Applied Geochemistry (v.16, #7-8)

Biogeochemistry of landfill leachate plumes by Thomas H Christensen; Peter Kjeldsen; Poul L Bjerg; Dorthe L Jensen; Jette B Christensen; Anders Baun; Hans-Jørgen Albrechtsen; Gorm Heron (659-718).
The literature has been critically reviewed in order to assess the attenuation processes governing contaminants in leachate affected aquifers. Attenuation here refers to dilution, sorption, ion exchange, precipitation, redox reactions and degradation processes. With respect to contaminants, focus is on dissolved organic matter, xenobiotic organic compounds, inorganic macrocomponents as anions and cations, and heavy metals. Laboratory as well as field investigations are included. This review is an up-date of an earlier comprehensive review. The review shows that most leachate contamination plumes are relatively narrow and do not in terms of width exceed the width of the landfill. The concept of redox zones being present in the plume has been confirmed by the reported composition of the leachate contaminated groundwater at several landfills and constitutes an important framework for understanding the behavior of the contaminants in the plume as the leachate migrates away from the landfill. Diverse microbial communities have been identified in leachate plumes and are believed to be responsible for the redox processes. Dissolved organic C in the leachate, although it appears to be only slowly degradable when the volatile organic acids are gone, apparently acts as substrate for the microbial redox processes. Several xenobiotic organic compounds have been found to be degradable in leachate contaminated groundwater, but degradation rates under anaerobic redox conditions have only been determined in a few cases. Apparently, observations in actual plumes indicate more extensive degradation than has been documented in the laboratory. The behavior of cations in leachate plumes is strongly influenced by exchange with the sediment, although the sediment often is very coarse and sandy. Ammonium seems to be subject to anaerobic oxidation, but the mechanisms are not yet understood. Heavy metals do not seem to constitute a significant pollution problem at landfills, partly because the heavy metal concentrations in the leachate often are low, and partly because of strong attenuation by sorption and precipitation. Although complexation of heavy metals with dissolved organic matter is significant, the heavy metals are in most cases still strongly attenuated in leachate-polluted aquifers. The information available on attenuation processes has increased dramatically during the last 15 a, but the number of well-documented full scale leachate plumes are still few and primarily from sandy aquifers. Thus, the diversity of attenuation processes in leachate plumes is probably not yet fully understood. Apparently, the attenuation processes in leachate plumes may for many contaminants provide significant natural remediation, limiting the effects of the leachate on the groundwater to an area usually not exceeding 1000 m from the landfill.

Tin has a larger number of its organometallic derivatives in commercial use than any other element. This has given rise to an increase of the worldwide production of organotin compounds during the last 50 years. Due to the wide industrial applications considerable amounts of the organotins have entered various ecosystems. While Sn in its inorganic form is considered to be non-toxic, the toxicological pattern of the organotin compounds is complex. Depending on the nature and the number of the organic groups bound to the Sn cation, some organotins show specific toxic effects to different organsims even at very low concentrations. Therefore, specific determination of the individual organotin compounds is required. In recent years new sensitve analytical techniques have been developed for the detection of organotin compounds in various environmental samples. High amounts of the toxic tributyltin and some other organotin derivatives can be found not only in water and sediments, but also various aquatic organisms and tissues of mammals and birds are contaminated by these compounds. First investigations of human blood and livers show enhanced concentrations for some organotin derivatives. In spite of legislative regulations of usage for organotins in numerous countries, these pollutants represent a risk for aquatic and terrestric ecosystems.

