Palaeogeography, Palaeoclimatology, Palaeoecology 386 (2013) 336–348

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Palaeogeography, Palaeoclimatology, Palaeoecology

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Examining the role of allogenous and autogenous factors in the long-termdynamics of a temperate headwater peatland (southern Québec, Canada)

Martin Lavoie a,⁎, Stéphanie Pellerin b, Marie Larocque c,d

a Département de géographie and Centre d'études nordiques, Université Laval, Québec (Quebec) G1V 0A6, Canadab Institut de recherche en biologie végétale and Jardin botanique de Montréal, Université de Montréal, 4101 Sherbrooke est, Montréal (Quebec) H1X 2B2, Canadac Département des sciences de la Terre et de l'atmosphère, Université du Québec à Montréal, C.P. 8888, Succursale Centre-Ville, Montréal (Quebec) H3C 3P8, Canadad Centre de Recherche pour l'étude et la simulation du climat à l'échelle régionale, Université du Québec à Montréal, C.P. 8888, Succursale Centre-Ville, Montréal (Quebec) H3C 3P8, Canada

⁎ Corresponding author. Tel.: +1 418 656 2131 2230E-mail addresses: martin.lavoie@cen.ulaval.ca (M. Lav

stephanie.pellerin.1@umontreal.ca (S. Pellerin), larocque.

0031-0182/$ – see front matter © 2013 Elsevier B.V. Allhttp://dx.doi.org/10.1016/j.palaeo.2013.06.003

a b s t r a c t

a r t i c l e i n f o

Article history:Received 29 October 2012Received in revised form 21 May 2013Accepted 3 June 2013Available online 11 June 2013

Keywords:CanadaPeatlandPaleoecologyPaleoclimateMacrofossilTestate amoebae

Plant macrofossil and testate amoebae analyses were conducted on a sedimentary core taken from a headwaterpeatland located near the summit of a hill at the northern extension of the AdirondackMountains (Québec, Canada).The aims were to reconstruct the developmental stages of the peatland and to examine the allogenous and autog-enous factors associated with its long-term dynamics. Results were compared with a quantitative paleoclimaticreconstruction based on the modern analog technique using pollen data from the same core. The long-termdevelopment of the peatland (pond—rich fen—intermediate fen—poor fen—bog) mainly reflects an autogenoushydroseral succession. Active peat accumulation under the relatively dry climate of the Early Holocene suggeststhat summer temperature was a critical factor in peat accumulation through enhanced biomass production.A major long-term decrease in net peat accumulation rates and a progressive decline of mean water-table depthoccurred during the Mid- to Late-Holocene (7900–500 cal yr BP), even though annual precipitation was abundantat the time. The high summer temperature associated to the highest evapotranspiration rates maintained a lowwater table which in turn led to strong humification of the peat. A similar, synchronous pattern in vertical peataccumulation dynamics characterized another nearby peatland. Based on these results, we suggest that smallpeatlands situated atop awatershed and/orwithin a smallwatershed are ecosystems sensitive to changes in precip-itation and/or evapotranspiration, due to their limited water supply.

© 2013 Elsevier B.V. All rights reserved.

1. Introduction

Long-term peatland development (vertical peat accumulation,hydroseral vegetation succession, lateral expansion, etc.) is influencedby complex interactions between allogenic (climate, basin topography,regional hydrology, anthropogenic disturbances) and autogenic (peatgrowth and decay, local hydrology, vegetation succession) factors(Payette andRochefort, 2001). Climate is recognized as themain allogen-ic factor driving the development of peatlands, especially ombrotrophicpeatlands (bogs), because their moisture balance is governed primarilyby summer effective precipitation, i.e., precipitationminus evapotranspi-ration (Charman et al., 2009). For this reason, the number of studiesusing bogs to reconstruct long-term regional hydroclimatic conditionshas increased dramatically over the past 20 years (e.g., Chiverrell,2001; Hughes et al., 2006; Booth, 2008; Loisel and Garneau, 2010;Vorren et al., 2012).While bogs are the type of peatlandmost often stud-ied for such reconstructions, Booth (2010) has demonstrated that

; fax: +1 418 656 2978.oie),marie@uqam.ca (M. Larocque).

rights reserved.

peatlands receiving small amounts of groundwater, for example, poorfens (transitional bogs), are also sensitive to hydroclimatic conditions.Moreover, he suggests that the theoretically higher climatic sensitivityof bogs versus poor fens remains to be empirically established.

Past water table levels or surface wetness fluctuations of peatlandshave mostly been linked to changes in summer effective precipitation.Because summer evapotranspiration is mainly governed by tempera-ture, it has further been suggested that summer temperatures areanother important driver of peat-based paleoclimatic records (Barberand Langdon, 2007). On the other hand, vertical peat build-up involvesautogenic processes that can later affect the morphology of the system,and eventually its internal hydrology, nutrient status and vegetationsuccession (Foster and Wright, 1990; Hu and Davis, 1995; Swindleset al., 2012). As a result, internal hydrological changes or transitionsmay occur even during periods of stable climate, due to autogenousprocesses (e.g., Morris et al., 2011; Swindles et al., 2012).

The difficulty in determining the specific role played by allogenic andautogenic factors during the evolution of a peatland remains an obstaclethat limits paleoclimatic reconstruction based on peat stratigraphy. Thisis especially true for study of a single site in a given region. The use of in-dependent paleoclimatic reconstructions may, however, help to identify

337M. Lavoie et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 386 (2013) 336–348

preponderant factors (e.g., Barber and Langdon, 2007). The objective ofthis research was to reconstruct the developmental stages (local vege-tation, trophic status) and water table levels of a temperate peatlandusing macrofossil and testate amoebae analysis. We studied a smallheadwater peatland located near the summit of CoveyHill, at the north-ern extension of the AdirondackMountains in southernQuébec, Canada(Fig. 1a). Headwater peatlands are likely to be particularly sensitive tochanges in regional climate, especially regional moisture balance,because of their small surface catchment area (Yu et al., 2003). Wecompared data on the he long-term dynamics of this site with a quanti-tative paleoclimatic reconstruction obtained using the modern analogtechnique based on pollen analyses performed on the same core usedto reconstruct the developmental stages. We hypothesized that thispeatland's long-term developmentwas sensitive to past climatic condi-tions due to its headwater position and the small size of its watershed.

2. Study area and site

CoveyHill is located 65 kmsouthwest ofMontréal (Québec, Canada)along the Canada/United States (New York State) border (Fig. 1a). Thehill is the most northward extension of the Adirondack Mountains. It

C

QUÉBEC

ONTARIO

U.S.A.

0 20 km

74°

Québec

Adirondacks Mountains

St. Lawrence River

New York State

a)

N

ridge

artificial pond

A

C

C‘

A-A’, B-B’, C

b)

Fig. 1. a) Location of Covey Hill in southern Québec at the Canada–USA border (New York StCovey Hill peatland (star). Also indicated is the location of neighboring Pin-Rigide peatland2011), as well as Lake Hertel in the St. Lawrence lowlands (Muller et al., 2003). b) Map of

covers an area of approximately 100 km2 and rises to about 345 m a.s.l.The north and east slopes of the hill are relatively steep (10% slope gra-dient), while the west side slopes gently down toward the St. Lawrenceplain. To the south, the relief is undulating and extends into the nextformation of the Adirondacks. The hill is located on Cambrian sandstoneof the Potsdam Group (Covey Hill Formation). Thick glacial depositsof reworked till and fluvioglacial sediments are present at its base(Tremblay et al., 2010). Surface deposits are absent from large areasnear the hilltop due to the erosional effect of the catastrophic drainageof proglacial Lake Iroquois (now Lake Ontario) through proglacial LakeVermont (now Lake Champlain) around 13,300–13,100 cal yr BP. Thisevent created a relatively impervious sandstone pavement (called FlatRocks) extending from below the peatland approximately 30 kmsoutheastward into the Champlain Valley in the United States(Rayburn et al., 2005, 2007, 2011; Franzi et al., 2007; J.A. Rayburn, per-sonal communication, 2012). This episode was followed by the marinetransgression of the Champlain Sea (Occhietti and Richard, 2003;Richard and Occhietti, 2005). The absence of seashells from Covey Hillat altitudes above 100 m (Tremblay, 2008) indicates that the upperpart of the hill, where the peatland is located, was not submerged inthe waters of the Champlain Sea.

OVEY HILL

W

45°N

Lake Champlain

MONTRÉAL

VermontState

St. Lawrence Lowlands

Pin-Rigide peatland

Lake Hertel

Lake Blueberry

A‘

B

B‘

Coring site for paleoecological analyses

Watershed limit

-C’Transects along which the stratigraphyof the organic deposit was described

ate), which constitutes the northward extension of the Adirondack Mountains, and the, for which paleoecological data are available (Lavoie and Pellerin, 2011; Lavoie et al.,the Covey Hill peatland.

