Aquifer Lithology Research Articles

The long-term impacts of anthropogenic and natural processes on groundwater deterioration in a multilayered aquifer

In many regions around the world, there are issues associated with groundwater resources due to human and natural factors. However, the relation between these factors is difficult to determine due to the large number of parameters and complex processes required. In order to understand the relation between land use allocations, the intrinsic factors of the aquifer, climate change data and groundwater chemistry in the multilayered aquifer system in Malaysia's Northern Kelantan Basin, twenty-two years hydrogeochemical data set was used in this research. The groundwater salinisation in the intermediate aquifer, which mainly extends along the coastal line, was revealed through the hydrogeochemical investigation. Even so, there had been no significant trend detected on groundwater salinity from 1989 to 2011. In contrast to salinity, as seen from the nitrate contaminations there had been significantly increasing trends in the shallow aquifer, particularly in the central part of the study area. Additionally, a strong association between high nitrate values and the areas covered with palm oil cultivations and mixed agricultural have been detected by a multiple correspondence analysis (MCA), which implies that the increasing nitrate concentrations are associated with nitrate loading from the application of N-fertilisers. From the process of groundwater salinisation in the intermediate aquifer, could be seen that it has a strong correlation the aquifer lithology, specifically marine sediments which are influenced by the ancient seawater trapped within the sediments.

Structural and Hydrogeological Controls on Hydrocarbon and Brine Migration into Drinking Water Aquifers in Southern New York.

Environmental concerns regarding the potential for drinking water contamination in shallow aquifers have accompanied unconventional energy development in the northern Appalachian Basin. These activities have also raised several critical questions about the hydrogeological parameters that control the naturally occurring presence and migration of hydrocarbon gases in shallow aquifers within petroliferous basins. To interrogate these factors, we analyzed the noble gas, dissolved ion, and hydrocarbon gas (molecular and isotopic composition) geochemistry of 98 groundwater samples from south-central New York. All samples were collected ≫1km from unconventional drilling activities and sample locations were intentionally targeted based on their proximity to various types of documented fault systems. In agreement with studies from other petroliferous basins, our results show significant correlations between elevated levels of radiogenic [4 He], thermogenic [CH4 ], and dissolved ions (e.g., Cl, Br, Sr, Ba). In combination, our data suggest that faults have facilitated the transport of exogenous hydrocarbon-rich brines from Devonian source rocks into overlying Upper Devonian aquifer lithologies over geologic time. These data conflict with previous reports, which conclude that hydrodynamic focusing regulates the occurrence of methane and salt in shallow aquifers and leads to elevated levels of these species in restricted flow zones within valley bottoms. Instead, our data suggest that faults in Paleozoic rocks play a fundamental role in gas and brine transport from depth, regulate the distribution of their occurrence in shallow aquifers, and influence the geochemistry of shallow groundwater in this petroliferous basin.

Climatic Water Balance and Hydrogeological characteristics of Lailan Basin, Southeast Kirkuk - North of Iraq

This paper examined the climatic water balance and hydrogeological conditions of the water bearing layers within Lailan basin. To achieve the water balance the meteorological data from Kirkuk station for the period (1970 to 2016) was used to calculate the water surplus and water deficit. Based on Mehta's model the water surplus (Ws) is equal to (127.86 mm/ year) representing 36.87 % of the total rainfall, while 63.13% of the total rainfall are water deficit. The study area is characterized by two main aquifer types, unconfined and semi-confined. Generally, groundwater recharge occurs from both sides of the basin toward the center and the general flow direction is from northeast to southwest. To determine the hydraulic properties of semi-confined aquifer, pumping and recovery tests data from seven wells in the study area were analyzed based on the Hantush-Jacob's (1955) and Theis recovery (1935) methods.The values of T, K ,Sc and S ranged from (79.63 � 753.8 m2/day ),(2.01 � 16.75 m/day ),(0.42 � 5.95 m2/day ) and (0.0068 - 6.134E-16 ) respectively . Due to the aquifer lithology heterogeneity the hydraulic properties varied from one location to another, reflecting the change of both porosity and permeability.

