Groundwater Recharge Conditions Research Articles

Биологические показатели и их значение в диагностике аллювиально-луговых почв

The priority issue that is covered in the article is the expediency of using biological indicators in the diagnosis of alluvial-meadow soils. In Azerbaijan, floodplain soils, common on terraces and alluvial fans of large rivers, where there are groundwater recharge conditions and the influence of the flood floodplain regime, have been widely studied. Alluvial-meadow soils develop under the meadow soil with forb-cereal groups and shrub vegetation under the active influence of groundwater occurring at a depth of 1.0–3.5 and surface (flood) moisture. Rich herbaceous vegetation causes the development of the sod process; as a result, a large amount of organic matter accumulates. Considering that various subtypes of floodplain soils are formed, under characteristic bioclimatic conditions, our goal was to study some biological indicators of alluvial-meadow soils of natural and cultivated cenoses. On the selected biotopes (virgin cenosis, near-terrass biotope, alluvial deposits of Shin-chai, as well as agrocenoses of cereals and tobacco), the group composition and amount of microbiota, complexes of invertebrates, phytomass and humus content were comparatively studied. The accounting of phytomass on the virgin cenosis showed that plant products amount to 363 g/m2 of raw and 26 g/m2 of dry mass. Possible relationships between individual biological and some physico-chemical parameters are considered. The results obtained can be used as biotests in the diagnosis of alluvial-meadow soils. Plants are the primary source of organic residues in the soil, their main function of which as a soil-forming plant is to create primary bioproducts and participate in the global biological cycle.

Simulation and Prediction of Groundwater Dynamics in Nagarjuna Sagar Right Canal (NSRC) Command for Normal and Extreme Groundwater Recharge Conditions

Groundwater Modeling is the best tool to optimize the different combinations and to select the best combination for sustainable groundwater management. Using computer models, best solution or scenario can optimize by creating model with real conditions. In this study, computer model Visual MODFLOW was applied to Nagarjuna Sagar Right Canal Command area to simulate the groundwater dynamics. The net area irrigated under Nagarjuna Sagar Right Canal is 4.75 lakh ha. The aquifer properties of various layers and boundary conditions were fed in to the model as input for calibration and validation of the model. After calibration and validation, the model was used to predict the groundwater dynamics in the study area using different recharge scenarios. The validated groundwater model was used to predict the groundwater levels in the study area for the years 2020, 2030 and 2040 with different recharge scenarios. Global climate model was used to generate future weather data. MarkSim developed by the International Centre for Tropical Agriculture (CIAT) was used to generate the weather parameters like maximum and minimum temperatures for the years 2020, 2030 and 2040. The different recharge scenarios with average, lowest and highest recharge over the study period and projected evapotranspiration have been used and revealed that the groundwater levels increase with the increase in recharge and decreases with the decrease in recharge. The results revealed that the groundwater depleted area would decrease with the highest recharge scenario and it would increase with the lowest recharge scenario in future. The deeper groundwater table would be expected in future at Chimakurthy and Thalluru villages of Prakasam district and Karempudi and Piduguralla villages of Guntur district in the study area. This condition may be due to the excess utilization of groundwater which is less than the groundwater recharge in particular villages. The construction of rainwater harvesting structures for artificial groundwater recharge in those areas should be carried out immediately.

Baseflow Trends for Midsize Carpathian Catchments in Poland and Slovakia in 1970–2019

Global warming affects, among many other things, groundwater recharge conditions. Over recent decades, this phenomenon in the Carpathians has been emphasized by the changing role of snowmelt recharge in winter and spring. The aim of the study was to assess baseflow trends in 20 medium-sized Carpathian catchments in Poland and Slovakia. The baseflow was calculated using Eckhardt’s digital filter. The trend analysis was performed using the non-parametric method separately for the series representing the baseflow throughout the whole year, and separately for seasons. The most evident changes were noted for the low baseflow in the summer and autumn, especially in foothill catchments. Statistically significant decreases in the low daily baseflow were expressed as a relative change, and ranged from −9% to −66% per 10 years for the summer, and from −12% to −82% per 10 years for the autumn. In winter and spring, trends in the low baseflow were not significant, except in high mountain catchments where 14% of increases in the low baseflow were noted in the winter and spring. The results indicate the changing role of snowmelt recharge in the Carpathians and the increasing problem of groundwater depletion in the summer and autumn, mainly in foothill areas.