338 M. Lavoie et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 386 (2013) 336–348

The regional climate is humid continental with a hot summer, coldwinter and abundant precipitation. The mean annual temperature is6.8 °C. The mean temperatures in January (coldest month) and July(warmest month) are −9.7 and 20.6 °C, respectively. The mean annualprecipitation is 1064 mm, 17% of which falls as snow (EnvironmentCanada, 2010). The surrounding forests belong to the Great Lakes andSt. Lawrence region (Rowe, 1972) and in the Québec portion, lie withinthe sugar maple–bitternut hickory bioclimatic domain (Bouchard andBrisson, 1996). On mesic sites, forests are mainly composed of sugarmaple (Acer saccharum), bitternut hickory (Carya cordiformis), Americanbasswood (Tilia americana), black ash (Fraxinus americana), Americanbeech (Fagus grandifolia) and yellow birch (Betula alleghaniensis). Thehill also shelters some exceptional plant communities not found else-where in the St. Lawrence plain, such as pine barrens on sandstonepavement characterized by white pine (Pinus strobus), red pine (Pinusresinosa) and jack pine (Pinus banksiana) on a thin ground cover oflichens, as well as mature hemlock groves (Tsuga canadensis). The areawas subjected to intensive tree cutting during the 19th and 20th centu-ries, mainly for agricultural purposes (Brisson and Bouchard, 2003). Thehill hosts the Covey Hill Natural Laboratory (Larocque et al., 2006), aresearch site equipped with instruments for long-term monitoring ofboth hydrological variables (climatic data, flow rates, groundwaterlevels) and a local endangered population of mountain dusky salaman-der (Dosmognatus ochrophaeus).

The Covey Hill peatland (45°00′29″ N; 73°49′36″W) is a 51 ha head-water Sphagnum-dominated bog located near the hill summit, at an alti-tude of approximately 300 m (Fig. 1b). It extends over an area 1370 mlong (east–west axis) with a maximum width of 670 m (north–southaxis). Its organic deposits lie directly on the sandstone pavement.According to Levison et al. (in press), the area aquifer contributinggroundwater to the peatland is 1.7 km2. Five plant assemblages wereidentified: three typical of open bog and two characterized by moreminerotrophic vegetation (Pellerin et al., 2009). A total of 56 plant specieswere recorded. Bog assemblages are characterized by shrub heathcommunities (Chamaedaphne calyculata, Andromeda polifolia var. latifolia,Kalmia angustifolia, K. polifolia, Rhododendron groenlandicum) on a contin-uous ground cover of Sphagnum hummocks and hollows (mainly S. fallaxand S. magellanicum). Southern and north-eastern portions of the bog aresurrounded by a 10–150 mwideminerotrophic lagg dominated by Alnusincana subsp. rugosa and Acer rubrum. Topography divides the peatlandinto two drainage basins (Fig. 1b). The eastern basin is drained by twosmall permanent streams that rapidly join to feed Blueberry Lake. Themaximum organic sediment thickness reported by Rosa et al. (2009) is320 cm. These authors have shown that peat thickness is highly variabledue to the step-likemorphology of the underlying bedrock. In the currentstudy, a sediment thickness of 360 cm was measured found in thedeepest part of the peatland. Direct precipitation feeds its ombrotrophicportion. Groundwater flow from the fractured aquifer feeds theminerotrophic portion (lagg), and is equivalent to 34–44% of the totalwater input to the peatland (Levison et al., in press).

3. Methods

3.1. Fieldwork

The sediment deposits were probed every 50–100 m along threetransects (A–A′, B–B′, C–C′; Fig. 1b) using a 50 × 5 cm Russian peatsampler (Jowsey, 1966). Subsamples 5-cm thick were collected fromeach core at regular intervals (25 cm) for further analysis of peat com-position (Girard-Cloutier, 2007). A complete sediment core 350-cmthick (Fig. 1b) was collected for paleoenvironmental reconstructionsusing a Box corer (100 × 8 × 8 cm; upper 100 cm of the deposit) anda Russian peat sampler (sediments below 100 cm depth). Sedimentscollected with the Russian sampler were extracted in 50-cm long sec-tions alternately from two boreholes separated by 20 cm. However, itwas not possible to retrieve the bottom-most 10 cm of the sediments

(350–360 cm) because they lie directly on the sandstone pavement,which prevents the tip of the Russian sampler from penetrating to col-lect the organic-mineral interface. The choice of coring site was basedon sediment thickness (the goal being to sample the thickest portionof organic deposits) and sediment stratigraphy (presence of silty gyttjaat the bottom). Sediments were wrapped in cellophane and in alumi-num foil for transport to the laboratory, where they were stored at5 °C until analysis.

3.2. Macrofossil analysis

Prior to specific analyses, sediments of the main core were cleanedand cut into continuous 1-cm thick slices. Subsamples (1 cm3) weretaken at regular intervals (4 cm) and analyzed for dry bulk density(g cm−3) and percent-weight organic matter by loss-on-ignition(550 °C; Heiri et al., 2001). Intervals used for macrofossil analysiswere 4 cm. In total, 87 samples were analyzed. Samples were preparedaccording to Bhiry and Filion (2001). Macroremains were separatedfrom the organic matrix by boiling the material for about 3 min in aweak 5% KOH solution for deflocculation. The material was thenwet-screened through a series of sieves of 0.850, 0.425 and 0.180 mmmesh. Remains of vascular plants, bryophytes, charcoal and sclerotiawere picked out, identified and counted using a stereomicroscope at 4to 40×magnification. The percentage of volume occupied by the differ-ent botanical groups (wood remains, roots and rootlets, herbaceousplants, brown mosses, Sphagnum, vascular leaves) was calculated. Ref-erences used in identifying plant remains were Montgomery (1977)and Lévesque et al. (1988), as well as the plant-macrofossil referencecollection of the Centre d'études nordiques (Laval University). Resultswere expressed in number of macrofossils per 100 cm3 of sediments.Macrofossil assemblage zones, labeled CHM (for Covey Hill Macrofossils),were defined according to changes in the relative abundance of vascularplants and main botanical groups. Botanical nomenclature for vascularplants follows VASCAN (Brouillet et al., 2011).

3.3. Testate amoebae analysis

Subsamples (2 cm3)were taken for fossil testate amoebae analysis at4 cm-intervals at depths from 0 to 309 cm. Sediments between 309 and350 cm depth could not be examined for testate amoebae content, sincethey were not composed of peat (see below). Standard methods wereused to isolate testate amoebae from the organic matter (e.g., Hendonand Charman, 1997; Charman et al., 2000; Booth et al., 2010/11). Sub-samples were boiled in distilled water (10 min.) and then screenedthrough a series of sieves with 0.350 and 0.150 mmmesh. Residual ma-terial was stained, mounted on glass slides and analyzed under a micro-scope (400× magnification). For each level, at least 150 tests (shells)were identified and counted, as this amount has been shown to recordmost species present in a sample (Payne and Mitchell, 2009). Test iden-tification was performed using the Charman et al. (2000) identificationkey with the modifications suggested by Booth and Sullivan (2007).The relative abundance of each taxon was calculated as a percentage ofthe total count. Pastwater table depths (cm)were inferred using a trans-fer function developed by Lamarre (2011) and Lamarre et al. (2012). Thistransfer function is based on 205 surface samples collected from 19peatlands across the province of Québec, and was build using C2 1.7.2software (Juggins, 2011). A weighted average tolerance downweightedclassical deshrinking model with bootstrapping cross validation(1000 cycles) was selected. This model obtained an r2 of 0.83 alongwith a maximum bias in residuals of 5.31 cm and a root mean squarederror of prediction (RMSEP) of 5.30 cm (Lamarre et al., 2012).

3.4. Radiocarbon dating

Thirteen samples (each one consisting of a few mg dry weight ofbulk sediments) were submitted for accelerator mass spectrometry

339M. Lavoie et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 386 (2013) 336–348

(AMS) radiocarbon dating (Table 1). Twelve samples were pretreatedand prepared at University Laval's 14C Laboratory and dated at theKerk Laboratory (Irvine University, California). One sample (fromthe bottom of the core) was dated at Beta Analytic (Florida). All radio-carbon dates (14C yr BP) were calibrated (cal yr BP) using the CALIB6.0.1 program (Stuiver and Reimer, 1993) and the INTCAL09 dataset(Reimer et al., 2009). Calibrated dates were rounded to the nearest10 years using 2-sigma cal age range. An age-depth model was builtby linear interpolation. The decision to use linear interpolation is jus-tified in this instance since the chronology is based on few 14C datesand since the selection of levels dated is based in part on sediment li-thology (Telford et al., 2004; Hughes et al., 2006; Loisel and Garneau,2010). A present-day age was assigned to the top of the core (0 cm).Results are expressed as calibrated years BP. A 210Pb chronologywas also constructed for the upper part of the core (0–50 cm). Mea-surements were performed on an alpha-spectrometer at GEOTOPResearch Center (Université du Québec à Montréal, Montréal). A dry0.5 g subsample from each 4-cm interval was analyzed for 210Pbactivity after spiking with a 209Po yield tracer (Lamarre et al., 2012).The constant rate of supply model was applied to calculate the ages(Appleby and Oldfield, 1978; Appleby, 2004).

