Applied Geochemistry (v.18, #5)

On the calculation of the surface area of different soil size fractions by S. Koptsik; L. Strand; N. Clarke (629-651).
A model that accounts for contributions to the total surface area (SA) by different size fractions of the soil is considered from a theoretical point of view. Calculations, based on continuous particle sizes and forms, explain SA mainly as a geometric SA. It is common for coarse soils to have a discrepancy between the measured SA, say inferred from adsorption of gases, and the calculated geometric area of up to two orders of magnitude. This discrepancy is removed by the present method. Size distribution is the main factor influencing the SA; taking particle forms into account resulted in a 2–3 times increase of SA. The several orders of magnitude range of grain sizes leads to crucial variations in the contributions that soil fractions make to weight, SA and number of grains. The fundamental lower limit of variation of soil properties, originating from the discrete nature of soils, is introduced. Despite the deterministic physical origin of SA, high sensitivity to the finest fractions can be considered on the environmental scale as a cause of the dual—stochastic and deterministic—nature of SA. Small variations of weight within experimental error and the fundamental limit may result in significant variations of SA, close to the same order of magnitude for coarse soils. An empirical equation () relates textural data to SA at landscape scale. It is applicable to a collection of samples, while individual samples must be characterised on a probabilistic basis.

87Sr/86Sr of archaeological skeletal tissues are increasingly used to reconstruct residential mobility and migration, but the post mortem preservation of biogenic Sr is often uncertain. Sample pre-treatment regimes, notably ‘solubility profiling’, have been used to remove diagenetic Sr prior to analysis, but doubts remain over their effectiveness. The investigation examines the effectiveness of solubility profiling by comparing the Sr content and 87Sr/86Sr composition of bone, dentine and enamel from two archaeological juveniles (Blackfriars, UK) before and after attempted decontamination. For both individuals leached samples of cortical bone and dentine had similar 87Sr/86Sr to those of soil leachates from the burial site, and are therefore thought to represent diagenetic 87Sr/86Sr. For both individuals samples of treated dental enamel have 87Sr/86Sr considerably more or less radiogenic than the soil leachates and other tissues. These are considered representative of biogenic Sr, i.e. Sr acquired in vivo. In effect, solubility profiling should have resulted in 87Sr/86Sr that were similar for all 3 tissues types and close to those of the untreated enamel. Experimental results show that tooth enamel 87Sr/86Sr remained largely unaffected by solubility profiling, and the process did not significantly alter the final 87Sr/86Sr of either dentine or cortical bone. It is concluded that the technique was ineffective in facilitating the recovery of biogenic Sr from these tissues.

At the remediated tailings Impoundment 1 at Kristineberg, Northern Sweden, installations of tension lysimeters were performed in the protective cover (10, 50, and 100 cm), in the oxidised tailings (150 cm), in the unoxidised secondarily enriched tailings (200 cm) and in the unoxidised tailings (260 cm). The lysimeters in the till protective cover contained relatively low concentrations of most elements. After infiltration through the sealing layer, consisting of 0.3 m compacted clayey till, pH decreased and conductivity, together with the concentrations of several major and trace elements, increased significantly. In the lysimeters installed in the tailings at depths of 150 and 200 cm average pH decreased to 3.4 at 150 cm and 3.2 at 200 and average conductivity increased to 2.9 mS/cm. Elements such as Al, Cd, Co, Fe, Mn, Mo, Ni,Pb, S, Si and Zn had the highest concentrations in the lysimeter at 200 cm depth. Examples of concentration averages for this lysimeter are Cd 600 μg/L, Fe 1500 mg/L, Mn 11 mg/L, Ni 1.06 μg/L, S 1800 mg/L, and Zn 190 mg/L. Between the depths of 200 and 260 cm the concentration of most elements decreased. The increase between the lysimeters at the depths of 150 and 200 cm can be explained by remobilization of secondarily retained oxidation products as well as from the continued oxidation. The decrease between the second and the third lysimeters is interpreted as co-precipitation with different Fe oxyhydroxides as well as adsorption onto secondarily formed minerals and primary mineral surfaces. Calculations of saturation indices indicate that several different hydroxides might precipitate at this level. This retainment takes place mainly due to the increase in pH. The pH increases from 3.2 up to 4–4.4 in this depth interval. Between the deepest lysimeter and the groundwater table, the element concentrations probably decrease even further. pH increases to 5–6.5 in the groundwater. Most of the pre-remediation oxidation products that are secondarily retained above or below the oxidation front and are released by the small amount of infiltrating water together with the present oxidation products are retained again during continued transport downwards. If the depth to the groundwater table is large enough, most of the metals released by the infiltrating water and the diffusing O2 do not reach the groundwater.