Prediction of hydrodynamic conditions in the influence zone of Stoilensky Mining and Beneficiation Plant

Sources of anthropogenic impact on hydrodynamic conditions in quarrying an area have been identified as the drainage system, tailings dump and groundwater intakes. It has been determined that the induced factors associated with the operation of Stoilensky Mining and Beneficiation Plant have formed the modern hydrogeological conditions of the area. The analysis of the hydrogeological conditions in the region was carried out. It was found that the drainage of the quarry led to a change of the conditions of groundwater recharge and discharge, to an increase in the filtration rate and in the aeration zone thickness. That contributed to the activation of rock leaching, flow of process water into aquifers, and to a change of water flow between aquifers. The groundwater levels of the Upper Jurassic measures decreased in pitwall rock mass. The groundwater ridge formed at the site of the tailings dump. The transformation of balance elements of groundwater formation took place in the area: the main source of recharge for the Upper Jurassic rocks is the tailings dump. The numerical model of groundwater seepage is described. The aquifer is modeled as a four-layered thickness. Simulation was carried out using MODFLOW program of GMS system. The predictive calculations took into account the expansion of pitwall, the reconstruction of the underground drainage system, the building-up of the tailings dump with thin pulp up to the project levels. It has been established that the Oskolets river is a source of the aquifer recharge as a result of operation of the drainage system of the quarry. At the same time, the Oskol river drains groundwater. It was revealed that the main inflow to the quarry formed due to groundwater from the Upper Jurassic rock mass and, in a smaller degree, from the Archaean–Proterozoic aquifer and due to atmospheric precipitation. The volumes of seepage of industrial water from the tailings dump have been determined.

Conditions of groundwater recharge in the hyperarid southern Atacama Desert

Weather systems that produced recharge to the aquifers in the Atacama Desert between 24.5 and 25.5°S were investigated using δ 18 O and δ 2 H data in groundwater and precipitation combined with remote sensing methods. Atmospheric systems that produced rain and snow from 1984 to 2017 were analysed using isotopic data for precipitation from the literature and this investigation. δ 18 O-lapse rates on a west to east transect for a series of precipitation events ranged from −5.0 to −1.1 ‰/km, which is similar to the global average. Groundwater stable isotopes plotted against the average elevation of the catchment basin for each spring or well sampled produce a lapse rate identical to precipitation isotopes but are enriched in δ 18 O relative to δ 2 H due to the effects of evaporation before water enters the groundwater system. Data show a seasonal cycle in the isotopic composition of precipitation, as does δ 2 H data obtained from Tropospheric Emission Spectrometer (TES) on-board the Aura satellite. These analyses demonstrate that an important source of moisture is the Pacific Ocean. Although usually discounted in climate and paleoclimate analyses of northern Chile, this source of moisture is consistent with two features of the regional land-atmosphere system. First, the hyper-arid core of the Atacama Desert at these latitudes lies in a secondary rain shadow created by the Cordillera de Domeyko which exceeds 4000 m a.s.l., which blocks further westward passage of moisture that might have crossed from the east over the Andes. Second, the weather events responsible for precipitation between 2000 and 2018 are distributed between winter systems which initiate from the south, and exceptional events at other times of the year in which moisture originates from the tropics. Particle tracking indicates that air masses resided between 10 and 30°S over the Pacific at least 4 days prior to weather events which produced rain, or snow that persisted on the ground for more than one month between 2000 and 2018, even though the triggers for these events originated in higher latitudes. Pacific moisture sources need to be better accounted for in paleoclimate studies and groundwater resources evaluation. • Precipitation collected in the southern part of the Atacama Desert is isotopically characterized. • Seasonal patterns are found in the isotope composition of precipitation and atmospheric water vapor. • Isotope data indicate moisture is derived from the Pacific Ocean, and is confirmed from particle tracking. • Groundwater isotope data indicates moisture has been derived from the Pacific Ocean on millennial timescales.

