Characterization of the groundwater flow regime and hydrochemistry of groundwater from the Buem formation,Eastern Ghana

This study demonstrates the application of multivariate statistical methods in definition of groundwater recharge and discharge areas in a sedimentary basin in Ghana. Q‐mode hierarchical cluster analysis (HCA) was applied to 57 hydrochemical data from the Buem formation in the northern part of the Volta Region in Ghana. R‐mode HCA and R‐mode factor analysis were then applied to the same dataset to reveal the processes controlling the hydrochemistry of groundwater from this hydrogeological formation. Results of both the Q‐ and R‐mode analyses were backed by graphical methods. The analyses revealed two major water types, differentiated by salinity levels into four spatial groundwater associations. The characteristics of the four groundwater types are discussed. The recharge areas are characterized by Ca? HCO₃ low salinity waters which evolve through rock–water interactions to Na? HCO₃ high salinity waters in the discharge areas. This study finds that the hydrochemistry of groundwater from this formation is mainly controlled by the weathering of minerals, principally silicates in the aquifer matrix. The effects of the chemistry of recharging precipitation are higher in the recharge areas, while mineral weathering tends to be severe close to the discharge areas in the groundwater flow regime. All the four spatial groundwater associations have low sodium content, but salinity levels increase towards the discharge areas, such that some of wells in the discharge areas may not be acceptable for irrigation on grounds of high salinities which might affect the osmotic potentials of plants. Copyright © 2011 John Wiley & Sons, Ltd.     

Water source characterization through spatiotemporal patterns of major,minor and trace element stream concentrations in a complex,mesoscale German catchment

The link between spatiotemporal patterns of stream water chemistry and catchment characteristics for the mesoscale Dill catchment (692 km²) in Germany is explored to assess the catchment scale controls on water quality and to characterize water sources. In order to record the spatiotemporal pattern, ‘snapshot sampling’ was applied during low, mean and high flow, including 73 nested sites throughout the catchment. Water samples were analysed for the elements Li, B, Na, Mg, Al, K, Ca, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Rb, Sr, Mo, Ba, Pb and U using inductively‐coupled‐plasma mass spectrometry, and for electric conductivity and pH. Principle component analysis and hierarchical cluster analysis were used to find typical element associations and to group water samples according to their hydrochemical fingerprints. This revealed regional hydrochemical patterns of water quality which were subsequently related to catchment attributes to draw conclusions about the controls on stream chemistry. It was found that various lithologic signals and anthropogenic point source inputs controlled the base flow hydrochemistry. During increased flows, stream waters were diluted causing additional hydrochemical variability in response to heterogeneous precipitation inputs and differences in aquifer storage capacities. The hydrochemical patterns further displayed in‐stream mixing of waters. This implied, that stream waters could be apportioned to the identified water sources throughout the catchment. The basin‐wide hydrochemical variability has the potential to outrange the tracer signatures typically inferred in studies at the hillslope scale and is able to strongly influence the complexity of the catchment output. Both have to be considered for further catchment scale tracer and modelling work. Despite the likelihood of non‐conservative behaviour, the minor and trace elements enhanced the rather qualitative discrimination of the various groundwater types, as the major cations were strongly masked by point source inputs. Copyright © 2007 John Wiley & Sons, Ltd.     

Assessment of seasonal groundwater quality and potential saltwater intrusion: a study case in Urmia coastal aquifer (NW Iran) using the groundwater quality index (GQI) and hydrochemical facies evolution diagram (HFE-D)

