Permafrost Wetlands Research Articles

Impacts of Spectral Characteristics of Dissolved Organic Matter on Methyl Mercury Contents in Permafrost Wetlands, Northeast China

Impacts of Spectral Characteristics of Dissolved Organic Matter on Methyl Mercury Contents in Permafrost Wetlands, Northeast China

Review article: Terrestrial dissolved organic carbon in northern permafrost

Abstract. As the permafrost region warms and permafrost soils thaw, vast stores of soil organic carbon (C) become vulnerable to enhanced microbial decomposition and lateral transport into aquatic ecosystems as dissolved organic carbon (DOC). The mobilization of permafrost soil C can drastically alter the net northern permafrost C budget. DOC entering aquatic ecosystems becomes biologically available for degradation as well as other types of aquatic processing. However, it currently remains unclear which landscape characteristics are most relevant to consider in terms of predicting DOC concentrations entering aquatic systems from permafrost regions. Here, we conducted a systematic review of 111 studies relating to, or including, concentrations of DOC in terrestrial permafrost ecosystems in the northern circumpolar region published between 2000 and 2022. We present a new permafrost DOC dataset consisting of 2845 DOC concentrations, collected from the top 3 m in permafrost soils across the northern circumpolar region. Concentrations of DOC ranged from 0.1 to 500 mg L−1 (median = 41 mg L−1) across all permafrost zones, ecoregions, soil types, and thermal horizons. Across the permafrost zones, the highest median DOC concentrations were in the sporadic permafrost zone (101 mg L−1), while lower concentrations were found in the discontinuous (60 mg L−1) and continuous (59 mg L−1) permafrost zones. However, median DOC concentrations varied in these zones across ecosystem type, with the highest median DOC concentrations in each ecosystem type of 66 and 63 mg L−1 found in coastal tundra and permafrost bog ecosystems, respectively. Coastal tundra (130 mg L−1), permafrost bogs (78 mg L−1), and permafrost wetlands (57 mg L−1) had the highest median DOC concentrations in the permafrost lens, representing a potentially long-term store of DOC. Other than in Yedoma ecosystems, DOC concentrations were found to increase following permafrost thaw and were highly constrained by total dissolved nitrogen concentrations. This systematic review highlights how DOC concentrations differ between organic- or mineral-rich deposits across the circumpolar permafrost region and identifies coastal tundra regions as areas of potentially important DOC mobilization. The quantity of permafrost-derived DOC exported laterally to aquatic ecosystems is an important step for predicting its vulnerability to decomposition.

Permafrost Wetlands Are Sources of Dissolved Iron and Dissolved Organic Carbon to the Amur‐Mid Rivers in Summer

AbstractDissolved iron (dFe) transported by the Amur River greatly contributes to phytoplankton growth in the Sea of Okhotsk. Nevertheless, there has been little research on the source of dFe to rivers, especially in the Amur‐Mid Basin, which is situated in a sporadic permafrost area. In the Amur‐Mid Basin, permafrost generally exists in wetlands in flat valleys, and these permafrost wetlands could be a source of dFe to rivers. To assess the importance of permafrost wetlands for dFe export, we conducted a local survey on land and soil characteristics of wetlands, and moreover analyzed the chemical composition (dFe, dissolved organic carbon [DOC], pH, and electrical conductivity [EC]) of 24 rivers with different watershed sizes in summer. As a result of local survey, the thickly accumulated peat soils in the permafrost wetland were almost saturated and rich in organic matter from the surface to a greater depth near the permafrost table. In addition, the coverage of such permafrost wetlands in watersheds showed significant positive correlations with dFe (r2 = 0.67, p = 1.7e−6) and DOC (r2 = 0.48, p = 1.8e−4) and a negative correlation with EC (r2 = 0.52, p = 7.7e−5). The dFe concentration was also correlated well with DOC concentration (r2 = 0.68, p = 7.3e−7) but not correlated with pH and watershed area. These findings are the first to indicate that permafrost wetlands in the Amur‐Mid Basin considerably contribute to dFe and DOC export to rivers, and their coverage primarily determines riverine dFe and DOC concentrations in summer.