In situ supplies of radiogenic He in residual soils of shallow granite aquifers: Spatial distribution of dissolved He throughout the Korean Peninsula

In Korea, where shallow weathered granitic aquifers are ubiquitous, several previous studies have reported strong radioactivity in shallow groundwater, which eventually led to the closure of production wells; however, no integrated study has analyzed factors controlling the spatial distribution of radionuclides in groundwater. Herein, we compiled the existing measurements of He, Ne, Ar, Kr, and Xe from 122 shallow wells (<200 m in depth) to differentiate and analyze the distribution of non-atmospheric (excess) 4He as a proxy for radionuclide accumulation in groundwater. The closed-system equilibration (CE) model accurately predicted the measured 4He in samples (root-mean-square deviation = 0.486), indicating its application in discerning the physical conditions of groundwater recharge in shallow granitic aquifers. Fifty-five samples were selected to identify the origin of strong radioactivity in shallow aquifers; low-quality samples were screened based on the (1) goodness of fit (>1%), (2) plausibility of modeled excess air concentrations (<0.05 cm3 STP/g), and (3) recharge temperature (5–20 °C). The distribution of excess He in the aquifers was largely dependent on the rock type, as defined by three distinct trends in He isotope excesses. Specifically, we observed (1) a large contribution of a mantle source of He isotopes, with values as high as ∼6.7 RA (RA = air = 1.39 × 10−6), on Jeju Island (quaternary basalt); (2) a small but significant contribution of mantle in Yanggu (Jurassic hornblende granite), with values up to 2.3 RA; and (3) a purely radiogenic source of 4He (i.e., no mantle contribution) throughout the remaining five granitic or sedimentary aquifers. Moreover, the shallow aquifer in Wonju (Jurassic biotite granite) exhibited a measurable amount of excess He, without large faults. The radiogenic sources scattered in the shallow granite aquifer caused localized 4He concentration peaks, even in young groundwaters (1.6–19.9 y). The concentration of radioelements peaked at a relatively shallow depth of 18.5 m, refuting the diffusive supply of radionuclides from the external deep reservoir. This was attributed to the high range of 4He accumulation rates (3.51 × 10−9 to 1.17 × 10−8 cm3STP/g/y), which originated from the high in-situ production of residual soils weathered from U-abundant protolith. The present study demonstrated that excess He quantified using the CE model can help identify the origin of strong radioactivity in shallow groundwater.

Isotope-Geochemical Studies of Groundwater in the Zapolyarny Region of the Nenets Autonomous Okrug

The aquifer of sandy deposits in the talik zone of the Pechora River valley was studied. The use of information on the distribution of tritium isotopes made it possible to clarify the recharge conditions of groundwater and their genetic structure in different parts of the aquifer. The tritium age of groundwater in coastal wells was 20–25 years, on the basis of which it was concluded that the groundwater that entered the aquifer before 1995–2000 was almost completely replaced. In wells, remote from the river bank, the age of the water is in the range from 20 to 50 years. However, unlike onshore wells, these groundwaters contain “bomb” water and old water that entered the aquifer be- fore 1952. The age of the old water reaches 12.9±2.5 thousand years. It has been established that the ratio between stable 13C and radioactive 14C isotopes of carbon changes with age, indicating an increase in the carbon exchange between dissolved inorganic carbon and soil carbon dioxide caused by permafrost thawing.

The dynamics of meteorological droughts over a semi-arid terrain in western India: A last five decadal hydro-climatic evaluation

Western Gujarat is one of the regions of India which has suffered from frequent drought events once every three years. High monsoonal variability on account of erratic rainfall, over-exploited aquifers, and poor groundwater recharge conditions in basaltic terrain are few reasons for drought spells over the study area. The study focuses on understanding more on drought regime and its patterns in the seven districts of Gujarat and its close linkages with the partial arid state therein using selected indicators of SPI, SPEI, rainy days, and daily rainfall intensity. However, if there persist events like drought or famine due to scanty or irregular rainfall, a study is deemed necessary to identify, confirm and characterize drought. The present study is largely focusing on such a scene where drought impacts over the Saurashtra region are assessed by evaluating climatic data of rainfall and temperature for each year of study. The deficit rainfall regime is explored for occurrences of a drought of varying severity between 1969 and 2018. The positive and negative patterns of the water regime are explored, and the anomalies are detected, signifying relationships among rainy days and drought-affected areas. Drought dynamics is detected for 17 years of drought occurrences with three years- 1972, 1987, and 2012 as major drought years and extreme drought was found to be widespread during post-monsoon months. The current work focuses on identifying and classifying drought spells with their severity extent for studying impacts of drought on the hydrological regimes in a longer perspective with SPI values below −1.5 in western India.

