Lanthanoid behaviour in an acidic landscape

Lanthanoids were studied in a boreal landscape where an abundance of acid sulfate soils and Histosols provide a unique opportunity to increase the understanding of how these metals behave in acidic soils and waters and interact with soil and aqueous organic matter. In the acid sulfate soils lanthanoids are mobile as reflected in high to very high concentrations in soil water and runoff (typically a few mg l⁻¹ but up to 12 mg l⁻¹) and abundant release by several relatively weak extractants (ammonium acetate EDTA, sodium pyrophosphate, hydroxylamine hydrochloride) applied on bulk soil. Normalisation with the lanthanoid pool in the underlying parent materials (sulphide-bearing sediments deposited in brackish-water) and soil water showed that the extensive release/retention in the acidic soil was accompanied by large, and variable, fractionation trends across the lanthanoid series. In low-order streams draining these soils, the lanthanoid concentrations were high and, as indicated by frontal ultrafiltration and geochemical modelling, largely dissolved (<1 kDa) in the form of the species LnSO₄⁺ and Ln³⁺. In other moderately acidic stream waters (pH 4.3-4.6), organic complexation was predicted to be important in the <1 kDa fraction (especially for the heavy lanthanoids) and strongly dominating in the colloidal phase (1 kDa-0.45 μm). Along the main stem of a stream in focus (catchment area of 223 km²), lanthanoid concentrations increased downstream, in particular during high flows, caused by a downstream increase in the proportion of acid sulfate soils which are extensively flushed during wet periods. The geochemical models applied to the colloidal Ln-organic phase were not successful in predicting the measured fractionation patterns.     

Stable carbon isotope composition of terrestrial leaves: inter‐ and intraspecies variability,cellulose and whole‐leaf tissue difference,and potential for climate reconstruction

Stable carbon isotope analysis of terrestrial plant leaves preserved in Quaternary lake sediments has the potential to provide high‐resolution reconstructions of past climatic conditions. Preferably, δ¹³C measurements should be made on a single leaf component, e.g. cellulose, but this approach is often precluded by limited leaf availability. Previous work suggests that reliable palaeoclimatic information also may be derived from δ¹³C measurements on whole‐leaf tissue, given a similar degree of leaf decomposition between samples. Leaf δ¹³C data for 12 Scandinavian species of dwarf‐shrubs, shrubs and trees, and a comparison of δ¹³C data on recent and late Holocene Salix herbacea leaves, revealed that the δ¹³C signal registered by holocellulose is largely reflected by measurements on whole‐leaf tissue. Holocellulose was found to be consistently enriched in ¹³C, although this δ¹³C offset was smaller for subfossil leaves. This supports the use of δ¹³C measurements on whole‐leaf tissue for climate reconstruction, at least for leaves preserved in soft, late Holocene sediments with minimal diagenetic effects. Leaf carbon and nitrogen data on fresh leaves of the same 12 Scandinavian species, and corresponding data on late Holocene Salix herbacea leaves, suggest that the leaf C:N ratio is a suitable indicator of the degree of leaf decomposition. Copyright © 2003 John Wiley & Sons, Ltd.     

On the influence of kriging parameters on the cartographic output—A study in mapping subglacial topography

Geostatistics provides a suite of methods, summarized as kriging, to analyze a finite data set to describe a continuous property of the Earth. Kriging methods consist of moving window optimum estimation techniques, which are based on a least-squares principle and use a spatial structure function, usually the variogram. Applications of kriging techniques have become increasingly wide-spread, with ordinary kriging and universal kriging being the most popular ones. The dependence of the final map or model on the input, however, is not generally understood. Herein we demonstrate how changes in the kriging parameters and the neighborhood search affect the cartographic result. Principles are illustrated through a glaciological study. The objective is to map ice thickness and subglacial topography of Storglaciären, Kebnekaise Massif, northern Sweden, from several sets of radio-echo soundings and hot water drillings. New maps are presented.     

Dormant bacteria in lake sediments as palaeoecological indicators

Lake sediments contain viable allochthonous bacteria that can be cultured and used for palaeoecological studies. To be a good palaeoindicator, a bacterium must be able to survive in sediments for long periods of time, but also be unable to reproduce in the lake bottom. Bacteria can survive the unfavourable environmental conditions in lake sediments as resting cells. The endospore is the most specialized form and gives the bacterium an extreme longevity. The oldest viable endospores isolated from lake sediments that we are aware of are about 9000 years old.Several species, mainly in the genera Thermoactinomyces, Bacillus and Clostridium, form endospores. Clostridium perfringens has been used as palaeoindicator for sewage pollution, while Thermoactinomyces vulgaris is an indicator for past agricultural activity in the boreal forest zone and a potential climatic indicator in other vegetation zones. Although isolation and enumeration of bacterial endospores from lake sediments is rather easy and has considerable potential as a powerful tool in palaeoecology, the number of studies using palaeoecological approaches is limited.     

Duration of soil cadmium and lead pollution from shale-based alum production

The scope of this study is to assess the present impact from an historical emission source, in order to provide information on the duration of this metal pollution problem.The present distribution of cadmium and lead, emitted from a Swedish alumworks between 1726–1840, was studied in soils, sediments and ground water. The soil data imply that cadmium has disappeared from the surface soils during the 150 to 250 years that have passed since the emissions ceased. Lead concentrations of the soil are elevated only within 200 m from the site of the works. Further away, the lead concentrations are almost at background level. A possible explanation for this pattern, is that lead dispersed in large particles has not yet fully disintegrated and leached down the soil profile, in contrast to the smaller particles deposited further away.The metal concentrations in the ground water wells are slightly higher than the Swedish average but probably governed by the pH of the water, rather than the occurrence of large amounts of metals. Elevated lead concentrations were found in a few sediment samples in the river mouth downstream from the works. These elevated concentrations coincided with the abundant occurrence of small particles of used shale, indicating their origin.Cadmium is not found, at present, in the soil around the alumworks in concentrations substantially above background levels. Consequently, it is likely that the cadmium deposited in the area, has leached through the upper layers of the soil profile on its way to the sea sediments. Likewise, the lead concentrations in the soil beyond 200 m from the alumworks are not above background levels which indicate that losses through leaching have occurred at a rate of 0.5 to 1.5% yr⁻¹.Finally, comparisons with other long-term perspective studies give an opportunity to discuss the rate for the disappearance of an environmental problem.