operation are analyzed. The results indicate that the lower reinjection temperature can generate a critical disturbance scope for the thermal reservoir during the exploitation process. The impact scope on the thermal reservoir can reach 210.3 m at a reinjection temperature of 25 °C, which is not conducive to maintaining the outlet temperature of production wells in the long-term. The reinjection rate significantly affects both the horizontal and vertical temperature fields of the thermal reservoir. Under reinjection conditions of 30 °C and 40 kg/s, the horizontal and vertical impact scope of the thermal reservoir are 262.3 and 588.5 m, respectively. The reinjection rate is inversely related to the outlet temperature. A decrease from 100% to 70% in the reinjection rate can increase the outlet temperature by 4.21%. However, a decrease in the reinjection rate will lead to a decline in the groundwater level. Therefore, balancing the variation in outlet temperature and groundwater level is crucial in practical engineering. [ABSTRACT FROM AUTHOR]

Dendritic stream networks are an intriguing subject for exploring the spatial and temporal variability of the rare and common bacterial biosphere, yet very few such studies have been conducted. We sampled riverine bacterioplankton at 13 sites in a subarctic riverine network across 3 years, with five sampling times each year. Ordinations showed a consistent pattern of downstream shift for both rare and abundant subcommunities. We also detected a temporal signal, with seasonal community shifts reflecting changes in water temperature and groundwater contribution, and an inter‐annual pattern where the year 2018 differed from other years. Phylogenetic turnover of the rare subcommunity indicated homogeneous selection, whereas the abundant subcommunity was mainly stochastically structured. Transiently rare taxa were the dominant type of rarity with the highest proportion at the headwater regions. The bacterioplankton community was characterized by a small group of core taxa that occurred at most sites with little temporal variation, a very large number of permanently or transiently rare taxa, and taxa shifting through time between the rare and abundant biosphere. While this basic structure could have been detected with less extensive temporal replication, a comprehensive understanding of the rare biosphere in riverine bacterioplankton can only be achieved via inter‐annual, spatially replicated sampling that covers the whole stream network. [ABSTRACT FROM AUTHOR]

The groundwater temperature is an important indicator of groundwater dynamic change. Therefore, comprehensively monitoring groundwater temperature, understanding its temporal and spatial distribution characteristics, and studying its change rule can not only reflect the hydrogeological characteristics of groundwater system, but also provide a basis for its identification and division. With an elevation of 3,500 m--2,400 m, the Heilongtan groundwater system of Lijiang, Yunnan Province is a typical mountain and basin landform with wide distribution of soluble rocks, strong development of karst, and combination of faults and folds. Its hydrogeological environment is complex, challenging the delimitation of spring area and groundwater system. Because the study area is located in the plateau mountainous area, and the temperature field of karst groundwater can also reflect the variation of groundwater temperature at different elevations in the mountain and canyon areas on the plateau, this study has a great referential significance for the research of groundwater in other similar areas. Based on previous research results as well as a large number of monitoring data on groundwater temperature obtained in the study area from June to November, 2018, the spatial-temporal variation characteristics of groundwater temperature in the spring area and the variation characteristics of borehole water temperature were compared and analyzed, and the indicative significance of these two types of variation characteristics were discussed. Meanwhile, the feasibility of system division of the Heilongtan spring area was verified. The results show that there is a good spatial correlation between the elevation of groundwater level and temperature, and the groundwater temperature in the recharge area at high altitude is low. From the recharge area to the discharge area, the water temperature experiences a gradual upward trend. The water temperature in the discharge area can also indicate the circulation of groundwater runoff. The lower the water temperature in the discharge area is, the smoother groundwater becomes. In terms of time, as groundwater receives a large amount of rainfall recharge during the flood season, the circulation of groundwater flow increases, which may result in a short storage time of water and the phenomenon that the groundwater temperature in the discharge area is closer to that in the recharge area and that the overall water temperature decreases. At the end of the flood season, as rainfall decreases, the circulation of groundwater flow weakens, and the underground water temperature in the discharge area rises in different degrees. In a certain depth below the surface, the groundwater temperature does not completely conform to the theoretical law that the temperature rises gradually with the increase of depth, On the contrary, the groundwater temperature will remain unchanged or decrease gradually with the increase of depth, the reasons of which can be summarized as follows. (1) The temperature of surface water formed by precipitation is higher than that of groundwater, and the groundwater will be heated during infiltration and recharge. (2) When a deep karst pipeline is developed, the groundwater will "wash" away the heat from the deep, and the groundwater temperature will decrease with the increase of depth. (3) If the vertical movement of groundwater is intense, with large up-and-down disturbances and good temperature exchange conditions, the temperature value will become relatively stable in this active zone. This phenomenon is found in all monitoring points in the discharge area, especially in the period of smooth groundwater flow. (4) Under the influence of solar radiation energy, the surface temperature shows diurnal and seasonal variations. The diurnal variation affects 1--2 m below the surface, and the seasonal variation affects 30 m below the surface. This study shows that there are similarities and differences in the groundwater temperature in the study area, and the groundwater temperature is a good indication for the delimitation of groundwater system. This study also verifies the rationality of the existing delimitation system in the study area. [ABSTRACT FROM AUTHOR]

The impacts of climate change-induced warming on our ecosystems can no longer be neglected, but our understanding of consequences for groundwater ecosystems in general and groundwater quality in particular is alarmingly incomplete. In this review, we therefore provide an overview of the current state of knowledge related to the impact of global warming on our precious groundwater resources. Groundwater warming in shallow aquifers is closely associated with increasing average land surface temperatures and has already reached + 1 K compared to pe-industrial times. Until the end of the twenty-first century, temperature increases in local groundwater of up to + 10 K are possible. Monitoring data, laboratory and field experiments all provide evidence that such temperature increases are sufficient to substantially modify groundwater quality through numerous and interlinked biogeochemical processes, which we have summarized in a conceptual overview. Warming impacts on groundwater are highly site-specific and spatially heterogeneous, which complicates their assessment and prediction. Locally, shallow unconfined and nutrient-rich floodplain aquifers are most susceptible to warming-induced changes. Importantly, processes affecting water quality are not only modified by a long-term rise in groundwater temperatures, but also in the short-term during weather extremes, which is of great relevance for riverbank filtration. At the regional scale, aquifers in cold regions impacted by permafrost thawing are especially vulnerable to warming. As the majority of temperature-sensitive processes affecting groundwater quality are not or only very slowly reversable, we pressingly require comprehensive mechanistic understanding before it is too late to develop suitable countermeasures and management strategies. [ABSTRACT FROM AUTHOR]

