Impacts of hydrological connectivity on the lateral movement of Water and Dissolved Organic Carbon in an Extracted Peatland

Peat extraction practices in Canada significantly alter the hydrology of peatlands, leading to increased dissolved organic carbon (DOC) production and transport, influencing downstream carbon dynamics in artificial drainage networks. Despite these changes, the mechanisms controlling the lateral movement of water and associated DOC transport remain poorly understood. This study was conducted from May 2022 to July 2023, examining hydrology and carbon dynamics in an actively extracted peatland in Rivière-du-Loup, Quebec. Three distinct hydrological periods were identified based on the runoff from the peatland: Summer 2022, Fall 2022, and Winter-Spring 2023. These periods marked transitions in the hydrological network’s connectivity, with each phase having unique DOC mobilization from the peat matrix.During the summer of 2022, high evapotranspiration (AET) rates (~ 2 mm/day) reduced the water storage, and the fields became disconnected from the drainage network. Although DOC concentrations remained relatively stable at 74.98  1.41 mg/l, in the drainage channels. The supply of DOC during the summer 2022 period was transport-limited, even during a site-scaled disturbance that increased drainage efficiency (the 2022 resurfacing event). During Fall 2022, lower AET rates (~ 1 mm/day) and increased water storage led to runoff generation in response to rainfall. The drainage network became connected during precipitation, allowing DOC transport from the peat matrix to the channels. The DOC concentration was similar to that of the summer period, but now runoff occurred and as a consequence there was DOC export. During the spring melt of 2023, the peat fields and channel network became hydrologically connected, but the frozen peat surfaces limited infiltration and DOC mobilization. We conjecture, based on the lack of increase in soil water and water tables in the fields that overland flow occurred. Since there was less interaction with the water stored in the peat matrix, the channel DOC concentrations were lowest at 20.30  2.60 mg/l.A water balance for the extracted peatland was calculated using measured precipitation (P) = 953mm, runoff (R) = 357 mm, and a change in storage (S) = -53mm, and an estimate of AET = 581 mm. The residual of the water balance (i.e., sum of errors and unmeasured losses) was approximately -38 mm. The runoff was equivalent to 37 % of the system’s outputs, and the exported DOC was 16.03 g DOC/ m2 during the entire study period. The total gaseous carbon (from CO2 and CH4) lost from the drainage network surfaces across the entire study site was ~ 3.64  0.48 g C/m2 for the study period. The losses of carbon through runoff are larger than those lost by gaseous emissions from the drainage network surface; however, gas fluxes from the drainage network do not result in an insignificant loss of carbon.This study highlights the dynamic role of hydrological connectivity in controlling DOC transport in extracted peatlands. Understanding these mechanisms provides critical insights for refining carbon loss accounting and improving peatland management practices in Canada

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