Hydrological control of dissolved organic carbon dynamics in a rehabilitated Sphagnum-dominated peatland: a water-table based modelling approach

• Published in: Hydrology and earth system sciences Vol. 22; no. 9; pp. 4907 - 4920
• Main Authors: Bernard-Jannin, Léonard, Binet, Stéphane, Gogo, Sébastien, Leroy, Fabien, Défarge, Christian, Jozja, Nevila, Zocatelli, Renata, Perdereau, Laurent, Laggoun-Défarge, Fatima
• Format: Journal Article
• Language: English
• Published: Katlenburg-Lindau Copernicus GmbH 20-09-2018; Copernicus Publications
• Subjects: Analysis; Biogeochemistry; Calibration; Carbon; Carbon sinks; Catchment area; Catchment models; Composition; Computer simulation; Control; Dissolved organic carbon; Dissolved organic matter; Drainage; Drainage control; Drawdown; Dynamics; Environmental aspects; Exports; Fluorescence; Groundwater table; Hydrologic models; Hydrology; Leaching; Modelling; Organic carbon; Organic matter; Peat; Peat bogs; Peatlands; Pore water; Restoration; Runoff; Sphagnum; Summer; Surface runoff; Water balance; Water balance (Hydrology); Water table
• ISSN: 1607-7938; 1027-5606; 1607-7938
• DOI: 10.5194/hess-22-4907-2018

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.