Hydrogeochemical characterization of water mineralization in Tebessa-Kasserine karst system (Tuniso-Algerian Transboundry basin)

Carbonate aquifers provide large parts of the water supply for more than a quarter of the world’s population. The geochemical assessment of these heterogeneous aquifers is a valuable endeavor to ensure a rational management and protection of groundwater resources. To secure its durability, regard to increasing water demands and climate challenges make the problem of prevalence of water scarcity, vulnerability, and drought conditions extremely complicated. In Tebessa–Kasserine basin (Tuniso-Algerian international border), karst aquifers are receiving increasing interest, as the area has typical karst landscape and the hydrogeological system mostly consists of carbonates formation. Thus, a thorough understanding of aquifer behavior and water mineralization origin using geochemical and statistical tools can lead to relevant information regarding karst processes, groundwater chemistry, and protection. Subsequently, this study represents a pioneer baseline of the hydrogeochemical characterization of karst features in this international border area and it aims to identify the origin of karst water mineralization, its spatial distribution, and factors influencing water composition. The hydrogeochemical assessment of the sampled waters shifts from low mineralized Ca-HCO3 waters to Ca-SO4 and Na–Cl water types. TDS values range from 10 to 490.66 mg/l. A Gibbs diagram indicates that karst waters have been recently recharged by direct rainfall infiltration. Water quality gets modified along pathways and dissolution, formations weathering, and ion exchange processes seem to be the predominant geochemical factors influencing water mineralization. The PCA confirms the spatial variability of water types and indicates that it largely depends on aquifer lithology and on geographical position of water points.

Radionuclides as natural tracers of the interaction between groundwater and surface water in the River Andarax, Spain

The identification of specific aquifers that supply water to river systems is fundamental to understanding the dynamics of the rivers' hydrochemistry, particularly in arid and semiarid environments where river flow may be discontinuous. There are multiple methods to identify the source of river water. In this study of the River Andarax, in the Southeast of Spain, an analysis of natural tracers (physico-chemical parameters, uranium, radium and radon) in surface water and groundwater indicates that chemical parameters and uranium clearly identify the areas where there is groundwater-surface water interaction. The concentration of uranium found in the river defines two areas: the headwaters with U concentrations of 2 μg L−1 and the lower reaches, with U of 6 μg L−1. Furthermore, variation in the 234U/238U isotopic ratio allowed us to detect the influence that groundwater from the carbonate aquifer has on surface water in the headwaters of the river, where the saline content is lower and the water has a calcium bicarbonate facies. The concentration of 226Ra and 222Rn are low in the surface waters: <1.6 × 10−6 μg L−1 and <5.1 × 10−12 μg L−1, respectively. There is a slight increase in the lower reaches where the water has a permanent flow, greater salinity and a calcium-magnesium-sulphate facies. All this is favoured by the influence of groundwater from the detritic aquifer on the surface waters. The results of this study indicate the utility in the use of physico-chemical and radiological data conjointly as tracers of groundwater-surface water interaction in semiarid areas where the lithology of aquifers is diverse (carbonate and detritic) and where evaporitic rocks are present.

Weathering and evaporation controls on dissolved uranium concentrations in groundwater – A case study from northern Burundi

The potential use of groundwater for potable water supply can be severely compromised by natural contaminants such as uranium. The environmental mobility of uranium depends on a suite of factors including aquifer lithology, redox conditions, complexing agents, and hydrological processes. Uranium concentrations of up to 734μg/L are found in groundwater in northern Burundi, and the objective of the present study was to identify the causes for these elevated concentrations. Based on a comprehensive data set of groundwater chemistry, geology, and hydrological measurements, it was found that the highest dissolved uranium concentrations in groundwater occur near the shores of Lake Tshohoha South and other smaller lakes nearby. A model is proposed in which weathering and evapotranspiration during groundwater recharge, flow and discharge exert the dominant controls on the groundwater chemical composition. Results of PHREEQC simulations quantitatively confirm this conceptual model and show that uranium mobilization followed by evapo-concentration is the most likely explanation for the high dissolved uranium concentrations observed. The uranium source is the granitic sand, which was found to have a mean elemental uranium content of 14ppm, but the exact mobilization process could not be established. Uranium concentrations may further be controlled by adsorption, especially where calcium-uranyl‑carbonate complexes are present. Water and uranium mass balance calculations for Lake Tshohoha South are consistent with the inferred fluxes and show that high‑uranium groundwater represents only a minor fraction of the overall water input to the lake. These findings highlight that the evaporation effects that cause radionuclide concentrations to rise to harmful levels in groundwater discharge areas are not only confined to arid regions, and that this should be considered when selecting suitable locations for water supply wells.