Groundwater-related thallium transfer processes and their impacts on the ecosystem: southwest Guizhou Province, China by Tangfu Xiao; Dan Boyle; Jayanta Guha; Alain Rouleau; Yetang Hong; Baoshan Zheng (675-691).
The small karstic watershed of Lanmuchang, in a Hg–Tl mineralized area in SW Guizhou Province, China, exhibits an enrichment of toxic Tl in groundwater and related stream water. This affords an excellent demonstration of the natural processes of Tl dispersion, and the resultant impact on the local ecosystem. The distribution of Tl in the water system follows a decreasing concentration pattern from deep groundwater to stream water to shallow groundwater. Tl shows high levels (13–1100 μg/L) in deep groundwater within the Tl-mineralized area, decreasing with distance away from the mineralized area to background levels (0.005 μg/L). The distribution of Tl in the water system is constrained by Tl mineralization, water–rock interactions and hydrogeological conditions. Tl concentrations in waters generally correlate with concentrations of total dissolved solids, sulphate, Ca and pH values, suggesting the contribution of water-rock interactions to water geochemistry. Water–rock interactions are driven by weathering of Tl-bearing sulfides which decreases pH values in groundwater, and by dissolution of limestone enhanced by acid fluids. Tl in stream water in both the base-flow and flood-flow regimes shows higher concentrations than it does in shallow groundwater that serves as the stream's source (mainly springs, dug-well flows and karstic cave waters). Concentrations of Tl in stream water in the flood-flow regime are generally lower than in the base-flow regime due to dilution effects, but those in the waters of mid-stream are almost the same as in the base-flow regime, probably due to contribution from Tl-rich soil water seepage or from acid mine drainage (AMD). Unexpectedly, Tl concentrations in stream water in both regimes are remarkably higher (2–30 fold) downstream than up- and mid-stream. These pronounced increases of Tl concentration are likely caused by unidentified discharges of deep groundwater through fractured zones to the downstream trace. The groundwater-related Tl transfer processes affect the ecosystem through contamination of water supply and arable soil and ultimately the food chain with undoubted risks to human health. Therefore, the results of this study are important for environmental planning and regulations, and will also serve as baseline data for future research on Tl natural dispersion processes.

In experiments of 7 days duration using voltammetric and radiotracer measurement techniques, the role of different particle types in the sorption of dissolved metal species in a disturbed deep-sea bottom seawater system were investigated. Resuspension of oxic to suboxic surface sediment into the bottom water in the deep sea (either by natural events or industrial activities like Mn nodule mining) has been shown to be followed quickly by scavenging of dissolved heavy metals, e.g. released from interstitial water, on the resuspended particles. Compared to other deep-sea particles (like clay minerals, calcite and apatite), Mn and Fe oxides and oxyhydroxides were found to be by far the most important phases in scavenging many dissolved heavy metals. Only Pb was sorbed strongly on all particles used, with highest affinity to carbonate fluorapatite. Caesium+ was significantly scavenged only by clay minerals like illite. The sorption experiments support a simple electrostatic model: Hydrated cations and labile cationic chloro-complexes in seawater like Mn2+, MnCl+, Co2+, Ni2+, Cu2+, Zn2+, Ba2+, and PbCl+, are preferentially adsorbed or ion-exchanged on the negatively charged surfaces of Mn oxides. In contrast, oxyanions and neutrally or negatively charged complexes like HVO4 2−, MoO4 2−, HAsO4 2−, UO2(CO3)2 2−, and PbCO3 0 associate with neutral to slightly positive amphoteric Fe oxyhydroxide particles. Metals forming strong chloro-complexes in seawater like Cd (CdCl2 0), are less readily sorbed by oxides than others. A comparison of the results of voltammetric and radiotracer techniques revealed that after fast sorption within the first hour, isotopic exchange dominated reactions on MnO2-rich particles in the following days. This was especially pronounced for Mn and Co which are bound to the Mn oxide surface via a redox transformation.

