River flooding as a driver of polygon dynamics: modern vegetation data and a millennial peat record from the Anabar River lowlands (Arctic Siberia)

[摘要] The spatial and temporal variability of a low-centred polygon on the easternfloodplain area of the lower Anabar River (72.070° N,113.921° E; northern Yakutia, Siberia) has been investigated using amulti-method approach. The present-day vegetation in each square metre wasanalysed, revealing a community of Larix, shrubby Betula,and Salix on the polygon rim, a dominance of Carex andAndromeda polifolia in the rim-to-pond transition zone, and apredominantly monospecific Scorpidium scorpioides coverage withinthe pond. The total organic carbon (TOC) content, TOC / TN (total nitrogen) ratio, grain size, vascular plantmacrofossils, moss remains, diatoms, and pollen were analysed for twovertical sections and a sediment core from a transect across the polygon.Radiocarbon dating indicates that the formation of the polygon started atleast 1500 yr ago; the general positions of the pond and rim have notchanged since that time. Two types of pond vegetation were identified,indicating two contrasting development stages of the polygon. The first was awell-established moss association, dominated by submerged or floatingScorpidium scorpioides and/or Drepanocladus spp. andovergrown by epiphytic diatoms such as Tabellaria flocculosaand Eunotia taxa. This stage coincides temporally with a period inwhich the polygon was only drained by lateral subsurface water flow, asindicated by mixed grain sizes. A different moss association occurred duringtimes of repeated river flooding (indicated by homogeneous medium-grainedsand that probably accumulated during the annual spring snowmelt),characterized by an abundance of Meesia triquetra and a dominance ofbenthic diatoms (e.g. Navicula vulpina), indicative of a relativelyhigh pH and a high tolerance of disturbance. A comparison of the localpolygon vegetation (inferred from moss and macrofossil spectra) with theregional vegetation (inferred from pollen spectra) indicated that the mossassociation with Scorpidium scorpioides became established duringrelatively favourable climatic conditions, while the association dominated byMeesia triquetra occurred during periods of harsh climaticconditions. Our study revealed a strong riverine influence (in addition toclimatic influences) on polygon development and the type of peat accumulated.

[学科分类] 地球化学与岩石