Applied Geochemistry (v.21, #1)
A geochemical evaluation of perennial spring activity and associated mineral precipitates at Expedition Fjord, Axel Heiberg Island, Canadian High Arctic by Christopher R. Omelon; Wayne H. Pollard; Dale T. Andersen (1-15).
Two groups of perennial springs are observed in the Canadian High Arctic at Expedition Fjord on Axel Heiberg Island at Colour Peak and Gypsum Hill. Saline discharge (∼1.3–2.5 molal NaCl) produces a variety of calcite (travertine) and gypsum-rich precipitates. Saturation index calculations of the spring waters at Colour Peak suggest CO2 degassing from the waters causes calcite precipitation. Gypsum precipitation dominates at Gypsum Hill, where spring waters have lower alkalinity and higher SO4 concentrations. Mineral accumulations form both channel and rimstone pool morphologies as a result of varying slope conditions. At Colour Peak, confined flow in steep slope areas develop massive structures in contrast to more friable, porous accumulations in areas where waters fan out on shallower slopes; these morphological variations lead to corresponding varying apparent rates of mineral precipitation. Mineral precipitation at Gypsum Hill is far less notable as a result of lower discharge rates and annual degradation by icing formation. Microscopic observations and geochemical analyses of the channel precipitates at Colour Peak reveal alternating light (calcite spar) and dark (anhedral microcrystalline calcite combined with organic matter and non-carbonate minerals) laminae. Rimstone pools forming in lower sections of spring discharge are composed of accumulations of large euhedral calcite crystals interbedded with allochthonous inputs. High concentration of dissolved solids is responsible for slow travertine precipitation rates, which occurs during winter. This precipitation is further retarded during summer months by the introduction of crystal growth inhibitors such as Fe3+ and deposition of organic matter and soil sediments.
Element fractionation by sequential extraction in a soil with high carbonate content by Margareta Sulkowski; Alfred V. Hirner (16-28).
The influence of carbonate and other buffering substances in soils on the results of a 3-step sequential extraction procedure (BCR) used for metal fractionation was investigated. Deviating from the original extraction scheme, where the extracts are analysed only for a limited number of metals, almost all elements in the soils were quantified by X-ray fluorescence spectroscopy, in the initial samples as well as in the residues of all extraction steps. Additionally, the mineral contents were determined by X-ray diffractometry. Using this methodology, it was possible to correlate changes in soil composition caused by the extraction procedure with the release of elements. Furthermore, the pH values of all extracts were monitored, and certain extraction steps were repeated until no significant pH-rise occurred. A soil with high dolomite content (27%) and a carbonate free soil were extracted. Applying the original BCR-sequence to the calcareous soil, carbonate was found in the residues of the first two steps and extract pH-values rose by around two units in the first and second step, caused mainly by carbonate dissolution. This led to wrong assignment of the carbonate elements Ca, Mg, Sr, Ba, and also to decreased desorption and increased re-adsorption of ions in those steps. After repetition of the acetic acid step until extract pH remained low, the carbonate was completely destroyed and the distributions of the elements Ca, Mg, Sr, Ba as well as those of Co, Ni, Cu, Zn and Pb were found to be quite different to those determined in the original extraction. Furthermore, it could be shown that the effectiveness of the reduction process in step two was reduced by increasing pH: Fe oxides were not significantly attacked by the repeated acetic acid treatments, but a 10-fold amount of Fe was mobilized by hydroxylamine hydrochloride after complete carbonate destruction. On the other hand, only small amounts of Fe were released anyway. Even repeated reduction steps did not destroy the amorphous Fe oxides completely, showing that 0.1 mol L−1 hydroxylamine hydrochloride was not strong enough to attack these oxides effectively.The extraction sequences were carried out not only on the soil samples, but also on their coarse and fine fractions (> or <2 μm). The fine fraction of the calcareous soil contained only 10% dolomite, but was enriched in organic matter and clay minerals, which also resulted in increased extract pH-values during the sequential extraction. Hence, the effects on ion release in the fine fraction were similar to those of the whole soil. Since the destruction of the organic matter was incomplete after regular oxidation, the H2O2-treatment of the fine fraction had to be repeated. The addition of the extractable amounts of the two fractions showed good agreement to the results obtained for extraction of the whole soils. Likewise the pH-values of the carbonate-free soil extracts did not increase significantly, therefore it was concluded that repetitions of extraction steps for this soil were not necessary.Extract-pHs should always be controlled so that extraction conditions are comparable; to be able to use the BCR extraction scheme or similar ones for carbonate- and organic-rich samples this is mandatory. Single extraction steps should be repeated if pH rises too much; additionally the oxidizing step should be performed more than twice for samples rich in organic substances, depending upon the violence of the reaction with H2O2. If these precautions are neglected the validity of the extraction data is likely to be questionable.
