Applied Geochemistry (v.27, #6)

Geochemical mapping using stream sediments in west-central Nigeria: Implications for environmental studies and mineral exploration in West Africa by Dan J. Lapworth; Katherine V. Knights; Roger M. Key; Christopher C. Johnson; Emmanuel Ayoade; Michael A. Adekanmi; Tunde M. Arisekola; Olugbenga A. Okunlola; Birgitta Backman; Mikael Eklund; Paul A. Everett; Robert T. Lister; John Ridgway; Michael J. Watts; Simon J. Kemp; Peter E.J. Pitfield (1035-1052).
► Regional geochemical mapping and multi-element analysis of stream sediment. ► Baseline geochemical signatures of major geological domains. ► High Zr concentrations (mean 0.2%) and placer deposits of Au, U, HFSE. ► Higher As and Cr associated with coastal sediments in south-west Nigeria.This paper provides an overview of regional geochemical mapping using stream sediments from central and south-western Nigeria. A total of 1569 stream sediment samples were collected and 54 major and trace elements determined by ICP-MS and Au, Pd and Pt by fire assay. Multivariate statistical techniques (e.g., correlation analysis and principal factor analysis) were used to explore the data, following appropriate data transformation, to understand the data structure, investigate underlying processes controlling spatial geochemical variability and identify element associations. Major geochemical variations are controlled by source geology and provenance, as well as chemical weathering and winnowing processes, more subtle variations are a result of land use and contamination from anthropogenic activity.This work has identified placer deposits of potential economic importance for Au, REE, Ta, Nb, U and Pt, as well as other primary metal deposits. Areas of higher As and Cr (>2 mg/kg and >70 mg/kg respectively) are associated with Mesozoic and younger coastal sediments in SW Nigeria. High stream sediment Zr concentrations (mean >0.2%), from proximal zircons derived from weathering of basement rocks, have important implications for sample preparation and subsequent analysis due to interferences. Associated heavy minerals enriched in high field strength elements, and notably rare earths, may also have important implications for understanding magmatic processes within the basement terrain of West Africa.This study provides important new background/baseline geochemical values for common geological domains in Nigeria (which extend across other parts of West Africa) for assessment of contamination from urban/industrial land use changes and mining activities. Regional stream sediment mapping is also able to provide important new information with applications across a number of sectors including agriculture, health, land use and planning.

► Stream water contains elevated Cu, Co, As, and Fe compared to backgrounds. ► Sediment and water guidelines were exceeded in some mine runoff samples. ► Mine waste and stream sediment exceeded the probable effect concentration for Cu. ► Stream water exceeded an LC50 for Co in rainbow trout by more than two orders of magnitude. ► Mine waste and stream sediment exceeded the probable effect concentration for As.The distribution of Cu, Co, As and Fe was studied downstream from mines and deposits in the Idaho Cobalt Belt (ICB), the largest Co resource in the USA. To evaluate potential contamination in ecosystems in the ICB, mine waste, stream sediment, soil, and water were collected and analyzed for Cu, Co, As and Fe in this area. Concentrations of Cu in mine waste and stream sediment collected proximal to mines in the ICB ranged from 390 to 19,000 μg/g, exceeding the USEPA target clean-up level and the probable effect concentration (PEC) for Cu of 149 μg/g in sediment; PEC is the concentration above which harmful effects are likely in sediment dwelling organisms. In addition concentrations of Cu in mine runoff and stream water collected proximal to mines were highly elevated in the ICB and exceeded the USEPA chronic criterion for aquatic organisms of 6.3 μg/L (at a water hardness of 50 mg/L) and an LC50 concentration for rainbow trout of 14 μg/L for Cu in water. Concentrations of Co in mine waste and stream sediment collected proximal to mines varied from 14 to 7400 μg/g and were highly elevated above regional background concentrations, and generally exceeded the USEPA target clean-up level of 80 μg/g for Co in sediment. Concentrations of Co in water were as high as in 75,000 μg/L in the ICB, exceeding an LC50 of 346 μg/L for rainbow trout for Co in water by as much as two orders of magnitude, likely indicating an adverse effect on trout. Mine waste and stream sediment collected in the ICB also contained highly elevated As concentrations that varied from 26 to 17,000 μg/g, most of which exceeded the PEC of 33 μg/g and the USEPA target clean-up level of 35 μg/g for As in sediment. Conversely, most water samples had As concentrations that were below the 150 μg/L chronic criterion for protection of aquatic organisms and the USEPA target clean-up level of 14 μg/L. There is abundant Fe oxide in streams in the ICB and several samples of mine runoff and stream water exceeded the chronic criterion for protection of aquatic organisms of 1000 μg/L for Fe. There has been extensive remediation of mined areas in the ICB, but because some mine waste remaining in the area contains highly elevated Cu, Co, As and Fe, inhalation or ingestion of mine waste particulates may lead to human exposure to these elements.

