Peatland development in relation to Holocene climatic change in Manitoba and Saskatchewan (Canada)

P. KUHRY, L. A. HALSEY, S. E. BAYLEY, AND D. H. VITT Department of Botany, University of Alberta, Edmonton, Alta., Canada T6G 2E9

Received April 30, 1991 Revision accepted December 16, 1991

Two peat cores from the southern boreal forest in south-central Manitoba and central Saskatchewan (Canada) were analyzed for microfossils, macrofossils, and physicochemical properties. Regional vegetation and local peatland development at these sites show the influence of warm and dry climatic conditions during the middle Holocene. Pollen assemblages at the base of the Manitoba site indicate the presence of grassland -parkland vegetation in the area prior to 4230 BP. At the Saskatchewan site, boreal forest was present throughout the development of the peatland from before 5020 BP to present. Both the Manitoba and Saskatchewan records suggest a more open - deciduous character of the regional vegetation cover during the middle Holocene in the southernmost part of the expanding boreal forest, in comparison with the modern southern mixed-wood boreal forest. The presence of a Typha latifolia-dominated marsh phase in the initial stages of development of both peatlands is indicative of marked water level fluctuations, likely due to frequent and severe periods of drought. Highest accumulation rates (1.24 mm peatla, and 69 g carbon/(m2 . a)) occur in the forested fen phase (4290-3710 BP) of the Saskatchewan site. Low accumulation rates (0.24 mm peatla, and 12 g carbon/(m2 . a)) in the bog phase (3710-960 BP) at this site are proba- bly due to interruption of peat deposition or even surficial erosion of the deposits. Accumulation rates at the Manitoba site (4230-0 BP) are less variable, ranging from 0.30 to 0.82 mm peatla and from 19 to 28 g carbon/(m2. a). Changes in accumulation rates at the Saskatchewan and Manitoba sites are not synchronous in spite of similarities in general development, indicating that, in addition to climate, local factors have played roles in the developmental histories of these peatlands.

Deux carottes de tourbe prtlevCes dans la partie mkridionale de la forst borCale, une dans le sud-centre du Manitoba et l'autre dans le centre de la Saskatchewan (Canada), ont CtC analyskes pour leur contenu en microfossiles, macrofossiles et leurs propriCtCs physico-chimiques. La vCgttation rCgionale et le dCveloppement des tourbikres locales dans ces rkgions reflk- tent l'influence de conditions climatiques chaudes et sbches durant I'Holockne moyen. Les assemblages de pollens i la base du site manitobain indiquent que, anterieurement i 4230 ans Av.P., la vCgCtation Ctait de type prairies - prairie-parc. Sur le site de la Saskatchewan, la forst borCale est prCsente tout au long du dCveloppement de la tourb2re depuis plus de 5020 ans Av.P. jusqu'h nos jours. Les donnCes obtenues pour les sites du Manitoba et de la Saskatchewan suggkrent que la vCgCtation rtgionale dans la partie la plus mkridionale de la forst borCale qui grandissait durant 1'Holockne moyen Ctait une forst plus dicidue et probablement plus ouverte que la forst boreale mixte actuellement prBsente au sud. La prCsence d'une phase markcageuse dominte par le Typha latifolia durant les stades initiaux de dBveloppement des tourbikres rCvble d'importantes fluctuations des niveaux d'eau certainement causCes par de frkquentes pCriodes de grandes ~Ccheresses. Les taux d'accumula- tion les plus ClevCs (1,24 mm de tourbela et 69 g de carbone/(m2 . a)) ont exist6 durant la phase de tourbikre basse boiste (4290-3710 ans Av.P.) au site de la Saskatchewan. Les faibles taux d'accumulation (0,24 mm de tourbela et 12 g de car- bone/(m2. a)) durant la phase de tourbikre ombrotrophe (3710-960 ans Av.P.) sur ce m&me site sont probablement le rCsultat d'une interruption de dtp6t de tourbe ou encore d'une Crosion h la surface des dCp6ts. Les taux d'accumulation au site rnanitobain (4230-0 ans Av.P.) sont plus constants : ils varient seulement de 0,30 h 0,82 rnm de tourbela et de 19 h 28 g de carbone/(m2 . a). Les changements dans les taux d'accumulation aux sites de la Saskatchewan et du Manitoba ne sont pas synchrones, en dCpit de certaines similitudes de leur dCveloppement gCnBral, ce qui rkvble que, en plus du climat, d'autres facteurs locaux ont influencC les histoires du dCveloppement de ces terrains tourbeux.

[Traduit par la rCdaction] Can. J . Earth Sci. 29, 1070-1090 (1992)

Introduction This paper presents detailed microfossil, macrofossil, and

physicochemical data on the developmental histories of two peatlands, one in south-central Manitoba and one in central Saskatchewan (Fig. 1, sites 1 and 2). Special attention is paid to the effects that a middle Holocene warm and dry climate had on wetland distribution and development and on peat accumulation rate.

Most paleoecological studies in the western interior of Canada have focused on regional vegetation history and lake develop- ment. Regional vegetation development has been reconstructed on the basis of palynological analyses of sediments from mostly small lake basins. Comprehensive overviews of the available data are presented by Ritchie (1976, 1985). One of the more noticeable events is the northward expansion of the grassland and parkland - boreal forest ecotone during the early- middle Holocene, which has been ascribed to increases in summer temperatures of up to 2°C (Ritchie 1976, 1987).

Extensive paleoecological studies of lake development have been conducted in Alberta. The results of these studies, which are based mainly on pollen and diatom analyses, are summa- rized by Schweger and Hickrnan (1989). The influence of warmer and drier conditions in the past is reflected in late flooding dates, lower water levels, and increased salinity in lake basins of central Alberta. Papers by Teller and Last (1981, 1982) have dealt with Holocene water level fluctuations of Lake Manitoba, as determined by sedimentological analyses. They concluded that the lake dried several times during the early -middle Holocene as a result of warmer and drier climatic conditions and differential crustal rebound of the basin.

Few papers have been published that focus on peatland development in the boreal region of western Canada. Detailed peat macrofossil studies that document local peatland vegeta- tion development were made by Zoltai and Johnson (1985) and Kubiw et al. (1989) in the foothills of the Rocky Mountains in western Alberta, and by Nicholson and Vitt (1990) and Kubiw

Printed in Canada / Imprim6 au Canada

Can

. J. E

arth

Sci

. Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

199.

201.

121.

12 o

n 06

/04/

13Fo

r pe

rson

al u

se o

nly.

KUHRY ET AL.

Ecoclimatic regions :

0 arctic

subarctic

boreal

transitional grassland (parkland)

grasslands

boreal southern Cordilleran (foothills)

mountain

FIG. 1. Map of the ecoclimatic-forest regions in the western interior of Canada (adapted from Rowe 1972 and Ecoregions Working Group 1989), showing the location of study sites. 1, Gypsurnville bog (this paper); 2, La Ronge bog (this paper); 3, Porcupine Mountain peatland (Nichols 1969); 4, Lynn Lake peatland (Nichols 1967); 5, Beauval bog (Vitt and Kuhry, in press); 6, Watharnan Lake bog (P. Kuhry, unpub- lished); 7, Buffalo Narrows bog (P. Kuhry, unpublished); 8, Elk Island Bog (Vance 1979); 9, Mariana Lakes peatland (Nicholson and Vitt 1990); 10, Riding Mountain site (Ritchie 1987); 11, Grand Rapids site (Ritchie and Hadden 1975); 12, Lake B site (Mott 1973); 13, Cycloid Lake site (Mott 1973); 14, Lake Manitoba (Teller and Last 1981).

et al. (1989) in the boreal forest of eastern Alberta. Papers on peat deposits by Mott and Jackson (1982) in the foothills of Alberta and by Nichols (1967, 1969) in the boreal region of Manitoba focused on regional vegetation development. These mainly palynological studies provide some information on the macrofossil content of the peat.

Zoltai and Vitt (1990) presented data on the age and distri- bution of peat deposits in Alberta, Saskatchewan, and Manitoba. They showed that peatlands in the southern part of the boreal

region, roughly south of 54"301N latitude, and in a narrow corridor along the foothills, roughly east of 1 15"001W longi- tude, started to develop only after 6000 BP. To the north and west of these lines peatlands are, in the majority of cases, older than 6000 BP. The delayed development of peatlands in the south was ascribed to warm and dry conditions during the early and middle Holocene, with summer temperatures up to 1 "C higher than today. Several papers have been published dealing with peat accumulation rates in the western interior of

Can

. J. E

arth

Sci

. Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

199.

201.

121.

12 o

n 06

/04/

13Fo

r pe

rson

al u

se o

nly.

