Particle size and mineralogical composition of inorganic colloids in waters draining the adit of an abandoned mine,Goesdorf, Luxembourg

Particle size distributions and the mineralogy of inorganic colloids in waters draining the adit of an abandoned mine (Goesdorf, Luxembourg) were quantified by single particle counting based on light scattering (100 nm–2 μm) combined with transmission electronic microscopy coupled with energy dispersive spectroscopy and selected area electron diffraction. This water system was chosen as a surrogate for groundwaters. The dependence of the colloid number concentration on colloid diameters can be described by a power-law distribution in all cases. Power-law slopes ranged from −3.30 to −4.44, depending on water ionic strength and flow conditions. The same main mineral types were found in the different samples: 2:1 phyllosilicates (illite and mica), chlorite, feldspars (albite and orthoclase), calcite and quartz; with a variable number of Fe oxide particles. The colloid mineralogical composition closely resembles the composition of the parent rock. Spatial variations in the structure and composition of the rock in contact with the waters, i.e. fissured rock versus shear joints, are reflected in the colloid composition. The properties of the study colloids, as well as the processes influencing them, can be considered as representative of the colloids present in groundwaters.     

Hepburn Spa: cold carbonated mineral waters of Central Victoria,South Eastern Australia

Hepburn Spring is the major cold carbonated mineral spring of the ‘Spa’ country of Central Victoria, in South Eastern Australia. The spring occurs in a small tributary valley of the Loddon River, 15 km away from the crest of the Great Dividing Range. The waters are effervescent, have an alkalinity of around 1,500 mg/L (as HCO₃ ⁻), are mildly acidic and have high iron concentrations. Hepburn Spring is one of nearly 100 small cold low flow carbonated mineral water springs that occur in the region. Hepburn Spring has been protected since 1865 in one of 34 ‘Special Mineral Spring Reserves’. By world standards the spring is small and not highly developed, but it retains much of its charm due to the bushland, forest setting. The bedrock of the region consists of indurated arkosic sandstones interbedded with carbonaceous shales and slates. The rocks are folded and cut by swarms of strongly developed meridional fissure fault systems. Hepburn Spring is situated on the fault and fold axes associated with the “Cornish line” and Gold mines have dewatered the spring on several occasions. After dewatering events the water level and flow recovered first and then the water composition and effervescence. The origin of the effervescent waters has attracted much attention; hypotheses include both a volcanic and a rock water reaction origin. The second hypothesis involves weathering of the carbonaceous and sometimes pyritic rock mass which contains only a few percent carbonate. This process produces high bicarbonate groundwater throughout Central Victoria. The Hepburn waters are a variant of these waters and it is suggested that controls on the carbonate solubility and redox conditions in the fissures flow systems results in effervescent waters as the waters ascend.     

Seasonally chemical weathering and CO<Subscript>2</Subscript> consumption flux of Lake Qinghai river system in the northeastern Tibetan Plateau

The major cation and anion compositions of waters from the Lake Qinghai river system (LQRS) in the northeastern Tibetan Plateau were measured. The waters were collected seasonally from five main rivers during pre-monsoon (late May), monsoon (late July), and post-monsoon (middle October). The LQRS waters are all very alkaline and have high concentrations of TDS (total dissolved solids) compared to rivers draining the Himalayas and the southeastern Tibetan Plateau. Seasonal variations in the water chemistry show that, except the Daotang River, the TDS concentration is high in October and low in July in the LQRS waters. The forward models were used to quantify the input of three main rivers (Buha River, Shaliu River, and Hargai River) from rain, halite, carbonates, and silicates. The results suggest that (1) atmospheric input is the first important source for the waters of the Buha River and the Shaliu River, contributing 36–57% of the total dissolved cations, (2) carbonate weathering input and atmospheric input have equal contribution to the Hargai River water, (3) carbonate weathering has higher contribution to these rivers than silicate weathering, and (4) halite is also important source for the Buha River. The Daotang River water is dominated by halite input owing to its underlying old lacustrine sediments. The water compositions of the Heima River are controlled by carbonate weathering and rainfall input in monsoon season, and groundwater input may be important in pre-monsoon and post-monsoon seasons. After being corrected the atmospheric input, average CO₂ drawdown via silicate weathering in the LQRS is 35 × 10³ mol/km² per year, with highest in monsoon season, lower than Himalayas and periphery of Tibetan Plateau rivers but higher than some rivers draining shields.     

