Permafrost carbon feedback (PCF) modeling has focused on gradual thaw of near-surface permafrost leading to enhanced carbon dioxide and methane emissions that accelerate global climate warming. These state-of-the-art land models have yet to incorporate deeper, abrupt thaw in the PCF. Here we use model data, supported by field observations, radiocarbon dating, and remote sensing, to show that methane and carbon dioxide emissions from abrupt thaw beneath thermokarst lakes will more than double radiative forcing from circumpolar permafrost-soil carbon fluxes this century. Abrupt thaw lake emissions are similar under moderate and high representative concentration pathways (RCP4.5 and RCP8.5), but their relative contribution to the PCF is much larger under the moderate warming scenario. Abrupt thaw accelerates mobilization of deeply frozen, ancient carbon, increasing 14C-depleted permafrost soil carbon emissions by ~125-190% compared to gradual thaw alone. These findings demonstrate the need to incorporate abrupt thaw processes in earth system models for more comprehensive projection of the PCF this century.
The (137)Cs-based chronological approach is suggested to identify the age of urban landscapes and the chronology of pollution of soil in residential areas. Three main pivot points constitute the basis of the chronological approach: beginning of the Atomic Era in 1945, the maximum input in 1963 and the Chernobyl accident in 1986. Application of (137)Cs as a timescale tracer was tested on the example of Ekaterinburg, a city in the Middle Urals region of Russia. The sampling of recent urban sediments of micro water bodies (puddles) was carried out in 210 locations in 2007-2010. The concentrations of Pb, Zn, Cu, Ni, Co, Mn and Fe, and activity concentrations of (137)Cs were measured. It was found that the (137)Cs concentrations in the puddle sediments correlated with the age of surrounding buildings determined by the year of construction. The correlations between the concentrations of metals and (137)Cs in the puddle sediments identified the major pollutants of the urban area, assessing their background concentrations and obtaining the average annual inputs.
Institute of Plant Sciences and Oeschger Center for Climate Change Research, University of Bern, Altenbergrain 21, CH-3013 Bern, Switzerland. willy.tinner@ips.unibe.ch
Recent observations and model simulations have highlighted the sensitivity of the forest-tundra ecotone to climatic forcing. In contrast, paleoecological studies have not provided evidence of tree-line fluctuations in response to Holocene climatic changes in Alaska, suggesting that the forest-tundra boundary in certain areas may be relatively stable at multicentennial to millennial time scales. We conducted a multiproxy study of sediment cores from an Alaskan lake near the altitudinal limits of key boreal-forest species. Paleoecological data were compared with independent climatic reconstructions to assess ecosystem responses of the forest tundra boundary to Little Ice Age (LIA) climatic fluctuations. Pollen, diatom, charcoal, macrofossil, and magnetic analyses provide the first continuous record of vegetation fire-climate interactions at decadal to centennial time scales during the past 700 years from southern Alaska. Boreal-forest diebacks characterized by declines of Picea mariana, P. glauca, and tree Betula occurred during the LIA (AD 1500-1800), whereas shrubs (Alnus viridis, Betula glandulosa/nana) and herbaceous taxa (Epilobium, Aconitum) expanded. Marked increases in charcoal abundance and changes in magnetic properties suggest increases in fire importance and soil erosion during the same period. In addition, the conspicuous reduction or disappearance of certain aquatic (e.g., Isoetes, Nuphar, Pediastrum) and wetland (Sphagnum) plants and major shifts in diatom assemblages suggest pronounced lake-level fluctuations and rapid ecosystem reorganization in response to LIA climatic deterioration. Our results imply that temperature shifts of 1-2 degrees C, when accompanied by major changes in moisture balance, can greatly alter high-altitudinal terrestrial, wetland, and aquatic ecosystems, including conversion between boreal-forest tree line and tundra. The climatic and ecosystem variations in our study area appear to be coherent with changes in solar irradiance, suggesting that changes in solar activity contributed to the environmental instability of the past 700 years.
This research work is devoted to analyzing the processes of accumulation and distribution of long-lived radionuclides of 90Sr and 137Cs in the components of water-sediment-macrophytes of Lake Malye Kirpichiky (Chelyabinsk region). The characteristic features of redistribution of radioactive substances, depending on the texture of the bottom sediments of the lake and the species composition of aquatic vegetation are shown. Also shown is the total stock of radionuclides in water and bottom sediments. The coefficients of 90Sr and 137Cs accumulation in bottom sediments and macrophytes have been calculated.
An environmental survey was performed in Lake Kyrtj?nn, a small lake within an abandoned shooting range in the south of Norway. In Lake Kyrtj?nn the total water concentrations of Pb (14?g/L), Cu (6.1?g/L) and Sb (1.3?g/L) were elevated compared to the nearby reference Lake Stitj?nn, where the total concentrations of Pb, Cu and Sb were 0.76, 1.8 and 0.12?g/L, respectively. Brown trout (Salmo trutta) from Lake Kyrtj?nn had very high levels of Pb in bone (104mg/kg w.w.), kidney (161mg/kg w.w.) and the gills (137mg/kg d.w), and a strong inhibition of the ALA-D enzyme activity were observed in the blood (24% of control). Dry fertilized brown trout eggs were placed in the small outlet streams from Lake Kyrtj?nn and the reference lake for 6 months, and the concentrations of Pb and Cu in eggs from the Lake Kyrtj?nn stream were significantly higher than in eggs from the reference. More than 90% of Pb accumulated in the egg shell, whereas more than 80% of the Cu and Zn accumulated in the egg interior. Pb in the lake sediments was elevated in the upper 2-5cm layer (410-2700mg/kg d.w), and was predominantly associated with redox sensitive fractions (e.g., organic materials, hydroxides) indicating low potential mobility and bioavailability of the deposited Pb. Only minor amounts of Cu and Sb were deposited in the sediments. The present work showed that the adult brown trout, as well as fertilized eggs and alevins, may be subjected to increased stress due to chronic exposure to Pb, whereas exposure to Cu, Zn and Sb were of less importance.