1072 CAN. 1. EARTH SCI. VOL. 29, 1992

Canada (Ovenden 1990; Zoltai 1991). Peat and carbon accumu- lation rates vary depending on peatland type (fens vs. bogs) and ecoclimatic region (boreal vs. subarctic). These papers, like the one by Zoltai and Vitt (1990), do not include detailed data on vegetation succession in individual peatlands. Data on the age, geographical location, and peat accumulation rates from the two peatlands presented in this paper will be compared with results from these more general treatments.

Our peatland developmental studies are directed toward an integration of available information concerning paleoenviron- mental change in the western interior of Canada. Results are compared with published data from the same area on peatland development (Nichols 1967, 1969), regional vegetation history (Nichols 1969; Mott 1973; Ritchie and Hadden 1975; Ritchie 1987), and lake level fluctuations (Teller and Last 1981).

Classification and distribution of wetlands in the western interior of Canada

Wetlands cover approximately 46 x lo6 ha or 26% of Alberta, Saskatchewan, and Manitoba (Zoltai 1988). The Cana- dian wetland classification system distinguishes five wetland types, mainly based on physicochemical properties (Zoltai 1988). Areas of shallow, open water are truly aquatic systems. Floating rooted aquatic macrophytes may be present but emer- gents are absent. Swamps and marshes are eutrophic ecosystems that do not accumulate thick deposits of peat (<40 cm of depth). They are characterized by hlgh seasonal water level fluc- tuations. Waters are slightly acidic -circumneutral to alkaline. Swamps are characterized by a well-developed tree or shrub layer, while marshes are dominated by emergents such as Typha, Cyperaceae, and other monocots. Both lack a moss-dominated ground layer. Mesotrophic -01igotrophic fens and oligotrophic bogs are wetlands that accumulate substantial amounts of peat ( > 40 cm of depth); thus they are peatlands. They have a well- developed ground layer dominated by mosses. Fens are minero- trophic peatlands, as they are in contact with groundwater. They have been subdivided into two categories based on vege- tation, each with distinctive surface water chemistry (Sjors 1950). Rich fens (pH > 5.5) are characterized by brown mosses, while poor fens (pH 4.0 - 5.5) are dominated by Sphagnum. Bogs are unique ecosystems that develop when ombrotrophic conditions exist, which means that all available water and nutrients are derived from precipitation. As a result, pH is lower than 4.5, and values of 3.0 -4.0 are common. Sphagnum spp. are the dominant mosses (Zoltai 1988).

Two main wetland regions can be distinguished in Alberta, Saskatchewan, and Manitoba. In the southern part, correspond- ing to the grassland-parkland ecoclimatic region, marshes and shallow eutrophic freshwater and saline ponds are preva- lent (Adams 1988). In the northern part, the boreal ecoregion, marshes are rare except on floodplains and deltas. Boreal shore-marshes along the margins of lakes and ponds that are subject to high seasonal water level fluctuations often have a patchy ground layer of brown mosses (Zoltai 1988), which distinguishes them from more southern marshes. Peatlands are almost exclusively found in the boreal, boreal southern cor- dilleran, and subarctic ecoclimatic regions (Zoltai 1988; Zoltai and Vitt 1990).

regional water table, excluding such local factors as damming (e'g, by beavers). A general survey of the local vegetation cover at each study site was made by visually estimating total cover- age of plant taxa for different vegetation layers in the peatland, which normally included the tree layer, shrub layer, herb layer, and ground layer. Conductivity and pH of the surface water were measured, using Merck Acilit and Neutralit pH paper, a Beckman 10 pH meter, and a type CDM 2e Copenhagen Radio- meter conductivity meter. Electric conductivity at 20°C was corrected for hydrogen ions (Sjors 1950). Peatlands were sur- veyed with a metal probe to find the deepest parts. Cores were taken with a 5 cm diameter, modified ~ a c a u l a ~ peat sampler. Coring was continued until mineral sediment was reached. After a field description, the material was stored in a half section of a 2 m long PVC pipe and wrapped with cellulose acetate for transportation.

In the laboratory, detailed stratigraphic descriptions were made. Known volumes of material-for physicochemical (4- 6 cm3), microfossil (0.5 - 3 cm3), and macrofossil (4 -6 cm3) analyses were taken with different-sized cork borers over a depth of 2-3 cm at regular intervals of 10 cm (except for the lowermost part of the cores). Samples for physicochemical analysis were dried and weighed to determine bulk density (expressed as g/cm3 of dry weight). Subsamples were taken for loss on ignition at 550°C (expressed as percent of dry weight). Subsamples of the lowermost part of the core were also ignited at 950°C to estimate the carbonate content of the mineral component of the deposit (Dean 1974). Carbon and nitrogen content (expressed as percent of dry weight) were calculated by igniting 2-3 mg subsamples at 975OC in a Controlled Equipment Corporation model 440 elemental analyzer.

For the preparation of microfossil slides, tablets with exotic Eucalyptus pollen (stock no. 106720, University of Lund, Sweden) were added at the beginning of the sample treatment. Tablets were dissolved in a 10% aqueous HC1 solution. Peat samples were treated with a boiling 10% aqueous KOH solution for deflocculation, followed by acetolysis. Basal samples con- taining a substantial amount of clay and sand were treated with a hot 10% Na4P207. 10H20 solution for deflocculation, followed by acetolysis and gravity separation with a bromo- form - alcohol mixture (specific gravity = 2). Residues were mounted on slides in glycerol jelly and sealed with paraffin. Pollen counting continued until the total of pollen sum ele- ments was at least 200 pollen grains (normally 250 -300). The pollen sum includes forest and grassland taxa that are well represented in the regional pollen-rain of the boreal, parkland, and grassland ecoregions (Lichti-Federovich and Ritchie 1968; Ritchie 1987). Some of these elements (e.g., Picea, Betula, Salix, and Gramineae), however, can be present in local wetland vegetation. Aquatic, marsh, fen, and bog pollen taxa, which are abundant only when present in the local wet- land vegetation, are excluded from- the pollen sum. These include Potamogeton, Typha latifolia, Cyperaceae, and Erica- ceae. Some fungal, algal, and animal microfossil types have been included inthe m&rofossil diagrams. Studies on European peat deposits have shown that these taxa indicate local condi- tions (e.g., Van Geel 1978; Van Geel et al . 1989). Frequen- cies of pollen, fern, moss, fungal, and algal spores, and other microfossils are expressed as percentages of the pollen sum.

Materials and methods A rough estimate of the abundance of fungal hyphae was Peatlands that did not form part of any major drainage system obtained by multiplying the estimated mean cover of hyphae

were chosen in order to have sites where peatland formation on the slide with the number of lines counted ( X 100) and and development were largely controlled by fluctuations in the dividing this by the pollen sum counted. Pollen concentrations

Can

. J. E

arth

Sci

. Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

199.

201.

121.

12 o

n 06

/04/

13Fo

r pe

rson

al u

se o

nly.

KUHRY ET AL. 1073

are given for the pollen sum total and for Picea, and are expressed as pollen grains/cm3. Influx curves are not pre- sented for the pollen sum total or Picea because such curves assume that the sedimentation rate between radiocarbon-dated horizons is constant. This assumption is doubtful in view of the highly variable sedimentation rates in peat sequences, as shown by results presented in this paper (see especially the La Ronge site). Instead, a mean pollen influx of Picea was calcu- lated for each radiocarbon-dated interval, and is expressed as pollen grains/(cm2 a).

Samples for macrofossil analysis were treated with a gently boiling 5% aqueous KOH solution for deflocculation, and subsequently cleaned of fine debris by rinsing through a 150 pm sieve. Each macrofossil sample was subdivided into convenient subsamples for analysis in a petri dish under a dis- secting microscope. Macrofossils were counted and expressed as numbers15 cm3 of material (e.g., seeds, twigs), or alterna- tively assessed as volume percentages of the sample used (e.g., epidermal remains, mosses). The total "macrofossil abundance" in each sample was calculated by first estimating, for each sub- sample, the cover percentage of the total macrofossil assemblage on the petri dish. By then summing the macrofossil cover esti- mates of all subsamples, a total cover was obtained for the entire sample. This total was recalculated on the basis of a constant sample volume of 5 cm3, and expressed as a percen- tage of the estimated total macrofossil cover of the top sample. In this way, samples with a lower total content of macrofossils compared with the top sample show a macrofossil abundance of less than 100%, while samples with a higher total content have abundances of more than 100 % . One of the main problems in expressing frequencies of mosses and plant tissue remains as volume percentages is that the percentage representation of a few remains in a sample that mostly passed through the 150 pm screen can be as high as that of many remains in a sample with a large total amount of macrofossils. Macrofossil abundance gives a semiquantitative estimate of the total amount of macrofossils in a sample, making the interpretation of volume percentages easier. At the peat-mineral sediment tran- sition, macrofossil abundance becomes low as a result of the high minerogenic content of the samples and, commonly, the extensive decomposition of the organic material. Within the peat deposit, macrofossil abundance is a measure of peat decomposition and compaction. Samples from only slightly decomposed and highly compacted parts of the peat deposit show a higher macrofossil abundance than the top sample.

