Regional Groundwater Flow System Research Articles

Correction: Simon et al. Wetland Management in Recharge Regions of Regional Groundwater Flow Systems with Water Shortage, Nyírség Region, Hungary. Water 2023, 15, 3589

In the original publication [...]

The effects of damming and dam regulation on a river–lake-aquifer system: 3D groundwater flow modeling of Poyang Lake (China)

Large numbers of dams are planned or constructed for hydroelectric power production, water supply, and flood control in many rivers around the world. While the social and environmental impacts of dams are now well-understood, there is little knowledge about the effects of dams on groundwater-surface water interactions in a complex lake–river-aquifer system. This study adopts a three-dimensional groundwater numerical model to quantify the potential impacts of dam construction, on regional groundwater flow system, exemplified by the proposed Poyang Lake Hydraulic Dam (PLHD) in China. Once implemented, the PLHD will regulate lake levels, artificially controlling the lake inundation area during the recession season (September-October) and the dry season (November-December). Modeling results indicated that the increase in lake infiltration induced by PLHD regulation would alter the regional water exchange pattern. The PLHD regulation will likely enhance the groundwater storage by 20.44 % in the general dry year (i.e., 2018), alleviating 78.1 % of the groundwater deficit in the extreme dry year (i.e., 2019). Additionally, the response of groundwater dynamics to the PLHD regulation exhibits significant spatial differences between the upstream and downstream areas of the dam, primarily depending on topographical changes. Overall, the PLHD regulation is most likely to impact groundwater levels across an area of approximately 5,700 km2, and the associated groundwater storage is anticipated to reach a stable state, under future long-term regulation. Our findings may guide policy-makers wishing to develop more suitable PLHD scheduling plans and floodplain protection strategies by providing reliable information regarding groundwater storage change and ecosystem succession.

Wetland Management in Recharge Regions of Regional Groundwater Flow Systems with Water Shortage, Nyírség Region, Hungary

Climate change and increasing human impacts are more emphasised in recharge regions, where the main flow direction is downward, resulting in negative water balance. Two wetlands located in the recharge position of regional groundwater flow systems were investigated in the Nyírség region, Hungary, as pilot areas for representing wetlands in similar hydraulic positions. Hydraulic data processes, chemical data evaluations, and numerical simulations revealed that the wetlands are fed via local flow systems, superimposing regional-scale recharge conditions in the area. The wetlands are discharge and flow-through types in connection with local flow systems. Nevertheless, in the case of significant regional water table decline—due to the high vulnerability of recharge areas to climate change—local flows are degraded, so they are not able to sustain the wetlands. To preserve the groundwater-dependent ecosystems in the areas, water retention at the local recharge areas of the wetlands may help in the mitigation of water level decline under present-day conditions. If the regional water table continues to decline, comprehensive water retention solutions are needed in the whole region. The results highlight that understanding the natural wetland–groundwater interactions at different scales is crucial for the preservation of wetlands and for successful water retention planning.

Using hydrogeochemical facies and signatures for groundwater characterization and evolution assessment in aquifers with contrasting climate and geology in Tanzania

