Response of belowground carbon, sulphur and iron cycling in fen soils

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Climate models predict increases in summer drought and intensive rainfalls in temperate and northern latitudes, which may alter the hydrologic and redox regime of wetlands, the single most important terrestrial carbon storage. The impact of drying and rewetting and potential inundation on ecosystem production and belowground carbon cycling and the coupling with redox processes, in particular of sulfur and iron, is not well understood to date. In this project the hydrologic regime of a wetland will be altered experimentally and the consequences on carbon cycling be analyzed and simulated. To this end, changes in soil water contents, temperatures and respiration rates will be quantified during and after manipulation. The availability, production, and consumption of relevant electron acceptors for respiration, i.e. oxygen, nitrate, sulfate, ferric iron, humic substances, is studied, as their dynamics strongly influences methane production. A laboratory study will serve to analyze the impact of a range of temperatures and drying intensity and duration on respiration. The obtained data will be combined with the data of the previous controlled mesocosm and field study to simulate the impact of hydrologic change on carbon cycling and methane dynamics using the ecosystem model ECOSYS. The parameterized and tested model will be used to simulate and analyze the interaction of biogeochemical processes occurring during drying and rewetting and the impact on carbon cycling on the decadal time scale.