Estimates of "decomposition" are based on the moss com- ponent of the macrofossils, where present. The decomposition curve gives a reciprocal value of the hierarchical preservation classes defined by Janssens (1983); "0" indicates almost intact moss plants, while "5" indicates the presence of detached, poorly preserved moss leaves.

Bulk organic samples for radiocarbon dating were taken at important transitional levels, after the general sequence of macrofossils was established. Samples were pretreated with HC1 to remove any carbonate contaminants and dated at the Alberta Environmental Centre in Vegreville.

For each section, analytical results are presented in three diagrams, a macrofossil diagram, a microfossil diagram, and a physicochemical diagram. Diagrams were drawn with the aid of the "MacPollen" computer program designed by Eisner and Sprague (1987). A subdivision made by visual inspection of the macrofossil diagram was applied to all diagrams of each core. Changes in macrofossil assemblages correlate well with those observed in the microfossil record.

Our reconstructions of peatland development are mainly based on the autecology of mosses (Gignac et al. 1991; J. A. Janssens, unpublished') and vascular plant taxa (Jeglum 1971) recog- nized in the macrofossil records. Local microfossil taxa provide additional evidence. Information regarding regional vegeta- tion development is used to place local peatland development in the context of regional ecoclimatic changes.

Gypsumville bog Description of the site

The peatland is located in south-central Manitoba (Fig. 1, site I), about 9 km east of Gypsumville (Fig. 2). Bedrock in the area is composed of Paleozoic carbonate rocks (Norris et al . 1982). The Laurentide ice sheet retreated from south- central Manitoba between 11 000 BP and 10 000 BP (Dyke and Prest 1987). Surficial deposits include glaciolacustrine clays of glacial Lake Agassiz, which drained from this area around 8000 BP (Lowden et al. 1977; Klassen 1983).

The area is located in the subhumid low-boreal ecoclimatic region of Canada, 15 krn southwest of the mid-boreal region and 75 km northeast of the transitional grassland (parkland) region (Ecoregions Working Group 1989). Climatic variables at Gypsumville for 195 1 - 1980 are given in Fig. 3. Growing degree days ( > 5°C) are 1508. The average frost-free period is 102 days (Canadian Climate Program 1982). According to Rowe (1972), the area is situated within the Manitoba lowlands forest region. Picea glauca and Populus spp., with some Abies balsamea and Betula papyrifera, are prominent on well-drained land. Pinus banksiana and Populus tremuloides are abundant on low ridges, along with Quercus macrocarpa to the south. In poorly drained areas Picea mariana and Larix laricina are dominant. To the south, in the transitional grassland (park- land) region (the Aspen -Oak forest region according to Rowe 1972), boreal conifers are absent, and Populus spp. and Quercus macrocarpa are the dominant tree taxa.

The Gypsumville peatland is a forested bog that occupies an area of approximately 5 km2. The stunted arboreal layer ( < 7 m in height) covers about 25 % of the peatland surface and is composed of Picea mariana (15 %) and Larix laricina (10%). The latter tree is not a typical ombrotrophic bog spe- cies (Ritchie 1987). The shrub layer is dominated by Ledum groenlandicum (coverage of up to 75 9%) and Chamaedaphne calyculata. A microrelief of hummocks and hollows is present, with height differences of up to 30 cm. Vaccinium vitis-idaea, Oxycoccus microcarpus, Rubus chamaemorus, and Sphagnum &scum are dominant on the hummocks, whereas Eriophorum sp., Pleurozium schreberi, Polytrichum cf. strictum, and Cladonia spp. are prominent in hollows. The cover of mosses is high ( > 75 %). The surface water has a pH of 4.1, and a cor- rected conductivity of 2 1 ps.

Peat core analyses and results A core was collected in the central area of the northern part

of the peatland (Fig. 2), from a hummock dominated by Ledum groenlandicum and Sphagnum &scum. The core had a length of 250 cm, including 9 cm of sticky grey-blue, glaciolacustrine clay containing some sand and gravel at the base. Ignition at

'J. A. Janssens. 1989. Ecology of peatland bryophytes and paleo- environmental reconstruction of peatlands using fossil bryophytes. Summary. Unpublished manuscript available from author (Depart- ment of Ecology, Evolution, and Behavior, University of Minnesota, 208 Zoology Building, 318 Church Street S.E., Minneapolis, Minn. 55455, U.S.A.).

Can

. J. E

arth

Sci

. Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

199.

201.

121.

12 o

n 06

/04/

13Fo

r pe

rson

al u

se o

nly.

CAN. 1. EARTH SCI. VOL. 29, 1992

98p30' W

W J J - z 5 3 "l" a N > 0

0 0 5 l k m l a 1

e l e v a t i o n -8z5' in f e e t

LAKE ST. M - l a k e

w e t l a n d

c o r i n g s i

FIG. 2. Location of Gypsumville bog in south-central Manitoba. 1 ft = 0.305 m.

950°C of the basal mineral samples produced no additional weight loss, and these samples showed no reaction to HC1 treat- ment. Three samples have been radiocarbon dated (Table 1). A detailed stratigraphic column and radiocarbon dates are given to the left of Figs. 4-6.

Local vegetation development Four phases are recognized in the developmental history of

Gypsumville bog (Figs. 4, 5): Phase A (250-220 cm) includes the mineral sediment - peat transition. Local peat accumulation started at about 4230 BP. This phase is charac- terized by the presence of macrofossils of such aquatic plants as Potamogeton, Sagittaria, and algae (including Chara and Cyanophyta), and the emergents Typha latifolia and Carex spp. Remains of Cladocera and Insectae, and siliceous sponge cysts (and sponge spicules in the microfossil record) are abun- dant. Mosses are rare, with the exception of some Sphagnum wamstorfii in the lowermost part of the phase at the mineral sediment - peat transition (note low macrofossil abundance). This seems to suggest that mesotrophic conditions suitable for the growth of this moss prevailed at the earliest stages of flood- ing of the depression. Later, a shallow pond with emergent, shore-marsh vegetation developed. Conditions were eutrophic, and waters circumneutral.

In phase B (220- 150 cm), which lasted until shortly prior to 1790 BP, Betula and Carex spp. macrofossils are found. The brown mosses Calliergon giganteum, Drepanocladus aduncus, and Campylium stellatum become abundant in the macrofossil record. Remains of Cladocera, Coleoptera, and Acaridae are found throughout the phase. The autecology of mosses indicates wet local conditions (water table at 3 - 16 cm depth), and a pH between 6.5 and 7.0. The local vegetation type is best described as an open, wet, rich fen. In the middle

part of the phase B (190- 160 cm, starting at ca. 2710 BP) a temporary reversal to marsh conditions is apparent, with pollen of Typha latifolia becoming more prominent and mosses declining in abundance.

In phase C (150- 140 cm) needles of Larix lan'cina and coniferous bark remains are found. Carex spp. remains are less abundant than in phase B, while leaf remains of Ledum are prominent. The wet, rich fen mosses of phase B are replaced by Sphagnum warnstorfii, Tomenthypnum nitens, and Aulacomnium palustre. Phase C represents a short period of rapid change. The fen became forested. The autecology of mosses indicates that local conditions became drier and gradually more oligo- trophic, which is substantiated by the appearance of fungal hyphae and the rhizopods Assulina and Amphitrema in the microfossil record (Van Gee1 et al. 1989). This rapid change in the local peatland ecosystem coincided with developments in the surrounding regional vegetation, indicated especially by the increased representation of pollen of Populus.

Phase D (140-0 cm) spans approximately the last 1790 radiocarbon years. Picea needles and coniferous bark remains are abundant, as are macrofossils (and pollen) of Ericaceae. Acaridae remains are common. Sphagnumfuscum is the dom- inant moss, indicating acidic (pH 4.0-4.5) and dry (water at 20-35 cm depth) conditions. Dry local conditions are cor- roborated by the abundance of fungi and the almost complete absence of algae in the microfossil record. In general terms, the local vegetation can be best described as an ombrotrophic forested bog.

Increased pollen percentages of Chenopodiaceae and Ambrosia in the uppermost 50 cm of the peat deposit indicate distur- bances in the extralocal vegetation, possibly as a result of fire and (or) anthropogenic influence. The presence of Cerealia and Brassica pollen in the uppermost 20 cm points to agricul-

Can

. J. E

arth

Sci

. Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

199.

201.

121.

12 o

n 06

/04/

13Fo

r pe

rson

al u

se o

nly.

