Interpreting the borehole water chemistry of the Permo-Triassic sandstone aquifer of the Liverpool area,UK

Using hydrogeological data, historical chemical data and the results of studies in adjacent aquifers, an interpretation of the water chemistry from a sparse network of boreholes is presented for the Liverpool area. The chemistry of the fresh groundwater samples is influenced by geology, pollution and pumping history. The oldest waters, present where the sandstone is covered by Quaternary deposits, are calcite-saturated, contain little NO⁻₃ and have low SO²⁻₄ and Cl⁻ concentrations. However, water from the Collyhurst Sandstone are depleted in HCO⁻₃ whatever the concentrations of the other anions. Samples from boreholes in areas where the sandstones are not covered by Quaternary deposits are characterized by very low alkalinity and pH, and by high NO⁻₃, SO²⁻₄, and Cl⁻. In the regions of the aquifer close to sandstone outcrop, or where the Quaternary deposits are thin, the water samples have higher alkalinity and pH, and lower anion concentrations. Scattered throughout the region are boreholes yielding waters with very high SO²⁻₄ concentrations: where associated with industrial sites, these waters also have high NO⁻₃ concentrations and industrial pollution is suspected. In rural areas the high SO²⁻₄ concentrations are derived from leakage through the sulphur-bearing tills in response to pumping-induced lowering of the piezometric surface. The distribution of borehole water types can be described with the help of a set of rules relating water type to hydrogeological features; these rules allow a map of hydrochemical distributions to be constructed. Saline groundwaters occur in the aquifer adjacent to the Mersey Estuary and have chemistry compositions equivalent to slightly modified, diluted Estuary water. With the exception of a single deep borehole sample, there is no indication of the widespread presence of ancient saline groundwaters in the base of the sandstone sequences as is found in the sandstones to the east of the study area. However, slightly saline, reduced waters occur below the Mercia Mudstone Group in the north of the area. Historical records give some indication of the changes in water chemistry distributions through time.     

Interstitial water and hydrochemistry of a mangrove forest and adjoining water system, south west coast of India

 Eh, pH, salinity, total alkalinity, dissolved O₂, NO₂ ^–, PO₄ ^–3, SiO₂ and NH₄ ⁺ of waters from a mangrove forest, an estuary and a creek connecting the mangrove forest and the estuary have been measured. Further, the chemistry of interstitial waters of surficial and core sediments from the mangrove forest have been analyzed for the above parameters, except dissolved oxygen. To understand the flux of nutrients from the mangrove forest to the adjoining estuary, creek waters were monitored during tidal phases. PO₄ ^–3, SiO₂ and NH₄ ⁺ were found to be at elevated levels in mangrove waters whereas NO₂ ^– shows no variation compared to the estuary. Dissolved O₂ is low in mangrove waters. PO₄ ^–3, NH₄ ⁺ and SiO₂ are several times higher in interstitial waters than in overlying waters. Several fold enrichment of PO₄ ^–3, NH₄ ⁺ and, to some extent, SiO₂ were measured in creek waters during ebbing relative to flooding, indicating that mangroves act as a perennial source for the above nutrients. Received: 26 May 1998 · Accepted: 21 July 1998     

Geochemical and Sr-isotopic characteristics of stream and spring waters from small-forested catchments at Seto,central Japan

Hydrogeochemical processes controlling surface water chemistry were examined in five small (<1.5 km ²) forested catchments that have contrasting bedrock lithologies of granite, and conglomerate, and are distributed in the southeast of Seto district, central Japan. Watersheds developed on these two bedrocks differ in their ability to neutralize atmospheric acid (pH ~4.5) deposition. The study was conducted to (1) characterize the hydrogeochemical processes controlling surface water chemistry, and (2) to elucidate acidification of spring and stream waters using data from three sampling campaigns conducted from August to October 2000. Stream and spring water solutes fall into two general groups according to concentration: alkaline, relatively high pH (5.2–7.7) and high cation concentrations (HCO ₃ ^-, Cl ^-, base cations), and dilute, low pH (4.2–5.5) waters. Concentrations of trace metals (Al, Ba, Sr) showed a strong negative correlation with pH, suggesting the mobility of these metals in the dissolved load of catchments underlain by Tokai conglomerate. The strontium isotope ratio ( ⁸⁷Sr/ ⁸⁶Sr) of rock and soil, plant, precipitation, and surface water samples was used to identify different reservoirs within the ecosystem. Low Si concentrations in stream and spring waters from the conglomerate area, with a relatively high pool of SiO ₂, >90 (wt%), suggest slow chemical weathering. The dissolved solute concentrations are generally of similar magnitude in stream waters within the catchments of similar bedrock lithology. The high inverse correlation ( r ²=0.72) between pH and SO ₄ ^– concentrations and the high positive correlation ( r ² =0.90) between Ba and SO ₄ ^– concentrations in waters draining Tokai conglomerate suggest that barite (BaSO ₄) is being dissolved in an acidic environment. The three catchments were identified as being sensitive to acidic deposition because the bedrock conglomerate provided little capacity to buffer acidic inputs. The soils from the granite area have a high cation-exchange capacity (CEC an average of 868 µmol/kg), and are nearly ten times greater than the soils from the conglomerate area. Because ion exchange, besides weathering, is the main source that counteracts soil acidification, the sensitivity to further acidification may increase.     

