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Water-logged peatlands store tremendous amounts of soil carbon (C) globally, accumulating C over millennia. As peatlands become disturbed by human activity, these long-term C stores are getting destabilized and ultimately released as greenhouse gases that may exacerbate climate change. Oxidation of the dissolved organic carbon (DOC) mobilized from disturbed soils to streams and canals may be one avenue for the transfer of previously stored, millennia-aged C to the atmosphere. However, it remains unknown whether aged peat-derived DOC undergoes oxidation to carbon dioxide (CO 2 ) following disturbance. Here, we use a new approach to measure the radiocarbon content of CO 2 produced from the oxidation of DOC in canals overlying peatland soils that have undergone widespread disturbance in Indonesia. This work shows for the first time that aged DOC mobilized from drained and burned peatland soils is susceptible to oxidation by both microbial respiration and photomineralization over aquatic travel times for DOC. The bulk radiocarbon age of CO 2 produced during canal oxidation ranged from modern to ~1300 years before present. These ages for CO 2 were most strongly influenced by canal water depth, which was proportional to the water table level where DOC is mobilized from disturbed soils to canals. Canal microbes preferentially respired older or younger organic C pools to CO 2 , and this may have been facilitated by the use of a small particulate organic C pool over the dissolved pool. Given that high densities of canals are generally associated with lower water tables and higher fire risk, our findings suggest that peatland areas with high canal density may be a hotspot for the loss of aged C on the landscape. Taken together, the results of this study show how and why aquatic processing of organic C on the landscape can enhance the transfer of long-term peat C stores to the atmosphere following disturbance., (© 2024 John Wiley & Sons Ltd.)

This study focuses on the physiological response of lettuce grown on Technosols designed for the remediation of soils polluted by potentially harmful elements (PHEs: As, Cd, Cu, Fe, Pb, and Zn). Lettuce plants were grown in five treatments: recovered (RS) and polluted soil (PS) as controls, and three Technosols (TO, TS, and TV) consisting of 60% PS mixed with 2% iron sludge, 20% marble sludge, and 18% organic wastes (TO: composted olive waste, TS: composted sewage sludge, and TV: vermicompost of garden waste). The main soil properties and PHE solubility were measured, together with physiological parameters related to phytotoxicity in lettuce such as growth, photosynthetic capacity, oxidative stress, and antioxidant defence. All Technosols improved unfavourable conditions of PS (i.e., neutralised acidity and enhanced OC content), leading to a significant decrease in Cd, Cu, and Zn mobility. Nevertheless, TV was the most effective as the reduction in PHEs mobility was higher. Furthermore, lettuce grown on TV and TO showed higher growth (+90% and +41%) than PS, while no increase in TS. However, lower oxidative stress and impact on photosynthetic rate occurred in all Technosols compared to PS (+344% TV, +157% TO, and +194% TS). This physiological response of lettuce proves that PHE phytotoxicity is reduced by Technosols. Thus, this ecotechnology constitutes a potential solution for soil remediation, with effectiveness of Technosols depending largely on its components. [ABSTRACT FROM AUTHOR]

Collembola play a key role in soil ecosystems by decomposing organic matter. Most of them inhabit the upper layers of the soil and are susceptible to contamination present in the pore water. These arthropods serve as model organisms in ecotoxicology for short and long-term exposure. This study aimed to assess the toxicity of three heavy metals (lead [Pb], cadmium [Cd], and copper [Cu]) using the springtail species Folsomia candida as the test organism, with mortality and growth inhibition as the measure of toxicity. We hypothesised that increasing metal concentrations in the soil would correspond to a growth reduction of Collembola. Each heavy metal was tested at a minimum of eight increasing concentrations in six replications. Twenty 10-12-day-old individuals were introduced into each test container filled with contaminated or control soil and incubated for 14 days. The test endpoints included growth inhibition determined by comparing F. candida growth rates in contaminated soil with those in control soil, as well as mortality rates. The EC50 values (mg/kg) for heavy metals were as follows: Cd = 66.89, Cu = 791.01, Pb = 10075.48. Our findings suggest that growth inhibition is a reliable indicator of Collembola toxicity to heavy metals. [ABSTRACT FROM AUTHOR]

