Preprints
https://doi.org/10.5194/hess-2021-585
https://doi.org/10.5194/hess-2021-585

  20 Dec 2021

20 Dec 2021

Review status: this preprint is currently under review for the journal HESS.

Water level variation at a beaver pond significantly impacts net CO2 uptake of a continental bog

Hongxing He1, Tim Moore1, Elyn R. Humphreys2, Peter M. Lafleur3, and Nigel T. Roulet1 Hongxing He et al.
  • 1Department of Geography, McGill University, Montreal, Quebec H3A OB9, Canada
  • 2Geography and Environmental Studies, Carleton University, Ottawa, ON, Canada
  • 3School of Environment, Trent University, Peterborough, ON, Canada

Abstract. The carbon (C) dynamics of northern peatlands are sensitive to hydrological changes owing to ecohydrological feedback. We quantified and evaluated the impact of water level variations in a beaver pond (BP) on the CO2 flux dynamics of an adjacent, raised Sphagnum – shrub-dominated bog in southern Canada. We applied the CoupModel to the Mer Bleue bog, where the hydrological, energy and CO2 fluxes have been measured continuously for over 20 years. The lateral flow from the bog to the BP was estimated by the hydraulic gradient between the peatland and the BP's water level and the vertical profile of peat hydraulic conductivity. The model outputs were compared with the measured hydrological components, CO2 flux and energy flux data (1998–2019). CoupModel was able to reproduce the measured data well. The simulation shows that variation in the BP water level (naturally occurring or due to management) influenced the bog net ecosystem exchange of CO2 (NEE). Over 1998–2004, the BP water level was 0.75 to 1.0 m lower than during 2017–2019. Simulated net CO2 uptake was 55 g C m−2 yr−1 lower during 1998–2004 compared to 2017–2019 when there was no BP disturbance, which was similar to the differences in measured NEE between those periods. Peatland annual NEE was well correlated with water table depth within the bog, and NEE also shows a linear relation with the water level at the BP, with a slope of −120 g CO2-C m−2 yr−1 m−1. The current modelling predicts the bog may switch from CO2 sink to source when the BP water levels drop lower than ~ 1.7 m below the peat surface at the eddy covariance tower, 250 m from the BP. This study highlights the importance of natural and human disturbances to adjacent water bodies in regulating net CO2 uptake function of northern peatlands.

Hongxing He et al.

Status: open (until 24 Feb 2022)

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Hongxing He et al.

Hongxing He et al.

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Short summary
We applied the CoupModel to quantify the impacts of natural and human disturbances to adjacent water bodies in regulating net CO2 uptake of northern peatlands. We found 1 m drops of the water level at the beaver pond, lower the peatland water table depth, 250 m away by 0.15 m and reduce the peatland net CO2 uptake by 120 g C m−2 yr−1 therefore even though bogs are ombrotrophic rainfed systems, the boundary hydrological conditions play an important role in regulating water storage and CO2 uptake.