RETRACTED ARTICLE: The hydrochemical framework of surface water basins in southern Ghana

Surface water resources play a crucial role in the domestic water delivery system in Ghana. In addition, sustainable food production is based on the quality and quantity of water resources available for irrigation purposes to supplement rain-fed agricultural activities in the country. The objective of this research was to determine the main controls on the hydrochemistry of surface water resources in the southern part of Ghana and assess the quality of water from these basins for irrigation activities in the area. R-mode factor and cluster analyses were applied to 625 data points from 6 river basins in southern Ghana after the data had been log transformed and standardized for homogeneity. This study finds that surface water chemistry in the south is controlled by the chemistry of silicate mineral weathering, chemistry of rainfall, fertilizers from agricultural activities in the area, as well as the weathering of carbonate minerals. A Gibb’s diagram plotted with total dissolved solids (TDS) on the vertical axis against (Na⁺ + K⁺)/(Ca²⁺ + K⁺ + Na⁺) on the horizontal axis indicates that rock weathering plays a significant role in the hydrochemistry. Activity diagrams for the CaO–Na₂O–Al₂O–SiO₂–H₂O and CaO–MgO–Al₂O₃–SiO₂–H₂O systems suggest that kaolinite is the most stable clay mineral phase in the system. In addition, an assessment of the irrigation quality of water from these basins suggests that the basins are largely low sodium—low to medium salinity basins, delivering water of acceptable quality for irrigation purposes.     

Geochemical Eccentricity of Ground Water Allied to Weathering of Basalts from the Deccan Volcanic Province,India: Insinuation on CO<Subscript>2</Subscript> Consumption

Analyses of 72 samples from Upper Panjhara basin in the northern part of Deccan Plateau, India, indicate that geochemical incongruity of groundwater is largely a function of mineral composition of the basaltic lithology. Higher proportion of alkaline earth elements to total cations and HCO₃>Cl + SO₄ reflect weathering of primary silicates as chief source of ions. Inputs of Cl, SO₄, and NO₃ are related to rainfall and localized anthropogenic factors. Groundwater from recharge area representing Ca + Mg–HCO₃ type progressively evolves to Ca + Na–HCO₃ and Na–Ca–HCO₃ class along flow direction replicates the role of cation exchange and precipitation processes. While the post-monsoon chemistry is controlled by silicate mineral dissolution + cation exchange reactions, pre-monsoon variability is attributable chiefly to precipitation reactions + anthropogenic factors. Positive correlations between Mg vs HCO₃ and Ca + Mg vs HCO₃ supports selective dissolution of olivine and pyroxene as dominant process in post-monsoon followed by dissolution of plagioclase feldspar and secondary carbonates. The pre-monsoon data however, points toward the dissolution of plagioclase and precipitation of CaCO₃ supported by improved correlation coefficients between Na + Ca vs HCO₃ and negative correlation of Ca vs HCO₃, respectively. It is proposed that the eccentricity in the composition of groundwater from the Panjhara basin is a function of selective dissolution of olivine > pyroxene followed by plagioclase feldspar. The data suggest siallitization (L < R and R _k) as dominant mechanism of chemical weathering of basalts, stimulating monosiallitic (kaolinite) and bisiallitic (montmorillonite) products. The chemical denudation rates for Panjhara basin worked out separately for the ground and surface water component range from 6.98 to 36.65 tons/km²/yr, respectively. The values of the CO₂ consumption rates range between 0.18 × 10⁶ mol//km²/yr (groundwater) and 0.9 × 10⁶ mol/km²/yr (surface water), which indicates that the groundwater forms a considerable fraction of CO₂ consumption, an inference, that is, not taken into contemplation in most of the studies.     

