Tephra analysis in ombrotrophic peatlands: A geochemical comparison of acid digestion and density separation techniques          下载免费PDF全文

T. P. ROLAND  H. MACKAY  P. D. M. HUGHES 《第四纪科学杂志》2015,30(1):3-8

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Simulating the Carbon Cycling of Northern Peatlands Using a Land Surface Scheme Coupled to a Wetland Carbon Model (CLASS3W-MWM)     

Jianghua Wu  Nigel T. Roulet  Mats Nilsson  Peter Lafleur  Elyn Humphreys 《大气与海洋》2013,51(4):487-506

Northern peatlands store approximately one-third of the terrestrial soil carbon (C), although they cover only 3% of the global land mass. Northern peatlands can be subdivided into bogs and fens based on their hydrology and biogeochemistry. Peatland hydrology and biogeochemistry are tightly coupled to climate and, therefore, may be very sensitive to climate variability and change. To address the fate of the large peatland soil C storage under a future changed climate, a peatland C model, the McGill Wetland Model (MWM), was coupled to a land surface climate model (the wetland version of the Canadian Land Surface Scheme, CLASS3W), referred as CLASS3W-MWM. We evaluated the CLASS3W-MWM for a bog (Mer Bleue, located at 45.41°N, 75.48°W, in eastern Canada) and a poor fen (Degerö Stormyr, located at 64°11′N, 19°33′E, in northern Sweden).

CLASS3W-MWM captured the magnitude and direction of the present day C cycling very well for both bogs and fens. Moreover, the seasonal and interannual variability were reproduced reasonably well. Root mean square errors (RMSE) were <0.65 and the degree of agreements (d*) were >0.8 for the components of net ecosystem production (NEP) for both the Mer Bleue bog and the Degerö Stormyr fen. The performance of the coupled model for both bog and fen is similar to that of the stand-alone MWM driven by observed weather rather than simulated surface and soil climate. This modelling study suggests that northern peatlands are hydrologically and thermally conservative ecosystems. It was also shown that C cycling for bogs and fens was more sensitive to changes in air temperature than precipitation. Changes in temperature within the Intergovernmental Panel on Climate Change (IPCC) projected range switch the peatlands from a present-day C sink to a source, but projected changes in precipitation still maintain the peatlands as a C sink, although to a somewhat lesser degree. Increase in atmospheric CO₂ concentration enhances C sequestration for both bogs and fens. Our sensitivity analysis suggests that northern peatlands respond to changes in temperature, precipitation and doubled CO₂ concentration in a highly non-linear way. The sensitivity of C cycling in northern peatlands with respect to changes in air temperature, precipitation and the concentration of atmospheric CO₂ together is not a simple addition or subtraction of the sensitivity of the individual changes. Therefore, the sensitivity of a combination of changes in temperature, precipitation and doubled CO₂ concentration is very different from the sensitivity of peatlands to each environmental variable on their own. Our sensitivity analysis suggests that fens have a narrower tolerance to climate changes than bogs.

RÉSUMÉ [Traduit par la rédaction] Les tourbières du Nord renferment approximativement le tiers du carbone se trouvant dans le sol terrestre, même si elles ne couvrent que 3% des terres du globe. On peut subdiviser les tourbières du Nord en tourbières hautes et en tourbières basses selon leur hydrologie et leur biogéochimie. L'hydrologie et la biogéochimie des tourbières sont intimement liées au climat et peuvent donc être très sensibles à la variabilité et au changement climatique. Pour étudier comment évoluera le stockage du carbone dans les grands terrains tourbeux sous un climat futur modifié, nous avons couplé un modèle de carbone de tourbière, le McGill Wetland Model (MWM), à un modèle climatique de surface terrestre (la version terres humides du CLASS3W canadien), c'est-à-dire le CLASS3W–MWM. Nous avons évalué le CLASS3W–MWM pour une tourbière haute (Mer Bleue, situé à 45,41°N, 75,48°O, dans l'est du Canada) et pour une tourbière basse ombrotrophe (Degerö Stormyr, situé à 64°11′N, 19°33′E, dans le nord de la Suède).

