UBC Theses and Dissertations
Annual greenhouse gas budget for a bog ecosystem undergoing restoration by rewetting Lee, Sung-Ching
Many peatlands have been drained and harvested for peat mining, which turned those landscapes into carbon (C) emitters. Rewetting of disturbed peatlands facilitates their ecological recovery, and may help them revert to carbon dioxide (CO₂) sinks. However, it may also cause substantial emissions of the powerful greenhouse gas (GHG) methane (CH₄). Our knowledge on year-round measurements of CO₂ and CH₄ fluxes in restored peatlands is currently very limited. This study quantifies C exchanges in a disturbed and rewetted area located in the Burns Bog Ecological Conservancy Area (BBECA) in Delta, BC, Canada. The BBECA is recognized as the largest raised bog ecosystem on North America’s West Coast. It was substantially reduced in size and degraded by peat mining and agriculture. Since 2005, the bog has been declared a conservancy area, and restoration efforts focus on rewetting disturbed ecosystems to recover Sphagnum and suppress fires. Year-round (16th June 2015 to 15th June 2016) turbulent fluxes of CO₂ and CH₄ were measured from a tower platform in an area rewetted in 2007 using the eddy-covariance (EC) technique. The annual CO₂ budget was -179 g CO₂-C m-² year-¹ and the annual CH₄ budget was 16 g CH₄-C m-² year-¹. Gross ecosystem productivity (GEP) exceeded ecosystem respiration (Re) during summer months (June-August), causing a net CO₂ uptake. In summer, high CH₄ emissions were measured. In winter (December-February), substantially lower CH₄ emissions and roughly equal magnitudes of GEP and Re made the bog C neutral. Oxygen limitation due to the high water table caused by ditch blocking suppressed Re. With low temperatures in winter, CH₄ emission was more suppressed than Re. The key environmental factors controlling the seasonality of these exchanges in the study area were downwelling photosynthetically active radiation and 5-cm soil temperature. Annual net GHG flux from CO₂ and CH₄ during the study period totaled to -23.48 g CO₂e m-² year-¹ and 1242.04 g CO₂e m-² year-¹ by using 100-year and 20-year global warming potential (GWP) values, respectively. Consequently, the ecosystem was almost CO₂e neutral annually on a 100-year time horizon but was a significant CO₂e source on a 20-year time horizon.
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