Role of Subsurface Brines in Salt Balance: The Case Study of the Caspian Sea and Kara Bogaz Bay

The water level of the Caspian Sea fluctuated significantly during recent history, without consensus for the cause. The varied chemistry of the Caspian, Kara Bogaz and sediment a interstitial waters provides a further insight. Element concentrations and ⁸⁷Sr/⁸⁶Sr ratios of the interstitial waters were compared to those of Caspian and Kara Bogaz open waters, and of acid-leached extractable components. The ⁸⁷Sr/⁸⁶Sr ratios of the interstitial waters are explained by addition of subterranean waters similar to nearby spring waters. These subterranean waters yield chemical characteristics such as a Cl/SO₄, ⁸⁷Sr/⁸⁶Sr, Ca/Sr and K/Rb ratios of respectively 80, 0.7086, 250 and 1,800. However, their addition does not explain the large difference in the K/Rb ratio of the Caspian and Kara Bogaz waters, respectively at 7,630 and 17,550, which implies also a leaching of salt deposits by the upward migrating subterranean waters. The sediments of the southern Caspian basin, with low Na, Cl and SO₄ in their interstitial waters, deposited apparently in an anoxic environment. The related chemical changes in the waters are also indicative of a recent change in the hydrologic regime, possibly induced by a changing morphology of the drainage basin.     

Chemical and isotopic examination of produced waters from the BP-Wolf lake in situ combustion pilot

The chemical and isotopic compositions of co-produced waters can be used to monitor the processes that take place during in situ combustion. Anticipated processes include mixing of waters, production of CO₂, production of high concentrations of dissolved sulphate and variations in water chemistry associated with heated zones. Water sources include pore waters in oil-bearing strata, waters in overlying or underlying aquifers, water condensed from previously injected steam, and waters associated with combustion. Waters from all sources may mix during production and interpretation of the combustion process can be refined by an understanding of water sources. Produced fluids from the BP-Wolf Lake pilot site in Alberta have been examined to evaluate the effectiveness of the chemical composition of water and the isotopic compositions of aqueous species for monitoring in situ combustion.Produced waters do not show simple conservative mixing behaviour. This suggests that multiple sources of water and other processes, including water-rock reactions, act to modify water compositions. At least three sources of produced waters can be recognized and these are interpreted to be formation water, injected steam and waters that have low Cl and high HCO₃ due to combustion. It is not possible to distinguish waters in the oil-bearing formation from regional waters present in aquifers that underlie the stimulated intervals. Dissolved aqueous species, such as SiO₂, Na, K (as Na/K) and Cl can be used to monitor the approach of the combustion front. Sulphate has been suggested as an indicator of approaching combustion and, although sulphate concentrations rise as combustion approaches a producing well, this indicator is not reliable in all cases. The use of all the above chemical parameters is recommended for detection of combustion zones during operation.The isotope composition of produced waters confirms that there has been significant water-rock interaction during combustion. Carbon isotope compositions of HCO₃ that range from −8 to −25% δ¹³C show that oil oxidation is a major contributor of CO₂ at high temperatures, but CO₂ produced by carbonate mineral dissolution becomes more significant as temperature decreases. Sulphate concentrations in waters produced during combustion can be an order of magnitude higher than those observed during steam stimulation. Both the oil (bitumen) and pyrite (FeS₂) are significant sulphur sources. Typically, the sulphur in both phases is in a reduced state and is available through oxidation associated with combustion. The δ³⁴S of dissolved sulphate in produced waters does not unequivocally identify either of the two major sources of sulphur. However, the relatively depleted δ³⁴ values for SO₄ suggest that the high sulphate concentrations generally associated with the approach of the combustion front result from the oxidation of pyrite.     

