Local Groundwater Flow Systems Research Articles

Characterizing groundwater heat transport in a complex lowland aquifer using paleo-temperature reconstruction, satellite data, temperature–depth profiles, and numerical models

Abstract. Heat is a naturally occurring, widespread groundwater tracer that can be used to identify flow patterns in groundwater systems. Temperature measurements, being relatively inexpensive and effortless to gather, represent a valuable source of information which can be exploited to reduce uncertainties on groundwater flow, and, for example, support performance assessment studies on waste disposal sites. In a lowland setting, however, hydraulic gradients are typically small, and whether temperature measurements can be used to inform us about catchment-scale groundwater flow remains an open question. For the Neogene Aquifer in Flanders, groundwater flow and solute transport models have been developed in the framework of safety and feasibility studies for the underlying Boom Clay formation as a potential host rock for geological disposal of radioactive waste. However, the simulated fluxes by these models are still subject to large uncertainties as they are typically constrained by hydraulic heads only. In the current study, we use a state-of-the-art 3D steady-state groundwater flow model, calibrated against hydraulic head measurements, to build a 3D transient heat transport model, for assessing the use of heat as an additional state variable, in a lowland setting and at the catchment scale. We therefore use temperature–depth (TD) profiles as additional state variable observations for inverse conditioning. Furthermore, a Holocene paleo-temperature time curve was constructed based on paleo-temperature reconstructions in Europe from several sources in combination with land surface temperature (LST) remotely sensed monthly data from 2001 to 2019 (retrieved from NASA's Moderate Resolution Imaging Spectroradiometer, MODIS). The aim of the research is to understand the mechanisms of heat transport and to characterize the temperature distribution and dynamics in the Neogene Aquifer. The simulation results clearly underline advection/convection and conduction as the major heat transport mechanisms, with a reduced role of advection/convection in zones where flux magnitudes are low, which suggests that temperature is also a useful indicator in a lowland setting. Furthermore, the performed scenarios highlight the important roles of (i) surface hydrological features and withdrawals driving local groundwater flow systems and (ii) the inclusion of subsurface features like faults in the conceptualization and development of hydrogeological investigations. These findings serve as a proxy of the influence of advective transport and barrier/conduit role of faults, particularly for the Rauw fault in this case, and suggest that solutes released from the Boom Clay might be affected in similar ways.

Numerical investigation of groundwater flow systems and their evolution due to climate change in the arid Golmud river watershed on the Tibetan Plateau

Climate warming is the greatest future challenge to the hydrosphere and the human community, especially in arid and semiarid regions. This study took the Golmud river watershed on the Tibetan Plateau as an example to numerically identify the development of groundwater flow systems in a large arid sedimentary basin and explore what would the dramatic climate warming pose on groundwater flow system. The numerical results show that the Golmud river watershed has developed three hierarchical groundwater flow systems. River seepage is the predominant recharge for the groundwater systems inside the basin. The local groundwater flow system discharges some 82.69% of all groundwater in the basin, followed by the intermediate system with 14.26% and the regional system with 3.05%. The local system is mainly distributed in the shallow area of the alluvial-pluvial fan at the piedmont and provides the dominant water resource for human exploitation and oasis ecological usages. Climate warming would increase about 30.78% of the quantity of the recharge water to the groundwater system inside the basin via river seepage due to the increasing precipitation and increased glacier melt in the headwater region of the watershed. These waters would pose disturbances to all groundwater flow systems but to different degrees. The local flow system exhibits the largest response to the climate warming with more than 90% of increased water cycled in and discharged through it. The significant groundwater level rising leads to the trailing edge of the overflow belt at the piedmont moving ∼5 km towards to the mountain pass, which would potentially pose a water disaster to the local region. The influences of climate warming on the intermediate and regional flow system are relatively limited. This study provides a preliminary understanding of the influences of climate warming on the groundwater flow systems in arid endorheic basins and is essential for tackling future climate change challenges faced by arid and semiarid regions.