Ground water colloid properties from the Bangombé system

The concentration and the role of colloids in the transport of elements in the vicinity of a fossil reactor at Bangombé, Gabon, were assessed. Colloid sampling was conducted in seven boreholes around and in the extinguished natural reactor. The ground waters are of Na–Mg–Ca–HCO₃ type, with variable salinities, pH 4.6–6.8 and anaerobic Eh values. Filtered ground water and colloid samples were taken from the reactor and the surroundings. Filtered fluids and colloid samples collected on membranes and resuspended in solution were analysed by ICP-MS and ICP-AES in order to examine the element association in the colloid phase within the size range 3000 to 400 to 50 nm. The colloid concentrations for the size 400 to 50 nm range from 80 to 300 ng ml⁻¹. They consist of silica particles associated with ferrihydrite coated with organics. Trace element results show that metals including Pb, Sc, Y, La, Ce, Pr, Nd, Bi, Th and U are associated to various degrees with the colloid phase. The distribution ratios of these trace elements between the water and the colloid phase (Kp) were experimentally determined. The high Pb distribution ratios of 10⁺⁷ ml g⁻¹ are specifically discussed. Values range from 10⁺⁶ to 10⁺⁵ ml g⁻¹for the trivalent elements (Sc, Y, La, Ce, … , Bi). For uranium, a Kp of the order of 10⁺⁵ ml g⁻¹ may be calculated and compared with data gained using the surface complexation model. These Kp values suggest that the uranium is partially sorbed or associated with ground water colloids. Measurements from the reactor zone show that about 2–4% of the uranium is associated with the colloid phase, which contributes partially to the uranium transport. The rather low colloid concentrations are due to the relatively high concentrations of Ca, Mg and Na in these quasi-neutral waters. These soluble elements contribute to the attachment of the colloids, restricting their transport. This indicates that the colloid phase may not be an important transport medium for the radionuclides in the Bangombé system if their association is reversible. The Bangombé colloid results are compared with those studied for other systems.     

Hydrogeochemical evaluation of groundwater in the lower Offin basin,Ghana

Alumino-silicate mineral dissolution, cation exchange, reductive dissolution of hematite and goethite, oxidation of pyrite and arsenopyrite are processes that influence groundwater quality in the Offin Basin. The main aim of this study was to characterise groundwater and delineate relevant water–rock interactions that control the evolution of water quality in Offin Basin, a major gold mining area in Ghana. Boreholes, dug wells, springs and mine drainage samples were analysed for major ions, minor and trace elements. Major ion study results show that the groundwater is, principally, Ca–Mg–HCO₃ or Na–Mg–Ca–HCO₃ in character, mildly acidic and low in conductivity. Groundwater acidification is principally due to natural biogeochemical processes. Though acidic, the groundwater has positive acid neutralising potential provided by the dissolution of alumino-silicates and mafic rocks. Trace elements’ loading (except arsenic and iron) of groundwater is generally low. Reductive dissolution of iron minerals in the presence of organic matter is responsible for high-iron concentration in areas underlain by granitoids. Elsewhere pyrite and arsenopyrite oxidation is the plausible process for iron and arsenic mobilisation. Approximately 19 and 46% of the boreholes have arsenic and iron concentrations exceeding the WHO’s (Guidelines for drinking water quality. Final task group meeting. WHO Press, World Health Organization, Geneva, 2004) maximum acceptable limits of 10 μg l⁻¹ and 0.3 mg l⁻¹, for drinking water.     

A Geochemical study of the groundwater in the Misli basin and environmental implications

The aim of this study was to determine geochemical properties of groundwater and thermal water in the Misli Basin and to assess thermal water intrusion into shallow groundwater due to over-extraction. According to isotope and hydrochemical analyses results, sampled waters can be divided into three groups: cold, thermal, and mixed waters. Only a few waters reach water–rock chemical equilibrium. Thermal waters in the area are characterized by Na⁺–Cl⁻–HCO₃⁻, while the cold waters by CaHCO₃ facies. On the basis of isotope results, thermal waters in the Misli basin are meteoric origin. In particular, δ¹⁸O and δ²H values of shallow groundwater vary from −10.2 to −12.2‰ and −71.2 to −82‰, while those of thermal waters range from −7.8 to −10.1‰ and from −67 to −74‰, respectively. The tritium values of shallow groundwater having short circulation as young waters coming from wells that range from 30 to 70 m in depth vary from 10 to 14 TU. The average tritium activity of groundwater in depths more than 100 m is 1.59 ± 1.16, which indicates long circulation. The rapid infiltration of the precipitation, the recycling of the evaporated irrigation water, the influence of thermal fluids and the heterogeneity of the aquifer make it difficult to determine groundwater quality changes in the Misli Basin. Obtained results show that further lowering of the groundwater table by over-consumption will cause further intrusion of thermal water which resulted in high mineral content into the fresh groundwater aquifer. Because of this phenomenon, the concentrations of some chemical components which impairs water quality in terms of irrigation purposes in shallow groundwaters, such as Na⁺, B, and Cl⁻, are highy probably expected to increase in time.     

