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Nitrous oxide production in floodplain soils as affected by flooding

Jörg Luster1, Christian Bruderer1, Pascal Niklaus2, Stefan Huxol3
1 Swiss Federal Research Institute WSL
2 University of Zürich
3 EAWAG Aquatic Research

P 3.10 in Fluxes between the atmosphere and ecosystems

Poster Session 2 on Tuesday, 16:30-18:00

In natural ecosystems, soil emissions of nitrous oxide (N2O) can be highly variable both in space and time. Several processes within the terrestrial N cycle produce or consume N2O, each process with specific optimum conditions with regard to the availability of water, oxygen, substrate and carbon. Thus, the spatiotemporal variability of environmental conditions as well as substrate and carbon availability determine the variability of net N2O production. Moreover, in order to assess the emission of N2O from a given location, the fate of N2O produced at greater soil depth has to be considered. The transport of this N2O depends strongly on the diffusive properties of the soil which in turn are determined by soil structure and moisture. Furthermore, it can be consumed in active sites of N2O reduction further up in the soil.

Semiterrestrial soils, including floodplain soils and gleysols, have developed and stand under the variable influence of groundwater. They undergo a characteristic cycling of water saturation and under-saturation, and as a consequence, frequent short-term fluctuations of the redox state, changing between oxic, suboxic and anoxic conditions. Since such an environment is conducive to the production of N2O, semiterrestrial soils are often found to be hotspots of N2O emissions. Furthermore, the drying phase after intensive floods was identified as „hot moment“ of N cycling and N2O emissions.

In this study, we wanted to identify the soil depth of main N2O production in the soils of a restored river floodplain, and how this was affected by flooding. For several time points before and after a flood we measured N2O emissions from the soil surface using closed chambers, as well as N2O concentration in soil air at several soil depths that was collected with gas permeable tubes. In addition, we estimated soil gas diffusivity in-situ based on the relaxation of radon concentration in a closed loop comprised of the gas permeable tubes and a Rn detector that had been filled with ambient air before. Based on all these data we calculated N2O production at several soil depths using the gradient method.

The results indicate that most of the time N2O was mainly produced in the topsoil. Only during the first few weeks of the drying phase after a major flood greater soil depths contributed strongly to emitted N2O. The presentation includes a discussion of the method used to calculate N2O production and an evaluation of the results with respect to potentially governing factors such as soil moisture and substrate availability.

Letzte Änderung 31.01.2014