Metal partitioning in sediments and mineralogical controls on the acid mine drainage in Ribeira da Água Forte (Aljustrel, Iberian Pyrite Belt, Southern Portugal) by Flávia Maia; Cláudia Pinto; João Carlos Waerenborgh; Mário A. Gonçalves; Cátia Prazeres; Ondina Carreira; Susana Sério (1063-1080).
► Organic-rich waste water drives the release of metals from acid drainage sediments. ► Precipitation/dissolution of Fe-hydroxides and sulfates controls water chemistry. ► Schwertmannite formation and transformation to Fe-hydroxides maintains low pH. ► Metals keep high concentration in solution with no effective attenuation mechanism.This work focuses on the geochemical processes taking place in the acid drainage in the Ribeira da Água Forte, located in the Aljustrel mining area in the Iberian Pyrite Belt. The approach involved water and stream sediment geochemical analyses, as well as other techniques such as sequential extraction, Mössbauer spectroscopy, and X-ray diffraction. Ribeira da Água Forte is a stream that drains the area of the old mine dumps of the Aljustrel mine, which have for decades been a source of acid waters. This stream flows to the north for a little over than 10 km, but mixes with a reduced, organic-rich, high pH waste water from the municipal waste water pools of the village. This water input produces two different results in the chemistry of the stream depending upon the season: (i) in the winter season, effective water mixing takes place, and the flux of acid water from the mine dumps is continuous, resulting in the immediate precipitation of the Fe from the acid waters; (ii) during the summer season, acid drainage is interrupted and only the waste water feeds the stream, resulting in the reductive dissolution of Fe hydroxides and hydroxysulfates in the stream sediments, releasing significant quantities of metals into solution. Throughout the year, water pH stays invariably within 4.0–4.5 for several meters downstream of this mixing zone even when the source waters come from the waste water pools, which have a pH around 8.4. The coupled interplay of dissolution and precipitation of the secondary minerals (hydroxides and sulfates), keeps the system pH between 3.9 and 4.5 all along the stream. In particular, evidence suggests that schwertmannite may be precipitating and later decomposing into Fe hydroxides to sustain the stream water pH at those levels. While Fe content decreases by 50% from solution, the most important trace metals are only slightly attenuated before the solution mixes with the Ribeira do Rôxo stream waters. Concentrations of As are the only ones effectively reduced along the flow path. Partitioning of Cu, Zn and Pb in the contaminated sediments also showed different behavior. Specific/non-specific adsorption is relevant for Cu and Zn in the upstream branch of Ribeira da Água Forte with acid drainage conditions, whereas the mixture with the waste water causes that the association of these metals with oxyhydroxide to be more important. Metals bound to oxyhydroxides are on the order of 60–70% for Pb, 50% for Cu and 30–60% for Zn. Organic matter is only marginally important around the waste water input area showing 2–8% Cu bound to this phase. These results also show that, although the mixing process of both acid and organic-rich waters can suppress and briefly mitigate some adverse effects of acid drainage, the continuing discharge of these waste waters into a dry stream promotes the remobilization of metals fixed in the secondary solid phases in the stream bed back into solution, a situation that can hardly be amended back to its original state.

► Buffering processes due to pyrite oxidation in Lusatian mining dumps release Ca. ► Calcium release leads to water quality controlling gypsum precipitation. ► Gypsum precipitation explains decreasing c(Ca) along with increasing I above 60 mM. ► Carbonate buffer formation explains c(Fe)/c(SO4) > 0.5 at pH > 5.0 and gypsum precipitation.Using groundwater quality data from the Lusatian post-mining district a hydrogeochemical model is derived for the evolution of mining affected groundwaters in pyrite-rich dumps which consist mainly of silicates and variable amounts of calcite. Pyrite oxidation paralleled by buffer processes leads to gypsum saturation in a significant portion of the water. Gypsum precipitation controls SO4 and Ca concentrations in groundwaters above an ionic strength (I) of 60 mM. It has been found that there is always a clear relationship between I, SO4 and Ca concentrations. In particular, there is a tendency that Ca concentrations decrease with increase in ionic strength above I  = 60 mM and a striking rareness of samples with SO4 concentrations between 20 and 30 mM above an ionic strength of 100 mM. These observations are explained by a genetic model. This model also explains the observed relationship between the c(Fe)/c(SO4)-ratio, the ionic strength, and the observed pH-values. Based on the field data and supported by geochemical equilibrium calculations, it is shown that silicate weathering along with calcite dissolution must be a significant buffering process at least in some areas.

► Pb isotope ratios in Lower Silesia are reported. ► The silicate rocks have variable 206Pb/207Pb from 1.17 to 1.38. ► The ores, coals, slags, soil O horizons have uniform 206Pb/207Pb from 1.17 to 1.18. ► Anthropogenic input affects Pb concentrations in soils from industrial sites. ► Natural processes causeincrease in Pb in soils formed far from industrial sites.To discriminate possible anthropogenic and lithogenic sources of Pb in Lower Silesia (SW Poland), the Pb isotope composition was investigated in a spectrum of rocks and anthropogenic materials as well as within 10 soil profiles. Silicate rocks in Lower Silesia have 206Pb/207Pb ratios that vary from 1.17 for serpentinites to 1.38 for gneisses, and this variability is reflected in the isotope composition of the mineral soil horizons. The Pb isotope composition of coals, ores and anthropogenic materials (slags and fly ashes) is rather uniform, with 206Pb/207Pb ratios ranging from 1.17 to 1.18. Similar ratios were observed in ore and coal samples from Upper Silesia. The O soil horizons also have uniform 206Pb/207Pb ratios of 1.17–1.18 and the heterogeneity of the 206Pb/207Pb ratios increases with depth in the soil profiles. Five soils, with varying Pb concentrations, analysed far from contamination centres, show consistent, approximately 2-fold enrichment in Pb concentration from the C to A horizons, which is consistent with natural re-distribution of Pb within the profiles. The increase in the Pb concentration is accompanied by a decrease in 206Pb/207Pb ratios, also attributed to natural Pb isotope fractionation. Four soil profiles from industrial areas show variable enrichments in Pb concentrations and these are attributed to anthropogenic input from air-borne pollutants or even slag particles at smelting sites. The implication is that a lithogenic Pb source can deviate from the basement rock composition, and detailed isotope characteristics of the geological background and natural enrichments in soils are often needed to determine the lithogenic/anthropogenic proportions of Pb in soils.