The physical–chemical characteristics of the groundwater in the Baza–Caniles detrital aquifer system indicate that a wide diversity of hydrochemical conditions exists in this semiarid region, defining geochemical zones with distinct groundwater types. The least mineralized water is found closest to the main recharge zones, and the salinity of the water increases significantly with depth towards the center of the basin. Geochemical reaction models have been constructed using water chemistry data along flow paths that characterize the different sectors of the aquifer system, namely: Quaternary aquifer, unconfined sector and shallow and deep confined sectors of the Mio–Pliocene aquifer. Geochemical mass–balance calculations indicate that the dominant groundwater reaction throughout the detrital system is dedolomitisation (dolomite dissolution and calcite precipitation driven by gypsum dissolution); this process is highly developed in the central part of the basin due to the abundance of evaporites. Apart from this process, there are others which influence the geochemical zoning of the system. In the Quaternary aquifer, which behaves as a system open to gases and which receives inputs of CO2 gas derived from the intensive farming in the area, the interaction of the CO2 with the carbonate matrix of the aquifer produces an increase in the alkalinity of the water. In the shallow confined sector of the Mio–Pliocene aquifer, the process of dedolomitisation evolves in a system closed to CO2 gas. Ca2+/Na+ cation exchange and halite dissolution processes are locally important, which gives rise to a relatively saline water. Finally, in the deep confined sector, a strongly reducing environment exists, in which the presence of H2S and NH+ 4 in the highly mineralized groundwater can be detected. In this geochemical zone, the groundwater system is considered to be closed to CO2 gas proceeding from external sources, but open to CO2 from oxidation of organic matter. The geochemical modeling indicates that the chemical characteristics of this saline water are mainly due to SO4 dissolution, dedolomitisation and SO4 reduction, coupled with microbial degradation of lignite.

Multi-element, multi-medium regional geochemistry in the European Arctic: element concentration, variation and correlation by Clemens Reimann; Galina Kashulina; Patrice de Caritat; Heikki Niskavaara (759-780).
A multi-medium, multi element regional geochemical survey has been carried out in an 188,000 km2 area in the Central Barents Region, Finland, Norway and Russia. Four different sample materials (terrestrial moss, O-, B- and C-horizons of podzol) were collected at the same sites throughout the area at a density of 1 site/300 km2. While moss predominantly reflects the atmospheric input of elements, the O-horizon reflects the complex interplay between atmosphere, biosphere and lithosphere. The B-horizon can be used to study the influence of soil-forming processes, while the C-horizon represents the composition of the lithosphere at each sample site and thus the geogenic background. The concentration, variation and correlation between 24 elements (Ag, Al, As, Ba, Bi, Ca, Cd, Co, Cu, Fe, K, Mg, Mn, Na, Ni, P, Pb, S, Si, Sr, Th, V, Zn) analysed with similar techniques in all 4 materials are compared. Some rare trace elements (Ag, As, Bi, Cd, Pb) appear to be considerably more enriched in the O-horizon of podzols than the main pollutants in the survey area (Ni, Cu, Co from the Russian nickel industry in Monchegorsk and Nikel-Zapoljarnij). Biological processes play an underestimated role in determining regional geochemistry at the earth's surface.

Vertical profiles of trace metals and acid-volatile sulphide in a dynamic sedimentary environment: Lake Ketel, The Netherlands by Gerard A van den Berg; Suzan E.J Buykx; Marc A.G.T van den Hoop; Lambertus M van der Heijdt; John J.G Zwolsman (781-791).
Fine-scale solid-phase trace metal and acid-volatile sulphide profiles are presented for sediment cores taken at four locations in Lake Ketel, a dynamic sedimentation basin of the river Rhine in The Netherlands. The purpose of this study was to relate these profiles to the dynamics of sediment transport in the lake. The internal cycling of solids in the lake affects the distribution of trace metals and acid-volatile sulphide in the sediments. Comparison of vertical profiles of trace metals and sulphide indicates significant spatial variation in the dynamics of sediment transport in Lake Ketel. The construction of a dredge spoil storage depot in 1996 seems to have significantly influenced the hydrodynamic and sediment dynamics in Lake Ketel. Consequently, deposition rates in Lake Ketel based on comparison of solid-phase trace metal concentrations in the sediments and historical levels in Rhine suspended matter can only be used as rough estimates.