Integration of a Shallow Soda Lake into the Groundwater Flow System by Using Hydraulic Evaluation and Environmental Tracers

Lake Velence is a shallow soda lake whose water level and water quality show a severely deteriorating tendency in recent years. Until recently, the groundwater component in the lake’s water budget has not been taken into consideration. To integrate the lake into the groundwater flow system at the regional scale, methods of “basin hydraulics” were applied. In addition, 17 water samples were collected for δ2H and δ18O, and for ΣU, 226Ra and 222Rn activity measurements to use these parameters as environmental tracers of groundwater contribution. Groundwater mapping revealed that groundwater recharges in Velence Hills and the local elevations south of the lake, whereas discharge occurs by the lake’s shoreline and along surface watercourses. The results indicated that Lake Velence is the discharge point of local groundwater flow systems known to be more sensitive to climate changes and anthropogenic activities (e.g., contamination, overexploitation). Groundwater and lake water have similar uranium activity concentrations serving as another sign of groundwater inflow into the lake. Therefore, it is necessary to consider both the groundwater component in the lake’s water management and its vulnerability regarding local and short-term changes in the catchment area.

Hummock-scale controls on groundwater recharge rates and the potential for developing local groundwater flow systems in water-limited environments

We use two-dimensional numerical models to identify controls on groundwater recharge, water table dynamics, and the sink-source function of fine-textured hummocks in water-limited environments. A silty clay loam hummock with aspen forest cover in the sub-humid Boreal Plains region of Canada is used to develop a conceptual model and calibrate a variably-saturated flow model to better investigate the dynamics of recharge, water table position, and lateral flow between the forested hummock and adjacent peatland. Scenario testing (achieved by raising and lowering the hydraulic conductivity by an order of magnitude and altering the hummock height and length) provides further understanding of the controls that hydraulic conductivity and hummock morphometry exert on recharge and forestland-peatland interactions. We find that the hydraulic conductivity of the glacial till has the largest control over recharge, followed by the hummock height and length and, lastly, annual atmospheric fluxes. Hummocks with higher hydraulic conductivity or long morphometric profiles are most often sinks of water as they promote increased root-water uptake, while taller hummocks with lower hydraulic conductivity tend to act as hydrologic sources for adjacent wetlands. The magnitude of annual recharge and water table elevation are poorly correlated with annual atmospheric fluxes due to the strong effects of multi-year storage deficits or surpluses; however, they are appreciably affected by decadal wet-dry cycles typical of the Boreal Plains climate. Additionally, we show that both distance along a hummock and elevation are key factors in controlling the spatial distribution of recharge at a single hummock. It is common to conceptualize the water table as a shallow and subdued replica of surface topography, where water flows from topographic highs (i.e., forestlands) to topographic lows (i.e., peatlands) in humid environments; however, as we show here, recharge rates, water table elevation, and the sink-source function of a forested hummock in water-limited environments is highly variable in time and space, and strongly dependent on both the hydrogeological and morphometric properties of the hummock.

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.
 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.
 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).
 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.

Effects of Downward Intrusion of Saline Water on Nested Groundwater Flow Systems

AbstractNested groundwater flow systems (NGFS) are commonplace in various hydrogeological environments, including endorheic basins and coastal aquifers. The subsystems of the NGFS can be spatially separated by streamlines around the internal stagnation points. At the discharge zones of the topographic depressions, saline water often emerges due to high evaporation in endorheic drainage basins or the combined effects of evaporation and intermittent seawater submersion in coastal areas. To date, there are limited studies that have considered the impact of local‐scale downward migration of saline plumes in the topographic depressions on the NGFS. In this study, the classic NGFS are revisited by considering saline water in their discharge zones. To quantify the effects of salinity in the discharge zones on the NGFS, scenarios of various salinities in the discharge zones are simulated. The displacements of the internal stagnation points are used to quantify the evolution of the NGFS in response to salinity changes in the discharge zones. The results show that, as the salinity in the discharge zones increases, the hydraulic gradient near the discharge zone can be significantly reduced, the internal stagnation points shift upward, and the local groundwater flow systems retreat upward so that their original spaces are replaced by intermediate or regional flow systems. The discharge zone is expanded, and the overall groundwater flow velocity magnitude of the entire system decreases with salinity. This study may shed light on the management of saline wetlands, for example, the control of groundwater salinization, evolution of saline groundwater basins, and seawater intrusion.