Although groundwater discharge is a critical stream temperature control process, it is not explicitly represented in many stream temperature models, an omission that may reduce predictive accuracy, hinder management of aquatic habitat, and decrease user confidence. We assessed the performance of a previously‐described process‐guided deep learning model of stream temperature in the Delaware River Basin (USA). We found lower accuracy (root mean square error [RMSE] of 1.71 versus 1.35°C) and stronger seasonal bias (absolute mean monthly bias of 1.06 vs. 0.68°C) for reaches primarily influenced by deep groundwater as compared to atmospheric conditions. We then tested four approaches for improving groundwater process representation: (a) a custom loss function leveraging the unique patterns of air and water temperature coupling characteristic of different temperature drivers, (b) inclusion of additional groundwater‐relevant catchment attributes, (c) incorporation of additional process model outputs, and (d) a composite model. The custom loss function and the additional attributes significantly improved the predictive accuracy in groundwater‐dominated reaches (RMSE of 1.37 and 1.26°C) and reduced the seasonal bias (absolute mean monthly bias of 0.44 and 0.48°C), but neither approach could identify holdout groundwater reaches. Variable importance analysis indicates the custom loss function nudges the model to use the existing inputs more efficiently, whereas with the added features the model relies on a broader suite of inputs. This analysis is a substantial step toward more accurately representing groundwater discharge processes in stream temperature models and will improve predictive accuracy and inform habitat management. Plain Language Summary: Groundwater flowing into streams and rivers can cool the water during the summer and warm it during the winter. This creates important habitat for animals like trout and dwarf wedgemussels. Resource managers use computer models of stream temperature, but most models do not simulate groundwater flows with much detail. Insufficient accounting for groundwater could lead to predicted temperatures that are less accurate or less trusted. We tested four ways of including groundwater in a stream temperature model. The particular model we used is a type of machine learning model termed "process‐guided deep learning" because it takes advantage of both the computational advances in machine learning and our collective understanding of the science of stream temperature. We found that two approaches, one that focused on patterns between the air temperature and water temperature and one that incorporated additional descriptions of each stream reach, significantly improved the temperature predictions. Our findings have important implications for stream temperature predictions, habitat management, and methods for incorporating scientific expertise into machine learning models. Key Points: Existing process‐guided deep learning stream temperature models perform poorly in reaches with groundwater‐controlled temperaturesA custom loss function or enhanced input data improved predictive performance in monitored but not hold‐out groundwater reachesThe loss function used existing input data more efficiently; the enhanced inputs model spread its reliance to a wider range of inputs [ABSTRACT FROM AUTHOR]

Although deep learning models for stream temperature (Ts) have recently shown exceptional accuracy, they have limited interpretability and cannot output untrained variables. With hybrid differentiable models, neural networks (NNs) can be connected to physically based equations (called structural priors) to output intermediate variables such as water source fractions (specifying what portion of water is groundwater, subsurface, and surface flow). However, it is unclear if such outputs are physically meaningful when only limited physics is imposed, and if structural priors have enough impacts to be identifiable from data. Here, we tested four alternative structural priors describing basin‐scale water temperature memory and instream heat processes in a differentiable stream temperature model where NNs freely estimate the water source fractions. We evaluated models' abilities to predict Ts and baseflow ratio. The four priors exhibited noticeably different behaviors in these two metrics and their tradeoffs, with some dominating others. Therefore, the better structural priors can be identified. Moreover, testing different priors yielded valuable insights: having a separate shallow subsurface flow component better matches observations, and a recency‐weighted averaging of past air temperature for calculating source water temperature resulted in better Ts and baseflow prediction than traditionally employed simple averaging. However, we also highlight the limitations when insufficient physical constraints are implemented: the internal variables (water source fractions) may not be adequately constrained by a single target variable (stream temperature) alone. To ensure the physical significance of the internal fluxes, one can either employ multivariate data for model selection, or include more physical processes in the priors. Plain Language Summary: A new framework called differentiable modeling combines the benefits from neural networks (NNs) and process‐based models. This framework can learn from big data while the process‐based model components (called prior knowledge, or priors) are intended to output intermediate physical variables. However, do such priors matter, can we tell if one set of priors is better than another, and do the intermediate outputs represent the intended physical concepts? We explore these questions with a differentiable stream temperature model where the NN replaces the hydrologic component and estimates parameters pertaining to the stream temperature module. The strong optimizing capability of NNs allows us to avoid some complexities and attribute the differences in model outcomes to the assumed priors. Testing different priors thus yielded many important lessons, for example, the need for having a separate shallow groundwater "bucket," the benefit of placing more importance on recent air temperature when estimating groundwater temperature, and the importance of describing in‐stream temperature. The results show lots of untapped potential with differentiable modeling and the data we have available. Key Points: We can identify better structural priors (process equations) using differentiable models, circumventing intertwined parameter issuesConsidering a separate bucket for shallow subsurface water improves both stream temperature and baseflow simulationThe models selected by the multivariate evaluation produce physically meaningful estimates of water source fractions [ABSTRACT FROM AUTHOR]

The quality of groundwater has been severely impacted by urbanization around coasts. The change in climate and land use patterns has deteriorated the quality and availability of groundwater. One of the main issues in contemporary groundwater quality research is dissolved organic carbon (DOC) in the water. The influence of DO, water level and water temperature on DOC in groundwater was identified in the current study by sampling 68 groundwater samples. The analytical results revealed that ~18% of total samples have DOC > 5 mg/L. The groundwater samples represented in the urban regions show high DOC. The samples with higher DOC correlated positively with dissolved inorganic ions, such as Ca, K, NO3, Fe and DO. Domestic wastewater, agricultural runoff and local geology all have an impact on the DOC of groundwater. Groundwater chemistry is shown to be controlled by both aerobic and anaerobic conditions based on the DOC's interactions with other ions. The study interrelates various sources, such as land use, geology, water level and temperature, to the DOC in groundwater and infers that the levels are higher in shallow groundwater, predominantly around the built-up region followed by the agricultural region. The temperature changes enhance the DOC in groundwater due to the variation in microbial activity. The shallow water level with a lower temperature shows the maximum DOC. Apart from the sediment organic matter and microbes, the study also attributes land use pattern to the source of DOC in groundwater. [ABSTRACT FROM AUTHOR]

