Overriding control of methane flux temporal variability by water table dynamics in a Southern Hemisphere, raised bog

Abstract

There are still large uncertainties in peatland methane flux dynamics and insufficient understanding of how biogeochemical processes scale to ecosystems. New Zealand bogs differ from Northern Hemisphere ombrotrophic systems in climatic setting, hydrology, and dominant vegetation, offering an opportunity to evaluate our knowledge of peatland methane biogeochemistry gained primarily from northern bogs and fens. We report eddy covariance methane fluxes from a raised bog in New Zealand over 2.5 years. Annual total methane flux in 2012 was 29.1 g CH 4 m À2 yr À1 , whereas during a year with a severe drought (2013) A correlation between daytime CO 2 uptake and methane fluxes emerged during times with shallow water tables, suggesting that controls on methane production were critical in determining fluxes, more so than oxidation. Water table recession through this shallow zone led to increasing methane fluxes, whereas changes in temperature during these periods were not correlated. Models of methane fluxes should consider drought-induced lags in seasonal flux recovery that depend on drought characteristics and location of the critical zone for methane production.

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

“…Overall, 76 % of the variance of the CH 4 fluxes was explained by T s,10 cm and WTH. The combination of soil temperature and WTH has also been shown to explain a large proportion of the observed variances in CH 4 fluxes in peatlands in other studies Goodrich et al, 2015).…”

“…Our annual CH 4 flux at 17 ± 1.0 g CH 4 -C m −2 yr −1 was comparable to an average natural temperate wetland CH 4 flux, which is typically around 15 g CH 4 -C m −2 yr −1 (Abdalla et al, 2016;Fortuniak et al, 2017;Nicolini et al, 2013;Turetsky et al, 2014). The CH 4 fluxes from a number of temperate and tropical pristine wetlands exceeded the CH 4 fluxes reported in this study, including emissions from marshes in the southwestern US (130 g CH 4 -C m −2 yr −1 ; Whiting and Chanton, 2001), tropical wetlands in Costa Rica (82 g CH 4 -C m −2 yr −1 ; Nahlik and Mitsch, 2010), marshes in the midwestern US (50 g CH 4 -C m −2 yr −1 , Koh et al, 2009), all three studies based on chamber measurements, and an ombrotrophic bog in New Zealand (29 and 21 g CH 4 -C m −2 yr −1 based on EC measurements; Goodrich et al, 2015).…”

Soil properties and sediment accretion modulate methane fluxes from restored wetlands

“…Chamber flux syntheses have demonstrated that water table depth, temperature, vegetation, disturbance, and wetland type are important modulators of wetland CH 4 flux (Turetsky et al, 2014). A similar understanding of the controls on CH 4 fluxes is emerging from eddy covariance studies, where temperature (Chu et al, 2014;Hendriks, van Huissteden, & Dolman, 2010;Olson, Griffis, Noormets, Kolka, & Chen, 2013;Rinne et al, 2007;Wille, Kutzbach, Sachs, Wagner, & Pfeiffer, 2008), recent C inputs Morin et al, 2014), wetland structure (Matthes, Sturtevant, Ver-faillie, Knox, & Baldocchi, 2014;McNicol et al, 2017), vegetation cover Rey-Sanchez, Morin, Stefanik, Wrighton, & Bohrer, 2017), and water table depth (Brown, Humphreys, Moore, Roulet, & Lafleur, 2014;Chamberlain, Boughton, & Sparks, 2015;Chamberlain et al, 2016;Chamberlain, Groffman, et al, 2017;Goodrich, Campbell, Roulet, Clearwater, & Schipper, 2015;Hendriks et al, 2007Hendriks et al, , 2010Sturtevant et al, 2016) have been identified as dominant controls across many wetland ecosystems. Combined chamber and eddy covariance studies have further improved our understanding of how drivers of small-scale flux variation scale to ecosystem fluxes (Forbrich et al, 2011;Morin et al, 2017;Rey-Sanchez et al, 2017).…”

Methane Feedbacks to the Global Climate System in a Warmer World

“…The time taken for methanogens to colonize areas where favorable CH 4 producing conditions have developed can be the critical factor (e.g., Bond-Lamberty et al, 2016;Schädel et al, 2016). The response of vegetation is considered to be slower, with 10-50% of global vegetation considered "highly vulnerable" to change underpredicted future climate scenarios (Gonzalez et al, 2010). Global fire frequency is expected to increase Stocks et al, 1998); at the same time fire occurrence may decrease as a result of anthropogenic land use changes (Andela & van der Werf, 2014;Knorr et al, 2016).…”

“…Only potential CH 4 release from methane hydrates and oceanic sinks are shown beyond 2100 because their impact prior to this is considered minimal (see section 7); the estimated permafrost emissions up to 2300 are shown for context. The emission mechanism timescales are based on microbial production (Bond-Lamberty et al, 2016;Treat et al, 2015), microbial consumption (Kwon et al, 2016;Merbold et al, 2009;van Winden et al, 2012), vegetation change (Elmendorf et al, 2012;Gonzalez et al, 2010;Lantz et al, 2013;Nauta et al, 2015), and fire regime (Harris et al, 2016;Moritz et al, 2005). The 2100 emission estimates for each environment are based on wetlands (Melton et al, 2013;Zhang et al, 2017), freshwaters (Tan andZhuang, 2015, andWik et al, 2016, estimates for northern lakes-above 50°N, as a proxy for all lakes, estuaries, and coastal sediment emissions; see section 5-are added to current estimates of freshwater emissions in , permafrost (Gao et al, 2013;Koven et al, 2015;Lawrence et al, 2015;McCalley et al, 2014;Schaefer et al, 2014), methane hydrates (Kretschmer et al, 2015;Ruppel & Kessler, 2017), soil sinks (Curry, 2007;Ridgwell et al, 1999), and the atmospheric OH sink .…”