Long-term and recent ecohydrological dynamics of patterned peatlands in north-central Quebec (Canada)

Abstract

Peatlands are natural ecosystems that provide archives of the hydrological cycle, ecological processes and terrestrial carbon dynamics. In the north-central region of Quebec (eastern Canada), patterned peatlands developed in topographic depressions of the Precambrian Shield following the Laurentide Ice Sheet retreat. These peatlands display characteristics similar to appa mires and other peatlands that developed at the ecotone between the open (taiga) and closed boreal forest biomes of the Northern Hemisphere, and also correspond to the biogeographic limit between ombrotrophic and minerotrophic peatlands. During the Neoglacial cooling period in northeastern Canada, patterned peatlands, mainly oligotrophic fens, registered a hydrological disequilibrium expressed by an increase in surface wetness as aquatic microforms expanded to the detriment of terrestrial surfaces. Ecohydrological trajectories were reconstructed from a detailed study of two patterned peatlands in order to document their sensitivity to climate variations. To do this, plant macrofossil and testate amoeba data were combined with peat carbon accumulation rates, C:N ratios, 210Pb and 14C chronologies. Data show that peatlands initiated ca 6500 cal. y BP as ombrotrophic or minerotrophic systems depending on site-specific conditions, followed by a general increase in surface wetness during the Neoglacial cooling until the end of the Little Ice Age. A relatively synchronous ecosystem state shift from oligotrophic to more ombrotrophic conditions was registered at the beginning of the 20th century in central and lateral cores of both study sites, evoking the likely influence of recent warming on peat accumulation. These results suggest a potential northward migration of the biogeographic limit of the ombrotrophic peatland distribution during the 20th century, which could have implications for the role of these ecosystems as C sinks at the continental scale. Overall, these peatlands have stored a mean carbon mass of ca 100 kg m− 2.

Widespread recent ecosystem state shifts in high‐latitude peatlands of northeastern Canada and implications for carbon sequestration

“…This northern subarctic region has experienced the highest relative increase in GDD0 and the highest relative decrease in moisture index since 1980 (Table 1 and Figure S2). These peatlands can supports the idea that these ecosystem shifts were driven by regional climate change (Piilo et al, 2019;Primeau & Garneau, 2021;Robitaille et al, 2021;van Bellen et al, 2013). Previous studies suggested that fens respond faster and stronger than Sphagnum bogs to human or climate-induced changes in environmental conditions (Kokkonen et al, 2019;Sim et al, 2021;Tahvanainen, 2011).…”

Carbon accumulation in peatlands along a boreal to subarctic transect in eastern Canada

“…After 3000 cal BP, the Bouleau and Mista peatlands registered conditions with fluctuating water tables, as registered in coastal peatlands by Magnan and Garneau (2014b), while peat C accumulation for Auassat decreased drastically (1.4 g C m −2 yr −1 ). We hypothesize that Auassat may have been affected by very short growing seasons as already recorded in eastern Canadian subarctic peatlands by Lamarre et al (2012), Robitaille et al (2021), and van Bellen et al (2013). The brief Medieval Climate Anomaly was not recorded in any core probably due to the absence of more precise radiocarbon dating in the corresponding horizons.…”

“…Subarctic regions currently record higher RERCA in northwestern Québec (147.1 g C m −2 yr −1 ; Lamarre et al, 2012), in north central Québec (141.4 g C m −2 yr −1 ; Robitaille et al, 2021), and in northeastern Québec (142.7 g C m −2 yr −1 ; Auassat) than boreal peatlands (83.5 g C m −2 yr −1 ; Loisel and Garneau, 2010) and in this study (86.1 and 84.47 g C m −2 yr −1 ; Bouleau and Mista respectively). The accelerated warming recorded in northernmost regions of Canada during the past decades (Zhang et al, 2019) may explain the higher RERCA values registered in the subarctic peatland of the Romaine watershed due to an increase in mean summer temperature and GDD 0 (Charman et al, 2013; Garneau et al, 2014).…”

Accelerated vegetation succession but no hydrological change in a boreal fen during 20 years of recent climate change

“…From 1850 to 2020, mean temperature of Finland rose from +0.4°C to +2.8°C in a trend with recent acceleration after 1970s (Mikkonen et al 2015). Development of wet aapa mire conditions has been connected to cool and wet phases of LIA (Arlen-Pouliot & Payette, 2015), and many paleoecological studies have found post-LIA increase of Sphagnum in northern fens (Loisel & Yu, 2013;Primeau & Garneau, 2021;Robitaille et al, 2021;van Bellen et al, 2018). Indeed, many of the changes in vegetation observed in our study were similar to what could be expected in northern fens in response to rising temperatures.…”

“…While it is uncertain how vegetation responds to climate change, the climate‐hydrological correlation of contemporary pattern suggests that northern fens may start to develop into raised bogs. Indeed, paleo‐records from boreal mires have shown recent increase of Sphagnum mosses and shift toward ombrotrophic conditions during the 20th century, coinciding with warming and lengthening of the growing season (Loisel & Yu, 2013; Primeau & Garneau, 2021; Robitaille et al., 2021; van Bellen et al., 2018). Change from rich fen to Sphagnum ‐dominated poor fen and bog vegetation means ecosystem‐scale shift and potential increase of carbon accumulation (Loisel & Bunsen, 2020; Loisel & Yu, 2013), and such processes can be triggered within few decades (Tahvanainen, 2011).…”