Uso de sistema de informação geográfica para a determinação da vulnerabilidade à contaminação de aquíferos fraturados: Bacia Hidrográfica do Rio São Domingos – São José de Ubá/RJ

A Bacia Hidrográfica do Rio São Domingos (BHRSD), localizada no Município de São José de Ubá, na Região Noroeste do Estado do Rio de Janeiro, é uma das porções do Estado situadas em terrenos cristalinos que são periodicamente afetadas pela escassez de recursos hídricos superficiais. O objetivo da pesquisa, a definição de um modelo de vulnerabilidade geral para os aquíferos fraturados, foi pautado na necessidade de proteção dos recursos hídricos subterrâneos da BHRSD. Por esta razão a BHRSD foi selecionada para esse estudo, pois apresenta características como dependência dos recursos hídricos subterrâneos em um substrato cristalino e severidade das secas recorrentes. A metodologia aplicada para avaliação da vulnerabilidade englobou as seguintes variáveis: densidade de lineamentos estruturais, litologia do aquífero, declividade, recarga e profundidade do topo do aquífero. Essas variáveis foram ponderadas de acordo com a sua influência na vulnerabilidade, a partir de uma análise multicritério, e incorporadas no BDG (Banco de Dados Geográficos). O SIG (Sistema de Informação Geográfica) mostrou-se uma útil ferramenta para o cálculo das classes de vulnerabilidade. Os resultados indicam que o método empregado foi adequado na avaliação da vulnerabilidade para os aquíferos fraturados da BHRSD, podendo ser aplicado a regiões que apresentem aspectos fisiográficos análogos, por indicar tendências próximas da realidade de campo. As classes de vulnerabilidade predominantes na BHRSD variam de moderada a muito alta, indicando a fragilidade dos sistemas aquíferos fraturados na região, que necessitam de um planejamento do uso e gestão adequada dos seus recursos.

Effects of Groundwater Flow on a Ground Source Heat Pump System

Heat advection by groundwater flow is known to improve the performance of ground heat exchangers (GHEs), but the effect of groundwater advection on performance is not yet fully understood. This numerical study examined how parameters related to groundwater flow, such as aquifer thickness, porosity, lithology, and groundwater flow velocity, affected the performance of a borehole GHE. Under a thin-aquifer condition (10 m, or 10% of the entire GHE length in this study), groundwater flow velocity had the greatest effect on heat flux. At a groundwater flow velocity of at least 10−4 m/s through a low-porosity aquifer filled with granite gravel with high thermal conductivity, the heat flux of a GHE was as much as 60% higher than that of a GHE in a setting without an aquifer. If the aquifer was as thick as 50 m, the high thermal conductivity of granite gravel doubled the heat flux of the GHE at a groundwater flow velocity of at least 10−5 m/s. Thus, not only groundwater flow velocity but also aquifer thickness and thermal conductivity were important factors. However, groundwater seldom flows at such high velocities, and porosity, gravel size and composition, and aquifer thickness vary regionally. Thus, in the design of ground source heat pump systems, it is not appropriate to assume a large groundwater effect.

87Sr/86Sr Ratios in Thermal Water from the Southern Upper Rhine Graben, Germany

The present study of thermal water from Bad Bellingen, Steinenstadt, Bad Krozingen, Mooswald, and Weinheim located in the southern part of the Upper Rhine Graben was undertaken in the framework of a multidisciplinary hydrogeochemical research project and concerns 87Sr/86Sr isotope investigation. The aquifer lithologies of thermal waters are Triassic Upper Muschelkalk, Jurassic Hauptrogenstein and Tertiary Miocene sediments. The 87Sr/86Sr ratios (N=9) range from 0.70912 to 0.71096. The Sr isotopic composition of thermal water is controlled by the fault system of the Rhine Graben rift. Fluids from Upper Muschelkalk aquifers ascent along the Eastern Boundary fault zone. The deep-water ascent most likely reaches into the crystalline basement.