We employed two compelling and distinct methods, Fourier Transform Infrared Spectroscopy (FTIR) and Ramped Pyrolysis Oxidation (Ramped PyrOx), to examine the quality of organic matter (OM) stored in four peatlands located along a latitudinal gradient (Tropical (4˚N), Subtropical (27˚N), Boreal (48˚N), and Polar (68˚N)). FTIR was used to quantify the relative abundance of carbohydrates, a relatively labile compound class, and aromatics, which are more recalcitrant, in a sample set of four peat cores. These samples were then prepared using Ramped PyrOx, a second, independent method of determining OM quality that mimics the natural diagenetic maturation of OM that would take place over long timescales. Previous large-scale studies using FTIR to evaluate OM quality have observed that it generally increases with increasing latitude (more carbohydrates, less aromatics). Here, we demonstrate that the Ramped PyrOx approach both validates and complements the FTIR approach. The data stemming from each Ramped PyrOx preparation was input to a model that generates an estimated probability density function of the activation energy (E) required to break the C bonds in the sample. We separated these functions into three fractions ("low E," "medium E," and "high E") to create Ramped PyrOx variables that could be quantitatively compared to the compound class abundance data from FTIR. In assessing the agreement between the two methods, we found three significant relationships between Ramped PyrOx and FTIR variables. Low E fractions and carbohydrate content were positively correlated (R2 = 0.51) while low E fractions were negatively correlated with aromatic content (R2 = 0.58). Medium E fractions were found to be positively correlated with aromatics (R2 = 0.69). [ABSTRACT FROM AUTHOR]

Tropical wetlands and freshwaters are major contributors to the growing atmospheric methane (CH4) burden. Extensive peatland drainage has lowered CH4 emissions from peat soils in Southeast Asia, but the canals draining these peatlands may be hotspots of CH4 emissions. Alternatively, CH4 oxidation (consumption) by methanotrophic microorganisms may attenuate emissions. Here, we used laboratory experiments and a synoptic survey of the isotopic composition of CH4 in 34 canals across West Kalimantan, Indonesia to quantify the proportion of CH4 that is consumed and therefore not emitted to the atmosphere. We find that CH4 oxidation mitigates 76.4 ± 12.0% of potential canal emissions, reducing emissions by ~70 mg CH4 m−2 d−1. Methane consumption also significantly impacts the stable isotopic fingerprint of canal CH4 emissions. As canals drain over 65% of peatlands in Southeast Asia, our results suggest that CH4 oxidation significantly influences landscape-scale CH4 emissions from these ecosystems. Canals draining vast areas of peatland in Southeast Asia may be hotspots for methane emissions. Perryman et al. surveyed dozens of canals in Indonesia and found that methane-eating microbes reduce emissions from these waterways by over 50%. [ABSTRACT FROM AUTHOR]

Peatlands are vital in the global carbon cycle, acting as significant sinks for carbon and releasing methane (CH4) and carbon dioxide (CO2) into the atmosphere. However, the complex interactions between environmental factors and the microbial communities responsible for these greenhouse gas emissions remain insufficiently understood. To address this knowledge gap, a pilot-scale mesocosm study was conducted to assess the impact of different terminal electron acceptors (TEAs), including sulfate (SO42-), humic acid (HA), and goethite, on CH4 and CO2 emissions and microbial community structures in peatlands. Our results revealed that the addition of TEAs significantly altered the CH4 and CO2 emissions. Specifically, the addition of SO42- nearly doubled CO2 production while substantially inhibiting CH4 emissions. The combined addition of SO42- and HA, as well as HA alone, followed a similar pattern, albeit with less pronounced effects on CH4. Goethite addition resulted in the highest inhibition of CH4 among all treatments but did not significantly increase CO2 production. Community composition and network analysis indicated that TEAs primarily determined the structure of microbial communities, with each treatment exhibiting distinct taxa networks. Proteobacteria, Acidobacteria, Chloroflexi, and Bacteroidetes were the most abundant phyla across all mesocosms. The presence of methanotrophs, including Methylomirabilales and Methylococcales, was linked to the inhibition of CH4 emissions in these mesocosms. This study provides novel insights into the spatial variability of microbial diversity and density in peatlands under various TEAs, emphasizing the role of methanogenesis and CO2 fluxes in carbon cycling. Our findings enhance the understanding of carbon cycling in microbe-rich environments exposed to TEAs and highlight the potential for future studies to investigate the long-term effects of TEAs on microbial communities, enzymes, and carbon storage. [ABSTRACT FROM AUTHOR]