Arsenic(V) adsorption onto α-Al2O3 between 25 and 70°C by Werner E. Halter; Hans-Rudolf Pfeifer (793-802).
The adsorption of As(V) onto α-Al2O3 was investigated at 25, 50 and 70°C using batch adsorption experiments. Results indicate that As is strongly adsorbed at low pH and gets progressively released to the fluid with increasing pH above 7. At any pH, increasing temperature favors aqueous species of As over surface species. Surface complexation constants were determined at the experimental temperatures by fitting the adsorption data. Adsorption reactions were then converted to semi-isocolumbic reactions, i.e. reactions with balanced like-charged aqueous species. Intrinsic adsorption constants of semi-isocolumbic reactions change linearly when plotted against inverse temperature, suggesting that the heat capacity of these reactions remains constant over the temperature range considered. This permitted thermodynamic parameters of intrinsic surface complexation constants to be determined. Changes in surface complexation constants result in a change in the surface speciation with increasing temperature. This change is similar to the one observed for aqueous species, i.e. increasing temperature favors less negatively charged species below a pH of 9 and more negatively charged species above a pH of 10. Comparison with the stability of As surface complexes with Fe suggests that surface complexes with Al are more stable.

Effect of sulfide impurities on the reactivity of pyrite and pyritic concentrates: a multi-tool approach by Roel Cruz; Valerie Bertrand; Marcos Monroy; Ignacio González (803-819).
Sulfide mineral oxidation, primarily pyrite and pyrrhotite, generates acid mine drainage during weathering. Successful management of acid generating wastes entails the suppression of the initiation of oxidation reactions. The reactivity of pyrite depends on ore mineralogy, including the effects of associated sulfide impurities. The electrochemical surface characterization study using cyclic voltammetry with carbon paste electrodes containing minerals particles (CPE-Mineral) is an effective tool for demonstrating how the various mineral characteristics work together to influence the overall reactivity of the mineral. This study was supported by chemical, mineralogical and leachate chemistry data. The results show that the presence of other sulfides in contact with pyrite at the beginning of the weathering process is the most important parameter affecting pyrite reactivity, which is likely to be oxidized and passivated. In more advanced stages of leaching, mineral coatings which passivate the pyrite surfaces tend to play the most important role in defining the reactivity of pyrite. The electrochemical response of pyritic samples in conjunction with the evolution of the chemical quality of the leach solution in the simple experimental device here used, could then provide valuable information on acid mine drainage generation.

The geological evolution of B in two UK sandstone aquifers is followed from precipitation chemistry through to groundwaters in both the unconfined and confined zones. Measurements have been made of major element geochemistry, B concentrations and B isotopic ratios. The isotopic measurements were carried out using ICP/MS following a simple preconcentration step. Isotopic measurements of rainfall show a bimodal distribution and it is suggested that enriched signatures are characteristic of Atlantic air over Britain and depleted signatures representative of continental air. In the marine Lower Greensand aquifer dissolution of glauconite results in the mobilisation of B and a correlation with SO4 suggests that this dissolution is related to the oxidation of pyrite which appears to be the SO4-forming reaction in the aquifer. In the non-marine Hastings beds isotopic ratios and a correlation with HCO3 suggest that B is associated with the dissolution of ferroan carbonates. In both aquifers the geochemical evolution of B is complex and more information is needed on the behaviour of B isotopes during evapotranspiration and groundwater recharge.

Implantation of recoiling radionuclides of U and Th radioactive series applied to estimation of surficial erosion of CaCO3 materials by Mario Voltaggio; Maurizio Palmisano; Alessandro Raponi; Simone Voltaggio (835-848).
A method to detect the extent of rainfall-dependent erosion of CaCO3 materials, based on implantation of recoiling nuclei of U–Th disequilibrium series (UTHIRN) is outlined here. Radon chambers provided natural implantation of short and medium-lived isotopes (212Pb and 210Pb) on surfaces of natural varieties of CaCO3. Equal thicknesses of CaCO3 were dissolved in order to measure the distribution of the recoiled nuclei inside the target material. The measured distribution was found to be consistent with the theoretical distribution expected for mechanisms of nuclear stopping. The 216Po half-recoil range (18 nm) obtained from the experimental curve was slightly higher than the theoretical one (16 nm).The ratio between residual and initial activity, monitored by non-destructive methods, was then used to calculate the eroded thickness of CaCO3 tablets. The ‘chemical’ and ‘mechanical’ contributions of the surficial erosive process were evaluated by leaching experiments and by simulated rainfall, respectively. Successively, the erosion rates produced during single rainfall events were compared with the experimentally obtained rates, using ternary diagrams (pH/ mm of rainfall/eroded thickness). The difference between the total eroded thickness measured by the proposed method (22.5 nm) and the total eroded thickness predicted by the theoretical model (16.9 nm) for the considered rainfalls was about 25%. The temporal resolution of the erosion rate, the extension of monitored area and the detail of the surficial eroded thickness (up to ∼40 nm) are notably improved by the UTHIRN method.

