Annual greenhouse gas budget for a bog ecosystem undergoing restoration by rewetting

Abstract

Abstract. Many peatlands have been drained and harvested for peat mining, agriculture, and other purposes, which has turned them from carbon (C) sinks into C emitters. Rewetting of disturbed peatlands facilitates their ecological recovery and may help them revert to carbon dioxide (CO 2 ) sinks. However, rewetting may also cause substantial emissions of the more potent greenhouse gas (GHG) methane (CH 4 ). Our knowledge of the exchange of CO 2 and CH 4 following rewetting during restoration of disturbed peatlands is currently limited. This study quantifies annual fluxes of CO 2 and CH 4 in a disturbed and rewetted area located in the Burns Bog Ecological Conservancy Area in Delta, BC, Canada. Burns Bog is recognized as the largest raised bog ecosystem on North America's west coast. Burns Bog was substantially reduced in size and degraded by peat mining and agriculture. Since 2005, the bog has been declared a conservancy area, with restoration efforts focusing on rewetting disturbed ecosystems to recover Sphagnum and suppress fires. Using the eddy covariance (EC) technique, we measured year-round (16 June 2015 to 15 June 2016) turbulent fluxes of CO 2 and CH 4 from a tower platform in an area rewetted for the last 8 years. The study area, dominated by sedges and Sphagnum, experienced a varying water table position that ranged between 7.7 (inundation) and −26.5 cm from the surface during the study year. The annual CO 2 budget of the rewetted area was −179 ± 26.2 g CO 2 -C m −2 yr −1 (CO 2 sink) and the annual CH 4 budget was 17 ± 1.0 g CH 4 -C m −2 yr −1 (CH 4 source). Gross ecosystem productivity (GEP) exceeded ecosystem respiration (R e ) during summer months (June-August), causing a net CO 2 uptake. In summer, high CH 4 emissions (121 mg CH 4 -C m −2 day −1 ) were measured. In winter (December-February), while roughly equal magnitudes of GEP and R e made the study area CO 2 neutral, very low CH 4 emissions (9 mg CH 4 -C m −2 day −1 ) were observed. The key environmental factors controlling the seasonality of these exchanges were downwelling photosynthetically active radiation and 5 cm soil temperature. It appears that the high water table caused by ditch blocking suppressed R e . With low temperatures in winter, CH 4 emissions were more suppressed than R e . Annual net GHG flux from CO 2 and CH 4 expressed in terms of CO 2 equivalents (CO 2 eq.) during the study period totalled −22 ± 103.1 g CO 2 eq. m −2 yr −1 (net CO 2 eq. sink) and 1248 ± 147.6 g CO 2 eq. m −2 yr −1 (net CO 2 eq. source) by using 100-and 20-year global warming potential values, respectively. Consequently, the ecosystem was almost CO 2 eq. neutral during the study period expressed on a 100-year time horizon but was a significant CO 2 eq. source on a 20-year time horizon.

Gap‐filling approaches for eddy covariance methane fluxes: A comparison of three machine learning algorithms and a traditional method with principal component analysis

“…In the following sections, we highlight one important characteristic for each site to emphasize how site-specific characteristics can influence gap-filling performance. Lee et al, 2017), which is lower than the typical range for wetlands (Barr et al, 2013;Falge et al, 2001). The average nighttime u * in this site is also lower than the typical range.…”

Methane emissions reduce the radiative cooling effect of a subtropical estuarine mangrove wetland by half

“…When considering the annual fluxes of both CO 2 and CH 4 together, this subtropical estuarine mangrove wetland would exert an overall negative net radiative forcing impact over the decadal to centurial timescales, with mean CO 2 -eq of −1,376 and −2,169 g CO 2 -eq m −2 year −1 over a 20 and 100 year time horizon, respectively ( Table 3). The difference in cooling impacts between the two timeframes was mainly due to the difference in lifetimes of the Herbst et al, 2013;Lee et al, 2017). The choice of GWP metrics could affect the estimated the warming or cooling impacts of an ecosystem over different time periods.…”

A Biogeochemical Compromise: The High Methane Cost of Sequestering Carbon in Restored Wetlands

“…Interpolations based on seasonal measurements, where necessary, are detailed in Petrescu et al (2015). More information can be found in the supporting information and existing literature (Chamberlain, Groffman, et al, 2017;Chu et al, 2015;Desai et al, 2015;Flanagan & Syed, 2011;Friborg et al, 2000Friborg et al, , 2003Herbst et al, 2013;Holm et al, 2016;Jammet et al, 2017;Krauss et al, 2016;Lee et al, 2016;Long et al, 2010;Mastepanov et al, 2008;Olson et al, 2013;Parmentier et al, 2011;Pugh et al, 2017;Rinne et al, 2007;Runkle et al, 2013;Sachs et al, 2010Sachs et al, , 2008Shurpali et al, 1993Shurpali et al, , 1995Tiemeyer, 2013;Y. Zhang et al, 2012;Zona et al, 2009).…”