Journal of Soils and Sediments, 2015, Vol.15(1), pp.1-12
Byline: Daniela Gildemeister (1,2), George Metreveli (1), Sandra Spielvogel (3), Sabina Hens (1,4), Friederike Lang (5), Gabriele E. Schaumann (1) Keywords: Cation bridges; Cross-link; Differential scanning calorimetry; Dissolved organic matter; Glass transition; Water molecule bridges Abstract: Purpose Precipitation of dissolved organic matter (DOM) by multivalent cations is important for biogeochemical cycling of organic carbon. We investigated to which extent cation bridges are involved in DOM precipitation and how cross-links by cations and water molecule bridges (WaMB) stabilise the matrix of precipitated DOM. Materials and methods DOM was precipitated from the aqueous extract of a forest floor layer adding solutions of Ca(NO.sub.3).sub.2, Al(NO.sub.3).sub.3 and Pb(NO.sub.3).sub.2 with different initial metal cation/C (Me/C) ratios. Precipitates were investigated by differential scanning calorimetry before and after ageing to detect cation bridges, WaMB and restructuring of supramolecular structure. Results and discussion Twenty-five to sixty-seven per cent of the dissolved organic carbon was precipitated. The precipitation efficiency of cations increased in the order Ca〈Al〈Pb, while the cation content of precipitates increased in the order Pb〈Ca〈Al. The different order and the decrease in the WaMB transition temperature (T*) for Al/C〉3 is explained by additional formation of small AlOOH particles. Thermal analysis indicated WaMB and their disruption at T* of 53--65 [degrees]C. Like cation content, T* increased with increasing Me/C ratio and in the order Ca〈Pb〈Al for low Me/C. This supports the general assumption that cross-linking ability increases in the order Ca〈Pb〈Al. The low T* for high initial Me/C suggests less stable and less cross-linked precipitates than for low Me/C ratios. Conclusions Our results suggest a very similar thermal behaviour of OM bound in precipitates compared with soil organic matter and confirms the relevance of WaMB in stabilisation of the supramolecular structure of cation-DOM precipitates. Thus, stabilisation of the supramolecular structure of the DOM precipitates is subjected to dynamics in soils. Author Affiliation: (1) Institute for Environmental Sciences, Group of Environmental and Soil Chemistry, Universitat Koblenz-Landau, Fortstr. 7, 76829, Landau, Germany (2) Umweltbundesamt, FG IV 2.2 Pharmaceuticals, Worlitzer Platz 1, 06844, Dessau-Ro[sz]lau, Germany (3) Department of Geography, Institute of Integrated Natural Sciences, Universitat Koblenz-Landau, Universitatsstr. 1, 56070, Koblenz, Germany (4) GN Dr. Netta Beratende Ingenieure und Geowissenschaftler, Bienengarten 3, 56072, Koblenz, Germany (5) Albert-Ludwigs-Universitat Freiburg, Institute of Forest Sciences, 79085, Freiburg i.Br., Germany Article History: Registration Date: 09/07/2014 Received Date: 02/04/2014 Accepted Date: 09/07/2014 Online Date: 30/07/2014 Article note: Responsible editor: Dong-Mei Zhou Electronic supplementary material The online version of this article (doi: 10.1007/s11368-014-0946-9) contains supplementary material, which is available to authorized users.
Cation bridges ; Cross-link ; Differential scanning calorimetry ; Dissolved organic matter ; Glass transition ; Water molecule bridges
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