KUHRY ET AL. 1075

WEATHER STATION: Gypsurnville . (Man.) ALTITUDE: 265 m. COORD.: 51°40'N; 98'44'W ECOCLlMATlC REGION: Subhumid Low-Boreal MEAN ANNUAL TEMPERATURE: +0.7*C MEAN ANNUAL PRECIPITATION: 418 mm

FIG. 3. Climate diagram for Gypsumville, Manitoba, 1951 - 1980 (Canadian Climate Program 1982).

turd activities in the area. These changes coincided with some changes in the local peatland ecosystem. The presence of the rhizopod Hyalosphenia in the microfossil record is of note. According to Van Gee1 (1978), this rhizopod indicates serious disturbance in the development of peatlands. The occurrence of needles and the increased representation of pollen of Lurix laricina in the top sample suggest that this tree taxon reappeared only recently on the peatland surface, where it is found today. The presence of Lurix laricina suggests the development of more minerotrophic conditions in the peatland, as it is abun- dant in fens but rare in ombrotrophic bogs (Ritchie 1987).

Regional vegetation development Pollen assemblages in phase A, especially the lower and

middle part, can be compared with recent pollen spectra from small lakes in the western interior of Canada. The Gypsumville macrofossil data indicate the local presence of open water dur- ing that period. The pollen spectrum from the grey-blue clay below the peat deposit shows high percentages (total of about 75%) of Gramineae, Artemisia, Ambrosia, Chenopodiaceae, and Compositae tubuliforae. These taxa are lacking in the macrofossil record (Figs. 4, 5), and most probably derive from regional grassland -parkland vegetation that existed sometime before the peat started to accumulate (prior to 4230 BP). When peatland development began, boreal conifers were present in the surrounding area, as indicated by the presence of a Picea needle and coniferous bark at the base of the peat. However, pollen assemblages of the middle part of phase A resemble most closely recent pollen spectra from the parkland ecoregion (Lichti-Federovich and Ritchie 1968; Ritchie 1987). Picea values are less than lo%, whereas grassland-parkland pollen

TABLE 1. Radiocarbon dates for Gypsumville bog, Manitoba

Laboratory Depth Sample Date number (cm) material (years BP)

AECV 1082C 137-155 Peat 1790 f 90 AECV 1081C 177-195 Peat 2710 f 100 AECV 1031C 232-239 Peat. 4230 + 100

reach percentages of up to 20%. Regional vegetation is therefore best described as an open woodland in which Picea was less abundant than in the modern southern mixed-wood boreal forest. Mean pollen influx of Picea, calculated for the dif- ferent radiocarbon-dated intervals, seems to support this state- ment. Between 4230 BP and 2710 BP <200 Picea pollen grains/(cm2 . a) were deposited on average, while after 2710 BP >200 grains/(cm2 . a) were deposited. However, care has to be taken when interpreting pollen percentages and pollen influx in these continental peat deposits. For instance, the per- centage and pollen influx increase of Picea pollen toward the top of the Gypsumville record can be partly due to the local appearance of this tree on the peatland surface. In general, pollen assemblages derived from fen and bog deposits cannot be compared directly with the recent pollen rain at small lake sites because of different depositional environments, local pollen production, and discontinuous peat sequences (see also La Ronge site).

Accumulation rates Mean values for the accumulation of peat, dry weight, organic

content, carbon content, nitrogen content, and C/N ratio were calculated for the different radiocarbon-dated intervals and for the entire peat deposit, based on the results of the physico- chemical analyses (Fig. 6, Table 2). These radiocarbon-dated intervals correspond to the upper part of phase A and the lower part of phase B (pond to fen), the upper part of phase B and part of phase C (mostly open fen), and part of phase C and phase D (mostly forested bog).

Mean accumulation of peat, dry weight, organic content, and carbon content decrease with increasing depth. In con- trast, nitrogen accumulation is higher in the lower intervals, probably due to higher availability from flowing water and increased nitrogen fixation in fens and marshes compared with bogs (Waughman and Bellamy 1980; Bowden 1987). Lower C/N ratios in phases A and B can largely be explained in this manner. The C/N ratio fluctuates in phase D, which shows a fairly homogenous macrofossil composition throughout, of mainly Sphagnumfuscum and Polytrichum cf. strictum (Fig. 4). Mean C/N values for living material of these mosses are of the order of 68 f 8 (n = 10) and 67 f 7 (n = 3), respectively (P. Kuhry, unpublished). Malmer and Holm (1984) showed that C/N ratios in the top layers of Swedish fens and bogs often decrease with depth, probably due to the loss of carbon during decomposition while much of the nitrogen remained fixed to the dead plant material. Low C/N ratios (560) at levels 110-90 cm and 60-20 cm in phase D thus suggest periods of higher peat decomposition. Higher decomposition rates at these levels are corroborated to some extent by the presence of visually more humified peat layers (Fig. 6) and higher pollen concentrations (Fig. 5), pointing to lower peat accumu- lation rates (Middeldorp 1986). Fungal sclerotia seem to be characteristic of these intervals (see also La Ronge site).

Can

. J. E

arth

Sci

. Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

199.

201.

121.

12 o

n 06

/04/

13Fo

r pe

rson

al u

se o

nly.

N N 2 2

VI 0 VI 0 0 0

V1 0 0 0 0

I I I I Depth (crn)

0 A3OilOO 2110i100 179Of90 C-)

14

I m m C dates (BP)

0- - wu r $25 s'uc Stratigraphy C 3 T 2 & g g D In 1 0 Phases

I I I Decomposition

zc g m

p? a P Macrofossil abundance

f B

z 0

6 O

a - B

m 0

T N- +I + Charcoal I

I -- + +

Roots (ectornycorrhizal)

zc+ --T CYPERACEAE

+ + CALLIERGON GlGANTrUM L.

DREPANOCCADUS ADUNCUS

CAMPYLlUM STEUATUM

SPHAGNUM WARNSTORFII

< "C

t'lc TOMENTHYPNUM NlENS

z m NL +---+ AULACOMNIUM PALUSTRE

I + + + wood I I I

me+++ + +- Coniferous bark

v POLYTRICHUM cf. STRICTUM

+ -+ POHLIA NUTANS

POHLIA cf. SPHAGNlCOLA

+ Other bryophytes

+ ;1 Other vascular plant remalns

I I I I b 1 m 101 0 I Phases

Can

. J. E

arth

Sci

. Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

199.

201.

121.

12 o

n 06

/04/

13Fo

r pe

rson

al u

se o

nly.

m 0 0 0

cn 0

0

I 0

Cn 0 0

I I I I I Depth (cm)

r 1 w 1 01 0 1 Phases

T , : CHARA obgonia SAGlTTARlA achenes

+ cf. SCIRPUS achenes

'I cl. ELEOCHARIS endocarps N

Blue-green algal colonies

RUMEX achenes

CHENOPODLACEAE seeds

WTAMOGETON ache=

TYPHA achenes %

"

$* CAREX achenes (trigonous)

F EJ- CAREX achenes (biconvex)

gN BETULA leaves

B z BETuLA fruits

BETULA scales

8 g GRAMINEAE fruits

.!A cf. ROSACEAE achenes

HI. LARlX LARlClNA needles z P

+ + + PlCEA needles

& 6 V + cf. PlCEA seeds

INSECTAE larvae caudal discs

Sponge cysts

CLADOCERA ephippia

COLEOPTERA elytra

1 ACARIDAE exoskeletons

SL

Other zoological remains I I I

b m 101 CI Phases

SPHAGNUM operwla 8 capsules

+ + + + + + LEDUMkaves

Other ericaceous remains

Fungal sclerotia

Other seeds-fruits + +

Can

. J. E

arth

Sci

. Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

199.

201.

121.

12 o

n 06

/04/

13Fo

r pe

rson

al u

se o

nly.

1 I I I i 1 uepm (cm) rl . . . 4230f 100 271 Of 100 1790f90 7 ' ' C dates (BP)

a,, = = 3 @:& r3 T~ c Stratigrapny C 3

3. .? = 7

Phases

Pollen concentration PIC^ (pollen sum elements)

Pollen concentration P/cm (PICEA)

PlCEA

PNUS

BETULA

CARPINUSIOSTRYA

UMJS

MYRICA

JUNIPERUS-type

ELAEAGNUS

VIBURNUM

GRAMINEAE < 40 pin

AMBROSIA

ARTEMlSlA

COMPOSITAE tubulillorae

SARCOBATUS

GRAMINEAE > 40 prn

BRASSICA

COMPOSITAE liguliflorae

THALICTRUM

LABIATAE

GALIUM

Pollen sum - 8

g '6 L 0

Can

. J. E

arth

Sci

. Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

199.

201.

121.

