For decades, tropical peatlands in Indonesia have been deforested and converted to other land uses, mainly oil palm plantations which now cover one-fourth of the degraded peatland area. Given that the capacity for peatland ecosystems to store carbon depends largely on hydrology, there is a growing interest in rewetting degraded peatlands to shift them back to a carbon sink. Recent estimates suggest that peatland rewetting may contribute up to 13 % of Indonesia\'s total mitigation potential from natural climate solutions. In this study, we measured CO2 and CH4 fluxes, soil temperature, and water table level (WTL) for drained oil palm plantations, rewetted oil palm plantations, and secondary forests located in the Mempawah and Kubu Raya Regencies of West Kalimantan, Indonesia. We found that peatland rewetting significantly reduced peat CO2 emissions, though CH4 uptake was not significantly different in rewetted peatland compared to drained peatland. Rewetting drained peatlands on oil palm plantations reduced heterotrophic respiration by 34 % and total respiration by 20 %. Our results suggest that rewetting drained oil palm plantations will not achieve low CO2 emissions as observed in secondary forests due to differences in vegetation or land management. However, extrapolating our results to the areas of degraded oil palm plantations in West Kalimantan suggests that successful peatland rewetting could still reduce emissions by 3.9 MtCO2 yr-1. This result confirms that rewetting oil palm plantations in tropical peatlands is an effective natural climate solution for achieving national emission reduction targets.

Peatlands deliver a variety of beneficial ecosystem services, particularly serving as habitats for a diverse array of species. Hynobius amjiensis is a critically endangered amphibian initially discovered in a Sphagnum-dominated peatland in Anji, China. The unique habitat requirements of H. amjiensis make it highly vulnerable to environmental changes. Here, we investigated the different breeding pools of H. amjiensis in the Sphagnum-dominated peatland (the type locality) for a one-year period to evaluate the interactions among the egg sacs present, water quality, and microbial communities (16S and 18S rRNA gene amplicon). The numbers of egg sacs were higher in the breeding pools located at the marginal area than those at the core area of the peatland. Similarly, the α-diversity of bacteria, fungi, and protists were lower in the core region compared to those at the edge of the peatland, perhaps due to water eutrophication. The microbial communities and water quality differed significantly among breeding pools and sampling months. The simpler microbial networks of the breeding pools in the core wetland may impact the numbers and health of the egg sacs. This study contributes to a better understanding of the effect of water quality on biodiversity in peatlands, and it can also guide regulations for wetland conservation and the protection of endangered species.

Permafrost thaw in northern peatlands causes collapse of permafrost peat plateaus and thermokarst bog development, with potential impacts on atmospheric greenhouse gas exchange. Here, we measured methane and carbon dioxide fluxes over 3 years (including winters) using static chambers along two permafrost thaw transects in northwestern Canada, spanning young (~30 years since thaw), intermediate and mature thermokarst bogs (~200 years since thaw). Young bogs were wetter, warmer and had more hydrophilic vegetation than mature bogs. Methane emissions increased with wetness and soil temperature (40 cm depth) and modelled annual estimates were greatest in the young bog during the warmest year and lowest in the mature bog during the coolest year (21 and 7 g C-CH4 m-2 year-1, respectively). The dominant control on net ecosystem exchange (NEE) in the mature bog (between +20 and -54 g C-CO2 m-2 year-1) was soil temperature (5 cm), causing net CO2 loss due to higher ecosystem respiration (ER) in warmer years. In contrast, wetness controlled NEE in the young and intermediate bogs (between +55 and -95 g C-CO2 m-2 year-1), where years with periodic inundation at the beginning of the growing season caused greater reduction in gross primary productivity than in ER leading to CO2 loss. Winter fluxes (November-April) represented 16% of annual ER and 38% of annual CH4 emissions. Our study found NEE of thermokarst bogs to be close to neutral and rules out large CO2 losses under current conditions. However, high CH4 emissions after thaw caused a positive net radiative forcing effect. While wet conditions favouring high CH4 emissions only persist for the initial young bog period, we showed that continued climate warming with increased ER, and thus, CO2 losses from the mature bog can cause net positive radiative forcing which would last for centuries after permafrost thaw.