Geochemical constraint on origin and evolution of solutes in geothermal springs in western Yunnan,China

Geothermal resources are very rich in Yunnan, China. However, source of dissolved solutes in geothermal water and chemical evolution processes remain unclear. Geochemical and isotopic studies on geothermal springs and river waters were conducted in different petrological-tectonic units of western Yunnan, China. Geothermal waters contain Ca–HCO₃, Na–HCO₃, and Na (Ca)–SO₄ type, and demonstrate strong rock-related trace elemental distributions. Enhanced water–rock interaction increases the concentration of major and trace elements of geothermal waters. The chemical compositions of geothermal waters in the Rehai geothermal field are very complicated and different because of the magma chamber developed at the shallow depth in this area. In this geothermal field, neutral-alkaline geothermal waters with high Cl, B, Li, Rb Cs, As, Sb, and Tl contents and acid–sulfate waters with high Al, Mn, Fe, and Pb contents are both controlled by magma degassing and water–rock interaction. Geothermal waters from metamorphic, granite, and sedimentary regions (except in the Rehai area) exhibit varying B contents ranging from 3.31 mg/L to 4.49 mg/L, 0.23 mg/L to 1.24 mg/L, and <0.07 mg/L, respectively, and their corresponding δ¹¹B values range from −4.95‰ to −9.45‰, −2.57‰ to −8.85‰, and −4.02‰ to +0.06‰. The B contents of these geothermal waters are mainly controlled by leaching host rocks in the reservoir, and their δ¹¹B values usually decrease and achieve further equilibrium with its surrounding rocks, which can also be proven by the positive δ¹⁸O-shift. In addition to fluid–rock reactions, the geothermal waters from Rehai hot springs exhibit higher δ¹¹B values (−3.43‰ to +1.54‰) than those yielded from other areas because mixing with the magmatic fluids from the shallow magma. The highest δ¹¹B of steam–heated waters (pH 3.25) from the Zhenzhu spring in Rehai is caused by the fractionation induced by pH and the phase separation of coexisting steam and fluids. Given the strong water–rock interaction, some geothermal springs in western Yunnan show reservoir temperatures higher than 180 °C, which demonstrate potential for electricity generation and direct-use applications. The most potential geothermal field in western Yunnan is located in the Rehai area because of the heat transfer from the shallow magma chamber.     

Sulphate adsorption capacity and pH of upland podzolic soils in Scotland: Effects of parent material,texture and precipitation chemistry

A regional survey of podzol B horizons has been carried out to investigate the effects of parent material and soil texture on sulphate (SO₄²⁻) adsorption capacity and pH in Scottish soils. Sulphate adsorption was measured on equilibration of the soils with 10 and 100 mg 1⁻¹ SO₄²⁻ solutions. The results showed that soil texture and soil parent material had a significant effect on SO₄²⁻ adsorption. Significant correlations were found between sulphur (S) deposition loads and SO₄²⁻ adsorption, and between precipitation pH and soil pH, but not between total hydrogen ion (H⁺) load and soil pH, even on sensitive soils. Relationships between the chemical composition of atmospheric deposition and soil pH could be marginally improved if the possible amelioration of acidification by base cation inputs, especially on sensitive soils, was taken into account.     

The effect of organic matter on chemical weathering: study of a small tropical watershed: nsimi-zoétélé site,cameroon

