Thorough wetting and drainage of a peat lysimeter
in a climate change scenario
M. Previati, D. Canone, E. urato, D. Gisolo, S. Ferrari, S. Ferraris
Interuniversity Department of Regional and
Urban Studies and Planning (DIST), Politecnico
di Torino and Universita' di Torino, Torino, Italy<
P. Teatini
Dept. of Civil, Environmental and Architectural Engineering,
University of Padova, Padova, Italy
M. Putti
Dept. of Mathematics, University of Padova, Padova, Italy
A peat deposit (Zennare basin, Venice coastland, Italy) was monitored in previous
field studies to investigate the hydrological response of organic soil to meteorological
dynamics. Field tests and modelling predictions highlighted the risk of the complete
loss of this peat layer during the next 50 years, due to oxidation enhanced by the
increased frequency of warmer periods. Unfortunately, despite the considerable
impacts that are expected to affect peat bogs (in this area and worldwide), only a few
experimental studies have been carried out to assess the hydrologic response of peat
to severe water scarcity. Because of that, an undisturbed 0.7 m3 peat monolith was
collected, transferred to the laboratory and instrumented. The total weight (representative
of the water content dynamics of the peat monolith as a whole), and two vertical
profiles of matric potentials and water content were monitored in controlled
water-scarce conditions. After an extended air-drying period, the monolith was used
as an undisturbed peat lysimeter and a complete cycle of wetting and drainage was
performed. Supplementary measurements of matric potential ψ and water content θ
are collected by testing peat subsamples on a suction table apparatus. A set of
water retention curves was determined in a range of matric potentials broader (ψ down to − 7 m)
than the current natural conditions in the field (minimum ψ = − 1 m).
While water content at saturation showed values similar to those in the original natural
conditions (θ ≅ 0.8), a remarkable loss of water holding capacity (even for low
potentials) has been highlighted, especially in deep layers that are now permanently
below the water table. The retention curves changed shape and values, with a more
pronounced hysteresis visible in an increasing distance between wetting and drying
data. Hydraulic non-equilibrium between the water content and water potential
could be a possible cause and it is worth modelling in future studies. The parameters
of the van Genuchten retention curves were obtained for the wetting and the drying
phases.
