Process studies on greenhouse gas exchange and N loss
The goal of this PhD project is the quantification and parameterization of CO2, CH4, N2O and NO/NO2 fluxes from arable land, grassland and forest soils in the framework of the TERENO project (www.tereno.net). The major focus of the work is on the elucidation of the processes underlying the production and consumption of these gases as well as their precursor substances. For this purpose, new methods are developed for the analysis of reactive intermediates of the different nitrogen turnover processes in the soil, such as hydroxylamine. These methods are applied to soil samples taken at the three different field sites of TERENO operated by IBG-3 (Selhausen, Rollesbroich, Wüstebach), combined with the quantification of CO2, CH4, N2O and NO/NO2. The obtained results are correlated with a range of soil parameters, such as soil water content, C content, C/N ratio, pH, and content of specific kations. One of the aims is to identify spatio-temporal correlation patterns, which might enable a prediction of trace gas fluxes from simple soil parameters.
For the determination of reaction kinetics, measurements are performed in dynamic mode in incubation experiments, i.e. with flushing the chamber headspace continuously and analyzing gas concentrations online with infrared laser instruments (for CO2, CH4, N2O) and with a chemoluminescence analyzer (for NO/NO2). This very innovative combination of these analyzers allows online measurements with high time resolution, which is of high importance for studying short-term effects of temperature and moisture changes, especially during freeze/thaw and drying/rewetting events. The work will be complemented with 15N labeling experiments to trace the fate of nitrogen in the different soils, including gaseous N2 losses.