More than half of the carbon pools in peatlands are stored in the soil layers below 30 cm, yet little is known about the carbon stabilizing factors at these depths. Although iron oxide minerals are considered to be important for stabilizing organic carbon (OC), their role in the preservation of OC in peatlands, especially in the deep layers, is poorly understood. Here, we collected 1 m soil profiles from six peatlands in Central and West China to quantitatively study the vertical distribution characteristics of iron-bound OC (Fe-bound OC), and the influencing physicochemical properties of the soil. The results showed that the content of reactive iron (FeR) was enriched in the top layer and decreased gradually with depth. While Fe-bound OC was positively correlated with FeR, its concentration did not decrease with depth in the peat profile. There were no obvious trends in the distributions of FeR and Fe-bound OC with water level fluctuations in the peat profile. In addition, the proportion of Fe-bound OC to soil organic carbon in the deep peat (31 to 100 cm) was equivalent to that in the surface peat (0 to 30 cm), indicating that iron oxide mineral provides comparable protection of OC in both layers. According to upper estimates of global peatland carbon storage (612 Pg), it could be predicted that 23.81 ± 11.75 Pg of OC is protected by association with FeR. These results indicated that iron oxide minerals are the effective \"rusty sink\" of OC sequestration in peatland, and a key factor for its long-term preservation. The results from this study make a valuable contribution to the carbon dynamics knowledgebase for peatlands, and provide a basis for improved predictive simulations.

Polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) are involuntary by-products of incomplete combustion and are highly toxic to humans and the environment. The Malaysian peat is often acidic or extremely acidic having high levels of chlorine and/or other organic acids that act as catalysts or precursors in PCDD/Fs formation. This study aims to predict PCDD/Fs emissions in peat soil using an artificial neural network (ANN) approach based on limited emission data and selected physico-chemical properties. The ANN\'s prediction performance is affected by uncertainties in its initial connection weights. To improve prediction performance, an optimisation algorithm, termed differential evolution (DE), is used to optimise the ANN\'s initial connection weights and bias. The study adopts several ANNs with fixed architecture to predict PCDD/Fs emissions, each consisting of a multilayer perceptron (MLP) with a backpropagation algorithm. Eight input variables and one output variable were adopted to train and test various neural network architectures using real-world datasets. The model optimisation procedure was conducted to ascertain the network architecture with the best predictive accuracy. The evolved ANN based on 5 hidden neurons, with the assistance of self-adaptive ensemble-based differential evolution with enhanced population sizing (SAEDE-EP), successfully produced the lowest MSEtest (6.1790 × 10-3) and highest R2 (0.97447) based on the mean among the other HNs. An evolutionary-optimised ANN-based methodology is a viable solution to predict PCDD/Fs in peat soil. It is cost-effective for pollution control, environmental monitoring and capable of aiding authorities prevent PCDD/Fs exposure, e.g., during a fire.

Nitrogen oxides (NOx) play an important role for atmospheric chemistry and radiative forcing. However, NOx emissions from the vast northern circumpolar permafrost regions have not been studied in situ due to limitations of measurement techniques. Our goals were to validate the offline analytical technique, and based on this, to widely quantify in situ NOx emissions from peatlands in the southern Eurasian permafrost region. To this end, we conducted a comparison of online and offline flux measurements in 2018 and 2019 using the synthetic air flushing, steady-state opaque chamber method. With differences in annual average and cumulative fluxes less than 0.1 μg N m-2 h-1 and 0.01 kg N ha-1 year-1, the online and offline fluxes were in good agreement, demonstrating the feasibility of conducting offline measurements in remote regions without power supply. The flux measurements over 2 years showed obvious NOx emissions of 0.05-0.14 and 0.13-0.30 kg N ha-1 year-1 in the hollow and hummock microtopography of permafrost peatlands, respectively. The rapid expansion of alder (Alnus sibirica) in the peatlands induced by permafrost degradation significantly increased soil mineral N contents and NOx emissions depending on the age of alder (0.64-1.74 and 1.44-2.20 kg N ha-1 year-1 from the alder forests with tree ages of 1-10 years and 11-20 years, respectively). Alder expansion also intensively altered the thermal state of permafrost including the sharp increases of soil temperatures during the non-growing season from October to April and active layer thickness. This study provides the first in situ evidences of NOx emissions from the northern circumpolar permafrost regions and uncovers the well-documented expansion of alders can substantially stimulate NOx emissions and thus, significantly affect air quality, radiative forcing, and ecosystem productivity in the pristine regions.

Peatland wildfires contribute significantly to the atmospheric release of light-absorbing organic carbon, often referred to as brown carbon. In this study, we examine the presence of nitrogen-containing organic compounds (NOCs) within marine aerosols across the Western Pacific Ocean, which are influenced by peatland fires from Southeast Asia. Employing ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) in electrospray ionization (ESI) positive mode, we discovered that NOCs are predominantly composed of reduced nitrogenous bases, including CHN+ and CHON+ groups. Notably, the count of NOC formulas experiences a marked increase within plumes from peatland wildfires compared to those found in typical marine air masses. These NOCs, often identified as N-heterocyclic alkaloids, serve as potential light-absorbing chromophores. Furthermore, many NOCs demonstrate pyrolytic stability, engage in a variety of substitution reactions, and display enhanced hydrophilic properties, attributed to chemical processes such as methoxylation, hydroxylation, methylation, and hydrogenation that occur during emission and subsequent atmospheric aging. During the daytime atmospheric transport, aging of aromatic N-heterocyclic compounds, particularly in aliphatic amines prone to oxidation and reactions with amine, was observed. The findings underscore the critical role of peatland wildfires in augmenting nitrogen-containing organics in marine aerosols, underscoring the need for in-depth research into their effects on marine ecosystems and regional climatic conditions.