The effect of organic matter during soil/water interaction is still a debated issue on the controls of chemical weathering in a tropical environment. In order to study this effect in detail, we focused on the weathering processes occurring in a small tropical watershed (Nsimi-Zoetélé, South Cameroon). This site offers an unique opportunity to study weathering mechanisms in a lateritic system within a small basin by coupling soil and water chemistry.The lateritic cover in this site can reach up to 40 m in depth and show two pedological distinct zones: unsaturated slope soils on the hills and/or elevated areas; and water-saturated soils in the swamp zone which represent 20% of the basin surface. The study present chemical analysis performed on water samples collected monthly from different localities between 1994–1997 and on soil samples taken during a well drilling in December 1997. The results suggest the existence of chemical and spatial heterogeneities of waters in the basin: colored waters flooding the swamp zone have much higher concentrations of both organic matter (i.e., DOC) and inorganic ions (e.g., Ca, Mg, Al, Fe, Th, Zr) than those from springs and groundwater from the hills. Nevertheless, these organic-rich waters present cation concentrations (Na, Ca, Mg, K) which are among the lowest compared to that of most world rivers. The main minerals in the soils are secondary kaolinite, iron oxi-hydroxides, quartz, and accessory minerals (e.g., zircon, rutile). We mainly focused on the mineralogical and geochemical study of the swamp zone soils and showed through SEM observations the textural characterization of weathered minerals such as kaolinite, zircon, rutile, and the secondary recrystallization of kaolinite microcrystals within the soil profile. Water chemistry and mineralogical observations suggest that hydromorphic soils of the swamp zone are responsible for almost all chemical weathering in the basin. Thus, in order to explain the increase of element concentration in the organic-rich waters, we suggest that organic acids enhance dissolution of minerals such as kaolinite, goethite, and zircon and also favors the transport of insoluble elements such as Al, Fe, Ti, Zr, and REE by chemical complexation. SiO₂(aq) concentrations in these waters are above saturation with respect to quartz. Dissolution of phytholithes (amorphous silica) may be responsible for this relatively high SiO₂(aq.) concentration. Al/Mg ratios obtained for the soil and the Mengong river waters show that a significant amount of Al does not leave the system due to kaolinite recrystallisation in the swamp zone soils. Geochemical data obtained for this watershed show the important contribution of vegetation and organic matter on chemical weathering in the swamp zone. Quantitatively we propose that the increasing amount in total dissolved solid (TDS) due to organic matter and vegetation effect is about 35%. In summary, this interaction between soils and waters occurs mostly in soils that are very depleted in soluble elements. Thus, the low concentration of major elements in these water is a direct consequence of the depleted nature of the soils.     

The hydrogeochemistry of the Lake Waco drainage basin,Texas

The origin of surface water chemistry in highly impacted drainage basins must be investigated on a drainage-basin scale if the causes of the pollution are to be elucidated. This study characterizes and deciphers the surface water chemistry of a nutrient polluted river system in central Texas. Four tributaries of the Lake Waco reservoir were chemically characterized temporally and spatially in order to gain a complete understanding of the nature and origin of dissolved solids being transported into the lake. Temporal chemical variations measured at the base of each of the drainage basins are repetitive and seasonal. The most periodic and well-defined variation is exhibited by nitrate concentrations although many of the other solutes show seasonal changes as well. These temporal chemical changes are controlled by seasonal precipitation. During rainy seasons, the shallow aquifer is recharged resulting in stream discharge that is high in nitrate, calcium, and bicarbonate. When the shallow flow system is depleted in the summer, stream waters are dominated by deeper groundwater and become rich in sodium. Spatial variations in the chemistry of South Bosque surface waters were characterized using the snapshot technique. The spatial distribution of nitrate in surface waters is controlled by fertilizer application to row crops and the location of a munitions factory. The concentrations of naturally derived solutes such as Ca⁺, Na⁺, Cl^–, and SO₄^–2are controlled by underlying lithologies.     

Iron monosulfide formation and oxidation in drain-bottom sediments of an acid sulfate soil environment

Iron monosulfide formation and oxidation processes were studied in the extensively drained acid sulfate soil environment of the Tweed River floodplain in eastern Australia. Porewater profiles of pH, Eh, SO₄²⁻, Fe²⁺, Fe³⁺, Cl⁻, HCO₃⁻, and metals (Cd, Co, Cr, Cu, Ni, Pb and Zn) were obtained using in situ dialysis membrane samplers (`peepers'). Concentrations of acid volatile S (AVS), pyrite, total S, reactive Fe, total and organic C, simultaneously extracted metals (SEMs) and total elemental composition by X-ray fluorescence, were determined on sediment samples. The oxidation of pyrite in the surrounding landscape provides a source of acidity, Fe, Al, SO₄ and metals, which are exported into the drainage system where they accumulate in the sediments and porewaters. Negative porewater concentration gradients of SO₄²⁻ and Fe²⁺, and large AVS concentrations in the sediments, indicate Fe monosulfides form rapidly under reducing conditions and consume acidity and metals. Oxidation of the sediments during previous drought episodes has resulted in the conversion of monosulfides and pyrite to oxidised Fe minerals and the release of acidity, SO₄²⁻, Fe³⁺, and metals to the surface waters. These formation and oxidation cycles show that Fe monosulfides play an important role in controlling water quality in the drainage system.     