► Dissolved oxygen and inorganic carbon, δ 18O–DO and δ 13C–DIC are investigated in groundwater. ► The site contains petroleum compounds in groundwater from operation as wood treatment facility. ► An increase in δ 18O–DO and decrease in δ 13C–DIC is consistent with aerobic microbial respiration. ► A weak correlation between δ 18O–DO and δ 13C–DIC may be caused by the remediation treatments. ► The presence of a suboxic zone suggests some DIC of unknown isotopic composition could be formed.The speciation and mobility of a variety of chemical species in groundwater are strongly influenced by redox and pH conditions. Dissolved O2 (DO) and dissolved inorganic C (DIC) concentrations are significant controls of these conditions, respectively. It is not always clear what the major processes are that influence changes in the concentration of DO and DIC across a groundwater flowpath. The combined use of the stable isotope compositions of DO (δ 18O–DO) and DIC (δ 13C–DIC) has the potential to help investigators discriminate between sources and sinks of DO and DIC in groundwater systems.A total of 31 monitoring wells were sampled to investigate changes in DO, DIC, δ 18O–DO and δ 13C–DIC in shallow groundwater at the Montana Pole and Treating Plant (MPTP), Butte, Montana, USA. The MPTP site contains significant quantities of petroleum hydrocarbons in soil and groundwater from historical operations as a wood treatment-preservative facility. Dissolved O2 concentrations decreased downgradient across the site (340–6.6 μmol L−1) while DIC concentration increased (3.6–12.8 mmol L−1). A general enrichment in δ 18O–DO (16.8–31.6‰) and depletion in δ 13C–DIC (−12.7‰ to −18.7‰) along the flowpath is consistent with aerobic microbial respiration. However, the correlation between δ 18O–DO and δ 13C–DIC was poor which may be caused in part by the remediation treatments being used to mitigate soil and groundwater contamination. The presence of an extensive suboxic zone near the center of the field area suggests that some DIC of unknown isotopic composition could have been added to the groundwater by anaerobic degradation of hydrocarbons. This idea is consistent with a limited amount of NO 3 - isotope data which suggest that denitrification is occurring at the MPTP site.

Uranium-series isotopes transport in surface, vadose and ground waters at San Marcos uranium bearing basin, Chihuahua, Mexico by Juan Carlos Burillo Montúfar; Manuel Reyes Cortés; Ignacio Alfonso Reyes Cortés; Ma. Socorro Espino Valdez; Octavio Raúl Hinojosa de la Garza; Diana Pamela Nevárez Ronquillo; Eduardo Herrera Peraza; Marusia Rentería Villalobos; María Elena Montero Cabrera (1111-1122).
► The physicochemical parameters of waters have been measured. ► 238U-series isotopes activities in waters have been measured by liquid scintillation counting. ► Activity ratios were calculated. ► Some published models were applied to them. ► The order of magnitude of transport parameters of uranium in waters at San Marcos have been assessed.In the U deposit area at San Marcos in Chihuahua, Mexico, hydrogeological and climatic conditions are very similar to the Nopal I, Peña Blanca U deposit, 50 km away. The physicochemical parameters and activity concentrations of several 238U-series isotopes have been determined in surface, vadose and ground waters at San Marcos. The application of some published models to activity ratios of these isotopes has allowed assessing the order of magnitude of transport parameters in the area. Resulting retardation factors in San Marcos area are Rf 238  ≈ 250–14,000 for the unsaturated zone and ≈110–1100 for the saturated zone. The results confirm that the mobility of U in San Marcos is also similar to that of the Nopal I U deposit and this area can be considered as a natural analog of areas suitable for geologic repositories of high-level nuclear waste.

► We examined the spring waters from Świętokrzyski National Park in Poland. ► We determined the stable S and O isotope ratios. ► The δ34S pattern is similar to that of rainwater, soils and geologic makeup. ► The δ18O–H2O is indicative of present vadose origin of spring waters. ► Sulfur reduction and oxidation of S species are dominant fractionation processes.This paper presents the results of an isotopic study of spring waters in Świętokrzyski (Holy Cross Mountain) National Park (ŚNP), south-central Poland. The δ34SV-CDT and δ18OV-SMOW of soluble sulfates (n  = 40) varied from 0.5‰ to 18.1‰ and from 3.5‰ to 12.2‰, respectively. The average δ34S values are closely similar to those of rainwater, soils and rocks (comprising scattered pyrite). This suggests that soluble sulfates in the springs originated from mixing of recent and historic deposition, sulfates derived from pyrite oxidation, and CS-mineralization in soils and debris. An additional anthropogenic sulfur input (inorganic fertilizer) occurs in the water of spring S-61 located in the Świętokrzyski National Park buffer zone. The δ18OV-SMOW of spring waters (n  = 4) were in the range of −10.6‰ to −10.2‰ indicating that they are derived from vadose groundwater in ŚNP. This was the first isotope study of spring waters in the national parks of Poland. It enabled the determination of sulfur pathways and discrimination between natural and anthropogenic sources of this element in a relatively pristine area.