Oxido-reduction sequence related to flux variations of groundwater from a fractured basement aquifer (Ploemeur area, France) by C. Tarits; L. Aquilina; V. Ayraud; H. Pauwels; P. Davy; F. Touchard; O. Bour (29-47).
This paper focuses on the chemical evolution of water during the exploitation of a fractured aquifer in a NO3-rich agricultural environment. During a ten year period, both production rate and chemical parameters were continuously measured in tap water obtained from a deep-water plant in Brittany, France. Changes in SO 4 2 - and NO 3 - were observed after pumping was initiated. Nitrate concentration decreased during the first 200 days and then stabilized at ∼5 ± 1 mg/L, while SO 4 2 - concentration increased rapidly over this period and then showed a steady state increase (0.01 mg/L/day). These changes are attributed to the development of equilibrium between the physical flow parameters and the chemical kinetics of autotrophic denitrification processes that occur in the pyrite-bearing fractures.The chemical characteristics of the groundwaters collected in 18 wells located around the site allow identification of two different areas. One is weakly influenced by pumping and is characterized by high NO 3 - concentrations and a short residence time. The second area is directly related to the main pumped well, and characterized by reduced NO 3 - levels combined with an increased SO 4 2 - production, resulting from the denitrification processes in the pyrite-bearing fractures. Over the last few years, a SO 4 2 - increase unrelated to denitrification has been recorded in some wells. Based on the NO 3 - , SO 4 2 - and Fe concentrations, this is attributed to oxidation of S minerals, coupled to FeIII reduction. Exploitation of the aquifer has led to a rapid transfer of the waters within the deep fractures. Their high velocities strongly control the chemical parameters and have led to a redox sequence that has promoted S oxidation, coupled with (1) O2, (2) NO 3 - , and (3) Fe reduction.
Phosphatase and microbial activity with biochemical indicators in semi-permafrost active layer sediments over the past 10,000 years by Yoshinori Takano; Hideaki Mori; Takeo Kaneko; Yoji Ishikawa; Katsumi Marumo; Kensei Kobayashi (48-57).
Core samples of boreal terrestrial sediments from depths of 0–300 cm at Rikubetsu, Hokkaido, Japan were analyzed for alkaline and acid phosphatase enzymatic activities. Enzymatic activities of alkaline phosphatase (ALP) and acid phosphatase (ACP) were greatest at the surface and decreased with depth; ALP and ACP activities were 25.5 and 22.0 nmol min−1 g−1, respectively, within the top 5 cm. These biological indicators were compared with measurements of microbial cell density and chemical indicators, including total organic C (TOC) and total hydrolyzed amino acids (THAA). The product–moment correlation coefficients (r) for ALP and ACP versus microbial cell density were 0.949 and 0.810, respectively. The coefficients for THAA and TOC versus ALP were 0.997 and 0.995, respectively. Vertical distributions of enzymatic activity are highly consistent with the observed microbial biomass profile and diagenetic organic matter in the sediment. However, the vertical profile of PO4 concentration shows a negative correlation coefficient for ALP and ACP of −0.937 and −0.855, respectively. Consequently, ALP and ACP were shown to be useful biomarkers of microbial activities in the terrestrial sediment over the past 10 ka at Rikubetsu, Hokkaido, Japan.