3.5. Paleoclimatic reconstruction

In a previous study (Pellerin et al., 2007), pollen analysis wasconducted to reconstruct the postglacial regional vegetation history ofCovey Hill from the same core used here. This pollen data allowed usto quantitatively reconstruct past climatic conditions. Quantitative re-constructions ofmean July air temperatures (°C),mean annual precipita-tion (mm year−1) andmean potential evapotranspiration (mm year−1)are based on the modern analog technique (e.g., Fréchette et al., 2008;Fréchette and de Vernal, 2013). This method uses pollen data and anupdated version (v.1.72) of the modern pollen network originally com-piled by Whitmore et al. (2005) for North America and Greenland. Themodern database includes 4833 sites distributed among 10 vegetationtypes (biomes). Modern climate variables were calculated from the Cli-mate Research Unit gridded climatology using 1961–1990 climatologicalaverages (New et al., 2002) and interpolated to the 4833 pollen sites

Table 1Radiocarbon dates of the core collected from the Covey Hill peatland.

Laboratory numbera Depth(cm)

Material dated

ULA-258UCIAMS 35027

50 Sphagnum peat

ULA-541UCIAMS 45044

60 Herbaceous and wood peat

ULA-542UCIAMS 45059

80 Herbaceous and wood peat

ULA-259UCIAMS 35028

100 Herbaceous and wood peat

ULA-543UCIAMS 45045

115 Herbaceous and wood peat

ULA-544UCIAMS 45046

130 Herbaceous and wood peat

ULA-205UCIAMS 33460

150 Herbaceous and wood peat

ULA-202UCIAMS 34487

200 Herbaceous and wood peat

ULA-203UCIAMS 33447

250 Herbaceous and wood peat

ULA-545UCIAMS 45047

275 Herbaceous and wood peat

ULA-204UCIAMS 33459

300 Herbaceous and wood peat

ULA-546UCIAMS 45048

309 Herbaceous and wood peat

Beta-245303 350 Silty gyttja

a ULA (Laval University); UCIAMS (University of California); Beta (Beta Analytic).

via lapse-rate collected bilinear interpolation. Whitmore et al. (2005)fully describe the method used to estimate modern climate data. Themodern data files and associated metadata are available on the webpages of the National Geophysical Data Center (http://www.ncdc.noaa.gov/paleo/pollen.html), the Laboratory for Palaeoclimatology andClimatology at the University of Ottawa (http://www.lpc.uottawa.ca/data/index.html), and the Department of Geography of the Universityof Wisconsin (http://www.geography.wisc.edu/faculty/williams/lab/Downloads.html). Pollen taxa compiled in the modern database weregrouped at the genus or family level, and spore taxa were excluded.Among the 77 pollen taxa (43 woody plants, 34 herbs) consideredhere for climate reconstruction, 53were recorded in the pollen diagramof Covey Hill. Similarity between fossil and modern pollen assemblagesis based on the squared chord distance (SCD) dissimilarity metric(Birks, 1977; Prentice, 1980; Overpeck et al., 1985; Gavin et al., 2003).SCD values vary between zero and 200. The SCD threshold adopted forthe present study is 35. Climate estimates are calculated from the fivebest modern analogs with a distance inferior to this threshold. If lessthan five analogs are found, no climate reconstruction is attemptedfor that sample. Climate reconstructions were performed with the“bioindic” package (ftp://ftp.cerege.fr/R/Package_bioindic) built on theR-platform (http://cran.r-project.org). The accuracy of the approach(RMSE) is estimated to ±1.6 °C (r2 = 0.92) for July air temperature,and ±207 mm (r2 = 0.81) for annual precipitation. These errors areclose to the actual standard deviation around the mean for July airtemperature and annual precipitation, which averages ±2.7 °C and107 mm at Covey Hill, respectively (Environment Canada, 2010).

4. Results and interpretation

4.1. Stratigraphy and chronology of the sediments

The bottom of the core (350–309 cm) consists of a green-brownsilty gyttja (Fig. 2), and constitutes the only sampling point in thepeatland where this type of sediment was found. The organic mattercontent is less than 10%, whereas the dry bulk densities display thehighest values for the entire core (mean = 1.23 g cm−3). The siltygyttja is overlain by peat up to the summit. From 309 to 48 cm, the

14C date(yr BP)

Calibrated rangeyr BP (2σ)

Mid-point(cal yr BP)

40 ± 15 43–58 50

505 ± 20 510–542 530

2445 ± 20 2592–2615 2600

4530 ± 20 5055–5180 5120

7075 ± 20 7854–7904 7880

7275 ± 20 8023–8162 8090

7635 ± 20 8389–8450 8420

8055 ± 20 8977–9024 9000

8930 ± 30 9917–10,081 10,000

9360 ± 30 10,505–10,674 10,590

10,360 ± 20 12,083–12,246 12,170

10,635 ± 30 12,637–12,804 12,720

12,080 ± 40 13,800–14,050 13,925

340 M. Lavoie et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 386 (2013) 336–348

matrix of the peat is mainly composed of herbaceous and woodremains, with the exception of abundant vascular leaves at the onsetof peat accumulation (309–288 cm), and a thin layer (204 cm) domi-nated by brown mosses. Although Sphagnum remains generally consti-tute less than 10% of sample volume, abundant Sphagnum leaves andstems are present in all samples. Organicmatter content increases grad-ually from 309 to 216 cm (30 to 95%) and then remains constantbetween216 cmand the top of the core (mean = 96%). The uppermost48 cm consists of a Sphagnum-dominated peat. A 4 cm-thick charcoallayer (48–52 cm) is present below the Sphagnum-dominated peat(Fig. 2). Elsewhere along transects A–A′, B–B′ and C–C′ (Fig. 1b), peatcomposition consists of a mixture of herbaceous and woody fragmentsfrom the bottom to ~50 cm from the surface, the upper part of thesediment consisting of Sphagnummosses (Girard-Cloutier, 2007).

A date of 13,925 cal yr BP was obtained at the bottom of the siltygyttja (Table 1 and Fig. 3). This date is probably too old, according tothe age estimate for the ice retreat and subsequent flooding eventsthat occurred between 13,300 and 13,100 cal yr BP in the hill area(J.A. Rayburn, personal communication, 2012). The maximum age forthe beginning of sediment accumulation was thus estimated to be13,100 cal yr BP. The onset of peat accumulation overlying the siltygyttja (309 cm) was dated 12,720 cal yr BP (Fig. 3). One sample takenat 50 cm yielded an age of 40 cal yr BP. This date was considered tooyoung, because in the pollen diagram it corresponds to an abruptincrease in the abundance of Ambrosia and other ruderal taxa (Pellerinet al., 2007). This change indicates the onset of human disturbancesin the region, which began early in the 19th century (Brisson andBouchard, 2003). The 210Pb chronology dates this layer to 1880 AD(125 cal yr BP; Fig. 3).

20 40 60 80 100 0.5 1.0 1.5

Depth

(cm

)

Woo

d re

main

Herba

ceou

s

14 C Dat

es

(cal

yr B

P)

Organ

ic m

atte

r

Dry b

ulk d

ensit

y

gr cm-3 Percentages

50 530

2600

5120 7880

8090

8420

9000

10 000

10 590

12 170 12 720

13 925

2.0 20 40 60 80 100 20 40

0

50

100

150

200

250

300

350

Sphagnum peat

Herbaceous and wooSilty gyttja

Herbaceous peatwith vascular leaves

Charcoal layer

Fig. 2. Radiocarbon dates, stratigraphy, organic matter content, dry bulk density and mainreconstruction.

Three main periods in net peat accumulation rates can be identified(after the accumulation of the silty gyttja). A high mean accumulationrate is evident between 12,720 and 7880 cal yr BP (309–115 cm;mean = 0.040 cm yr−1). This is followed by a major decline, from7880 to 530 cal yr BP (115–60 cm; mean = 0.007 cm yr−1). The netaccumulation rate increases at the summit of the core (60–0 cm;b500 cal yr BP). This latter portion corresponds in part to the acrotelm,where peat is less decomposed. According to thismodel, 194 cmof peat(309–115 cm) accumulated during the first 4840 years of this process(from 12,720 to 7880 cal yr BP). This corresponds to 63% of the verticalaccumulation, whereas only 37% of the vertical peat accumulation(115–0 cm) occurred during the last 7880 years.