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The effect of water temperature variation in a river channel on groundwater temperature in the confined aquifer it cuts can be generalized to a one-dimensional thermal convection-conduction problem in which the boundary water temperature rises instantaneously and then remains constant. The basic equation of thermal transport for such a problem is the viscous Burgers equation, which is difficult to solve analytically. To solve this problem, the Cole–Hopf transform was used to convert the second-order nonlinear thermal convection-conduction equation into a heat conduction equation with exponential function-type boundary conditions. Considering the difficulty of calculating the inverse of the image function of the boundary function, the characteristics and properties of the Laplace transform were used to derive the theoretical solution of the model without relying on the transformation of the boundary function, and the analytical solution was obtained by substituting the boundary condition into the theoretical solution. The analytical solution was used to analyze the temperature response laws of aquifers to parameter variation. Subsequently, a 40-day numerical simulation was conducted to analyze the boundary influence range and the results from the analytical method were compared to those from the numerical method. The study shows that: (1) the greater the distance from the river canal and the lower the aquifer flow velocity, the slower the aquifer temperature changes; (2) the influence range of the river canal boundary increases from 18.19 m to 23.19 m at the end of simulation period as the groundwater seepage velocity v increases from 0.08 m/d to 0.12 m/d; (3) the relative errors of the analytical and numerical methods are mostly less than 5%, confirming the rationality of the analytical solution. [ABSTRACT FROM AUTHOR]

This study aimed at the analysis and modelling of the groundwater temperature at the water table in different regions of Slovakia. In the first part, the analysis of the long-term trends of air and soil/ground temperature to a depth of 10 m is presented. The average annual soil/groundwater temperatures at different depths were the same but lower than the annual average air temperature by about 0.8 °C. The long-term trend analysis of the air temperature and soil temperature at a depth of up to 10 m in Slovakia showed that the air and soil/ground water temperature have risen by 0.6 and 0.5 °C, respectively, per decade over the past 30 years. The second part of the study aimed at modelling the daily groundwater temperatures at depths of 0.6–15 m below the surface. The simple groundwater temperature model was constructed based on a one-dimensional differential Fourier heat conduction equation. The given model can be used to estimate future groundwater temperature trends using regional air temperature projections calculated for different greenhouse gas emission scenarios. [ABSTRACT FROM AUTHOR]

This study put forward a scheme of heating the groundwater by using the heat supply tower (HST) when the temperature of the groundwater drops yearly. Fluent was used to conduct a 3‐D numerical simulation of heat and mass transfer between air and water in the tower. Taking the Shenyang area as an example, the influence of different air parameters was analyzed. When air velocity was 2.0 m/s and water flow velocity was 1.0 m/s, the heat supply performance was the best. When outdoor dry bulb temperature was 34°C, the contact heat transfer increased underground water temperature by 1.4°C. When wet bulb temperature of air was 23.7°C and the dew point temperature of water vapor was 20.0°C, the condensation heat transfer increased underground water temperature by 2.0 4.0°C. The total temperature rise of water in HST was 3.0 ~ 5.0°C when it was in contact with air, which can effectively alleviate the problem of groundwater temperature decrease. In this study, the static analysis method was used to analyze the economy of the tower and solar energy heat supplement. The conclusion was that the heating cost of the heating tower is lower. [ABSTRACT FROM AUTHOR]

[Display omitted] • Models consider groundwater (GW) inflow, conduction, shading, and other heat fluxes. • Equilibrium temperature deficit concept is used as scenario comparative benchmark. • GW inflow and riparian shading most strongly drive changes in temperature signals. • These scenarios support process-based interpretation of paired air–water metrics. • GW source depth and inflow magnitude affect climate change thermal resilience. Headwater stream temperature often exhibits spatial variation at the kilometer-scale, but the relative importance of the underlying hydrogeological processes and riverine perturbations remains poorly understood. In this study, we investigated the relative importance of groundwater (GW) and other processes on downstream annual stream temperature signal characteristics using deterministic heat budget model (HFLUX) scenarios within an idealized stream reach representative of mountainous forested conditions. We summarized annual stream thermal regimes from the relationship of paired sinusoidal air and water temperature signals (amplitude ratio, phase lag, and mean ratio). Results showed that downstream changes in annual temperature depended on the thermal gradient between water and the hypothetical equilibrium temperature (where all heat fluxes sum to zero). GW inflow, riparian shading, and the boundary input signal were the most significant factors affecting downstream annual water temperature signals, while flow volume and channel dimensions impacted how quickly annual temperature signals changed. Effects of GW were dominated by advective rather than conductive heat exchange processes, but conduction played a larger role when GW input was more spatially diffuse. Our results indicated several mechanisms by which local processes may affect stream thermal resilience to disturbances and can help guide management of wildfire and climate change. [ABSTRACT FROM AUTHOR]

This paper discusses the application of Fresnel Lens Concentrator for Solar Water Heater which is a case study in Indonesia. The purpose of this study was to find an empirical equation of the relationship between Direct Normal Irradiance (Ib) and focal point temperature (Tf). The research location is Latitude: 7.9553 °S and Longitude: 112.6145 °E. The SM-206 solar power meteris used. The Fresnel lenses are made of PMMA material. Its specifications are: diameter = 1000 mm; weight = 2 kg; thickness = 2 mm; groove pitch = 0.5 mm and focal length = 880 mm. The main experimental setup consists of a PMMA Fresnel lens and a receiver. The conical cavity receiver has specifications; geometric concentration ratio, CRg = 8, and V = 2 Liters. Temperature measurement is done using a temperature data acquisition system. The K-type thermocouple is used to measure: 1) ambienttemperature (Ta); 2) the focal point temperature (Tf); 3) receiverwall temperature (Tr); 4) watertemperature (Tw). The experiment obtained the results of the empirical equation for the relationship between Direct Normal Irradiance (Ib) and focal point temperature (Tf). The increase in solar radiation produces a focus temperature, exponentially. At DNI 858 W/m2 it can produce a focal temperature of up to 1064 °C. The efficiency of the receiving cavity of the thermal cone which contains 2 litres of water and CRg = 8 under conditions of relatively Direct Normal Irradiance (Ib = 675 W/m2) is about 10.61 %. Furthermore, the energy that can be generated in heating water is 0.17-0.32 MJ, in 100 minutes. Heat convection and radiation loss can be reduced by adding an insulating layer to the walls and coating the surface with black. [ABSTRACT FROM AUTHOR]