Le CLASS3W–MWM a très bien capturé la grandeur et la direction du recyclage actuel du carbone, tant pour les tourbières hautes que pour les tourbières basses. De plus, la variabilité saisonnière et interannuelle a été raisonnablement bien reproduire. Les écarts-types étaient <0,65 et les degrés de concordance (d*) étaient >0,8 pour les composantes de la production nette de l’écosystème tant pour la tourbière haute Mer Bleue que pour la tourbière basse Degerö Stormyr. La performance du modèle couplé pour la tourbière haute et la tourbière basse est semblable à celle du MWM autonome piloté par des conditions observées plutôt que par un climat simulé de la surface et du sol. Cette étude par modèle suggère que les tourbières du Nord sont des écosystèmes hydrologiquement et thermiquement conservatifs. Il a aussi été démontré que le recyclage du carbone pour les tourbières hautes et basses était plus sensible aux changements dans la température de l'air que dans les précipitations. Des changements de température de l'ordre de ceux projetés par le Groupe d'experts intergouvernemental sur l’évolution du climat (GIEC) font que les actuels puits de carbone que constituent les tourbières se transforment en sources, mais les changements projetés dans les précipitations maintiennent encore les tourbières comme des puits de carbone, quoique dans une moindre mesure. L'accroissement de la concentration du CO₂ atmosphérique améliore la séquestration du carbone à la fois pour les tourbières hautes et les tourbières basses. Notre analyse de sensibilité suggère que les tourbières du Nord réagissent aux changements dans la température et les précipitations et à une concentration doublée de CO₂ d'une façon fort peu linéaire. La sensibilité du recyclage du carbone dans les tourbières du Nord par rapport aux changements dans la température de l'air, les précipitations et la concentration du CO₂ atmosphérique ensemble n'est pas une simple addition ou soustraction de la sensibilité aux changements individuels. Par conséquent, la sensibilité à une combinaison de changements dans la température et les précipitations et à une concentration doublée de CO₂ est très différente de la sensibilité des tourbières à chaque variable environnementale prise seule. Notre analyse de sensibilité suggère que les tourbières basses ont une plus faible tolérance aux changements climatiques que les tourbières hautes.  相似文献   

Modelling two‐dimensional steady‐state groundwater flow and flow sensitivity to boundary conditions in blanket peat complexes     

D. R. Lapen  J. S. Price  R. Gilbert 《水文研究》2005,19(2):371-386

This study used a two‐dimensional steady‐state finite‐element groundwater flow model to simulate groundwater flow in two Newfoundland blanket peat complexes and to examine flow system sensitivity to changes in water table recharge and aquifer properties. The modelling results were examined within the context of peat‐forming processes in the two complexes. Modelled flow compared favourably with observed flow. The sensitivity analyses suggested that more highly decomposed bog peat along bog margins probably has/had a positive impact on net peat accumulation within bog interiors. Peat with lower hydraulic conductivity along bog margins effectively impedes lateral drainage, localizes water table drawdown to extreme bog margins, and elevates water tables along bog interiors. Peat formation and elevated water tables in adjacent poor fens/laggs currently rely on placic and ortstein horizons impeding vertical drainage and water flow inputs from adjacent bogs. Modest reductions in atmospheric recharge were found to govern bog‐flow‐system geometries in a way that would adversely affect paludification processes in adjacent fens/laggs. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

Testate amoebae as proxies for mean annual water‐table depth in Sphagnum‐dominated peatlands of North America     

