Palsa Peatlands Research Articles (Page 1)

Abstract. Global warming is profoundly impacting northern ecosystems, particularly those underlain by permafrost. Permafrost-affected peat plateaus, called palsa peatlands, consist of mounds with peat and mineral soil covering ice lenses. When permafrost thaws, palsas can collapse and undergo significant hydrological changes to form wet mires. This affects the physical structure of the soil and as a result, the communities of soil-dwelling organisms, such as nematodes. Although the role of nematodes in carbon cycling is not fully understood, they can influence greenhouse gas emissions through interactions with plants and microbes. This study examined the effects of palsa degradation and experimental warming on nematode feeding guilds (bacterivores, fungivores, root feeders, and omni-carnivores) in northern Norway, where permafrost is rapidly thawing. Our findings showed that intact, vegetated palsas supported higher abundances of all nematode feeding guilds. With warming, bacterivorous and omni-carnivorous nematodes were negatively affected. Additionally, we observed a shift in dominance of bacterivores to fungivores over the summer, suggesting a temporal shift in the predominant decomposition pathway. No direct relationships were found between changes in any of the guild abundances and measured CO2 and CH4 fluxes. This study highlights the fact that expected warming and the degradation of palsas may have varied but had predominantly negative impacts on different nematode feeding guilds. Given the role of soil nematodes in nutrient cycling and other soil processes, their decline under warmer conditions could have ecosystem-level consequences in these palsa peatlands.

Abstract. Climate warming is degrading palsa peatlands across the circumpolar permafrost region. Permafrost degradation may lead to ecosystem collapse and potentially strong climate feedbacks, as this ecosystem is an important carbon store and can transition to being a strong greenhouse gas emitter. Landscape-level measurement of permafrost degradation is needed to monitor this impact of warming. Surface subsidence is a useful metric of change in palsa degradation and can be monitored using interferometric synthetic-aperture radar (InSAR) satellite technology. We combined InSAR data, processed using the ASPIS algorithm to monitor ground motion between 2017 and 2021, with airborne optical and lidar data to investigate the rate of subsidence across palsa peatlands in northern Sweden. We show that 55 % of Sweden's eight largest palsa peatlands are currently subsiding, which can be attributed to the underlying permafrost landforms and their degradation. The most rapid degradation has occurred in the largest palsa complexes in the most northern part of the region of study, also corresponding to the areas with the highest percentage of palsa cover within the overall mapped wetland area. Further, higher degradation rates have been found in areas where winter precipitation has increased substantially. The roughness index calculated from a lidar-derived digital elevation model (DEM), used as a proxy for degradation, increases alongside subsidence rates and may be used as a complementary proxy for palsa degradation. We show that combining datasets captured using remote sensing enables regional-scale estimation of ongoing permafrost degradation, an important step towards estimating the future impact of climate change on permafrost-dependent ecosystems.

The study focuses on palsa and high-centered polygonal peatlands. Engineering surveys for construction in bumpy permafrost peatlands are complicated by the lack of clear criteria for distinguishing between different types of mounds, such as palsa and high-centered polygonal peatlands. These mounds differ in height, shape, and distribution of their main engineering components. These two kinds of bumpy permafrost peatlands respond to human impact in rather different ways throughout structure operation, necessitating distinct safeguards. In this sense, techniques for more precise mound identification needs to be developed early on in engineering and environmental surveying. Examining the distribution of the carbon to nitrogen ratio in the peat that covers the mounds could be one strategy. The remaining landforms known as high-centered polygonal peat blocks were created "passively" by thermokarst processes along the frost-breaking cracks, with vein ice separating them. Palsa peat massifs are mostly found in the sporadic permafrost zone, though they are also frequently observed in the discontinuous and even continuous permafrost development zones, such as the Norilsk region, the Putorana plateau, the Mirny region of Yakutia, Chukotka and Kamchatka, etc. The thickness of peat on both convex and flat surfaces It is typically high, ranging from 1 to 3 meters, but rising to 5 meters and occasionally 8 to 9 meters on convex mounds. Palsa and high-centered polygonal peatlands exhibit distinctive genesis, height, shape, and distribution of engineering and geological characteristics, particularly ice content. Improved methods for identifying mounds during early stages of engineering and environmental studies are needed. One approach could be to analyze the carbon and nitrogen ratios in the peat covering the mounds. Palsa peatlands have higher carbon content (50-55% on average) and lower nitrogen content (0.5-2.0%) compared to high-centered polygonal peatlands (35-40% carbon and 1.5-2.5% nitrogen). The C/N value in peatlands varies, with palsa ranging from 30-36 (reaching -240) and high-centered polygonal peatlands rarely exceeding 25-27 (often 10-20).