Using Environmental Tracers to Characterize Groundwater Flow Mechanisms in the Fractured Crystalline and Karst Aquifers in Upper Crocodile River Basin, Johannesburg, South Africa

Environmental isotope tracers were applied in the Upper Crocodile River Basin, Johannesburg, South Africa, to understand the groundwater recharge conditions, flow mechanisms and interactions between surface and subsurface water. Stable isotope analysis indicated that recharge into the fractured quartzite aquifer occurs through direct mechanisms. The high variability in the stable isotope signature of temporal samples from Albert Farm spring indicated the importance of multiple samples for groundwater characterization, and that using a single sample may be yielding biased conclusions. The observed inverse relationship between spring discharge and isotope signature indicated the traces of rainfall amount effect during recharge, thereby suggesting piston groundwater flow. It is deduced that a measured discharge value can be used in this relationship to calculate the isotopic signature, which resembles effective rainfall. In the shallow alluvial deposits that overlie the granitic bed-rock, piezometer levels and stable isotopes revealed an interaction between Montgomery stream and interflow, which regulates streamflow throughout the year. This suggests that caution should be taken where hydrograph separation is applied for baseflow estimates, because the stream flow that overlies such geology may include significant interflow. The hydrochemistry evolution was observed in a stream fed by karst springs. As pH rises due to CO2 degassing, CaCO3 precipitates, thereby forming travertine moulds. The values of saturation indices that were greater than zero in all samples indicated supersaturation by calcite and dolomite and hence precipitation. Through 14C analysis, groundwater flow rate in the karst aquifer was estimated as 11 km/year, suggesting deep circulation in karst structures.

Groundwater pumping modeling for the sustainable management of urban water supply in Faisalabad city, Pakistan

Groundwater is considered as the primary source of urban water supply in major cities of the world. Rapid industrial development and increase in population have deteriorated the quality of groundwater of Faisalabad, Pakistan. The overexploitation of groundwater caused depletion of groundwater level, and evaluation of groundwater status has become critical for the sustainability of urban water supply. This paper’s main objective is to present the overexploitation effect on aquifer based on historical and existing groundwater situations, and future groundwater conditions are projected based on six different scenarios. The transient groundwater model was developed coupling Groundwater Vista with MODFLOW to simulate the impact of groundwater pumping on the Chenab River’s bed well field. Water table was calibrated and validated for 13 years (1992 to 2005) and 5 years (2006 to 2010), respectively, and model performance evaluation indicators, represented the model’s reliability for further application. Moreover, the steep gradient of the groundwater head contour was observed in the well-field’s southern area, and resultantly steady-state condition has been established. Future urban water supply conditions were projected by implementing six scenarios based on the groundwater pumping system’s existing capacity for 2030. With 90% pumping capacity, the system forecasted a decline in the water table from 0.6 to 1.3 m year−1, respectively. Groundwater recharge conditions evaluated and forecast results represented a drop of 0.45 m year−1 till 2030 during optimization. Factual and detailed information is projected for future scenarios based on existing developed models that explain groundwater pumping strategies for sustainable urban water supply management.

Numerical Modelling of the Mulino Delle Vene Aquifer (Northern Italy) as a Tool for Predicting the Hydrogeological System Behavior under Different Recharge Conditions

