Permafrost Peatlands Research Articles

Warming climate forcing impact from a sub-arctic peatland as a result of late Holocene permafrost aggradation and initiation of bare peat surfaces

Effects of permafrost aggradation on greenhouse gas (GHG) dynamics and climate forcing have not been previously quantified. Here, we reconstruct changes in GHG balances over the late Holocene for a sub-arctic peatland by applying palaeoecological data combined with measured GHG flux data, focusing on the impact of permafrost aggradation in particular. Our data suggest that permafrost initiation around 3000 years ago resulted in GHG emissions, thereby slightly weakening the general long-term peatland cooling impact. As a novel discovery, based on our chronological data of bare peat surfaces, we found that current sporadic bare peat surfaces in subarctic regions are probably remnants of more extensive bare peat areas formed by permafrost initiation. Paradoxically, our data suggest that permafrost initiation triggered by the late Holocene cooling climate generated a positive radiative forcing and a short-term climate warming feedback, mitigating the general insolation-driven late Holocene summer cooling trend. Our work with historical data demonstrates the importance of permafrost peatland dynamics for atmospheric GHG concentrations, both in the past and future. It suggests that, while thawing permafrost is likely to initially trigger a change towards wetter conditions and consequent increase in CH4 forcing, eventually the accelerated C uptake capacity under warmer climate may overcome the thaw effect when a new hydrological balance becomes established.

Soil Microbial Community Response to Permafrost Degradation in Palsa Fields of the Hudson Bay Lowlands: Implications for Greenhouse Gas Production in a Warming Climate

AbstractPermafrost thaw in northern peatlands alters the ground thermal conditions, moisture, and chemistry that control microbial activity responsible for the production of greenhouse gases (GHGs) like methane from decomposing organic matter. This paper examines interactions between microbial communities, peat chemistry, moisture content, and temperature in the context of degrading palsa fields in the vast (372,000 km2), carbon rich, and rapidly warming permafrost peatlands of the Hudson Bay Lowlands. The temperature sensitivities of microbial GHG production and consumption from palsa and fen peat were assessed, and microbial community structure was examined as a potential constraint on GHG production in relation to changes in peat chemistry associated with thermokarst encroachment and active layer deepening. High CH4 production was observed from thermokarst peat, under controlled moisture and temperature conditions, associated with increased pH. A shift in methanogen taxonomic and metabolic diversity favoring aceticlastic methanogenesis was associated with changes in peat chemistry and pH from palsa to thermokarst fen peat. In palsa peat, CH4 production rates were lowest but most sensitive to temperature variations, due to recalcitrant carbon compounds. CH4 production was highly sensitive to increased temperatures, yet was balanced by high temperature sensitivity of CH4 oxidation in oxic conditions, consistent with the low temperature sensitivity of fluxes observed in field studies from other permafrost peatlands. Building on the microbial controls in this study, future work should explore how permafrost degradation and increased hydrological connectivity to mineral substrates are changing in this globally significant permafrost peatland, and how this impacts net CH4 emissions.

Predicted Vulnerability of Carbon in Permafrost Peatlands With Future Climate Change and Permafrost Thaw in Western Canada

AbstractClimate warming in high‐latitude regions is thawing carbon‐rich permafrost soils, which can release carbon to the atmosphere and enhance climate warming. Using a coupled model of long‐term peatland dynamics (Holocene Peat Model, HPM‐Arctic), we quantify the potential loss of carbon with future climate warming for six sites with differing climates and permafrost histories in Northwestern Canada. We compared the net carbon balance at 2100 CE resulting from new productivity and the decomposition of active layer and newly thawed permafrost peats under RCP8.5 as a high‐end constraint. Modeled net carbon losses ranged from −3.0 kg C m−2 (net loss) to +0.1 kg C m−2 (net gain) between 2015 and 2100. Losses of newly thawed permafrost peat comprised 0.2%–25% (median: 1.6%) of “old” C loss, which were related to the residence time of peat in the active layer before being incorporated into the permafrost, peat temperature, and presence of permafrost. The largest C loss was from the permafrost‐free site, not from permafrost sites. C losses were greatest from depths of 0.2–1.0 m. New C added to the profile through net primary productivity between 2015 and 2100 offset ∼40% to >100% of old C losses across the sites. Differences between modeled active layer deepening and flooding following permafrost thaw resulted in very small differences in net C loss by 2100, illustrating the important role of present‐day conditions and permafrost aggradation history in controlling net C loss.