Dissolved aluminium in interstitial waters of recent terrigenous marine sediments from the North Atlantic Ocean

The vertical distribution of dissolved Al in interstitial waters of recent marine sediments has been determined using a fluorimetric analytical method adapted for interstitial water analysis. The results suggest that diagenetic reactions occur in the sediment soon after deposition. A narrow depth zone acting as a source of dissolved Al is found in each core. Outside this zone Al appears to be removed from solution and its concentration decreases to values of 1.5 μgAl/l or less, comparable to those of open ocean waters. Dissolved Al and SiO₂ concentrations in interstitial waters close to the sediment-seawater interface are linearly correlated in most cases, suggesting that the geochemistry of Al may be related to the behaviour of biogenic silica in marine sediments.     

Evaluation of aluminum speciation in surface waters in China and its environmental risk assessment

As the ongoing global research on acid precipitation is developing in depth, more and more attention has been paid to the ecological effects of aluminum (Al) due to its toxicity to plants and animals, which is caused by acid precipitation. As a very serious problem of terrestrial and aquatic environmental acidification occurs in China, especially in southwestern China, a systematic investigation of Al speciation in these regions is very important. In this paper, the Al speciation results of surface waters in China are reported and its ecological impacts is evaluated. More than 100 water samples were collected from about twenty provinces of China. Driscoll's Al speciation scheme combined with the modified MINQEL computer model is used for speciation of Al. This study shows that the ecological impacts of acidification are quite different between China and Western countries, because of different geographical environments and geological settings. In Western countries, acidification is mainly caused by NO₂^-. Due to low concentrations of K⁺, Na⁺, Ca²⁺, Mg²⁺, the buffer capacities of soil and water are weak. Therefore, natural waters can be acidified to pH<5 very easily, resulting in a considerable mobilization of Al and worsening of the ecological environment. In China, acid precipitation is mainly in the form of sulfuric acid. In northwestern China, concentrations of K⁺, Na⁺, Ca²⁺, Mg²⁺ are high in soil and surface waters. This leads to much higher capacity and a high resistance ability to acidification. The pH values of waters in this region are high (around 7) and no serious Al toxicity is found at present. However, in northeastern and southeastern China, the soil is rich in Al (unsaturated aluminosilicates in northeastern China, saturated aluminosilicates in north and central China, aluminum-rich soil in southeastern and southwestern China). The concentrations of K⁺, Na⁺, Ca²⁺, Mg²⁺ in soil and waters are lower than those of northwestern China. Therefore the buffer capacity is limited. Numerous surface waters have already been acidified and pH values declined to 5. The impacts of Al toxicity on ecological systems in these regions are very serious, especially in Jiangxi, Hubei Provinces and Chongqing Municipality.     

Solubility relationships of aluminum and iron minerals associated with acid mine drainage

The ability to properly manage the oxidation of pyritic minerals and associated acid mine drainage is dependent upon understanding the chemistry of the disposal environment. One accepted disposal method is placing pyritic-containing materials in the groundwater environment. The objective of this study was to examine solubility relationships of Al and Fe minerals associated with pyritic waste disposed in a low leaching aerobic saturated environment. Two eastern oil shales were used in this oxidizing equilibration study, a New Albany Shale (unweathered, 4.6 percent pyrite), and a Chattanooga Shale (weathered, 1.5 percent pyrite). Oil shale samples were equilibrated with distilled-deionized water from 1 to 180 d with a 1∶1 solid-to-solution ratio. The suspensions were filtered and the clear filtrates were analyzed for total cations and anions. Ion activities were calculated from total concentrations. Below pH 6.0, depending upon SO ₄ ²⁻ activity, Al³⁺ solubility was controlled by AlOHSO₄ (solid phase) for both shales. Initially, Al³⁺ solubility for the New Albany Shale showed equilibrium with amorphous Al(OH)₃. The pH decreased with time, and Al³⁺ solubility approached equilibrium with AlOHSO_4(s). Below pH 6.0, Fe³⁺ solubility appeared to be regulated by a basic iron sulfate solid phase with the stoichiometric composition of FeOHSO_4(s). The results of this study indicate that below pH 6.0, Al³⁺ solubilities, are limited by basic Al and Fe sulfate solid phases (AlOHSO_4(s) and FeHSO_4(s)). The results from this study further indicate that the acidity in oil shale waters is produced from the hydrolysis of Al³⁺ and Fe³⁺ activities in solution. These results indicate a fundamental change in the stoichiometric equations used to predict acidity from iron sulfide oxidation. The results of this study also indicate that water quality predictions associated with acid mine drainage can be based on fundamental thermodynamic relationships. As a result, waste management decisions can be based on waste-specific/site-specific test methods.     