Geothermal wells with depths of 4.3 and 4.1 km were drilled into an enhanced geothermal system (EGS) in Pohang, Republic of Korea. After five times of hydraulic fracturing, the groundwater level of the geothermal wells decreased after a Mw 5.5 earthquake in Pohang. The objective of this study was to monitor the groundwater level and temperature and determine the hydrogeological and hydrochemistry of two geothermal wells (PX-1 and PX-2) and one monitoring well (EXP-1) at the EGS site. The hydrochemical data of the EGS wells was also compared with the groundwater characteristics of eight wells at the National Groundwater Monitoring Station (NGMS). First, groundwater samples were collected from a depth of approximately 700 m, and an automatic water level recorder was used to monitor changes in the groundwater level and temperature for two years at the EGS site. Second, groundwater level and temperature data in the NGMS wells were collected from the National Groundwater Information Center's website and annual report on groundwater monitoring for comparisons with the EGS site. The results showed that the rate of groundwater increase was in the order PX-2, PX-1, and EXP-1, and the temperature decrease was the fastest in PX-1 and similar between PX-2 and EXP-1. The eight wells in the NGMS showed only temporary changes. The groundwater in the EGS is the Na-Cl type, but that in the NGMS is a mixture of the Ca-HCO3 and Na-HCO3 type. The EGS site has not yet recovered from the earthquake. [ABSTRACT FROM AUTHOR]

Water temperature is increasingly acknowledged as a key variable for the sustainable management of lotic environments. Thermal variability in rivers dictates in large part the ecosystem functions of these water bodies. River thermal sensitivity (TS), defined in this work as the value of the regression slope between water and air temperature (Tair) measurements, is often used to determine how river temperature regime is expected to vary as climate evolves. This study proposes a method to contextualize climate conditions during the river temperature‐monitoring period in order to define a common basis to compare TS values calculated for different stations distributed across various climatic regions in the province of Québec (Canada). Nine climate classes were defined based on Tair and precipitation. Annual climate conditions were classified according to their anomalies compared to a reference period (1981–2010). For the reference climate class ("Normal–Normal" conditions), results indicate contrasted summer TS values between Québec rivers and within rivers. Furthermore, observed summer TS variations between climate classes underline the need to account for climate conditions when studying spatial variations in river thermal sensitivity. Climate contextualization also allows us to study the potential role of previous conditions. Rivers were grouped according to their drainage basins characteristics to examine spatial variability in TS for the chosen reference climate conditions. River slope, station elevation and geographic location partly explained TS spatial variability. Useful proxies are needed to describe the relative contribution of groundwater to river temperature and to potentially improve the group classification results. [ABSTRACT FROM AUTHOR]

To collect and unify data about all geothermal resources in Serbia, a database was formed. The database allows us to perceive the geothermal resources of Serbia and their potential for utilization. Based on the data available in the geothermal database, the estimated temperatures of reservoirs, heat power, and geothermal energy utilization were calculated. The database contains 293 geothermal records (springs, boreholes) registered at 160 locations, with groundwater temperatures in the range between 20 and 111 °C. The maximum expected temperature of the reservoir is 146 °C according to the use of a SiO2 geothermometer. Some thermal water is cooled due to mixing with cold, shallow water. Geothermal resources are mostly used for balneology and recreation, and less for heating, water supply, bottling, fish and animal farms, agriculture, and industrial. 26% of all geothermal resources is used by the local population or has not been used at all. The annual utilization of geothermal energy for direct heat is 1507 TJ/yr, and the estimated capacity of geothermal energy in Serbia is 111 MWt. The results of analytical work were presented in the form of maps with a geological and hydrogeological background. Thermal waters are mostly located within an area of Tertiary magmatism. Three geothermal potential areas are identified in Serbia: Pannonian basin-Vojvodina Province, the Mačva-Srem area and area from Jošanička Banja to Vranjska Banja (southern Serbia). Based on chemical analyses, four hydrochemical facies are distinguished. Thermal water mainly belongs to the NaHCO3 or CaMgHCO3 hydrochemical facies, usually depending on the primary aquifer type: karst, karst-fissured, intergranular or fissured. [ABSTRACT FROM AUTHOR]

This study presents the groundwater flow and salinity dynamics along a river estuary, the Werribee River in Victoria, Australia, at local and regional scales. Along a single reach, salinity across a transverse section of the channel (~80 m long) with a point bar was monitored using time‐lapse electrical resistivity (ER) through a tidal cycle. Groundwater fluxes were concurrently estimated by monitoring groundwater levels and temperature profiles. Regional porewater salinity distribution was mapped using 6‐km long longitudinal ER surveys during summer and winter. The time‐lapse ER across the channel revealed a static electrically resistive zone on the side of the channel with a pronounced cut bank. Upward groundwater flux and steep vertical temperature gradients with colder temperatures deeper within the sediment suggested a stable zone of fresh groundwater discharge along this cut bank area. Generally, less resistive zones were observed at the shallow portion of the inner meander bank and at the channel center. Subsurface temperatures close to surface water values, vertical head gradients indicating both upward and downward groundwater flux, and higher porewater salinity closer to that of estuary water suggest strong hyporheic circulation in these zones. The longitudinal surveys revealed higher ER values along deep and sinuous segments and low ER values in shallow and straighter reaches in both summer and winter; these patterns are consistent with the local channel‐scale observations. This study highlights the interacting effects of channel morphology, broad groundwater–surface water interaction, and hyporheic exchange on porewater salinity dynamics underneath and adjacent to a river estuary. [ABSTRACT FROM AUTHOR]