Natural arsenic contamination in waters from the Pesariis village,NE Italy

High arsenic (As) concentrations, >900 μg/L, were measured in Ca–Mg–SO₄ waters from springs and drainages in the village of Pesariis in the Carnic Alps (NE Italy). Oxidation of the outcropping arsenian marcasite ore deposits of the area is proposed as the mechanism for As release into oxygenated waters during runoff. Nevertheless, the limited extension of the ore deposit and the relatively low As content of the mineralization suggest that sulfide weathering might not be the only process responsible for the highest As concentration in groundwaters. An additional mechanism involves As adsorption onto ferric iron particulate during oxidation, the drawdown in reducing environment at depth during water infiltration, and the release of ferrous iron and sorbed arsenic to the water columns by reductive dissolution of hydrous ferric oxides (HFO). This yields the observed Fe–As correlation. Newly formed HFO precipitates when groundwaters discharge to aerated conditions, leading to the removal of As, which strongly partitions into the iron-rich sediments, adsorbed onto the surface of amorphous Fe₂O₃·xH₂O. The calculated and measured As concentration in sediments exceeds 10% by weight. Furthermore, geochemical and isotopic data indicate that the As-rich reservoir partly mixes with shallower aquifers, commonly tapped for drinking supply, representing a natural hazard for inhabitants.     

Mineral weathering rates calculated from spring water data: a case study in an area with intensive agriculture,the Morais Massif,northeast Portugal

This study identifies and quantifies the water–rock interactions responsible for the composition of 25 spring waters, and derives the weathering rates of rock-forming minerals in a complex of petrologic units containing ultramafics, amphibolites, augengneisses and micaschists. Bulk chemical analyses were used to calculate the mineralogical composition of these rocks; the composition of the rock-forming minerals were determined by microprobe analyses. The soils developed on augengneisses and micaschists contain predominantly halloysite; on the other units mixtures of halloysite and smectites. The mineralogical and chemical data on rocks and soils are essential for writing the proper weathering reactions and for solving mole balances between the amounts of weathered primary minerals and secondary products formed (soils and solutes in groundwater). Ground waters emanating in springs were collected in 3 consecutive seasons, namely late Summer, Winter and Spring, and analyzed for major components. Using an algorithm based on mole and charge balance equations, the average concentrations of the solutes were linked with a combination of possible weathering reactions. To sort out the best match of weathering reactions and the concomitantly generated water composition, the results were checked against the limiting condition of similarity between the predicted and actual clay mineral abundance in the soils. Having selected the best-fit weathering reactions, the mineral weathering rates could also be calculated by combining the median discharge rates and recharge areas of the springs and normalizing the rates by the mineral abundance. For the one case—plagioclase—for which comparison with published results was possible, the results compare favorably with rates calculated by other groups. For the most abundant primary minerals the following order of decreasing weathering rates was found (in moles/(ha·a·%mineral)): forsterite (485) > clinozoisite (114) > chlorite (49) > plagioclase (45) > amphibole (28). In as far as this order differs from commonly used orders of weatherability, this has to be due to differences in the hydrologic regime within this area and between this and other case studies. As additional objective, the authors wanted to explain the effects of contributions by sources other than water-rock interactions. The latter processes are coupled with acquisition of carbonate alkalinity and dissolved silica. Contributions by sources other than water–rock interactions are manifest by the Cl⁻, SO²⁻₄ and NO⁻₃ concentrations. It was possible to approximate the contribution of atmospheric deposition. More importantly, knowledge of the application and composition of fertilizers enabled assessment of the effects of farming on the composition of ground waters emanating in the springs. It was also possible to estimate how selective uptake of nutrients and cations by vegetation as well as ion-exchange processes in the soil modified the spring water composition. Using this rather holistic approach, it is possible to satisfactorily explain how spring waters, in this petrologically and agriculturally diverse area, acquired their composition.     

CO2 and sulfuric acid controls of weathering and river water composition

Reactions of CO₂ with carbonate and silicate minerals in continental sediments and upper part of the crystalline crust produce HCO₃⁻ in river and ground waters. H₂SO₄ formed by the oxidation of pyrite and reacting with carbonates may produce CO₂ or HCO₃⁻. The ratio, ψ, of atmospheric or soil CO₂ consumed in weathering to HCO₃⁻ produced depends on the mix of CO₂ and H₂SO₄, and the proportions of the carbonates and silicates in the source rock. An average sediment has a CO₂ uptake potential of ψ = 0.61. The potential increases by inclusion of the crystalline crust in the weathering source rock. A mineral dissolution model for an average river gives ψ = 0.68 to 0.72 that is within the range of ψ = 0.63 to 0.75, reported by other investigators using other methods. These results translate into the CO₂ weathering flux of 20 to 24 × 10¹²mol/yr.     

