Martin Lavoie

A Database and Synthesis of Northern Peatland Soil Properties and Holocene Carbon and Nitrogen Accumulation

Here, we present results from the most comprehensive compilation of Holocene peat soil properties with associated carbon and nitrogen accumulation rates for northern peatlands. Our database consists of 268 peat cores from 215 sites located north of 45°N. It encompasses regions within which peat carbon data have only recently become available, such as the West Siberia Lowlands, the Hudson Bay Lowlands, Kamchatka in Far East Russia, and the Tibetan Plateau. For all northern peatlands, carbon content in organic matter was estimated at 42 ± 3% (standard deviation) for Sphagnum peat, 51 ± 2% for non-Sphagnum peat, and at 49 ± 2% overall. Dry bulk density averaged 0.12 ± 0.07 g/cm3, organic matter bulk density averaged 0.11 ± 0.05 g/cm3, and total carbon content in peat averaged 47 ± 6%. In general, large differences were found between Sphagnum and non-Sphagnum peat types in terms of peat properties. Time-weighted peat carbon accumulation rates averaged 23 ± 2 (standard error of mean) g C/m2/yr during the Holocene on the basis of 151 peat cores from 127 sites, with the highest rates of carbon accumulation (25–28 g C/m2/yr) recorded during the early Holocene when the climate was warmer than the present. Furthermore, we estimate the northern peatland carbon and nitrogen pools at 436 and 10 gigatons, respectively. The database is publicly available at https://peatlands.lehigh.edu.

Postglacial water-level changes of a small lake in southern Québec, Canada

Sediment stratigraphy and palaeobotanical data from five cores were used to reconstruct the postglacial water-level changes of a small lake in southern Québec. The cores were taken along two transects from the centre of the lake to the margins. Lake level was relatively high before 11 000 cal. BP, when sedimen tation was characterized by the deposition of silty gyttja (.13 000 cal. BP) and marl (13 000–11 000 cal. BP). From 11 000 to 7000 cal. BP, a sediment hiatus was indicated by the lack of two regional pollen zones between the marl and the overlying gyttja, suggesting either nondeposition or erosion of the previously deposited sedi ments due to a low lake level. The lake level was approximately 2 m lower than present on the basis of macrofossil assemblages. A rise in the water level of about 1 m occurred around 7000 cal. BP, which was interrupted by a second lowering between 6100 and 4400 cal. BP, as indicated by a hiatus in the pollen stratigra phy. During this low period, the water level was at least 2 m lower than present. The last 4400 years are characterized by a continuous rise. The lake-level fluctuations are broadly synchronous with other palaeo hydrological records in northeastern United States, Ontario, and Subarctic Québec, implying broad-scale climatic control.

Isolation and water-level fluctuations of Lake Kachishayoot, Northern Québec, Canada

This study combines different methods, including grain size, macrofossil, and pollen analyses, to reconstruct paleogeographical and paleoclimatological conditions for periods before, during, and after the isolation of a small lake (Lake Kachishayoot) in northern Quebec. After the retreat of the Laurentide Ice Sheet around 8000 14C yr B.P., the area was submerged by the Tyrrell Sea. The transition from marine to lacustrine environment occurred about 5400 yr B.P. Two major periods of water-level fluctuations were inferred from organic and mineral sediments: a high water level that occurred after 3200 yr B.P. and a low water level that started before 2200 yr B.P. Our chronological data for the first period are consistent with those from nearby Lac des Pluviers and from other lakes in east central Canada and in the northeastern United States. During the low-water-level period, however, there is no evidence for minor fluctuations, whereas other lakes in northern Quebec and east-central Canada underwent several brief lowerings. Long-term changes in atmospheric circulation caused by changing global boundary conditions likely explained long-term water-level fluctuations of Lake Kachishayoot.

Environmental factors explaining the vegetation patterns in a temperate peatland

Although ombrotrophic temperate peatlands are important ecosystems for maintaining biodiversity in eastern North America, the environmental factors influencing their flora are only partly understood. The relationships between plant species distribution and environmental factors were thus studied within the oldest temperate peatland of Québec. Plant assemblages were identified by cluster analysis while CCA was used to related vegetation gradients to environmental factors. Five assemblages were identified; three typical of open bog and two characterized by more minerotrophic vegetation. Thicker peat deposit was encounter underlying the bog assemblages while higher water table level and percentage of free surface water distinguished the minerotrophic assemblages. Overall, the floristic patterns observed were spatially structured along the margins and the expanse. The most important environmental factors explaining this spatial gradient were the percentage of free surface water and the highest water-table level.

Late-Holocene palaeoecology of a polygonal peatland on the south shore of Hudson Strait, northern Québec, Canada

In order to document climate fluctuations during the late Holocene in Nunavik (in the Québec Arctic), a 182 cm peat core extracted from a polygonal peatland in the Salluit region was subjected to macrofossil and pollen analysis. Peat accumulation began around 4500 cal. BP in the peatland and 2340 cal. BP in the core site following the formation of frost cracks and ice wedges. Four distinct Holocene climatic changes were identified. Between 1910 and 1100 cal. BP, the climate was clement (similar to today’s climate), which favoured the growth of several species of Sphagnum (from poorly minerotrophic to ombrotrophic conditions). Colder and drier conditions starting around 1100 cal. BP are evidenced by the disappearance of Sphagnum and aeolian sedimentation. A short return to more clement conditions occurred around 870 cal. BP and lasted until 670 cal. BP. Subsequently, the climate once again became colder and drier, which induced significant aeolian activity. Late-Holocene local vegetation changes recorded in the peat core were probably induced by permafrost degradation and aggradation, associated with regional warming and a subsequent cooling trend.