Mapping and understanding the vulnerability of northern peatlands to permafrost thaw at scales relevant to community adaptation planning

Developing spatially explicit permafrost datasets and climate assessments at scales relevant to northern communities is increasingly important as land users and decision makers incorporate changing permafrost conditions in community and adaptation planning. This need is particularly strong within the discontinuous permafrost zone of the Northwest Territories (NWT) Canada where permafrost peatlands are undergoing rapid thaw due to a warming climate. Current data products for predicting landscapes at risk of thaw are generally built at circumpolar scales and do not lend themselves well to fine-scale regional interpretations. Here, we present a new permafrost vulnerability dataset that assesses the degree of permafrost thaw within peatlands across a 750 km latitudinal gradient in the NWT. This updated dataset provides spatially explicit estimates of where peatland thermokarst potential exists, thus making it much more suitable for local, regional or community usage. Within southern peatland complexes, we show that permafrost thaw affects up to 70% of the peatland area and that thaw is strongly mediated by both latitude and elevation, with widespread thaw occuring particularly at low elevations. At the northern end of our latitudinal gradient, peatland permafrost remains climate-protected with relatively little thaw. Collectively these results demonstrate the importance of scale in permafrost analyses and mapping if research is to support northern communities and decision makers in a changing climate. This study offers a more scale-appropriate approach to support community adaptative planning under scenarios of continued warming and widespread permafrost thaw.

Permafrost Thaw Increases Methylmercury Formation in Subarctic Fennoscandia.

Methylmercury (MeHg) forms in anoxic environments and can bioaccumulate and biomagnify in aquatic food webs to concentrations of concern for human and wildlife health. Mercury (Hg) pollution in the Arctic environment may worsen as these areas warm and Hg, currently locked in permafrost soils, is remobilized. One of the main concerns is the development of Hg methylation hotspots in the terrestrial environment due to thermokarst formation. The extent to which net methylation of Hg is enhanced upon thaw is, however, largely unknown. Here, we have studied the formation of Hg methylation hotspots using existing thaw gradients at five Fennoscandian permafrost peatland sites. Total Hg (HgT) and MeHg concentrations were analyzed in 178 soil samples from 14 peat cores. We observed 10 times higher concentrations of MeHg and 13 times higher %MeHg in the collapse fen (representing thawed conditions) as compared to the peat plateau (representing frozen conditions). This suggests significantly greater net methylation of Hg when thermokarst wetlands are formed. In addition, we report HgT to soil organic carbon ratios representative of Fennoscandian permafrost peatlands (median and interquartile range of 0.09 ± 0.07 μg HgT g–1 C) that are of value for future estimates of circumpolar HgT stocks.

Holocene dynamics of an inland palsa peatland at Wiyâshâkimî Lake (Nunavik, Canada)

ABSTRACT This study examines the Holocene evolution of an inland subarctic permafrost peatland located on the north bank of Wiyâshâkimî Lake (Nunavik, northeastern Canada). The analysis of plant macrofossils allowed us to reconstruct the succession of the trophic conditions of a palsa and a filled thermokarst pond. The accumulation of organic matter began at around 6290 cal. y BP. The evolution of the site then followed three stages: a pond (6290–5790 cal. y BP), a minerotrophic peatland (5790–4350 cal. y BP) and an ombrotrophic peatland (from 4350 cal. y BP). The establishment of permafrost caused a palsa to form at around 170 cal. y BP, which corresponds to the coldest period of the Little Ice Age in northeastern Canada. A subsequent degradation of the palsa and the formation of a thermokarst pond were induced by the climate warming that began at the turn of the 20th century. The analysis of plant macrofossils from an adjacent filled thermokarst pond indicated three phases of development over a short 450-year period: subaquatic, minerotrophic, and ombrotrophic phases. When combined with previous studies of filled thermokarst ponds in northern Québec, this result indicates that ponds are rapidly filling in with vegetation and acting as carbon sinks.