Atmospheric Pb-pollution by pre-medieval mining detected in the sediments of the brackish karst lake An Loch Mór, western Ireland by G. Schettler; R.L. Romer (58-82).
This paper presents results of geochemical investigations of lake sediments from the karst lake An Loch Mór, Aran Islands, including the first highly resolved record of atmospheric Roman Pb pollution for Ireland. The natural Pb influx into the lake is largely contributed by 3 Pb components, which differ in their isotopic composition: detrital influx of Pb from the siliciclastic input, dissolved influx of Pb released by weathering of the local limestone, and dissolved influx of seawater Pb. The balance between the 3 Pb components varies in concert with the hydrological evolution of the lake. The influx of Pb in dissolved form is estimated by geochemical mass balance assuming that the siliciclastic influx is characterised by the Pb/Al-ratio of the Late Glacial clastic sediments. It typically accounts for 50–80% of total Pb input in the Holocene sediments of An Loch Mór. The natural dissolved influxes of Pb, Sc, and Y reach a similar order of magnitude. Normalisation with Sc and Y is applied to quantify contributions from anthropogenic Pb. Based on continuous sampling of 1 cm sample slices, variations in the influx of Roman Pb could be reconstructed at a time resolution of c. 5 a. Combined geochemical and Pb isotope mass balance is used to characterise the isotopic composition of anthropogenic Pb. Distinctly enhanced influx of anthropogenic Pb occurs in the 1st and 2nd century AD and shows high variability on decadal scale. This is in contrast to central European Pb records, which document a gradual increase and decrease in ancient atmospheric pollution by Roman Pb. The reconstructed high variability in the influx of Roman Pb in An Loch Mór documents variations in the wind regime of western Europe, temporarily favouring the transport of atmospheric Pb to western Ireland.
Arsenic-rich groundwater in an urban area experiencing drought and increasing population density, Perth, Australia by S.J. Appleyard; J. Angeloni; R. Watkins (83-97).
Groundwater in the Gwelup groundwater management area in Perth, Western Australia has been enriched in As due to the exposure of pyritic sediments caused by reduced rainfall, increased groundwater abstraction for irrigation and water supply, and prolonged dewatering carried out during urban construction activities. Groundwater near the watertable in a 25–60 m thick unconfined sandy aquifer has become acidic and has affected shallow wells used for garden irrigation. Arsenic concentrations up to 7000 μg/L were measured in shallow groundwater, triggering concerns about possible health effects if residents were to use water from household wells as a drinking water source. Deep production wells used for public water supply are not affected by acidity, but trends of progressively increasing concentrations of Fe, SO4 and Ca over a 30-a period indicate that pyrite oxidation products extend to the base of the unconfined aquifer. Falling Eh values are triggering the release of As from the reduction of Fe(III) oxyhydroxide minerals near the base of the unconfined aquifer, increasing the risk that groundwater used as a drinking water source will also become contaminated with high concentrations of As.
Iron nutrition and possible lead toxicity: An appraisal of geophagy undertaken by pregnant women of UK Asian communities by Peter W. Abrahams; Mark H. Follansbee; Andrew Hunt; Barry Smith; Joanna Wragg (98-108).
A cultural transfer of geophagy is evident in the UK, with soils imported from Bengal being deliberately consumed mainly by pregnant Asian women. Two samples purchased from ethnic shops were subjected to a 2-part acid–alkaline in vitro physiologically based extraction test (PBET) procedure, representing the stomach and small intestine of the human digestive system respectively, to determine the bioaccessibility of elements. Despite the low bioaccessibility of Fe, with the quantity of soil consumed one sample can provide 41–54% of this mineral nutrient required by a 15–18 year old female, with the other sample providing 90–119%. Significant amounts of Ca, Cu and Mn are also supplied to the consumer, whilst further research investigating the possible effects of Pb toxicity on the geophagist would seem to be justified.
Lead and zinc in formation waters, Alberta Basin, Canada: Their relation to the Pine Point ore fluid by Brian Hitchon (109-133).