Hatchery salmonid smolts are often reared using groundwater with elevated temperatures to maximize growth. Previous work has shown that rearing hatchery smolts in surface water with a more natural thermal regime resulted in increased return rates of adult landlocked Atlantic salmon (Salmo salar). We evaluated whether landlocked Atlantic salmon reared in surface water with a natural temperature regime have altered physiological smolt characteristics compared with fish reared in groundwater with elevated winter temperatures. Hatchery fish were sampled three consecutive years from January to May. Additional fish were released as smolts, recaptured, and compared with fry-stocked smolts. Surface water smolts had earlier peaks of plasma T4, lower T3 levels, later peak cortisol, and lower gill Na+/K+-ATPase activity as compared with groundwater smolts. After release and recapture, surface water fish had elevated plasma T4 and gill Na+/K+-ATPase activity compared with groundwater fish, but less than stream-reared fish. Elevated plasma T4 in surface water fish in the hatchery and after release may have promoted imprinting and other aspects of smolt development, contributing to the higher adult return rates of a cohort reared in surface water. [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]

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]

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]

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]

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]

The Lower Jurassic aquifer is the main target for exploitation of geothermal waters in the Polish Lowlands as it covers over 80% of the area of Poland. Particularly favorable geothermal conditions dominate in the Mogilno-Łódź Trough (central part of the Polish Lowlands), where that aquifer occurs at greatest depth, which results in high temperatures of geothermal waters. The main Lower Jurassic reservoirs in that area are Sinemurian, Pliensbachian, and Upper Toarcian sandstones. These sediments show high lithofacial variability, which results in local changes of hydrogeothermal parameters. Such local variability can be effectively estimated using the seismic data and the interpretation of well logs. Both methods were used for determination of depths to the top surface of Lower Jurassic formation and of distribution of porosity, and clay content, which enabled the researchers to recognize the spatial arrangement of groundwater horizons. The study area is a local structure within the Mogilno-Łódź Trough, in the vicinity of Malanów village. This is a synclinal structure built of Lower Jurassic strata close to the Turek Salt Pillow. Temperature of groundwater in that structure exceeds 80 °C and favorable reservoir parameters ensure relevant discharge. Sandstone horizons show thicknesses over 50 m, low clay contents and porosity around 0.15–0.20. [ABSTRACT FROM AUTHOR]

Conserving coldwater stream ecosystems in a warming world requires understanding how water temperature changes will affect the sustainability of coldwater fish populations such as brook charr (Salvelinus fontinalis). To date, many models for predicting stream temperature have either assumed spatially uniform (inaccurate) air-stream temperature relationships or required expensive measurement of hydrometeorological drivers (e.g., solar radiation, convection) in a manner impractical for fisheries management. Hence, we developed an accurate, cost-effective, management-relevant modeling approach for projecting how changes in air temperature, precipitation, and groundwater inputs will affect coldwater stream temperatures and brook charr survival and growth in Michigan, USA. Precipitation- and groundwater-corrected models predicted stream temperatures more accurately than air-stream temperature models. Projected stream warming intensified in proportion to simulated air temperature warming and was most extreme in surface runoff-dominated streams with limited groundwater-driven thermal buffering. However, groundwater-dominated streams will not invariably provide sufficient coldwater habitats for brook charr survival and growth if groundwater temperatures increase or groundwater inputs decline due to reduced precipitation. Amid resource limitations, fisheries managers can use the stream temperature modeling approach described herein to predict effects of climate change on brook charr survival and growth and take actions to facilitate their sustainability in riverine systems. [ABSTRACT FROM AUTHOR]

Stream temperature has been increasing in tandem with air temperature, with potentially negative impacts on cold‐water fish such as salmon. Assessing future stream temperature change is critical for developing effective management responses. Empirical models of stream thermal sensitivity generally predict less future warming compared to physically based models. Here we reconcile these discrepancies by using a process‐based hydrology and temperature model to simulate daily flow and water temperature for forested headwater catchments in a maritime region under both historic and projected future climatic conditions. The primary reason that the empirical approach underestimates thermal response to climate change is that it does not account for thermal memory in the catchment, especially related to the effect of snow cover. Empirical thermal sensitivities thus may underestimate stream temperature response to future climate warming. In addition, groundwater‐fed streams may only resist warming in the short‐medium term, due to lagged response of groundwater temperature. More process‐based understanding and modeling of stream thermal regimes is needed to effectively manage aquatic ecosystems. Key Points: Empirical stream thermal sensitivities underestimate how stream temperature will respond to climate changeCatchment heat storage influences summer temperatures, especially in the seasonal snow zoneGroundwater‐fed streams will only resist warming in the short‐medium term, due to lagged response of groundwater temperature [ABSTRACT FROM AUTHOR]

The problem of distinguishing the source of water inrush in mines and tunnels has been addressed by studying the specific case of significant water inrush along the haulage roadway of the Beiyangzhuang Mine and applying three different methods to determine the source of the water inrush from a range of angles. The first of these methods was to determine the source by analyzing the dynamic response law of the groundwater in the water filling aquifers, including a Quaternary porous aquifer and a Cambrian-Ordovician karst aquifer. The second was to establish a linear equation for stratum burial depth and ground temperature to calculate water temperature. The source of water inrush is identified by comparing the calculated water temperature for the filling aquifer and the measured water temperature at the water inrush point. The third was to analyze the hydrochemical types of the water filling aquifers and water inrush point samples using a Piper diagram, followed by Fisher discriminant analysis to discriminate water inrush sources with eight hydrochemical components; the mixture ratio is roughly evaluated based on chloride mass balance. These three methods consistently showed that the primary source of water inrush is karst water. The hydrogeochemistry discrimination analysis further indicated that the mixing ratio of karst water to pore water was about 6.0, suggesting that this method is the powerful and more practical of the three methods tested. The results presented here provide significant guidance for the management of mine water inrush. [ABSTRACT FROM AUTHOR]

