Ecosystem Respiration in a Cool Temperate Bog Depends on Peat Temperature But Not Water Table

Abstract

Ecosystem respiration (ER) is an important but poorly understood part of the carbon (C) budget of peatlands and is controlled primarily by the thermal and hydrologic regimes. To establish the relative importance of these two controls for a large ombrotrophic bog near Ottawa, Canada, we analyzed ER from measurements of nighttime net ecosystem exchange of carbon dioxide (CO 2 ) determined by eddy covariance technique. Measurements were made from May to October over five years, 1998 to 2002. Ecosystem respiration ranged from less than 1 lmol CO 2 m )2 s )1 in spring (May) and fall (late October) to 2-4 lmol CO 2 m )2 s )1 during mid-summer (July-August).As anticipated, there was a strong relationship between ER and peat temperatures (r 2 = 0.62). Q 10 between 5°to 15°C varied from 2.2 to 4.2 depending upon the choice of depth where temperature was measured and location within a hummock or hollow. There was only a weak relationship between ER and water-table depth (r 2 = 0.11). A laboratory incubation of peat cores at different moisture contents showed that CO 2 production was reduced by drying in the surface samples, but there was little decrease in production due to drying from below a depth of 30 cm. We postulate that the weak correlation between ER and water table position in this peatland is primarily a function of the bog being relatively dry, with water table varying between 30 and 75 cm below the hummock tops. The dryness gives rise to a complex ER response to water table involving i) compensations between production of CO 2 in the upper and lower peat profile as the water table falls and ii) the importance of autotrophic respiration, which is relatively independent of water-table position.

Influence of water table level and soil properties on emissions of greenhouse gases from cultivated peat soil

“…Optimal conditions for soil respiration could probably be achieved with tensions lower than 40 cm water column since the soil was quite dry with higher tensions (air-filled pore space ≥23 %, Figure 6). The findings in the lysimeter study, with highest CO 2 emissions at the intermediate water Lafleur et al (2005) and Mäkiranta (2009). Berglund (1996) showed that plant growth was better at high water tables (40 cm compared to 60 and 70 cm) on peat soils with similar pore size distribution as Örke, but compacted peat soil types required deeper drainage in order to avoid aeration problems.…”

“…The influence of water table level was questioned by Joosten & Clarke (2002), who found that the highest mineralisation rate was observed with the groundwater level at 80-90 cm depth, but that a groundwater level at 17-60 cm still had 80% of the maximum mineralisation rate. Several authors (Freeman et al, 1996;Aerts and Ludwig, 1997;Maljanen et al, 2001;Campbell et al, 2004;Lafleur et al, 2005;Nieveen et al, 2005) argue that the correlation between groundwater depth (and therefore top soil moisture content) and CO 2 emission is poor. N 2 O emissions from cultivated peat soils show a great variation in time and space and depend on a number of factors (Regina et al, 2004) such as drainage, peat type, climate and fertilisation.…”

The Impact of Experimental Temperature and Water Level Manipulation on Carbon Dioxide Release in a Poor Fen in Northern Poland

“…Many studies documented that main factors impacting soil respiration (R ECO ) and therefore carbon emissions are air temperature (Bubier et al 1998;Bortoluzzi et al 2006;Davidson et al 2006;Heijmans et al 2013) or peat temperature (Chapman and Thurlow 1996;Silvola et al 1996;Lafleur et al 2005;Juszczak et al 2013;D'Angelo et al 2016). Approximate 1°C temperature increase at subarctic peatlands resulted in increases of R ECO values and mobilization of carbon that was located in deeper peat layers (Dorrepaal et al 2009).…”

“…Understanding the importance of biotic and abiotic controls on carbon fluxes from peatlands is, therefore, crucial to infer the role of climate change on the feedback of carbon to the atmosphere (Turetsky et al 2002;Limpens et al 2008). Additionally, water table drawdown, and long periods without rain, can thus significantly impact the structure of the microbial community (Jaatinen et al 2007) and the functioning of peatlands (Weltzin et al 2003;Bragazza 2008), which then can (temporarily) shift from C sinks to C sources (Lafleur et al 2005;Lund et al 2012).…”

“…Therefore, R ECO seems mainly driven by abiotic conditions, such as soil moisture and temperature (Komulainen et al 1999;Dorrepaal et al 2009). However, the relative importance of temperature and hydrological conditions for R ECO is unclear and seems to depend on their relative effect on autotrophic and heterotrophic pathways, which might be decoupled (Lafleur et al 2005). Remarkably, the effect of vegetation on heterotrophic respiration seems to be larger than the effect of temperature (Ward et al 2015) or water table (Turetsky et al 2008), highlighting the importance of these biotic controls on peatland carbon fluxes.…”