A water-table dependent reservoir model to investigate the effect of drought and vascular plant invasion on peatland hydrology

- We observed water table fluctuations in peatlands with or without vascular plants.
- We propose a model to describe water table fluctuations in peatland.
- The runoff coefficient is considered to be water table dependent.
- Vascular plants were found to limit the water percolation through the peat.
- After a drought, the peat needs more than a hydrological cycle to refill.

SummaryThis paper investigates the peat saturation and the air entrapment dynamics in a peatland, estimated from the water table fluctuations. A reservoirs model of water table fluctuations in a double-porosity peat is proposed, by calculating the stored water in effective porosity of the peat from precipitation and evapotranspiration datasets. Calculations conceptualize vascular plant consumption through a crop coefficient. Changes in water storage, located in the effective porosity of the peat, are described through a maximum infiltration rate and a maximum storage capacity. Water discharges take place in runoff and percolation reservoirs. The runoff coefficient is considered to be water table dependent. This model was tested on a peatland that has experienced strong water table fluctuations caused by summer drought and/or by vascular plant water consumption. A water table dependent runoff model appeared to be adequate to describe the water table fluctuations in peatland. From this model, vascular plants were found to increase the crop coefficient and to limit percolation through the peat. The high water table depth in winter was found to change with the years and is related to an equilibrium between slow infiltration in peat versus percolation plus evapotranspiration. In this disturbed peatland, even if overland flows occurred after a drought, the re-saturation of effective porosity was slow with about 30% of air trapped in the porosity 6 months after the drought period. The effects of a drought on peat saturation were observed over more than a single hydrological cycle. This can affect the biogeochemical processes controlling the C cycle in peatland.