No abstract

Soil wettability (quantified in terms of contact angle, CA) is crucial for physical, chemical, and biological soil functioning. As the CA is determined by components present within the outmost nanometer of particles, this study applied X-ray photoelectron spectroscopy (XPS) with a maximum analysis depth of 10 nm to test the relationship between CA and surface elemental composition, using soil samples from a chronosequence where CA increased from 0° (0 yrs) to about 98° (120 yrs). Concurrently, as seen by XPS, C and N content increased and the content of O and the mineral-derived cations (Si, Al, K, Na, Ca, Mg, Fe) decreased. The C content was positively correlated with CA and least squares fitting indicated increasing amounts of non-polar C species with soil age. The contents of O and the mineral-derived cations were negatively correlated with CA, suggesting an increasing organic coating of the minerals that progressively masked the underlying mineral phase. The atomic O/C ratio was found to show a close negative relationship with CA, which applied as well to further sample sets of different texture and origin. This suggests the surface O/C ratio to be a general parameter linking surface wettability and surface elemental composition.

No abstract

Natural attenuation maybe a cost-efficient option for bioremediation of contaminated sites but requires knowledge about the activity of degrading microbes under in situ conditions. In order to link microbial activity to the spatial distribution of contaminant degraders, we combined the recently improved in situ microcosm approach, so-called 'direct-push bacterial trap' (DP-BACTRAP), with nano-scale secondary ion mass spectrometry (NanoSIMS) analysis on samples from contaminated constructed wetlands. This approach is based on initially sterile microcosms amended with (13)C-labelled benzene as a source of carbon and energy for microorganisms. The microcosms were introduced directly in the constructed wetland, where they were colonised by indigenous microorganisms from the sediment. After incubation in the field, the samples were analysed by NanoSIMS, scanning electron microscopy (SEM) and fluorescence microscopy in order to visualise (13)C-labelled microbial biomass on undisturbed samples from the microcosms. With the approach developed, we successfully visualised benzene-degrading microbes on solid materials with high surface area by means of NanoSIMS. Moreover, we could demonstrate the feasibility of NanoSIMS analysis of unembedded porous media with a highly complex topography, which was frequently reasoned to not lead to sufficient results.