Response of methanogenic community and their activity to temperature rise in alpine swamp meadow at different water level of the permafrost wetland on Qinghai-Tibet Plateau.

Wetlands are an important source of atmospheric methane (CH4) and are sensitive to global climate change. Alpine swamp meadows, accounting for ~50% of the natural wetlands on the Qinghai-Tibet Plateau, were considered one of the most important ecosystems. Methanogens are important functional microbes that perform the methane producing process. However, the response of methanogenic community and the main pathways of CH4 production to temperature rise remains unknown in alpine swamp meadow at different water level in permafrost wetlands. In this study, we investigated the response of soil CH4 production and the shift of methanogenic community to temperature rise in the alpine swamp meadow soil samples with different water levels collected from the Qinghai-Tibet Plateau through anaerobic incubation at 5°C, 15°C and 25°C. The results showed that the CH4 contents increased with increasing incubation temperature, and were 5-10 times higher at the high water level sites (GHM1 and GHM2) than that at the low water level site (GHM3). For the high water level sites (GHM1 and GHM2), the change of incubation temperatures had little effect on the methanogenic community structure. Methanotrichaceae (32.44-65.46%), Methanobacteriaceae (19.30-58.86%) and Methanosarcinaceae (3.22-21.24%) were the dominant methanogen groups, with the abundance of Methanotrichaceae and Methanosarcinaceae having a significant positive correlation with CH4 production (p < 0.01). For the low water level site (GHM3), the methanogenic community structure changed greatly at 25°C. The Methanobacteriaceae (59.65-77.33%) was the dominant methanogen group at 5°C and 15°C; In contrast, the Methanosarcinaceae (69.29%) dominated at 25°C, and its abundance showed a significant positive correlation with CH4 production (p < 0.05). Collectively, these findings enhance the understanding of methanogenic community structures and CH4 production in permafrost wetlands with different water levels during the warming process.

Non-climate environmental factors matter to Holocene dynamics of soil organic carbon and nitrogen in an alpine permafrost wetland, Qinghai‒Tibet Plateau

Studies on the responses of soil organic carbon (SOC) and nitrogen dynamics to Holocene climate and environment in permafrost peatlands and/or wetlands might serve as analogues for future scenarios, and they can help predict the fate of the frozen SOC and nitrogen under a warming climate. To date, little is known about these issues on the Qinghai‒Tibet Plateau (QTP). Here, we investigated the accumulations of SOC and nitrogen in a permafrost wetland on the northeastern QTP, and analyzed their links with Holocene climatic and environmental changes. In order to do so, we studied grain size, soil organic matter, SOC, and nitrogen contents, bulk density, geochemical parameters, and the accelerator mass spectrometry (AMS) 14C dating of the 216-cm-deep wetland profile. SOC and nitrogen contents revealed a general uptrend over last 7300 years. SOC stocks for depths of 0–100 and 0–200 cm were 50.1 and 79.0 kgC m−2, respectively, and nitrogen stocks for the same depths were 4.3 and 6.6 kgN m−2, respectively. Overall, a cooling and drying trend for regional climate over last 7300 years was inferred from the declining chemical weathering and humidity index. Meanwhile, SOC and nitrogen accumulated rapidly in 1110–720 BP, while apparent accumulation rates of SOC and nitrogen were much lower during the other periods of the last 7300 years. Consequently, we proposed a probable conceptual framework for the concordant development of syngenetic permafrost and SOC and nitrogen accumulations in alpine permafrost wetlands. This indicates that, apart from controls of climate, non-climate environmental factors, such as dust deposition and site hydrology, matter to SOC and nitrogen accumulations in permafrost wetlands. We emphasized that environmental changes driven by climate change have important impacts on SOC and nitrogen accumulations in alpine permafrost wetlands. This study could provide data support for regional and global estimates of SOC and nitrogen pools and for global models on carbon‒climate interactions that take into account of alpine permafrost wetlands on the northeastern QTP at mid-latitudes.

