Michelle Garneau

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.

Toward dynamic global vegetation models for simulating vegetation-climate interactions and feedbacks: recent developments, limitations, and future challenges.

There is a lack in representation of biosphere-atmosphere interactions in current climate models. To fill this gap, one may introduce vegetation dynamics in surface transfer schemes or couple global climate models (GCMs) with vegetation dynamics models. As these vegetation dynamics models were not designed to be included in GCMs, how are the latest generation dynamic global vegetation models (DGVMs) suitable for use in global climate studies? This paper re- views the latest developments in DGVM modelling as well as the development of DGVM-GCM coupling in the frame- work of global climate studies. Limitations of DGVM and coupling are shown and the challenges of these methods are highlighted. During the last decade, DGVMs underwent major changes in the representation of physical and biogeochemi- cal mechanisms such as photosynthesis and respiration processes as well as in the representation of regional properties of vegetation. However, several limitations such as carbon and nitrogen cycles, competition, land-use and land-use changes, and disturbances have been identified. In addition, recent advances in model coupling techniques allow the simulation of the vegetation-atmosphere interactions in GCMs with the help of DGVMs. Though DGVMs represent a good alternative to investigate vegetation-atmosphere interactions at a large scale, some weaknesses in evaluation methodology and model design need to be further investigated to improve the results.

Paleoenvironments of the Canadian high arctic derived from pollen and plant macrofossils: Problems and potentials

Abstract Analyses of peat sections, lake sediments and ice cores provide information about Late-Quaternary arctic environments. Palynomorphs and plant macrofossils from each of these three types of sediments record different aspects of the environment with particular spatial and temporal scales of resolution. In the Arctic, the limits to the interpretation of past environments are particularly significant. Problems of low pollen concentrations, long-distance transport, stratigraphic inversions and contamination by fossils from older deposits are more serious in this region due to the biogeographic context that characterizes these high latitudes and influences the particular ecological and geomorphological processes. However, recent work has shown that past environments can be reconstructed from evidence preserved in high arctic sediments and ice cores, if these problems are taken into account before their interpretation.

Holocene carbon accumulation rates from three ombrotrophic peatlands in boreal Quebec, Canada: Impact of climate-driven ecohydrological change

Understanding the processes controlling peatland carbon (C) sequestration is critical to anticipate potential changes in the global C cycle in response to climate change. Although identification of these factors may be relatively straightforward on seasonal timescales, at centennial to millennial timescales complexities arise because of interactions between climate, vegetation, hydrology and long-term ecological processes. To better understand the factors controlling long-term C accumulation, Holocene rates of C sequestration were quantified from three pristine ombrotrophic peatlands in boreal Quebec, northeastern Canada (52°N, 75–76°W). Bulk density and loss-on-ignition analyses, combined with radiocarbon dating and age–depth modelling, were used to estimate long-term apparent rates of carbon accumulation. Past changes in vegetation and water-table depth were obtained from plant macrofossil and testate amoeba analysis. Earliest regional peat accumulation started ~7520 cal. BP, with long-term rates of C sequestration varying between 14.9 and 22.6 g/m2 per yr. High C sequestration rates occurred during the mid Holocene when relatively stable Sphagnum section Acutifolia communities were present, while low rates were found during the cooler late Holocene when Cyperaceae and ligneous vegetation were more dominant. However, C sequestration was highly variable among cores, implying that local topography, geomorphology and hydrology, or disturbance factors such as fire, mediate the influence of climate on C accumulation. Reconstructed water-table depths reveal several dry shifts since 3000 cal. BP, suggesting that episodic cold and dry conditions during the late Holocene may have contributed to lower C sequestration rates. Given the intensity of the water-table shifts at these times, we hypothesize that recurrent episodes of frozen subsurface peat might have intensified surface drying. As projected by climate scenarios, anticipated warmer and wetter conditions may lead to greater stability of hummock Sphagna cover and increased C sequestration potential in boreal peatlands.

Recent peat accumulation rates in minerotrophic peatlands of the Bay James region, Eastern Canada, inferred by 210Pb and 137Cs radiometric techniques.

(210)Pb and (137)Cs dating techniques are used to characterise recent peat accumulation rates of two minerotrophic peatlands located in the La Grande Rivière hydrological watershed, in the James Bay region (Canada). Several cores were collected during the summer 2005 in different parts of the two selected peatlands. These minerotrophic patterned peatlands are presently affected by erosion processes, expressed by progressive mechanical destruction of their pools borders. This erosion process is related to a water table rise induced by a regional increase of humidity since the last century. The main objective of the present paper is to (1) evaluate if (210)Pb and (137)Cs dating techniques can be applied to build accurate chronologies in these environments and (2) detect changes in the peat accumulation rates in regard to this amplification of humidity. In both sites, unsupported (210)Pb shows an exponential decreasing according to the depth. Chronologies inferred from (210)Pb allow to reconstruct peat accumulation rates since ca. 1855 AD. The (137)Cs data displayed evident mobility and diffusion, preventing the establishment of any sustained chronology based on these measurements. In the two sites, peat accumulation rates inferred from (210)Pb chronologies fluctuate between 0.005 and 0.038 g cm(-2) yr(-1). As a result, the rise of the water table during the last decade has not yet affected peat accumulation rates.

