Contrasting Temperature Sensitivity of CO₂ Exchange in Peatlands of the Hudson Bay Lowlands, Canada

Abstract

It remains uncertain how the net ecosystem CO2 exchange (NEE) of diverse peatlands will respond to warming. Here we compare five years of eddy covariance measurements of NEE and estimates of gross primary productivity and ecosystem respiration between a fen dominated by deciduous vegetation and an adjacent bog with evergreen vegetation in the Canadian Hudson Bay Lowlands. At the bog, daily net CO2 uptake lasted from snowmelt to snow cover onset, while at the fen, net CO2 uptake was delayed in spring and ended earlier in fall. Greater midsummer net CO2 uptake at the fen compensated for shoulder season net CO2 losses resulting in similar annual NEE at the two sites (fen: −52 ± 16 g C m−2, bog: −80 ± 14 g C m−2). Observations of a satellite‐based productivity index also suggest lower shoulder season and higher peak vegetation productivity at these deciduous versus evergreen plant‐dominated peatlands. The response of NEE to warmer weather differed between sites. Warming during the shoulder seasons increased net CO2 uptake at the evergreen plant‐dominated bog, while it increased net CO2 losses at the fen where deciduous leaves had not yet emerged or had senesced. In contrast, warmer weather during the peak growing season appeared to reduce net CO2 uptake more at the bog than the fen resulting from both increasing ecosystem respiration and decreasing gross primary productivity. In the short term, warming will likely decrease annual net CO2 uptake of these and similar peatlands, although the magnitude will depend on factors including vegetation dynamics and seasonality of warming.

Peat Carbon Vulnerability to Projected Climate Warming in the Hudson Bay Lowlands, Canada: A Decision Support Tool for Land Use Planning in Peatland Dominated Landscapes

“…Negative correlations between NEE and peat temperature indicate bogs were more likely than fens to be net CO 2 sinks at warmer temperature (Table 3). This finding is broadly consistent with a 70 days longer CO 2 sink period for the bog compared to the fen measured at the eddy covariance towers (Helbig et al, 2019). Bogs were also more likely to be net CO 2 sinks when WTL deepened.…”

“…Bogs were also more likely to be net CO 2 sinks when WTL deepened. However, differences between bog and fen responses to temperature and WTL were not reflected in annual or seasonal (May-October) NEE fluxes in the current study or at the eddy covariance towers (Helbig et al, 2019).…”

“…Peatlands were net CO 2 sinks of 58 ± 1.07 g CO 2 -C m −2 d −1 , a result that did not differ between bogs and fens. Additionally, mean NEE was on the high end (smaller sink) of the range in annual NEE (−1.62 to −0.48 g CO 2 -C m −2 d −1 ) measured for a bog and fen at eddy covariance towers in the north-central part of the study area (Humphreys et al, 2014;Helbig et al, 2019). In the current study, and for baseline conditions, bogs and fens were net CO 2 sources (positive correlations) about 14-23% of the time, respectively (Table 3).…”

“…Temperature measurements selected were restricted to the surface peat (i.e., 0-30 cm) to represent the approximate range in depth of the long-term acrotelm in peatlands in the study area (Bunbury et al, 2012;O'Reilly et al, 2014). Mean CH 4 emissions were compared against those from independent published studies from the Hudson Bay Lowlands (Turetsky et al, 2014;Webster et al, 2018) and CO 2 fluxes were compared with those measured at two eddy covariance flux towers in the north-central part of the study area operated by the Ontario Ministry of Environment, Conservation, and Parks (Humphreys et al, 2014;Helbig et al, 2019).…”

Modeling Holocene Peatland Carbon Accumulation in North America

“…The large discontinuity among different simulation regions resulted from implementing different sets of parameters during the regional simulation (Table 1). It is worth noting that the model has not been parameterized for the HBL peatlands, which might have biased our regional estimates given that the HBL peatlands are the largest peatland area in North America (e.g., Helbig et al, 2019; Humphreys et al, 2014; McLaughlin & Webster, 2014; Packalen et al, 2014).…”