4.2. Developmental stages of the peatland

Results of macrofossil (Fig. 4) and testate amoebae (Fig. 5) analysesare described concurrently, in order to reconstruct both the develop-mental stages of the peatland as well as the water-table depth fluctua-tions at the sampling point. Five main developmental stages weredefined according to the composition of the sediments and the plant–macrofossil assemblages.

Zone CHM-I, at the bottom of the core (350–309 cm;>12,720 cal yr BP), corresponds to the accumulation of silty gyttja.Macrofossil assemblages are dominated by aquatic species (Chara spp.,Potamogeton spp., Ranunculus aquatilis var. diffusus). Seeds of sedges(Carex spp.) as well as remains of Daphnia sp. and Cristatella mucedoare also present. This zone reflects the initial existence of a small shal-low pond located in a depression of the fractured sandstone pavement.

s

Roots

and

root

lets

Uniden

tified

Mac

rofo

ssil

zone

s

Sphag

num

Vascu

lar le

aves

Brown

mos

ses

87

Percentages

60 80 100 20 40 60 80 20 40 60 80 100 20 20 40

CHM-I

CHM-IIa

CHM-IIb

CHM-III

CHM-IVa

CHM-IVb

CHM-V

d peat

Continuous presenceof Sphagnum <10%

Continuous presenceof Sphagnum <10%

botanical groups (expressed as percentages) of the core analyzed for paleoecological

Calibrated years BP

50

100

200

250

300

350

150

14 000 12 000 10 000 8000 6000 4000 2000 0

Dep

th (

cm)

Dates(cal yr BP)

50

530

2600

5120

7880 8090

8420

9000

10 000

10 590

12 170

12 720

13 925

0.016

0.050

0.071

Pla

nt-m

acro

foss

il zo

nes

CHM-I

65 cm of peataccumulationin 7760 years

194 cm of peat accumulation in 4840 years

Likely too old

CHM-IIa

CHM-IIb

CHM-III

CHM-IVa

CHM-IVb

CHM-V

0.025

?

0.400 cm yr-1

0.001

0.008

0.005

0.061

0.086

0.042

0.016

1880 AD(125 cal yr BP)

50 cm of peataccumulationin 125 years

1880 1900 1920 1940 1960 1980 2000

Years (A.D.)D

epth

(cm

)

0

10

20

30

40

50

Portion of the core dated by 210Pb activity

186060

Drainage of proglacial Lake Iroquois

Interpolation

Radiocarbon dates

210Pb

Fig. 3. Age-depth model of the sedimentary core. Net sediment accumulation rates (cm yr−1) are indicated. Symbols used to describe the composition of the organic matter matrixare defined in Fig. 2.

341M. Lavoie et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 386 (2013) 336–348

Zone CHM-II (309–210 cm; 12,720–ca. 9200 cal yr BP) correspondsto the onset of peat accumulation after the infilling of the pond. Localconditions were very wet and pools were likely present, as indicated bythe abundance of aquatic species remains (Chara spp., Najas flexilis,Potamogeton spp., Nympheaceae) and Cristatella mucedo statoblasts. Theabundant remains of leaves of vascular plants found in the peat matrix(309–288 cm)most likely correspond to those ofMyrica gale, as indicatedby high pollen percentages of this species in the pollen diagram (Pellerinet al., 2007). Zone CHM-IIwas divided into two subzones. Themain differ-ence between subzones CHM-IIa (310–275 cm; 12,720–10,590 cal yr BP)and CHM-IIb (275–210 cm; 10,590–ca. 9200 cal yr BP) is the presence, insubzone IIb, of Larix laricina and herbaceous plants (Polygonum spp.,Scirpus spp., Scheuchzeria palustris, Dulichium arundinaceum, Hypericum spp.).No testate amoebae were found in the peat. Zone CHM-II likelycorresponds to a wet rich fen.

Zone CHM-III (210–142 cm; ca. 9200-ca. 8290 cal yr BP) is character-ized by the disappearance of aquatic species and a major increase in theabundance of Larix laricina remains, suggesting that local conditionsprogressively became poorer and drier. The first remains of ericaceousspecies (Andromeda polifolia var. latifolia; Chamaedaphne calyculata;Kalmia spp.) also appear. Other species identified include Alnus sp. (likelyAlnus incana subsp. rugosa), Carex spp., Viola spp., Hypericum spp. andEriophorum spp. As with the previous zone, no testate amoebae werefound, except at horizon 152 cm (Archerella flavum, Difflugia pulex).Zone CHM-III likely corresponds to an intermediate fen.

Zone CHM-IV (142–50 cm; ca. 8290 to 125 cal yr BP), covering along period that saw the establishment of poor minerotrophic condi-tions, was divided into two subzones (IVa and IVb). The beginning ofZone IV also marks the continuous appearance of testate amoebae spe-cies (Fig. 5). The main changes observed in assemblage composition oftestate amoebae correspond fairly closely to the two macrofossil sub-zones. Net sediment accumulation rates (Fig. 3) were very low insubzone IVa (142–96 cm; ca. 8290-ca. 4620 cal yr BP) and in themain part of subzone IVb (96–50 cm; ca. 4620–125 cal yr BP). Picea

spp. (likely P. mariana) succeeds Larix laricina, which disappearscompletely. Remains of Andromeda glaucophylla var. polifolia (IVa),Carex spp. (IVb) are also abundant, as are those of Cenococcumgraniforme (IVb), a mycorrhizal fungus associated with the roots of nu-merous peatland shrubs and trees (Thormann et al., 1999). Severallevels contain abundant charcoal pieces, especially in subzone IVb.

Testate amoebae assemblages of subzone IVa are dominated byDifflugia pulex and Archerella flavum, indicating that thewater table aver-aged between 16 and 24 cm depth at the time. An increase of the watertable likely occurred around 6500 cal yr BP (108 cm). Although therepresentation of Trigonopyxis arcula, a species associatedwith generallydry conditions (Booth, 2008), reaches 20% here, species associatedwith humid conditions, particularly Archerella flavum and Amphitremawrightianum, constitute 69% of the testate amoebae assemblages at thislevel. The simultaneous presence of species characteristic of humid anddry conditions could be the result of the very slow rate of sedimentaryaccumulation, which would have promoted a mixing of assemblagesfrom different water table levels and periods. In subzone IVb, testateamoebae assemblages are in a first step dominated mainly byHyalosphenia subflava (96–80 cm), a species characteristic of dry habi-tats (Booth, 2008), reflecting significantly drier local conditions (waterlevel between 26 and 38 cm depth) than those found at lower levels. Agradual rise in water table level characterizes the upper portion of thesubzone where a marked decline of H. subflava and the dominance ofCyclopyxis arcelloides can be observed.

Zone CHM-V (50–0 cm; 125 cal yr BP to Present) is characterized bythe accumulation of a Sphagnum peat, indicating the establishment ofombrotrophic conditions. Fossil plant remains reflect the current localflora of the bog (Pellerin et al., 2009), i.e., Chamaedaphne calyculata,Kalmia spp. and Eriophorum spp., while Picea spp. has almost completelydisappeared. Among testate amoebae, the representation of Cyclopyxisarcelloides decreases dramatically in favor of Difflugia pristis, a specieswhose distribution is optimal when the water table is at a level of9.23 cm (±9.03 cm), as well as Pseudodifflugia fulva andNebela militaris,

Larix

laric

ina (L

-S)

Betula

sp. (

S)

Picea

spp.

(L)

Betula

pop

ulifo

lia (S

)

Betula

pap

yrife

ra (S

)

Betula

ceae

(S)

Cham

aeda

phne

calyc

ulata

(B-F

-L-S

)

Alnus s

p. (S

)

Myr

ica g

ale (S

)

Kalmia

spp.

(S)

Carex

spp.

(S)

Chara

spp.

(O)

Viola

spp.

(S)

Potam

oget

on sp

p. (S

)

Najas f

lexilis

(S)

Scirpu

s spp

. (S)

Dulich

ium a

rund

inace

um (S

)

Nymph

eace

ae (S

)

Hyper

icum

spp.

(S)

Erioph

orum

spp.

(S)

Scheu

chze

ria p

alustr

is (S

)

Comar

um p

alustr

e(S

)

Cyper

acea

e (S

)

Daphn

ia sp

. (Ep)

Crista

tella

muc

edo

(St)

Cenoc

occu

m g

ranif

orm

e (S

c)

Charc

oals

Depth

(cm

)

0

50

100

150

200

250

300

350

14 C Dat

es

(cal

yr B

P)

CHM-I

13 925

50 530

2600

5120 7880

8090

8420

9000

10 000

10 590

12 170 12 720

Zone

486-539

3

71

26

25

73

14

6

168

454

87

5

4

30

104

119-858

7-9

12

36-51 83

56-64 3

3

3

2

9

16

3

43

8

7

11

28

34

861

637

450

135

Ep: ephippia B: buds

F: fruits L: leaves

O: oogones S: seeds

Sc: sclerotia St: statoblasts

Polygo

num

spp.

