Biogeochemical interface formation in soils as controlled by different components
Principal investigators: Prof. Dr. Ingrid Kögel-Knabner, Dr. Katja Heister
Co-worker: Cordula Vogel
The formation of soil interfaces is controlled by the type of particle surface(s) present and the assemblage of organic matter and mineral particles. We consider clay minerals, iron oxides and charcoal as major components controlling the formation of interfaces relevant for sorption of organic chemicals, as they control the assemblage of organic matter and mineral particles. The objective of our project is to gain insight into the spatial and temporal development of biogeochemical interfaces in soils by studying the development of biogeochemical interfaces in a long-term laboratory incubation experiment with so-called artificial soils consisting of model compounds.
Our approach is based on the following hypotheses:
• The formation of biogeochemical interfaces in soils is primarily controlled by the type(s) of particle surface that form the interface. Clay minerals, iron (hydr)oxides and charcoal are considered to exhibit those surfaces that are most important for interface formation and for sorption and aging of organic chemicals entering the soil.
• Interface architecture is controlled by the formation of organo-mineral associations high in surface area and microporosity. Its formation requires the presence of both clay minerals and iron oxides.
• Sorptive properties of the interface for hydrophobic organic chemicals like phenanthrene in artificial soils develop similar to natural soils in the presence of both clay minerals and iron oxides.
We study the formation of interfaces in batch incubation experiments with inoculated artificial soils consisting of model compounds (clay minerals, iron oxide, char) and natural soil samples. Results showed a relevant contribution of both clay minerals and iron oxides to the formation of organo-mineral associations as sorptive interface for hydrophobic organic chemicals. Thus, we intend to focus our work in the second phase of the project on the characterization of the interface as formed by organic matter associated with clay minerals and iron oxides. In order to unravel the role of clay minerals and iron oxides in interface formation and maturation, we will focus on the aspects of microporosity and the architecture of the biogeochemical interfaces on the nanometer scale.
The interfaces formed by the interaction of minerals with organic matter will be characterized by BET-N2 and EGME methods and 13C and 129Xe NMR spectroscopy for determination of specific surface area, sorptive domains in the organic matter and microporosity.
A suite of different microscopic techniques ranging from reflected-light microscopy at the mm scale to scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) at the micrometer scale and secondary ion mass spectrometry at the nanometer scale (NanoSIMS) will be applied to analyze the elemental and isotopic composition of the interfaces.
Sorption experiments on both artificial and natural soil samples will be continued with 13C labelled phenanthrene. NanoSIMS will be used to detect those specific sorption sites.
Collaborations are established with the following groups:
Characterization of the biogeochemical interfaces:
• J. Bachmann (Hannover): hydrophobicity, surface charge
• M. Gerzabek (Vienna): sorption of MCPA and bentazone
• M. Kersten (Mainz): X-ray computed tomography
• F. Lang (Berlin): micro-aggregates, diffusion of organic pollutants
• G. Schaumann (Koblenz-Landau): differential scanning calorimetry, 1H NMR relaxometry
• M. Spiteller (Dortmund): sorption
• K.U. Totsche (Jena): atomic force microscopy
Degradation of organic chemicals, microbiology:
• E. Kandeler (Hohenheim): analysis of MCPA degraders, soil enzyme activity
• A. Miltner (Leipzig): SEM, phenanthrene degradation
• M. Schloter (Munich): function of microbial communities
• K. Smalla (Braunschweig): composition of microbial communities