Silicate and carbonate mineral weathering in soil profiles developed on Pleistocene glacial drift (Michigan, USA): Mass balances based on soil water geochemistry

Geochemistry of soil, soil water, and soil gas was characterized in representative soil profiles of three Michigan watersheds. Because of differences in source regions, parent materials in the Upper Peninsula of Michigan (the Tahquamenon watershed) contain only silicates, while those in the Lower Peninsula (the Cheboygan and the Huron watersheds) have significant mixtures of silicate and carbonate minerals. These differences in soil mineralogy and climate conditions permit us to examine controls on carbonate and silicate mineral weathering rates and to better define the importance of silicate versus carbonate dissolution in the early stage of soil-water cation acquisition.Soil waters of the Tahquamenon watershed are the most dilute; solutes reflect amphibole and plagioclase dissolution along with significant contributions from atmospheric precipitation sources. Soil waters in the Cheboygan and the Huron watersheds begin their evolution as relatively dilute solutions dominated by silicate weathering in shallow carbonate-free soil horizons. Here, silicate dissolution is rapid and reaction rates dominantly are controlled by mineral abundances. In the deeper soil horizons, silicate dissolution slows down and soil-water chemistry is dominated by calcite and dolomite weathering, where solutions reach equilibrium with carbonate minerals within the soil profile. Thus, carbonate weathering intensities are dominantly controlled by annual precipitation, temperature and soil pCO₂. Results of a conceptual model support these field observations, implying that dolomite and calcite are dissolving at a similar rate, and further dissolution of more soluble dolomite after calcite equilibrium produces higher dissolved inorganic carbon concentrations and a Mg²⁺/Ca²⁺ ratio of 0.4.Mass balance calculations show that overall, silicate minerals and atmospheric inputs generally contribute <10% of Ca²⁺ and Mg²⁺ in natural waters. Dolomite dissolution appears to be a major process, rivaling calcite dissolution as a control on divalent cation and inorganic carbon contents of soil waters. Furthermore, the fraction of Mg²⁺ derived from silicate mineral weathering is much smaller than most of the values previously estimated from riverine chemistry.     

Contaminant dispersion at the rehabilitated Mary Kathleen uranium mine, Australia

This study reports on the transfer of contaminants from waste rock dumps and mineralised ground into soils, sediments, waters and plants at the rehabilitated Mary Kathleen uranium mine in semi-arid northwest Queensland. Numerous waste rock dumps were partly covered with benign soil and the open pit mine was allowed to flood. The mineralised and waste calc-silicate rock in the open pit and dumps has major (>1 wt%) Ca, Fe and Mg, minor (>1,000 ppm) Ce, La, Mn, P and S, subminor (>100 ppm) Ba, Cu, Th and U, and trace (<100 ppm) As, Ni, Pb, Y and Zn values. Consequently, chemical and physical weathering processes have acted on waste rock and on rock faces within the open pit, mobilising many elements and leading to their dispersion into soils, stream sediments, pit water and several plant species. Chemical dispersion is initiated by sulfide mineral breakdown, generation of sulfuric acid and formation of several soluble, transient sulfate minerals as evaporative efflorescent precipitates. Radiation doses associated with the open pit average 5.65 mSv year⁻¹; waste dumps commonly have lower values, especially where soil-covered. Surface pit water is slightly acid, with high sulfate values accompanied by levels of U, Cu and Ni close to or above Australian water guideline values for livestock. Dispersion of U and related elements into soils and stream sediments occurs by physical (erosional) processes and from chemical precipitation. Plants growing in the mine void, on waste dumps and contaminated soil display evidence of biological uptake of U, LREE, Cu and Th and to a lesser degree of As, Ni, Pb, Y and Zn, with values being up to 1–2 orders of magnitude above background sites for the same species. Although rehabilitation procedures have been partly successful in reducing dispersion of U and related elements into the surrounding environment, it is apparent that 20 years after rehabilitation, there is significant physical and chemical mobility, including transfer into plants.     