(S)

Trees

Andro

med

a po

lifolia

var.

latifo

lia (L

-S)

Shrubs

Ranun

culus

aqu

atilis

var.

diffu

sus (

S)

Herbs and aquatics

CHM-IIa

CHM-IIb

CHM-III

CHM-IVa

CHM-IVb

Analysts : A.-M. Girard-Cloutier and É.C. Robert

CHM-V

200 400 2 10 20 4 1 2 100 20 20 40 2 1 10 10 50 4 2 10 20 20 40 2 2 1 1 1 4 4 2 4 4 6 10 20 100

Number of macrofossils / 100 cm3

Fig. 4. Macrofossil diagram of the sedimentary core. Symbols used to describe the composition of the organic matter matrix are defined in Fig. 2.

342M.Lavoie

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Palaeogeography,Palaeoclimatology,Palaeoecology

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336–348

0

20

40

60

80

100

120

140

160

180

200

220

240

260

280

0 2 0 0 2 0 0 2 0 4 0 0 2 0 4 0 0 2 0 0 2 0 4 0 6 0 8 0 0 2 0 0 2 0 4 0 6 0 8 0 100 0 0 2 0 4 0 6 0 8 0 0 2 0 4 0 6 0 8 0 100 0 0 0 0 0 2 0 0 2 0 0 8 1 6 2 4 3 2 4 0

Depth

(cm

) Am

phitr

ema

wright

ianum

Arcell

a dis

coide

s

Arche

rella

flavu

m

Difflug

ia pr

istis

Hyalos

phen

ia ele

gans

Pseud

odiffl

ugia

fulva

Nebela

milit

aris

Difflug

ia pu

lex

Assuli

na se

minu

lum

Cyclop

yxis

arce

lloide

s

Hyalop

shen

ia su

bflav

a

Assuli

na m

usco

rum

Heleop

era

sylva

tica

Hyalos

phen

ia m

inuta

Crypt

odiffl

ugia

ovifo

rmis

Trigo

nopy

xis a

rcula

Trine

ma

- Cor

ythion

Inferred water table

300

320

340

360

Plant macrofossil

zones

Sections where no testate amoebae were found Analysist: A. Lamarre

14 C Dat

es

(cal

yr B

P)

cm

50 530

10 000

2600

5120

9000

8420

7880

8090

10 590

12 170 12 720

13 925

CHM-I

CHM-IIa

CHM-IIb

CHM-III

CHM-IVa

CHM-IVb

CHM-V

Percentages

Fig. 5. Testate amoebae diagram of the sedimentary core and inferred water table depths. Symbols used to describe the composition of the organic matter matrix are defined in Fig. 2.

343M.Lavoie

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344 M. Lavoie et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 386 (2013) 336–348

two species that are generally associated with drier conditions but thatare also characterized by high tolerance level (16.3 ± 12.2 cm and17 ± 9.9 cm, respectively). In Zone CHM-V, water level varied between14 and 24 cm depths.

4.3. Paleoclimatic reconstruction

Paleoclimatic reconstructions based on the modern analog tech-nique are presented in Fig. 6. Close analogs for all fossil pollen assem-blages exist in the modern database, with SCD lower than 35 for allsamples (mean SCD = 7.8). The dissimilarity between fossil samplesand modern analogs was slightly higher for the Late Glacial periodthan for the Holocene. The SCD of the fifth analog averages 8.97 forthe Late Glacial samples, whereas it is 7.41 for the Holocene samples.The coldest conditions for the entire postglacial period occurred duringthe constitution of a tundra vegetation cover, corresponding to the LateGlacial period. Conditions warmed progressively from the beginningof sedimentation until around 9000 cal yr BP for July temperatures,which rose from 13 °C to 19 °C. Summer temperatures seem to haveremained relatively stable subsequently, with only a few minor fluctu-ations, fluctuating around an average of 19 °C. Average annual precipi-tation was also minimal during the Late Glacial period (mean =420 mm yr−1), then rose to reach a maximum around 10,140 cal yrBP (915 mm yr−1). Precipitation remained stable after that time,aside from a few fluctuations, until around 7300 cal yr BP (mean =810 mm yr−1). Finally, a marked increase characterizes the last7300 years (mean = 1030 mm yr−1). Average annual evapotranspira-tion tendencies follow a pattern very similar to that of the warmestmonth, remaining relatively stable since 9000 cal yr BP (mean =670 mm yr−1).

5. Discussion

To assess whether the long-term dynamics of the peatland havebeen governed by allogenic and/or autogenous factors, we comparedthe developmental stages and net peat accumulation rates, first withthe quantitative paleoclimatic reconstruction and thenwith past fluctu-ations in the levels of several lakes in southernQuébec and northeastern

14C Dates(cal yr BP)

50 530

2600

5120 7880

8090

8420

9000

10 000

10 590

12 170 12 720

13 925

Dep

th (

cm)

0

50

100

150

200

250

300

350

Mean temperature - July

0 5 10 15 20 25

Mean annual prec

0 400 800

mm yr-1

Fig. 6. Climatic quantitative reconstruction obtained using the modern analog technique. Ointervals for each parameter corresponding to the five best modern analogs are indicated byshown (Pellerin et al., 2007).

New England (Fig. 7), which are known to reflect changes in regionalhydroclimatic conditions.

5.1. The pond stage

At the location of the sediment core studied, the accumulation of siltygyttja began during the Late Glacial period in a shallow pond (ZoneCHP-I; >12,720 cal yr BP). This pond was likely very small, since nosilty gyttja was found elsewhere in the peatland. Although the 14C dateobtained at the bottom of the core is too old in view of the paleogeo-graphical event associated to the catastrophic breakout of proglacialLake Iroquois around 13,300–13,100 cal yr BP following the ice retreat(Rayburn et al., 2005, 2007, 2011; Franzi et al., 2007), the onset of sedi-mentation likely began rapidly after this event (J.A. Rayburn, personalcommunication, 2012). The climate at this timewas mild enough to cre-ate conditions favorable for the growth of a vegetation cover analogousto modern open herb/shrub tundra (Fig. 6; Richard, 1994; Pellerinet al., 2007), as well as for biological productivity in the pond. Althoughthis period was characterized by the coldest conditions of the postglacialperiod, summer temperatureswere constantly increasing. The open veg-etation environment on the hill and the very limited surface sedimentsleft behind by the outbreak of Lake Iroquois likely favored runoff, thuscontributing to significant surface water inflow into the pond. Assumingthat sedimentation began around 13,100 cal yr BP, the pond stagewouldhave been only 300 to 400 years in duration.

5.2. The rich and intermediate fen stages

When the infilling of the pond was achieved in 12,720 cal yr BP,terrestrialization began with an initial rich fen with pools (ZoneCHM-II; 12,720 to ca. 9200 cal yr BP), followed by an intermediatefen (Zone CHM III; ca. 9200–ca. 8290 cal yr BP). Larix laricina waspresent locally during the period represented by subzone CHM-IIb,and its abundance then increased, as is evident in Zone CHM-III.Apparent vertical peat accumulation rates were indeed high in zonesCHM-II and III (Fig. 3). Peat accumulation during the 4500 years of therich and intermediate stages alone represents 54% of the total verticalaccumulation at the coring site (Fig. 7).

ipitations

1200 1600

Potential evapotranspiration

0 400 800 1000 200 600

mm yr-1

Postglacial regionalvegetation history

TundraHerbs/Shrubs

Lichen woodland Picea - Populus

Mixed forest Abies - Betula - Pinus

Deciduous forest Acer - Betula - Pinus

Tsuga - Fagus

Anthropogenic period

n each curve, the thick black line corresponds to a 3-point moving average. Confidencedashed lines. A summary of the postglacial regional vegetation history of Covey Hill is

Lake Hertel (Muller et al., 2003) Nulhegan Basin (Munroe, 2012)

Lake Mégantic (Loewen et al., 2005) Lake Albion (Lavoie and Richard, 2000)

0

2000

4000

6000

8000

10 000

12 000

14 000

Cal

ibra

ted

year

s B

PCovey Hill

CHM-IIRich fen

with pools

IVa

IVb

CHM-IVPoor fen

IIa

IIb

Low

net

pea

t acc

umul

atio

n ra

tes

0

10

20

30

40

50 60

70

80

90 100

Per

ecen

tage

s of

net

ver

tical

pea

t acc

umul

atio

n th

roug

h tim

e

Pin-Rigide

0

10 20

30 40 50

60 70

80

90

100

Per

ecen

tage

s of

net

ver

tical

pea

t acc

umul

atio

n th

roug

h tim

e

Low

net

pea

t acc

umul

atio

n ra

tes

Peatland dynamics

Mea

n Ju

ly te

mpe

ratu

re a

nd m

ean

annu

al e

vapo

tran

spira

tion

Mea

n an

nual

rec

ipita

tions

Postglacial climate Periods of highest

values Periods of

low lake-levels

Lake

Alb

ion

(sou

ther

n Q

uébe

c)

Lake

Még

antic

(so

uthe

rn Q

uebe

c)

Nul

hega

n B

asin

(no

rthe

rn V

erm

ont)

West East

Lake

Her

tel

(sou

ther

n Q

uébe

c)

Drainage of proglacial Lake Iroquois

CHM-IIIIntermediate fen

CHM-VBog

CHM-IPond

Fig. 7. Summary of the developmental stages of the Covey Hill peatland, vertical peat accumulation dynamics of Pin-Rigide peatland (modified from Lavoie and Pellerin, 2011),postglacial climate deduced from the pollen-climate transfer function, and periods of low lake-levels in southern Québec and northern New England (selected studies).