12 o

n 06

/04/

13Fo

r pe

rson

al u

se o

nly.

m 0 6 Ln 0

a 0

u 0 0 0

I I I I I J Depth (crn)

I m In1 0 I Phases I I I

UMBaLlFERAE

CARYOPHYLLACEAE

ONAGRACEAE

ROSACEAE + + + + + cf. CORNUS

RANUNCULUS

Other pollen

KKIGETLM

LYCOPODIUM reticulate

Other fern spores

POTl'M3GETON

MYRlOPHYLLUM

NPHA LATlFOLlA

.2 TRIGLOCHIN-type

+ 4 POTENTILIA

+ + + Algal microfossil types

z P CERATOPHYUUM hairs

Sponge spicules

ER KXEE

ii -

N m - -

Fungal microfossil types

Fungal hyphae

ASSULINA 0

I I I Phases

Can

. J. E

arth

Sci

. Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

199.

201.

121.

12 o

n 06

/04/

13Fo

r pe

rson

al u

se o

nly.

CAN. J. EARTH SCI. VOL. 29, 1992

Light unhurnified

Dark hurnified Sand

Clay Gravel

FIG. 6. Physicochemical data, Gypsumville bog. (Analysis by Linda Halsey.)

TABLE 2. Mean accumulation rates and C/N ratios for Gypsumville bog, Manitoba

Age Depth Vegetation Peat Dry weight Organic Carbon Nitrogen (years BP) (cm) type (mmla) (gl(m2 . a)) (g/(m2 . a)) (g/(m2 . a)) (g/(m2 . a)) C/N

0 - 1790 0- 146 Forested bog 0.82 65.82 61.66 28.65 0.51 56 1790-2710 146- 186 Open fen 0.43 59.35 54.30 27.51 1.43 19 2710-4230 186-231 Pond to fen 0.30 55.75 42.18 19.41 1.17 17

0-4230 0-231 Pond to bog 0.55 60.79 53.06 25.08 0.95 26

La Ronge bog

Description of the site The peatland is located about 1 km inland from the south-

western shore of Lac La Ronge in central Saskatchewan (Fig. 1, site 2), about 17 km south of the town of La Ronge (Fig. 7). Bedrock in the area consists of Devonian limestone and dolomite (Norris et al . 1982). Ice retreated from this part of the Canadian western interior between 11 000 BP and 10 000 BP (Dyke and Prest 1987). Surficial deposits include glaciolacustrine clays deposited in glacial Lake Agassiz, which

drained from this area around 9000 BP (Schreiner 1983). Climatic conditions at La Ronge airport, for 1951 - 1980,

are given in Fig. 8. Growing degree days ( > 5 "C) are 1262, and the average frost-free period is 104 days (Canadian Climate Program 1982). The area is located within the subhumid rnid- boreal ecoclimatic region, 15 krn southwest of the high-boreal region and 200 km north of the transitional grassland (park- land) region (Ecoregions Working Group 1989). It is situated within the Upper Churchill forest region of Rowe (1972). Picea glauca and Populus spp. are characteristically found on

Can

. J. E

arth

Sci

. Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

199.

201.

121.

12 o

n 06

/04/

13Fo

r pe

rson

al u

se o

nly.

KUHRY ET AL. 1081

L A RONGE

FIG. 7. Location of La Ronge bog in

well-drained sites. Pinus banksiana is restricted to sand plains and low ridges. Poorly drained areas are occupied by Picea mariana and Larix laricina.

The La Ronge peatland is a forested bog covering an area of approximately 1 krn2. The stunted arboreal layer reaches 3 m in height and consists exclusively of Picea mariana, which covers 30% of the peatland. The shrub layer (60% coverage) is dominated by Ledum groenlandicum, with some Chamaedaphne calyculata. A microtopography of hummocks and hollows is present. Vaccinium vitis-idaea, Oxycoccus micro- carpus, Rubus chamaemorus, Drosera rotundifolia, Sphagnum fuscum, and Polytrichum cf. stricturn are prominent on the hummocks, and Pleurozium schreberi and Cladonia spp. are abundant in the hollows. Mosses cover > 75 % of the ground layer. The pH is 4.0 and the corrected conductivity 42 $3.

Peat core analyses and results The core was taken in the northeastern part of the peatland

(Fig. 7) from a hummock dominated by Ledum groenlandicum and Sphagnum fuscum. Although the area is located outside the zone of discontinuous permafrost (Brown 1967), icy peat lenses were encountered (and penetrated with difficulty) at 50-60 cm and 200 cm (July 29, 1989). Mineral sediment (sticky grey-blue clay with some sand and gravel) was reached at 272 cm. Carbonates are not present in these mineral sedi- ments, as ignition at 950°C did not result in additional weight loss, and no reaction to HCl treatment was observed. Four radiocarbon dates are available (Table 3). Stratigraphy and radiocarbon dates are shown to the left of Figs. 9 - 11.

central Saskatchewan. 1 ft = 0.305 m.

Local vegetation development The development of the peatland has been subdivided into

four phases (Figs. 9, 10): Phase A (295 -230 cm) includes the transition from mineral sediment to peat. Local peat accumu- lation began about 5020 BP. Phase A lasted until approximately 4290 BP. Macrofossils of emergent plants such as Typha latifolia and Carex spp., and Betula remains are abundant. Pollen of the aquatic taxa Potamogeton and Myriophyllum occur in low frequencies. Algal and fungal microfossil taxa are abundant, which suggests the presence of both wet and relatively dry microhabitats. Remains of Cladocera, Coleoptera, and Acaridae are prominent throughout the phase. Mosses are all but absent, except in the lowermost part of the phase where some Sphagnum wamstoifii (see low total abundance of macro- fossils) is present. This indicates that mesotrophic conditions prevailed at the earliest stages of flooding of the depression. Later a marsh vegetation, with some open pools, developed, indicating eutrophic conditions and circumneutral waters.

In phase B (230- 160 cm), dated from 4290 BP to slightly older than 3710 BP, Larix laricina needles, Betula fruits and leaves, and Carex spp. achenes are abundant. Macrofossils of Coleoptera and Acaridae are found. Remains of brown mosses, including Calliergon giganteum, Drepanocladus cf. lapponicus, and Bryum cf. pseudotriquetrum, are also present. The aute- cology of these mosses indicates relatively wet conditions (3 - 10 cm above mean water table), with pH between 6.5 and 7.0. The presence of Sphagnum warnstoifii indicates locally drier microhabitats. The local conditions suggested by the moss cover are corroborated by the occurrence of both algal

Can

. J. E

arth

Sci

. Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

199.

201.

121.

12 o

n 06

/04/

13Fo

r pe

rson

al u

se o

nly.

1082 CAN. J . EARTH SCI. VOL. 29. 1992

WEATHER STATION: La Ronge Airport (Sask.) TABLE 3. Radiocarbon dates for La Ronge bog, Saskatchewan ALTITUDE: 375 m. COORD.: 55'09'N; 105Y5'W ECOCLIMATIC REGION: Subhumid Mid-Bored Laboratory Depth Sample Date MEAN ANNUAL TEMPERATURE: -0.8.C number (cm) material (years BP) MEAN ANNUAL PRECIPITATION: 485 rnm

"C rnrn AECV 1086C 80-95 Peat 960 + 90 AECV 1085C 146-165 Peat 3710 f 90 AECV 1083C 220-235 Peat 4290 f 100

I r 100 AECV 1034C 257-270 Peat 5020 + 110

FIG. 8. Climate diagram for La Ronge airport, Saskatchewan, 1951 - 1980 (Canadian Climate Program 1982).

and fungal taxa in the microfossil record. Local vegetation is best described as a forested rich fen.

Phase C (160- 150 cm) represents a period of rapid change. Needles of Lurix laricina and Picea are present. Macrofossils of Betula and Carex spp., which are abundant in phases A and B, are not found in phase C. Among the animal taxa, only Acaridae are common. Aulacomniumpalustre, Tomenthypnum nitens, and Sphagnum fuscum become the dominant mosses. The autecology of these mosses indicates a mean water table at a depth of about 18-28 cm, and pH values ranging from 6.0 to 4.5. As in phases A and B, algal and fungal microfossil taxa are abundant. Local conditions in the forested fen evidently became drier and more oligotrophic than in phase B.

Phase D (150 -0 cm) represents approximately the last 37 10 radiocarbon years. Picea needles and ericaceous remains are common, and Sphagnum fuscum is the dominant moss. This moss indicates dry and oligotrophic conditions. Oligotrophication is corroborated by the appearance of the rhizopod Assulina in the microfossil record (Van Gee1 et al . 1989). Dry conditions are also indicated by the abundance of fungi and the almost complete absence of algae. Acaridae are present throughout the phase. The local vegetation is a forested bog.