Carbon-14 study of groundwater in the sedimentary rocks at the Tono study site, central Japan by T. Iwatsuki; S. Xu; Y. Mizutani; K. Hama; H. Saegusa; K. Nakano (849-859).
Isotopic investigations using 14C of groundwater were carried out to understand the hydraulic conditions in the sedimentary rocks at the Tono study site, central Japan. 14C activities of groundwater observed range from 2 to 32 % Modern Carbon (pMC). Measured 14C activities of groundwater are corrected by the isotopic mass balance model based on 14C activities, δ13C values, concentrations of the dissolved inorganic carbon (DIC) and δ13C values of non-active carbon dissolved into the groundwater from carbonate minerals and organics. Assuming that the groundwater reservoir is comparable to the piston flow situation, the relative 14C ages of groundwaters were calculated from the corrected 14C activity. The relative 14C age suggests that the groundwater infiltration from the upper part of the sedimentary rocks to the lower part takes several thousands of years, or that the groundwater in the lower part of sedimentary rocks is derived from long distance flow from the surface through the unconformity between the sedimentary rocks and basement granite. The flow rate calculated by relative 14C ages shows similar values to those estimated by computer simulation using hydraulic pressure and conductivity data. Hydraulic conditions at the Tono study site inferred from 14C activity agree with those suggested from hydrogeological analyses. Isotopic approaches using 14C activity can be applied as geochemical evaluation for interpretations from the hydraulic study.

French SON 68 nuclear glass alteration mechanisms on contact with clay media by S Gin; P Jollivet; J.P Mestre; M Jullien; C Pozo (861-881).
The leaching behavior of the nonradioactive French SON 68 (R7T7-type) nuclear glass was investigated in the presence of FoCa7 clay. Static experiments were carried out at 90°C under conditions favorable to convective transfer. Three test environments were compared: a clay medium, the same clay medium doped with 2.5 wt.% silica gel, and pure water. These experiments showed that in raw clay the glass alteration rate remained near the initial value for several hundred days, whereas in pure water at the same temperature and with the same glass-surface-area-to-solution-volume (S/V) ratio the alteration rate quickly dropped by several orders of magnitude after the formation of a protective gel layer. This major difference between the two media can be attributed to transfer of the principal gel-forming elements (Si, Al, Ca) into the clay medium as a result of sorption phenomena and probably the precipitation of silicate phases. The addition of silica gel to the clay not only neutralizes the clay sorption capacity, but also protects the glass from significant alteration (the glass was altered appreciably less than in pure water). This article discusses the mechanisms limiting the glass alteration kinetics in the test media. The gel that forms by reconstitution of hydrolyzed glass species at the glass/clay interface is shown to constitute a diffusion barrier whose effectiveness depends to a large degree on the conditions under which species are removed by the external medium. Interpreting the experimental data from this standpoint leads to a reexamination of the classic model in which the glass alteration kinetics are inhibited by the dissolved silicon content.