► Infiltration regime of river water is examined using CFCs, stable isotopes and 3H. ► The tracers reveal the infiltration regime of river water and pathway in groundwater. ► Leakage of river water and upwelling of palaeo-water are found along flowpath zone. ► The groundwater recharge will be overestimated if monitored runoff losses are used.Environmental tracers (CFCs, stable isotopes 18O, 2H, and 3H) and major ions were employed to study river infiltration and groundwater recharge in the aquifer system in the basin of the Lower Heihe River, Northwest China. Three groups of waters have been recognized: (1) young groundwater, connected to the river, with large variation of CFC apparent ages ranging from <10 a to 40 a, and δ18O and δ2H values which are similar to the river water; (2) regional background water, unaffected by the river, having CFC apparent ages >40 a, and being depleted in 18O and 2H compared with the river water; and (3) groundwater in Gurinai, a grassland located about 100 km from the river, in which the predominant discharge is from the Badain Jaran desert, with CFC apparent ages ranging from 25 to >50 a and being enriched in 18O and 2H compared to the river water. The groundwater along the river contains CFCs and 3H down to depths of about 120 m, and the shallow groundwater exhibits CFC apparent ages in a wide range which are not dependent on the well depth. Groundwaters along the river show a similar trend of enrichment in 18O and 2H as the river water whereas groundwaters in depression cones are depleted in heavier isotopes, and have low CFC and 3H concentrations. The CFC apparent age of the groundwater increases with increasing distance downstream, indicating that the dominant part of the groundwater is from infiltration of river water in the upper reaches. Modifications of groundwater recharge are reflected in variations of stable isotope compositions, as well as CFC and 3H concentrations in the groundwater that was recharged from the river over the last decades. Despite recharging from river water, groundwater abstraction has induced a water balance deficit. The riparian ecosystem in the Ejina Oasis is constrained by both decreased river flow and increased groundwater abstraction. The vegetation degradation in the Ejina Oasis is controlled not only by natural aridification but also worsened by heavy groundwater abstraction and decreased river flow.

An anomalous thermal water from Hofsstadir western Iceland: Evidence for past CO2 flushing by H. Kristmannsdóttir; Á.E. Sveinbjoernsdóttir (1146-1152).
► The geothermal water at Hofsstadir is the most depleted in δ18O in all Iceland. ► The water bears evidence for past CO2 flushing. ► The δ2H and δ18O is significantly lighter than present day precipitation. ► The chemistry of the water indicates intensive and prolonged water–rock interaction. ► The 14C concentration of the water is low, about 7.4 pMC.The geothermal field at Hofsstadir northern Snæfellsnes peninsula, Iceland produces low-temperature geothermal water with about 5.4‰ salinity. The fluid temperature is 87 °C, near the reservoir temperature of 90 °C as assessed from mineral solution/equilibrium conditions. The stable isotopic ratios δ2H and δ18O show that the water is significantly lighter than present day precipitation anywhere on the Snæfellsnes peninsula. It is offset from the meteoric water line towards isotopically depleted 18O values, most likely due to CO2(g) – H2O exchange at earlier times during evolution of the system. Such a concentration of stable isotopes is unique for Icelandic groundwaters and has not been encountered anywhere else in Iceland. The water may either have its origin far north of the Bay of Breidafjörður in the highland of the western fjordlands or dating back to a Pre-Holocene age when local precipitation was considerably lighter due to the cold climate at that time. The water is highly concentrated in Ca in comparison with seawater and also compared to that of geothermal saline water elsewhere, which indicates intensive and prolonged water–rock interaction. The 14C concentration is low, about 7.4 pMC (percent modern C), compared to the cold local groundwater of about 74.6 pMC. δ13C for the thermal and cold waters is −4.9‰ and −2.3‰, respectively. The geothermal water is used for heating the small town of Stykkishólmur through a central heat exchanger plant due to the high salinity of the water. The outbuilding of a health resort has been planned and the water has been used successfully for the treatment of psoriasis and is claimed to have beneficial effects in bathing therapy for rheumatism as well as for drinking cures.

Source and origin of active and fossil thermal spring systems, northern Upper Rhine Graben, Germany by Anselm Loges; Thomas Wagner; Thomas Kirnbauer; Susanne Göb; Michael Bau; Zsolt Berner; Gregor Markl (1153-1169).
► Thermal springs and fossil geothermal mineralization at the northern margin of the Rhine Graben are genetically related. ► Thermal springs have a common deep source in the Variscan basement. ► Systematic chemical and isotopic variations suggest large-scale two component mixing. ► Thermal spring systems were active over at least 800 kyrs.Thermal water samples and related young and fossil mineralization from a geothermal system at the northern margin of the Upper Rhine Graben have been investigated by combining hydrochemistry with stable and Sr isotope geochemistry. Actively discharging thermal springs and mineralization are present in a structural zone that extends over at least 60 km along strike, with two of the main centers of hydrothermal activity being Wiesbaden and Bad Nauheim. This setting provides the rare opportunity to link the chemistry and isotopic signatures of modern thermal waters directly with fossil mineralization dating back to at least 500–800 ka. The fossil thermal spring mineralization can be classified into two major types: barite-(pyrite) fracture filling associated with laterally-extensive silicification; and barite, goethite and silica impregnation mineralization in Tertiary sediments. Additionally, carbonatic sinters occur around active springs. Strontium isotope and trace element data suggest that mixing of a hot (>100 °C), deep-sourced thermal water with cooler groundwater from shallow aquifers is responsible for present-day thermal spring discharge and fossil mineralization. The correlation between both Sr and S isotope ratios and the elevation of the barite mineralization relative to the present-day water table in Wiesbaden is explained by mixing of deep-sourced thermal water having high 87Sr/86Sr and low δ34S with shallow groundwater of lower 87Sr/86Sr and higher δ34S. The Sr isotope data demonstrate that the hot thermal waters originate from an aquifer in the Variscan crystalline basement at depths of 3–5 km. The S isotope data show that impregnation-type mineralization is strongly influenced by mixing with SO4 that has high δ34S values. The fracture style mineralization formed by cooling of the thermal waters, whereas impregnation-type mineralization precipitated by mixing with SO4-rich groundwater percolating through the sediments.