Linking soil organic carbon mineralization with soil microbial and substrate properties under warming in permafrost peatlands of Northeastern China

Permafrost peatlands are important pools of soil carbon. Soil organic carbon (SOC) mineralization and its temperature sensitivity in permafrost peatlands are crucial for predictions of soil carbon-climate feedback. However, little is known about the changes in SOC mineralization and its mechanism in response to environmental change in the permafrost peatlands of Northeastern China. We collected seven permafrost peatland soils from Greater and Lesser Khingan Mountains in Northeastern China to investigate how the responses of microbes and labile substrates control the mineralization of SOC in the laboratory incubation study. The results show that temperature and sampling sites affected the mineralization of SOC. Elevated temperatures significantly increased the rate of carbon mineralization across the peatland soils. The mean sensitivity of SOC mineralization to temperature (Q10 value) was 2.96. The increase in substrate availability and microbial abundance in parallel with the increase in temperature is responsible for the high rates of decomposition of the organic carbon pools. We found that the mineralization of soil carbon positively correlated with the concentrations of soil dissolved organic carbon (DOC), NH4+-N, NO3−-N, as well as the abundances of bacteria, fungi, methanotrophs and nirK denitrifiers. Moreover, the content of DOC positively correlated with the abundances of soil bacteria, methanotrophs and nirK denitrifiers, indicating that the influences of soil microbial abundances on carbon mineralization were strongly mediated by the availability of carbon substrates. Our findings provide novel insights into the effects of increasing temperatures on the relationship between microbial communities and labile substrates and their roles in carbon decomposition in permafrost peatlands.

New progress achieved in seasonal dynamics of dissolved organic carbon of permafrost peatland through Chinese–United States EcoPartnership relationships

AbstractPermafrost peatland plays an important role in the global carbon (C) cycle, and dissolved organic carbon (DOC) is one of the most important components to C budgets in this system. Through the Chinese–United States EcoPartnership program, Dr Xianwei Wang, Li Sun, and Prof Changchun Song et al. from the Northeast Institute of Geography and Agroecology of Chinese Academy of Sciences and Prof Aixin Hou from the Louisiana State University observed dynamics of DOC concentrations and specific ultraviolet absorbance at 254 nm (SUVA254) obtained from soil porewater of permafrost peatlands for two growing seasons in the Great Hing'an Mountains, Northeast China. Soil porewater DOC concentrations varied greatly with depths during the growing season, ranging between 22.08 and 65.02 mg L−1. There was no significant relationship between DOC concentrations and SUVA254. DOC concentrations were higher in autumn and increased as the seasonal thaw depth increased. DOC concentrations of supra‐permafrost water at freeze–thaw boundary were also higher than those at the other soil depths. Temperature and thawing depth had been shown to affect DOC concentrations at different soil depths. Our finding suggests that warming and deepening of the active layer likely increase the DOC productions in the permafrost peatland, which may influence the C balance in these C‐enriched ecosystems.

Impact of freeze-thaw cycles on organic carbon and metals in waters of permafrost peatlands

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 (−20 °C) and 5 h thawing (4 °C) in the laboratory using representative 0.22 μm-filtered waters from NE European permafrost peatland: leachates of vegetation and soil, and natural surface waters (depression, thermokarst lake and river). Only minor (<5%–15%) changes of DOC concentrations, SUVA254 and molecular weight were observed in all leachates and the depression water. In contrast, several trace elements (Fe, Al, P, Mn, As, and REE) exhibited sizable variations during FTC (>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 (−39 and −94%, respectively), Al (−9 and −85%), and Mn (−10 and −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-metals-colloids in large lakes and rivers, thus regulating aquatic transport of DOC and metals from soils to the Arctic Ocean.

Unexpected greening in a boreal permafrost peatland undergoing forest loss is partially attributable to tree species turnover.

Time series of vegetation indices derived from satellite imagery are useful in measuring vegetation response to climate warming in remote northern regions. These indices show that productivity is generally declining in the boreal forest, but it is unclear which components of boreal vegetation are driving these trends. We aimed to compare trends in the normalized difference vegetation index (NDVI) to forest growth and demographic data taken from a 10ha mapped plot located in a spruce-dominated boreal peatland. We used microcores to quantify recent growth trends and tree census data to characterize mortality and recruitment rates of the three dominant tree species. We then compared spatial patterns in growth and demography to patterns in Landsat-derived maximum NDVI trends (1984-2019) in 78 pixels that fell within the plot. We found that NDVI trends were predominantly positive (i.e., "greening") in spite of the ongoing loss of black spruce (the dominant species; 80% of stems) from the plot. The magnitude of these trends correlated positively with black spruce growth trends, but was also governed to a large extent by tree mortality and recruitment. Greening trends were weaker (lower slope) in areas with high larch mortality, and high turnover of spruce and birch, but stronger (higher slope) in areas with high larch recruitment. Larch dominance is currently low (~11% of stems), but it is increasing in abundance as permafrost thaw progresses and will likely have a substantial influence on future NDVI trends. Our results emphasize that NDVI trends in boreal peatlands can be positive even when the forest as a whole is in decline, and that the magnitude of trends can be strongly influenced by the demographics of uncommon species.