Coastal aquifers are at threat of salinization in most parts of the world. This work investigated the seasonal hydrochemical evolution of coastal groundwater resources in Urmia plain, NW Iran. Two recently proposed methods have been used to comparison, recognize and understand the temporal and spatial evolution of saltwater intrusion in a coastal alluvial aquifer. The study takes into account that saltwater intrusion is a dynamic process, and that seasonal variations in the balance of the aquifer cause changes in groundwater chemistry. Pattern diagrams, which constitute the outcome of several hydrochemical processes, have traditionally been used to characterize vulnerability to sea/saltwater intrusion. However, the formats of such diagrams do not facilitate the geospatial analysis of groundwater quality, thus limiting the ability of spatio-temporal mapping and monitoring. This deficiency calls for methodologies which can translate information from some diagrams such Piper diagram into a format that can be mapped spatially. Distribution of groundwater chemistry types in Urmia plain based on modified Piper diagram using GQI_Piper(mix) and GQI_Piper(dom) indices that Mixed Ca–Mg–Cl and Ca-HCO₃ are the dominant water types in the wet and dry seasons, respectively. In this study, a groundwater quality index specific to seawater intrusion (GQI_SWI) was used to check its efficiency for the groundwater samples affected by Urmia hypersaline Lake, Iran. Analysis of the main processes, by means of the Hydrochemical Facies Evolution Diagram (HFE-Diagram), provides essential knowledge about the main hydrochemical processes. Subsequently, analysis of the spatial distribution of hydrochemical facies using heatmaps helps to identify the general state of the aquifer with respect to saltwater intrusion during different sampling periods. The HFE-D results appear to be very successful for differentiating variations through time in the salinization processes caused by saltwater intrusion into the aquifer, distinguishing the phase of saltwater intrusion from the phase of recovery, and their respective evolutions. Both GQI and HFE-D methods show that hydrochemical variations can be read in terms of the pattern of saltwater intrusion and groundwater quality status. But generally, in this case (i.e. saltwater and not seawater intrusion) the HFE-D method was presented better efficiency than GQI method (including GQI_Piper and GQI_SWI).     

The seasonal variation of streamwater chemistry in three forested Mediterranean catchments

Streamwater chemistry is described for three streams draining undisturbed, evergreen broad-leaved forested catchments on phyllites in NE Spain: two streams with no or negligible flow in summer are located in the Prades massif, and one perennial stream is in the wetter Montseny mountains. Weekly data for a study period of 2–4 years are provided to (1) describe the seasonal variations in streamwater chemistry, (2) analyse the relationship between stream discharge and solute concentrations using a two-component mixing model and (3) search for patterns of temporal variation in stream solute concentrations after discounting the effects of discharge. At Prades, concentrations of all analysed ions, except NO⁻₃, showed marked seasonal variations in stream water, whereas at Montseny only ions related to mineral weathering (HCO⁻₃, Na⁺, Ca²⁺ and Mg²⁺) showed strong seasonality. Ion concentrations were more closely dependent on instantaneous discharge at Montseny than at Prades. The residuals of the relationship between solute concentrations and discharge retained a strong seasonality at Prades, but not at Montseny. These differences are related to the major hydrochemical processes that determine the streamwater chemistry at each site. The same processes are probably operative in the three catchments, but are of varying relative importance. At Montseny, the mixing of waters of different chemical composition seems to be the major process controlling streamwater chemistry, although the soilwater end-member composition predicted by the mixing model applied did not match the measured soilwater chemistry. In the drier Prades catchments, the two major hydrochemical processes determining the seasonal variation of streamwater chemistry are (1) the restart of flow after the summer drought, which flushes out the solutes accumulated during the dry period, and (2) the seasonal changes in groundwater chemistry that result from the interplay of water residence time, temperature and CO₂ partial pressure. In Mediterranean catchments with relatively high precipitation, such as Montseny, the seasonal variation in the streamwater chemistry is largely determined by the same processes as at humid-temperate sites, whereas in drier Mediterranean catchments, such as Prades, the major hydrochemical processes are clearly distinct.     

An Application of HFE-D for Evaluating Sea Water Intrusion in Coastal Aquifers of Southern Vietnam

The coastal aquifers and inland waters of the Long Xuyen Quadrangle and Ca Mau Peninsula of southern Vietnam have been significantly impacted by sea water intrusion (SI) as a result of recent anthropogenic activities. This study identified the evolution and spatial distribution of hydrochemical conditions in coastal aquifers at this region using Hydrochemical Facies Evolution Diagram (HFE-D) and Geographical Information System mapping. Hydraulic heads and water chemistry were measured at 31 observation wells in four layered aquifers during dry and rainy seasons in early (2005), and more recent (2016), stages of agricultural development. Hydrochemical facies associated with intrusion or freshening stages were mapped in each aquifer after assigning mixing index values to each facies. The position of groundwater freshening and SI phases differed in Holocene, Upper Pleistocene, Middle Pleistocene, and Lower Pleistocene aquifers. The geographic position of freshening and intrusion fronts differ in dry and rainy seasons, and shifted after 11 years of groundwater abstraction in all four aquifers. The spatial and temporal differences in hydrochemical facies distributions according to HFE-D reflect the relative impact of SI in the four aquifers. The study results provide a better understanding of the evolution of groundwater quality associated with SI in a peninsular coastal aquifer system, and highlight the need for improving groundwater quality and management in similar coastal regions.     