Arsenic contamination of drinking water in Ireland: A spatial analysis of occurrence and potential risk.

The presence of arsenic in groundwater has become a global concern due to the health risks from drinking water with elevated concentrations. The Water Framework Directive (WFD) of the European Union calls for drinking water risk assessment for member states. The present study amalgamates readily available national and sub-national scale datasets on arsenic in groundwater in the Republic of Ireland. However, due to the presence of high levels of left censoring (i.e. arsenic values below an analytical detection limit) and changes in detection limits over time, the application of conventional statistical methods would inhibit the generation of meaningful results. In order to handle these issues several arsenic databases were integrated and the data modelled using statistical methods appropriate for non-detect data. In addition, geostatistical methods were used to assess principal risk components of elevated arsenic related to lithology, aquifer type and groundwater vulnerability. Geographic statistical methods were used to overcome some of the geographical limitations of the Irish Environmental Protection Agency (EPA) sample database. Nearest-neighbour inverse distance weighting (IDW) and local indicator of spatial association (LISA) methods were used to estimate risk in non-sampled areas. Significant differences were also noted between different aquifer lithologies, indicating that Rhyolite, Sandstone and Shale (Greywackes), and Impure Limestone potentially presented a greater risk of elevated arsenic in groundwaters. Significant differences also occurred among aquifer types with poorly productive aquifers, locally important fractured bedrock aquifers and regionally important fissured bedrock aquifers presenting the highest potential risk of elevated arsenic. No significant differences were detected among different groundwater vulnerability groups as defined by the Geological Survey of Ireland. This research will assist management and future policy directions of groundwater resources at EU level and guide future research focused on understanding arsenic mobilisation processes to facilitate in guiding future development, testing and treatment requirements of groundwater resources.

Contrasting transit times of water from peatlands and eucalypt forests in the Australian Alps determined by tritium: implications for vulnerability and the source of water in upland catchments

Abstract. Peatlands are a distinctive and important component of many upland regions that commonly contain distinctive flora and fauna which are different from those of adjacent forests and grasslands. Peatlands also represent a significant long-term store of organic carbon. While their environmental importance has long since been recognised, water transit times within peatlands are not well understood. This study uses tritium (3H) to estimate the mean transit times of water from peatlands and from adjacent gullies that contain eucalypt forests in the Victorian Alps (Australia). The 3H activities of the peatland water range from 2.7 to 3.3 tritium units (TUs), which overlap the measured (2.9 to 3.0 TU) and expected (2.8 to 3.2 TU) average 3H activities of rainfall in this region. Even accounting for seasonal recharge by rainfall with higher 3H activities, the mean transit times of the peatland waters are &lt; 6.5 years and may be less than 2 years. Water from adjacent eucalypt forest streams has 3H activities of 1.6 to 2.1 TU, implying much longer mean transit times of 5 to 29 years. Cation ∕ Cl and Si ∕ Cl ratios are higher in the eucalypt forest streams than the peatland waters and both of these water stores have higher cation ∕ Cl and Si ∕ Cl ratios than rainfall. The major ion geochemistry reflects the degree of silicate weathering in these catchments that is controlled by both transit times and aquifer lithology. The short transit times imply that, unlike the eucalypt forests, the peatlands do not represent a long-lived store of water for the local river systems. Additionally, the peatlands are susceptible to drying out during drought, which renders them vulnerable to damage by the periodic bushfires that occur in this region.

Different hydraulic responses to the 2008 Wenchuan and 2011 Tohoku earthquakes in two adjacent far-field wells: the effect of shales on aquifer lithology

Zuojiazhuang and Baodi are two adjacent wells (~50 km apart) in northern China. The large 2008 M w 7.9 Wenchuan and 2011 M w 9.1 Tohoku earthquakes induced different co-seismic water-level responses in these far-field (>1000 km) wells. The co-seismic water-level changes in the Zuojiazhuang well exhibited large amplitudes (~2 m), whereas those in the Baodi well were small and unclear (~0.05 m). The mechanism of the different co-seismic hydraulic responses in the two wells needs to be revealed. In this study, we used the barometric responses in different frequency domains and the phase shifts and amplitude ratios of the tidal responses (M2 wave), together with the well logs, to explain this inconformity. Our calculations show that the co-seismic phase shifts of the M2 wave decreased or remained unchanged in the Baodi well, which was quite different from the Zuojiazhuang well and from the commonly accepted phenomena. According to the well logs, the lithology of the Baodi well is characterized by the presence of a significant amount of shale. The low porosity/permeability of shale in the Baodi well could be the cause for the unchanged and decreased phase shifts and tiny co-seismic water-level responses. In addition, shale is one of the causes of positive phase shifts and indicates a vertical water-level flow, which may be due to a semi-confined aquifer or the complex and anisotropic fracturing of shale.