Microbial abundance and enzymatic activity from tussock and shrub soil in permafrost peatland after 6-year warming

Soil microbes and enzymes in permafrost peatland are sensitive to temperature changes, which might result in more potential loss of carbon and increase in available nitrogen from permafrost peatlands in a warming world. We previously demonstrated that 3-year warming could affect soil microbial abundance and enzymatic activity. However, soil microbial abundance and enzymatic activity in permafrost peatlands under long-term climate warming is not well understood. Therefore, a 6-year field manipulation experiment was used to assess the impact of long-term warming on soil microbial abundance and enzymatic activity in a permafrost peatland in northeastern China. Results showed that 6-year warming increased the abundance of bacteria in 0 to 15 cm soil under tussock and from shrub rhizosphere, fungi from shrub non-rhizosphere, and archaea under tussock and from the rhizosphere of shrub. These increased microbial abundances could stimulate soil carbon cycling and accelerate soil carbon loss in permafrost peatland under warming. Six-year warming increased methanogen abundance in 0 to 15 cm soil and methanotroph abundance in 15 to 30 cm soil under tussock, indicating that warming could enhance CH4 cycling. Soil nirS-denitrifier abundance from the 0 to 15 cm shrub rhizosphere increased under warming, thereby suggesting that warming stimulated denitrification and N2O emission. β-Glucosidase activity in 0 to 15 cm soil under tussock and from shrub rhizosphere increased, but invertase activity in 15 to 30 cm soil under tussock and from shrub rhizosphere showed opposite tendency under warming. DOC content tended to increase in the 0 to 15 cm rhizosphere soil, but decreased in shrub non-rhizosphere soil. Warming increased NH4+–N content in both rhizosphere and non-rhizosphere soil. Positive correlations between abundances of bacteria, archaea, contents of DOC, and NH4+–N in 0 to 15 cm soil suggest that increases in bacterial and archaeal abundance could indicate higher carbon and nitrogen availability in topsoil of permafrost peatlands under warming. The results offer new insights into the response of plant–soil-microbe interactions in permafrost peatlands to climate change.

Lichen, moss and peat control of C, nutrient and trace metal regime in lakes of permafrost peatlands

Permafrost thaw in continental lowlands produces large number of thermokarst (thaw) lakes, which act as a major regulator of carbon (C) storage in sediments and C emission in the atmosphere. Here we studied thaw lakes of the NE European permafrost peatlands - shallow water bodies located within frozen peat bogs and receiving the majority of their water input from lateral (surface) runoff. We also conducted mesocosm experiments via interacting lake waters with frozen peat and dominant ground vegetation - lichen and moss. There was a systematic decrease in concentrations of dissolved C, CO2, nutrients and metals with an increase in lake size, corresponding to temporal evolution of the water body and thermokarst development. We hypothesized that ground vegetation and frozen peat provide the majority of C, nutrients and inorganic solutes in the water column of these lakes, and that microbial processing of terrestrial organic matter controls the pattern of CO2 and nutrient concentrations in thermokarst lakes. Substrate mass-normalized C, nutrient (N, P, K), major and trace metal release was maximal in moss mesocosms. After first 16 h of reaction, the pCO2 increased ten-fold in mesocosms with moss and lichen; this increase was much less pronounced in experiments with permafrost peat. Overall, moss and lichen were the dominant factors controlling the enrichment of the lake water in organic C, nutrients, and trace metals and rising the CO2 concentration. The global significance of obtained results is that the changes in ground vegetation, rather than mere frozen peat thawing, may exert the primary control on C, major and trace element balance in aquatic ecosystems of tundra peatlands under climate warming scenario.