Numto Nature Park (Western Siberia) is one of the southernmost locations of frozen peatlands. In 2019–2022, soil temperatures were measured there using an automatic monitoring system. The measurements were carried out for Murshik Hemic Cryic Histosol on flat palsa peatlands and frost mounds. The temperature for Folic Albic Podzol was measured for reference. The average annual temperature of the soil surface was found to be positive in all study areas: + 0.8 °C on the frost mound; +1.3 °C on the flat palsa peatlands; and + 4.5 °C in Folic Albic Podzol. The low temperature on the frost mound is due to the low snow cover, so the soil surface cools down to the minimum in winter. As for flat palsa peatlands, peat remains frozen all year round, starting from a depth of 0.5 m. On the frost mound, at the same time, the depth of seasonal thawing is 2 m. In winter, the frost penetration on the mound doesn't reach the permafrost table, revealing its probable degradation in case of further climate warming. According to the soil thermal regime classification, the soil on the frost mound falls into the category of long-term seasonally frozen soils, while high palsa peatlands nearby Nadym Town belong to the permafrost type. Data from the nearby meteorological station show a trend of rising air temperature and rainfall. An analysis of the soil temperature regime and the course of exogenous processes demonstrate that Murshik Hemic Cryic Histosol on high palsa peatlands is unstable. Permafrost persists there due to the low thickness of the snow cover on the peaks, which facilitates winter cooling. If the snow-cover height increases, permafrost is likely to melt there.

Temperature Sensitivity of СO2 Efflux from the Surface of Palsa Peatlands in Northwestern Siberia as Assessed by Transplantation Method

Palsa peatland soils are known as significant terrestrial storage of the Earth’s soil carbon. The response of these soils to changing climate may result in a strong feedback to global carbon balance. In laboratory, we investigated the effect of rising temperatures on the upper (T1) and lower (T2) horizons of Turbic Histic Cryosols using sequential (S) and equal-time (ET) methods. The S method was applied to estimate the response of organic carbon mineralization rate (R) to sequential temperature increase from 5 to 30°C; the ET method was used to study the response of the basal (microbial) respiration rate to equal-time incubation at 5, 15, and 25°C. The Q10 coefficient was calculated. In the T1 horizon, both methods (S and ET) demonstrated a positive response of respiration to the rise in temperature. The respiration intensity increased by 91 and 84%, respectively. In the T2 horizon, it increased by 93 and 91%, respectively. However, despite the overall positive response of soil respiration to the rise in temperature, the Q10 values demonstrated differences in the temperature sensitivity of soil respiration. These values were maximal in the cold (5–15°C) range for both horizons. For most of temperature ranges, Q10 was higher for T2 than for T1. For the T1 horizon and S method, Q10 slightly varied (2.7–3.0), whereas in the case of the ET method, it decreased by 3.3 times from the cold (4.9) to the warm 15–25°C (1.5) temperature range. For the T2 horizon, the S method also did not cause significant shifts in Q10 (3.0–3.5); the ET method caused a decrease in Q10 by 1.5 times from the cold (4.3) to the warm (2.8) temperature range. To sum up, the ET method leads to a wider variation of Q10 values in comparison with the S method thus indicating its better applicability for temperature sensitivity studies with palsa peatland soils under laboratory conditions.

Experimental modeling of thaw lake water evolution in discontinuous permafrost zone: Role of peat, lichen leaching and ground fire.

The response of methanogens to thawing permafrost is an important factor for the global greenhouse gas budget. We tracked methanogenic community structure, activity, and abundance along the degradation of sub-Arctic palsa peatland permafrost. We observed the development of pronounced methane production, release, and abundance of functional (mcrA) methanogenic gene numbers following the transitions from permafrost (palsa) to thaw pond structures. This was associated with the establishment of a methanogenic community consisting both of hydrogenotrophic (Methanobacterium, Methanocellales), and potential acetoclastic (Methanosarcina) members and their activity. While peat bog development was not reflected in significant changes of mcrA copy numbers, potential methane production, and rates of methane release decreased. This was primarily linked to a decline of potential acetoclastic in favor of hydrogenotrophic methanogens. Although palsa peatland succession offers similarities with typical transitions from fen to bog ecosystems, the observed dynamics in methane fluxes and methanogenic communities are primarily attributed to changes within the dominant Bryophyta and Cyperaceae taxa rather than to changes in peat moss and sedge coverage, pH and nutrient regime. Overall, the palsa peatland methanogenic community was characterized by a few dominant operational taxonomic units (OTUs). These OTUs seem to be indicative for methanogenic species that thrive in terrestrial organic rich environments. In summary, our study shows that after an initial stage of high methane emissions following permafrost thaw, methane fluxes, and methanogenic communities establish that are typical for northern peat bogs.