Mineral protection controls soil organic carbon stability in permafrost wetlands

Mineral protection can slow the effect of warming on the mineralization of organic carbon (OC) in permafrost wetlands, which has an important impact on the dynamics of soil OC. However, the response mechanisms of wetland mineral soil to warming in permafrost areas are unclear. In this study, the soil of the southern edge of the Eurasian permafrost area was selected, and bulk and heavy fraction (HF) soil was subjected to indoor warming incubation experiments using physical fractionation. The results showed that the HF accounted for 51.25 % of the total OC mineralization in the bulk soil, and the δ13C value of the CO2 that was emitted in the HF soil was higher than that of the bulk soil. This indicates the potential availability of mineral soil and that the mineralized OC in the HF was the more stable component. Additionally, the mineralization of the mineral subsoil after warming by 10 °C was only about half of the increase in the organic topsoil, and the temperature sensitivity was significantly negatively correlated with the Fe/Al oxides to OC ratio. The results indicate that under conditions of permafrost degradation, the physical protection of mineral soil at high latitudes is essential for the stability of OC, which may slow the trend of permafrost wetlands becoming carbon sources.

Warming in Cold Seasons Increases the Abundance of Ground-Dwelling Collembola in Permafrost Wetlands.

The consideration of environmental factors has long been crucial to developing theories about the spatial variability of species diversity. However, the effects of global warming on Collembola, in permafrost wetlands, are largely unknown. Understanding how Collembola are affected by climate warming is important as they directly affect the community assembly and decomposition processes of plant litter within soil ecosystems. A peatland area in a cold temperate monsoon climate zone in the Great Hing'an Mountains of Northeast China was selected as the study area. Collembola were captured using an aspirator after five years of simulated warming using open top chambers (OTCs). Sampling in different growth seasons showed different characteristics in the control (CK) and warming (OTCs) treatment. Further, the results showed that (1) warming treatment increased the species richness and abundance of Collembola in the different seasons, except in May, (2) warming increased Collembola abundance in permafrost wetlands, and the warming effect was more significant during the cold season (about eight times in April), (3) species composition differed significantly in the control and warming treatment in May and September, and (4) the Collembola species composition in permafrost wetlands was mainly determined by air humidity, indicating different responses of Collembola species to the indirect effect of warming on water availability. We found that warming was the primary factor positively affecting the abundance of Collembola. An increase of Collembola abundance and community alteration to warming could have profound cascading effects on the microbes and plants they feed on in permafrost wetlands.

Linking soil organic carbon mineralization with soil variables and bacterial communities in a permafrost-affected tussock wetland during laboratory incubation

Microtopography can cause great soil heterogeneity in both abiotic and biotic factors, which leads to different soil organic matter decomposition rates. However, the quantitative effects of soil variables and microbial properties on soil organic carbon (SOC) mineralization in microfeatures in permafrost wetlands largely remain unknown. Here, soil samples of 0–10 cm from hummocks and hollows in a permafrost-affected tussock wetland were collected for laboratory incubation. The results showed that the temperature sensitivities (Q10 value) of SOC mineralization were 3.14 and 2.44 for hummocks and hollows, respectively. After an 80-day laboratory incubation, the microfeatures had no significant effects on the relative abundance of bacteria, but significantly affected bacterial α-diversity (Shannon indices) of soil. The incubation temperature also separated the bacterial community structure of the two microfeatures. Laboratory warming and the microfeatures influenced the SOC mineralization rate by regulating bacterial communities and labile substrates, with a joint contribution of 72 % of the total variances in SOC mineralization. Our study quantified the differences in soil variables, bacterial community indices, and their contribution to SOC mineralization between the two microfeatures in a permafrost-affected wetland, and thus improved our understanding of the microbial processes driving soil carbon cycling in permafrost regions.