The role of wetland expansion and successional processes in methane emissions from northern wetlands during the Holocene

The contribution from northern high latitude wetlands are a major uncertainty in the atmospheric methane (CH4) budget throughout the Holocene. We reconstructed CH4 emissions from northern peatlands from 13,000 BP to present using an empirical model based on observations of peat initiation (>3600 dates), peatland type (>250 peat cores), and observed CH4 emissions in order to explore the effects of changes in wetland type on CH4 emissions over the end of the late glacial and the Holocene. Fen area increased steadily before 8000 BP as fens formed in major wetland complexes. After 8000 BP, new fen formation continued but widespread peatland succession (to bogs) and permafrost aggradation occurred. Reconstructed CH4 emissions from peatlands increased rapidly between 10,600 BP and 6900 BP due to fen formation and expansion. Emissions stabilized after 5000 BP at 42 ± 25 Tg CH4 y−1 as high-emitting fens transitioned to lower-emitting bogs and permafrost peatlands. Widespread permafrost formation in northern peatlands after 1000 BP decreased CH4 emissions by 20%–34 ± 21 Tg y−1 by the present day and suggests peatland CH4 emissions will increase with permafrost thaw.

Functional capacities of microbial communities to carry out large scale geochemical processes are maintained during ex situ anaerobic incubation.

Mechanisms controlling CO2 and CH4 production in wetlands are central to understanding carbon cycling and greenhouse gas exchange. However, the volatility of these respiration products complicates quantifying their rates of production in the field. Attempts to circumvent the challenges through closed system incubations, from which gases cannot escape, have been used to investigate bulk in situ geochemistry. Efforts towards mapping mechanistic linkages between geochemistry and microbiology have raised concern regarding sampling and incubation-induced perturbations. Microorganisms are impacted by oxygen exposure, increased temperatures and accumulation of metabolic products during handling, storage, and incubation. We probed the extent of these perturbations, and their influence on incubation results, using high-resolution geochemical and microbial gene-based community profiling of anaerobically incubated material from three wetland habitats across a permafrost peatland. We compared the original field samples to the material anaerobically incubated over 50 days. Bulk geochemistry and phylum-level microbiota in incubations largely reflected field observations, but divergence between field and incubations occurred in both geochemistry and lineage-level microbial composition when examined at closer resolution. Despite the changes in representative lineages over time, inferred metabolic function with regards to carbon cycling largely reproduced field results suggesting functional consistency. Habitat differences among the source materials remained the largest driver of variation in geochemical and microbial differences among the samples in both incubations and field results. While incubations may have limited usefulness for identifying specific mechanisms, they remain a viable tool for probing bulk-scale questions related to anaerobic C cycling, including CO2 and CH4 dynamics.

Divergent responses of permafrost peatlands to recent climate change

Permafrost peatlands are found in high-latitude regions and store globally-important amounts of soil organic carbon. These regions are warming at over twice the global average rate, causing permafrost thaw, and exposing previously inert carbon to decomposition and emission to the atmosphere as greenhouse gases. However, it is unclear how peatland hydrological behaviour, vegetation structure and carbon balance, and the linkages between them, will respond to permafrost thaw in a warming climate. Here we show that permafrost peatlands follow divergent ecohydrological trajectories in response to recent climate change within the same rapidly warming region (northern Sweden). Whether a site becomes wetter or drier depends on local factors and the autogenic response of individual peatlands. We find that bryophyte-dominated vegetation demonstrates resistance, and in some cases resilience, to climatic and hydrological shifts. Drying at four sites is clearly associated with reduced carbon sequestration, while no clear relationship at wetting sites is observed. We highlight the complex dynamics of permafrost peatlands and warn against an overly-simple approach when considering their ecohydrological trajectories and role as C sinks under a warming climate.