Phase D can be subdivided into two parts. The lower part (150 -90 cm), dated between 37 10 BP and 960 BP, is charac- terized by abundant fungal sclerotia. A layer at 125 cm, with a low abundance of Sphagnum fuscum, and common roots with ectomycorrhizae and coniferous bark suggests that peat growth was interrupted. A very low peat accumulation rate for this interval supports this interpretation (Table 4). Changes can also be observed in the extralocal vegetation in the lower

part of phase D. Pollen of Betula, Salix, and Populus show some increases, whereas these taxa are absent from the macro- fossil record. Populus is not a peatland taxon, and Salix, and Betula, although common in marshes and fens, are rare in bogs. The upper part of phase D (90 -0 cm), representing the last 960 radiocarbon years, shows a continuously high represen- tation of Sphagnumfuscum with some Sphagnum magellanicum. Compared with the lower part of phase D, local conditions appear to have become somewhat wetter, allowing for more continuous and (or) faster accumulation of peat (Table 4).

Regional vegetation development The occurrence of Picea and Lurix laricina needles in the

basal deposits indicates that boreal conifers were present in the area when the peat started to accumulate (Fig. 9). At first, the forest may have had a somewhat more open character, as sug- gested by the higher frequency of Chenopodiaceae in the pollen record (Fig. 10). This taxon is lacking in the macrofossil record, and its pollen probably derives from extralocal vegetation. Mean Picea pollen influx is highly variable for the different radiocarbon-dated intervals of the La Ronge peat deposit: 1500 grains/(cm2 . a) in phase A; 3100 grains/(cm2 . a) in phase B; 200 grains/(cm2 . a) in phase D. Pollen influx could be expected to be highest in phase D when Picea mariana was present on the peatland surface. Clearly, local factors includ- ing interruption in peat deposition (and possibly even erosion) can significantly influence pollen influx values. The increase of Picea pollen influx from phase A to phase B may indicate increasing Picea cover in the extralocal vegetation.

Accumulation rates Mean values for the accumulation of peat, dry weight, organic

content, carbon content, nitrogen content and C/N ratio were calculated for the upper part of phase A (marsh vegetation type), phase B and part of phase C (forested fen), part of phase C and the lower part of phase D (mostly forested bog), the upper part of phase D (forested bog), and the entire peat deposit (Table 4). These calculations are based on the physicochemical analyses given in Fig. 11.

Nitrogen accumulation is high in the marsh phase and the forested fen phase, probably due to its high availability from flowing water and increased nitrogen fixation in fens and marshes compared with bogs (Waughman and Bellamy 1980; Bowden 1987). Accumulation rates are especially high in the forested fen phase. The lower part of the forested bog phase is characterized by very low accumulation rates. CIN ratios in this interval are low compared with those in the upper part of the phase, while the macrofossil composition is similar. This may indicate a higher degree of decomposition of the peat (see Malmer and Holm 1984). As in the case of Gypsumville bog, this interval of increased decomposition is marked by the presence of fungal sclerotia. The accumulated evidence for the lower part of phase D (3710-960 BP), including low mean

Can

. J. E

arth

Sci

. Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

199.

201.

121.

12 o

n 06

/04/

13Fo

r pe

rson

al u

se o

nly.

KUHRY ET AL. 1083

accumulation rates, low C/N ratios, the presence of a root layer, and the abundance of fungal sclerotia, points to an interval of interrupted peat deposition or even erosion of the deposits.

Discussion and conclusions Paleobotanical analyses reveal similar developmental path-

ways for Gypsumville bog (south-central Manitoba) and La Ronge bog (central Saskatchewan). At the Gypsumville site an eutrophic shallow pond with Potamogeton and algae (Chara and Cyanophyta) first developed. Emergent marsh vegetation types, characterized by abundant Typhu latifolia and a lack of mosses, were present at both sites. Subsequently, wet, rich fens characterized by Betula, Carex, and brown mosses devel- oped. At La Ronge this fen became immediately forested with Larix laricina but at Gypsumville this species appeared only in the later stages of the fen phase. The transition from fen to bog was presumably very fast at both sites. The associated change in inferred pH from > 6 in the wet rich fen to < 5 in the bog occurred over a very short interval of the peat cores ( - 20 cm) . At present relatively few peatlands can be found that have pH values of 5.0-6.0 (Gorham et al. 1984). Chemi- cally this can easily be explained as the region along the acidity -alkalinity gradient where HC07 alkalinity becomes zero (Gorharn 1956). The suggestion by Vitt and Kuhry (in press) that the rarity of peatlands of this pH is largely due to the short period of time that these peatlands exist in the developmental sequence is corroborated by our results.

The pond and marsh - fen - bog developmental sequence described above has also been observed at the Porcupine Mountain site of Nichols (1969), where palynological, strati- graphic, and macrofossil data suggest the following local vege- tation development: A shallow pond with Potamogeton, and Typha latifolia and Carex along the shores, developed between 6670 BP and 5 140 BP; this was followed by Carex-dominated vegetation with substantial peat accumulation, most probably a fen, although some Typha latifolia was still present; after a rapid change at 4180 BP, a sphagnum-dominated peatland developed.

The chronologies of the local vegetation successions at the Gypsumville, La Ronge, and porcupine Mountain sites are not identical. Especially noteworthy is the transition toward the Sphagnum-dominated phase, which occurred much more recently at the Gypsumville site (ca. 1790 BP) than at the La Ronge and Porcupine Mountain sites (ca. 3710 BP and 41 80 BP, respectively). However, the following generaliza- tions can be made:

(1) Peat accumulation in all three peatlands began after 6000 BP. Flooding of depressions (possibly of an intermittent nature) could have occurred before that date, with accumula- tion of some organic material or marsh peat, but never typical fen or bog peat. These early flooding events were observed at the Porcupine Mountain site by Nichols (1969) and at two sites reported by Zoltai and Vitt (1990).

(2) The first stage in the development of these peatlands is characterized by abundant Typha latifolia and the rarity of mosses. This marsh vegetation suggests frequent and severe periods of drought, as it is rare in poorly drained depressions in the mixed-wood boreal forest (Zoltai 1988) but abundant in potholes of the grassland -parkland region (Millar 1969; Adarns 1988). Similar marsh vegetation types have also been recorded in the initial stages of peatland development in the low-boreal ecoclimatic regions of western Saskatchewan (Beauval bog; Vitt

and Kuhry, in press) and in central Alberta (Elk Island National Park; Vance 1979). A marsh phase is lacking farther north at Lynn Lake, Manitoba (Nichols 1967), two sites in Saskatche- wan (P. Kuhry, unpublished), and the Mariana Lakes peatland in Alberta (Nicholson and Vitt 1990).

(3) When peat accumulation began, boreal conifers were present near all three sites. This is indicated by the presence of Picea (and Larix) needles at or near the base of the peat deposits at Gypsumville, La Ronge, and Porcupine Mountain. However, relatively high percentages of nonarboreal elements and low percentages of Picea in the lowermost pollen assem- blages of the Gypsumville and La Ronge sites suggest a differ- ent character of the middle Holocene regional vegetation cover than the modern southern mixed-wood boreal forest. Stands of boreal forest alternated with stands of deciduous forest and (or) more open areas. The data of Nichols (1969) from Porcu- pine Mountain corroborate this suggestion. Basal pollen assem- blages from his core can be compared with recent pollen assemblages from small lakes, as a pond was present initially at the Porcupine Mountain site. Nichols stated that between 6670 BP and 4180 BP, open prairie vegetation was present in the area, with Betula prominent nearby but Picea absent. This interpretation, however, can be questioned because of rela- tively high Picea representation in the basal pollen assem- blages (up to 30%) compared with its present-day frequency ( < 20 %) in the grassland - parkland pollen rain (Lichti- Federovich and Ritchie 1968; Ritchie 1987), and the presence of a Picea needle in this interval. However, the high represen- tation of herbaceous elements (20 -40 %) probably indicates a more open regional vegetation cover. It is interesting to note that at present the most southerly located peatlands in the Canadian western interior are found in areas where a mosaic of deciduous and boreal forest is present (Elk Island National Park, Zoltai 1975; Riding Mountain National Park, Ritchie 1987).

The relatively late initiation of peat accumulation, the con- sistent occurrence of a marsh phase in these peatlands, and the more open - deciduous character of the regional vegetation cover can all be explained in terms of a warm and dry middle Holocene climate. Substantial peat accumulation was inhibited until conditions gradually became cooler and moister after 6000 BP (Zoltai and Vitt 1990), and in our study area (south- central Manitoba and central Saskatchewan) especially after 4500 BP. Moister conditions toward the end of the Holocene are indicated as well by consistently high water levels in Lake Manitoba, which before 4500 BP showed several periods during which the lake completely dried (Teller and Last 1981). Gradu- ally cooler and moister climatic conditions are also reflected in the regional vegetation, with the boreal forest encroaching on the grassland-parkland region between 6000 BP and 3000 BP (Mott 1973; Ritchie 1976, 1985; this study). In the southernmost part of this expanding boreal forest, the vegeta- tion cover was more open, with deciduous and boreal forest stands (Nichols 1969; Ritchie and Hadden 1975; this study). This probably reflects more periods of drought, a feature that is also suggested by the initial presence of Typha communities at our sites, which floristically show clear affinities to marshes of the grassland -parkland ecoclimatic region.