345M. Lavoie et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 386 (2013) 336–348

The final infilling of the pond and beginning of peat accumulationcoincidedwith a progressive increase in temperatures. The average tem-perature of the warmest month continued to rise until 9000 cal yr BP.Although average annual precipitation increased steadily until10,500 cal yr BP, it was still below today's levels. Precipitation remainedstable after that time until ca. 7300 cal yr BP, suggesting that regionalhydroclimatic conditions were drier than today. Other paleoecologicalindices suggest drier regional conditions during the Early Holocene.Charcoal particles were found to be passably abundant in severalsedimentary sequences from temperate regions of eastern NorthAmerica, which suggests more frequent wildfires (e.g., Clark et al., 1996;Maenza-Gmelch, 1997; Carcaillet and Richard, 2000). Low water levelswere also recorded in several lakes (Fig. 7), especially in southern Québec(Lavoie and Richard, 2000; Muller et al., 2003; Loewen et al., 2005) andnorthern Vermont (Munroe, 2012). Drier conditions were probably alsopresent in central New York between 10,800 and 9200 cal yr BP(Mullins et al., 2011). Depending on location, these low levels date frombetween 11,000 and 9000 cal yr BP.

Since the vertical development of Covey Hill peatland (and likely itslateral growth through paludification) during the Early Holoceneoccurred under a relatively dry climate, temperature was probably acritical factor in peat accumulation, which occurred through enhancedbiomass production (Clymo et al., 1998). Despite the small size of itsgroundwater contributing area, precipitation was likely sufficient tofeed the site through infiltration in the surrounding bedrock andgroundwater outcropping in the peatland to maintain minerotrophicconditions over the entire peatland ecosystem.

5.3. The poor fen and bog stages

The establishment of poor minerotrophic conditions (Zone CHM-IV)occurred around 8200 cal yr BP. The transition from Zone CHM-III toZone CHM-IV was characterized in part by the disappearance ofLarix laricina and the appearance of Picea mariana, a species adapted topoorer conditions (Montague and Givnish, 1996). The gradual hydroseralchange from rich fen to intermediate fen to poor fen was probably

346 M. Lavoie et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 386 (2013) 336–348

controlled by autogenic changes consequent to vertical build-up of thepeat. However, local conditions in thepoor fen stagewereprobablynearlyombrotrophic (transitional bog), as suggested by evidence such as thepresence of testate amoebae with ombrotrophic affinities, the presenceof Sphagnum remains andan abundance ofmacroscopic charcoal in sever-al levels (Fig. 4). The charcoal layer found 50 cm below the soil surfacewas also present at all other coring sites along the three transects(Fig. 1b; Girard-Cloutier, 2007), which indicates that peatland conditionswere sufficiently dry to allow fires to occur. Some studies have indeedshown that the presence ofmacroscopic charcoal in soils is clear evidenceof in situ fire (Ohlson and Tryterud, 2000; Carcaillet et al., 2001). In thecase of the Covey Hill peatland, fires likely started in the surroundingfire-prone Pine Barrens (Meilleur et al., 1994) and then spread to thepeatland. The absence of charcoal layers in Zones II (rich fen) and III(intermediate fen) is probably linked to the fact that local conditionswere too humid to allow fire in situ. True ombrotrophic conditions(Sphagnum peat) occurred only recently (125 cal yr BP).

The poor fen stage is characterized by very lownet peat accumulationrates between 7880 and 500 cal yr BP (Fig. 3). During this ~7300 year-long period, 115 cm of peat accumulated vertically, representing only37% of the total vertical accumulation (Fig. 7). Although no quantitativemeasurement was carried out for this purpose, organic matter in thissection of the core was estimated qualitatively to be highly humified.This low accumulation over such a long period of time suggests thatsurface conditions of the peatland were dry and oxygenated. This hy-pothesis is corroborated by testate amoebae assemblages, which showa gradual reduction in the average position of the water table (Fig. 5).However, paleoclimatic reconstructions inferred from pollen data showthat average annual precipitation was higher than that of the EarlyHolocene (Fig. 7). Average summer temperatureswas also higher duringthis low accumulation period than previously.

In undisturbed poor fens and bogs, the main factors controllingwater-table level are precipitation and evapotranspiration during thesummer period (Charman et al., 2009). The opposite trend evident inthis instance between low net peat accumulation rates and reconstructedprecipitation records suggests that although precipitation was abundant,water table level remained low, likely due to high summer temperaturesand evapotranspiration (Fig. 7). The low water table level might havefavored perpetuation of oxygenated conditions and decomposition oforganic matter. This interpretation is supported by the fact that a similarand synchronous pattern was also observed in a peatland (Pin-Rigide)located 10 km north of Covey Hill (Fig. 1a). At this site, where the peatalso lies directly on the bedrock, only 127 cm of peat accumulated overa 10,250 year-period (Lavoie and Pellerin, 2011; Lavoie et al., 2011). Asharp decline in peat accumulation rates began at about 8270 cal yr BP,mainly after 7520 cal yr BP (Fig. 7). Vertical accumulation during thelast 7500 years represents only 28% of total vertical accumulation. Thissimilar and synchronous pattern in two peatlands of the same regionsupports the suggestion that therewas a climatic control on peat accumu-lation linked to high evapotranspiration under high summer temper-atures. A small headwater lake located close to Covey Hill in theSt. Lawrence Lowlands (Lake Hertel; Fig. 1a) also shows evidence of ep-isodes of low levels over the past 8000 years (Fig. 7;Muller et al., 2003).These low levels could have been influenced, at least in part, by thesame climatic events that influenced the two peatlands. Finally, lownet peat accumulation rates were observed in Ontario for a smallshrub swamp between around 7200 and 1500 cal yr BP (Bunting andWarner, 1999). The authors suggested that the strong decrease wasassociated to the maximum Holocene temperatures, which led to pro-gressive drying out of the site, and in turn to increased decay rates.

6. Conclusion

The successional stages of the Covey Hill peatland (pond—richfen—intermediate fen—poor fen—bog) have also been observed inother temperate peatlands in eastern North America. However,

hydroseral changes are asynchronous between these peatlands, andsometimes even between different sectors of the same site. Thisasynchronicity suggests that hydroseral succession is mainly a resultof internal dynamics, linked to vertical peat accumulation, that con-tinuously change surface hydrological conditions, nutrient contentsand thus floristic communities.

Covey Hill and nearby Pin-Rigide peatlands show similar trendswith regard to the dynamics of vertical peat accumulation from theirorigins onward. Accumulation rates diminished abruptly and relativelysynchronously after the establishment of poor fen (Covey Hill) and bog(Pin-Rigide) conditions in response to high summer temperatures andhigh evapotranspiration. To our knowledge, such a sharp decrease insediment accumulation rates, extending over several millennia, hasnot been observed in other temperate peatlands of southern Québecand northeastern New England for which paleoecological and chrono-logical data are available. The large watershed of these other peatlandsmaintains a sufficient water supply to sustain thewater table level evenunder drier hydroclimatic conditions, or higher summer evapotranspi-ration. These peatlands are also much larger than the Covey Hill site.In light of this study, we suggest that small peatlands situated above awatershed and/or within small watersheds are ecosystems that are infact highly sensitive to small changes in precipitation and/or evapo-transpiration, due to their limitedwater supply. The Covey Hill peatlandwas a poor fen over a very long period. Ourfindings concurwith Booth'ssuggestion (2010) that poor fens, like bogs, may be sensitive to regionalpaleoclimatic changes.

