The role of mobile organic matter and biocolloids for the properties of and interactions with biogeochemical interfaces in soil

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Soil‘s function as filter and transformer of matter input is controlled by the interplay of physical, chemical and biological interactions at biogeochemical interfaces (BGIs). Properties of these BGIs at the local scale are decisive for interactions of dissolved and colloidal substances including biocolloids. Local scale processes (e.g. (de)sorption, pore-diffusion, adhesion of microorganisms, biodegradation) seem to govern the macroscopic phenomena of retardation and transformation at the continuum scale. The objectives of this proposal are thus to (I) explore the role of mobile organic matter including biocolloids for the properties of BGIs, to (II) quantify the proportion of the immobile void volume (PIVV), to (III) unravel the rates and processes of interactions of dissolved and colloidal compounds with BGIs and PIVV on the local, and to (IV) link it with the phenomena of retardation and transformation on the continuum scale in mechanistic ways. Organic and inorganic solutes with different molecular properties will serve as “process tracers” to probe PIVV as well as interactions with and properties of BGIs. The fundamental challenge will be to integrate the information obtained at different scales – nano-scale and molecular information by spectro-microscopy and computational chemistry, aggregate-scale information, and 3D-structural core scale information by tomography – into a general framework of flow, transport and transformation of organic chemicals on the pedon scale.