Mucilaginibacter Phenanthrenivorans sp. nov., a Novel Phenanthrene Degradation Bacterium Isolated from Wetland Soil

BJC16-A38T, a Gram-negative, aerobic and non-motile rod-shaped strain was isolated from a permafrost wetland soil sample. BJC16-A38T was oxidase- and catalase-positive, and produced pale yellow colonies on modified R2A agar plates. The 16S rRNA gene sequence of BJC16-A38T shared the highest sequence similarity with those of Mucilaginibacter xinganensis BJC16-A31T (97.44%), Mucilaginibacter gotjawali SA3-7T (96.79%) and Mucilaginibacter frigoritolerans FT22T (96.14%). Phylogenetic analysis revealed that BJC16-A38T formed a separate lineage together with strain M. xinganensis BJC16-A31T in the genus Mucilaginibacter. BJC16-A38T contained menaquinone-7 (MK-7) as the predominant isoprenoid quinine. Major fatty acids in cells were iso-C15:0, summed feature 3 (16:1ω7c/16:1ω6c) and iso-C17:03-OH. BJC16-A38T contained phosphatidylethanolamine, two unknown polar lipids, six unidentified phospholipids and an unidentified aminolipid. The Genome of BJC16-A38T was sequenced using the Genome Analyzer IIx sequence platform and 38 contigs were produced in total with an average G + C percentage of 44.00%. The average nucleotide identity (ANI) of BJC16-A38T with respect to those of M. xinganensis BJC16-A31T, M. gotjawali SA3-7T and M. frigoritolerans FT22T were 79.60%, 77.24% and 77.58%, respectively. Digital DNA-DNA hybridization (DDH) values between BJC16-A38T and the tree reference strains were 21.30%, 19.60% and 19.70%, respectively. BJC16-A38T exhibited phenanthrene biodegradation activity that can degrade 88.02% phenanthrene in the MM medium after 7days cultivation. Phenotypic, chemotaxonomic, phylogenetic and genomic characteristics concluded that strain BJC16-A38T represents a novel species of the genus Mucilaginibacter. Hence, the name Mucilaginibacter phenanthrenivorans sp. nov. is proposed. The type strain is BJC16-A38T (= CGMCC 1.12693T = NBRC 110383T).

Effects of Permafrost Degradation on Soil Carbon and Nitrogen Cycling in Permafrost Wetlands

Climate change is one of the greatest threats to high-latitude permafrost and leads to serious permafrost degradation. However, few attention has been paid to whether peat soil carbon or nitrogen is sensitive to permafrost degradation. This study has selected three typical sample areas (MoHe-continuous permafrost, TaHe-Island-shaped melting permafrost, Jagdaqi-Island-shaped melting permafrost) as research object to compare the response rate and degree of peat soil carbon and nitrogen under permafrost degradation. The results show that soil organic carbon and nitrogen contents are the highest in 0–10 cm soil and permafrost regions show obvious surface aggregation. The carbon content of different types of frozen soil decreases with the depth of soil layer, and the differences are significant (p &amp;lt; 0.01). The distribution pattern of total nitrogen content in each soil layer among different permafrost types is Mohe &amp;lt; Tahe &amp;lt; Jagedaqi. And when it is getting vertically deeper than the surface layer, there is no significant difference between the soil layers in soil profile. The study also focuses on the variations of carbon and nitrogen content in different soil layers of peatland in typical permafrost regions. The results show that soil carbon responds faster to the degradation of frozen soil than soil nitrogen. Moreover, the accumulation degree of soil carbon is also significantly higher than soil nitrogen. Under climate change and for better permafrost conservation, it is necessary to study how the peatland’s soil carbon and the nitrogen are influenced by the permafrost degradation in high latitude.

Contribution of the nongrowing season to annual N2O emissions from the permafrost wetland in Northeast China.