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Abstract. Palsa peatlands are a significant carbon pool in the global carbon cycle and are projected to change by global warming due to accelerated permafrost thaw. Our aim was to use stable carbon isotopes as indicators of palsa degradation. Depth profiles of stable carbon isotopes generally reflect organic matter dynamics in soils with an increase of δ13C values during aerobic decomposition and stable or decreasing δ13C values with depth during anaerobic decomposition. Stable carbon isotope depth profiles of undisturbed and degraded sites of hummocks as well as hollows at three palsa peatlands in northern Sweden were used to investigate the degradation processes. The depth patterns of stable isotopes clearly differ between intact and degraded hummocks at all sites. Erosion and cryoturbation at the degraded sites significantly changes the stable carbon isotope depth profiles. At the intact hummocks the uplifting of peat material by permafrost is indicated by a turning in the δ13C depth trend, and this assessment is supported by a change in the C / N ratios. For hollows isotope patterns were less clear, but some hollows and degraded hollows in the palsa peatlands show differences in their stable carbon isotope depth profiles indicating enhanced degradation rates. We conclude that the degradation of palsa peatlands by accelerated permafrost thawing can be identified with stable carbon isotope depth profiles. At intact hummocks δ13C depth patterns display the uplifting of peat material by a change in peat decomposition processes.

In the sporadic permafrost zone of the James Bay region in northwestern Quebec (Canada), permafrost has been showing signs of advanced degradation for the past 50 years. Several palsa peatlands are...

Palsa peatlands, permafrost-affected peatlands characteristic of the outer margin of the discontinuous permafrost zone, form unique ecosystems in northern-boreal and arctic regions, but are now degrading throughout their distributional range due to climate warming. Permafrost thaw and the degradation of palsa mounds are likely to affect the biogeochemical stability of soil organic matter (that is, SOM resistance to microbial decomposition), which may change the net C source/sink character of palsa peatland ecosystems. In this study, we have assessed both biological and chemical proxies for SOM stability, and we have investigated SOM bulk chemistry with mid-infrared spectroscopy, in surface peat of three distinct peatland features in a palsa peatland in northern Norway. Our results show that the stability of SOM in surface peat as determined by both biological and chemical proxies is consistently higher in the permafrost-associated palsa mounds than in the surrounding internal lawns and bog hummocks. Our results also suggest that differences in SOM bulk chemistry is a main factor explaining the present SOM stability in surface peat of palsa peatlands, with selective preservation of recalcitrant and highly oxidized SOM components in the active layer of palsa mounds during intense aerobic decomposition over time, whereas SOM in the wetter areas of the peatland remains stabilized mainly by anaerobic conditions. The continued degradation of palsa mounds and the expansion of wetter peat areas are likely to modify the bulk SOM chemistry of palsa peatlands, but the effect on the future net C source/sink character of palsa peatlands will largely depend on moisture conditions and oxygen availability in peat.

Methane-oxidizing bacteria (MOB) that possess the soluble form of methane monooxygenase (sMMO) are present in various environments, but unlike the prevalent particulate methane monooxygenase (pMMO), the in situ activity of sMMO has not been documented. Here we report on the environmental transcription of a gene (mmoX) for this enzyme, which was attributed mainly to MOB lacking a pMMO. Our study indicates that the sMMO is an active enzyme in acidic peat ecosystems, but its importance for the mitigation of methane releases remains unknown.

