Inhaltszusammenfassung

Soil organic matter (SOM) controls large part of the processes occurring at biogeochemical interfaces in soil and may contribute to sequestration of organic chemicals. In this contribution, the idea that sequestration of or ganic chemicals is driven by physicochemical SOM matrix aging, and its consequences for transport processes will be discussed. In contrast to chemical aging processes, physical matrix aging involves changes in the supramolecular arrangement of SOM molecul...Soil organic matter (SOM) controls large part of the processes occurring at biogeochemical interfaces in soil and may contribute to sequestration of organic chemicals. In this contribution, the idea that sequestration of or ganic chemicals is driven by physicochemical SOM matrix aging, and its consequences for transport processes will be discussed. In contrast to chemical aging processes, physical matrix aging involves changes in the supramolecular arrangement of SOM molecules and molecule segments. Organic chemicals can be entrapped in nanovoids, which can tranform to a semi-persistent cage. Persistence of entrapment directly depends on the rigidity and stability of the cage. Water molecule bridges (WaMB) and cation bridges (CaB) between segments of soil organic matter (SOM) have been found to stabilize the supramolecular SOM matrix and are therefore suspected to control immobilization of organic chemicals in soil. Contaminants sequestered by WaMB or CaB can be immobilized or released suddenly upon changes in environmental conditions like moisture, temperature or melting. Understanding their dynamics is highly important to model the reaction of soil as well as release and transport of organic chemicals on changes in climatic conditions. While the idea of CaB in solid soil organic matter is more and more accepted, there is increasing evidence that such cross-links are not relevant in all types of soil organic matter, depending on the spatial distribution of charged functional groups in the OM. Only if distances between functional groups are sufficient, CaB can form. Larger distances can be bridged by CaB-WaMB associations. Also interfacial properties are dynamic. Soil wettability can with increasing involvement of functional groups in CaB-WaMB associations. In the extreme case, high concentrations of multivalent cations can hydrophobize surfaces of SOM. Associations of CaB and WaMB evolve slowly and form a supramolecular network in SOM. Those dynamic associations can fix molecular arrangements inducing water repellency and increase kinetic barriers for the release and uptake of water and sorption and transport of organic chemicals in soil.» weiterlesen» einklappen

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