Origin and mobility of hexavalent chromium in North-Eastern Attica, Greece by D. Moraetis; N.P. Nikolaidis; G.P. Karatzas; Z. Dokou; N. Kalogerakis; L.H.E. Winkel; A. Palaiogianni-Bellou (1170-1178).
► An integrated framework identify the origin of Cr(VI) in Oropos plain. ► Geogenic Cr(VI) is evident in Oropos plain. ► Cr(VI) leaching rates calculated for two soils. ► Heavy liquid separation showed chromite grains (clasts) in alluvial sediments. ► Princeton Transport Code model simulates geogenic origin Cr(VI) in groundwater.An integrated framework that is comprised of field surveys of groundwater, surface water and soils, laboratory process experiments and hydrologic and geochemical modeling is used to identify the origin (anthropogenic versus geogenic sources), fate and transport of hexavalent Cr in Tertiary and Quaternary deposits of Oropos plain in Greece. Groundwater and soils were analyzed in May 2008 and exhibited considerable Cr concentrations. Mineralogical analysis and micro-XRF analysis of the heavy soil fractions (metallic components) showed Cr bearing phases like chromites, Cr-silicate phases with positive correlation between Si, Al, Fe and Cr soil concentrations. Column experiments showed the Cr(VI) desorption ability of soils, e.g. concentration of 20 μg L−1 was detected after the application of 50 mm of rain. The groundwater model simulated the variability of Cr concentrations emanating from both anthropogenic and geogenic sources, successfully using rate constants obtained from the laboratory experiments, e.g. 4.24 nM h−1 for serpentine soil and 0.77 nM h−1 for soil in alluvial deposits. The mineralogical and geochemical results support a geogenic origin for Cr in soils and groundwater of Oropos plain while modeling results suggest that contaminants transported by Asopos River have affected only the upper layers of the subsurface in the vicinity of the river. The framework can be used to establish background concentrations or clean up levels of Cr-contaminated soils and groundwater.

Fluorine adsorption by volcanic soils at Mt. Etna, Italy by Walter D’Alessandro; Sergio Bellomo; Francesco Parello (1179-1188).
► F sorption of the soils increases radially from the summit craters of the volcano. ► Sorption capacity positively correlated with soil pH, clay content and weathering index. ► Soils with highest F sorption are found were the aquifers are more vulnerable. ► The Etnean soils protect the aquifers from excessive meteoric F input.Fluorine adsorption experiments were performed on 28 samples of the first 5 cm of topsoil collected on the flanks of Mt. Etna. The soil samples were equilibrated with F-rich rainwater (3.25 mg/L) at a soil/water weight ratio of 1/25. Aliquots of the supernatant were collected after 1, 7, 72, 720 and 5640 h and analysed for F content. The soil samples could be subdivided into three groups based on their F-adsorption behaviours after 1 h and at the end of the experiment: (1) negative adsorption (F released from the soil to the solution) after 1 h and negative or moderately positive adsorption at the end, (2) from negative after 1 h to strongly positive adsorption at the end, and (3) always strong positive adsorption. The adsorption capacity of the soils was positively correlated with the soil pH, the contents of finer granulometric fractions (clay and silt) and the weathering stage (as quantified by the chemical alteration index). The most F adsorbing soils are found at the periphery of the volcano where aquifers are more vulnerable to contamination due to the shallower depth of the water table. This study further evidences the importance of the Etnean soils in protecting groundwater from an excessive magmatic F input.

Ni(II) sorption on natural chlorite by Åsa Zazzi; Anna-Maria Jakobsson; Susanna Wold (1189-1193).
► We have studied the sorption of Ni(II) to chlorite surface under different conditions. ► The sorption was pH dependent, max at pH ∼ 8 (Kd  = ∼10−3  cm3/g). ► A 2-pK NEM model and three surface complexes gave the best fit to the sorption results using FITEQL.Sorption of Ni(II) onto chlorite surfaces was studied as a function of pH (5–10), ionic strength (0.01–0.5 M) and Ni concentration (10−8–10−6  M) in an Ar atmosphere using batch sorption with radioactive 63Ni as tracer. Such studies are important since Ni(II) is one of the major activation products in spent nuclear fuel and sorption data on minerals such as chlorite are lacking. The sorption of Ni(II) onto chlorite was dependent on pH but not ionic strength, which indicates that the process primarily comprises sorption by surface complexation. The maximum sorption was at pH ∼ 8 (Kd  = ∼10−3  cm3/g). Desorption studies over a period of 1–2 weeks involving replacement of the aqueous solution indicated a low degree of desorption. The acid–base properties of the chlorite mineral were determined by titration and described using a non-electrostatic surface complexation model in FITEQL. A 2-pK NEM model and three surface complexes, Chl_OHNi2+, Chl_OHNi(OH)+ and Chl_OHNi(OH)2, gave the best fit to the sorption results using FITEQL. The high Kd values and low degree of desorption observed indicate that under expected groundwater conditions, a large fraction of Ni(II) that is potentially leachable from spent nuclear fuel may be prevented from migrating by sorption onto chlorite surfaces.