Acknowledgments

This research received financial support from the Natural Sciencesand Engineering Research Council of Canada (M. Lavoie) and the EJBLFoundation (S. Pellerin, M. Larocque). Access to the peatland was madepossible by Nature Conservancy of Canada, Québec. The authors wouldlike to thank E.R. Robert, A.-M. Girard-Cloutier, G. Magnan, H. Asnong,B. Fréchette, A. Lamarre and J.A. Rayburn for their technical and scientificcontributions. The English translation of the textwas revised byK. Grislis.Thoughtful comments from T. Corrège (Editor-in-Chief) and two anony-mous reviewers were greatly appreciated.

References

Appleby, P.G., 2004. Chronostratigraphic techniques in recent sediments. In: Last,W.M., Smol, J.P. (Eds.), Tracking Environmental Change Using Lake Sediments.Basin Analysis, Coring, and Chronological Techniques, vol. 1. Kluwer AcademicPublishers, Dordrecht, pp. 171–203.

Appleby, P.G., Oldfield, F., 1978. The calculation of lead-210 dates assuming a constantrate of supply of unsupported 210Pb to the sediment. Catena 5, 1–8.

Barber, K.E., Langdon, P.G., 2007. What drives the peat-based palaeoclimate record? Acritical test using multi-proxy climate records from northern Britain. QuaternaryScience Reviews 26, 3318–3327.

Bhiry, N., Filion, L., 2001. Analyse des macrorestes végétaux. In: Payette, S., Rochefort, L.(Eds.), Écologie des Tourbières du Québec-Labrador. Les Presses de l'UniversitéLaval, Québec, pp. 259–273.

Birks, H.J.B., 1977. Modern pollen rain and vegetation of the St. Elias Mountains, YukonTerritory. Canadian Journal of Botany 55, 2367–2382.

Booth, R.K., 2008. Testate ameobae as proxies for mean annual water-table depth inSphagnum-dominated peatlands of North America. Journal of Quaternary Science23, 43–57.

Booth, R.K., 2010. Testing the climate sensitivity of peat-based paleoclimatic reconstructionsin mid-continental North America. Quaternary Science Reviews 29, 720–731.

Booth, R.K., Sullivan, M., 2007. Key of Testate Amoebae Inhabiting Sphagnum-dominatedPeatlands with an Emphasis on Taxa Preserved in Holocene Sediments. LehighUniversity, Bethlehem.

Booth, R.K., Lamentowicz, M., Charman, D.J., 2010/11. Preparation and analysis of testateamoebae in peatland palaeoenvironmental studies. Mires and Peat 1–7 (Article 02).

Bouchard, A., Brisson, J., 1996. Domaine de l'érablière à Caryer cordiforme. In: Bérard, J.(Ed.), Manuel de Foresterie. Ordre des ingénieurs forestiers du Québec and Pressesde l'Université Laval, Québec, pp. 160–170.

Brisson, J., Bouchard, A., 2003. In the past two centuries, human activities have causedmajor changes in the tree species composition of southern Québec, Canada.Ecoscience 10, 236–246.

Brouillet, L., Coursol, F., Favreau, M., Anions, M., Bélisle, P., Desmet, P., 2011. VASCAN, labase de données des plantes vasculaires du Canada. Canadensys, Montréal (www.data.canadensys.net/vascan).

347M. Lavoie et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 386 (2013) 336–348

Bunting, M.J., Warner, B.G., 1999. Late Quaternary vegetation dynamics and hydroseraldevelopment in a shrub swamp in southern Ontario, Canada. Canadian Journal ofEarth Sciences 36, 1603–1616.

Carcaillet, C., Richard, P.J.H., 2000. Holocene changes in seasonal precipitationhighlighted by fire incidence in eastern Canada. Climate Dynamics 16, 549–559.

Carcaillet, C., Bouvier, M., Fréchette, B., Larouche, A.C., Richard, P.J.H., 2001. Comparisonof pollen-slide and seiving methods in lacustrine charcoal analyses for local andregional fire history. The Holocene 11, 467–476.

Charman, D.J., Hendon, D., Woodland, W.A., 2000. The identification of testate amoebae(Protozoa: Rhizopoda) in peats. Quaternary Research Association, Technical GuideNo. 9.

Charman, D.J., Barber, K.E., Blaauw, M., Langdon, P.G., Mauquoy, D., Daley, T.J., Hughes,P.D.M., Karofeld, E., 2009. Climate drivers for peatland palaeoclimate records.Quaternary Science Reviews 28, 1811–1819.

Chiverrell, K.D., 2001. A proxy of late Holocene climate change fromMay Moss, northeastEngland. Journal of Quaternary Science 16, 9–29.

Clark, J.S., Royall, P.D., Chumbley, C., 1996. The role of fire during climate changein an eastern deciduous forest at Devil's Bathbub, New York. Ecology 77,2148–2166.

Clymo, R.S., Turunen, J., Tolonen, K., 1998. Carbon accumulation in peatland. Oikos 81,368–388.

Environment Canada, 2010. Moyenne climatique de la station Hemmingford Four windsQuébec, 1961–2009. http://www.climate.weatheroffice.ec.gc.ca/climateData/dailydata.

Foster, D.R., Wright, H.E., 1990. Role of ecosystem development and climate change inbog formation in central Sweden. Ecology 71, 450–463.

Franzi, D.A., Rayburn, J.A., Knuepfer, P.L.K., Cronin, T.M., 2007. Late Quaternary historyof northeastern New York and adjacent parts of Vermont and Quebec. Guidebook,70th Annual reunion Northeast Friends of the Pleistocene.

Fréchette, B., de Vernal, A., 2013. Evidence for large-amplitude biome and climatechange in Atlantic Canada during the last interglacial and mid-Wisconsinan periods.Quaternary Research 79, 242–255.

Fréchette, B., de Vernal, A., Guiot, J., Wolfe, A.P., Miller, G.H., Fredskild, B., Kerwin, M.W.,Richard, P.J.H., 2008. Methodological basis for quantitative reconstruction of airtemperature and sunshine from pollen assemblages in Arctic Canada and Greenland.Quaternary Science Reviews 27, 1197–1216.

Gavin, D.G., Oswald, W.W., Wahl, E.R., Williams, J.W., 2003. A statistical approach toevaluating distance metrics and analog assignments for pollen records. QuaternaryResearch 60, 356–367.

Girard-Cloutier, A.-M., 2007. Reconstitution des étapes de développement de latourbière de la colline de Covey en Montérégie. B.Sc. Thesis Université Laval,Québec.

Heiri, O., Lotter, A.F., Lemcke, G., 2001. Loss on ignition as a method for estimatingorganic and carbonate content in sediments: reproducibility and comparability ofresults. Journal of Paleolimnology 25, 101–110.

Hendon, D., Charman, D.J., 1997. The preparation of testate amoebae (Protozoa:Rhizopoda) samples from peat. The Holocene 7, 199–205.

Hu, F.S., Davis, R.B., 1995. Postglacial development of a Maine bog and paleoenvironmentalimplications. Canadian Journal of Botany 73, 638–649.

Hughes, P.D.M., Blundell, A., Charman, D.J., Bartlett, S., Daniell, J.R.G., Wojatschke, A.,Cahmbers, F.M., 2006. An 8500 cal. year multi-proxy climate record from a bogin eastern Newfoundland: contributions of meltwater discharge and solar forcing.Quaternary Science Reviews 25, 1208–1227.

Jowsey, P.C., 1966. An improved peat sampler. New Phytologist 65, 245–248.Juggins, S., 2011. The C2 Program, Version 1.7.2. Newcastle University, Newcastle upon

Tyne, U.K.Lamarre, A., 2011. Développement d'une fonction de transfert au moyen des

thécamoebiens et reconstitution des conditions paléoenvironnementales holocènesd'une tourbière à palses, Kuujjuarapik, Québec nordique. M.Sc. Thesis Université duQuébec à Montréal, Montréal.

Lamarre, A., Garneau, M., Asnong, H., 2012. Holocene paleohydrological reconstructionand carbon accumulation of a permafrost peatland using testate amoebae andmacrofossil analyses, Kuujjuarapik, subarctic Quebec, Canada. Reviewof Palaeobotanyand Palynology 186, 131–141.

Larocque, M., Leroux, G., Madramootoo, C., Lapointe, F.J., Pellerin, S., Bonon, J., 2006.Mise en place d'un laboratoire naturel sur le mont Covey Hill (Québec, Canada).VertigO 17, 1–11.

Lavoie, M., Pellerin, S., 2011. Étude paléoécologique de la tourbière de la réserveécologique du Pin-Rigide. Research report presented to theMinistère duDéveloppementdurable, de l'Environnement et des Parcs du Québec.

Lavoie, M., Richard, P.J.H., 2000. Postglacial water-level changes of a small lake insouthern Québec, Canada. The Holocene 10, 621–634.

Lavoie, M., Pellerin, S., Larocque, M., 2011. Holocene dynamics of two temperatepeatlands: paleohydrological implications. Proceedings of the IAH-CNC conference,Québec City, Aug. 28–Sept. 1, 2011.