The potential positive feedback between global aquatic deoxygenation and methane (CH4) emission emphasizes the importance of understanding CH4 cycling under O2‐limited conditions. Increasing observations for aerobic CH4‐oxidizing bacteria (MOB) under anoxia have updated the prevailing paradigm that MOB are O2‐dependent; thus, clarification on the metabolic mechanisms of MOB under anoxia is critical and timely. Here, we mapped the global distribution of MOB under anoxic aquatic zones and summarized four underlying metabolic strategies for MOB under anoxia: (a) forming a consortium with oxygenic microorganisms; (b) self‐generation/storage of O2 by MOB; (c) forming a consortium with non‐oxygenic heterotrophic bacteria that use other electron acceptors; and (d) utilizing alternative electron acceptors other than O2. Finally, we proposed directions for future research. This study calls for improved understanding of MOB under anoxia, and underscores the importance of this overlooked CH4 sink amidst global aquatic deoxygenation. [ABSTRACT FROM AUTHOR]

Satellite imagery has become a major source for identifying and mapping terrestrial and planetary landforms. However, interpretating landforms and their significance, especially in changing environments, may still be questionable. Consequently, ground truth to check training models, especially in mountainous areas, can be problematic. This paper outlines a decimal format, [dLL], for latitude and longitude geolocation that can be used for model interpretation and validation and in data sets. As data have positions in space and time, [dLL] defined points, as for images, can be associated with metadata as nodes. Together with vertices, metadata nodes help build 'information surfaces' as part of the Digital Earth. This paper examines aspects of the Critical Zone and data integration via the FAIR data principles, data that are; findable, accessible, interoperable and re-usable. Mapping and making inventories of rock glacier landforms are examined in the context of their geomorphic and environmental significance and the need for geolocated ground truth. Terrestrial examination of rock glaciers shows them to be predominantly glacier-derived landforms and not indicators of permafrost. Remote-sensing technologies used to track developing rock glacier surface features show them to be climatically melting glaciers beneath rock debris covers. Distinguishing between glaciers, debris-covered glaciers and rock glaciers over time is a challenge for new remote sensing satellites and technologies and shows the necessity for a common geolocation format to report many Earth surface features. [ABSTRACT FROM AUTHOR]

Dissolved organic matter (DOM) plays a significant role in the nutrient supply, energy flow, and pollutant transportation in the wetland ecosystem. However, little is known about the effect of the decomposition of different organic materials in alpine wetland water on the DOM characteristics. By conducting a 90-day decomposition experiment with the addition of different organic materials (peat soil, yak manure, and plant litter) alone or their combinations into alpine wetland water, we characterized the water DOM using three-dimension excitation-emission matrix spectroscopy. The results showed that the decomposition of organic materials significantly affected the chemical properties, sources, humification degree, and composition of the water DOM. The decomposition increased dissolved organic carbon and dissolved total nitrogen in the water. For most of the water samples, a fluorescence index ranging from 1.4 to 1.7 and a biological index of less than 0.8 may indicate that both autochthonous and allochthonous sources contributed to the water DOM, which may primarily rely on allochthonous sources. UVA (37.55–46.81% of total fluorescent components) and UVC fulvic-like substances (29.91–35.53% of total fluorescent components) dominated the water DOM compositions. Among the treatments, additions of peat soil and yak manure led to the highest and the lowest humification degree of the water DOM, respectively. For the treatment of the combination decomposition of all three organic materials, the yak manure may stimulate microbial activity and facilitate the decomposition of plant litter and peat soil and, therefore, boost the humic-like substances in the water DOM. These findings may help the development of wetland biomass management with the objective of maintaining alpine wetland ecosystem services. [ABSTRACT FROM AUTHOR]