Water scarcity periods will increase in frequency and magnitude in the near future, especially in Mediterranean regions, and proper groundwater management has been recognized as a key issue to mitigate possible impacts. In this context, numerical models acquire a special relevance to quantify the availability of water resources and predict their behavior under changing climate conditions. This work shows the procedure followed to model a mountainous fractured aquifer located in the northern Apennines (Italy) using an open source code. This aquifer feeds springs with an average discharge of about 96.8 L/s. Even though they are not exploited at the moment, these springs might represent a relevant resource of freshwater for public water supply and are essential for ecosystem sustainment. The main limitation faced to model the aquifer in a realistic way is the lack of data, which hinders the calibration of the model. A nonconventional procedure was followed to obtain information on the hydraulic parameters. The hydraulic conductivity is computed from a steady-state calibration for which a limited number of groundwater head observations are available, whilst information concerning the storage coefficient is obtained analytically from the spring discharge recession curve. Finally, the model is used for predicting the system behavior under different groundwater recharge scenarios. Numerical simulations and analytical approximations reveal that the studied aquifer can provide fresh water under different groundwater recharge conditions and has the capacity to smooth the effects of short drought periods, representing an option for water management strategies in the region.

Karst Landscape and Development Features of the Cambrian Ordovician Period in Huainan Region

Huainan is located at the boundary between north and south of China. Due to its unique geotectonic location and long geological evolution history, Huainan has formed a special karst landform. The karst landscape and karst development process of the Cambrian Ordovician in this area are analyzed from the aspects of stratigraphic distribution, crustal movement evolution and groundwater recharge conditions. It is concluded that large karst caves are developed in the karst multi-shun layer in the study area, in carbonate rocks. The surface development of the joint fissures is mostly filled with calcite, the erosive gully is developed in the concentrated area of the flowing water, and the karst landscape such as the beaded karst is developed near the fault zone.

Tracing groundwater recharge conditions based on environmental isotopes and noble gases, Lom depression, Bulgaria

Study regionLom depression, Bulgaria. Study focusA multi-tracer investigation was applied to identify the recharge conditions and isotope hydrological character of four aquifers in the Lom depression (Northwest Bulgaria) using environmental isotopes (δ18O, δ2H, δ13C, 3H, 14C) and noble gases. The radiocarbon age model of Ingerson and Pearson was used to estimate the mean residence time of groundwater samples from four aquifers (Dacian, Pontian, Meotian, Sarmatian). Our study focuses on the study of recharge conditions and provides an additional information to hydrodynamic understanding of the four aquifers. New hydrological insights for the regionThe mean residence time of groundwater samples represent the last twelve thousand years. In addition to a recently recharged groundwater sample, some samples represent the early Holocene and samples closely correspond to the late Pleistocene or the transition time between the early Holocene – late Pleistocene. The lower noble-gas recharge temperature values may indicate that the recharge occurred during the Late Glacial–Holocene climatic transition. These data can also be used to verify the existence of paleowater from the Pontian and Sarmatian aquifers on a trend of the mean residence time of older water heading north away from the study area. Besides the paleoclimatological investigation, it was determined that the Pontian aquifer has no hydraulic connection with the Danube River. The sandy layers and lenses forming the Dacian aquifer are apparently hydraulically isolated and therefore have high degree of heterogeneity.

Multi-tracing of recharge seasonality and contamination in groundwater: A tool for urban water resource management

In this study, sources of recharge and contamination in urban groundwater and in groundwater underneath a forest in the same aquifer were determined and compared. Data on hydro-chemical parameters and stable isotopes of water were collected in urban and forest springs in the Kharkiv region, Ukraine, over a period of 12 months. Groundwater transit time and precipitation contribution were calculated using hydrogeological data and stable isotopes of water to delineate groundwater recharge conditions. Hydro-chemical data, stable isotopes and emerging contaminants were used to trace anthropogenic groundwater recharge and approximate sewage and tap water contributions to the aquifer. The results indicated that each spring had unique isotopic signatures that could be explained by recharge conditions, groundwater residence time, and specific mixing patterns with sewage and water leaks. Elevated nitrate content, stable isotopes of nitrate, and the presence of emerging pollutants (mainly illicit drugs) in most of the urban springs confirmed mixing of urban groundwater with sewage leaks. These leaks amounted to up to 25% of total recharge and exhibited seasonal variations in some springs. Overall, the results show that urban groundwater receives variable seasonal contributions of anthropogenic components that increase the risk to the environment and human health, and reduce its usability for drinking water production. The multi-tracing approach presented can be useful for other cities worldwide that have similar problems of poor water management and inadequate sewage and water supply infrastructure.