Groundwater vulnerability assessment is a measure of potential groundwater contamination for areas of interest. The main objective of this study is to modify original DRASTIC model using four objective methods, Weights-of-Evidence (WOE), Shannon Entropy (SE), Logistic Model Tree (LMT), and Bootstrap Aggregating (BA) to create a map of groundwater vulnerability for the Sari-Behshahr plain, Iran. The study also investigated impact of addition of eight additional factors (distance to fault, fault density, distance to river, river density, land-use, soil order, geological time scale, and altitude) to improve groundwater vulnerability assessment. A total of 109 nitrate concentration data points were used for modeling and validation purposes. The efficacy of the four methods was evaluated quantitatively using the Area Under the Receiver Operating Characteristic (ROC) Curve (AUC). AUC value for original DRASTIC model without any modification of weights and rates was 0.50. Modification of weights and rates resulted in better performance with AUC values of 0.64, 0.65, 0.75, and 0.81 for BA, SE, LMT, and WOE methods, respectively. This indicates that performance of WOE is the best in assessing groundwater vulnerability for DRASTIC model with 7 factors. The results also show more improvement in predictability of the WOE model by introducing 8 additional factors to the DRASTIC as AUC value increased to 0.91. The most effective contributing factor for ground water vulnerability in the study area is the net recharge. The least effective factors are the impact of vadose zone and hydraulic conductivity. [ABSTRACT FROM AUTHOR]

Highlights • Mathematical model of DCMD system integrated with PT plant was developed and solved in MATLAB software. • Effect of feed water temperature on permeate flux and freshwater production has been presented. • Performance of PT solar power plant has been evaluated in terms of capacity factor and gross-to-net conversion factor. • Performance of DCMD system has been assessed in terms of evaporation efficiency and specific energy consumption. Abstract This paper investigates performance and economic evaluation of integrating 50 MWe parabolic-trough (PT) plant with direct-contact membrane distillation (DCMD) system for electricity and freshwater production in Abu Dhabi, United Arab Emirates. The evaluations of PT plant were performed utilizing SAM software. Maximum and minimum electrical energy generation was estimated to be 13.5 GWh and 7.71 GWh in May and December, respectively. Similarly, the cooling water requirement fluctuated from 856 m3/day to 1440 m3/day in December and May, respectively. The economic evaluation showed that the nominal and real levelized electricity cost was 24.54 cents per kWh and 19.3833 cents per kWh, respectively. The performance evaluation of DCMD system was performed by solving DCMD mathematical model in MATLAB® Software. An increase in feed temperature from 30 °C to 45 °C increased the permeate flux from 5.19 kg/m2 h to 20.01 kg/m2 h, and evaporation efficiency from 39.2% to 54.98%, respectively. Furthermore, it was assessed that proposed PT plant integrated with DCMD system could produce up to 14.33 m3 of freshwater per day with a water production cost of $0.64/m3. It was revealed that the integration of DCMD system with PT plant could be a sustainable and economical approach to cope with increasing demand of freshwater and electricity. [ABSTRACT FROM AUTHOR]

Highlights • Optimizing the conjunctive use of surface water and groundwater at the regional scale. • Promoting the economic benefits of water resource systems while considering the penalties and risks. • Reflecting uncertainties expressed as discrete intervals and probability distributions. • Obtaining various water planning alternatives under different climate change scenarios. Abstract The shortage of water resources and the increasing competition among water users have highlighted the importance of the water allocation problem. Water availability is crucial for water resource allocation and changes frequently, leading to the necessity to predict available water. This paper develops a framework aimed to plan regional water allocations under different representative concentration pathways (RCP) scenarios using an interval parameter conditional value-at-risk (CVaR) two-stage stochastic programming model. This framework combines prediction and optimization to reflect climate change, the uncertainty of water system and the coordination between water resources allocation and risk. The feasibility and practicality of the framework are demonstrated by its application in a real-world case study in the Lower Songhua River Basin in northeast China. Comparison between the results of the developed model and actual conditions show that 11.61 × 108 m3 volume of water supply can be saved after optimization, indicating that the developed model tends to allocate water in a more efficient way. The ratio of surface water to groundwater is reduced from 2:1 to 1.62:1. The proposed model has practical relevance for saving water and alleviating groundwater overexploitation. The approach is applicable to most areas with severe water shortages and groundwater overexploitation, and decision makers can determine the appropriate options for water resources allocation based on risk preferences and actual conditions. [ABSTRACT FROM AUTHOR]

Climate change is one of if not the most pressing challenge modern society faces. Increasing temperatures are observed all over the planet and the impact of climate change on the hydrogeological cycle has long been shown. However, so far we have insufficient knowledge on the influence of atmospheric warming on shallow groundwater temperatures. While some studies analyse the implication climate change has for selected wells, large-scale studies are so far lacking. Here we focus on the combined impact of climate change in the atmosphere and local hydrogeological conditions on groundwater temperatures in 227 wells in Austria, which have in part been observed since 1964. A linear analysis finds a temperature change of C0.7-0.8K in the years from 1994 to 2013. In the same timeframe surface air temperatures in Austria increased by 0.5-0.3 K, displaying a much smaller variety. However, most of the extreme changes in groundwater temperatures can be linked to local hydrogeological conditions. Correlation between groundwater temperatures and nearby surface air temperatures was additionally analysed. They vary greatly, with correlation coefficients of of all wells. Overall, the step-wise representation provides a slightly more accurate picture of observed temperatures than the linear trend. [ABSTRACT FROM AUTHOR]

Plasticity in the larval life history of the Ezo salamander Hynobius retardatus has been reported. In the present study, we monitored larvae of this salamander species in a fragmented forest in the environs of Sapporo, Japan. Overwintering larvae were detected in one of the two ponds examined, i.e., in the pond that was permanent, with water supplied from several spring-fed points. Four seasonal transition phases in water temperature were observed because of the abundant spring-fed groundwater supply and canopy cover from May to October. These phases included a warming period, a constant-high period, a cooling period, and a constant-low period. During the constant-low period, premetamorphic larvae that had already emerged during the cooling period were continuously detected; however, the composition of the developmental stages remained unchanged, with larval growth progressing slowly. There is apparently a critical temperature that represents the threshold for metamorphosis initiation. The critical temperature is expected to be slightly higher than the groundwater temperature at the spring-fed points. Emigration of overwintered larvae resumed during the warming period and continued during the constant-high period in the year following hatching. In the nearby temporary pond, the one-year-old cohort completed metamorphosis during the summer of the hatch year. [ABSTRACT FROM AUTHOR]