Hydrogeochemical evolution and potability evaluation of saline contaminated coastal aquifer system of Rajnagar, Odisha, India: A geospatial perspective

The present article reports the results of a comprehensive hydrogeochemical study carried out across the coastal aquifer system of Rajnagar block, Kendrapara district, Odisha, India. The research involved collection of representative groundwater samples during the pre- and post-monsoon seasons with in situ as well as laboratory measurement of various hydrogeochemical variables. Analysis of the subsurface water samples portrays an alkali dominated water type during the pre-monsoon season whereas alkaline earth has a significantly increased influence during the post-monsoon period. However, the aquifer system displays an even distribution of strong and weak acids for both the monsoonal regimes. The hydrogeochemistry is controlled by aquifer lithology with a general occurrence of ion exchange and acid–base reaction processes across the study area. Spatial disposition of major cations indicates freshening of this coastal aquifer system in S–N and SW–NE directions. Potability analysis of the samples is suggestive of widespread unsuitability for domestic, agriculture and industrial uses. The extensive occurrence of salinity hazards, sodium hazards and magnesium hazards across the terrain makes the groundwater unsafe for domestic and agricultural utilization while industrial potability analysis suggests the aquifer system is moderately corrosive but non-incrusting. Post-monsoon however, the subsurface waters display a general decrease in hazardous nature with increased suitability for various uses.

Determination of the main factors controlling chemistry of Bibitalkhone karst spring, Southwest Iran

Bibitalkhone spring with an average annual discharge of 2 m3/s is one of the important karstic springs in the Southwest of Iran which has a special hydrochemical behavior different from the other karstic springs. This study shows that the dominant water types of the spring are Cl–Na and HCO3–Ca for dry (approximately 8 months of year) and rainy (about 4 months of year) periods, respectively. While the host rock of the spring is composed of limestone and dolomite, the dominant type of the spring water doesn’t match the lithology of the host aquifer. The monthly physico-chemical parameters and major ions of the spring measured for 24 months (from October 2012 to September 2014) and the results analyzed using factor analysis and hydrochemical diagrams (including the composition, dissolution domains and Piper diagrams) to understand the odd behavior of this spring and also the factors which control the spring hydrochemistry. The oxygen-18 and deuterium contents of the spring water measured in four periods at February (rainy period), June (after the rainy period), October (before the next rainy period) and December (the next rainy period) of 2013. The results indicate that the water chemistry of the Bibitalkhone spring is controlled by various factors. One of the most important factors is the input of exotic waters from the neighboring karstic catchment which has circulated within a lithology of high limestone purity. Although these waters contribute to recharge of the Bibitalkhone spring throughout the year, their effect is more obvious during the rainy period. The other important factor is the dissolution of salty/gypsum layers (mostly salt). These layers are in direct contact with the southern limb of the host aquifer and their effects on the chemistry of spring water are more evident in the dry period. However, the available structural evidences suggest that the tectonic factor plays an important role in the chemistry of the spring water, since the main faults in the region somehow control the two previous factors.

A global review on ambient Limestone-Precipitating Springs (LPS): Hydrogeological setting, ecology, and conservation

