89 resultados para Canada
Resumo:
Testate amoebae have been used widely as a proxy of hydrological change in ombrotrophic peatlands, although their response to abiotic controls in other types of mire and fenland palaeo-environments is less well understood. This paper examines the response of testate amoebae to hydroseral and other environmental changes at Mer Bleue Bog, Ontario, Canada, a large ombrotrophic peatland, which evolved from a brackish-water embayment in the early Holocene. Sediments, plant macrofossils and diatoms examined from a 5.99 m core collected from the dome of the bog record six stages of development: i) a quiet, brackish-water riverine phase (prior to ca. 8500 cal BP); ii) a shallow lake (ca. 8500–8200 cal BP); iii) fen (8200–7600 cal BP); iv) transitional mire (7600–6900 cal BP); v) pioneer raised mire (6900–4450 cal BP); and vi) ombrotrophic bog (4450 cal BP-present).
Testate amoebae, notably small (<25 µm diameter) specimens of Centropyxis aculeata type, first appear in low abundances in sediments ascribed to the lacustrine phase. Diatoms from the same horizons record a shallowing in water depth, a decline in salinity and the development of emergent macrophytic vegetation, which may have provided favourable conditions for testate amoeba colonization. The testate amoeba communities of the inferred fen phase are more diverse and include centropyxids, cyclopyxids, Arcellidae and Hyalospheniidae, although the assemblages show some differences to those recently reported in modern European fen environments. The Fen–Bog Transition (FBT) is also dominated by C. aculeata type. The change in testate amoeba communities around this key transition is apparent in the results of Detrended Correspondence Analysis (DCA), and appears to reflect a latent nutrient gradient and a secondary moisture gradient. DCA analyses of plant macrofossil remains around the FBT show a similar trend, although the sensitivity of the two proxies to the inferred environmental changes differs. Comparisons with other regional mid-Holocene peatland records confirm the important influence of reduced effective precipitation on the testate amoeba communities during the initiation and development of Sphagnum-dominated, raised bog communities.
Resumo:
ABSTRACT High resolution records of mid-late Holocene hydro-climatic change are presented from Mer Bleue Bog, eastern Ontario. Past climatic changes in this region have previously been inferred from lake sediments, but rain-fed peatlands can offer additional insights into the spatial and temporal pattern of moisture availability. In this study, reconstructed water table depths are based on a testate amoeba-derived transfer function developed for the region and changes in bog surface wetness are compared with plant macrofossil and peat humification data.
RÉSUMÉ Nous présentons les enregistrements hautes résolutions des variations hydrologique durant la second moitié de l’Holocène pour les tourbières Mer Bleue á l’est de l'Ontario. Précédemment, les changements climatiques de cette région ont été dérivés à partir de prélèvement de sédiments de lac. Mais ils s’avèrent que les tourbières ombrotrophes offrir un éclairage supplémentaire sur les schémas de répartition spatiale et temporelle de la disponibilité de l'humidité. Dans cette étude, des profondeurs reconstruites de nappe phréatique sont basées sur un modèle de function de transfert d’amibes (Arcellinida) et des changements de l’humidité de surface de la tourbière sont comparés avec les macrofossils et au humification de tourbe dans une analyse multi-proxy.