Mineral species control of aluminum solubility in sulfate-rich acidic waters

The identification of the mineral species controlling the solubility of Al in acidic waters rich in sulfate has presented researchers with several challenges. One of the particular challenges is that the mineral species may be amorphous by X-ray diffraction. The difficulty in discerning between adsorbed or structural sulfate is a further complication. Numerous studies have employed theoretical calculations to determine the Al mineral species forming in acid sulfate soil environments. The vast majority of these studies indicate the formation of a mineral species matching the stoichiometry of jurbanite, Al(OH)SO₄·5H₂O. Much debate, however, exists as to the reality of jurbanite forming in natural environments, particularly in view of its apparent rare occurrence. In this work the use of Al, S and O K-edge XANES spectroscopy, in combination with elemental composition analyses of groundwater precipitates and a theoretical analysis of soluble Al concentrations ranging from pH 3.5 to 7, were employed to determine the mineral species controlling the solubility of Al draining from acid sulfate soils into Blacks Drain in north-eastern New South Wales, Australia. The results indicate that a mixture of amorphous Al hydroxide (Al(OH)₃) and basaluminite (Al₄(SO₄)(OH)₁₀·5H₂O) was forming. The use of XANES spectroscopy is particularly useful as it provides insight into the nature of the bond between sulfate and Al, and confirms the presence of basaluminite. This counters the possibility that an Al hydroxide species, with appreciable amounts of adsorbed sulfate, is forming within these groundwaters.Below approximately pH 4.5, prior to precipitation of this amorphous Al(OH)₃/basaluminite mixture, our studies indicate that the Al³⁺ activity of these acidic sulfate-rich waters is limited by the availability of dissolved Al from exchangeable and amorphous/poorly crystalline mineral species within adjacent soils. Further evidence suggests the Al³⁺ activity below pH 4.5 is then further controlled by dilution with either rainwater or pH 6-8 buffered estuarine water, and not a notional Al(OH)SO₄ mineral species.     

The impact of water-rock interaction and vegetation on calcium isotope fractionation in soil- and stream waters of a small, forested catchment (the Strengbach case)

This study aims to constrain the factors controlling the calcium isotopic compositions in surface waters, especially the respective role of vegetation and water-rock interactions on Ca isotope fractionation in a continental forested ecosystem. The approach is to follow changes in space and time of the isotopic composition and concentration of Ca along its pathway through the hydro-geochemical reservoirs from atmospheric deposits to the outlet of the watershed via throughfalls, percolating soil solutions and springs. The study is focused on the Strengbach catchment, a small forested watershed located in the northeast of France in the Vosges mountains. The δ^44/40Ca values of springs, brooks and stream waters from the catchment are comparable to those of continental rivers and fluctuate between 0.17 and 0.87‰. Soil solutions, however, are significantly depleted in lighter isotopes (δ^44/40Ca: 1.00-1.47‰), whereas vegetation is strongly enriched (δ^44/40Ca: −0.48‰ to +0.19‰). These results highlight that vegetation is a major factor controlling the calcium isotopic composition of soil solutions, with depletion in “light” calcium in the soil solutions from deeper parts of the soil compartments due to preferential ⁴⁰Ca uptake by the plants rootsystem. However, mass balance calculations require the contribution of an additional Ca flux into the soil solutions most probably associated with water-rock interactions. The stream waters are marked by a seasonal variation of their δ^44/40Ca, with low δ^44/40Ca in winter and high δ^44/40Ca in spring, summer and autumn. For some springs, nourishing the streamlet, a decrease of the δ^44/40Ca value is observed when the discharge of the spring increases, with, in addition, a clear covariation between the δ^44/40Ca and corresponding H₄SiO₄ concentrations: high δ^44/40Ca values and low H₄SiO₄ concentrations at high discharge; low δ^44/40Ca values and high H₄SiO₄ concentrations at low discharge. These data imply that during dry periods and low water flow rate the source waters carry a Ca isotopic signature from alteration of soil minerals, whereas during wet periods and high flow rates admixture of significant quantities of ⁴⁰Ca depleted waters (vegetation induced signal) from uppermost soil horizons controls the isotopic composition of the source waters. This study clearly emphasizes the potential of Ca isotopes as tracers of biogeochemical processes at the water-rock-vegetation interface in a small forested catchment.     