Robert K. Booth 《第四纪科学杂志》2008,23(1):43-57

Peatland‐inhabiting testate amoebae are sensitive indicators of substrate‐moisture conditions and have increasingly been used in palaeohydrological studies. However, to improve accuracy of testate‐amoeba‐based hydrological inferences, baseline ecological data on rare taxa, a larger geographic network of calibration sites, and incorporation of long‐term estimates of water‐table depth are needed. Species–environment relationships at 369 sites from 31 peatlands in eastern North America were investigated. Long‐term estimates of water‐table depth were obtained using the method of polyvinyl (PVC) tape‐discolouration. Transfer functions were developed using a variety of models, and validated through jackknifing techniques and with an independent dataset where water‐table depths were directly measured throughout the growing season. Results indicate that mean annual water‐table depth can be inferred from testate amoeba assemblages with a mean error of 6 to 8 cm, although there is a slight systematic bias. All transfer function models performed similarly and produced similar reconstructions on a fossil sequence. In a preliminary effort towards development of a comprehensive North American calibration dataset, data from this study were combined with previous studies in Michigan and the Rocky Mountains (n = 650). This combined dataset had slightly larger mean errors of prediction (8–9 cm) but includes data for several rare taxa. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Seasonal ground ice impacts on spring ecohydrological conditions in a western boreal plains peatland     

Brandon Van Huizen  Richard M. Petrone  Jonathan S. Price  William L. Quinton  John W. Pomeroy 《水文研究》2020,34(3):765-779

Peatlands in the Western Boreal Plains act as important water sources in the landscape. Their persistence, despite potential evapotranspiration (PET) often exceeding annual precipitation, is attributed to various water storage mechanisms. One storage element that has been understudied is seasonal ground ice (SGI). This study characterized spring SGI conditions and explored its impacts on available energy, actual evapotranspiration, water table, and near surface soil moisture in a western boreal plains peatland. The majority of SGI melt took place over May 2017. Microtopography had limited impact on melt rates due to wet conditions. SGI melt released 139mm in ice water equivalent (IWE) within the top 30cm of the peat, and weak significant relationships with water table and surface moisture suggest that SGI could be important for maintaining vegetation transpiration during dry springs. Melting SGI decreased available energy causing small reductions in PET (<10mm over the melt period) and appeared to reduce actual evapotranspiration variability but not mean rates, likely due to slow melt rates. This suggests that melting SGI supplies water, allowing evapotranspiration to occur at near potential rates, but reduces the overall rate at which evapotranspiration could occur (PET). The role of SGI may help peatlands in headwater catchments act as a conveyor of water to downstream landscapes during the spring while acting as a supply of water for the peatland. Future work should investigate SGI influences on evapotranspiration under differing peatland types, wet and dry spring conditions, and if the spatial variability of SGI melt leads to spatial variability in evapotranspiration.  相似文献   

Three-dimensional reconstruction of carbon accumulation and CH4 emission during nine millennia in a raised mire     

ATTE KORHOLA  JUKKA ALM  KIMMO TOLONEN  JUKKA TURUNEN  H GNE JUNGNER 《第四纪科学杂志》1996,11(2):161-165

A three-dimensional model, based on numerous vertical and horizontal ¹⁴C datings and GIS simulation from a concentrically domed mire in southern Finland, demonstrates considerable variation in actual (net) rate of carbon accumulation (ARCA) through time. Lateral growth between 9000 and 3000 yr ago accounts for only 25% of the total carbon sequestration, whereas bog formation after ombrotrophication is responsible for the remaining 75%. On the other hand, the most rapid increase in landscape CH₄ flux occurred between 4500 and 3000 yr ago, the period of the fastest horizontal growth. In addition to autecological factors, a climatic shift towards cooler and wetter conditions is a plausible mechanism for maintaining accelerated carbon accumulation.  相似文献   