Hydrogeological characteristics of the Omaruru Delta Aquifer System in Namibia

Sustainable utilization of groundwater in parts of hyper-arid Sub-Saharan Africa, like the Namib Desert, is always a challenge due to lack of resources and data. For the Omdel Aquifer in the Omaruru catchment, Namibia, issues to investigate include the lack of information on the geology and hydrogeological setting, the hydraulic properties and geometry of the aquifer at the inflow and outflow sections, groundwater recharge conditions upstream of the aquifer, and the impact of artificial recharge. In this desert environment, the methods applied are hydrogeological surveys and site visits, together with interpretation of geological, hydrological and geomorphological data from investigations carried out to define the hydrogeological characteristics of the Omdel Aquifer. The bedrock geometry of the aquifer indicates that the Main channel (one of four palaeochannels) is the largest reservoir of stored fresh groundwater, estimated at 133 Mm3, and it is deeper than the other three channels, with an average sediment thickness of 80 m. All groundwater chemistry facies of the selected boreholes tapping the Omdel Aquifer reveal a NaCl character, indicating a coastal environment. The yield of the Omdel Aquifer is estimated to have increased from 2.8 Mm3/year before construction of a recharge enhancement dam to 4.6 Mm3/year after the construction. This paper focuses on the understanding of hydrogeological characteristics of the Omaruru Delta Aquifer System in terms of groundwater recharge and discharge, groundwater dynamics within the aquifer and groundwater chemistry, in order to assess whether the current abstractions are operating within the hydrogeological limits of sustainability.

Characterisation of groundwater recharge conditions and flow mechanisms in bedrock aquifers of the Johannesburg area, South Africa

Groundwater is the major source of water and a critical resource for socioeconomic development in semi-arid environments like the Johannesburg area. Environmental isotopes are employed in this study to characterise groundwater recharge and flow mechanisms in the bedrock aquifers of Johannesburg, which is known for polluted surface water. With the exception of boreholes near the Hartbeespoort Dam, groundwater in the study area was derived from meteoric water that has undergone some degree of evaporation before recharge, possibly via diffuse mechanisms. Boreholes that tap groundwater from the Transvaal Supergroup Formation show depletion in δ18O and δ2H values. This is attributed to diffuse recharge through weathering fractures at high elevation that are undergoing deep circulation or recharge from depleted rainfall from the high-latitude moisture sources. The influence of focused recharge from the Hartbeespoort Dam was observed in the boreholes north of the dam, possibly as a result of the north–south trending fault lines and the north-dipping fractures in the bedding planes of quartzites. This is also supported by a reservoir water budget method which indicated a mean annual net flux of 2,084,131 m3 from Hartbeespoort Dam recharging groundwater per annum. Using tritium in the dam and boreholes located at 750 m and 5400 m downstream, average groundwater flow velocity was estimated as 202 m/year. An open system was observed in shale, andesite and granitic-gneiss aquifers indicating soil CO2 as a dominant source of carbon (δ13C) in groundwater. A closed system was also observed in dolomitic aquifers indicating carbonate dissolution as the predominant source of carbon.

Fifty years of groundwater science in Korea: a review and perspective

We present a review of groundwater studies over the past 50 years (1968–2017) in Korea. With economic and agricultural growth, water demand has been expanding, and groundwater development is gradually increasing. Initially, groundwater studies were largely focused on using pumping and slug tests to understand aquifers in Korea. However, the interest has expanded to groundwater monitoring and data analyses, as many national and local networks for monitoring groundwater quantity and quality have been implemented. Frequent severe droughts in recent decades have led to research on the design and pilot tests for managed aquifer recharge, especially on the volcanic island of Jeju and agricultural areas. As groundwater development and its use has increased, groundwater contamination is becoming a public grievance. Thus, effective investigation of contaminated groundwater and its efficient remediation are big issues in the Research and Development (R & D) sector. The recent Gyeongju earthquake posed an additional challenge for Korean groundwater scientists to develop a method to predict earthquakes using groundwater monitoring. Furthermore, changes in precipitation patterns caused by the changing climate aggravate groundwater recharge conditions. The country has seen many academic and technical achievements in groundwater science, but many issues remain to be resolved in the near future.