Lévesque, P.E.M., Dinel, H., Larouche, A., 1988. Guide Illustré des MacrofossilesVégétaux des Tourbières du Canada. Agriculture Canada, Publication #1817.

Levison, J.K., Larocque, M., Fournier, V., Gagné, S., Pellerin, S., Ouellet, M.A., 2013.Dynamics of a headwater system and peatland under current conditions andwith climate change. Hydrological Processes (in press).

Loewen, B., Chapdeleine, C., Richard, P.J.H., 2005. Holocene shoreline occupations andwater-level changes at Lac Mégantic, Québec. Canadian Journal of Archaeology29, 267–288.

Loisel, J., Garneau, M., 2010. Late Holocene paleoecohydrology and carbon accumula-tion estimates from two boreal peat bogs in eastern Canada: Potential and limitsof multi-proxy archives. Palaeogeography, Palaeoclimatology, Palaeoecology 291,493–533.

Maenza-Gmelch, T.E., 1997. Vegetation, climate, and fire during the late-glacial-Holocenetransition at Spruce Pond, Hudson Highlands, southeastern New York, USA. Journal ofQuaternary Science 12, 15–24.

Meilleur, A., Bouchard, A., Bergeron, Y., 1994. The relation between geomorphologyand forest community types of the Haut-Saint-Laurent, Quebec. Vegetatio 111,173–192.

Montague, T.G., Givnish, T.J., 1996. Distribution of black spruce versus eastern larchalong peatland gradients: relationship to relative stature, growth rate, and shadetolerance. Canadian Journal of Botany 74, 1514–1532.

Montgomery, F.H., 1977. Seeds and Fruits of Plants of Eastern Canada and NortheasternUnited States. University of Toronto Press, Toronto.

Morris, P.J., Belyea, L.R., Baird, A.J., 2011. Ecohydrological feedbacks in peatlanddevelopment: a theoretical modelling study. Journal of Ecology 99, 1190–1201.

Muller, S.D., Richard, P.J.H., Guiot, J., de Beaulieu, J.-L., Fortin, D., 2003. Postglacialclimate in the St. Lawrence lowlands, southern Québec: pollen and lake-levelevidence. Palaeogeography, Palaeoclimatology, Palaeoecology 193, 51–72.

Mullins, H.T., Patterson, W.P., Teece, M.A., Burnett, A.W., 2011. Holocene climate andenvironmental change in central New York (USA). Journal of Paleolimnology 45,243–256.

Munroe, J.S., 2012. Lacustrine records of post-glacial environmental change from theNulhegan Basin, Vermont, USA. Journal of Quaternary Science 27, 639–648.

New, M., Lister, D., Hulme, M., Makin, I., 2002. A high-resolution data set of surfaceclimate over global land areas. Climate Research 21, 1–25.

Occhietti, S., Richard, P.J.H., 2003. Effet réservoir sur les ages 14C de laMer de Champlain àla transition Pléistocène–Holocène: révision de la chronologie de la déglaciation auQuébec méridional. Géographie Physique et Quaternaire 57, 115–138.

Ohlson, M., Tryterud, E., 2000. Interpretation of the charcoal record in forest soils:forest fires and their production and deposition of macroscopic charcoal. The Holocene10, 519–525.

Overpeck, J.T., Webb III, T., Prentice, I.C., 1985. Quantitative interpretation of fossilpollen spectra: dissimilarity coefficients and the method of modern analogs.Quaternary Research 23, 87–108.

Payette, S., Rochefort, L., 2001. Écologie des tourbières du Québec-Labrador. Les Pressesde l'Université Laval, Québec.

Payne, R.J., Mitchell, E.A.D., 2009. How many is enough? Determining optimal counttotals for ecological and palaeoecological studies of testate amoebae. Journal ofPaleolimnology 42, 483–495.

Pellerin, S., Larocque, M., Lavoie, M., 2007. Rôle hydrologique et écologique régional dela tourbière de Covey Hill. Research report presented to the EJLB Foundation.

Pellerin, S., Lagneau, A., Lavoie, M., Larocque, M., 2009. Environmental factors explainingthe vegetation patterns in a temperate peatland. Comptes Rendus Biologies 332,720–731.

Prentice, I.C., 1980. Multidimensional scaling as a research tool in Quaternarypalynology: a review of theory andmethods. Review of Palaeobotany and Palynology31, 71–104.

Rayburn, J.A., Knuepfer, P.L.K., Franzi, D.A., 2005. A series of large, Late Wisconsinanmeltwater floods through the Champlain and Hudson Valleys, New York State,USA. Quaternary Science Reviews 24, 2410–2419.

Rayburn, J.A., Franzi, D.A., Knuepfer, P.L.K., 2007. Evidence from the lake ChamplainValley for a later onset of the Champlain Sea and implications for late glacial meltwaterrouting to the North Atlantic. Palaeogeography, Palaeoclimatology, Palaeoecology 246,62–74.

Rayburn, J.A., Cronin, T.M., Franzi, D.A., Knuepfer, P.L.K., Willard, D.A., 2011. Timing andduration of North American glacial lake discharges and the Younger Dryas climatereversal. Quaternary Research 75, 541–551.

Reimer, P.J., Baillie, M.G.L., Bard, E., Bayliss, A., Beck, J.W., Blackwell, P.G., Bronk Ramsey,C., Buck, C.E., Burr, G.S., Edwards, R.L., Friedrich, M., Grootes, P.M., Guilderson, T.P.,Hajdas, I., Heaton, T.J., Hogg, A.G., Hughen, K.A., Kaiser, K.F., Kromer, B., McCormac,F.G., Manning, S.W., Reimer, R.W., Richards, D.A., Southon, J.R., Talamo, S., Turney,C.S.M., van der Plicht, J., Weyhenmeyer, C.E., 2009. IntCal09 and Marine09radiocarbon age calibration curves, 0–50,000 years cal BP. Radiocarbon 51,1111–1150.

Richard, P.J.H., 1994. Wisconsinan Late-glacial environmental change in Québec:a regional synthesis. Journal of Quaternary Science 9, 165–170.

Richard, P.J.H., Occhietti, S., 2005. 14C chronology for ice retreat and inception ofChamplain Sea in the St. Lawrence Lowlands, Canada. Quaternary Research 63,353–358.

Rosa, É., Larocque, M., Pellerin, S., Gagné, S., Fournier, B., 2009. Determining thenumber of manual measurements required to improve peat thickness estima-tions by ground penetrating radar. Earth Surface Processes and Landforms 34,377–383.

Rowe, J.S., 1972. Forest Regions of Canada. Fisheries and Environment Canada, CanadianForest Service, Ottawa.

Stuiver, M., Reimer, P.J., 1993. Extended 14C database and revised CALIB radiocarboncalibration program. Radiocarbon 35, 315–330.

Swindles, G.T., Morris, P.J., Baird, A.J., Blaauw, M., Plunkett, G., 2012. Ecohydrologicalfeedbacks confound peat-based climate reconstruction. Geophysical Research Letters39, L11401.

Telford, R.J., Heegaard, E., Birks, H.J.B., 2004. All age-depth models are wrong: but howbadly? Quaternary Science Reviews 23, 1–5.

Thormann, M.N., Currah, R.S., Bayley, S.E., 1999. The mycorrhizal status of the dominantvegetation along a peatland gradient in southern boreal Alberta, Canada. Wetlands19, 438–450.

Tremblay, T., 2008. Hydrostratigraphie et géologie du Quaternaire dans le basin-versantde la rivière Châteauguay, Québec. M.Sc. Thesis Université du Québec à Montréal,Montréal.

348 M. Lavoie et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 386 (2013) 336–348

Tremblay, T., Nastev, M., Lamothe, M., 2010. Grid-based hydrostratigraphic 3D modellingof the Quaternary sequence in the Châteauguay River watershed, Quebec. CanadianWater Resources Journal 35, 377–398.

Vorren, K.D., Eldegard Jensen, C., Nilssen, E., 2012. Climate changes during the last c.7500 years as recorded by the degree of peat humification in the Lofoten region,Norway. Boreas 41, 13–30.

Whitmore, J., Gajewski, K., Sawada, M., Williams, J.W., Shuman, B., Bartlein, P.J., Minckley, T.,Viau, A.E., Webb III, T., Shafer, S., Anderson, P., Brubaker, L., 2005. Modern pollen data

from North America and Greenland for multiscale paleoenvironmental applications.Quaternary Science Reviews 24, 1828–1848.

Yu, Z., Campbell, I.D., Campbell, C., Vitt, D.H., Bond, G.C., Apps, M.J., 2003. Carbonsequestration in western Canadian peat highly sensitive to Holocene wet-dry climatecycles at millennial timescales. The Holocene 13, 801–808.