Mean accumulation rates at the Gypsumville and La Ronge sites are similar to the values reported for boreal wetlands by Ovenden (1990). Very high peat and carbon accumulation rates, calculated for the forested, wet, rich fen phase at La Ronge (1.24 mm/a and 69 g/(m2 . a), respectively), are also reported by Ovenden for woody sedge peat (up to 2 mm/a and

Can

. J. E

arth

Sci

. Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

199.

201.

121.

12 o

n 06

/04/

13Fo

r pe

rson

al u

se o

nly.

h) N 2 A

ul 0 U) 0 0 L8l 0 0 0 0 0 I I I I I I Depth (cm)

- 5020f 11 0 4290f 100 371 Of 90 960i90

m = m D " C dates (BP)

n- ?-

C 3 Stratigraphy 3 . . . . . - - . . .

2 5 -. m' ?. a =

I P a0 o 0 Phases 1 I1

Macrofossil abundance

Roots (ectomycorrhizal)

cf. TYPHA

CYPERACEAE (surficial)

CYPERACEAE (rhizomal)

SPHAGNUM WARNSTORFll

DREPANOCIADUS cf. LAPPONCUS

BRYUM cf. PSEUDOTRQUETRUM

CAMPYLIUM STELIATUM

TOMENlHYPNUM NITENS

AUIACOMNIUM PALUSTRE

wood

Coniferous bark

SPHAGNUM FUSCUM

PLElROZlUM SGREBERI

SPHAGNUM MAGELLANCUM

WLYTRICHUM cf. STRICTUM

Other bryophytes

Other vascular plant remains

1 D 1 m [n 1 1 Phases

Can

. J. E

arth

Sci

. Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

199.

201.

121.

12 o

n 06

/04/

13Fo

r pe

rson

al u

se o

nly.

N N d A

u 0 UI 0 C1 VI 0 0 0 9 0 I 1 I I I 1 Depth (cm)

Phases

TYPHA achenes

RUMEX achmes

CICUTA seeds

CAREX achenes (trigonous)

CAREX achenes (biconvex)

RANUNCULUS achenes

BETULA fruits

BETULA scales

BETULA anthers

BETULA leaves

GRAMINEAE fruits

CARYOPHYLLACEE seeds

cf. EPlLOBlUM seeds

LARlX LARlClNA needles

PlCEA needles

cf. PlCEA seeds

SPHAGNUM opercula 8 capsules

Fungal sclerotia

LEDUM leaves

OXYCOCCUS leave5

ERCACEAE seeds

Other seeds-fruits

CLADOCERA ephippia

+ E: .. mi + - COLEOPTERA etytra

ACARIDAE exoskeletons

7 ++ 'w++ Other zoological remains

I" I I I

I B P In 1 o Phases

Can

. J. E

arth

Sci

. Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

199.

201.

121.

12 o

n 06

/04/

13Fo

r pe

rson

al u

se o

nly.

CAN. J. EARTH SCI. VOL. 29, 1992

xnvs I-

mtKn -L - -=, - S n N l V

f ma 0 PI - E -

C 0 8 8

g a ? $ (s~uewqe uns uellod)

0 o d a +3/d

UOlIRIIU83UO1 Ue110d nmm

Can

. J. E

arth

Sci

. Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

199.

201.

121.

12 o

n 06

/04/

13Fo

r pe

rson

al u

se o

nly.

KUHRY ET AL. 1087

Can

. J. E

arth

Sci

. Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

199.

201.

121.

12 o

n 06

/04/

13Fo

r pe

rson

al u

se o

nly.

CAN. J. EARTH SCI. VOL. 29, 1992

- - 2

s -

Light unhumified

Pear Organics

Dark humified Sand Distinct charcoal layer

Clay Gravel 1 Frozen peat horizon

FIG. 1 1 . Physicochemical data, La Ronge bog. (Analysis by Linda Halsey.)

TABLE 4. Mean accumulation rates and C/N ratios for La Ronge bog, Saskatchewan

Age Depth Vegetation Peat Dry weight Organic Carbon Nitrogen (years BP) (cm) type (mmla) (g/(m2 . a)) (g/(m2 . a)) (g/(m2 . a)) (g/(m2 . a)) C/N

0-960 0-87 Forested bog 0.91 70.09 69.13 31.65 0.46 69 960-3710 87- 154 Forested bog 0.24 29.22 28.39 12.52 0.26 48

3710-4290 154-226 Forested fen 1.24 184.40 171.76 69.59 3.29 21 4290 - 5020 226 - 265 Marsh 0.53 94.63 84.01 35.03 2.25 16

0-5020 0-265 Marsh to bog 0.53 64.48 60.24 26.04 0.94 28

61 g/(m2 . a), respectively). At the La Ronge site, mean values for bog peat accumulation are variable. A low peat accumulation rate for the lower interval (0.24 mmla), lasting from 3710 BP to 960 BP, is explained by interruption of peat deposition (or even erosion of peat deposits), as suggested by the presence of a root layer. At the Porcupine Mountain site, peat accumulation rates for the bog phase are also variable, being 0.15 mm/a between 4180 BP and 2450 BP, 0.39 mm/a between 2000 BP and present, and 0.89 mmla between 2450 BP

and 2000 BP (Nichols 1969). As at the La Ronge site, the two intervals with low accumulation rates contain root layers, sug- gesting that interruptions in peat deposition occurred. Root layers are absent in the interval of rapid accumulation.

Based on the data at hand, no relationship can be discerned between regional climatic change and the fen-to-bog succes- sion or changes in peat accumulation rate in forested bogs. The fen-bog succession and the changes in accumulation rates at the Gypsumville, La Ronge, and Porcupine Mountain sites are

Can

. J. E

arth

Sci

. Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

199.

201.

121.

12 o

n 06

/04/

13Fo

r pe

rson

al u

se o

nly.

KUHRY ET AL. 1089

not synchronous. Local edaphic and autogenic factors obvi- ously play a very important role. Many more sites must be studied to develop a comprehensive picture of the influence of climate on peatland development. Clearly, the delayed develop- ment of peatlands to the south, along with the presence of Typha latifolia communities when the peatlands first formed were climatically induced. It can also be suggested that certain local events in the fen and the bog phases were associated with changes in the surrounding vegetation. This is most clearly illustrated in the Gypsumville record, where an expansion of Populus in the regional vegetation at ca. 1790 BP coincided with the fen-to-bog transition, and changes in the extralocal vegetation in more recent times correlated with disturbances in the local peatland ecosystem. This could suggest that climatic change influenced both regional upland and local peatland vegetation types. However, it has been clearly documented that vegetation in a catchment influences the hydrology of the area (Bosch and Hewlett 1982; Kovacs et al. 1989). A forest cover (especially coniferous) results in a reduced but probably more stabilized water yield. Local disturbances in the sur- rounding forest may cause hydrological changes that could affect the peatland ecosystem. Clearly, more studies are needed, but the very marked present-day and past co-occurrence of boreal conifers and peat-forming systems in the southern boreal region seems to be related to both regional climatological and local hydrological interactions.

Acknowledgments This study was made possible through a Natural Sciences

and Engineering Research Council of Canada Strategic Grant to Drs. S. E. Bayley, D. H. Vitt, and D. W. Schindler, for which we are grateful. We thank R. Craik and C. Mackesey for their assistance in the field, and Dr. C . E. Schweger and H. Friebe for their help with the identification of pollen types. Dr. L. D. Arnold (Vegreville, Alberta) is acknowledged for the radiocarbon dating.

Adams, G. D. 1988. Wetlands of the prairies of Canada. In Wetlands of Canada. Edited by National Wetlands Working Group. Environ- ment Canada, Ecological Land Classification Series, no. 24, pp. 158-198.

Bosch, J. M., and Hewlett, J. D. 1982. A review of catchment experiments to determine the effect of vegetation changes on water yield and evapotranspiration. Journal of Hydrology, 55: 3 -23.

Bowden, W. B. 1987. The biogeochemistry of nitrogen in freshwater wetlands. Biogeochemistry, 4: 3 13 - 332.

Brown, R. J. E. 1967. Permafrost in Canada. National Research Council Canada, Division of Building Research, Publication NRC 9769.

Canadian Climate Program. 1982. Canadian climate normals 195 1 - 1980. Environment Canada, Ottawa.