Soil microorganisms play crucial roles in the stability of the global carbon pool, particularly in permafrost peatlands that are highly sensitive to climate change. Microtopography is a unique characteristic of peatland ecosystems, but how microtopography affects the microbial community structures and their functions in the soil is only partially known. We characterized the bacterial and fungal community compositions by amplicon sequencing and their abundances via quantitative PCR at different soil depths in three microtopographical positions (hummocks, flats, and hollows) in permafrost peatland of the Greater Xing\'an Mountains in China. The results showed that the soil of hummocks displayed a higher microbial diversity compared to hollows. Microtopography exerted a strong influence on bacterial community structure, while both microtopography and soil depth greatly impacted the fungal community structure with variable effects on fungal functional guilds. Soil water content, dissolved organic carbon, total phosphorus, and total nitrogen levels of the soil mostly affected the bacterial and fungal communities. Microtopography generated variations in the soil water content, which was the main driver of the spatial distribution of microbial abundances. This information stressed that the hummock-flat-hollow microtopography of permafrost peatlands creates heterogeneity in soil physicochemical properties and hydrological conditions, thereby influencing soil microbial communities at a microhabitat scale. Our results imply that changes to the water table induced by climate warming inducing permafrost degradation will impact the composition of soil microbes in peatlands and their related biogeochemical functions, eventually providing feedback loops into the global climate system.

Subfossil pine and oak tree trunks were excavated during exploitation of the Budwity peatland in Northern Poland. Based on dendrochronological analysis, the woodland successions in peatland were reconstructed and correlated with moisture dynamics of the peatland ecosystem inferred from the high-resolution multi-proxy analysis of the peatland deposits. From the results of dendrochronological analysis and the 14C wiggle matching methods, four floating pine chronologies (5882-5595; 5250-5089; 3702-3546; and 2222-1979 mod. cal BP) and two oak chronologies (4932-4599 and 4042-3726 mod. cal BP) were developed. The organic sediments of the peatland (6 m thick) were deposited over approximately nine thousand years. The lower complex (525-315 cm) comprises minerogenic peat, while the upper complex (315.0-0.0 cm) is composed of ombrogenic peat. Subfossil tree trunks are distributed across various peat horizons, which suggests multiple stages of tree colonisation followed by subsequent dying-off phases. Multiproxy sediment analyses (lithological, geochemical and δ13C stable isotope, pollen, plant macrofossils, Cladocera, diatom, and Diptera analyses) indicate that the two earliest phases of pine colonisation (5882-5595 and 5250-5089 mod. cal BP) and the two stages of oak colonisation (4932-4599 and 4042-3726 mod. cal BP) were associated with periodic drying of the peatland. Conversely, tree dying-off phases occurred during periods of increased water levels in the peatland, coinciding with stages of increasing climate humidity during the Holocene. The two most recent phases of pine colonisation occurred during the ombrogenic stage of mire development. Remnants of the dead forest from these phases, marked by subfossil trunks still rooted in the ground, were preserved and exposed presently during peat exploitation, approximately 2.5 m below ground level. The identified phases of tree colonisation and subsequent dying-off phases show correlation with analogical phenomena observed in the other investigated European peatlands.

Peatlands, shaped by centuries of human activities, now face a primary threat from mining activities. Vulnerable to drainage and hydrological instability, peatland areas encounter challenges that compromise their ecological integrity. This study hypothesised that permanent water reservoirs within mines could serve as refugia for water beetles from adjacent areas prone to drying in the summer. Employing standard methods, including entomological scraping and water traps, samples were collected. Results revealed that, in most cases, water beetles exhibited a preference for the Nature 2000 area untouched by mining. Despite unfavourable conditions, the Nature 2000 area showcased a more diverse water beetle fauna. Remarkably, the selected Nature 2000 area, despite its identified degradation based on flora, remained a biodiversity hotspot for peatland water beetle fauna. The study underscores the significance of assessing insects, particularly beetles, as rapid responders to environmental changes. This evaluation holds crucial implications for peatland restoration planning and decision-making regarding mining investments in proximity to peatland areas.