Biogeochemical interface formation in soils as controlled by different components
Principle investigators: Prof. Dr. I. Kögel-Knabner, Dr. K. Heister
Co-worker: G. Pronk
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, all exhibiting high surface area and microporosity, as major soil components forming interfaces associated with organic matter which control the formation of interfaces relevant for sorption of organic chemicals. The objective of our project is to gain insight into the spatial and temporal development of these organo-mineral interfaces that develop during the incorporation of organic matter in mineral soils.
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 in turn for sorption and ageing of the organic chemicals.
• Interface architecture is controlled by the formation of organo-mineral associations.
• The presence of iron oxides leads to the formation of organo-mineral associations high in surface area and microporosity with a specific effect on the soil interface. This is also controlled by the distribution of different iron oxide species.
• Soil interfaces formed by organo-mineral associations also contribute to ageing of the organic chemicals, since interactions at interfaces can result in increased viscosity, surface tension and chemical diversity of the organic compound, thus decreasing the mobility and increasing the persistence of the chemical.
We intend to study the formation of interfaces with artificial soils and natural soil samples. Artificial soils will be produced in a long-term biogeochemical laboratory incubation experiment. Starting from simple systems, the complexity of the artificial soil systems will be increased until they mimic natural soils as good as possible. The components considered will be quartz, clay minerals (illite, montmorillonite), ferrihydrite and charcoal, manure as organic carbon source and a microbial inoculum extracted from a natural soil. Natural soil samples will be obtained from different well-described field sites that are used by several groups within the priority programme.
Characterisation of the interface properties includes measurement of specific surface area and microporosity (BET-N2 and EGME method, 129Xe NMR spectroscopy), description of surface morphology by environmental scanning electron microscopy combined with energy dispersive X-ray spectroscopy (ESEM-EDX) to illustrate the elemental distribution and X-ray absorption near edge spectroscopy (XANES) to identify the spatial distribution of iron species on the micro- and nanoscale.
Organic matter will be removed selectively from the samples by oxidation with either H2 O2 or NaOCl to get insight into the contribution of organo-mineral associations to the formation of microporous interfaces.
Biogeochemical interface characteristics in natural soils and artificial soils matured for selected time intervals will be analysed and evaluated with respect to their sorptive behaviour of selected organic chemicals (phenanthrene, hexadecane and at a later stage fenhexamid).
Cooperations within the priority programme:
Prof. Dr. K.U. Totsche, Prof. Dr. M. Kästner, Prof. Dr. K. Smalla, Prof. Dr. M.H. Gerzabek, Prof. Dr. J. Bachmann, Prof. Dr. G. Schaumann
Heister, K., Höschen, C., Pronk, G.J., Mueller, C.W., Kögel-Knabner, I. 2012. NanoSIMS as a tool for characterizing soil model compounds and organomineral associations in artificial soils. J. Soil. Sediment. 12,75-85.
Ding, G.-C., H. Heuer, S. Zühlke, M. Spiteller, G.J. Pronk, K. Heister, I. Kögel-Knabner, K. Smalla. 2010. Soil type-dependent responses to phenanthrene as revealed by determining the diversity and abundance of polycyclic aromatic hydrocarbon ring-hydroxylating dioxygenase genes by using a novel PCR detection system. Appl. Environ. Microbiol. 76, 4765-4771.