The conservation of decorated caves is highly dependent on airflows in the karst network and through the surrounding host rock. Airflows are driven by the pressure gradient and influenced by the shape of the karst conduits and the permeability of the carbonate rock massif. Cosquer Cave is an Upper Paleolithic decorated cave, half submerged in a coastal karst, where conservation is also dependent on the cave's pools connected to the sea. Hydroclimatic data, such as air pressure and temperature and the water level inside and outside the cave, have been measured for several years to identify the main processes governing the water level variations, the airflows, and the air renewal. The data show unusual behavior for a karst: the karst air pressure is nearly always higher than the atmospheric pressure. As a result, the water level in the cave is below the sea level. The daily variations of the sea tide provide an assessment of the cave volume above the water level in the pools. Although the cave air is confined by the rock and the seawater, there are also external air inflows during short pressurization events connected with waves that can produce and force air bubbles to flow along submarine open fissures or karst conduits inside the massif. Moreover, the effective permeability of the carbonate rocks to air at the massif scale is inferred from the cave air pressure decrease over the summer season by applying Darcy's law in a partially saturated medium. Six years of data show that permeability varies from year to year and according to the cumulative rainfalls during the spring and summer. The driest years are correlated with a higher permeability, a faster air pressure decrease in the cave, and a faster rise in the pools' water level. In the future, in the context of climate change, a perturbation of the rock permeability is then expected in the near-surface caves, which will impact airflows in decorated caves and may alter their fragile hydroclimatic stability. [ABSTRACT FROM AUTHOR]

Soil acidification is a global environmental problem with significant impacts on agricultural production, environmental protection, and ecosystem health. Soil acidification is widespread in China, affecting crop yields, agricultural product quality, and biodiversity. Since the 1980s, much work has been done on acidic soils in China, but it is controversial whether excessive nitrogen fertilizer application can lead to soil acidification mechanisms. To address the above issues, we conducted a meta-analysis of 115 published papers to integrate and analyze the effects of N fertilizer application on soil acidification and biological properties from 1980 to 2024. We also quantified the effect of nitrogen fertilization on soil acidification and biological changes under different climatic conditions. The results showed that under long-term application of nitrogen fertilizers in China from 1980 to 2024, soil pH decreased by an average of 15.27%, and the activities of soil urease, nitrate reductase, nitrite reductase, catalase, glutamate dehydrogenase, and glutamate synthetase decreased by an average of 9.82–22.37%. The soil microbial community richness (Chao1 index) increased by 6.53%, but the community diversity (Shannon index) decreased by 15.42%. Among the dominant soil microorganisms, the relative abundance of bacteria decreased by an average of 9.67–29.38% and the abundance of gene expression of nifH, amoA-AOA, amoA-AOB, and qnorB decreased by 9.92–19.83%. In addition, we found that the mean annual temperature and rainfall impacted soil acidification via their effect on soil microbial diversity and community composition. This study provides a scientific basis for an in-depth understanding of the spatial and temporal variation of soil acidification and biological properties in China. [ABSTRACT FROM AUTHOR]

