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Weathering in a regolith on the Werenskioldbreen forefield (SW Spitsbergen) : modelling of pore water chemistry

Kwaśniak-Kominek M., Manecki M., Rzepa G., Płonka A. M., Górniak D.

Annales Societatis Geologorum Poloniae

2016

Vol. 86, No. 3

249--264

The mineral framework and pore waters of glacial sediments exposed in the foreland of Weren- skioldbreen in SW Spitsbergen were sampled and analyzed to model the evolution of pore water chemistry, representing the advancement of weathering in a chronosequence. Three samples were taken at distances representing snapshots of approximately 5, 45 and 70 years of exposure. Complementary mineralogical analyses of the mineral framework and chemical analyses of pore waters, coupled with thermodynamic modelling of mineral-water interactions were applied. Recently uncovered sediments of the bottom moraine underwent very little weathering underneath the glacier cover; both the sediments and pore waters in the forefield of the Werenskioldbreen represent a very immature system. Poorly sorted sediments were deposited by the glacier and not reworked by fluvioglacial waters. The ratio of ‘amorphous iron’ to ‘free iron’ Feo/Fed increases with distance from the glacier terminus from 0.30 through 0.36 to 0.49, typical for fresh glacial till. The increase in saturation with CO2 (from p(CO2) –3.8 to –2.4) and the concentration of all major ions in pore waters (from 123 to 748 mg/L total dissolved solids, TDS) was observed in this young chronosequence. The waters evolved from carbonate- dominated to sulphate-dominated, indicating that with progress in weathering the dominating processes are equilibration with carbonates, oxidation of sulphides and the influence of gypsum precipitation by seasonal freeze-thaw cycles. Mass balance calculations and inverse modelling of the composition of pore waters, verified by microscopic observations of alteration on the surfaces of mineral grains, allowed thermodynamic confirmation of the fact that the relative significance of carbonate weathering decreases and that of sulphate increases down the chronosequence. The participation of silicate minerals in weathering is low, indicating a relatively immature stage of weathering within this particular chronosequence. It is significant that the morphology of etch pits and the formation of secondary phases apparent on mineral surfaces were identical, regardless of the distance from the glacier terminus. This might indicate that the mechanisms of particular weathering processes at the mineral-water interface are the same at the initial as well as at the more mature stages and do not change at least within ca. 70 years of exposure.

Allocation of elements in a chronosequence of silver birch afforested on former agricultural lands

Gawęda T., Małek S., Zasada M., Jagodziński A. M.

Drewno : prace naukowe, doniesienia, komunikaty

2014

vol. 57, nr 192

107--

Research on the effect of birch regeneration on changes occurring in the environment on former farmlands included a quantitative and qualitative analysis of the biomass growing on the research plots. Five experimental plots were selected in the Mazovia region: two in Dobieszyn and the Kampinos National Park and one in Kozienice. The analysis performed on each plot was concerned with the amount and chemical composition of biomass in four patches of vegetation, characterised by the different ages of the birch trees growing there. The vegetation patches were classified according to age group, i.e. I: 1–4 years old, II: 5–8 years old, III: 9–12 years old and IV: over 12 years old. Biomass samples were collected in the field and determined in kg DM/ha using the following components: roots, stem, bark, branches, assimilation apparatus, litterfall and the total biomass of the other (except birch) plants. For all the above-mentioned groups, the content of the elements N, C, S, Ca, K, Mg, Na, P, Mn, Cu, Fe, Zn, Pb, and Cd was determined. This allowed us to obtain both the values of the concentrations of particular substances and their allocation in both the organic matter and litterfall. The aim of the research was to discover whether the allocation of elements changes with the age of birch growing on former farmland.