Dean, W. E. 1974. Determination of carbonate and organic matter in calcareous sediments and sedimentary rocks by loss on ignition: comparison with other methods. Journal of Sedimentary Petrol- ogy, 44: 242-248.

Dyke, A. S., and Prest, V. K. 1987. Late Wisconsinan and Holocene history of the Laurentide Ice Sheet. GBographie physique et Quaternaire, 41: 237 -263.

Ecoregions Working Group. 1989. Ecoclimatic regions of Canada, first approximation. Environment Canada, Ecological Land Clas- sification Series, no. 23.

Eisner, W., and Sprague, A. P. 1987. MacPollen: Pollen counting on the microcomputer. Pollen et Spores, 29: 461 -470.

Gignac, L. D., Vitt, D. H., Zoltai, S. C., and Bayley, S. E. 1991. Bryophyte response surfaces along climatic, chemical, and physi-

cal gradients in peatlands of western Canada. Nova Hedwigia, 53(1-2): 27-71.

Gorham, E. 1956. On the chemical composition of some bog waters from the Moor House nature reserve. Journal of Ecology, 44: 377-384.

Gorham, E., Bayley, S. E., and Schindler, D. W. 1984. Ecological effects of acid deposition upon peatlands: a neglected field in "acid-rain" research. Canadian Journal of Fisheries and Aquatic Sciences, 41: 1256- 1268.

Janssens, J. A. 1983. A quantitative method for stratigraphic analysis of bryophytes in Holocene peat. Journal of Ecology, 71: 189- 196.

Jeglum, J. K. 1971. Plant indicators of pH and water level in peat- lands at Candle Lake, Saskatchewan. Canadian Journal of Botany, 49: 1661 - 1676.

Klassen, R. 1983. Lake Agassiz and the late glacial history of north- ern Manitoba. In Glacial Lake Agassiz. Edited by J. T. Teller and L. Clayton. Geological Association of Canada, Special Paper 26, pp. 97-115.

Kovacs, G., Zuidema, F., and Marsalek, J. 1989. Human intervention in the terrestrial water cycle. In Comparative hydrology: An ecologi- cal approach to land and water resources. Edited by M. Falkenmark and T. Chapman. United Nations Educational, Scientific and Cul- tural Organization, Paris, pp. 105 - 130.

Kubiw, H., Hickman, M., and Vitt, D. H. 1989. The developmental history of peatlands at Muskiki and Marguerite lakes, Alberta. Canadian Journal of Botany, 67: 3534 -3544.

Lichti-Federovich, S., and Ritchie, J. C. 1968. Recent pollen assem- blages from the Western Interior of Canada. Review of Palaeo- botany and Palynology, 7: 297-344.

Lowden, J. A., Robertson, I. M., and Blake, W., Jr. 1977. Geologi- cal Survey of Canada radiocarbon dates XVII. Geological Survey of Canada, Paper 77-7.

Malmer, N., and Holm, E. 1984. Variation in the CIN-quotient of peat in relation to decomposition rate and age determination with 'I0Pb. Oikos, 43: 171 - 182.

Middeldorp, A. A. 1986. Functional palaeoecology of the Hahnenmoor raised bog ecosystem-A study of vegetation history, production and decomposition by means of pollen density dating. Review of Palaeobotany and Palynology , 49: 1 - 73.

Millar, J. B. 1969. Observations on the ecology of wetland vege- tation. Environment Canada, Canadian Wildlife Service, Report Series, no. 6, pp. 49-56.

Mott, R. J. 1973. Palynological studies in central Saskatchewan: pollen stratigraphy from lake sediment sequences. Geological Sur- vey of Canada, Paper 72-49.

Mott, R. J., and Jackson, L. E., Jr. 1982. An 18 000 year palynological record from the southern Alberta segment of the classical Wiscon- sinan "Ice-free Corridor." Canadian Journal of Earth Sciences, 19: 504-513.

Nichols, H. N. 1967. The post-glacial history of vegetation and climate at Ennadai Lake, Keewatin, and Lynn Lake, Manitoba (Canada). Eiszeitalter und Gegenwart, 18: 176 - 197.

Nichols, H. N. 1969. The late Quaternary history of vegetation and climate at Porcupine Mountain and Clearwater Bog, Manitoba. Arctic and Alpine Research, 1: 155 - 167.

Nicholson, B. J., and Vitt, D. H. 1990. The paleoecology of a peat- land complex in continental western Canada. Canadian Journal of Botany, 68: 121 -138.

Norris, A. W., Uyeno, T. T., and McCabe, H. R. 1982. Devonian rocks of the Lake Winnipegosis - Lake Manitoba Outcrop Belt, Manitoba. Geological Survey of Canada, Memoir 392.

Ovenden, L. E. 1990. Peat accumulation in northern wetlands. Quaternary Research, 33: 377-386.

Ritchie, J. C. 1976. The late-Quaternary vegetational history of the Western Interior of Canada. Canadian Journal of Botany, 54: 1793- 1818.

Ritchie, J. C. 1985. Quaternary pollen records from the Western Interior and the Arctic of Canada. In Pollen records of Late- Quaternary North American sediments. Edited by V. M. Bryant, Jr.

Can

. J. E

arth

Sci

. Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

199.

201.

121.

12 o

n 06

/04/

13Fo

r pe

rson

al u

se o

nly.

1090 CAN. J . EARTH SCI. VOL, 29, 1992

and R. G. Holloway. American Association of Stratigraphic Paly- nologists Foundation, Austin, pp. 327-352.

Ritchie, J. C. 1987. Postglacial vegetation of Canada. Cambridge University Press, New York.

Ritchie, J. C., and Hadden, K. A. 1975. Pollen stratigraphy of Holo- cene sediments from the Grand Rapids area, Manitoba, Canada. Review of Palaeobotany and Palynology, 19: 193-202.

Rowe, J. S. 1972. Forest regions of Canada. Canada Department of Environment, Publication 1300.

Schreiner, B. T. 1983. Lake Agassiz in Saskatchewan. In Glacial Lake Agassiz. Edited by J. T. Teller and L. Clayton. Geological Association of Canada, Special Paper 26, pp. 75-96.

Schweger, C. E., and Hickman, M. 1989. Holocene paleohydrology of central Alberta: testing the general-circulation-model climate simulations. Canadian Journal of Earth Sciences, 26: 1826 - 1833.

Sjors, H. 1950. On the relation between vegetation and electrolytes in north Swedish mire waters. Oikos, 2: 241 -258.

Teller, J. T., and Last, W. M. 1981. Late Quaternary history of Lake Manitoba, Canada. Quaternary Research, 16: 97 - 116.

Teller, J. T., and Last, W. M. 1982. Pedogenic zones in postglacial sediment of Lake Manitoba, Canada. Earth Surfaces, Processes and Landforms, 7: 367 -379.

Vance, R. E. 1979. Late Holocene paleoecology of the Aspen park- land region of western Canada. M. A. thesis, University of Alberta, Edmonton.

Van Geel, B. 1978. A palaeoecological study of Holocene peat bog

sections in Germany and The Netherlands. Review of Palaeo- botany and Palynology, 25: 1 - 120.

Van Geel, B., Coope, G. R., and Van der Hammen, T. 1989. Palaeoecology and stratigraphy of the late glacial type section at Usselo (The Netherlands). Review of Palaeobotany and Palynol- ogy, 60: 25-129.

Vitt, D. H., and Kuhry, P. In press. Changes in moss-dominated wet- land ecosystems. In Bryophytes and lichens in a changing environ- ment. Edited by J. W. Bates and A. M. Farmer. Oxford University Press, Oxford.

Waughrnan, G. J., and Bellamy, D. J. 1980. Nitrogen fixation and the nitrogen balance in peatland ecosystems. Ecology, 61 : 1185 - 1 198.

Zoltai, S. C. 1975. Southern limit of coniferous trees on the Canadian Prairies. Environment Canada, Forestry Service, Northern Forest Research Centre, Information Report NOR-X-128.

Zoltai, S. C. 1988. Wetland environments and classification. In Wet- lands of Canada. Edited by C. D. A. Rubec. Environment Canada, Ecological Land Classification Series, no. 24, pp. 1 -24.

Zoltai, S. C. 1991. Estimating the age of peat samples from their weight: a study from west-central Canada. The Holocene, 1: 68-73.

Zoltai, S. C., and Johnson, J. D. 1985. Development of a treed bog island in a minerotrophic fen. Canadian Journal of Botany, 63: 1076- 1085.

Zoltai, S. C., and Vitt, D. H. 1990. Holocene climatic change and the distribution of peatlands in Western Interior Canada. Quater- nary Research, 33: 23 1 -240.

Can

. J. E

arth

Sci

. Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

199.

201.

121.

12 o

n 06

/04/

13Fo

r pe

rson

al u

se o

nly.