This study investigated the thermal regime of shallow groundwater in the Turin area (NW Italy), where the large energy demand has motivated a new interest for renewable sources, such as the use of ground-source heat pumps for domestic heating and cooling. The vertical variability of the groundwater temperature between the ground surface and 10-20 m was detected: deeper temperatures were higher than shallow temperatures in spring, while a decrease with depth occurred in autumn. These variations are connected with the heating and cooling cycles of the ground surface due to the seasonal temperature oscillation. Variations below the seasonal oscillation are likely to be connected with the presence of advective heat transport due to the groundwater flow, according to the hydraulic features of a shallow aquifer. Temperature values mostly ranged between 12 and 14 °C in rural areas, while the values were between 14 and 16 °C below the Turin city. This groundwater warming is attributed to a widespread urban heat island phenomenon linked to warmer land surface temperatures in Turin city. Sparse warm outliers are connected with point heat sources and site-specific conditions of land and subsurface use, which may cause the aquifer temperature to rise. A relatively stable temperature below the seasonal fluctuation zone combined with high productivity and legislated limits for deeper groundwater use represent favourable conditions for a large-scale diffusion of groundwater heat pumps within the shallow aquifer. Moreover, this heat surplus should be regarded as a resource for future geothermal installations. [ABSTRACT FROM AUTHOR]

• Paired air and stream water temperature metrics can provide an alternate or complementary method for assessing post-fire hydrologic change. • Results suggest increases in the magnitude of shallow groundwater discharge post-fire for sites with minimal pre-fire groundwater influence. • Watershed pre-fire stream-groundwater connectivity influences post-fire vulnerability to subsurface hydrologic change. Within the western United States, increasingly severe and frequent wildfires may alter the magnitude, timing, and quality of water exported from burned areas by streams. Post-fire hydrologic studies often focus on peak stream flow responses to shifts in runoff generation or on annual streamflow yield response to changes in evapotranspiration following fire. However, the magnitude and duration of wildfire effects on groundwater recharge, changes in subsurface routing, and consequences for stream low flows sourced predominately by baseflow are poorly understood. Here, we demonstrate an approach using the amplitude and phase of paired annual air and stream water temperature signals to broadly identify changes in watershed subsurface flow contributions after fire. Watersheds were classified using pre-fire temperature data, as having air-coupled (i.e., reduced apparent groundwater signature), deep groundwater, or shallow groundwater stream temperature signals. Changes in pre- and post-fire paired air and stream water temperature metrics were compared for locations (n = 17) spanning a large range of physiographic and climatic conditions across the western United States. Pre- and post-fire comparisons were computed by quantile using bootstrapped confidence intervals (ci = 95), as well as in aggregate using Kruskal-Wallis and post-hoc Dunn tests. Statistical comparisons of pre- and post-fire temperature metrics suggest that overall, watersheds classified as having minimal groundwater influence are the most likely to experience fire-induced subsurface hydrologic change. More specifically, watersheds classified as having air-coupled or shallow groundwater signals experienced increases in the magnitude of groundwater discharge, with more stable annual thermal regimes post-fire that are less-coupled to ambient air temperature. These findings form the basis of a conceptual framework for watershed resistance to subsurface hydrologic change following fire that can be broadly applied as a first approximation for water management, impacts on aquatic habitat, and post-wildfire response planning. [ABSTRACT FROM AUTHOR]

• Heat-transfer properties were analyzed to see how changes in hydraulic velocity and recharge rate allocation affected them. • The GWHP system's heat-transfer efficiency is evaluated by controlled physical studies in a lab setting. • A variety of pumping and recharge well layout schemes, and their effects on heat transfer efficiency, are analyzed. A groundwater heat pump (GWHP) is a form of ground-source heat pump that utilizes groundwater as its heat source and offers great efficiency, significant energy savings, and little pollution. As a GWHP system runs, thermal breakthrough is a crucial feature of system design that can result in a progressive shift in pumping water temperature and negatively impact GWHP performance. Variation in the groundwater flow field is crucial for heat transfer in terms of pumping and recharging well groups, especially when high porosity and permeability aquifers are taken into account, as this has a direct impact on the development of the groundwater temperature field. The primary goal of this study was to evaluate the impact of groundwater flow field variation due to groundwater velocity and recharge rate allocation changes on heat-transfer characteristics using laboratory physical experiments, to study the evolution trends of the groundwater flow field and groundwater temperature field, and to compare and determine various pumping and recharge well-group layout schemes to improve GWHP operation efficiency. The test results showed that the rise rate of pumping water temperature and the thermal breakthrough occurrence time increase with the increase of groundwater velocity, and when the groundwater velocity is the same, the thermal breakthrough occurrence time and the rise rate of pumping water temperature in the vertical well layout scheme are 0.48–0.76 times and 1.36–4.0 times that of the parallel well layout scheme, respectively. In addition, the recharge rate allocation has a greater impact on the parallel well layout scheme but a smaller impact on the vertical well layout scheme. The physical test results can provide a scientific basis for future research. [ABSTRACT FROM AUTHOR]

Two lowland catchments in the U.K. were sampled throughout 2010–11 to investigate the dominant controls on dissolved organic matter quantity and composition. The catchments had marked differences in terms of nutrient status, land cover and contrasting lithologies resulting in differences in the dominant flow pathways (groundwater vs. surface water dominated). The Upper Wylye is a chalk stream with a baseflow index of 0.98, draining a catchment dominated by intensive agricultural production. Millersford Brook is a lowland peat catchment with a baseflow index of 0.43, draining a semi-natural catchment with heather moorland and coniferous forest. Samples were collected weekly between October 2010 and September 2011 from eleven sampling locations. Samples were analysed to determine dissolved organic carbon, nitrogen and phosphorus fractions with DOM composition evaluated via the DOC:DON ratio, DOC:DOP ratio, specific UV absorption at 254 nm, absorbance ratio ( a 250 : a 365 ) and the spectral slope parameter between 350 and 400 nm ( S 350–400 ). Significant differences were observed in all determinands between the catchments, over time, and spatially along nutrient enrichment and geoclimatic gradients. Seasonal variation in preferential flow pathways mobilising groundwater-derived DOM were identified as likely controls on the delivery of DOM in the permeable chalk dominated catchment. Steeper S 350–400 values and elevated a 250 : a 365 ratios in this catchment suggest material of a lower bulk aromatic C content and molecular weight delivered during the winter months when compared to the summer. DOC:DON ratios were markedly lower in the chalk catchment than the peatland catchment, reflecting the paucity of organic matter within the mineral soils of the chalk landscape, and higher fertiliser application rates. This manuscript highlights that DOM composition varies according to catchment landscape character and hydrological function. [ABSTRACT FROM AUTHOR]