This study aimed at characterizing groundwater evolution using hydrogeochemical facies and signatures in two basins with contrasting climate and geology, one in the central part and the other in the eastern coast of Tanzania. The Kimbiji (humid, unconsolidated) aquifer is covered by an unconfined layer in the upper parts and a confined layer in the lower parts, with strong artesian flow characteristics while groundwater in the Singida (semi-arid, consolidated) aquifer occurs in weathered shallow layers and in fractures of basement rocks. Fieldwork involved water sampling from precipitation, deep and shallow boreholes, springs and surface water from rivers and lakes in the two study areas. These were specifically conducted for hydrogeochemical analyses to unravel hydrogeochemical facies and signatures in the two aquifers. Physico-chemical water quality parameters [i.e., pH, electrical conductivity (EC) and total dissolved solids (TDS)] were measured in situ using HANNA HI 9829 Multiparameter Analyzer. Standard procedures for water sampling, preservation, transportation, and chemical analyses of major ions were conducted as documented in previous studies. Samples were carried and stored at 4 °C prior to their shipping and analyses at Water analysis and testing in environmental regions (WATER) laboratory in Iringa, Tanzania. The mechanism controlling groundwater geochemistry were revealed by assessing the reactions between groundwater and aquifer minerals. Chloro-Alkaline indices (CAIs) were used to study cation exchange processes between the groundwater and its host environment at stagnancy and/or during groundwater travel. The Gibbs ratio 1 values were found to range from 0.26 to 0.94 and Gibbs ratio 2 values ranged from 0.11 to 0.95. The majority of the samples irrespective of the contrast in climate and geology were observed to fall in the rock–water interaction zone. This is attributed to chemical weathering processes where the dissolution of rock forming minerals takes place. Some samples exhibited replacement of Na+ by Ca2+ or Mg2+ (S18), loss of Na+ through precipitation of evaporate rocks (S11, S13, S16, S19), and water flowing through crystalline rocks (S1, S2, S4, S6, S8, S10, S12, S13, S14, S21). The ratio Na+: Ca2+ > 1.0 (S1, S4, S8, S10, S12, S14, S17, S18, S19, S21) explains base ion exchange while the ratio < 1 implies a reverse ion exchange (S2, S6, S11, S13, S16).The Ca2+: SO42− + HCO3− ratio < 1.0 connotes groundwater flowing through a normal hydrological cycle (S1, S4, S8, S10, S12, S14, S17, S18, S2, S6, S11, S13, S21) and a ratio greater than 1 is an indication of Ca2+–Cl− brines (S16, S19). The HCO3−: Cl− hydrogeochemical signatures divided the Singida aquifer into upper water flow course, where groundwater recharge occurs (S52, S54, S56, S57, and S58) and the discharge zone, (S53, S59, S60, S61) which is a lower groundwater flow course. Interestingly, the Mg2+ + Ca2+: Na+ + K+ ratios as well confirmed that the Singida aquifer is a lower groundwater flow course (discharge zone). The greater than 1 Na+: Ca2+ ratios confirm the dominance of base ion exchange in the Singida aquifer as it has been explained by the CAIs and the Piper diagram. The Gibbs diagrams revealed that the hydrochemistry of groundwater in the Kimbiji and Singida aquifers are mainly in the rock weathering region, affirming that there is high dissolution with rock forming minerals. This is thus one of the main controls of groundwater mineralization in the two study areas. The similarity of hydrogeochemical signatures between a distant surface water body, Lake Inkhanoda and Mwankoko borehole in the Singida aquifer is an indication that there is a discernible interaction between groundwater and surface water, further revealing that the Singida aquifer is fed by sub-regional and regional groundwater flow systems.

Basin-Scale Hydraulic Evaluation of Groundwater Flow Controlled Biogenic Gas Migration and Accumulation in the Central Pannonian Basin

Biogenic or microbial methane has an increasing share in the global gas resource base, though its exploration still faces challenges and welcomes innovations. Critical elements of its migration and accumulation models are the groundwater flows which gather and transport the gas in aqueous solution, and the seal rocks or aquifers which lead groundwater flows horizontally over great distances. This paper intends to introduce the hydraulic trap concept into these models, which is able to drive fluids horizontally without an overlying seal rock. Since hydraulic traps can evolve as a result of the interplay of regional groundwater flow systems, the basin-scale hydraulic evaluation methodology which was developed for the analysis of these systems was further improved by this study to focus on their interplay. The improved methodology was applied on measured hydraulic data in a study area in the Central Pannonian Basin (Hungary) around the Hajdúszoboszló gas field where as a result, the first groundwater flow controlled dissolved biogenic gas migration and accumulation model could be set up. In addition, the proposed methodology can be used in any terrestrial sedimentary basin, and in particular, where topography-driven flow systems are underlaid by an abnormal pressure regime.