Caesium uptake by Callovian–Oxfordian clayrock under alkaline perturbation by S. Gaboreau; F. Claret; C. Crouzet; E. Giffaut; Ch. Tournassat (1194-1201).
► Caesium sorption on clayrock under alkaline perturbation was experimented. ► A predictive ion exchange model was successful in reproducing Cs uptake data. ► Competitive effect from alkaline species intrusion in the clayrock is well predicted.The potential effect of near-field alkaline perturbation in clayrocks on Cs retention was explored. Batch experiments were conducted to measure Cs sorption on Callovian–Oxfordian rock samples in alkaline perturbed conditions. Experimental results evidenced a marked effect of alkaline perturbation on the Cs retention properties of Callovian–Oxfordian rock samples. Using a modelling approach, this effect could be attributed to the competition of K+, originating from the alkaline solution, for Cs sorption sites on illite surfaces. Experimental results also showed that Cs sorption tends to increase with time. Additional experiments on a mineralogical assemblage representative of a Callovian–Oxfordian rock/concrete interface after long term alkaline perturbation showed that this mineralogical assemblage has a similar efficiency for Cs uptake as the intact clay rock, showing that long term alkaline perturbation of clayrocks and resulting mineralogical changes do not affect the barrier performance considerably with regard to Cs retention.

Diffusion of landfill leachate through compacted natural clays containing small amounts of carbonates and sulfates by Isabel S. De Soto; Ana I. Ruiz; Carlos Ayora; Rosario García; Mercedes Regadio; Jaime Cuevas (1202-1213).
► Numerical description of reactions between raw clay materials and landfill leachates. ► Use of chloride concentration profiles to trace transport and reaction processes in clays. ► Consideration of coupled geochemical processes including precipitation of minerals. ► Precipitation of calcite can reduce the porosity, and modify transport properties.Diffusion of a synthetic urban landfill leachate through compacted natural illitic clays and the role of reactive accessory minerals (carbonates and gypsum) in the geochemical behavior of major soluble ions are evaluated. The leachate is composed of NH 4 + and Na+ (0.25 M) balanced by Cl (0.25 M), acetate (0.1 M) and HCO 3 - (0.15 M). The pH is 7.8 and it is typical of the mature stage of organic matter degradation within an urban landfill. Laboratory scale diffusion tests were performed over 4 months (long term experiment, LT) and 2 weeks (short term experiment, ST). The ST experiments were designed to allow the measurement of the Cl gradient as a diffusion tracer in the compacted clay. In the LT experiments the chemical gradients were already at steady state, but geochemical reactions involving dissolution of gypsum and precipitation of calcite were observed. Evolution of pore-water chemistry, mineralogy, cation exchange properties, and the specific surface of clays were determined. Numerical simulations were carried out using the geochemical code RETRASO. Chloride transport, precipitation of carbonates, pH buffering, and Ca2+/ NH 4 + cation exchange reactions took place in the laboratory tests. Apparent Cl diffusion coefficients were determined by direct modeling of the ST tests and validated with the LT experiments. These coefficients were considered in the simulation of transport coupled with experimentally calculated exchange constants and dissolution/precipitation reactions of gypsum and carbonates. Sulfate reduction coupled with acetate oxidation has been proven to be relevant in the sample with significant concentration of SO 4 2 - (Bailén). This process also includes significant precipitation of carbonates (mainly calcite) and causes a decrease of SO 4 2 - in the porewater.

► Water hyacinth has been tested for removal of Zn, Cu, Pb and Cd after their entry into a fresh water body. ► Initial concentrations quickly decreased in the order Pb ≈ Cu ≫ Cd ≈ Zn. ► Efficiency of metal removal was distinctly higher at pH 8 than at pH 6. ► The bioconcentration factor in a whole plant exceeds 2000 at pH 8. ► Water hyacinth can be recommended for the control of non-point source pollution of water bodies.The removal efficiency of water hyacinth for Zn, Cu, Pb and Cd after their entry into an undisturbed fresh water body was studied using minicosms placed within a reservoir. Variable parameters were water pH (6 or 8), single or multi-metal additions, and the plant biomass. The initial concentrations of Zn, Cu, Pb and Cd in water (500, 250, 250 and 50 μg/L, respectively) quickly decreased in the order Pb ≈ Cu ≫ Cd ≈ Zn in the first days. Metal removal was more efficient at pH 8 than at pH 6, and it was only slightly higher for single metals compared to multi-metal additions. After 8 days the remaining amounts of metals relative to their initial concentrations for multi-metal pollution treatments were 8% and 24% (Cu), 11% and 26% (Pb), 24% and 50% (Cd), and 18% and 57% (Zn) at pH 8 and pH 6, respectively. Increasing plant biomass promoted faster metal removal. The bioconcentration factor (the ratio of the metal concentration in whole plants to the initial metal concentration in water) exceeds 2000 for all metals (with the exception of Zn and Cd at pH 6). It was concluded that the water hyacinth can be successfully used for fast removal of metals in the initial stage of water body remediation.

Colloid generation during water flow transients by Claude Degueldre; Ana Benedicto (1220-1225).
► New data on physico-chemical transients that are the source of colloid concentration increases. ► For the first time, groundwater colloids are studied from a well instrumented transient system. ► The low ionic strength groundwater makes the Grimsel colloid suspension stable for testing over days. ► The impact in earth and planetary science is anticipated e.g. very sensitive method to detect seismic features.In quasi-stagnant groundwater aquifer colloids are found to have constant concentration and size distribution under constant flow conditions. In transient conditions induced by water flow rate variations, increases of colloid concentration and size distribution are observed. The present study focuses on colloids from water of a well instrumented short bore hole in the water bearing fissure around the migration zone of the laboratory tunnel at the Grimsel Test Site, Switzerland. The low ionic strength groundwater makes the colloid suspension stable. In this system, increases in concentration and size distribution by factors of 1.5–30, according to the colloid size (50–2000 nm), are observed when the flow rate increases, as a pulse, by factors of 20–40 in 6–10 s. Colloid generation by flow transient requires a minimum impulse (threshold) that is colloid size dependant.