Springs are biodiversity hotspots and unique habitats that are threatened, especially by water overdraft. Here we review knowledge on ambient-temperature (non-geothermal) freshwater springs that achieve sufficient oversaturation for CaCO3 -by physical CO2 degassing and activity of photoautotrophs- to deposit limestone, locally resulting in scenic carbonate structures: Limestone-Precipitating Springs (LPS). The most characteristic organisms in these springs are those that contribute to carbonate precipitation, e.g.: the mosses Palustriella and Eucladium, the crenophilous desmid Oocardium stratum, and cyanobacteria (e.g., Rivularia). These organisms appear to be sensitive to phosphorus pollution. Invertebrate diversity is modest, and highest in pools with an aquatic-terrestrial interface. Internationally, comprehensive legislation for spring protection is still relatively scarce. Where available, it covers all spring types. The situation in Europe is peculiar: the only widespread spring type included in the EU Habitat Directive is LPS, mainly because of landscape aesthetics. To support LPS inventorying and management to meet conservation-legislation requirements we developed a general conceptual model to predict where LPS are more likely to occur. The model is based on the pre-requisites for LPS: an aquifer lithology that enables build-up of high bicarbonate and Ca2+ to sustain CaCO3 oversaturation after spring emergence, combined with intense groundwater percolation especially along structural discontinuities (e.g., fault zones, joints, schistosity), and a proper hydrogeological structure of the discharging area. We validated this model by means of the LPS information system for the Emilia-Romagna Region (northern Italy). The main threats to LPS are water diversion, nutrient enrichment, and lack of awareness by non-specialized persons and administrators. We discuss an emblematic case study to provide management suggestions. The present review is devoted to LPS but the output of intense ecological research in Central Europe during the past decades has clearly shown that effective conservation legislation should be urgently extended to comprise all types of spring habitats.

An integrative geospatial and hydrogeochemical analysis for the assessment of groundwater quality in Mahakalapara Block, Odisha, India

A comprehensive hydrogeochemical and geospatial analysis has been carried out for the assessment of geochemical evolution and groundwater potability of the coastal aquifer system underlying the Mahakalapara Block, Odisha, India. The major ion chemistry of groundwater is primarily made up of alkali cations and strong acidic anions having a strong influence of the aquifer lithology. Geochemical analysis of the sample points towards the occurrence of dissolution and ion exchange processes across the study area. Spatially the former is the principal influencing process along the western part of the block whereas the latter is active across the entire study area. Increased alkali and chloride concentration during post-monsoon period indicates potential saline and formational water influences. Potability analysis of the samples is suggestive of widespread unsuitability for domestic, agricultural and industrial uses. All the evaluating parameters except pH and residual sodium carbonate indicate a general unsafe characteristic of the subsurface water for domestic and agricultural utility. From an industrial perspective, the subsurface waters are corrosive but not incrusting.

Remote sensing and geophysical survey applications for delineating near-surface palaeochannels and shallow aquifer in the United Arab Emirates

This study integrates remote sensing data and geoelectrical dipole–dipole resistivity to delineate near-surface palaeochannels and shallow aquifer in the northern part of Abu Dhabi Emirate, United Arab Emirates. The shuttle imaging radar images and shuttle radar topographic mission DEM were used to delineate near-surface palaeochannels visually based on the contrast between bright and dark tone and automatically using the eight-direction flow model. The delineated palaeochannels were validated by comparing the textural features evident from advanced land observing satellite-phased array type L-band synthetic aperture radar images and determining whether these patterns were different. Field observation and geoelectrical dipole–dipole resistivity method was used to define the depth of palaeochannels and lithology of the shallow aquifer. The remote sensing and geophysical investigations in the UAE, including the study area, indicate the presence of buried palaeochannels with south-west and north-west flow directions from Oman Mountain. The study area can be of economic importance to the local population.

Exploration of hydrothermal carbonate magnesium isotope signatures as tracers for continental fluid aquifers, Schwarzwald mining district, SW Germany