Chemical and Strontium Isotopic Compositions of the Hanjiang Basin Rivers in China: Anthropogenic Impacts and Chemical Weathering

The Hanjiang River, the largest tributaries of the Changjiang (Yangtze) River, is the water source area of the Middle Route of China’s South-to-North Water Transfer Project. The chemical and strontium isotopic compositions of the river waters are determined with the main purpose of understanding the contribution of chemical weathering processes and anthropogenic inputs on river solutes, as well as the associated CO₂ consumption in the carbonate-dominated basin. The major ion compositions of the Hanjiang River waters are characterized by the dominance of Ca²⁺ and HCO₃ ⁻, followed by Mg²⁺ and SO₄ ²⁻. The increase in TDS and major anions (Cl⁻, NO₃ ⁻, and SO₄ ²⁻) concentrations from upstream to downstream is ascribed to both extensive influences from agriculture and domestic activities over the Hanjiang basin. The chemical and Sr isotopic analyses indicate that three major weathering sources (dolomite, limestone, and silicates) contribute to the total dissolved loads. The contributions of the different end-members to the dissolved load are calculated with the mass balance approach. The calculated results show that the dissolved load is dominated by carbonates weathering, the contribution of which accounts for about 79.4% for the Hanjiang River. The silicate weathering and anthropogenic contributions are approximately 12.3 and 6.87%, respectively. The total TDS fluxes from chemical weathering calculated for the water source area (the upper Hanjiang basin) and the whole Hanjiang basin are approximately 3.8 × 10⁶ and 6.1 × 10⁶ ton/year, respectively. The total chemical weathering (carbonate and silicate) rate for the Hanjiang basin is approximately 38.5 ton/km²/year or 18.6 mm/k year, which is higher than global mean values. The fluxes of CO₂ consumption by carbonate and silicate weathering are estimated to be 56.4 × 10⁹ and 12.9 × 10⁹ mol/year, respectively.     

Size and composition of inorganic colloids in a peri-alpine, glacial flour-rich lake

From June 2004 to October 2005, particle size distributions (PSD) and the mineralogy of inorganic colloids in Lake Brienz, a glacial flour-rich Swiss lake, and in its tributaries (the Aare and Lütschine rivers), were quantified by single particle counting based on light scattering (0.1-2 μm) combined with transmission electronic microscopy coupled with energy dispersive spectroscopy and selected area electron diffraction. The two lake tributaries differ in terms of the geology of their catchment area and in their hydrology: the River Lütschine’s glacial regime is unperturbed, while the River Aare has been significantly modified by hydroelectric installations. The dependence of the colloid concentration numbers on colloid diameters can be described by a power-law distribution in all cases. The power-law slopes in the River Aare were consistently smaller, and the total colloid number concentrations consistently higher, (mean values: −3.89 and 6.2 × 10⁸ mL⁻¹, respectively) than in the River Lütschine (−3.61 and 1.7 × 10⁸ mL⁻¹). The measured PSD in the lake were dependent on season and depth: homogenous in the whole epilimnion in winter and modified by river intrusions in summer. In this season, the presence of a river turbid plume above the thermocline is a significant source of colloids in the epilimnion, where their concentration was high (mean value: 5.1 × 10⁷ mL⁻¹). The same main mineral types were found in the different systems: 2:1 minerals, feldspars, chlorite and quartz; with a few particles of oxides. Differences in their relative concentrations in the rivers, essentially reflecting the geological differences of the respective catchment areas, made it possible to trace the origin of the mineral colloids present in lake surface waters throughout the year. The relationship between colloid size and mineralogy was assessed, showing that different minerals have distinct size distributions. In the rivers, where almost no aggregates were observed, PSD would essentially be the result of the nature (particle formation and mineralogy) of the colloids, whereas in the lake, aggregation and sedimentation processes would also play a role, particularly in summer.     