Identification of Recharge Controls For Groundwater Aquifer System By Stable Water Isotopes

A decrease in groundwater level, especially shallow groundwater, occurred in the residential areas, and Padjadjaran University of Jatinangor part of Manglayang slope, a volcanic region at West Java Indonesia. This is due to an imbalance between groundwater input and extraction. This research aims to compile data on physical characteristics of rock lithology containing groundwater, and identifying various layers of groundwater carriers. Groundwater samples were taken in the aquifer system at the study area of the Manglayang volcanic region, and analyses using the composition diagram method and chemical analysis were conducted. The old volcanic deposit was found based on geological mapping, hydrogeology, electrical sounding measure, and boring in the area at the distal and media regime. The tuff deposit with pale soil, young deposit product is dominant in the area where there are lava and lava dome that reached the peak. There are also three types of lava, which is basalt augite, basalt, and andesite. Springwater was found at the 650 - 800 mdpl elevation. It has the facies Ca, Mg HCO3 (Calcium, Magnesium bicarbonate), and facies Mg HCO3 (Magnesium bicarbonate). The area has a local groundwater flow system above the elevation of 900 MSL and an intermediate groundwater flow system below elevation 900 MSL. The study found water catchment area is located in two places, which are zone in the elevation 900 to 1100 m with local flow patterns and 1379 m to 1697 m system intermediate. From these results, a zoning map can be developed based on the distribution of rocks and the sequences of rock formation. The study can also be utilized to determine the conservation zones' location based on the forms of delivery from each layer of rock.

The Control of Groundwater Flow Systems and Geochemical Processes on Groundwater Chemistry: A Case Study in Wushenzhao Basin, NW China

The lowest reaches of a large-scale basin could be the discharge areas of local, intermediate and regional groundwater flow systems with significantly distinct travel distances and travel times. This study aims to delineate the groundwater chemical characteristics and the mechanism controlling the chemical evolution in the lowest reaches of the Wushenzhao Cretaceous basin, NW China. A total of 38 groundwater samples were collected and were chemically classified into five distinct water types by means of a Piper Plot. According to the hydrogeological setting and groundwater age, the spatial distribution of these water types is found to be associated with hierarchically nested groundwater flow systems (local and regional system): Types 1, 2, 3 and 4 belong to the local groundwater flow system, while type 5 belongs to the regional flow system. Graphical plots, stable isotopes and geochemical modeling techniques were used to interpret the observed compositions. The results show the dominance of carbonate and gypsum dissolution in type 1 waters; ion exchange in types 2, 3 and 4; and evaporite dissolution in type 5. In addition, human activities in the form of extensive irrigation also affect the chemical compositions of type 1 water. These findings are important for the sustainable management of groundwater resources in the study area.

Hydrologic function of a moderate-rich fen watershed in the Athabasca Oil Sands Region of the Western Boreal Plain, northern Alberta

Peatlands are a dominant land feature in the Athabasca Oil Sands Region (AOSR) of the Western Boreal Plain (WBP), comprising >50% of the total land area, many of which are moderate-rich fens. The carbon stocks of moderate-rich fens in the WBP are susceptible to degradation through anthropogenic- and climate-related factors, yet, few studies have aimed to understand their hydrologic function. This study, located in a meltwater channel belt characterized by relatively thin outwash sand and gravel (∼6 m) underlying the peat, provides the first hydrological assessment of a moderate-rich fen in the AOSR. The lithology, hydrological function and groundwater geochemistry all point to the dominance of a local flow system supplying groundwater to the fen areas, evidenced by a thick (∼16 m) and shallow (∼7 m below ground surface) aquitard underlying the outwash, restricting hydrological connectivity between the fen and underlying regional aquifers. Vertical hydraulic gradients between the peat and underlying outwash aquifer, and horizontal hydraulic gradients between the fen and upland varied in response to both short-term and seasonal precipitation trends. Groundwater discharge to the fen was enhanced during wet periods characterized by high rainfall. Conversely, flow reversals (groundwater recharge; fen to underlying aquifer and upland), and subsequently, enhanced fen water table drawdown persisted during extended dry periods. This local groundwater flow-system influences recharge/discharge patterns at Poplar Fen, with hydraulic head in the underlying outwash aquifer highly susceptible to fluctuations in the presence and absence of precipitation-driven recharge from adjacent uplands. Moderate-rich fens similar to that studied here will likely become more susceptible to drying in the future due to a changing climate, leading to enhanced water table drawdown, peat oxidation and subsequent decomposition, vulnerability to wildfire, and seral succession to a more ombrogenous peatland system.

Moisture availability in the southwest United States over the last three glacial-interglacial cycles.