New operational method of testing colloid complexation with metals in natural waters by Ekaterina Vasyukova; Oleg S. Pokrovsky; Jérôme Viers; Bernard Dupré (1226-1237).
Natural colloid separation at different pH using dialysis membrane allows quantitative evaluation of trace element complexation.Display Omitted► Dialysis assessed the distribution of trace elements (TEs) between colloidal and dissolved (<1 kDa) phases. ► Proportion of colloidal forms was measured as a function of solution pH (from 3 to 8). ► Two groups of elements can be distinguished according to their behaviour during dialysis. ► Results allow prediction of colloidal form proportion in organic- and Fe-rich boreal waters.A dialysis procedure was used to assess the distribution coefficients of ∼50 major and trace elements (TEs) between colloidal (1 kDa–0.22 μm) and truly dissolved (<1 kDa) phases in Fe- and organic-rich boreal surface waters. These measurements allowed quantification of both TE partitioning coefficients and the proportion of colloidal forms as a function of solution pH (from 3 to 8). Two groups of elements can be distinguished according to their behaviour during dialysis: (i) elements which are strongly associated with colloids and exhibit significant increases of relative proportion of colloidal forms with pH increase (Al, Ba, Cd, Co, Cr, Cu, Fe, Ga, Hf, Mn, Ni, Pb, rare earth elements (REEs), Sr, Th, U, Y, Zn, Zr and dissolved organic C) and (ii) elements that are weakly associated with colloids and whose distribution coefficients between colloidal and truly dissolved phases are not significantly affected by solution pH (As, B, Ca, Cs, Ge, K, Li, Mg, Mo, Na, Nb, Rb, Sb, Si, Sn, Ti, V). Element speciation was assessed using the Visual MINTEQ computer code with an implemented NICA-Donnan humic ion binding model and database. The model reproduces quantitatively the pH-dependence of colloidal form proportion for alkaline-earth (Ba, Ca, Mg, Sr) and most divalent metals (Co, Cd, Mn, Ni, Pb, Zn) implying that the complexation of these metals with low molecular weight organic matter (<1 kDa fraction) is negligible. In contrast, model prediction of colloidal proportion (fraction of 1 kDa–0.22 μm) of Cu2+ and all trivalent and tetravalent metals is much higher than that measured in the experiment. This difference may be explained by (i) the presence of strong metal-binding organic ligands in the <1 kDa fraction whose stability constants are several orders of magnitude higher than those of colloidal humic and fulvic acids and/or (ii) coprecipitation of TE with Fe(Al) oxy(hydr)oxides in the colloidal fraction, whose dissolution and aggregation controls the pH-dependent pattern of TE partitioning. Quantitative modeling of metal – organic ligand complexation and empirical distribution coefficients corroborate the existence of two colloidal pools, formerly reported in boreal surface waters: “classic” fulvic or humic acids binding divalent transition metals and alkaline-earth elements and large-size organo-ferric colloids transporting insoluble trivalent and tetravalent elements.

Analysis of raw soils and their re-suspended PM10 fractions: Characterisation of source profiles and enrichment factors by D. Cesari; D. Contini; A. Genga; M. Siciliano; C. Elefante; F. Baglivi; L. Daniele (1238-1246).
► Composition of soils and resuspended PM10 was obtained in different sites. ► Enriched elements had larger abundances in resuspended PM10. ► Spatial variability of abundances were estimated for several soil categories. ► A two-threshold scheme for evaluation of enrichment of PM10 was developed. ► Thresholds values for local and planetary references were evaluated.In this work, the inorganic chemical profiles of soil samples collected at different sites in the Salentum peninsula (Italy, Apulia region) are discussed. The samples were re-suspended in the laboratory, for PM10 sampling, using a ventilated wooden chamber and were then chemically analysed measuring the abundances of 17 elements. Different land use categories of soils (olive grove, arable land, vineyards, sand, and urban dust) were included in the 50 samples analysed: 45 collected in background areas and five collected in the urban area of Lecce. The objectives were to compare the chemical profiles of raw soil and re-suspended PM10 for different crustal sources and to estimate the potential improvements in the calculation of the enrichment factors of atmospheric PM10. The variability of elemental abundances in samples of the same category of soil collected in different zones was of the same order of magnitude as the differences observed between the various categories of soil. This allows the calculation of a weighted average composition of soil and urban dust and the corresponding weighted average composition of re-suspended PM10. In re-suspended PM10 from average background soil, all of the elements except Ca, Na, K and V have larger abundances with respect to raw soil. In urban dust, this is limited to Ca, V and Mg. The crustal enrichment factors (EFs) of atmospheric PM10 were evaluated by considering different reference elements and different reference tables. Results indicated that it is possible to apply a two-threshold (S 1 and S 2) scheme for the interpretation of EF, with thresholds derived from uncertainty in soil categories and from the choice of the reference element. A specific element is likely of crustal origin if EF <  S 1 and likely of anthropogenic origin if EF >  S 2. Between the two thresholds, the element can be considered of mixed origin. The thresholds vary according to the geological composition used in the evaluation of EF. If the average composition of local re-suspended soils is used, the thresholds are S 1  = 2 and S 2  = 4. If raw soil is used, the thresholds become S 1  = 5 and S 2  = 10. If the average upper-crust composition from literature data is used, the thresholds further increase to S 1  = 10 and S 2  = 20.