Evaluation of groundwater hydrochemical characteristics and mixing behavior in the Daying and Qicun geothermal systems,Xinzhou Basin

This paper examines groundwater hydrochemical characteristics during mixing between thermal and non-thermal groundwater in low-to-medium temperature geothermal fields. A case study is made of Daying and Qicun geothermal fields in the Xinzhou basin of Shanxi province, China. The two geothermal fields have similar flow patterns, with recharge sourced from precipitation in mountain areas heated through a deep cycle, before flowing into overlying Quaternary porous aquifers via fractures. Hydrochemical features of 60 ground- and surface water samples were examined in the context of hydrogeologic information. The average temperatures of the deep geothermal reservoirs are estimated to be 125 °C in Daying field, and 159 °C in Qicun field, based on Na–K–Mg geothermometry, while slightly lower estimates are obtained using silica geothermometers. Hydrochemical features of thermal water are distinct from cold water. Thermal groundwater is mainly Cl·SO₄–Na type, with high TDS, while non-thermal groundwater is mostly HCO₃–Ca·Mg and HCO₃–Ca type in the Daying and Qicun regions, respectively. Hydrogeochemical processes are characterized by analyzing ion ratios in various waters. Higher contents of some minor elements in thermal waters, such as F, Si, B and Sr, are probably derived from extended water–rock interaction, and these elements can be regarded as indicators of flow paths and residence times. Mixing ratios between cold and thermal waters were estimated with Cl, Na, and B concentrations, using a mass balance approach. Mixing between ascending thermal waters and overlying cold waters is extensive. The proportion of water in the Quaternary aquifer derived from a deep thermal source is lower in Daying geothermal field than in Qicun field (5.3–7.3% vs. 6.3–49.3%). Mixing between thermal and non-thermal groundwater has been accelerated by groundwater exploitation practices and is enhanced near faults. Shallow groundwater composition has also been affected by irrigation with low-temperature thermal water.     

The origin and the formation laws of groundwater and mine water chemistry in the Eastern Donets Basin

Successive classification modeling of multivariate observations was used to objectively identify and quantitatively describe four major hydrogeochemical directions of changes in mine water chemistry and two hydrogeochemical trends for groundwater in the Eastern Donets Basin (two types of vertical hydrogeochemical zonality). Processes along the first hydrogeochemical direction result in the formation of acid sulfate mineralized water, those along the second direction form neutral chloride-sulfate waters, those along the third direction form sulfate-chloride and chloride, and those along the fourth direction form soda, hydrocarbonate-sulfate-chloride waters; the processes of sulfur oxidation and water mixing play the main role in the formation of water chemistry. In the case of groundwater, the first trend (direct zonality) manifests itself in the formation of highly mineralized chloride sodium water (mineralization of up to 60–80 g/l), while the second trend (inverse zonality) results in the formation of moderately mineralized soda hydrocarbonate-chloride and chloride sodium water (1–3 g/l). The genesis of water chemistry is explained with the engagement of infiltration, sedimentation, and evaporation-condensation hypotheses. Giving preference to the evaporation-condensation genesis of groundwater chemistry according to the second trend, the authors came to the conclusion that the Eastern Donets Basin is promising in terms of oil and gas accumulations.     