The source of the ore fluid for the Pine Point Zn–Pb deposit has been controversial for decades. Both formation waters from deep in the basin and geothermal fluids from the Precambrian basement have been considered as sources of the ore in this carbonate-hosted deposit. A database of 694 analyses of Pb and Zn in formation waters from the Alberta Basin bears on this controversy. These waters have a mean content of 4.66 mg L−1 Pb and 6.88 mg L−1 Zn. For each of these metals, the maximum content is 360 mg L−1 and the median content is 0.9 mg L−1. In 71% of the samples Pb > Zn, with a mean ratio of 2.3:1. This is in contrast to the Pb:Zn ratio of formation waters in other sedimentary basins and geothermal waters but is consistent with that in brines from the Canadian Shield. Geochemical modelling using SOLMINEQ.88 shows that Pb and Zn occur mainly as the MeCl 4 2 - complex. It is not possible to produce a sulphide precipitate with Zn > Pb, such as the ore at Pine Point, from a formation water with Pb > Zn, even when the formation water carries the metals in the absence of H2S, and the metals are precipitated by H2S-rich brines. Therefore, the present formation waters are a poor candidate for the source of the metals at Pine Point. It is more likely that geothermal fluids rising along the Great Slave Lake Shear Zone were the source of the metals. Additional evidence for this alternate source includes: (1) the very homogeneous, non-radiogenic character of the Pb isotopes in galena; (2) the absence of a thermal anomaly along the Great Slave Lake Shear Zone; (3) a Famennian time of deposition (based on Rb–Sr dating of sphalerite), when overburden was thin and reservoir temperature low; and (4) the distribution of sphalerite and galena in the subsurface of the Alberta Basin in relation to major crustal discontinuities and normal faults cutting the crystalline basement. Exploration for other Zn–Pb deposits should therefore focus on the location of suitable shear zones and faults up which geothermal fluids might have migrated, rather than the flow and composition of formation waters.
Boron content of Lake Ulubat sediment: A key to interpret the morphological history of NW Anatolia, Turkey by N. Kazancı; Ö. Toprak; S.A.G. Leroy; S. Öncel; Ö. Ileri; Ö. Emre; P. Costa; K. Erturaç; E. McGee (134-151).
Freshwater Lake Ulubat (c. 1.5 m deep and c. 138 km2) receives sediment from a 10.414 km2 area in the seismically active Susurluk Drainage Basin (SDB) of NW Turkey. The B and trace element contents of the lake infill seem to be a link between the fresh landforms of the SDB and the lacustrine sediment. Deposition in Lake Ulubat has been 1.60 cm a−1 for the last 50 a according to radionucleides; however the sedimentation rate over the last millennium was 0.37 cm a−1 based on 14C dating. The B content of the lacustrine infill displays a slight increase at 0.50 m and a drastic increase at 4 m depth occurring c. 31 a and c. 1070 a ago, respectively. Probably the topmost change corresponds to the start of open mining in the SDB and the second one to the natural trenching of borate ore-deposits. These dates also show indirectly a 1.4 cm a−1 erosion rate during the last millennium as the borate beds were trenched up to 15 m. By extrapolation, it is possible to establish that the formation of some of the present morphological features of the southern Marmara region, especially river incision, began in the late Pleistocene, and developed especially over the last 75 ka.
Elevated tungsten and cobalt in airborne particulates in Fallon, Nevada: Possible implications for the childhood leukemia cluster by Paul R. Sheppard; Gary Ridenour; Robert J. Speakman; Mark L. Witten (152-165).
