Abstract
Abstract. Hydrological disturbances could increase dissolved organic carbon (DOC) exports through changes in runoff and leaching, which reduces the potential carbon sink function of peatlands. The objective of this study was to assess the impact of hydrological restoration on hydrological processes and DOC dynamics in a rehabilitated Sphagnum-dominated peatland. A conceptual hydrological model calibrated on the water table and coupled with a biogeochemical module was applied to La Guette peatland (France), which experienced a rewetting initiative on February 2014. The model (eight calibrated parameters) reproduced water-table (0.1<NS<0.61) and pore-water DOC concentrations (2<RMSE<11 mg L−1) in a time series (1 April 2014 to 15 December 2017) in two contrasting locations (rewetted and control) in the peatland. Hydrological restoration was found to impact the water balance through a decrease in slow deep drainage and an increase in fast superficial runoff. Observed DOC concentrations were higher in summer in the rewetted location compared to the control area and were linked to a difference in dissolved organic matter composition analyzed by fluorescence. Hydrological conditions, especially the severity of the water-table drawdown in summer, were identified as the major factor controlling DOC-concentration dynamics. The results of the simulation suggest that the hydrological restoration did not affect DOC loads, at least in a short-term period (3 years). However, it impacted the temporal dynamics of DOC exports, which were the most episodic and were mainly transported through fast surface runoff in the area affected by the restoration, while slow deep drainage dominated DOC exports in the control area. In relation to dominant hydrological processes, exported DOC is expected to be derived from more recent organic matter in the top peat layer in the rewetted area, compared to the control area. Since it is calibrated on water-table and DOC concentration, the model presented in this study proved to be a relevant tool in identifying the main hydrological processes and factors controlling DOC dynamics in different areas of the same peatland. It is also a suitable alternative to a discharge-calibrated catchment model when the outlet is not easy to identify or to monitor.
Highlights
Sphagnum-dominated peatlands represent a major stock of the global soil carbon (C) pool (Gorham, 1991)
dissolved organic carbon (DOC) dynamics in peatlands has been found to be strongly controlled by site hydrology, especially by the water-table depth (WTD)
This study suggests that this hydrological control on DOC fluxes affects the source of DOC exported from the peatland, in relation to the difference in dissolved organic matter (DOM) composition observed with the fluorescence analysis
Summary
Sphagnum-dominated peatlands represent a major stock of the global soil carbon (C) pool (Gorham, 1991). L. Bernard-Jannin et al.: Modelling dissolved organic carbon in peatlands al., 2009; Strack et al, 2008, 2015). Bernard-Jannin et al.: Modelling dissolved organic carbon in peatlands al., 2009; Strack et al, 2008, 2015) Hydrological disturbances such as drainage can lead to increased DOC exports in relation to WTD variations (Strack et al, 2008; Worrall et al, 2007). Hydrological restoration can be undertaken to re-establish peatland functioning (Menberu et al, 2016) with a potential impact on DOC dynamics and exports (Glatzel et al, 2003; Strack et al, 2015; Worrall et al, 2007)
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