The significance of magnesium isotope (δ26Mg) fractionation in the continental hydrothermal domain is poorly explored. Here, a detailed Mg isotope dataset from various aquifer host rocks and corresponding hydrothermal carbonate precipitates from the Schwarzwald mining area in SW Germany is documented and discussed. This study is motivated by the very considerable existing data set on hydrothermal mineralizations in the study area and the excellent regional control of sampling points. Based on structural, mineralogical and microthermometrical arguments, we here subdivide three clusters of veins: (i) Permian, (ii) Jurassic–Cretaceous and (iii) post-Cretaceous (Cenozoic). The focus is on clusters ii and iii and their corresponding, texturally older hydrothermal fluid inclusion-rich, coarse-grained, low-Mg calcite and dolomite–ankerite solid solutions and younger, oscillatory zoned low-Mg calcite and dolomite–ankerite solid solution crystals precipitated from fluids with temperatures between 50 and 350°C. In terms of their δ26Mg ratios, three characteristic groups of hydrothermal carbonates can be distinguished: (i) Jurassic–Cretaceous veins (δ26Mg=−3.38 to −0.82‰) in the central Schwarzwald precipitated from fluids containing a significant proportion of sedimentary cover-derived waters. They yield 26Mg-depleted Mg isotope signatures typical of sedimentary carbonate lithologies. (ii) Jurassic–Cretaceous vein carbonates in the southern Schwarzwald precipitated from mainly basement-derived fluids with 26Mg-enriched signatures (δ26Mg=−1.22 to +0.05‰). Supporting evidence for the origin of these fluids comes from Sr–C–Pb isotope systematics and trace element compositional variations of fahlore and sphalerite. The Mg isotope variations are controlled by differences in fluid source characteristics dominate over variations exerted by mineralogical differences (where low-Mg calcites are generally, but not in all cases, more depleted in 26Mg compared to dolomite–ankerite solid solutions). (iii) Post-Cretaceous (Cenozoic), Rhinegraben-related veins represent a complex tectonic juxtaposition of different aquifer lithologies. As expected, this phase spans the full range from silicate to carbonate Mg isotope signatures (+0.45 to −3.4‰). Magnesium isotope data are supported by textural analyses (optical and cathodoluminescence microscopy), electron microprobe, microthermometry and published radiogenic 87Sr/86Sr isotope systematics. Our data are not in agreement with a significant temperature-controlled Δ26Mgfluid-calcite and no obvious relation between fluid salinity and hydrothermal carbonate δ26Mg is found. The results of this study suggest that hydrothermal carbonate magnesium isotope ratios have a significant potential as tracer of hydrothermal fluid sources and corresponding aquifer lithologies.

Impact of lateral variations of geologic facies on water resources in homogeneous basins: example of tertiary plateaus in the Paris Basin

Spatial disparity of run-off conditions during low-water period in homogeneous watersheds depends on the degree of incision of valleys, but may also be influenced by a structural partitioning or some lateral variations in the aquifer lithology. For small basins (area <300 km2), often hydrometrically unsupervised, campaigns of serial flow measurements, gauging, conductivity and temperature are achieved. The Ardre basin, localised in the Tertiary formations of the Paris Basin is used as a workshop basin. Results validated by hydrological and physico-chemical profiles show increased hydrological yields in the basin which correspond to the increase in the thickness of aquifers and their porosity. These lateral variations of facies and of aquifer thicknesses are related to Eocene sedimentary conditions (Lutetian) for homogeneous basins, which explain the spatial disparity of water resources.

An innovative procedure to assess multi-scale temporal trends in groundwater quality: Example of the nitrate in the Seine–Normandy basin, France

• Large and heterogeneous dataset: how to improve the assessment of trends. • Punctual and regional assessment of groundwater quality. • Homogeneity and nonparametric tests to determine recent groundwater quality trends. • We modify geostatistical approach to create spatial unit for regional trend analysis. • Improving the management of groundwater in compliance with the WFD requirements. The European Water Framework Directive (WFD) asks Member States to identify trends in contaminant concentrations in groundwater and to take measures to reach a good chemical status by 2015. In this study, carried out in a large hydrological basin (95,300 km 2 ), an innovative procedure is described for the assessment of recent trends in groundwater nitrate concentrations both at sampling point and regional scales. Temporal variograms of piezometric and nitrate concentration time series are automatically calculated and fitted in order to classify groundwater according to their temporal pattern. These results are then coupled with aquifer lithology to map spatial units within which the modes of diffuse transport of contaminants towards groundwater are assumed to be the same at all points. These spatial units are suitable for evaluating regional trends. The stability over time of the time series is tested based on the cumulative sum principle, to determine the time period during which the trend should be sought. The Mann–Kendall and Regional-Kendall nonparametric tests for monotonic trends, coupled with the Sen-slope test, are applied to the periods following the point breaks thus determined at both the sampling point or regional scales. This novel procedure is robust and enables rapid processing of large databases of raw data. It would therefore be useful for managing groundwater quality in compliance with the aims of the WFD.