Carbonate chemistry of groundwater from chalk,Givendale, East Yorkshire

Precipitation, soil and spring waters from an outlier of Chalk were analysed over a one year period for field pH, and contents of Ca⁺², Mg⁺², HCO₃^? and other dissolved solids. Measured soil log PCO₂ (atm) varied between a minimum of ?2.60 and maximum of ?1.46, and could be predicted from measurements of soil temperature. Soil waters evolved under open system conditions with respect to soil CO₂, and were undersaturated with calcite during the winter recharge period.The chemistry of the springs is related to their topographic position. Group 1 springs, located below a feather edge of chalk, had both their minimum and maximum PCO₂s predicted by the soil CO₂ data, suggesting open system CO₂ evolution. Group 2 springs, located along the scarp slope had minimum PCO₂s predicted by the soil data, but maximum PCO₂s which could only be explained by a closed system evolution from the maximum soil CO₂ observed. Group 1 springs were close to calcite saturation, whereas Group 2 springs were significantly undersaturated with calcite. The two groups could be identified by linear discriminant analysis of measured Ca²⁺, pH and HCO₃^? concentrations.     

Application of geochemistry and radioactivity in the hydrogeological investigation of carbonate aquifers (Sierras Blanca and Mijas,southern Spain)

The chemical characteristics, ³H contents and radioactivity of groundwaters from the Sierras Blanca and Mijas (Southern Spain) have been studied in relation to the chemical composition and radioactivity of the aquifer host rocks, and the residence time of the water. The Sierras Blanca and Mijas are made up of calcitic and dolomitic marbles of Triassic age. The groundwaters that drain the calcitic marbles (which outcrop principally in the western Sierra Blanca) have less mineralization, which descreases quickly with recharge (as does the ³H content), and the gross alpha and beta activities are below detection limit. This is due to the short residence time of water inside the aquifers which are conduit flow systems. The waters of the dolomitic marbles (eastern Sierra Blanca and Sierra Mijas) have higher and less variable mineralization and contain greater concentrations of Mg²⁺, SiO₂ and SO²⁻₄ (ions normally associated with slow flows). The ³H contents are more uniform with time (indicating an older age) and there is detectable natural radioactivity, because the waters have a longer residence time in the aquifers, which are diffuse flow systems.     

Rare earth elements,neodymium and strontium isotopic systematics in mineral waters: evidence from the Massif Central,France

Rare Earth Elements (REEs), and Sr and Nd isotope distributions, have been studied in mineralized waters from the Massif Central (France). The CO₂-rich springs are characterized by a neutral pH (6–7) associated with total dissolved solids (TDS) from 1 to 7 g l⁻¹. The waters result from the mixing of very mineralized water pools, thought to have equilibrated at a temperature of around 200°C with superficial waters. These two mineral water pools evidenced by Sr isotopes and dissolved REEs could reflect 2 different stages of water–rock interaction and an equilibrium with different mineral assemblages.The concentrations of individual dissolved REEs and total dissolved REEs (ΣREE), in the mineral waters examined, vary over several orders of magnitude but are not dependent on the main parameters of the waters (TDS, T°C, pH, Total Organic C). The dissolved REE concentrations presented as upper continental crust normalized patterns show HREE enrichment in most of the samples. The time evolution of REE patterns does not show significant fluctuations except in 1 borehole, located in the Limagne d’Allier area, which was sampled on 16 occasions over an 18 month period. Ten samples are HREE-enriched, whereas 6 samples show flat patterns.The aqueous speciation of REEs shows that CO²⁻₃ complexes dominate (>80%) over the free metal, F⁻, SO²⁻₄ and HCO⁻₃ complexes. The detailed speciation demonstrates that the fractionation of REEs (i.e. the HREE enrichment) in CO₂-rich and pH neutral fluids is due essentially to the predominance of the CO²⁻₃ complexes.The Sr isotopic composition of the mineral waters in the Massif Central shows different mixing processes; in the Cézallier area at least 3 end-member water types exist. The most dilute end-member is likely to originate as poorly mineralized waters with minimal groundwater circulation. Two other mineralized end-members are identified, although the link between the geographical location of spring outflow and the mixing proportion between the 2 end-members is not systematic. The range in ϵ_Nd(0) for mineralized waters in the Massif Central correlates well with that of the known parent rocks except for 4 springs. One way to explain the ϵ_Nd(0) in these instances is a contribution from drainage of volcanic rocks. The isotopic systematics help to constrain the hydrogeological models for this area.     