The natural environment of the Québec City region during the Holocene

Abstract In the St Lawrence River valley the 10,000-year period following the Wisconsinian glaciation was marked by major geographic and climatic changes which influenced the development of plant communities. In this paper the Holocene environments in the Québec City region have been reconstructed on the basis of palaeogeographic and palaeoecological data. Fluctuations in relative sea level, particularly in recent millennia, are of particular interest in light of Québecs situation as a marine gateway on the St Lawrence. Changes in plant cover since Euro-American settlement some 400 years ago are principally due to forest clearing for agriculture and more recently to urban development.

Développement D'une Vaste Tourbière Ombrotrophe Non Perturbée en Contexte Périurbain au Québec Méridional

Abstract: The Grande-Plée-Bleue peatland in southern Quebec is the second largest undisturbed ombrotrophic peat bog south of the St. Lawrence River. Macrofossil analysis of 2 sediment cores was performed to reconstruct the developmental stages (flora, trophic stages) of a sector of this ecosystem located in a peri-urban area. Organic accumulation began around 9500 cal. y BP (calibrated years before present) in one or several small, shallow ponds after the retreat of the postglacial Goldthwait Sea. The spatial growth of the peatland took place through paludification to the detriment of a forest that was initially composed of balsam fir and white birch. Ombrotrophic conditions formed very early in the history of the site, around 8300 cal. y BP. Since that time, the bogs vegetation cover (composition, structure) has been quite stable. The longterm dynamics of the peatland was controlled by autogenous factors. However, more humid conditions were present locally between ca 1050 and ca 400 cal. y BP Similar indications have also been found in other bogs of southern Quebec for the same period, which suggests a change in regional hydroclimatic conditions.

Cliff-Top Eolian Sedimentation Reflecting Mid- to Late-Holocene Environmental Changes at Anticosti Island, Gulf of St. Lawrence, Eastern Canada

Abstract The study site (Cape Sandtop) consists of a 15 m high marine terrace exposed to strong easterly winds, at the eastern end of Anticosti Island in the Gulf of St. Lawrence (Québec, Canada), where eolian sedimentation occurred. Sections at the terrace edge exposed thick, well-humified, buried organic deposits with many wood fragments. Sedimentological and plant-macrofossil analyses were conducted from four sections to provide a chronology of eolian activity and to evaluate the causal factors for the development of treeless plant communities. Plant remains indicate that Cape Sandtop was forested between 6520 and ca. 4740 cal YBP. After ca. 4740 cal YBP, the terrace experienced a rapid change from coastal conifer forests and treed fen to marshes. Sustained erosional activity by easterly winds along the upper limestone cliff and the terrace edge started 1560 cal YBP and caused peat burial. The key factors responsible for cliff-top eolian sedimentation were relative sea level changes, increased exposure to easterly winds associated with higher elevation (15 m asl) of the marine terrace and sediment availability. In spite of its limited extent, this coastal site appeared as a system that was sensitive to environmental changes during the Mid- to Late-Holocene.

Recent Vegetation Dynamics and Hydrological Changes in Bogs Located in an Agricultural Landscape

This study aims to reconstruct the recent dynamics of two bogs located in an agricultural landscape and to determine which factors favour tree expansion, the most salient change recently reported in treeless peatlands. The vegetation and hydrological dynamics of the bogs as well as land use changes in the vicinity were reconstructed using a combination of paleoecological, paleohydrological, and historical approaches. It was hypothesized that upland deforestation indirectly induced atmospheric mineral dust deposition on sites, thus increasing nutrient availability and triggering forest expansion. Results indicated that a widespread, but asynchronous tree expansion occurred in both bogs during the 20th century. However, no evidence suggesting that nutrient enrichment favoured the phenomenon was found. Forest expansion seems rather to have been favoured by drying of the peat surface, as a decrease of the water table depth coincided with the beginning of the forest encroachment on both sites. This drying correlated with the establishment of an in situ artificial drainage ditch on one site and with agricultural development in the catchment of the other. Local historical factors of each site apparently override regional factors such as climate anomalies or upland deforestation in explaining rapid, abrupt changes in bogs.

Late Glacial and Holocene Vegetation History in the Northern Foothills of the Adirondack Mountains

ABSTRACT The postglacial history of vegetation at a regional scale is mainly governed by climate. However, the action of other environmental factors can lead to differentiation of the long-term vegetation dynamics in locations that are in proximity. In this context, the vegetation history of Covey Hill, at the northern tip of the Adirondack Mountains, was reconstructed using pollen analysis of a sediment core collected in a bog near the hilltop. This history was then compared with that of other sites in the Adirondacks, in the St. Lawrence Lowlands and in the Appalachian foothills to determine whether differentiations had occurred between sites across the landscape. Regionally, climate seems to have been the main driver of vegetation development. Differences between sites are most pronounced in regard to relative abundance of aspen and alder, and mostly occurred during the Late Glacial and early Holocene. Unlike other sites, fires occurred frequently on Covey Hill for several millennia, and most probably allowed the long-term maintenance of a rare pine barren. Finally, drier conditions are probably partly responsible for the hemlock decline evident around 5100 cal BP.