► A biomass nutrient uptake stoichiometry of K1.0Mg1.0Ca1.4 is introduced. ► Solid phase data may be used to add equations to mass-balance matrices. ► Formerly agricultural barren land increases runoff and chemical weathering rates. ► Anthropogenic activity may influence chemical weathering rates of small watersheds.Paired watersheds are used to develop a deciduous nutrient uptake stoichiometry. The watersheds are those of the House Rock Run and the Brubaker Run located in the Pennsylvania Appalachian Piedmont, USA. These two watersheds are nearly identical with respect to bedrock, regolith, climate, geomorphology, morphometry, baseflow hydrology, and type and successional stage of forest vegetation. They only differ by the percentage of deciduous forest cover, with House Rock Run having 59% and Brubaker Run having 76%. From differences in their stream chemistries the biomass nutrient uptake stoichiometry of K1.0Mg1.0Ca1.4 was determined. This stoichiometry applies to an aggrading deciduous biomass and differs from those previously used which were derived from net primary production (NPP) data. The difference may reflect that macronutrients in plant tissue may also originate from atmospheric inputs and/or decomposing biomass. Although this stoichiometry may not be applied to all deciduous forest-covered watersheds, it is likely an improvement over a stoichiometry determined from NPP data.Mass-balance calculations of mineral weathering rates often suffer from the number of unknowns exceeding the number of equations. To add equations to the mass-balance matrices two methods are introduced. The first method employs Zr-normalized bulk chemical compositions of bedrock and soil to calculate a mass transfer coefficient for chemical weathering. The second approach uses chemical formulae and modal abundances of primary minerals undergoing complete dissolution during weathering. Both methods allow for calculation of weathering rate constraints without biomass and cation exchange influences. These constraints serve as additional equations in the mass-balance matrix. This study finds that the watershed with the higher percentage of recently abandoned agricultural fields previously used for growing row crops has the higher chemical weathering rate. The higher chemical weathering rate reflects greater runoff resulting from reduced evapotranspiration.

► Hydrogeochemical modelling of fluid–rock interactions driven by seawater injection. ► Reproduces measured compositional trends of produced oil field water. ► Indicates that fluid–rock interactions achieve near-equilibrium conditions. ► Identifies scale-minerals and quantifies their conversion in water legs and wells. ► Reveals a dependence of mineral conversion on the content of injected seawater.A hydrogeochemical model is presented and applied to quantitatively elucidate interdependent reactions among minerals and formation water–seawater mixtures at elevated levels of CO2 partial pressure. These hydrogeochemical reactions (including scale formation) occur within reservoir aquifers and wells and are driven by seawater injection. The model relies on chemical equilibrium thermodynamics and reproduces the compositional development of the produced water (formation water–seawater mixtures) of the Miller field, UK North Sea. This composition of the produced water deviates from its calculated composition, which could result solely from mixing of both the end members (formation water and seawater). This indicates the effect of hydrogeochemical reactions leading to the formation and/or the dissolution of mineral phases.A fairly good match between the modelled and measured chemical composition of produced water indicates that hydrogeochemical interactions achieve near-equilibrium conditions within the residence time of formation water–seawater mixtures at reservoir conditions. Hence the model enables identification of minerals (including scale minerals), to quantitatively reproduce and to predict their dissolution and/or formation. The modelling results indicate that admixing of seawater into formation water triggers the precipitation of Sr–Barite solid solution, CaSO4 phases and dolomite. In contrast, calcite and microcrystalline quartz are dissolved along the seawater flow path from the injection well towards the production well. Depending on the fraction of seawater admixed, interdependent reactions induce profound modifications to the aquifer mineral phase assemblage. At low levels of seawater admixture, Ba–Sr sulfate solid solution is precipitated and coupled to concurrent dissolution of calcite and microcrystalline quartz. Massive dissolution of calcite and the formation of CaSO4 phases and dolomite are triggered by intense seawater admixture. Hydrogeochemical modelling to reproduce observed compositional trends, resulting from an increase of the seawater fraction, can help (1) to explain changing production properties and (2) to predict the type and the degree of scaling depending on the content of injected seawater.

Variations in fluid chemistry and membrane phospholipid fatty acid composition of the bacterial community in a cold storage groundwater system during clogging events by Alexandra Vetter; Kai Mangelsdorf; Markus Wolfgramm; Kerstin Rauppach; Georg Schettler; Andrea Vieth-Hillebrand (1278-1290).
► First biogeochemical monitoring of a geothermally used aquifer (cold storage). ► Indication of biological mediated clogging events by microbial biomarkers. ► Application of novel PLFA ratios to evaluate the contribution of microbes in clogging events. ► Fluid constituents as potential electron donor and acceptors for microbial life.In order to monitor the operating mode of the cold storage of the German Parliament (North German Basin) the fluid chemistry and the phospholipid fatty acid (PLFA) composition of the indigenous microbial community have been monitored from August 2006 to August 2009. During this time two periods of reduced injection (clogging events) characterized by Fe precipitates and microbial biofilms in filters occurred in the injection wells impairing the operating state of the investigated cold storage. The fluid monitoring revealed the presence of sufficient amounts of potential C and energy sources (e.g. DOC and SO 4 2 - ) in the process water to sustain microbial life in the cold storage. In times of reduced injection the PLFA inventory of the microbial community differs significantly from times of normal operating phases indicating compositional changes in the indigenous microbial ecosystem. The most affected fatty acids (FAs) are 16:1ω7c (increase), 16:1ω7t (decrease) and 18:1ω7c (increase), interpreted to originate mainly from Fe and S oxidizers, as well as branched FA with 15, 16 and 17 C atoms (decrease) most likely representing sulfate-reducing bacteria (SRB). Based on this variability, PLFA ratios have been created to reflect the increasing dominance of biofilm forming S and Fe oxidizers during the disturbance periods. These ratios are potential diagnostic tools to assess the microbiological contribution to the clogging events and to find appropriate counteractive measures (e.g. mechanical cleaning vs disinfection). The correlation between changes in the PLFA composition and the operational state suggests that microbially mediated processes play a significant role in the observed clogging events in the investigated cold storage.