[1] Thermokarst wetlands and ponds in the subarctic, which are located in land surface depressions resulting from permafrost melt, are strong sources of CH 4 , but little is known about respiration processes supporting these emissions. We determined CH 4 fluxes and concentration profiles of dissolved gases and anions and some d 13 C ratios of CO 2 and CH 4 in a thermokarst pond and adjacent smaller thermokarst depressions in the forest tundra near Igarka, northern Siberia in August 2006. Methane was emitted at 110-170 mg m À2 d À1 and produced mostly by CO 2 reduction, which also provided high Gibbs free energies on the order of 50-70 KJ mol À1 H 2 due to high H 2 concentrations. The diffusive flux calculated from CH 4 gradients in the floating mat contributed <2% to emissions. CH 4 was apparently not oxidized deeper than 20 cm into the floating mat and the water body below. Anaerobic respiration required to reproduce nonsteady state CO 2 concentration maxima in the floating mat above the water body was 30-80 nmol cm À3 d À1 or 250 mg m À2 d À1 and thus on a similar order of magnitude as CH 4 fluxes. The results suggest that floating mat-covered thermokarst ponds located in northern Siberian bogs effectively convert recently fixed carbon into CH 4 and thus allow for emissions independently from the finite, bog-derived carbon source. The relative contribution of recently fixed and old bog-derived carbon to C fluxes requires further investigation, however.

The concentration of 50 chemical elements in the leaves of Populus suaveolens Fischer and Betula pendula Roth growing in tailings dumps and dumps of gold deposits in Eastern Transbaikalia (Baley) was studied. It was found that the highest concentration of most elements was in the leaves of plants growing at the ZIF-2 tailings dump, and the lowest was on the sands of the thorium tailings dump and sand–pebble soil at the dredge gold mining site. Populus suaveolens differed from Betula pendula by a higher concentration of most chemical elements. A feature of the elemental composition of birch was a significant concentration of Mn and Ba in relation to poplar. The concentration of a number of chemical elements significantly exceeded the clark of terrestrial plants, as well as the maximum permissible levels of concentration of elements established for feed and medicinal plant raw materials.