Ice-wedge polygon mires feature a micro-relief of dry ridges, shallow wet depressions, deeper wet troughs and transitional sites, resulting in a local mosaic of vegetation. The correct recognition of these landscape elements in palaeoecological studies of peat sections requires insight about the suitability of proxies and their potential for palaeoecological reconstruction in order to reconstruct vegetation and wetness patterns as well as dynamics. This paper analyses a 105.5 cm long peat section with a base dating to about 4000 cal yr BP from an ice-wedge polygon mire near Kytalyk (NE Siberia). Pollen, macrofossils, testate amoebae, geochemistry and sediment properties were analysed in order to compare the suitability of these proxies to reconstruct past surface wetness. The proxies show similar wetness trends. Pollen and geochemistry data did not always permit wetness reconstruction, the former because many pollen types do not allow the identification of taxa at a low taxonomic resolution, the latter because later taphonomic processes modify chemical variables in deeper peat layers. Macrofossils provided the most detailed wetness reconstruction, because they could be identified to genera or species, for which the moisture requirements are accurately known from their present-day distribution in ice-wedge polygons. All proxies, except geochemistry, show an obvious change from wet to dry conditions at around 20 cm depth. However, as the proxies sometimes show contradictory results, a multi-proxy approach is preferable over a single proxy interpretation as it allows the reconstruction of environmental development in a broader palaeoecological context. Figure 2 Location of ice-wedge polygon Lhc11 near the Kytalyk research station along the Berelekh River: (A, B) the study area, indicated are the most important landforms; (C) satellite image of the study area (GeoEye image from 2010, 0.5 m resolution, by courtesy of K. van Huissteden, Vrije Universiteit, Faculty of Earth and Life Sciences, Amsterdam); and (D) ice-wedge polygon Lhc11. This figure is available in colour online at wileyonlinelibrary.com/journal/ppp 78 A. Teltewskoi et al.
Plant growth in arctic tundra is known to be commonly limited by nitrogen. However, biogeochemical interactions between soil, vegetation and microbial biomass in arctic ecosystems are still insufficiently understood. In this study, we investigated different compartments of the soil-vegetation system of polygonal lowland tundra: bulk soil, inorganic nutrients, microbial biomass and vegetation biomass were analyzed for their contents of carbon, nitrogen, phosphorus and potassium. Samples were taken in August 2011 in the Indigirka lowlands (NE Siberia, Russia) in a detailed grid (4 m × 5 m) in one single ice-wedge polygon. We used a stoichiometric approach, based on the N/P ratios in the vegetation biomass and the investigated soil fractions, to analyze limitation relations in the soil-vegetation system. Plant growth in the investigated polygonal tundra appears to be co-limited by nitrogen and phosphorus or in some cases only limited by nitrogen whereas potassium is not limiting plant growth. However, as the N/P ratios of the microbial biomass in the uppermost soil horizons were more than twice as high as previously reported for arctic ecosystems, nitrogen mineralization and fixation may be limited at present by phosphorus. We found that only 5 % of the total nitrogen is already cycling in the biologically active fractions. On the other hand, up to 40 % of the total phosphorus was found in the biologically active fractions. Thus, there is less potential for increased phosphorus mineralization than for increased nitrogen mineralization in response to climate warming, and strict phosphorus limitation might be possible in the long-term
In ice-wedge polygon mires, small-scaled microrelief of ridges enclosing small depressions results in a short-distance vegetation mosaic. The correct recognition of these landscape elements in palaeoecological studies of peat sections in order to reconstruct their patterns and dynamics requires insight in the short-distance relationship between vegetation and pollen deposition. This paper presents an analysis of pollen surface samples in a high-resolution (1 m) transect across an ice-wedge polygon near Kytalyk (NE Siberia), including a discussion on the morphology of some critical pollen types and non-pollen palynomorphs (NPPs). We found a strong correlation between vegetation and surface elevation and a fair correspondence between pollen deposition and vegetation. Distribution of NPPs reflects surface elevation well, with algal spores dominating deep spots and testate amoebae prevailing on higher spots. Peak pollen/spore values unrelated to high species coverages (e.g. of Salix, Betula, Sphagnum, Poaceae) indicate that single plants within a population may cause the bulk of the pollen production. The absence of pollen of taxa with an important presence in the vegetation (e.g. Utricularia) must be attributable to low pollen productivity. Distributional patterns point at pollen transport by water in the polygon troughs/ depressions. Our study shows that Arctic pollen records mainly reflect short-distance vegetation patterns. Palaeosequences consequently allow accurate reconstruction of local microtopography and its dynamics, but should not be overinterpreted in terms of changing (over)regional vegetation patterns and associated drivers.
The reconstruction of past environments by means of macrofossil and pollen analysis is commonly based on the modern ecological preferences of the taxa that may have produced these fossils. Here we present a modelling approach, in which we use modern vegetation-surface height relationships to quantify past surface heights in an Arctic ice-wedge polygon mire. Vegetation composition and ground surface height (GSH) were assessed in a polygon mire near Kytalyk (Northeastern Siberia). Cluster analysis revealed five plant communities, which are clearly separated with respect to ground surface height, frost surface height and coverages of open water and vegetation. Based on the composition of modern vegetation we constructed two sets of potential fossil types (plant macrofossils and pollen), an extensive one and a more restricted one to reflect different conditions of preservation and recognisability. We applied Canonical Correspondence Analysis to model the relationships between potential fossil types and measured GSH. Both models show a strong relationship between modelled and measured GSH values and a high accuracy in prediction. Finally, we used the models to predict GSH values for Holocene peat samples and found a fair correspondence with expert-based multi-proxy reconstruction of wetness conditions, even though only a minor part of the encountered fossils were represented in the GSH models, illustrating the robustness of the approach. Our approach can be used to reconstruct palaeoenvironmental conditions in a more objective way and can serve as a template for further palaeoecological studies.
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