FLOW REVERSALS IN PEATLANDS INFLUENCED BY LOCAL GROUNDWATER SYSTEMS     

K. J. DEVITO  J. M. WADDINGTON  B. A. BRANFIREUN 《水文研究》1997,11(1):103-110

Piezometric head data from various depths were examined at two peatlands in Ontario, Canada and one peatland in Sweden influenced by small-scale, shallow groundwater systems. Data from different hydrogeological settings show reversals in groundwater flow leading to discharge in topographically high regions of peatlands in isolation from large-scale groundwater flow. It is suggested that subsurface flow within peat can reverse in direction in response to water deficit and water-table drawdown. The data presented here refute the assumption that local groundwater flow in peatlands is unidirectional and further illustrate the fact that measurable subsurface water flow can occur at depth in peat isolated from large-scale groundwater flow systems. In the light of implicit assumptions made by many workers on water movement in peatlands, especially when connected to small-scale groundwater systems, the consequences of such reversals are paramount in understanding the hydrology and biogeochemistry of peatlands. © 1997 by John Wiley & Sons, Ltd.  相似文献   

Vegetation and environments since the Last Glacial Maximum in the Southern Tablelands,New South Wales          下载免费PDF全文

GEOFF HOPE 《第四纪科学杂志》2014,29(8):778-788

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The effect of climate change on carbon in Canadian peatlands   总被引：3，自引：0，他引：3  

Charles Tarnocai   《Global and Planetary Change》2006,53(4):222

Peatlands, which are dominant features of the Canadian landscape, cover approximately 1.136 million km², or 12% of the land area. Most of the peatlands (97%) occur in the Boreal Wetland Region (64%) and Subarctic Wetland Region (33%). Because of the large area they cover and their high organic carbon content, these peatlands contain approximately 147 Gt soil carbon, which is about 56% of the organic carbon stored in all Canadian soils.A model for estimating peatland sensitivity to climate warming was used to determine both the sensitivity ratings of various peatland areas and the associated organic carbon masses. Calculations show that approximately 60% of the total area of Canadian peatlands and 51% of the organic carbon mass in all Canadian peatlands is expected to be severely to extremely severely affected by climate change.The increase in average annual air temperature of 3–5 °C over land and 5–7 °C over the oceans predicted for northern Canada by the end of this century would result in the degradation of frozen peatlands in the Subarctic and northern Boreal wetland regions and severe drying in the southern Boreal Wetland Region. In addition, flooding of coastal peatlands is expected because of the predicted rise in sea levels. As a result of these changes, a large part of the carbon in the peatlands expected to be severely and extremely severely affected by climate change could be released into the atmosphere as carbon dioxide (CO₂) and methane (CH₄), which will further increase climate warming.  相似文献   

Satellite-based peatland mapping: Potential of the MODIS sensor     

Dirk Pflugmacher  Olga N. Krankina  Warren B. Cohen 《Global and Planetary Change》2007,56(3-4):248

Peatlands play a major role in the global carbon cycle but are largely overlooked in current large-scale vegetation mapping efforts. In this study, we investigated the potential of the Moderate Resolution Imaging Spectroradiometer (MODIS) to capture the extent and distribution of peatlands in the St. Petersburg region of Russia by analyzing the relationships between peatland cover fractions derived from reference maps and  1-km resolution MODIS Nadir BRDF-Adjusted Reflectance (NBAR) data from year 2002.First, we characterized and mapped 50 peatlands from forest inventory and peat deposit inventory data. The peatlands represent three major nutritional types (oligotrophic, mesotrophic, eutrophic) and different sizes (0.6–7800 ha). In addition, parts of 6 peatlands were mined for peat and these were mapped separately. The reference maps provided information on peatland cover for 1105 MODIS pixels. We performed regression analysis on 50% of the pixels and reserved the remainder for model validation. Canonical correlation analysis on the MODIS reflectance bands and the peatland cover fractions produced a multi-spectral peatland cover index (PCI), which served as the predictor in a reduced major axis (RMA) regression model. The results suggest a high potential for mapping peatlands with MODIS. The RMA regression models explained much of the variance in the PCI (r² = 0.74 for mined and r² = 0.81 for unmined peatlands). Model validation showed high correlation between observed versus predicted peatland cover (mined: r = 0.87; unmined: r = 0.92). We used the models to derive peatland cover estimates for the St. Petersburg region and compared the results to current MODIS land cover maps.  相似文献