Mineralogical and sorption characteristics of Ankara Clay as a landfill liner by G.A. Sezer; A.G. Türkmenoǧlu; E.H. Göktürk (711-717).
Mineralogical and sorption capacity characteristics of Ankara Clay, which is widespread around the Ankara region, Turkey, have been studied for the purpose of its potential use as a landfill liner. This clay is Pliocene in age and was deposited in a fluvial environment. Mineralogically it consists mainly of illite, smectite, chlorite and kaolinite minerals. The non- clay minerals, quartz, feldspars, calcite and Fe–Ti oxides are detected. Its cation exchange capacity (CEC) is determined as 41 meq/100 g using the Ag–Tu method. The retention of the heavy metal cations follows the order of Pb2+> Cu2+> Zn2+>Mn2+, Cd2+. These characteristics, together with its known engineering properties, suggest that Ankara Clay can be utilized as a component of a barrier system. These findings also indicate the potential usage of widespread occurring fluvial clays as landfill liners.

The dissolved He content and He isotope ratio are proxy indicators of groundwater evolution in the Shimokita peninsula. The record of 3H and excess bomb tritiogenic 3He reveals the intrusion depth of shallow and young groundwater into deep groundwater. The record of tritiogenic 3He suggests that prior to the period of nuclear testing, the natural production level of 3H irradiated by cosmic rays was probably 6 TU. Helium isotope ratios in the groundwater converge to that of the regional crustal He with increasing depth and dissolved He content. The regional degassed He has a 3He/4He (R) ratio of 7.24 × 10−7 which consists of 6% mantle He (with R=1. 1 × 10−5) and 94% radiogenic He (with R=1 ×10−8). The magnitude of degassing He flux is 5×10−9 m3/m2 a. Based on the accumulation of He, and taking into consideration the degassing He flux, groundwater at depths greater than 300 m below sea level is estimated to be stagnant, exhibiting residence times in excess of 102 Ka.

Geochemical cycling of phosphorus in rivers by William A. House (739-748).
Concentrations of contaminants in fresh waters are controlled, not only by point and diffuse sources within the catchment, but by a multitude of biogeochemical reactions (riverine processes) that may occur in the water column during transport. As an example, the results of mass-balance studies using “snapshot” field sampling techniques for P transport in a large river in Northern England (R. Swale) are summarised to identify the processes that contribute to internal cycling within the river, and their relative size compared with the total export of P. The interaction of P with sediments is an important factor controlling concentrations of soluble P in the water column, during both low and high river-flows, with in-river storage in some instances amounting to >30% of the load throughput. Antecedent weather conditions are identified as important in controlling the pool of fine sediment and associated P available for remobilisation during storm pulses. Examples of P reactions with sediments that have been identified from field studies are briefly reviewed. Firstly, a mass-balance approach to elucidate the net interaction of P with river bed-sediments is presented and then two specific interactions of P with sediments are discussed: (a) the coprecipitation of phosphate with calcite in lakes during phytoplankton blooms and in benthic algal biofilms on river sediments and (b) the formation of vivianite in the anoxic zone of bed-sediment in eutrophic lakes and rivers. Phosphate coprecipitation with calcite is an important mechanism controlling P concentrations in some hardwater lakes, and has been found to contribute as much as 30% of the dry mass associated with the colonisation and development of algal biofilms on hardwater river beds. Vivianite has been detected in anoxic river sediments (up to 20% by mass) receiving treated sewage, although little is known about the conditions of formation and how widespread the occurrence of vivianite is in sediments.

