Highly-resolved imaging in aggregated soils: Which are the interfaces formed by interaction of water flow oxygen transport and biodegradation?

Principle investigators: Prof. Dr. S. Oswald, Dr. D. Lazik

Co-worker: N. Rudolph

Objectives:
- Non-invasively map dissolved oxygen (DO) in structured porous media, with high spatial and temporal resolution
- Determine water content, again via imaging methods, also enabling a fully quantitative interpretation of the DO measurements
- Observe impact of DO gradients on degradation and vice versa

Hypotheses:
- Biodegradation of chemicals does occur in spatial patters related to local availability of oxygen
- Microbes in aggregates may create oxygen depletion by their activity resulting in local degradation zones
- Existing two-dimensional DO-imaging method (fully saturated conditions) can be modified to quantitatively observe DO in partly water filled pore spaces with high resolution

Scientific approach:
Dissolved oxygen is the primary electron acceptor for most degradation process in soil. Although dissolved oxygen concentrations can be high, where soil water is well connected to the atmosphere via gas phase pathways, at the same time there are numerous reactions consuming dissolved oxygen. Thus, at places of higher water saturation aerobic reactions create complex, dynamic oxygen patterns. In turn, these oxygen patterns limit the progress of reactions and respiration activities. However, due to the inherent inaccessibility of soil, biogeochemical processes are often studied on the micro-scale only, with localized measurements integrating over a volume of influence, or with some degree of destruction. And the same holds true for soil water content measurements. We plan to overcome these difficulties by applying two non-destructive imaging techniques. Via these techniques we will be able to directly determine dissolved oxygen concentrations and water content with high spatial and temporal resolution. The measurements will make use of an optical fluorescence imaging technique based on an oxygen specific fluorescence inhibitor and of dynamic imaging of water contents by neutron radiography, X-ray tomography and/or optical methods. The highly-resolved data sets of water content and dissolved oxygen distribution shall allow the identification of oxygen depletion zones, gradients and gas-water distributions.

Cooperations within the priority programme:
PD Dr. H.-J. Vogel, Dr. A. Miltner, PD Dr. T. Baumann

Publications:
Rudolph, N., Esser, H.G., Carminati, A., Moradi, A.B., Hilger, A., Kardjilov, N., Nagl, S., Oswald, S.E. 2012. Dynamic oxygen mapping in the root zone by fluorescence dye imaging combined with neutron radiography. J. Soil. Sediment. 12,63-74.

Oswald1 Osawald2
Poster Oswald