Acid neutralizing processes in an alpine watershed front range, Colorado, U.S.A.—1: Buffering capacity of dissolved organic carbon in soil solutions

Soil interstitial waters in the Green Lakes Valley, Front Range, Colorado were studied to evaluate the capacity of the soil system to buffer acid deposition. In order to determine the contribution of humic substances to the buffering capacity of a given soil, dissolved organic carbon (DOC) and pH of the soil solutions were measured. The concentration of the organic anion, Ai⁻, derived from DOC at sample pH and the concentration of organic anion, Ax⁻ at the equivalence point were calculated using car☐yl contents from isolated and purified humic material from soil solutions. Subtracting Ax⁻ from Ai⁻ yields the contribution of humic substances to the buffering capacity (A_equiv.⁻). Using this method, one can evaluate the relative contribution of inorganic and organic constituents to the acid neutralizing capacity (ANC) of the soil solutions. The relative contribution of organic acids to the overall ANC was found to be extremely important in the alpine wetland (52%) and the forest-tundra ecotone (40%), and somewhat less important in the alpine tundra sites (20%). A failure to recognize the importance of organic acids in soil solutions to the ANC will result in erroneous estimates of the buffering capacity in the alpine environment of the Front Range, Colorado.     

Evaluation of the solute geothermometry of thermal springs and drilled wells of La Primavera (Cerritos Colorados) geothermal field,Mexico: A geochemometrics approach

A detailed study on the solute geothermometry of thermal water (18 springs and 8 drilled wells) of La Primavera geothermal field (LPGF) in Mexico has been carried out by employing a geochemical database compiled from the literature and by applying all the available solute geothermometers. The performance of these geothermometers in predicting the reservoir temperatures has been evaluated by applying a geochemometrics (geochemical and statistical) method. The springs of the LPGF are of bicarbonate type and the majority have attained partial-equilibrium chemical conditions and the remaining have shown non-equilibrium conditions. In the case of geothermal wells, water is dominantly of chloride-type and, among the studied eight geothermal wells, four have shown full-equilibrium chemical conditions and another four have indicated partial-equilibrium conditions. All springs of HCO₃^−​ type water have provided unreliable reservoir temperatures, whereas the only one available spring of SO₄²⁻ type water has provided the reservoir temperature nearer to the average BHT of the wells. Contrary to the general expected behavior, spring water of non-equilibrium and geothermal well water of partial-equilibrium chemical conditions have indicated more reliable reservoir temperatures than those of partially-equilibrated and fully-equilibrated water, respectively. Among the chemical concentration data, Li and SiO₂ of two springs, SO₄²⁻ and Mg of four springs, and HCO₃ and Na concentrations of two geothermal wells were identified as outliers and this has been reflected in very low reservoir temperatures predicted by the geothermometers associated with them (Li–Mg, Na–Li, Na–K–Mg, SiO₂ etc.). Identification of the outlier data points may be useful in differentiating the chemical characteristics, lithology and the physico-chemical and geological processes at the sample locations of the study area.In general, the solute geothermometry of the spring waters of LPGF indicated a dominantly (94%) of underestimated deep reservoir temperatures, whereas in the case of the geothermal wells, many temperatures (54%) are underestimated, some are (43%) overestimated and a very small number (3%) are similar to an average bottom-hole temperatures (BHT) of the wells. 28 out of the total applied 29 geothermometers for spring waters have predicted the deep reservoir temperatures that are characterized by statistically significant large differences compared to the average BHTs of the geothermal wells. In the case of waters of the geothermal wells, 23 out of the total applied 28 geothermometers have predicted the reservoir temperatures similar (statistically no significant differences) to the BHTs of the corresponding geothermal wells.