Application of Multivariate Statistical Techniques for Characterization of Groundwater Quality in the Coastal Aquifer of Nador,Tipaza (Algeria)

The study focuses on the characterization of the groundwater salinity on the Nador coastal aquifer (Algeria). The groundwater quality has undergone serious deterioration due to overexploitation. Groundwater samplings were carried out in high and low waters in 2013, in order to study the evolution of groundwater hydrochemistry from the recharge to the coastal area. Different kinds of statistical analysis were made in order to identify the main hydrogeochemical processes occurring in the aquifer and to discriminate between different groups of groundwater. These statistical methods provide a better understanding of the aquifer hydrochem-istry, and put in evidence a hydrochemical classification of wells, showing that the area with higher salinity is located close to the coast, in the first two kilometers, where the salinity gradually increases as one approaches the seaside and suggests the groundwater salinization by sea-water intrusion.     

Hydrogeochemistry of thermal and mineral water springs of the Azores archipelago (Portugal)

Mineral and thermal water chemistry from the Azores archipelago was investigated in order to discriminate among hydrochemical facies and isotopic groups and identify the major geochemical processes that affect water composition. A systematic geochemical survey of mineral and thermal water chemistry was carried out, incorporating new data as well as results from the literature. The Azores are a volcanic archipelago consisting of nine islands and samples were collected at São Miguel, Graciosa, Faial, São Jorge, Pico and Flores islands. Hydrothermal manifestations show the effects of active volcanism on several islands. Discharges are mainly related to active Quaternary central volcanoes, of basaltic to trachytic composition, but also some springs are related to older dormant or extinct volcanoes.Multivariate analysis – principal component and cluster analysis – enables classification of water compositions into 4 groups and interpretation of processes affecting water compositions. Groups 1 and 2 discharge from perched-water bodies, and mostly correspond to Na–HCO₃ and Na–HCO₃–Cl type waters. These groups comprise of cold, thermal (27 °C–75 °C) and boiling waters (92.2 °C–93.2 °C), with a wide TDS range (77.3–27, 145.7 mg/L). Group 3 is made of samples of dominated Na–SO₄ from very acid boiling pools (pH range of 2.02–2.27) which are fed by steam-heated perched-water bodies. Group 4 is representative of springs from the basal aquifer system and corresponds to Na–Cl type fluids, with compositions dominated by seawater.Results are used to further develop a conceptual model characterizing the geochemical evolution of the studied waters. Mineral and thermal waters discharging from perched-water bodies are of meteoric origin and chemically evolve by absorption of magmatic volatiles (CO₂) and by a limited degree of rock leaching. Existing data also suggest mixture between cold waters and thermal water. Water chemistry from springs that discharge from the basal aquifer system evolves by mixing with seawater; although, processes such as absorption of magmatic volatiles (CO₂), rock leaching and mixture with hydrothermal waters are not excluded by the data because the actual composition of these waters deviates from that expected considering only conservative mixing between fresh and seawater.     

Groundwater—Surface waters interactions at slope and catchment scales: implications for landsliding in clay‐rich slopes

Understanding water infiltration and transfer in soft‐clay shales slopes is an important scientific issue, especially for landsliding. Geochemical investigations are carried out at the Super‐Sauze and Draix‐Laval landslides, both developed in the Callovo‐Oxfordian black marls, with the objective to define the origin of the groundwater. In situ investigations, soil leaching experiments and geochemical modeling are combined to identify the boundaries of the hydrological systems. At Super‐Sauze, the observations indicate that an external water flow occurs in the upper part of the landslide at the contact between the weathered black marls and the overlying formations, or at the landslide basement through a fault network. Such external origin of water is not observed at the local scale of the Draix‐Laval landslide but is detected at the catchment scale with the influence of deep waters in the streamwater quality of low river flows. Hydrogeological conceptual models are proposed emphasizing the role of the interactions between local (slope) and regional (catchment) flow systems. The observations suggest that this situation is a common case in the Alpine area. Expected consequences of the regional flows on slope stability are discussed in term of rise of pore water pressures and physicochemical weathering of the clay shales.     

Formation of High-Alkali Groundwater in Upper Aquifers

Generalized observational data on groundwater chemistry and the results of modeling geochemical processes allowed us to establish that the formation of high-carbonate alkaline waters follows two ways, i.e., calcium and soda. It is shown that the formation of alkaline waters in semiarid and arid zones can be facilitated by acid atmospheric precipitation, which forms the concentration of Ca in groundwater sufficiently high to initiate ion exchange processes resulting in the formation of H₂CO₃–Na waters. Ion exchange is shown to be a boundary process, which facilitates the transition from calcium to soda way of groundwater metamorphization with subsequent increase in the carbonate content and alkalinity of groundwater.     