Permafrost regions store large amounts of soil organic carbon and nitrogen, which are major sources of greenhouse gas. With climate warming, permafrost is thawing and releasing an abundance of greenhouse gases into the atmosphere and contributing to climate warming. Numerous studies have shown the mechanism of nitrous oxide (N2O) emissions from the permafrost region during the growing season. However, little is known about the temporal pattern and drivers of nongrowing season N2O emissions from the permafrost region. In this study, N2O emissions from the permafrost region were investigated from June 2016 to June 2018 using the static opaque chamber method. We aimed to quantify the seasonal dynamics of nongrowing season N2O emissions and their contribution to the annual budget. The results showed that the N2O emissions ranged from - 35.75 to 74.16μgm-2h-1 with 0.89 to 1.44kgha-1 being released into the atmosphere during the nongrowing season in the permafrost region. The permafrost wetland types had no significant influence on the nongrowing season N2O emissions due to the nitrate content. The cumulative N2O emissions during the nongrowing season contributed to 41.96-53.73% of the annual budget, accounting for almost half of the annual emissions in the permafrost region. The driving factors of N2O emissions were different among the nongrowing season, growing season, and entire period. The N2O emissions from the nongrowing season and total 2-year observation period were mainly affected by soil temperature, which could explain 3.01-9.54% and 6.07-14.48% of the temporal variation in N2O emissions, respectively. In contrast, the N2O emissions from the growing season were controlled by soil temperature, water table level, pH, NH4+-N, NO3--N, total nitrogen, total organic carbon, and C/N ratio, which could explain 14.51-45.72% of the temporal variation of N2O emissions. Nongrowing season N2O emissions are an essential component of annual emissions and cannot be ignored in the permafrost region.

Type Classification and Engineering Stability Evaluation of Permafrost Wetlands on the Qinghai–Tibet Plateau

On the Qinghai–Tibet Plateau area, the permafrost and the wetlands are interdependent to form a symbiotic system, called permafrost wetlands (PWs). Due to the extremely complex hydrothermal conditions, the PWs greatly impact road stability. Thus, it is necessary to classify PWs in terms of engineering characteristics and evaluate their engineering stability. In this study, the typical diseases of subgrade in permafrost wetland areas are analyzed based on field investigation. Then, the permafrost type, waterlogged area ratio, and meadow development degree are used as the main indicators for classifying PWs by a three-level division method. Finally, a scheme for the engineering stability evaluation of PWs was established based on the fuzzy comprehensive theory and used for the pre-evaluation of the engineering stability for the proposed Qinghai 224 highway. The results indicate that the longitudinal cracks and uneven deformation are the main road diseases in this area, caused by the combined effect of permafrost, waterlogged areas, and meadow development. The PWs are divided into 15 types according to the engineering characteristics. Waterlogged area ratio and meadow development degree are proven to represent the development of underlying permafrost. The influencing factors include climatic environment, permafrost property, and wetland conditions, which have decreased influence on the engineering stability of PWs. The engineering stability of k230 + 100 and k255 + 400 is evaluated as basically stable and less stable, and the corresponding measures are adopted. At present, no significant damage occurred on the two road sections. The results suggest that the evaluation model in this article can be used to pre-evaluate the engineering stability of PWs.

Driving Factors on Greenhouse Gas Emissions in Permafrost Region of Daxing'an Mountains, Northeast China

AbstractPermafrost regions are an important source of greenhouse gases. However, the effects of different permafrost wetland types on greenhouse gas emissions and the driving factors are still unclear in the permafrost region. Here, we selected three typical permafrost wetlands from the Daxing'an Mountains to investigate the effects of permafrost wetland types on greenhouse gas emissions. The cumulative N2O, CO2, and CH4 emissions were 84–122, 657,942–1,446,121, and 173–16,924 kg km−2, respectively. The linear mixed effects model indicated that N2O emissions were significantly affected by the NO3−‐N content, whereas CO2 emissions were mainly driven by soil temperature, water table level, and NO3−‐N content. CH4 emissions were affected by soil temperature and water table level. Permafrost wetland types significantly affected the average and cumulative N2O, CO2, and CH4 emissions. The cumulative N2O emissions were highest in the Larix gmelinii ‐ Carex appendiculata (LC) wetland and lowest in the Betula fruticosa Pall. (B) wetland, driven by NO3−‐N content. The cumulative CO2 emissions were highest in the B wetland and lowest in the L. gmelinii ‐ Ledum palustre var. dilatatum (LL) wetland. The cumulative CH4 emissions from B wetland were significantly higher than those from LL and LC wetlands. The differences in cumulative CO2 and CH4 emissions were driven by the water table level. Our findings indicate that NO3−‐N content affect the spatial‐temporal variation of N2O emissions, whereas water table level influence the spatial‐temporal variation of CO2 and CH4 emissions in the permafrost region of the Daxing'an Mountains.