Greenhouse gas emissions-- fluxes and processes

Greenhouse gas emissions-- fluxes and processes , Greenhouse gas emissions-- fluxes and processes , کتابخانه دیجیتال جندی شاپور اهواز

Sphagnum δ13C values as indicators of palaeohydrological changes in a peat bog

Late-Holocene peat stratigraphy of a Canadian boreal peat bog was examined to evaluate the potential of Sphagnum δ13C values as surface moisture proxy indicators. Isotopic measurements were compared to testate amoebae-inferred water-table depth reconstructions, plant macrofossil assemblages and past decomposition levels inferred by colorimetric humification. AMS radiocarbon dates were coupled with 210Pb dates to establish peat chronology. Although the mechanisms underlying carbon fractionation processes in peatlands are not well understood, we demonstrate that Sphagnum δ 13C values have potential for palaeohydrological reconstructions, since variations presented by the isotopic values can generally be correlated with the other proxy records, especially during drier episodes.

Effects of permafrost aggradation on peat properties as determined from a pan-Arctic synthesis of plant macrofossils

Permafrost dynamics play an important role in high-latitude peatland carbon balance and are key to understanding the future response of soil carbon stocks. Permafrost aggradation can control the magnitude of the carbon feedback in peatlands through effects on peat properties. We compiled peatland plant macrofossil records for the northern permafrost zone (515 cores from 280 sites) and classified samples by vegetation type and environmental class (fen, bog, tundra and boreal permafrost, and thawed permafrost). We examined differences in peat properties (bulk density, carbon (C), nitrogen (N) and organic matter content, and C/N ratio) and C accumulation rates among vegetation types and environmental classes. Consequences of permafrost aggradation differed between boreal and tundra biomes, including differences in vegetation composition, C/N ratios, and N content. The vegetation composition of tundra permafrost peatlands was similar to permafrost-free fens, while boreal permafrost peatlands more closely resembled permafrost-free bogs. Nitrogen content in boreal permafrost and thawed permafrost peatlands was significantly lower than in permafrost-free bogs despite similar vegetation types (0.9% versus 1.5% N). Median long-term C accumulation rates were higher in fens (23g C m(-2)yr(-1)) than in permafrost-free bogs (18g C m(-2)yr(-1)) and were lowest in boreal permafrost peatlands (14g C m(-2)yr(-1)). The plant macrofossil record demonstrated transitions from fens to bogs to permafrost peatlands, bogs to fens, permafrost aggradation within fens, and permafrost thaw and reaggradation. Using data synthesis, we have identified predominant peatland successional pathways, changes in vegetation type, peat properties, and C accumulation rates associated with permafrost aggradation.

Holocene carbon dynamics of boreal and subarctic peatlands from Québec, Canada

Peatlands constitute major sinks of organic carbon (C) and play a key role in the global C cycle. Here, we present a synthesis of peat records from six ecoclimatic regions in Québec, Canada, in order to quantify Holocene patterns of C accumulation and relationships with contemporary climate data. Average long-term apparent rates of C accumulation (LORCA) were calculated for 21 peat cores and range from 10 to 70 g C/m2/yr with a mean of 26.1 (standard error of mean (SEM) = 3.6) g C/m2/yr, which is slightly higher than the mean value for northern peatlands as a whole (Loisel et al., 2014). We found that regional climate has been a major factor controlling long-term peatland C accumulation and that site-specific factors may explain some variability between sites. Our data show that LORCA tend to decrease with latitude. The lowest LORCA are found in the northernmost peatlands located at the boreal forest/forest-tundra ecotone, whereas the highest values are recorded in the peatlands along the St. Lawrence Estuary, characterized by the highest mean summer temperature, number of growing degree-days above 0°C and mean annual precipitation. Temporal variations in Holocene C accumulations rates were synthesized for 16 peat cores, which show high values during the mid-Holocene (6000–4000 cal. yr BP) followed by a decline during the Neoglacial cooling, especially between 2000 and 1200 cal. yr BP. Our study contributes to a better understanding of sensitivity of peatland C balance to climate change in a poorly documented part of the circumboreal region.

Object-based classification of a SPOT-4 image for mapping wetlands in the context of greenhouse gases emissions: the case of the Eastmain region, Québec, Canada

(Studies on greenhouse gases (GHG) emitted by hydroelectric reservoirs have shown until now that the fate of carbon, following impoundment, seems to reach the fate of carbon in natural aquatic ecosystems after a decade or so. To adequately assess this assumption and then obtain the net GHG emissions from the Eastmain-1 hydroelectric reservoir, the carbon stock and GHG emissions from peatlands and different succession stages of forested areas need to be characterized prior to the reservoir impoundment. It is therefore important to characterize the carbon flow process (surface fluxes and sequestrated carbon) from these terrestrial systems prior to impoundment. The Canadian Wildlife Service of Environment Canada, Québec region, has developed an approach for mapping wetlands using Landsat/RADARSAT-1 satellite images. The method is based on image segmentation using the Definiens Professional software. The top-down object-based classification is based on the Canadian Wetland Classification System and quickly and precisely identifies ecologically meaningful wetland polygons. The main objective of this study is to produce a wetland map of the Eastmain River watershed using a SPOT-4 image aimed at identifying five classes of wetlands (bog, fen, marsh, swamp, shallow water) for a geographical unit of at least 1 ha, and to add to the peatland classes a description of their components, such as pool complexes and vegetation structures, to assign measured carbon values to these different peatland classes and scale up the data to obtain a regional carbon budget. The second objective of the study consists in determining whether SPOT-4 images can be used to map wetlands, using the object-based method developed with Landsat/RADARSAT-1 images, and if a finer spatial resolution would improve the wetland mapping results by adding information on wetland components. The SPOT-4 classification using the object-based method allowed the five main wetland classes to be identified in addition to pool complexes in three density classes (isolated, low density, and high density) and “bogs”/“fens” vegetation structure (treed or open) in peatland classes. Validation was done at two levels: (i) between the five classes of wetlands, and (ii) between pool complexes and vegetation structures. The overall accuracy was 81% for the first level and 75% for the second.