Trace metal content was measured in airborne particulates in five towns located in west central Nevada with an emphasis on Fallon, where 16 cases of childhood leukemia were diagnosed recently. Airborne dust samples were collected using portable, high-volume particulate air samplers, and each filter was chemically analyzed by acid-dissolution, inductively coupled plasma mass spectroscopy. Tungsten was the most notable metal in Fallon dust, with cobalt of secondary but still important interest. Tungsten and cobalt were elevated in Fallon relative to comparison towns of west central Nevada, and within Fallon they co-varied closely temporally and spatially. These results were obtained and confirmed in two different collections during two different seasons of the year and using entirely different hardware and different types of filters. By weight of multiple lines of evidence, the source of tungsten and cobalt in airborne particulates in Fallon is probably not natural, but rather a hard-metal facility located in Fallon should tentatively be considered a candidate source of the airborne exposure of these metals within Fallon. Neither tungsten nor cobalt has yet to be definitively associated with childhood leukemia, but cobalt and tungsten carbide together are probably carcinogenic to humans. We concur with calls by others for more research in Fallon, and we recommend that cobalt be added into the toxicological studies, especially as an interactive factor with tungsten.
Characterization and quantification of biomarkers from biomass burning at a recent wildfire site in Northern Alberta, Canada by Angelika Otto; Rina Gondokusumo; Myrna J. Simpson (166-183).
The composition of organic matter (OM) in pine vegetation and soil samples from a pine forest which was charred by a wildfire was analyzed using solid-state nuclear magnetic resonance (13C NMR) and gas chromatography–mass spectrometry (GC–MS) of solvent extracts to study the effects of thermal alteration on soil organic matter (SOM). The NMR data revealed the presence of unaltered biomolecules (cellulose, proteins) and low contents of aromatic C (15%) in the charred pine wood and cones while the charred soil samples exhibited higher contents of aromatic C (39–56%). The solvent extraction of charred and uncharred plant and soil samples yielded diterpenoids, triterpenoids, steroids, a series of aliphatic lipids, phenols and carbohydrates indicating the predominant input of higher plant OM and minor contributions from microorganisms and/or fauna. The lower yield of solvent extractable aliphatic lipids in the charred samples versus the uncharred samples suggests that these compounds are thermally degraded during a wildfire. Molecular markers for the burning of cellulose (levoglucosan, mannosan, galactosan) were detected in all charred samples. The comparison of charred and uncharred samples allowed the identification of unaltered pine derived biomolecules and their thermal alteration products in the charred samples. Terpenoid and steroid biomolecules were in part altered during incomplete combustion to aromatic, unsaturated and polar derivatives (“pyromolecules”) that still retained the characteristic skeleton of their precursors. Since some of the polar degradation products found in the charred soils can be generated either from thermal or microbial degradation, the aromatic and unsaturated hydrocarbon products are preferred as molecular markers for SOM burning. Ratios of biological precursors to aromatic (diterpenoids) or unsaturated products (steroids) indicate that the cyclic lipids in the pine wood and the soil surface horizon were highly altered. In conclusion, the solvent extractable lipids and carbohydrates in charred SOM are valuable, source-specific molecular markers for the burning of plant biomass and for tracing the biogeochemistry of charred residues in soils.
Element discharge from pyritic mine tailings at limited oxygen availability in column experiments by Maria E. Malmström; Magdalena Gleisner; Roger B. Herbert (184-202).
Sulfide mineral oxidation in mine tailings deposits poses a long term threat to surrounding ground water and surface waters. Soil or water cover remediation aims at reducing the rate of sulfide mineral oxidation by decreasing the O2 ingress rate. In this study, the authors addressed the rate of sulfide oxidation and pH buffering in ∼33 months long, well-controlled laboratory studies of water saturated columns of sulfidic mine tailings from the Kristineberg site in Sweden at reduced O2 availability. The element discharge rates slowly declined towards a quasi-steady state over hundreds of days. Non-reactive tracer tests showed an anomalously large dispersion, indicating strong flow heterogeneity, possibly including preferential flow and/or stagnant water zones. Congruent dissolution of pyrite and sphalerite by injected oxidants (dissolved O2 and Fe(III)) adequately explained the discharge rate of Fe, S and Zn at quasi-steady state. Arsenic, Pb and Cu were partly retained in the tailings. Base cation discharge rates, and thus pH buffering, were apparently controlled by the rate of acidity production, with actual pH levels, available mineral surface area, and water residence times being of less importance.