The discovery of surface runoff in the megadunes of Badain Jaran Desert, China, and its significance

The Badain Jaran Desert exhibits the greatest difference in altitude of all of the world’s deserts. On the slopes of megadunes in the desert, there are physical and chemical deposits produced by surface runoff. In addition, we have observed rarely-seen infiltration-excess surface runoff in the megadune depressions as well as spring streams at the base of megadunes. We used electron microscopy, energy spectrum analysis, infiltration experiments, moisture content determinations and grain-size analysis to study the mineral and chemical composition of the runoff precipitates, and grain-size of the deposits associated with the runoff, together with the hydrological balance in the megadune area, and the atmospheric precipitation mechanism responsible for groundwater recharge and for supplying water to lakes. The observations of shallow runoff and infiltration-excess surface runoff indicate the occurrence of strong and effective precipitation in summer, which would provide an important source for groundwater recharge. Several lines of evidence, such as the physical and chemical deposits resulting from shallow subsurface runoff, spring streams, infiltration-excess runoff, and gravity capillary water with a moisture content of 3–6%, demonstrate that precipitation reaches the base of the megadunes through infiltration and subsequently becomes groundwater. The chemical deposits, such as newly-formed calcite and gypsum, and gray-black physical deposits, as well as different stages in the development of fan-shaped landforms resulting from shallow subsurface runoff, indicate that groundwater recharge in the area is the result of long-term precipitation, rather than intermittent individual major rainfall events. Fine sand layers with a low infiltration capacity lead to subsurface runoff emerging at the ground surface. Five factors play an important role in maintaining a positive water balance and in replenishing groundwater via rainfall: effective rainfall as a water source, the high infiltration capacity of the sands enabling rainfall to rapidly become capillary water in the dunes, low evapotranspiration rates due to the sparse vegetation, the fact that the depth of the sand layer influenced by evaporation is shallow enough to maximize the deep infiltration of rainfall, and rapidly-moving gravity capillary water in the sandy dunes. These five factors together constitute a mechanism for groundwater recharge from rainfall, and explain the origin of the groundwater and lakes in the area. Our findings represent a significant advance in research on the hydrological cycle, including groundwater recharge conditions and recharge mechanisms, in this desert region.

New perspectives for noble gases in oceanography

AbstractConditions prevailing in regions of deep water formation imprint their signature in the concentrations of dissolved noble gases, which are conserved in the deep ocean. Such “recharge conditions” including temperature, salinity, and interactions with sea ice are important in view of ocean‐atmosphere CO2 partitioning. Noble gases, especially the temperature sensitive Kr and Xe, are well‐established tracers to reconstruct groundwater recharge conditions. In contrast, tracer oceanography has traditionally focused on He isotopes and the light noble gases Ne and Ar, which could be analyzed at the required high precision. Recent developments of analytical and data interpretation methods now provide fresh perspectives for noble gases in oceanography.

Numerical analysis of groundwater flow and potential in parts of a crystalline aquifer system in Northern Ghana

The groundwater flow system in a crystalline aquifer system in parts of Northern Ghana was simulated and calibrated under steady-state conditions. The objective was to estimate the regional distribution of a key aquifer hydraulic parameter (the hydraulic conductivity) and recharge and also to predict possible effects of different abstraction and groundwater recharge scenarios on the sustainability of groundwater resources in the area. The study finds that the hydraulic conductivity field is quite homogeneous and has values ranging between 1.70 and 2.24 m/day. There is an apparent dominance of regional groundwater flow systems compared to local flow systems. This is probably attributed to the homogeneity in the hydraulic conductivity field and the absence of complex local relief. Estimated groundwater recharge ranges between 0.036 and 0.164 m/yr representing 3.6 and 16.4 % of the local annual precipitation, respectively. Substantial subsurface inflows and outflows have also been simulated through general head boundaries. The simulation suggests that under the current conditions of groundwater recharge estimated at calibration, the system can sustain increment in groundwater abstraction by up to 50 % without any significant changes in the groundwater flow geometry and drawdowns in the hydraulic heads. However, significant drawdowns will be expected in the wake of 100 % increment in groundwater abstraction and a reduction in recharge by 10 % during the 20-year period. Under such conditions, the flow geometry will significantly be altered and a reversal in groundwater flow will be observed.