Pre-earthquake and postearthquake temperature changes were documented in two hot springs at Xiangcheng. Pre-earthquake changes were documented in spring I, 13 days before and 106 km away from the Ms 5.8 Zhongdian earthquake. The 11-year cutoff spring spouted again, and the spouted water was 24°C hotter than the former escaping gas. Postearthquake changes were documented in spring II following the 2008 Mw 7.9 Wenchuan earthquake, approximately 425 km away from the epicenter. Temperature in spring II showed a step-like increase with a magnitude of 4°C induced by the earthquake. Spring I which is 0.3 m apart from spring II did not show a sudden change following the earthquake. However, temperatures in the two springs were identical after the Wenchuan earthquake. It indicates that the earthquake generated new hydraulic connectivity between springs I and II, and the heat transport between the two springs accounts for the postearthquake temperature changes. [ABSTRACT FROM AUTHOR]

Stream thermal regimes are controlled by the interactions of external and internal energy fluxes with the water in the channel. Solar radiation is typically the dominant driver of stream water temperature, but streambed heat fluxes can be important in forested headwater streams. Past studies have presented seemingly disparate formulae for quantifying streambed heat advection from upwelling groundwater. This note details the sources of the differences in these alternative formulations. The equations illustrate the difficulties of attempting to isolate the thermal influence of groundwater-surface water interactions and highlight future research opportunities. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A measurement buoy with attached sensors has been deployed at our study area to monitor hydrodynamics, water properties, and water quality conditions. High-resolution temporal data have been collected and streamed into an online system that is accessible in nearly real-time. However, in certain circumstances the sensors may fail to provide continuous and high quality data. This results in gaps or corrupted values. The aim of this study was to reconstruct the faulty values. This paper proposes a method based on a data-driven model, using an Artificial Neural Network combined with a Genetic Algorithm to generate a synthetic data series. The generated data can be used as a patch for the incomplete measured data. Additional improvements were achieved by removing seasonal patterns from the original time series using a wavelet decomposition prior to the data-driven model training process. Comparisons with a standard missing-data imputation method using the Kohonen self-organizing map were made to further asses the performance of the proposed data-driven model. The algorithm was applied to water temperature data, but the same approach is applicable to other parameters of interest. [ABSTRACT FROM AUTHOR]

• Time-lapse electrical resistivity before, during, and after the intermittent river flooding. • Resistivity used to characterize the transient and spatial connectivity transitions. • Resistivity changes due to water saturation characterized connectivity transitions. • Resistivity changes after connection occurred were dominated by river temperature. • Resistivity sensitivity to temperature was also used to characterized infiltration. In the current era of rapid environmental changes, more rivers are projected to dry up and transition to disconnected systems in unprecedented duration and frequency. However, river-groundwater interactions, including connectivity, remain a challenge to characterize, especially for managed-ephemeral rivers such as the lower Rio Grande in southern New Mexico, where conjunctive use for irrigated agriculture is prevalent. This investigation used a noninvasive and spatially distributed geophysical method for mapping the disconnection/connection of groundwater with the Rio Grande River, which has been validated with ancillary data that includes river flow, water levels in the river and adjacent wells, and river and groundwater temperature and electrical conductivity. Time-lapse monitoring of electrical resistivity before, during, and after the river flooding season was used to characterize the transient and spatial connectivity of the water table with the Rio Grande, from disconnection to connection, and back to disconnection. The relationships between electrical conductivity from the geophysical analysis versus the large array of ancillary data helped to narrow down the driver of observed temporal changes in connectivity after the transition from disconnection to connection. The results convey that water temperature is potentially the main influence on the changing electrical conductivity after the connectivity transition. The surface water temperature showed a direct and strong correlation to the electrical conductivity of shallow sediments, which was similar to the river stage/groundwater elevation drivers of infiltration. Time-lapse electrical resistivity can be used to monitor river-groundwater connectivity throughout the intermittency cycle, due to its sensitivity to changes in both water saturation and temperature. [ABSTRACT FROM AUTHOR]

To investigate the effects of temperature on the CO storage in the deep saline aquifers, we set up a 2-D non-isothermal numerical model with simulating the CO injection into the aquifers at a low temperature. The evolution of the CO plume and the temperature in the aquifer were studied, and using temperature signal to monitor the arrival of CO plume was also evaluated. In addition, the deviance of the isothermal model was analyzed. The results show when the cold CO is injected into the aquifers, the aquifer can be divided into three zones in the direction away from the injection well during the injection period: temperature drop zone, temperature transition zone, and temperature rise zone. The temperature rise can reach approximately 1 °C in the temperature rise zone during the injection period, which should be enough for the temperature sensor to detect the arrival of the CO plume. However, the value of the temperature rise reduces with distance from the injection well. Consequently, we indicate that it is not suitable to monitor the long-term migration of the CO plume using temperature signal, especially after the injection stops. The initial formation temperature strongly affects the evolution of the CO plume and the temperature distribution after the CO injection. Not only the storage is safer, but also using temperature signal to monitor CO plume is more feasible in the cold aquifer. The deviance of the isothermal model is small in the mass fraction of dissolved CO and the arrival time of CO plume throughout the simulation. However, the deviance of pressure buildup is great and increases with time (up to 15 %) during the injection period. The non-isothermal model is necessary to accurately assess the pressure buildup around the injection well during the CO injection period. [ABSTRACT FROM AUTHOR]