Laboratory observations of solute transport in groundwater basins

This paper introduces a method of groundwater pollution source identification obtained from laboratory by a physical instrument of Flow System Sand-Box Model. A Unit basin of a simple flow system and a Tóthian basin of a hierarchically nested flow structure are introduced as case studies. We add step-input solutes at recharge zones, separately or simultaneously, to obtain the breakthrough curves (BTCs) at each discharge zone. For the Unit basin, its BTC shows a gradual upward trend with a decreasing slope but with two more pronounced steps, which differs a lot from previous results of analytical and numerical solutions. These steps are caused by the settings of the current physical instrument as no solutes are input at the upper two discharge ports. For the Tóthian basin, internal steps may exist due to the late-time arrival of intermediate and regional groundwater flow systems. Although the Unit basin and Tóthian basin can both have internal steps in the BTCs, they are due to different reasons. By jointly solving solute mass balance equations with water mass balance equations, the circulation rate for each flow system is calculated, which quantitatively explains the phenomena encountered in the experiment and highlights the important contributions of intermediate and regional flow systems to the entire groundwater circulation. We indirectly obtain the pulse-input BTCs by deriving the step-input BTCs respective to time, which is also the residence time distribution (RTD) of the groundwater basin, that the groundwater pollution sources can be identified. The pulse-input BTC is characterized by peaks and sloping tails. The peaks correspond to the intermediate and regional groundwater flow systems. The sloping tails indicate the rate at which solutes are flushed out or contaminants fade away. By inputting tap water into the groundwater basin to purify the contaminations, we conduct self-purification experiments. The shapes of the solute-input curves and the self-purification curves are systematically symmetrical. As the self-purification experiment has less external interference, it is possible to use the self-purification curves to characterize and identify the groundwater flow system. This study proposes a physical method for identifying sources of groundwater contamination, and achieves a comprehensive understanding of the law of solute transport in groundwater basins, which could guide the prevention of non-point contamination at the basin scale.

Combining spectral analysis and geochemical tracers to investigate surface water–groundwater interactions: A case study in an intensive agricultural setting (southern Guatemala)

An increase in the frequency of severe hydrological events has highlighted the importance of sustainable water management in intensive agricultural regions. In a warming climate, improved understanding and stewardship of water resources are needed to guarantee water supply, ensure food security, and build resilience against extreme events. In this study, we evaluate a framework that combines spectral analysis and geochemical tracers as a potential tool for (1) gaining valuable insights into surface water (SW)–groundwater (GW) interactions, and (2) providing guidance for improved water management in an intensive agricultural basin in southern Guatemala. The framework proves to be useful in revealing important water dynamics, exposing key feedback mechanisms for water availability and quality. With the use of power density functions and hydrochemistry (T, pH, EC, and major ions), two specific interaction regimes (influent and effluent) were identified and delimited for the main watercourse. These segments are estimated to interact at high rates with the shallow aquifer in the river channel proximities and would lose influence towards the basin flanks. Furthermore, the δ2H and δ18O values indicate that regional groundwater flow systems play an essential role in the basin groundwater recharge. Lastly, we established three influence zones that depict the spatial extent of the SW-GW interactions within the basin. With these zones, we provide recommendations that will allow for further investigation and application into better water management strategies regulating groundwater development and land use activities within the agricultural context of the area.

Regional groundwater flow system characterization of volcanic aquifers in upper Awash using multiple approaches, central Ethiopia

ABSTRACT Characterization of the groundwater flow systems is important for sustainable water resource management decision-making. We have used vertical profiles of electrical conductivity (EC) and water temperature taken at 2 m intervals during drilling of 109 boreholes, and samples for stable isotope analysis (δ 18O, δ 2H) taken from 47 boreholes to characterize groundwater recharge, flow and discharge. 222Rn measurements and piezometric evidence were used to complement results from the EC and stable isotopes. The converging evidence shows that groundwater in the study area is characterized by a mix of two different groundwater flow systems: i) the deep groundwater systems are connected to the regional groundwater flow originating from the highlands, outside the surface water basin, ii) the shallow groundwater systems get recharge from local rains. The local recharge zones are located in highly urbanized and industrialized zones posing risk to recharge reduction and pollution. Therefore, attention should be given to protect groundwater resources from contamination and increase groundwater resilience to climate change.