Active microbial communities of deep crystalline bedrock fracture water were investigated from seven different boreholes in Olkiluoto (Western Finland) using bacterial and archaeal 16S rRNA, dsrB, and mcrA gene transcript targeted 454 pyrosequencing. Over a depth range of 296-798?m below ground surface the microbial communities changed according to depth, salinity gradient, and sulphate and methane concentrations. The highest bacterial diversity was observed in the sulphate-methane mixing zone (SMMZ) at 250-350?m depth, whereas archaeal diversity was highest in the lowest boundaries of the SMMZ. Sulphide-oxidizing e-proteobacteria (Sulfurimonas sp.) dominated in the SMMZ and ?-proteobacteria (Pseudomonas spp.) below the SMMZ. The active archaeal communities consisted mostly of ANME-2D and Thermoplasmatales groups, although Methermicoccaceae, Methanobacteriaceae, and Thermoplasmatales (SAGMEG, TMG) were more common at 415-559?m depth. Typical indicator microorganisms for sulphate-methane transition zones in marine sediments, such as ANME-1 archaea, a-, ß- and d-proteobacteria, JS1, Actinomycetes, Planctomycetes, Chloroflexi, and MBGB Crenarchaeota were detected at specific depths. DsrB genes were most numerous and most actively transcribed in the SMMZ while the mcrA gene concentration was highest in the deep methane rich groundwater. Our results demonstrate that active and highly diverse but sparse and stratified microbial communities inhabit the Fennoscandian deep bedrock ecosystems.
The rates of sulfate reduction (SR) and the diversity of sulfate-reducing bacteria (SRB) were studied in the sediments of the Posol'skaya banka elevation in the southern part of Lake Baikal. SR rates varied from 1.2 to 1641 nmol/(dm3 day), with high rates (> 600 nmol/(dm3 day)) observed at both deep-water stations and in subsurface silts. Integral SR rates calculated for the uppermost 50 cm of the sediments were higher for gas-saturated and gas hydrate-bearing sediments than in those with low methane content. Enrichment SRB cultures were obtained in Widdel medium for freshwater SRB. Analysis of the 16S rRNA gene fragments from clone libraries obtained from the enrichments revealed the presence of SRB belonged to Desulfosporosinus genus, with D. lacus as the most closely related member (capable of sulfate, sulfite, and thiosulfate reduction), as well as members of the order Clostridiales.
We characterized spatial patterns of surface sediment concentrations of seven polychlorinated biphenyls (PCBs), seven polycyclic aromatic hydrocarbons (PAHs), three chlorinated pesticides, and five metals in Norwegian waters and Skagerrak. In total, we analyzed 5036 concentrations of 22 chemical substances that were measured between 1986 and 2014 at 333 sampling sites by means of generalized additive models (GAMs). We found that GAMs with organic carbon content of the sediment and latitude and longitude as co-variates explained as ca. 75% of the variability of the contaminant sediment concentrations. For metals, a predominantly hotspot-driven spatial pattern was found, i.e., we identified historical pollution hotspots (e.g., Sørfjord in western Norway) for mercury, zinc, cadmium, and lead. Highest concentrations of PAHs and PCBs were found close to densely populated and industrialized regions, i.e., in the North Sea and in the Kattegat and Skagerrak. The spatial pattern of the PCBs suggests the secondary and diffuse atmospheric nature of their sources. Atmospheric inputs are the main sources of pollution for most organic chemicals considered, but north of the Arctic circle, we found that concentrations of PAHs increased from south to north most likely related to a combination of coal-eroding bedrock and the biological pump. The knowledge acquired in the present research is essential for developing effective remediation strategies that are consistent with international conventions on pollution control.
Laboratory batch experiments have been performed with sediment and groundwater obtained from two sites in Denmark to study the aerobic biodegradation of vinyl chloride (VC) and cis-1,2-dichloroethylene (c-1,2-DCE) to assess the natural aerobic biodegradation potential at two sites. The experiments revealed that VC was degraded to below the detection limit within 204 and 57 days at the two sites. c-1,2-DCE was also degraded in the experiments but not completely. At the two sites 50% and 35% was removed by the end of the experimental period of 204 and 274 days. The removal of c-1,2-DCE seems to occur concomitantly with VC indicating that the biodegradation of c-1,2-DCE may depend on the biodegradation of VC. However, in both cases natural groundwater was mixed with sediment and consequently there may be other compounds (e.g. ammonium, natural organic compound etc.) that serves as primary substrates for the co-metabolic biodegradation of c-1,2-DCE. At one of the sites methane was supplied to try to enhance the biodegradation of VC and c-1,2-DCE. That was successful since the time for complete biodegradation of VC decreased from 204 days in the absence of methane to 84 days in the presence of methane. For c-1,2-DCE the amount that was biodegraded after 204 days increased from 50% to 90% as a result of the addition of methane. It seems like a potential for natural biodegradation exists at least for VC at these two sites and also to some degree for c-1,2-DCE.