Palsa peatlands occupy extensive areas in Western Siberia which is one of the most paludified flat lowlands of the world. Climatic changes in Western Siberia are more dramatic compared with other northern regions, and changes in palsa landscapes are more notable due to the severe continental climate here. The distribution, peculiarities and climate-indication capacities of West Siberian palsas are poorly known outside Russia. Thus, Western Siberia is one of the most interesting vast natural polygons for studying climate-driven changes in the landscapes. This paper aims to fill the gap in knowledge on West Siberian palsas and their capacity as a climate regulator. We present issues in distribution, typology and cyclic development of palsa peatlands and their actual climate-driven changes. We also analyse the role of palsas in the atmospheric cycle of CO2, and the hydrology of the palsa regions.

West Siberian palsa peatlands: distribution, typology, cyclic development, present-day climate-driven changes, seasonal hydrology and impact on CO2 cycle.

We analyzed the fossil insect fauna of a palsa peatland located 10 km south and east of the treeline in subarctic Quebec (57°45′N, 76°15′W) to detect any changes in the species composition during the Holocene epoch and to infer past environmental conditions in the study area. A minimum of 802 beetle individuals were recovered from a 2-m peat section, representing 51 taxa (18 identified to the species level) and 8 families. Trechus crassiscapus, Eucnecosum brunnescens, and Olophrum rotundicolle were the most common species found in the peat. The insect assemblage was quite stable through the study interval (5850–1950 BP). The formation of the palsa (where the peat section was excavated) occurred probably after 1950 BP, raising the soil surface above water level and preventing additional peat accumulation. The proportion of boreal forest species in the faunal assemblage is high (88%). The only arctic (tundra) species found were Amara alpina and Pterostichus arcticola. Many species were out of their modern distribution range, but since collection localities are scarce in subarctic Quebec, the modern range of these species may extend to the study site. A mutual climatic range analysis, employing beetles identified to the species level, showed that the mean July temperature of the study area between 5850 and 1950 BP was possibly 2.8–5.5 °C higher than during the 20th century. This assertion is supported by other paleoecological data (pollen and charcoal remains) suggesting a cooling trend in the study area after 2000 BP. However, since the last 2000 years are missing from the sampled peat section, it was not possible to quantify the impact of the cooling trend on the beetle fauna.

Long-Term Monitoring of Permafrost Change in a Palsa Peatland in Northern Quebec, Canada: 1983–1993

Changes in the spatial distribution of permafrost in the Ouiatchouane palsa peatland (northern Quebec) were monitored from 1957 to present, using aerial photographs taken in 1957 (starting date) and three field surveys in 1973, 1983, and 1993, respectively. Between 1983 and 1993, palsa degradation occurred at about the same rate as between 1957 and 1983, although minor differences in rate of permafrost decay during the three periods (1957-1973, 1973-1983, 1983-1993) may be attributed in part to misidentification of marginal permafrost landforms. Permafrost degradation appeared to be influenced by height of individual palsas and their location within the peatland. Since 1983, thermokarst ponds have been progressively invaded by sedges and Sphagnum, a situation promoting successional peatland development and palsa formation as suggested by the presence of a small incipient palsa. Although the main geomorphic process at work is palsa degradation, permafrost aggradation is possible under present climatic conditions. 28 refs., 3 figs., 1 tab.

Plant and animal macrofossils (vascular plant, moss, fungus, bryozoan, cladoceran and coleoptera remains) were analyzed to reconstitute the development of a palsa peat located at the northwestern forest limit of subarctic Quebec (57°45′N., 76°15′W.) and to detect any black spruce (Picea mariana) remains older than the presumed time of arrival of the species in the study area (4560 BP), after the deglaciation. The oldest peat deposits were formed in a fen with many shallow pools between 5850 and 4500 BP. The flora was mainly composed of aquatic taxa (Ranunculus trichophyllus, Potamogeton spp., Hippuris vulgaris). Around 4500 BP, there was a shift from a very wet fen to a sedge fen with Potentilla palustris and Menyanthes trifoliata. From 3700 to 1950 BP, most plant remains were wood fragments of dwarf birch (Betula glandulosa). The formation of the palsa occurred after 1950 BP. The development of this peatland is similar to that of other palsa peatlands of subarctic Quebec, except that it is characterized by the presence of a thick peat layer composed of Betula glandulosa fragments at the top of the palsa. There were no black spruce remains older than 4560 BP. Three peaks of coleoptera abundance were identified at 4400, 3800, and 2700 BP, respectively. Most of the coleoptera taxa being hygrophilous, it was not possible to infer structural changes in the peatland from their fragments. Key words: palsa peatland, macrofossil analysis, subarctic Quebec, Betula glandulosa, Picea mariana, beetles.