Permafrost regions are under particular pressure from climate change resulting in wide-spread landscape changes, which impact also freshwater chemistry. We investigated a snapshot of hydrochemistry in various freshwater environments in the lower Kolyma river basin (North-East Siberia, continuous permafrost zone) to explore the mobility of metals, metalloids and non-metals resulting from permafrost thaw. Particular attention was focused on heavy metals as contaminants potentially released from the secondary source in the permafrozen Yedoma complex. Permafrost creeks represented the Mg-Ca-Na-HCO3-Cl-SO4 ionic water type (with mineralisation in the range 600-800 mg L-1), while permafrost ice and thermokarst lake waters were the HCO3-Ca-Mg type. Multiple heavy metals (As, Cu, Co, Mn and Ni) showed much higher dissolved phase concentrations in permafrost creeks and ice than in Kolyma and its tributaries, and only in the permafrost samples and one Kolyma tributary we have detected dissolved Ti. In thermokarst lakes, several metal and metalloid dissolved concentrations increased with water depth (Fe, Mn, Ni and Zn - in both lakes; Al, Cu, K, Sb, Sr and Pb in either lake), reaching 1370 mu g L-1 Cu, 4610 mu g L-1 Mn, and 687 mu g L-1 Zn in the bottom water layers. Permafrost-related waters were also enriched in dissolved phosphorus (up to 512 mu g L-1 in Yedoma-fed creeks). The impact of permafrost thaw on river and lake water chemistry is a complex problem which needs to be considered both in the context of legacy permafrost shrinkage and the interference of the deepening active layer with newly deposited anthropogenic contaminants.

The Central part of the Oka Plateau lying in the East Sayan Mountains is still a poorly studied area of southern Siberia as regards its paleogeography. This gap can be partially replenished by the results of the present study. This study is focused on reconstruction of the central Oka Plateau environment in the Middle-Late Holocene. The pollen from bottom sediments of Sagan-Nur Lake provided a qualitative reconstruction of the vegetation in the catchment area of the lake as well as the quantitative reconstruction of dominant vegetation types obtained via the biomization method. The reconstruction suggests the dominance of the tundra vegetation consisting of dwarf birch, alder, and willow with patches of spruce and larch between about 8120 and 7000 cal. yr BP. The climate was sharp continental with high soil moisture resulting from summer permafrost thaw. The expansion of the forest biome began in the Central Oka Plateau at about 7000 cal. yr BP due to climate warming, hydrological network reconstruction resulting from complete thaw of regional glaciers and degradation of the permafrost rocks. Around 3200 cal. yr BP, the larch forests with the participation of Siberian pine started spreading across the Sagan-Nur Lake catchment area, thus suggesting colder conditions than before. The obtained reconstructions can help identifying the promising lakes and their catchment areas in the East Sayan Mountains for potential sustainable development through special projects (e.g., educational, tourist, environmentally protected).

Air and ground temperatures measured in Eastern Siberia has been compiled and analyzed. The analysis of mean annual air temperatures measured at 52 meteorological stations within and near the East-Siberian transect during the period from 1956 through 1990 demonstrates a significant and statistically significant (at 0.05 level) positive trend ranging from 0.065 to 0.59 degrees C/ 10 yr. A statistically significant (at 0.05 level) positive trend was also observed in mean annual ground temperatures for the same period. The permafrost temperature reflects changes in air temperature on a decadal time scale much better than on an interannual time scale. Generally, positive trends in mean annual ground temperatures are slightly smaller in comparison with trends in mean annual air temperatures, except for several sites where the discordance between the air and ground temperatures can be explained by the winter snow dynamics. The average trend for the entire region was 0.26 degrees C/10 yr for ground temperatures at 1.6 in depth and 0.29 degrees C/10 yr for the air temperatures. The most significant trends in mean annual air and ground temperatures were in the southern part of the transect, between 55 degrees and 65 degrees N. Numerical modeling of ground temperatures has been performed for Yakutsk and Tiksi for the last 70 yr. Comparing the results of these calculations with a similar time series obtained for Fairbanks and Barrow in Alaska shows that similar variations of ground temperatures took place at the same time periods in Yakutsk and Fairbanks, and in Tiksi and Barrow. The decadal and longer time scale fluctuations in permafrost temperatures were pronounced in both regions. The magnitudes of these fluctuations were on the order of a few degrees centigrade. The fluctuations of mean annual ground temperatures were coordinated in Fairbanks and Yakutsk, and in Barrow and Tiksi. However, the magnitude and timing of these fluctuations were slightly different for each of the sites. (C) 2006 Elsevier B.V. All rights reserved.