不同氮素添加量对大兴安岭冻土区泥炭地植物细根形态的影响模拟研究

为探讨氮素营养环境变化对冻土区泥炭地植物细根形态的影响，在大兴安岭泥炭地开展了不同浓度氮素添加模拟试验，添加量分别为0 g N m^-2 a^-1（CK）、6 g N m^-2 a^-1（N1）、12 g N m^-2 a^-1（N2）和24 g N m^-2 a^-1（N3）。在2020年8月和9月，利用微根管技术观测泥炭地不同深度（0-20 cm、20-40 cm）土壤中的植物细根形态，应用WinRHIZO图像分析软件分析根系特征。结果表明，在表层土壤（0-20 cm）中植物细根的总根长、总表面积、总体积和根长密度随施氮量增加而增加，其中8月份N3处理下细根总根长、总表面积、总体积和根长密度显著高于其他处理（P< 0.05），N2处理下细根总表面积、总体积显著高于对照组和N1处理；9月份N3处理下细根总根长和根长密度显著高于对照组，总表面积和总体积显著高于对照组和N1处理。说明高浓度氮素添加在一定程度上缓解了植物氮素限制，能够显著促进表层土壤（0-20 cm）中植物细根的生长，但对亚表层土壤（20-40 cm）中细根的影响幅度小于表层土壤。;In order to investigate the effects of nitrogen nutrient environment changes on the morphology of fine roots in permafrost peatlands, we conducted a nitrogen additions field experiment in the Daxing'an Mountains, Northeast China. Four levels of N treatments were applied including 0 g N m^-2 a^-1 (CK), 6 g N m^-2 a^-1 (N1), 12 g N m^-2 a^-1 (N2), and 24 g N m^-2 a^-1 (N3). In August and September 2020, minirhizotron observation method was applied to monitor the morphology of fine roots in different depths (0-20 cm, 20-40 cm), and the root characteristics were analyzed by WinRHIZO software. The results showed that the total root length, total surface area, total volume and root length density of plant fine roots in the surface peat layer (0-20 cm) were increased with the increase of nitrogen application. In August, the total root length, total surface area, total volume and root length density in N3 treatment were significantly higher than those in other treatments, while in N2 treatment, total surface area and total volume of fine roots were significantly higher than those in control group and N1 treatment (P< 0.05). In September, the total root length and root length density in N3 treatment were significantly higher than those in control group, and the total surface area and total volume of fine roots in N3 treatment were significantly higher than those in control group and N1 treatment (P< 0.05). The results show that nitrogen additions can relieve the nitrogen limitation of plants and can significantly promote the growth of fine roots in the surface peat layer (0-20 cm), but the influence of fine root growth in subsurface layer (20-40 cm) is less than that in the surface peat layer.

Biogeochemistry of macrophytes, sediments and porewaters in thermokarst lakes of permafrost peatlands, western Siberia

The chemical composition of thermokarst lake ecosystem components is a crucial indicator of current climate change and permafrost thaw. Despite high importance of macrophytes in shallow permafrost thaw lakes for control of major and trace nutrients in lake water, the trace element (TE) partitioning between macrophytes and lake water and sediments in the permafrost regions remains virtually unknown. Here we sampled dominant macrophytes in thermokarst lakes of discontinuous and continuous permafrost zones in the Western Siberia Lowland (WSL) and measured major and trace elements in plant biomass, lake water, lake sediments and sediment porewater. All six plant species (Hippuris vulgaris L., Glyceria maxima (Hartm.) Holmb., Comarum palustre L., Ranunculus spitzbergensis Hadac, Carex aquatilis Wahlenb s. str., Menyanthes trifoliata L.) sizably accumulated macronutrients (Na, Mg, Ca), micronutrients (B, Mo, Nu, Cu, Zn, Co) and toxicants (As, Cd). Accumulation of other trace elements, including rare earth elements (REE), in macrophytes relative to pore waters and sediments was highly variable among species. Using miltiparametric statistics, we described the behavior of ТЕ across two permafrost zones and identified several group of elements depending on their sources in the lake ecosystems and their affinity to sediments and macrophytes. Under future climate warming and shifting the permafrost border to the north, we anticipate an increasing uptake of heavy metals and lithogenic low mobile elements such as Ti, Al, Cr, As, Cu, Fe, Ni, Ga, Zr, and REEs by macrophytes in the discontinuous permafrost zone and Ba, Zn, Pb and Cd in the continuous permafrost zone. This may eventually diminish transport of metal micronutrients and geochemical tracers from soils to lakes and rivers and further to the Arctic Ocean.