Preliminary estimate of CO2 output from Pantelleria Island volcano (Sicily, Italy): evidence of active mantle degassing by Rocco Favara; Salvatore Giammanco; Salvatore Inguaggiato; Giovannella Pecoraino (883-894).
Total CO2 output from fumaroles, bubbling and water dissolved gases and soil gases was investigated at Pantelleria Island volcano, Italy. The preliminary results indicate an overall output of 0.39 Mt a−1 of CO2 from the island. The main contribution to the total output was from diffuse soil degassing (about 0.32 Mt a−1), followed by dissolved CO2 (0.034 Mt a−1), focussed soil degassing (0.028 Mt a−1) and bubbling CO2 (0.013 Mt a−1). The contribution of CO2 from fumarole gases was found to be negligible (1.4×10−6 Mt a−1). Carbon-13 values for CO2 coupled with those for associated He in gases from fumaroles and sites of focussed soil degassing clearly rule out any significant organic CO2 component and suggest a common mantle origin for these gas species. The inferred mantle source beneath Pantelleria would seem to have peculiar geochemical characteristics, quite distinct from those of mantle producing MORB but compatible with those of magmatic sources of central Mediterranean and central European volcanoes. These findings indicate that the Pantelleria volcanic complex is a site of active mantle degassing that is worthy of attention for future geochemical surveillance of the island.

Coalbed gases in the Lower Silesian Coal Basin (LSCB) of Poland are highly variable in both their molecular and stable isotope compositions. Geochemical indices and stable isotope ratios vary within the following ranges: hydrocarbon (CHC) index CHC=CH4/(C2H6+ C3H8) from 1.1 to 5825, wet gas (C2+) index C2+=(C2H6+ C3H8+ C4H10+ C5H12) / (CH4+ C2H6+ C3H8+ C4H10+ C5H12) 100 (%) from 0.0 to 48.3%, CO2–CH4 (CDMI) index CDMI=CO2/(CO2+ CH4) 100 (%) from 0.1 to 99.9%, δ13C(CH4) from −66.1 to −24.6‰, δD(CH4) from −266 to −117‰, δ13C(C2H6) from −27.8 to −22.8‰, and δ13C(CO2) from −26.6 to 16.8‰. Isotopic studies reveal the presence of 3 genetic types of natural gases: thermogenic (CH4, higher gaseous hydrocarbons, and CO2), endogenic CO2, and microbial CH4 and CO2. Thermogenic gases resulted from coalification processes, which were probably completed by Late Carboniferous and Early Permian time. Endogenic CO2 migrated along the deep-seated faults from upper mantle and/or magma chambers. Minor volumes of microbial CH4 and CO2 occur at shallow depths close to the abandoned mine workings. “Late-stage” microbial processes have commenced in the Upper Cretaceous and are probably active at present. However, depth-related isotopic fractionation which has resulted from physical and physicochemical (e.g. diffusion and adsorption/desorption) processes during gas migration cannot be neglected. The strongest rock and gas outbursts occur only in those parts of coal deposits of the LSCB which are dominated by large amounts of endogenic CO2.

A total of 48 samples, feed (run-of-mine) coals and their combustion residues (fly ash and bottom ash) were systematically collected twice a week over a 4 week period (June 1998) from two boiler units (I and II) of the Cayirhan power plant (630 MW) that burns zeolite-bearing coals of late Miocene age. The feed coals are high in moisture (22.8% as-received) content and ash (44.9%) yield and total S content (5.1%), and low in calorific value (2995 kcal/kg). The mineralogy of the feed coals contains unusually high contents of the zeolites (clinoptilolite/heulandite and analcime), which are distributed within the organic matter of coal. Other minerals determined are gypsum, quartz, feldspar, pyrite, dolomite, calcite, cristobalite and clays. Common minerals in the crystalline phase of the combustion residues are anhydrite, feldspar, quartz, hematite, lime and Ca–Mg silicate. Minor and trace amounts of magnetite, cristobalite, maghemite, gehlenite, calcite and clinoptilolite/heulandite are also present in the combustion residues. Trace element contents of the feed coals, except for W, fall within the estimated range of values for most world coals; however, the mean values of Mn, Ta, Th, U and Zr are near maximum values of most world coals. Elements such as As, Bi, Ge, Mo, Pb, Tl, W and Zn are enriched more in the fly ash compared to the bottom ash.