Evolutionary history of the groundwater system in the Pearl River Delta (China) during the Holocene

Abstract Coastal groundwater reservoirs are sensitive to the complicated evolution of marine transgressions and regressions in river delta regions. We integrated hydrogeological investigation and hydrogeochemical data with numerical modeling to assess the evolution of the groundwater system in the Pearl River Delta’s aquifer system (in southeastern China). We studied the effects of flow dynamics and redox conditions on the biogeochemical processes of nutrients in the regional groundwater flow systems in response to the transient states related to variable paleoprecipitation and seawater salinity decline from the late Pleistocene to the Holocene. The results from paleo-hydrogeological reconstruction of the aquifer-aquitard system showed that the saline groundwater formed by paleo-seawater intrusion was still present in the old marine aquitard and affected groundwater salinity and chemicals in the adjacent aquifers, while most of the groundwater in the shallow young marine aquitard has been freshened by infiltrated old/fresh rainwater. Consequently, total ammonium and carbon stored in the Pearl River Delta were estimated to be (1.91 ± 1.13) × 107 mol m–1 and (5.74 ± 4.05) × 107 mol m–1, respectively, and the ammonium and bicarbonate fluxes derived from groundwater discharge to the sea were calculated as (90.6 ± 55.9) mol m–1 yr–1 and (301.02 ± 196.23) mol m–1 yr–1, respectively. If the buried ammonium in the delta is released to the sea, it would be equivalent to nearly 205 ± 123 yr of Pearl River fluvial loading. These findings suggest that the chemicals trapped in the deltaic aquifer system during the Holocene could contribute to future ocean eutrophication and acidification.

Characteristic of regional groundwater flow system: case modeling study in Longzici karst spring area, North China

Characteristic of regional groundwater flow system: case modeling study in Longzici karst spring area, North China

Glacial Melt in the Canadian Rockies and Potential Effects on Groundwater in the Plains Region

The prevailing concern in the Western Canadian Plains is that glaciers from the eastern Canadian Rocky Mountains (CRM) are losing mass, thus affecting groundwater recharge in the Plains. The generally accepted hypothesis is that those glaciers are the geological source of groundwater for aquifers located in the Plains. The aquifers located in this region, close to the eastern part of the Rockies, represent a major source of water for the local population. It is believed that aquifer recharge originates as infiltration from snowmelt and ice in the Front Ranges of the eastern Rockies. A growing concern relates to the significant glacier melt estimated from glacier mass balances, which indicate that glaciers and ice fields have experienced considerable mass losses over the last 15 years, between 1 and 5 km3 per year, thus reducing recharge. However, deep groundwater flow under melting glacier conditions in mountainous regions is poorly understood. In this study, three 2D numerical hydrogeological models are built in order to simulate the groundwater flow under the glaciers from the Main and Front Ranges of the CRM and the Plains in the province of Alberta, Canada. Numerical results and a sensitivity analysis indicate that up to three different regional groundwater-flow systems are present in the region. These systems reveal the time- and space-scales associated with the combination of a mountainous region, foothills, Plains, and deep geological conditions. Based on the current knowledge of the hydrogeology of the study area and numerical modelling results, it is highly unlikely that the melting of glaciers affects groundwater in the Plains in the immediate future. The contribution of glacier water in the eastern part of the Rockies is time-dependent with delayed groundwater flows of 1000s of years in the Front ranges, 1000s to 100,000s of years in the foothills and Foreland; and 100,000s to millions of years to the Plains, at the regional scale.

Application of short time series analysis for the hydrodynamic characterization of a coastal karst aquifer: the Salento aquifer (Southern Italy)

Abstract Daily precipitation and groundwater level data, registered at 7 rain gauge stations and 11 monitoring wells in the Salento coastal karst aquifer (Southern Italy) were subject to short time series analyses to evaluate the hydrodynamic response of the aquifer. Results show that the Salento karst system has in general great storage capacity, which suggests a poor degree of aquifer karstification, and dominance in the permeability structure of not well-developed hierarchical karst networks. Baseflow generally dominates on quick flow, which only occasionally occurs. The dominant hydraulic behaviour is unimodal baseflow with a bimodal baseflow and quick flow one from time to time. Some local specific features, which emerge depending on the rainfall frequency and depth, and the geological and structural characteristics, point out that some components of the permeability structure, as the epikarst and major faults, only activate depending on the characteristics of the input. The study is novel because the analyses concerned specific sets of hydrological years from 2007 to 2011; also, because the analysis was conducted for a coastal karst aquifer of significant size, characterized by a regional groundwater flow system with an unsteady lower boundary, without inland freshwater springs, and significant exploitation by wells.