Soil Moisture and Aromatic-Containing Compounds Control Soil Organic Carbon Associated with Iron Oxides in Permafrost Wetland Soils Along the Yarlung Tsangbo River, Tibet

Soil Moisture and Aromatic-Containing Compounds Control Soil Organic Carbon Associated with Iron Oxides in Permafrost Wetland Soils Along the Yarlung Tsangbo River, Tibet

Repeat-Pass Interferometric Speckle

The Gaussian speckle model for homogeneously distributed targets is commonly assumed to apply in repeat-pass radar interferometric analyses, for instance, in deformation estimation. This is despite widespread evidence from snapshot intensity observations indicating deviations from Gaussianity, as many natural land surfaces are intrinsically heterogeneous. The concern is that neglecting heterogeneity will deteriorate the phase estimates and induce underestimation of the uncertainty. Here, we introduce and theoretically characterize compound models that extend the Gaussian speckle model for repeat-pass stacks by representing heterogeneity in intensity and phase. In two L-band repeat-pass data sets, we find pervasive deviations from Gaussianity. Our estimates suggest that the heterogeneity in intensity is largely due to time-invariant, rather than dynamic, texture. Deviations from Gaussianity associated with phase heterogeneity are generally less pronounced. One notable exception with large estimated phase heterogeneity occurs over a permafrost wetland, where degrading ice wedges induce subsidence that is variable on the resolution scale. For deformation analyses, accounting for heterogeneity has, on average, a moderate impact on the phase estimates and the estimated phase uncertainty, which increases by 10% on average. However, in intrinsically heterogeneous areas, such as the permafrost wetland, the accuracy of the phase estimate can realistically improve by up to 20%, and the predicted phase uncertainty increases by 30%. The improvements in phase estimation accuracy and in the quality of the uncertainty estimates when accounting for heterogeneous speckle can, on occasion, make a notable difference for subtle or small-scale deformation.

Seasonal Variations of Dissolved Iron Concentration in Active Layer and Rivers in Permafrost Areas, Russian Far East

Dissolved iron (dFe) in boreal rivers may play an important role in primary production in high-latitude oceans. However, iron behavior in soils and dFe discharge mechanism from soil to the rivers are poorly understood. To better understand iron dynamics on the watershed scale, we observed the seasonal changes in dFe and Dissolved Organic Carbon (DOC) concentrations in the river as well as dFe concentration in soil pore waters in permafrost watershed from May to October. During snowmelt season, high dFe production (1.38–4.70 mg L−1) was observed in surface soil pore waters. Correspondingly, riverine dFe and DOC concentrations increased to 1.10 mg L−1 and 32.3 mg L−1, and both were the highest in the year. After spring floods, riverine dFe and DOC concentrations decreased to 0.15 mg L−1 and 7.62 mg L−1, and dFe concentration in surface soil pore waters also decreased to 0.20–1.28 mg L−1. In late July, riverine dFe and DOC concentrations increased to 0.33 mg L−1 and 23.6 mg L−1 in response to heavy rainfall. In August and September, considerable increases in dFe concentrations (2.00–6.90 mg L−1) were observed in subsurface soil pore waters, probably because infiltrated rainwater developed reducing conditions. This dFe production was confirmed widely in permafrost wetlands in valley areas. Overall, permafrost wetlands in valley areas are hotspots of dFe production and greatly contribute to dFe and DOC discharge to rivers, especially during snowmelt and rainy seasons.

