Project leader: Dr. Manon Janssen (University of Rostock)

Peat soils strongly differ from mineral soils in terms of hydro-physical properties. They are characterized by a low bulk density and a high porosity of up to >90 vol% depending on their origin and degradation state. Peat soils have, thus, an important water storage function substantially facilitating the resilience of landscapes to precipitation and temperature extremes. The total soil water storage capacity refers to the water the peat can store under saturated conditions. The drainage of peatlands reduces their water storage capacity considerably and it is unknown to what extent it can be restored upon rewetting. The accumulation of new peat after rewetting is expected to play a crucial role, and also modifies water fluxes in the peat profile. Increasing frequency and intensity of summer droughts as extreme events are expected even in rewetted peatlands. The associated drying of the peat causes shrinkage and alters its hydro-physical properties, with potentially irreversible changes to the soil structure. Also the release and transport of dissolved substances such as DOC are severely impacted by droughts and subsequent rewetting.

The objectives of B5 are thus (1) to characterize the hydro-physical characteristics of newly accumulated fen peat in rewetted peatlands, and to assess its effect on water storage, water fluxes and resilience against extreme events in peat soil profiles, (2) to evaluate the consequences of alternate drying and wetting on hydro-physical properties of fen peat as a function of peat type and drying intensity, and (3) to understand how droughts effect the release of DOC from rewetted fens. We hypothesize that the regulative functions of peat soils in the water cycle recover upon rewetting by the formation of new peat, and that droughts alter both the soil hydraulic functions and the release of DOC. We will address the objectives using a combination of state-of-the-art techniques including laboratory soil column experiments, X-ray computed tomography, field monitoring, and Richard’s equation based numerical soil hydrological modelling. We will explore the dynamics of hydro-physical peat properties, state variables and DOC export as a function of drought-associated drying and rewetting scenarios at the laboratory and soil profile scale. Peat column experiments and analysis of field water samples will reveal the effect of droughts on the hydro-physical soil properties and on the release of DOC as a function of peat and pore water properties as well on the solute transport properties of peat under rewetting conditions. We will characterize how peat functions that are related to the pore structure recover upon rewetting to relate peat pore structure information to water storage and flux.