Modelling Groundwater Fluctuations and the Frequency of Movement of a Landslide in the Terres Noires Region of Barcellonnette (France)

Onn the basis of measurements of hydrological parameters and field monitoring of a landslide in the Terres Noires in the basin of Barcelonnette (France), a hydrological model was developed, describing groundwater fluctuations in relation to precipitation. These groundwater fluctuations can be used as input to a stability model in order to assess the temporal frequency of instability of the landslide. The calculated groundwater fluctuations, which can forecast years with landslide incidents, were roughly calibrated against dated movements obtained by dendrochronological research. The hydrological system of the landslide can be understood through a three-layer sequence: a rather permeable colluvial top layer underlain by a less permeable colluvial second layer, both overlying the nearly impermeable in situ non-weathered black marls (Terres Noires). The mean Ksat value for the matrix flow in the top layer is 15·7 cm/day and in the underlying layer 0·7 cm/day. However, water fluxes in these layers occur by two types of groundwater flow: matrix flow obeying Darcy's law, and more rapid gravitational flow through preferential flow paths, increasing the conductivity by a factor of 10 to 100, as cube method Ksat measurements revealed. The model shows long-term yearly fluctuations of the phreatic surface, with peaks at the end of winter, as well as at the beginning of spring, and minimum values during the dry summer period. These long-term fluctuations are explained by the high drainage capacity of the top colluvial layer and the relatively low vertical water fluxes within the underlying colluvial layer. The model shows that maximum critical peak height conditions of the groundwater, causing instability, occur in wet seasons, with at least six consecutive months with high amounts (more than 60 mm) of precipitation. © 1997 by John Wiley & Sons, Ltd.     

Hydrological processes in the different landscape zones of alpine cold regions in the wet season,combining isotopic and hydrochemical tracers

Studies on hydrological processes are often emphasized in resource and environmental studies. This paper identifies the hydrological processes in different landscape zones during the wet season based on the isotopic and hydrochemical analysis of glacier, snow, frozen soil, groundwater and other water sources in the headwater catchment of alpine cold regions. Hydrochemical tracers indicated that the chemical compositions of the water are typically characterized by: (1) Ca? HCO₃ type in glacier snow zone, (2) Mg? Ca? SO₄ type for surface runoff and Ca? Mg? HCO₃ type for groundwater in alpine desert zone, (3) Ca? Mg? SO₄ type for surface water and Ca? Mg? HCO₃ type for groundwater in alpine shrub zone, and (4) Ca? Na? SO₄ type in surface runoff in the alpine grassland zone. The End‐Members Mixing Analysis (EMMA) was employed for hydrograph separation. The results showed that the Mafengou River in the wet season was mainly recharged by groundwater in alpine cold desert zones and shrub zones (52%), which came from the infiltration and transformation of precipitation, thawed frozen soil water and glacier‐snow meltwater. Surface runoff in the glacier‐snow zone accounted for 11%, surface runoff in alpine cold desert zones and alpine shrub meadow zones accounted for 20%, thawed frozen soil water in alpine grassland zones accounted for 9% of recharge and precipitation directly into the river channel (8%). This study suggested that the whole catchment precipitation did not produce significant surface runoff directly, but mostly transformed into groundwater or interflow, and finally arrived in the river channel. Copyright © 2011 John Wiley & Sons, Ltd.     

Regional changes in groundwater flow patterns and effects on groundwater composition

Wetlands on the Vecht river plain in the Netherlands are threatened by pollution of ground water on the adjacent ridge ‘Het Gooi’. To assess the impact of this pollution, information is needed on the present groundwater flow pattern and hydrochemical processes occurring during flow. In the determination of hydrochemical processes past changes in flow patterns must be taken into consideration.

Over the past 600 years impoldering and groundwater extraction have induced important hydrological changes in the study area. Exercises with a two-dimensional finite difference groundwater model were used to study the effects of these changes on regional groundwater flow patterns. Steady-state simulations along a vertical section were carried out for four different points in time, namely, the 14th century, 1885, 1941 and 1985. Changes in flow patterns are inferred from a comparison of the steady-state simulations. The results indicate that groundwater flow changed from a simple pattern under natural conditions to a complex flow pattern dominated by artificially man-controlled hydraulic heads at present.