The projected long-term drying of the southwest (SW) United States in response to climate warming raises a sobering alarm for this already water-limited region, yet the climatic controls on moisture availability over longer time scales remain a topic of debate. Here, we present a 350,000-year record of past water table fluctuations in Devils Hole 2 cave that are driven by variations in recharge amount to the local groundwater flow system. Because of the unprecedented length and precision of our record, we can observe variations in regional moisture availability over the last three glacial-interglacial cycles at a millennial-scale resolution. The timing of past water table rises and falls (>9 m in amplitude) closely coincides with the expansion and reduction of Northern Hemisphere ice volume, which in turn influences the position and intensity of westerly winter storms on orbital time scales. Superimposed on this long-term trend are millennial-scale highstands recorded during the last glaciation that coincide with North Atlantic Heinrich events. Earlier millennial-scale highstands provide the first evidence of multiple short-lived wet periods in the SW United States linked to coeval cooling intervals in the North Atlantic during marine isotope stages 6 and 8. The Devils Hole 2 water table record is currently the longest independently dated paleomoisture record in the SW United States and thus provides a critical testbed to examine the controls on regional moisture availability over larger time scales.

Sistemas Aquíferos da porção centro-norte da Bacia Sanfranciscana e estimativa do fluxo regional

Com área aproximada de 125.000 km², a porção centro-norte da Bacia Sanfranciscana abriga o Sistema Aquífero Urucuia, responsável pela manutenção do fluxo de base dos tributários da margem esquerda da Bacia do Rio São Francisco. Recentemente, estudos de subsuperfície identificaram aquíferos permo-triassicos subjacentes, cujas rochas reservatório eram atribuídas, anteriormente, ao Sistema Aquífero Urucuia. Esses aquíferos foram correlacionados aos aquíferos Sambaíba e Motuca, da Bacia do Parnaíba. O complexo arcabouço hidrogeológico configurado por este grupo de aquíferos favoreceu a coexistência de sistemas de fluxo locais e regional. Os sistemas de fluxo locais, caracterizados por apresentarem áreas de recarga e de descarga adjacentes e dirigidos principalmente no sentido leste, drenam 991 m³/s das águas do SAU como fluxo de base para as bacias dos rios São Francisco, Tocantins e Parnaíba. O sistema de fluxo regional estimado em 29 m³/s, com direção de escoamento NW, paralela ao eixo longitudinal da Bacia Sanfranciscana, descarrega a água subterrânea dos aquíferos permo-triassicos para a Bacia do Rio Tocantins. A retirada de água por meio de poços tubulares profundos dos reservatórios permo-triassicos afeta o escoamento de base dos rios tributários do Rio Tocantins. Face às peculiaridades hidrogeológicas constatadas, os modelos atuais de gestão de recursos hídricos da Bacia Sanfranciscana devem ser reavaliados.

Modes, hydrodynamic processes and ecological impacts exerted by river–groundwater transformation in Junggar Basin, China

The hydrodynamic processes and impacts exerted by river–groundwater transformation need to be studied at regional and catchment scale, especially with respect to diverse geology and lithology. This work adopted an integrated method to study four typical modes (characterized primarily by lithology, flow subsystems, and gaining/losing river status) and the associated hydrodynamic processes and ecological impacts in the southern part of Junggar Basin, China. River–groundwater transformation occurs one to four times along the basin route. For mode classification, such transformation occurs: once or twice, controlled by lithological factors (mode 1); twice, impacted by geomorphic features and lithological structures (mode 2); and three or four times, controlled by both geological and lithological structures (modes 3 and 4). Results also suggest: (1) there exist local and regional groundwater flow subsystems at ~400 m depth, which form a multistage nested groundwater flow system. The groundwater flow velocities are 0.1–1.0 and <0.1 m/day for each of two subsystems; (2) the primary groundwater hydro-chemical type takes on apparent horizontal and vertical zoning characteristics, and the TDS of the groundwater evidently increases along the direction of groundwater flow, driven by hydrodynamic processes; (3) the streams, wetland and terminal lakes are the end-points of the local and regional groundwater flow systems. This work indicates that not only are groundwater and river water derived from the same source, but also hydrodynamic and hydro-chemical processes and ecological effects, as a whole in arid areas, are controlled by stream–groundwater transformation.