Application of methods for evaluating aquifer-system parameters: case of soil in My Thuan bridge, Vinh Long province

Determining hydrogeological parameters is one of the important tasks of groundwater dynamics, in which the storage coefficient is anindispensable parameter to predict subsidence. Compaction and water-level data were assumed to collect data from a boreholeextensometer recorded and groundwater pumping test in My Thuan bridge, Vinh Long province to estimate elastic and inelasticspecific coefficient (S) in aquifer-system. The purpose of this study is to estimated and compared specific storage by three methodssuch as Theis’s method, Riley’s method and Galloway’s study in My Thuan bridge site, Vinh Long province. The final value of thestorage coefficient is 0.00052. The results of this study also are the basis for calculating settlement and the impact that mining mayhave on regional groundwater flow systems.

Intensified salinity intrusion in coastal aquifers due to groundwater overextraction: a case study in the Mekong Delta, Vietnam.

Groundwater salinization is one of the most severe environmental problems in coastal aquifers worldwide, causing exceeding salinity in groundwater supply systems for many purposes. High salinity concentration in groundwater can be detected several kilometers inland and may result in an increased risk for coastal water supply systems and human health problems. This study investigates the impacts of groundwater pumping practices and regional groundwater flow dynamics on groundwater flow and salinity intrusion in the coastal aquifers of the Vietnamese Mekong Delta using the SEAWAT model-a variable-density groundwater flow and solute transport model. The model was constructed in three dimensions (3D) and accounted for multi-aquifers, variation of groundwater levels in neighboring areas, pumping, and paleo-salinity. Model calibration was carried for 13 years (2000 to 2012), and validation was conducted for 4 years (2013 to 2016). The best-calibrated model was used to develop prediction models for the next 14 years (2017 to 2030). Six future scenarios were introduced based on pumping rates and regional groundwater levels. Modeling results revealed that groundwater pumping activities and variation of regional groundwater flow systems strongly influence groundwater level depletion and saline movement from upper layers to lower layers. High salinity (>2.0 g/L) was expected to expand downward up to 150 m in depth and 2000 m toward surrounding areas in the next 14 years under increasing groundwater pumping capacity. A slight recovery in water level was also observed with decreasing groundwater exploitation. The reduction in the pumping rate from both local and regional scales will be necessary to recover groundwater levels and protect fresh aquifers from expanding paleo-saline in groundwater.

Review of geothermal conditions of Hungary

The heat flow map of Hungary was presented in the Atlas of Geothermal Resources in Europe in 2002 and was last updated in 2005. Since that time several geothermal projects, e.g. TransEnergy (2010-13), assessment of the geothermal potential of the Drava basin (2013) Paks-II, NPP (2016) and continuous drilling activity in the country have been in progress. Large amount of temperature data became available, which allowed the update of the Geothermal Database of Hungary and the compilation of an updated heat flow map and temperature maps.&#x0D; The heat flow is determined based on the Fourier law using the thermal conductivities of rocks and temperature gradient calculated from temperature observations in boreholes and wells. The thermal conductivity is known from laboratory measurements made on core samples. The thermal conductivities and the temperature data are stored in the Geothermal Database of Hungary.&#x0D; The heat flow is calculated in 2001 boreholes and wells using the Bullard-plot technique. The mean heat flow in Hungary is 90 mW/m2, varying between 30 mW/m2 and 120 mW/m2. The high values are found over buried basement highs in the eastern and southern part of the country, while the low values are located in the recharge areas of karstic flow systems. In the sedimentary basins, where the thickness of the Neogene and Quaternary sediments reaches 5-7 km, the heat flow is slightly below the mean value (80-90 mW/m2) due to the cooling effect of sedimentation. These basins contain the main thermal water aquifer in Hungary utilized for district heating and green house heating. The buried basement highs characterized by high heat flow (100-120 mW/m2) are potential sites to create artificial geothermal reservoirs by hydraulic fracturing (EGS).&#x0D; Temperature maps at 500 m, 1 km, 2 km and 3 km depths were also compiled. Similarly to the heat flow, the temperature anomalies strongly reflect the local and regional groundwater flow systems.