The computer simulations are used to estimate the effect of changes in flow patterns on regional groundwater composition. Data on the distribution of chloride and oxygen-18 in ground water provide a verification of the estimated effects and information on the present position of the fresh-brackish groundwater interface in the study area. Isochrones calculated by the model are used to estimate the position of this front where data on water composition are absent. The future displacement of the fresh-brackish groundwater front is inferred from the position of successive isochrones, assuming that the present flow pattern will remain in steady state.

The computer simulations provide a general framework for the determination of hydrochemical processes in future studies addressing the impact of groundwater pollution on wetlands in the river plain.     

THE POSSIBILITIES OF GEOPHYSICAL METHODS APPLIED FOR INVESTIGATING THE IMPACT OF MAN ON THE GEOLOGICAL MEDIUM*

Geophysical methods can be applied to investigate the harmful effect of man's activities on the environment: the study of specific electrical resistivities and natural electric fields of filtrational origin makes it possible to control the penetration of exogenic pollutants into soil as well as desalinization and secondary salinization of soils; electrometric and seismometric methods allow to observe the groundwater level near water reservoirs thus evaluating the harmful effect of backing up natural groundwater flow; contrasting properties of bedrocks and rocks in a landslide body permit application of seismic and electrical prospecting methods. Observation of the changes in specific electrical resistivities with time on the slopes of quarries is an effective method of assessing slope stability and predicting landslide hazard. Mining activities, groundwater pumping, and oil extraction are the main causes of endogenic pollution of geological medium; surface and borehole geophysical methods make it possible to assess vertical and horizontal displacements of the interfaces between salty and fresh subterranean waters resulting from an extensive exploitation of water supply sources; activation of geodynamic processes associated with mining activities is determined from the data of ‘regime’ electrometric, seismometric, gravimetric, and inclinometric observations. Geophysical methods are applied widely for studying the intensification of physico-geological processes under the impact of man. A specific object of electrometric investigations is degradation of permafrost and intensification of karst processes in soluble rocks. The principal advantage of geophysical investigations lies in the possibility of creating high spatial and temporal density of observations permitting an extensive employment of statistical methods in the assessment of the impact of man on the geological medium.     

Hydrochemical Analyses and Evaluation of Groundwater Resources of North Jordan

The hydrochemical analyses of twenty-three springs were used to determine the properties and types of groundwater of the Tertiary-Quaternary Aquifer of northern Jordan. The result shows that the geological formation influences the quality of the investigated groundwater more than the anthropogenic factors. The water of the Quaternary-Tertiary aquifer is enriched in Ca⁺⁺ due to the dissolution of the nearby carbonate rocks. The investigated water has a low EC values with Ca(Na)-HCO₃ water type. Most springs belong to this hydrochemical facies except Malka. Groundwater in the Malka wells has high salinity with NaCl waters and a strong Ca(Mg)-HCO₃ facies (900 to 1000 mg/l TDS). The area long-term hydrochemical data have been also evaluated; general trend of increase of the analyzed ion was observed. Bicarbonate represents the most abundant anion in the studied water, which exceeds the permissible limits. Nitrates (NO ₃ ^? ) also exceed the permissible limit and are the most common contaminant in the investigated water. Data on dissolved major and trace elements (K⁺, Na⁺, Mg²⁺, Ca²⁺, Cl^?, SO ₄ ^2? , Fe, Zn, Cu and Pb) in the investigated water revealed that the concentrations lie within the natural background range. The positive correlation values between various ions indicate that most of ions come from same lithological sources. According to the residual sodium carbonate, and EC values, the studied springs are suitable for agricultural purposes.     

Seawater intrusion into coastal aquifers

The hydrological, hydrophysical, and hydrochemical aspects of the interaction between marine waters and groundwater in the adjacent land territory as a manifestation of the general process of interaction between surface and subsurface waters. Most attention is concentrated on the marine water intrusion into aquifers. Recent achievements in the field of modeling seawater intrusion into coastal aquifers are reviewed.     