Simulation of the impact of managed aquifer recharge on the groundwater system in Hanoi, Vietnam

A transient numerical groundwater flow model using MODFLOW-NWT was set up and calibrated for Hanoi city, Vietnam, to understand the local groundwater flow system and to suggest solutions for sustainable water resource management. Urban development in Hanoi has caused a severe decline of groundwater levels. The present study evaluates the actual situation and investigates the suitability of managed aquifer recharge (MAR) to stop further depletion of groundwater resources. The results suggest that groundwater is being overexploited, as vast cones of depression exist in parts of the study area. Suitable locations to implement two MAR techniques—riverbank filtration and injection wells—were identified using multi-criteria decision analysis based on geographic information system (GIS). Three predictive scenarios were simulated. The relocation of pumping wells towards the Red River to induce riverbank filtration (first scenario) demonstrates that groundwater levels can be increased, especially in the depression cones. Groundwater levels can also be improved locally by the infiltration of surplus water into the upper aquifer (Holocene) via injection wells during the rainy season (second scenario), but this is not effective to raise the water table in the depression cones. Compared to the first scenario, the combination of riverbank filtration and injection wells (third scenario) shows a slightly raised overall water table. Groundwater flow modeling suggests that local overexploitation can be stopped by a smart relocation of wells from the main depression cones and the expansion of riverbank filtration. This could also avoid further land subsidence while the city’s water demand is met.

Potential impact of climate change on groundwater resources in the Central Huai Luang Basin, Northeast Thailand

The Central Huai Luang Basin is one of the important rice producing areas of Udon Thani Province in Northeastern Thailand. The basin is underlain by the rock salt layers of the Maha Sarakham Formation and is the source of saline groundwater and soil salinity. The regional and local groundwater flow systems are the major mechanisms responsible for spreading saline groundwater and saline soils in this basin. Climate change may have an impact on groundwater recharge, on water table depth and the consequences of waterlogging, and on the distribution of soil salinity in this basin. Six future climate conditions from the SEACAM and CanESM2 models were downscaled to investigate the potential impact of future climate conditions on groundwater quantity and quality in this basin. The potential impact was investigated by using a set of numerical models, namely HELP3 and SEAWAT, to estimate the groundwater recharge and flow and the salt transport of groundwater simulation, respectively. The results revealed that within next 30years (2045), the future average annual temperature is projected to increase by 3.1°C and 2.2°C under SEACAM and CanESM2 models, respectively, while the future precipitation is projected to decrease by 20.85% under SEACAM and increase by 18.35% under the CanESM2. Groundwater recharge is projected to increase under the CanESM2 model and to slightly decrease under the SEACAM model. Moreover, for all future climate conditions, the depths of the groundwater water table are projected to continuously increase. The results showed the impact of climate change on salinity distribution for both the deep and shallow groundwater systems. The salinity distribution areas are projected to increase by about 8.08% and 56.92% in the deep and shallow groundwater systems, respectively. The waterlogging areas are also projected to expand by about 63.65% from the baseline period.

Modification of the SWAT model to simulate regional groundwater flow using a multicell aquifer

AbstractThe soil and water assessment tool (SWAT) has been widely used and thoroughly tested in many places in the world. The application of the SWAT model has pointed out that 2 of the major weaknesses of SWAT are related to the nonspatial reference of the hydrologic response unit concept and to the simplified groundwater concept, which contribute to its low performance in baseflow simulation and its inability to simulate regional groundwater flow. This study modified the groundwater module of SWAT to overcome the above limitations. The modified groundwater module has 2 aquifers. The local aquifer, which is the shallow aquifer in the original SWAT, represents a local groundwater flow system. The regional aquifer, which replaces the deep aquifer of the original SWAT, represents intermediate and regional groundwater flow systems. Groundwater recharge is partitioned into local and regional aquifer recharges. The regional aquifer is represented by a multicell aquifer (MCA) model. The regional aquifer is discretized into cells using the Thiessen polygon method, where centres of the cells are locations of groundwater observation wells. Groundwater flow between cells is modelled using Darcy's law. Return flow from cell to stream is conceptualized using a non‐linear storage–discharge relationship. The SWAT model with the modified aquifer module, the so‐called SWAT‐MCA, was tested in 2 basins (Wipperau and Neetze) with porous aquifers in a lowland area in Lower Saxony, Germany. Results from the Wipperau basin show that the SWAT‐MCA model is able (a) to simulate baseflow in a lowland area (where baseflow is a dominant source of streamflow) better than the original model and (b) to simulate regional groundwater flow, shown by the simulated groundwater levels in cells, quite well.

How does the groundwater influence the water balance of a lowland lake? A field study from Lake Stechlin, north-eastern Germany

The subsurface catchment of Lake Stechlin is quite complex. Water level measurements in groundwater wells with different screen depths show that groundwater in the lake’s catchment may partly discharge to the lake and partly leak to deeper aquifers. Simple steady-state 2D vertical modelling of eight different scenarios (different leakage areas, different hydraulic conductivities) was conducted in order to explore the local and regional groundwater flow system around Lake Stechlin and the origin and possible magnitude of lacustrine groundwater discharge. A comparison of the different scenarios with in situ measurements of lacustrine groundwater discharge by temperature sticks and seepage meters revealed that only a part of the groundwater recharge in the catchment discharges to the lake while the rest leaks into deeper aquifers. This implies a differentiation of the subsurface catchment into a local and a regional flow system and impacts on travel times and chemical reaction time scales.