Characterisation of short-term extreme methane fluxes related to non-turbulent mixing above an Arctic permafrost ecosystem

Abstract. Methane (CH4) emissions from biogenic sources, such as Arctic permafrost wetlands, are associated with large uncertainties because of the high variability of fluxes in both space and time. This variability poses a challenge to monitoring CH4 fluxes with the eddy covariance (EC) technique, because this approach requires stationary signals from spatially homogeneous sources. Episodic outbursts of CH4 emissions, i.e. triggered by spontaneous outgassing of bubbles or venting of methane-rich air from lower levels due to shifts in atmospheric conditions, are particularly challenging to quantify. Such events typically last for only a few minutes, which is much shorter than the common averaging interval for EC (30 min). The steady-state assumption is jeopardised, which potentially leads to a non-negligible bias in the CH4 flux. Based on data from Chersky, NE Siberia, we tested and evaluated a flux calculation method based on wavelet analysis, which, in contrast to regular EC data processing, does not require steady-state conditions and is allowed to obtain fluxes over averaging periods as short as 1 min. Statistics on meteorological conditions before, during, and after the detected events revealed that it is atmospheric mixing that triggered such events rather than CH4 emission from the soil. By investigating individual events in more detail, we identified a potential influence of various mesoscale processes like gravity waves, low-level jets, weather fronts passing the site, and cold-air advection from a nearby mountain ridge as the dominating processes. The occurrence of extreme CH4 flux events over the summer season followed a seasonal course with a maximum in early August, which is strongly correlated with the maximum soil temperature. Overall, our findings demonstrate that wavelet analysis is a powerful method for resolving highly variable flux events on the order of minutes, and can therefore support the evaluation of EC flux data quality under non-steady-state conditions.

Emissions from thaw ponds largely offset the carbon sink of northern permafrost wetlands

Northern regions have received considerable attention not only because the effects of climate change are amplified at high latitudes but also because this region holds vast amounts of carbon (C) stored in permafrost. These carbon stocks are vulnerable to warming temperatures and increased permafrost thaw and the breakdown and release of soil C in the form of carbon dioxide (CO2) and methane (CH4). The majority of research has focused on quantifying and upscaling the effects of thaw on CO2 and CH4 emissions from terrestrial systems. However, small ponds formed in permafrost wetlands following thawing have been recognized as hotspots for C emissions. Here, we examined the importance of small ponds for C fluxes in two permafrost wetland ecosystems in northern Sweden. Detailed flux estimates of thaw ponds during the growing season show that ponds emit, on average (±SD), 279 ± 415 and 7 ± 11 mmol C m−2 d−1 of CO2 and CH4, respectively. Importantly, addition of pond emissions to the total C budget of the wetland decreases the C sink by ~39%. Our results emphasize the need for integrated research linking C cycling on land and in water in order to make correct assessments of contemporary C balances.