Hydrogeochemistry and fractionation of boron isotopes in the inter-dune aquifer system of Badain Jaran Desert, China

Groundwater flow systems can be topography-controlled in arid, mountainous, and/or permeable areas. Previous theoretical studies indicated that local groundwater flow systems were usually less developed or even did not exist in recharge-controlled flow systems, and the whole flow system was dominated by regional groundwater flow system. However, the occurrence and role of local groundwater flow systems in real recharge-controlled aquifer systems are rarely addressed. The Badain Jaran Desert is featured by hyper dry climate, mega sand dune-lake landscapes, and highly permeable loose sediments, making it an ideal natural laboratory to address these issues. In this study, the local groundwater flow system and its interaction with saline lake water in the desert inter-dune aquifer are investigated via hydrogeochemical and isotopic approaches. The stable boron isotopic compositions reveal the existence of local groundwater flow systems in the hyper arid climate condition. The fresh local flow systems regulate not only the lake water volume and the lake water-groundwater mixing process, but also the ion contents and isotopic compositions of saline groundwater and lake water. Lake water-groundwater interaction manifests as fresh groundwater discharge and saline lake water intrusion. This study demonstrates that boron fractionation is applicable in deciphering groundwater flow patterns and lake water-groundwater interaction in the arid aquifer systems.

Szemelvények az elmúlt két évtized ELTE-n végzett, medenceléptékű hidrogeológiai kutatásaiból

Az Eötvös Loránd Tudományegyetem (ELTE) Általános és Alkalmazott Földtani Tanszékének hidrogeológiai kutató és oktatócsoportja (Tóth József és Erzsébet Hidrogeológia Professzúra) tevékenységének középpontjában a felszínalatti vízáramlásoknak és kapcsolódó jelenségeknek a hidraulikus folytonosság alaptételére épülő medenceléptékű és rendszer szemléletű megközelítése áll. A jelen tanulmány e megközelítést történeti felvezetéssel és a korábbi, rétegtani (hidrosztratigráfiai) alapú „artézi” paradigmával szembeállítva mutatja be. A folyamatosan fejlesztett medenceléptékű hidrogeológiai kutatási módszertant röviden tárgyaljuk, a technikai részletek helyett kiemelve az alkalmazott módszertani megközelítések magyarázatát. Ezek közül legnagyobb jelentőséggel a kutakban mérhető hidraulikai adatok medenceléptékű, azaz medencehidraulikai elemzése bír, amelynek eredménye a „valós vízáramlási rendszermodell” felállítása. Ennek megfelelően kutatás történetünkből a medenceléptékű és különösen a medencehidraulikai eredményeket szemlézzük a továbbiakban, említve az ezekáltal összefüggésrendszerbe helyezett és egyéb módszerekkel vizsgált jelenségeket is. Az ország területének nagyrészét lefedő kutatásaink domborzattól és kőzettípustól (sziliciklasztos vagy karbonátos) függetlenül kimutatták a kőzetváz hidraulikus folytonosságát és a gravitáció vezérelte regionális felszínalatti vízáramlási rendszerek jelenlétét. Ezek medenceléptékben fedetlen, csapadékvízből utánpótlódó és közel hidrosztatikus nyomásrezsimű tartománya alatt a mélymedencékben abnormális nyomásrezsimek (túlnyomásos vagy alulnyomásos) fedett, és nem vagy csak korlátozottan utánpótlódó tartományai találhatók. E komplex hidraulikai helyzettel és a felszínalatti víz áramlások földtani és környezeti hatótényező szerepével számos felszíni (szikesedés, felszín alatti víztől függő ökoszisztémák, FAVÖKO-k stb.), és felszín alatti (hipogénbarlangképződés, szénhidrogén csapdázódás stb.) jelenség és folyamat nyert magyarázatot.

