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  • 1
    Language: English
    In: Soil Science Society of America Journal, Nov-Dec, 2004, Vol.68(6), p.1853(10)
    Description: Recent [N.sub.2] adsorption studies have suggested a 'pore clogging' effect on mineral soil phases caused by organic matter coatings. For methodological reasons, this pore clogging effect has been studied only after drying. Our hypothesis was that pore clogging is affected by drying of organic coatings. In our study, we used AlOOH, which has been equilibrated with dissolved organic matter (DOM) and polygalacturonic acid [[PGA; [([C.sub.6][H.sub.8][O.sub.6]).sup.n]]. To test our hypothesis, we determined the porosity of moist and freeze-dried AlOOH samples. Freeze-dried samples were analyzed by [N.sub.2] adsorption, moist samples by [sup.1]H-nuclear magnetic resonance (NMR). In addition, the samples were characterized by environmental scanning electron microscopy--energy dispersive x-ray spectroscopy (ESEM-EDX). Both, DOM and PGA significantly reduced specific surface area (SS[A.sub.BET]) of AlOOH by 34 [m.sup.2][g.sup.-1](15%) and 77 [m.sup.2] [g.sup.-1] (36%). The reduction in SS[A.sub.BET] normalized to the amount of C sorbed was 1.0 [m.sup.2] [mg.sup.-1] DOM-C and 5.9 [m.sup.2] [mg.sup.-1] PGA-C. Dissolved OM reduced the pore volume of micro- and small mesopores 〈3 nm whereas PGA also reduced the volume of larger pores. The [sup.1]H-NMR results of moist samples showed that PGA sorption reduced the amount of water in pores 〈4 nm. In addition, the pore size maximum of AlOOH increased by 150%. Polygalacturonic acid coatings created new interparticle pores of about 10- to 70-nm size that are not stable upon freeze-drying. Porosity changes upon DOM-treatment were not commensurable by [sup.1]H-NMR. Our results indicate that clogging of micro- and small mesopores is not an artifact of freeze-drying. Polygalacturonic acid seems not only to cover the mouth of AlOOH-nanometer pores but also to fill them.
    Keywords: Soil Mineralogy -- Research
    ISSN: 0361-5995
    E-ISSN: 14350661
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  • 2
    Language: English
    In: Journal of Plant Nutrition and Soil Science, April 2004, Vol.167(2), pp.177-183
    Description: Risk assessment of heavy metal input into forest ecosystems requires information about metal fluxes from the forest floor (organic layer) into the mineral soil. Common methods for the monitoring of element fluxes are generally time‐consuming and expensive. Additionally, the reliability of the results is in part contested especially for trace elements, showing very low concentrations which are sometimes even below analytical detection limit. We used ion exchange resin tubes installed below the forest floor to determine heavy metal and As fluxes at 25 forest monitoring sites in Germany. Chloride tracer experiments and the comparison of our data with throughfall and lysimeter data, determined within the Level II monitoring network, proved the accuracy of our method. Mean trace element fluxes based on the resin method were 50 g As ha yr, 2 g Cd ha yr, 168 g Cu ha yr, 176 g Ni ha yr, and 186 g Pb ha yr.The results show that the organic layer may change into a source of heavy metals after emission has decreased. Austauscherharzröhren zur Bestimmung des Spurenelementeintrags in Mineralböden auf Waldstandorten Der Schwermetalleintrag von der Humusauflage in den Mineralboden ist eine wichtige Größe zur Risikoabschätzung der Schwermetallflüsse in Waldökosystemen. Herkömmliche Methoden zur Erfassung von Elementflüssen sind zeit‐ und kostenaufwändig. Bei Spurenelementen verringern analytische Probleme die Aussagekraft der ermittelten Daten. Mithilfe von Röhren, die mit Ionenaustauscherharz gefüllt sind und unterhalb der Humusauflage in den Boden eingebracht werden, haben wir auf 25 Waldstandorten Schwermetall‐ und As‐Flüsse gemessen. Chlorid‐Tracer‐Experimente und der Vergleich unserer Daten mit Stoffflussdaten aus dem Level‐II‐Monitoring bestätigen, dass mit unserer Methode Elementflüsse von der Humusauflage in den Mineralboden zuverlässig erfasst werden können. Mit den Austauscherharzröhren haben wir folgende durchschnittliche Elementflüsse bestimmt: 50 g As ha a, 2 g Cd ha a, 168 g Cu ha a, 176 g Ni ha a und 186 g Pb ha a. Die Ergebnisse zeigen, dass die Humusauflage nach Rückgang anthropogener Einträge zur Schwermetallquelle wird.
    Keywords: Heavy Metals ; Arsenic ; Forest Soils ; Element Fluxes ; Exchange Resin Tubes
    ISSN: 1436-8730
    E-ISSN: 1522-2624
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  • 3
    Language: English
    In: Geoderma, 2004, Vol.123(1), pp.153-162
    Description: Use of soil archives provides the opportunity to retrospectively analyze changes in soil properties. We used the distribution of heavy metals between the exterior and interior of aggregates in recent and archived samples to derive (1) temporal trends in metal concentrations and distribution across aggregates and (2) to assess aggregate turnover times. We collected 11 topsoils under grassland and forest along a transect from Moscow to a distance of 50 km from the city centre and at a background location. Furthermore, we analyzed six topsoils sampled between 1910 and 1954 at some of the locations. We fractionated aggregates 〉1 cm into interior and exterior portions. Except at one contaminated site, heavy metal concentrations were low (Cd: 0.09-0.33 mg kg (super -1) , Cu: 6.8-24 mg kg (super -1) , Pb: 6.7-31 mg kg (super -1) , Zn: 25-54 mg kg (super -1) ), comparable with background levels in central Europe. They were not related to the distance to Moscow indicating that Moscow was no point source for the studied soils. During the last century, contents of heavy metals in soils increased inside and decreased outside the city. In Moscow, the heavy metal accumulation in the aggregate exterior relative to the interior was more pronounced in recent than in archived samples reflecting a higher recent than historic deposition. However, there was also an increase in heavy metal concentrations in the interior of recent compared with archived aggregates. Thus, the studied aggregates were turned over at least once during the last 50-90 years at all sites. This limited the build-up of metal concentration gradients in aggregates.
    Keywords: Archived Soil Samples ; Heavy Metals ; Soil Aggregates ; Small-Scale Heterogeneity ; Aggregate Stability ; Agriculture
    ISSN: 0016-7061
    E-ISSN: 1872-6259
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