Factorial kriging with external drift: a case study on the Penedono Region, Portugal by A.C. Batista; A.J. Sousa; M.J. Batista; L. Viegas (921-929).
Factorial kriging has been used in geochemical exploration for the estimation and cartography of the spatial components of the variables, helping with the identification and interpretation of geochemical anomalies. Those spatial components appear by the decomposition of the variables in its several structural components, given by the variograms. In this paper a new form of factorial kriging is introduced, by using the geologic information as an external drift. This was achieved considering as an external variable (external drift) sample co-ordinates on the first axis resultant from a principal component analysis (PCA), interpreted as a lithological factor. With this type of geostatistical technique each point appears in the resultant maps as a combination of geochemical and geological information, attending the geographic localization of the samples. This technique was tested on a set of 2450 sediment samples collected on a 640 km2 area, between the Trás-os-Montes e Alto Douro and the Beira Alta regions. From the 34 initial elements analyzed (10 major elements P2O5, SiO2, Al2O3, Fe2O3, MgO, CaO, Na2O, K2O, TiO2 and MnO expressed in oxide percentage and 24 elements expressed in ppm As, Bi, Ag, Sb, W, B, Cu, Pb, Zn, Sn, Nb, Li, Be, Zr, Y, La, Ba, Cd, Mo, V, Cr, Co, Ni and Sr) only the results obtained for 2 of them are presented in this work. The first was Sn, which is associated with some mineralisation in this region and the other one was Zn, which shows similar behavior in the whole area, with the exception of a small region.

Weathering in an upland catchment on granitic parent material has been studied by chemical and mineralogical analyses of soils. Long-term weathering rates for base cations, calculated from chemical analyses of the mineral horizons from soil profiles using Zr as an internal, immobile, index element, are among the smallest recorded for Scottish soils (1.7–3.1 meq m−2 a−1), indicating that these soils are susceptible to acid deposition. Sodium is the base cation lost to the greatest extent from the soils, due to weathering of plagioclase feldspar, mainly in the coarse size-fractions. Calcium is lost not only from plagioclase feldspar, but also from hornblende, grains of which show dissolution etch pits and denticulate surface features when examined by scanning electron microscopy. Weathering of hornblende, present in basic inclusions in the granite, is a significant weathering process in these soils. A range of values for 87Sr/86Sr ratios in stream-waters confirms the spatial variability of the material supplying Ca to the streams. The current weathering rate, calculated from input–output budgets to be 28.9 meq m−2 a−1, is much greater than the long-term weathering rate, but small compared to other catchments on similar parent material.

A series of experiments were conducted to investigate the influence of ionic strength on Sr2+ sorption by the bacteria Shewanella alga, hydrous ferric oxide (HFO) and bacteria-HFO composite solids. Sorption of Sr2+ to S. alga exhibited a strong dependence on ionic strength with the maximum concentration of solid phase Sr (BSrmax) decreasing from 79 μmol g−1 under dilute aqueous conditions to 4 μmol g−1 at high ionic strength (0.1M NaNO3). Corresponding apparent surface complex formation (KS Sr) values for S. alga increased from 10−0.51 to 10−0.26 with increasing ionic strength, implying that only high affinity sites remain to bind Sr2+ under conditions of increased ionic strength. In contrast, Sr2+ sorption to HFO surfaces was independent of ionic strength with BSrmax and KS Sr remaining relatively constant (approximately 1 μmol g−1 and 10−2.1, respectively) under increasing ionic strength conditions. The ionic strength dependent sorptive behaviour exhibited by S. alga is consistent with electrostatic outer-sphere complexation reactions occurring in the diffuse layer, whereas inner-sphere complexation reactions account for the Sr2+ sorption behaviour of HFO. The bacteria-HFO composite solid exhibited moderate ionic strength dependence with maximum binding capacities decreasing from 34 μmol g−1 (dilute conditions) to 24 μmol g−1 (0.1 M NaNO3). These results suggest that Fe3+ sorption and precipitation at the bacterial surface alters the electrochemical surface properties of the composite solid, buffering the effects of increased ionic strength on subsequent Sr2+ sorption.