山西省4口井(泉)水化学特征与水氡映震效能研究

对山西4口水化学观测井（泉）及周边地表水进行水化学和氢氧同位素分析,利用Piper图、durov图、Na-K-Mg三角图等方法研究其水化学特征及成因,得出井（泉）水岩平衡程度、热储温度、地下水循环深度及地下水补给来源详情;分析了井（泉）水氡测项映震特征,应用水氡映震效果与水岩平衡程度、地下水循环深度表现出的特征,评价了地震监测效能。评价结果显示夏县井、奇村井优于临猗井,适于开展地震水化学观测;定襄泉应用该水化学方法评价尚存不足之处,需要探索适用于该类观测泉点的物理与化学相结合的评价方法。     

Origin and dynamics of groundwater salinity in the alluvial plains of western Delhi and adjacent territories of Haryana State,India

Groundwater salinity is a widespread problem and a challenge to water resources management. It is an increasing concern in the alluvial plains of Delhi and neighbouring Haryana state as well as a risk for agricultural production water supply and sustainable development. This study aims to identify potential sources of dissolved salts and the driving mechanisms of salinity ingress in the shallow aquifer. It combines a comprehensive review of environmental conditions and the analysis of groundwater samples from 25 sampling points. Major ions are analysed to describe the composition and distribution of saline groundwater and dissolution/precipitation dynamics. Density stratification and local upconing of saline waters were identified by multilevel monitoring and temperature logging. Bromide–chloride ratios hold information on the formation of saline waters, and nitrate is used as an indicator for anthropogenic influences. In addition, stable isotope analysis helps to identify evaporation and to better understand recharge processes and mixing dynamics in the study region. The results lead to the conclusion that surface water and groundwater influx into the poorly drained semiarid basin naturally results in the accumulation of salts in soil, sediments and groundwater. Human‐induced changes of environmental conditions, especially the implementation of traditional canal and modern groundwater irrigation, have augmented evapotranspiration and led to waterlogging in large areas. In addition, water‐level fluctuations and perturbation of the natural hydraulic equilibrium favour the mobilisation of salts from salt stores in the unsaturated zone and deeper aquifer sections. The holistic approach of this study demonstrates the importance of various salinity mechanisms and provides new insights into the interference of natural and anthropogenic influences. Copyright © 2011 John Wiley & Sons, Ltd.     

Joint interpretation of hydrological and geophysical data: electrical resistivity tomography results from a process hydrological research site in the Black Forest Mountains,Germany

The use of electrical resistivity tomography (ERT; non‐intrusive geophysical technique) was assessed to identify the hydrogeological conditions at a surface water/groundwater test site in the southern Black Forest, Germany. A total of 111 ERT transects were measured, which adopted electrode spacings from 0·5 to 5 m as well as using either Wenner or dipole‐dipole electrode arrays. The resulting two‐dimensional (2D) electrical resistivity distributions are related to the structure and water content of the subsurface. The images were interpreted with respect to previous classical hillslope hydrological investigations within the same research basin using both tracer methods and groundwater level observations. A raster‐grid survey provided a quasi 3D resistivity pattern of the floodplain. Strong structural heterogeneity of the subsurface could be demonstrated, and (non)connectivities between surface and subsurface bodies were mapped. Through the spatial identification of likely flow pathways and source areas of runoff, the deep groundwater within the steeper valley slope seems to be much more connected to runoff generation processes within the valley floodplain than commonly credited in such environmental circumstances. Further, there appears to be no direct link between subsurface water‐bodies adjacent to the stream channel. Deep groundwater sources are also able to contribute towards streamflow from exfiltration at the edge of the floodplain as well as through the saturated areas overlying the floodplain itself. Such exfiltrated water then moves towards the stream as channelized surface flow. These findings support previous tracer investigations which showed that groundwater largely dominates the storm hydrograph of the stream, but the source areas of this component were unclear without geophysical measurements. The work highlighted the importance of using information from previous, complementary hydrochemical and hydrometric research campaigns to better interpret the ERT measurements. On the other hand, the ERT can provide a better spatial understanding of existing hydrochemical and hydrometric data. Copyright © 2009 John Wiley & Sons, Ltd.