若尔盖高原湿地泥炭沼泽土亚硝酸盐还原酶（nirK）反硝化细菌群落结构分析

PDF HTML阅读 XML下载 导出引用 引用提醒 若尔盖高原湿地泥炭沼泽土亚硝酸盐还原酶（nirK）反硝化细菌群落结构分析 DOI: 10.5846/stxb201607151442 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金（41201256）。 Analyzing the nitrate reductase gene (nirK) community in the peat soil of the Zoige Wetland of the Tibetan Plateau Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:若尔盖泥炭湿地是世界少有的低纬度永久冻土湿地，具有高海拔、高紫外辐射、高有机质的特点。该区域N2O的排放量对全球气候变暖有重要影响。对若尔盖高原湿地泥炭沼泽土中的亚硝酸盐还原酶（nirK）反硝化细菌群落结构多样性进行分析，以期揭示该区域N2O释放的微生物调控机制。基于若尔盖高原湿地泥炭沼泽土的理化性质和反硝化活性（PDA），结合限制性酶切片段长度多态性（Restriction fragment length polymorphism， RFLP）技术、克隆文库及分子测序对该生态系统中的nirK反硝化细菌群落结构及多样性进行分析。反硝化活性测定结果显示：阿西地区>麦溪地区>分区地区，反硝化活性与土壤有机碳、总氮和丰富度呈显著正相关（P < 0.05）。Shannon-wiener多样性指数以阿西最高、分区最低。3个样品中共测序15条nirK基因代表序列，系统发育表明若尔盖高原湿地优势nirK反硝化菌群为变形门菌群。其中，阿西地区主要为α-变形菌门，麦溪地区主要为β-变形菌门，分区地区无法确定优势种群。冗余分析（Redundancy analysis， RDA）显示：有效钾和有效磷是影响nirK反硝化细菌群落结构的关键环境因子。本论文显示，若尔盖高原湿地存在着明显的反硝化作用，调控这些反硝化作用的nirK反硝化细菌多样性较高，且与土壤有效钾和有效磷密切相关。 Abstract:The Zoige Wetland, which is located in the northeast of the Tibetan Plateau, is a typical low latitude permanent permafrost wetland, with high altitude intensive ultraviolet radiation and high soil organic matter content. The nitrous oxide fluxes in this area are critical to global warming. The main objective of this study was to elucidate the diversity and structure of the nitrate reductase (nirK) gene denitrifier community, and to further explore the microbial mediated mechanism of N2O release in this climatically extreme area. Based on the soil physicochemical properties and denitrifying activity (PDA) analysis, restriction fragment length polymorphism (RFLP), clone library and sequencing were further used to analyze the diversity and structure of the nirK gene in the denitrifier community. The results showed that the highest activity of PDA was detected in the Axi soil, while the lowest activity was in the Fenqu soil. The PDA was significantly and positively correlated with soil organic carbon, total nitrogen and nirK gene richness (P < 0.05). The highest and lowest Shannon-Wiener diversity indices were detected in Axi and Fenqu soils, respectively. Based on the RFLP patterns, 15 different nirK gene clones were selected for sequencing and further phylogenetic analysis. The phylogenetic analysis showed that the majority of the nirK-denitrifiers in the peat soil of the Zoige Wetland belonged to Proteobacteria, and the dominant species in the Axi soil were Alphaproteobacteria, whereas Betaproteobacteria species dominated in the Maixi soil. The dominant nirK denitrifiers remained unidentified in the Fenqu soil. Redundancy analysis (RDA) was used to explore the possible relationship between the nirK denitrifiers community and soil physicochemical parameters, and the results showed that soil available potassium and available phosphorus were the two most important factors in shaping nirK denitrifier communities. In conclusion, the current study revealed obvious denitrifying activities in the Zoige Plateau Wetland. The nirK gene denitrifying community, which plays an important role in mediating the denitrifying process, was relatively diverse and positively influenced by soil available potassium and available phosphorus. 参考文献 相似文献 引证文献

Mercury and methylmercury biogeochemistry in a thawing permafrost wetland complex, Northwest Territories, Canada

AbstractIn arctic and sub‐arctic environments, mercury (Hg), more specifically toxic methylmercury (MeHg), is of growing concern to local communities because of its accumulation in fish. In these regions, there is particular interest in the potential mobilization of atmospherically deposited Hg sequestered in permafrost that is thawing at unprecedented rates. Permafrost thaw and the resulting ground surface subsidence transforms forested peat plateaus into treeless and permafrost‐free thermokarst wetlands where inorganic Hg released from the thawed permafrost and draining from the surrounding peat plateaus may be transformed to MeHg. This study begins to characterize the spatial distribution of MeHg in a peat plateau–thermokarst wetland complex, a feature that prevails throughout the wetland‐dominated southern margin of thawing discontinuous permafrost in Canada's Northwest Territories. We measured pore water total Hg, MeHg, dissolved organic matter characteristics and general water chemistry parameters to evaluate the role of permafrost thaw on the pattern of water chemistry. A gradient in vegetation composition, water chemistry and dissolved organic matter characteristics followed a toposequence from the ombrotrophic bogs near the crest of the complex to poor fens at its downslope margins. We found that pore waters in poor fens contained elevated levels of MeHg, and the water draining from these features had dissolved MeHg concentrations 4.5 to 14.5 times higher than the water draining from the bogs. It was determined through analysis of historical aerial images that the poor fens in the toposequence had formed relatively recently (early 1970s) as a result of permafrost thaw. Differences between the fens and bogs are likely to be a result of their differences in groundwater function, and this suggests that permafrost thaw in this landscape can result in hotspots for Hg methylation that are hydrologically connected to downstream ecosystems. Copyright © 2016 John Wiley &amp; Sons, Ltd.