Sorption reversibility kinetics in the ternary system radionuclide–bentonite colloids/nanoparticles–granite fracture filling material

The kinetics of radionuclide desorption from bentonite colloids and subsequent sorption onto fracture filling material can influence colloid-facilitated radionuclide migration in ground water. To shed light on the significance of these issues batch-type experiments using a cocktail of strong and weak sorbing radionuclides as well as FEBEX bentonite colloids in the presence of fracture filling material from Grimsel (Switzerland) under Grimsel ground water conditions have been conducted. Results show that tri- and tetravalent radionuclides, ²³²Th(IV), ²⁴²Pu(IV) and ²⁴³Am(III) are clearly colloid associated in contrast to ²³³U(VI), ²³⁷Np(V) and ⁹⁹Tc(VII). Concentrations of colloid-borne ²³²Th(IV), ²⁴²Pu(IV) and ²⁴³Am(III) decrease after ∼100 h showing desorption from bentonite colloids while ²³³U(VI) and ⁹⁹Tc(VII) concentrations remain constant over the entire experimental time of 7500 h thus showing no interaction either to colloids or to the fracture filling material. ²³²Th(IV) and ²⁴²Pu(IV) data yield a slower dissociation from colloids compared to ²⁴³Am(III) indicating stronger RN–colloid interaction. In the case of ²³⁷Np(V), a decrease in concentration after ∼300 h is observed which can be explained either by slow reduction to Np(IV) and subsequent sorption to mineral surfaces in accordance with the evolution of pe/pH and/or by a slow sorption onto the fracture filling material. No influence of the different fracture filling material size fractions (0.25–0.5 mm, 0.5–1 mm and 1–2 mm) can be observed implying reaction independence of the mineral surface area and mineralogical composition. The driving force of the observed metal ion desorption from colloids is binding to fracture filling material surfaces being in excess of the available colloid surface area (76:1, 55:1 and 44:1 for the 0.25–0.5 mm, 0.5–1 mm and 1–2 mm size fraction of the FFM, respectively).     

Arsenic in surface- and up to 90°C ground waters in a basalt area,N-Iceland: processes controlling its mobility

The concentrations of As in surface- and up to 90 °C ground waters in a tholeiite flood basalt area in N-Iceland lie in the range <0.03–10 μg/kg. With few exceptions surface waters contain <0.5 μg/kg As whereas ground waters generally contain >0.5 μg/kg As. The As content of ground waters increases on the whole with rising temperature. Arsenic is highly mobile in the basalt-water environment of the study area. An insignificant fraction of the As dissolved from the rock is taken up into secondary minerals. Arsenic is less mobile than B but considerably more mobile than Na which has the highest mobility among the major aqueous components. A significant fraction of the As in the basalt occurs in an easily soluble form. The As hosted in the primary minerals is expected to be concentrated in the titano-magnetite. This mineral is stable in contact with both surface- and ground waters and does not, therefore, supply As to the water, explaining the difference in mobility between As and B. Aqueous As concentrations are a reflection of water/rock ratios, i.e. how much rock a given quantity of water has dissolved. This ratio increases with increasing temperature and increasing residence time of the water in contact with the rock. The distribution of As species has been calculated on the assumption of equilibrium at the redox potential retrieved from measurement of aqueous Fe(II) and Fe(III) concentrations. These calculations indicate that pentavalent As is stable in surface waters and in ground waters with an in situ pH of <10 and would occur mostly as H₂AsO₄⁻ and HAsO₄⁻². In higher pH ground waters the concentrations of the arsenite species H₂AsO₃⁻ is significant at equilibrium, up to 65% of the total dissolved As.     

Groundwater resources of the middle and upper Odra River basin, southwestern Poland

 The total amount of groundwater resources in the middle and upper Odra River basin is 5200×10³ m³/d, or about 7.7% of the disposable groundwater resources of Poland. The average modulus of groundwater resources is about 1.4 L/s/km². Of the 180 'Major Groundwater Basins' (MGWB) in Poland, 43 are partly or totally located within the study area. The MGWB in southwestern Poland have an average modulus of groundwater resources about 2.28 L/s/km² and thus have abundant water resources in comparison to MGWB from other parts of the country. Several types of mineral waters occur in the middle and upper Odra River basin. These waters are concentrated especially in the Sudety Mountains. Carbon-dioxide waters, with yields of 414 m³/h, are the most widespread of Sudetic mineral waters. The fresh waters of the crystalline basement have a low mineralization, commonly less than 100 mg/L; they are a HCO₃–Ca–Mg or SO₄–Ca–Mg type of water. Various hydrochemical compositions characterize the groundwater in sedimentary rocks. The shallow aquifers are under risk of atmospheric pollution and anthropogenic effects. To prevent the degradation of groundwater resources in the middle and upper Odra River basin, Critical Protection Areas have been designated within the MGWB. Received, January 1995 Revised, May 1996, August 1997 Accepted, August 1997     