Influence of Seasonal Pumping on Groundwater Sources and Flow System, Nagaoka Plain, Japan.

Intensive groundwater development in the urban area of the Nagaoka Plain, Japan, has induced changes in the pH and saturation index of calcite in groundwater. To account for these chemical changes, it is important to determine seasonal variations of recharge and the groundwater flow system in the aquifer. This study identified the sources and flow system of groundwater in this urban area by a comprehensive method using stable isotope data and a numerical groundwater model of the Nagaoka Plain. Stable isotope evidence shows that the groundwater is recharged by meteoric water originating from low-elevation areas rather than the mountains surrounding the plain. The water table in the study area is drawn down during the winter and recovers in the other seasons. Numerical modeling shows that discharge occurs primarily along the Shinano River during the recovery period, whereas discharge is centered in urbanized areas during the drawdown period, when a conical depression of the water table stimulates recharge from the immediate area. These results are indications of a local groundwater flow system, with its recharge area between the Shinano River and the urban areas, which is governed by intensive seasonal groundwater extraction.

Analysis of hydrogeochemical facies in groundwater of upper part of Cross River Basin, southeastern Nigeria

Upper Cross River Hydrogeological Basin lies within latitudes 60 021N to 60 241N and longitudes 80 001E to 80 161E, and is generally underlain by shales of Asu River group of Albian age. The area has Histories of intensive mineralization which influenced groundwater system, resulting to occurrence of different water types. This study determines the various water types via evaluation of major ion concentration from representative water samples collected across the area. Twenty (20) water samples were analyzed using Spectrophotometer of HACH DR/2010 series, and results showed that groundwater in the area is generally hard and polluted with TDS in some places. Statistical inspection was performed on the results using aqua-chem, and it delineated five hydro-chemical facies, namely: Ca-Mg-Cl-S04, Ca-Mg-HCO3-Cl-SO4, Ca-Mg-HCO3, Na-K-HCO3 and Na-K-Cl-SO4; all lie between slight acidic and weak alkaline water. These chemical facies (water types) diffused from non-point sources in urban area and point source from south of Abakaliki town. The dispersion of the facies plumes is possibly controlled by advection process through structural weak zones such as fractures. Hydraulic heads determined from hand-dug wells indicate local potentiometric surfaces, hence, showed local groundwater flow system which is possibly controlled by the underlying low permeable aquicludes formed by shales. The protective capacity of the aquitards was somewhat reduced by the permeating fractures which exposed the aquifers to polluting effects of mineralized water-types.

Influence of vertical and lateral heat transfer on permafrost thaw, peatland landscape transition, and groundwater flow

AbstractRecent climate change has reduced the spatial extent and thickness of permafrost in many discontinuous permafrost regions. Rapid permafrost thaw is producing distinct landscape changes in the Taiga Plains of the Northwest Territories, Canada. As permafrost bodies underlying forested peat plateaus shrink, the landscape slowly transitions into unforested wetlands. The expansion of wetlands has enhanced the hydrologic connectivity of many watersheds via new surface and near‐surface flow paths, and increased streamflow has been observed. Furthermore, the decrease in forested peat plateaus results in a net loss of boreal forest and associated ecosystems. This study investigates fundamental processes that contribute to permafrost thaw by comparing observed and simulated thaw development and landscape transition of a peat plateau‐wetland complex in the Northwest Territories, Canada from 1970 to 2012. Measured climate data are first used to drive surface energy balance simulations for the wetland and peat plateau. Near‐surface soil temperatures simulated in the surface energy balance model are then applied as the upper boundary condition to a three‐dimensional model of subsurface water flow and coupled energy transport with freeze‐thaw. Simulation results demonstrate that lateral heat transfer, which is not considered in many permafrost models, can influence permafrost thaw rates. Furthermore, the simulations indicate that landscape evolution arising from permafrost thaw acts as a positive feedback mechanism that increases the energy absorbed at the land surface and produces additional permafrost thaw. The modeling results also demonstrate that flow rates in local groundwater flow systems may be enhanced by the degradation of isolated permafrost bodies.