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

Abstract

Hydrological disturbances could increase dissolved organic carbon (DOC) exports through runoff and leaching, reducing the potential carbon sink function of peatlands. The objective of this study was to assess the impact of hydrological restoration 15 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 action on February 2014. The model (ten calibrated parameters) reproduced water table and pore water DOC concentration time series (01/04/2014 to 15/07/2017) in two contrasted locations (rewetted and control) of the peatland. Hydrological restoration was found to impact the water balance through a decrease in slow deep drainage and 20 an increase in fast superficial runoff. Observed DOC concentrations were higher in summer in the rewetted location compared to the control and were linked with a difference in dissolved organic matter composition analyzed by fluorescence.Hydrological conditions, especially the severity of the water table drawdown, were identified as the major factors controlling DOC concentration dynamics. The results of the simulation suggest that the hydrological restoration did not affect DOC loads, at least on a short-term period (3 years). However, it impacted the temporal dynamics of DOC exports, which were the 25 most episodic and 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 with dominant hydrological processes, exported DOC is expected to be derived from more recent organic matter of the top peat layer in the rewetted area than in 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 to identify the main hydrological processes and factors controlling DOC dynamics in different areas of the same peatland. It is 30 also a suitable alternative to a discharge calibrated catchment model when the outlet is not easily identifiable.Hydrol. Earth Syst. Sci. Discuss., https://doi

Peatland Contribution to Stream Organic Carbon Exports From a Montane Watershed

“…The coupled monitoring of fDOM, turbidity, and discharge shows that all the stream organic carbon concentration peaks are triggered by a simultaneous discharge elevation. However, stream organic carbon concentration peaks are not proportional to discharge (Figure ) and other high‐frequency parameters such as temperature and water table levels must be included in models to understand their variability (Bernard‐Jannin et al, ; Binet et al, ; Birkel et al, ; Tunaley et al, ).…”

“…Moreover, the high DOC concentration peaks at the outlet occurred several hours before the low DOC concentration peaks at inlet n°4, confirming that the peatland is the source of DOC in the watershed. Higher DOC concentrations at the outlet result from (1) the transfer of DOC enriched “preevent” porewater previously stored within the peat column (Tetzlaff et al, ; Tunaley et al, ) and (2) the leaching of subsurface nonsaturated peat by event water (Bernard‐Jannin et al, ).…”

“…These sensors have revealed unexpected temporal variability for organic carbon concentrations in streams draining peatlands (Austnes, ; Grayson & Holden, ; Koehler et al, ; Pellerin et al, ; Ryder et al, ; Strohmeier et al, ; Tunaley et al, ). Associated with high‐frequency meteorological and hydrological surveys, stream organic carbon concentration monitoring contributes to a better understanding of the carbon mobilization processes and temporality in the watersheds (Bernard‐Jannin et al, ; Birkel et al, ). High‐frequency sensing of streams is also an effective way to compare and question the relevancy of stream carbon export assessments based on sporadic water samples (Walling & Webb, ).…”

Effect of freezing on the microstructure of a highly decomposed peat material close to water saturation when used prior to X-ray micro computed tomography

“…Highly decomposed Sphagnum and Molinia peats were sampled in duplicate (samples A and B) in sites which were intensively studied by D' Angelo et al (2016), Bernard-Jannin et al (2018 and Leroy et al (2018Leroy et al ( , 2019aLeroy et al ( and 2019b. Large undisturbed samples (15´15´25 cm 3 ) were collected between 25 and 40 cm depth when the groundwater table level was close to the soil surface.…”

The information system of the French Peatland Observation Service: Service National d'Observation Tourbières – A valuable tool to assess the impact of global changes on the hydrology and biogeochemistry of temperate peatlands through long term monitoring

“…Bertrand et al (2021) evaluated WTD to meteorological parameters and simulated future WTD under various IPCC scenarios. Bernard‐Jannin et al (2018) used the WTD dataset from La Guette to set up a model describing the dissolved organic C (DOC) concentration in peat water. They were able to identify the most relevant hydrological processes and factors determining DOC dynamics across a range of conditions at the same site.…”