Warming threatens the microbial communities in middle-high latitude peatland: Evidence from testate amoebae

Testate amoebae contribute significantly to belowground ecological processes like nutrient cycling, but a decline in their nutrient cycling functions in peatlands is expected due to global climate warming. We studied the dynamics of testate amoebae communities in relation to soil environmental variables in a permafrost peatland that experienced in situ experimental warming for a 7-yr period. Experimental warming reduced testate amoebae biomass by 41%. Redundancy analyses showed that testate amoebae community structure was correlated with water table depth and soil temperature (these explained 10% of the variance in community structure) and dissolved organic carbon (which explained 2.2% of the variance). Our results demonstrated that warming-induced changes to the water table depth affected the testate amoebae community in peatland, which could have consequences for the stability of the microbial food web and carbon cycling in peatland ecosystems.

Dispersed ground ice of permafrost peatlands: Potential unaccounted carbon, nutrient and metal sources

The physical and chemical consequences of massive ground ice (wedges) melt upon permafrost thaw is one of the central issues of environmental research linked to climate warming in the Arctic. Little is known about the chemical properties of dispersed ground ice abundant throughout permafrost peatlands that can easily melt with increasing active layer thickness (ALT). This is especially pertinent in continental lowlands, that account for sizeable areas of the Arctic, and contain high amount of organic carbon in both solid (peat) and liquid (porewater) phases. Here we studied 8 peat cores (0–130 cm depth)—comprised of porewater from the active layer (0–45 cm) as well as ice dispersed in frozen peat (40–130 cm)—across a latitudinal profile of Western Siberia Lowland (WSL) extending from discontinuous into continuous permafrost zones. Dissolved Organic Carbon (DOC), alkali and alkaline-earth metals (Ca, Mg, Sr, Ba, Li, Rb, Cs), sulfate, phosphorus, some trace elements (Al, Fe, Mn, Zn, Ni, Co, V, As, Y, REE, Zr, Hf, U) were sizably [more than 3 times] enriched in peat ice compared to peat porewaters from the active layer. In most sampled cores, there was a local maximum of strong enrichment (up to factors between 14 and 58) in DOC, P, Ca, Mg, Mn, Fe, Sr, As located 30–50 cm below the active layer. This maximum likely occurred due to solute concentration during full freezing of the soil column during winter. There was a sizable correlation between DOC, Al, Fe and other major and trace element concentrations that suggests strong control of organic complexes and organo-mineral (Al, Fe) colloids on element migration throughout the peat profile. The pool of C, major cations and trace metals in peat ice (40–130 cm) was approximately 3–55 times higher than the pool of these elements in porewaters from the active layer (0–40 cm). A 1-m increase of the ALT over the next 100 years is capable of mobilizing 58 ± 38 Tg of DOC from soil ice into the rivers and lakes of the WSL latitudinal belt (63–67 °N). This fast lateral export of C (3.7 ± 2.7 t C km−2 y−1) may double current C yields in WSL rivers (3.4 ± 1.3 t C km−2 y−1). A strong increase (150–200%) in riverine export of Zn, P and Cs may also occur while other micronutrients (Fe, Ni, Co, Ba, Mo, Rb) and toxicants (Cd, As, Al) may be affected to a lesser degree (20–30% increase). We propose a global peat ice inventory in permafrost regions is essential for assessing the consequences of permafrost thaw on surface aquatic systems.

Structural Characterization of Dissolved Organic Matter in Permafrost Peatland Lakes

Thermokarst lakes result from the thawing of ice-rich permafrost and are widespread across northern landscapes. These waters are strong emitters of methane, especially in permafrost peatland regions, where they are stained black by high concentrations of dissolved organic matter (DOM). In the present study, we aimed to structurally characterize the DOM from a set of peatland thermokarst lakes that are known to be intense sites of microbial decomposition and methane emission. Samples were collected at different depths from three thermokarst lakes in the Sasapimakwananisikw (SAS) River valley near the eastern Hudson Bay community of Kuujjuarapik–Whapmagoostui (Nunavik, Canada). Samples were analyzed by spectrofluorometry, Fourier-transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (NMR), and elemental analysis. Fluorescence analyses indicated considerable amounts of autochthonous DOM in the surface waters of one of SAS 1A, indicating a strong bioavailability of labile DOM, and consequently a greater methanogenic potential. The three lakes differed in their chemical composition and diversity, suggesting various DOM transformations phenomena. The usefulness of complementary analytical approaches to characterize the complex mixture of DOM in permafrost peatland waters cannot be overlooked, representing a first step towards greater comprehension of the organic geochemical properties of these permafrost-derived systems.