Despite the importance of soil and surface waters freezing in permafrost landscapes, the behaviour of dissolved organic carbon (DOC), nutrients and metals during periodic freeze-thaw cycles (FTC) remains poorly known. The on-going climate warming is likely to increase the frequency of FTC in continental aquatic settings, which could modify the chemical composition of waters. In this study, we conducted 9 repetitive cycles of overnight freezing (similar to 20 degrees C) and 5 h thawing (4 degrees C) in the laboratory using representative 0.22 mu m-filtered waters from NE European permafrost peatland: leachates of vegetation and soil, and natural surface waters (depression, thermokarst lake and river). Only minor (10%). The leachates and the depression water were enriched in trace elements, whereas the thermokarst lake and the river demonstrated a decrease in concentration of Fe (similar to 39 and similar to 94%, respectively), Al (similar to 9 and similar to 85%), and Mn (similar to 10 and similar to 79%) during FTC. Overall, the observations demonstrated an increase in aliphatic low molecular weight organic matter (OM), and the precipitation of Fe, Al hydroxides and organo-mineral particles. Therefore, enhanced of frequency of FTC can favour the release of metals and toxicants from acidic OM-rich surface waters and maintain stable OM-metalscolloids in large lakes and rivers, thus regulating aquatic transport of DOC and metals from soils to the Arctic Ocean. (C) 2021 Elsevier Ltd. All rights reserved.

Forty soil and lichen samples and sixteen soil horizon samples were collected in the mining and surrounding areas of the Yamal-Nenets autonomous region (Russian Arctic). The positive matrix factorization (PMF) model was used for the source identification of PAHs. The results of the source identification showed that the mining activity was the major source of PAHs in the area, and that the mining influenced the surrounding natural area. The 5+6-ring PAHs were most abundant in the mining area. The lichen/soil (LAS) results showed that 2+3-ring and 4-ring PAHs could be transported by air and accumulated more in lichens than in the soil, while 5+6-ring PAHs accumulated more in the soil. Strong relationships between the quotient of soil/lichen (Q(SL)) and Log K-OA and Log P-L and between the quotient of lichen/histic horizon soil and K-OW were observed. In addition, hydrogeological conditions influenced the downward transport of PAHs. Particularly surprising is the discovery of the high levels of 5 + 6 rings in the permafrost table (the bottom of the active layer). One hypothesis is given that the global climate change may lead to further depth of active layer so that PAHs may migrate to the deeper permafrost. In the impact area of mining activities, the soil inventory for 5+6-ring PAHs was estimated at 0.14 +/- 0.017 tons on average. (C) 2019 Elsevier Ltd. All rights reserved.

Questions Is the macrolichen Usnea antarctica a nurse' species to Antarctic flora? Are positive plantplant interactions more frequent than negative interactions in Antarctic ecosystems? Are microclimatic modifications by cushions of U.antarctica responsible for the nurse effect? Location Two sites in Antarctica: King George Island, South Shetland (62 degrees 11S, 58 degrees 56W; 62 degrees 11S, 58 degrees 59W). Methods We evaluated the association of plant species with U.antarctica cushions by recording species growing in equivalent areas within and outside U.antarctica cushions. Additionally, we performed transplant experiments with Deschampsia antarctica individuals to assess if U.antarctica cushions enhance plant survival. In both study sites we monitored temperature, moisture and nutrient status of soil outside and within the cushions to provide insights into potential mechanisms underlying possible interactions between U.antarctica and other plant species. Results Eight out of 13 species were positively associated with cushions of the widespread lichen U.antarctica, while only one species (U.aurantiaco-atra) showed a negative association with U.antarctica. Survival of Deschampsia was enhanced when growing associated with U.antarctica cushions. Our results indicate that cushions ameliorated the extreme conditions of Antarctic islands through increased temperature and soil moisture, decreased radiation and evaporative water loss and increased nutrient availability. Conclusions The nurse effect of U.antarctica is verified. Cushions of this macrolichen may be a key component in structuring the Antarctic landscape and maintaining local species richness, and their presence might influence range expansion of other species.