Physics-inspired integrated space–time artificial neural networks for regional groundwater flow modeling

Abstract. An integrated space–time artificial neural network (ANN) model inspired by the governing groundwater flow equation was developed to test whether a single ANN is capable of modeling regional groundwater flow systems. Model-independent entropy measures and random forest (RF)-based feature selection procedures were used to identify suitable inputs for ANNs. L2 regularization, five-fold cross-validation, and an adaptive stochastic gradient descent (ADAM) algorithm led to a parsimonious ANN model for a 30 691 km2 agriculturally intensive area in the Ogallala Aquifer of Texas. The model testing at 38 independent wells during the 1956–2008 calibration period showed no overfitting issues and highlighted the model's ability to capture both the observed spatial dependence and temporal variability. The forecasting period (2009–2015) was marked by extreme climate variability in the region and served to evaluate the extrapolation capabilities of the model. While ANN models are universal interpolators, the model was able to capture the general trends and provide groundwater level estimates that were better than using historical means. Model sensitivity analysis indicated that pumping was the most sensitive process. Incorporation of spatial variability was more critical than capturing temporal persistence. The use of the standardized precipitation–evapotranspiration index (SPEI) as a surrogate for pumping was generally adequate but was unable to capture the heterogeneous groundwater extraction preferences of farmers under extreme climate conditions.

Characterization of Surface Evidence of Groundwater Flow Systems in Continental Mexico

The dynamics of the underground part of the water cycle greatly influence the features and characteristics of the Earth’s surface. Using Tóth’s theory of groundwater flow systems, surface indicators in Mexico were analyzed to understand the systemic connection between groundwater and the geological framework, relief, soil, water bodies, vegetation, and climate. Recharge and discharge zones of regional groundwater flow systems were identified from evidence on the ground surface. A systematic hydrogeological analysis was made of regional surface indicators, published in official, freely accessible cartographic information at scales of 1:250,000 and 1:1,000,000. From this analysis, six maps of Mexico were generated, titled “Permanent water on the surface”, “Groundwater depth”, “Hydrogeological association of soils”, “Hydrogeological association of vegetation and land use”, “Hydrogeological association of topoforms”, and “Superficial evidence of the presence of groundwater flow systems”. Mexico’s hydrogeological features were produced. The results show that 30% of Mexico is considered to be discharge zones of groundwater flow systems (regional, intermediate, and recharge). Natural recharge processes occur naturally in 57% of the country. This work is the first holistic analysis of groundwater in Mexico carried out at a national–regional scale using only the official information available to the public. These results can be used as the basis for more detailed studies on groundwater and its interaction with the environment, as well as for the development of integrative planning tools to ensure the sustainability of ecosystems and satisfy human needs.

Hydrobiogeochemical evolution along the regional groundwater flow systems in volcanic aquifers in Kumamoto, Japan

Kumamoto is known as the largest groundwater city in Japan. Geochemical modeling (saturation indices and mineral stability diagram) was applied in this area for better understanding a hydrogeochemical evolution in volcanic aquifers in regional scale with additional constraint from stable isotopic dataset. Geochemical evolutionary model was interpreted along the water flow dynamics. In total 136 water samples were collected from wells, springs, and rivers in and around the major groundwater flow lines for geochemical analyses. Our results indicated that plagioclase is the major weathering reactant in aquifers with secondary important weathering minerals of pyroxenes. These reactions facilitate current hydrochemical signatures and produce secondary minerals of kaolinite or halloysite and smectite in later stage. Observed hydrogeochemical processes can be distinguished into two distinct criteria along flow regime. The first processes are material loads from the surface (mixing of contaminants and river waters) and initial stage of silicate weathering, resulting in the formation of Ca-HCO3, Ca-NO3–HCO3, and Ca–Mg–Na-HCO3 type waters. These processes prevail in aquifers at the recharge to lateral flow zones with relatively shorter residence time of 55 years. Microbiological reduction reactions dominate over these areas and salinization occurs at the coast that changes aquifer waters to be Na-Cl type. Proposed models and approach shown in this study may be useful and applicable in interpreting systems in other volcanic aquifer systems at similar climate conditions and for sustainable water resources management.