Groundwater Evolution and Mineral Alteration Reactions in the Basaltic Rock Sequence of Mt. Wasserkuppe, Germany: A Case Study

Groundwater sampling was accomplished in the basaltic sequence of the Rh?n mountain range, Germany, in order to investigate hydrochemical groundwater evolution and to delineate mineral alteration reactions involved in natural weathering. The hydrochemical compositions of near-surface groundwaters indicate a Ca/Mg–HCO₃ type with near-neutral pH and evolve to a Na–HCO₃ type with high pH at greater depth. Column experiments were performed with basaltic and phonolitic rock samples to determine individual mineral alteration reactions. The basic reactions could be related to the alteration of olivine, Ca-pyroxene, plagioclase, pyrrhotite, and feldspathoids under formation of secondary clay minerals (smectites, illite) and goethite. The mineral alteration reactions deduced from the leaching experiments by inverse modelling were found to be consistent with the mineral reactions associated with the natural groundwaters. The reactions calculated for groundwater evolution involve the alteration of primary and secondary minerals to produce low-T mineral phase. The conversion of secondary Na-beidellite to illite occurs at a later stage of groundwater evolution, reducing the concentrations of K⁺ and Mg²⁺. Near-surface groundwaters do not indicate significant cation exchange. Initial cation exchange requires elevated pH values, with Mg²⁺ removed from solution preferred to Ca²⁺. Na-alkalisation of the groundwaters at greater depth suggests the exchange of Na⁺ for Mg²⁺ and Ca²⁺ on Na-beidellite, supported by cation exchange on coatings of iron hydroxides as alteration products. Among the mature high-pH groundwater at greater depth, the dissolution of anorthite and albite has significant effect on groundwater composition.     

Hydrogeochemical properties of CO2-rich thermal–mineral waters in Kayseri (Central Anatolia), Turkey

The present study highlights the hydrogeological and hydrogeochemical characteristics of the CO₂-rich thermal–mineral waters in Kayseri, Turkey. These waters of Dokuzpınar cold spring (DPS) (12–13°C), Yeşilhisar mineral spring (YMS) (13–16°C), Acısu mineral spring (ACMS) (20–22.5°C), Tekgöz thermal spring (TGS) (40–41°C), and Bayramhacı thermal-mineral spring (BTMS) (45–46.5°C) have different physical and chemical compositions. The waters are located within the Erciyes basin in the Central Anatolian Crystalline complex consisting of three main rock units. Metamorphic/crystalline rocks occur as the basement, sedimentary rocks of Upper Cretaceous-Quaternary age form the cover, and volcanosedimentary rocks Miocene-Quaternary in age represent the extrusive products of magmatism acting in that period. All these units are covered unconformably by terrace and alluvial deposits, and travertine occurrences have variable permeability. Dokuzpinar cold spring, YMS and ACMS localized mainly along the faults within the region have higher Na⁺ and Cl⁻ contents whereas TGS and BTMS have higher amounts of Ca²⁺ and HCO ₃ ⁻ . The high concentrations of Ca²⁺ and HCO ₃ ⁻ are mainly related to the high CO₂ contents resulting from interactions with carbonate rocks. Whereas the high Na⁺ content is derived from the alkaline rocks, such as syenite, tuff and basalts, the Cl⁻ is generally connected to the dissolution of the evaporitic sequences. These waters are of meteoric-type. BTMS deviates from meteoric water line. The content is related to the increases in the δ¹⁸O compositions due to mineral–water interaction (re-equilibrium) process. CO₂-dominated YMS and ACMS with low temperatures have higher mineralizations. Yeşilhisar mineral spring, ACMS, TGS and BTMS are oversaturated in terms of calcite, aragonite, dolomite, goethite and hematite, and undersaturated with respect to gypsum, halite and anhydrite. Yeşilhisar mineral spring, ACMS and BTMS are also characterized by recent travertine precipitation. Dokuzpınar cold spring is undersaturated in terms of the above minerals. The higher ratios of Ca/Mg and Cl/HCO₃, and lower ratios of SO₄/Cl in BTMS than TGS suggest that TGS has shallow circulation compared to BTMS, and/or has much more heat-loss enroute the surface. The sequence of hydrogeochemical and isotopic compositions of the waters is in an order of DPS>YMS>ACMS>TGS>BTMS and this suggests a transition period from a shallow circulation to a deep circulation path.