Annual Greenhouse Gas Budget for a Recently Rewetted Raised Bog Ecosystem

Rewetting of peatlands drained and disturbed by peat mining facilitates their ecological recovery, and may help them revert to carbon dioxide (CO₂) sinks. However, rewetting of disturbed peatlands may also cause substantial emissions of methane (CH₄). We measured year-round fluxes of CO₂ and CH₄ from a disturbed and recently rewetted raised bog ecosystem located in the Burns Bog Ecological Conservancy Area (BBECA), a 20 km² bog located in the Fraser River Delta, near Vancouver, BC, Canada. The ecosystem studied was disturbed by peat mining ~40 years ago. Since 2005, the bog has been declared a conservancy area, and a major restoration effort by rewetting using a large-scale ditch blocking program to maintain natural Sphagnum regeneration has been underway for five years.

We measured the year-round turbulent fluxes of CO₂ and CH₄ using the eddy-covariance (EC) approach from 10^th June 2015 to 30^th June 2016. The flux tower was built on a floating platform and equipped with EC systems comprising Campbell Scientific Inc. CSAT3 3-D sonic anemometers and CO₂ and CH₄ open-path analyzers (LI-COR Inc. LI-7500 and LI-7700, respectively), and several sensors for measuring micrometeorological variables. The daily average net ecosystem exchange (NEE) of CO₂ was -0.98 (±2.74) and -0.14 (±1.54) g C m^-2 day^-1 in summer and winter months, respectively. The daily average CH₄ emission was 0.15 (±0.36) and 0.09 (±0.96) g C m^-2 day^-1 in summer and winter months, respectively. The daily average net GHG flux from CO₂ and CH₄ totaled to 1.63 g CO₂e m^-2 day^-1 (-2.33 for CO₂, 3.96 for CH₄) in the second half of 2015 by using global warming potential (GWP). Oxygen limitation due to the high water table caused by the restoration strategy suppressed ecosystem respiration (R_e) and promoted substantial CH₄ formation under anoxic conditions in the summer months. With low temperatures in winter months, CH₄ emission was more suppressed than Re. The key environmental factors controlling the seasonal dynamics of these exchanges in the BBECA were soil temperature and water table depth.