Effects of root mat buoyancy and heterogeneity on floating fen hydrology

“Floating fen ecosystems are home to several protected habitats and species. Their development and conservation require special
attention regarding water management. Although they are known to be heterogeneous and partially buoyant, their root mats are
simulated in hydrological models as homogeneous, static systems. The objective of this study is to quantify root mat
heterogeneity and buoyancy and to assess their effects on groundwater flow and transport, and to determine if these factors need
to be taken into account in modelling.
We conducted field measurements of root mat heterogeneity and buoyancy in the ‘Nieuwkoopse Plassen’, the Netherlands. We
found that hydraulic conductivity varied over four orders of magnitude and negatively correlated with degree of decomposition,
resulting in a zonation of high conductivity near the surface and low conductivity in the deeper layers. Also, we found that the
root mat moved vertically with the surface water. It became more buoyant with higher temperatures, but less buoyant with
increasing groundwater levels relative to the surface.
We implemented the findings in a semi-steady state hydrological model of a floating fen to compare the effects with other
parameters. The profound heterogeneity had a limited effect on the water budget, but a clear effect on the flow lines and thus
should be taken into account when modelling transport processes in floating fens. Although buoyancy affected the relative
groundwater level near the root mat edge, it did not affect the water budget or the flow lines and may therefore be neglected in
water budget modelling.”

Copyright © 2015 John Wiley & Sons, Ltd.

(Citaat: Stofberg, S.F., Engelen, J. van, et al. Effects of root mat buoyancy and heterogeneity on floating fen hydrology – Ecohydrology (2016))