Geochemical models of the impact of acidic groundwater and evaporative sulfate salts on Boulder Creek at Iron Mountain, California by David C Keith; Donald D Runnells; Kenneth J Esposito; John A Chermak; David B Levy; Steven R Hannula; Malcolm Watts; Larry Hall (947-961).
During dry season baseflow conditions approximately 20% of the flow in Boulder Creek is comprised of acidic metals-bearing groundwater. Significant amounts of efflorescent salts accumulate around intermittent seeps and surface streams as a result of evaporation of acid rock drainage. Those salts include the Fe-sulfates — rhomboclase ((H3O)Fe3+(SO4)2·3H2O), ferricopiapite (Fe3+ 5(SO4)6O(OH)·20H2O), and bilinite (Fe2+Fe2 3+(SO4)4·22H2O); Al-sulfates — alunogen (Al2(SO4)3·17H2O) and kalinite (KAl(SO4)2·11H2O); and Ca- and Mg-sulfates — gypsum (CaSO4·2H2O), and hexahydrite (MgSO4·6H2O). The dissolution of evaporative sulfate salt accumulations during the first major storm of the wet season at Iron Mountain produces a characteristic hydrogeochemical response (so-called “rinse-out”) in surface waters that is subdued in later storms. Geochemical modeling shows that the solutes from relatively minor amounts of dissolved sulfate salts will maintain the pH of surface streams near 3.0 during a rainstorm. On a weight basis, Fe-sulfate salts are capable of producing more acidity than Al- or Mg-sulfate salts. The primary mechanism for the production of acidity from salts involves the hydrolysis of the dissolved dissolved metals, especially Fe3+. In addition to the lowering of pH values and providing dissolved Fe and Al to surface streams, the soluble salts appear to be a significant source of dissolved Cu, Zn, and other metals during the first significant storm of the season.

The <2 mm fraction of 605 samples of the C-horizon of podzols collected from an area of 188,000 km2 in the European Arctic was analysed for more than 40 chemical elements. The results were used to construct geochemical maps which showed clear regional distribution patterns, notwithstanding the very low sample density of 1 site per 300 km2. Some of these patterns fit established lithological boundaries. Others fit lineament structures in the area and underline the relative importance of certain tectonic directions some of which have not yet been delineated on existing geological maps. Some mark large-scale hydrothermal events and related alteration. Finally, some are connected with prominent, known ore deposits occurring in the area. However, several large deposits and even famous metallogenic provinces (Fe, Ni/Cu) are hardly, or not at all, reflected in the regional geochemical maps. In their present definitions geochemical provinces and metallogenic provinces are thus not necessarily related. Special geochemical features can occur at very different scales. The term geochemical province is so imprecise in terms of processes leading to regional-scale geochemical features that it should be avoided. Low-density geochemistry can be used to aid the interpretation of the geological evolution of large regions. It can also be used to find prospective areas within such regions.

Evaluation of the environmental impact of volcanic emissions from the chemistry of rainwater: Mount Etna area (Sicily) by A Aiuppa; P Bonfanti; L Brusca; W D’Alessandro; C Federico; F Parello (985-1000).
The S, halogen and NO3 contents of rainwater samples from the Etnean area were studied in order to define the environmental impact of plume emissions on the local environment. Samples, collected on a network of 11 bulk rain gauges, show significant variability in anion content, which can be ascribed to different meteorological and environmental conditions at each sampling site and to a variable distance from the different source areas. Data analysis suggests that S, F, Cl and Br are mainly magma-derived, whereas NO3 mainly originates from anthropogenic sources. Samples collected from sites close to craters display considerable temporal variability, with increased anion concentrations being recorded during periods of intense plume degassing. Variations in precipitation also induce significant modifications in the chemistry of the meteoric-derived Etnean groundwaters.

Soil Resources and the Environment by Peter Abrahams (1001).