In this study, adverse impacts of heavy metal pollution, originating from mining, smelting and panning activities, on the aquatic ecosystem of the Lean River in south China, were evaluated by integrating the chemical, toxicological and ecological responses of single and multiple metals in overlying water, surface sediment and floodplain topsoil. The assessment results indicated that a highly localized distribution pattern was closely associated with the pollution sources along the river bank. Based on the combined indices, deterioration of local environmental quality was induced mainly by two sources. One was strong acidity and a large amount of Cu in the drainage from the Dexing Cu Mine. Another was high concentrations of Pb and Zn in the effluents released from many smelters and mining/panning activities in the riparian zone. Some possible suggestions on source control may be effective in dealing with these issues.

Similarity between C, N and S stable isotope profiles in European spruce forest soils: implications for the use of δ34S as a tracer by Martin Novák; František Buzek; Anthony F Harrison; Eva Přechová; Iva Jačková; Daniela Fottová (765-779).
Stable isotope systematics of C, N and S were studied in soils of 5 European forest ecosystems. The sites were located along a North–South transect from Sweden to Italy (mean annual temperatures from +1.0 to +8.5 °C, atmospheric deposition from 2 to 19 kg N ha−1 a−1, and from 6 to 42 kg S ha−1 a−1). In Picea stands, the behavior of C, N and S isotopes was similar in 3 aspects: (1) assimilation favored the lighter isotopes 12C, 14N and 32S; (2) mineralization in the soil profile left in situ residues enriched in the heavier isotopes 13C, 15N and 34S; and (3) NO3–N as well as SO4–S in soil solution was isotopically lighter compared to the same species in the atmospheric input. In this study, emphasis was placed on S isotope profiles which so far have been investigated to a much lesser extent than those of C and N. Sulfate in monthly samples of atmospheric input had systematically higher δ34S ratios than total soil S at the 0–5 cm depth, on average by 4.0‰. Sulfate in the atmospheric input had higher δ34S ratios than in deep (>50 cm) lysimeter water, on average by 3.2‰. Organic S constituted more than 50% of total soil S throughout most of the profiles (0–20 cm below surface). There was a tendency to isotopically heavier organic S and lighter inorganic SO4–S, with ester SO4–S heavier than C-bonded S at 3 of the 5 sites. With an increasing depth (0 to 20 cm below surface), δ13C, δ15N and δ34S ratios of bulk soil increased on average by 0.9, 4.2 and 1.6‰, respectively, reflecting an increasing degree of mineralization of organic matter. The isotope effects of C, N and S mineralization were robust enough to exist at a variety of climate conditions and pollution levels. In the case of S, the difference between isotope composition of the upper organic-rich soil horizon (lower δ34S) and the deeper sesquioxide-rich soil horizons (higher δ34S) can be used to determine the source of SO4 in streams draining forests. This application of δ34S as a tracer of S origin was developed in the Jezeřı́ catchment, Czech Republic, a highly polluted site suffering from spruce die-back. In 1996–1997, the magnitude and δ34S of atmospheric input (20 kg S ha−1 a−1, 5.8‰) and stream discharge (56 kg S ha−1 a−1, 3.5‰) was monitored. Export of S from the catchment was 3 times higher than contemporary atmospheric input. More than 50% of S in the discharge was represented by release of previously stored pollutant S from the soil. Stable isotope systematics of Jezeřı́ soil S (mean of 2.5‰ in the O+A horizon, 4.8‰ in the B horizon, and 5.8‰ in the bedrock) suggests that most of the soil-derived S in discharge must come from the isotopically light organic S present in the upper soil horizon, and that mineralized organically-cycled S is mainly flushed out during the spring snowmelt. The fact that a considerable proportion of incoming S is organically cycled should be considered when predicting the time-scale of acidification reversal in spruce die-back affected areas.