Peatland pools are unvegetated, inundated depressions that cover up to 30 % of the surface of many temperate and boreal peatlands and that are net carbon (C) sources within C-accumulating ecosystems. The emission of carbon dioxide (CO 2) and methane (CH 4) from peatland pools comes from the degradation of organic matter (OM) that comprises the surrounding matrix. It is, however, not clear how decomposition rates in pools, which define their function and distinguish them from other aquatic ecosystems, vary spatially and what mechanisms drive these variations. We first quantified rates of OM decomposition from fresh litter at different depths in six pools of distinct morphological characteristics in a temperate ombrotrophic peatland using litterbags of Sphagnum capillifolium and Typha latifolia over a 27-month period. Rates of decomposition were faster for T. latifolia than S. capillifolium and, overall, faster at the pool surface and decreased with increasing depth. We then measured potential CO 2 and CH 4 production from the sediments of the same six pools by performing 35 d laboratory incubations. Pool sediment chemistry was variable among pools and influenced the production of CH 4 and CO 2 from sediments, with decreasing CO 2 production with increasing OM humification and decreasing CH 4 production with increasing nitrogen-to-phosphorus ratio. Both CH 4 production and CO 2 production from pool sediments were higher in the 1 m deep pools but similar in the shallow < 1 and the > 1.5 m deep pools. When combining both experiments, our results indicate that OM decomposition in peatland pools is highly variable and mostly related to the environmental conditions in which it occurs as a function of general pool depth rather than to OM chemistry. Overall, we show that OM degradation and C emissions in peatland open-water pools may increase over time in warmer and drier climate conditions. [ABSTRACT FROM AUTHOR]

Higher-dimensional models of peatland development are required to analyse the influence of spatial heterogeneity and complex feedback mechanisms on peatland behaviour. However, the current models exclude the mechanical process that leads to uncertainties in simulating the spatial variability in the water table position, vegetation composition, and peat physical properties. Here, we propose MPeat2D, a peatland development model in two dimensions, which considers mechanical, ecological, and hydrological processes together with the essential feedback from spatial interactions. MPeat2D employs poroelasticity theory that couples fluid flow and solid deformation to model the influence of peat volume changes on peatland ecology and hydrology. To validate the poroelasticity formulation, the comparisons between numerical and analytical solutions of Mandel's problems for two-dimensional test cases are conducted. The application of MPeat2D is illustrated by simulating peatland growth over 5000 years above a flat and impermeable substrate with free-draining boundaries at the edges, using constant and variable climate. In both climatic scenarios, MPeat2D produces lateral variability in the water table depth, which results in the variation in the vegetation composition. Furthermore, the drop in the water table at the margin increases the compaction effect, leading to a higher value of bulk density and a lower value of active porosity and hydraulic conductivity. These spatial variations obtained from MPeat2D are consistent with the field observations, suggesting plausible outputs from the proposed model. By comparing the results of MPeat2D to a one-dimensional model and a two-dimensional model without the mechanical process, we argue that mechanical–ecohydrological feedbacks are important for analysing spatial heterogeneity, shape, carbon accumulation, and resilience of peatlands. [ABSTRACT FROM AUTHOR]

Tropical peatlands in Southeast Asia have experienced widespread subsidence due to forest clearance and drainage for agriculture, oil palm and pulp wood production, causing concerns about their function as a long-term carbon store. Peatland drainage leads to subsidence (lowering of peatland surface), an indicator of degraded peatlands, while stability/uplift indicates peatland accumulation and ecosystem health. We used the Advanced Pixel System using the Intermittent SBAS (ASPIS-DInSAR) technique with biophysical and geographical data to investigate the impact of peatland drainage and agriculture on spatial patterns of subsidence in Selangor, Malaysia. Results showed pronounced subsidence in areas subjected to drainage for agricultural and oil palm plantations, while stable areas were associated with intact forests. The most powerful predictors of subsidence rates were the distance from the drainage canal or peat boundary; however, other drivers such as soil properties and water table levels were also important. The maximum subsidence rate detected was lower than that documented by ground-based methods. Therefore, whilst the APSIS-DInSAR technique may underestimate absolute subsidence rates, it gives valuable information on the direction of motion and spatial variability of subsidence. The study confirms widespread and severe peatland degradation in Selangor, highlighting the value of DInSAR for identifying priority zones for restoration and emphasising the need for conservation and restoration efforts to preserve Selangor peatlands and prevent further environmental impacts. [ABSTRACT FROM AUTHOR]

This study evaluated the impact of different land use types on groundwater dissolved organic carbon (DOC) concentrations and annual DOC efflux from drained peatlands to catchment runoff, providing insights into the mechanisms of carbon stock changes in peatland soils. We measured groundwater chemical properties and various environmental variables, and calculated daily runoff and evapotranspiration for 2021 to estimate monthly and annual DOC efflux and analyzed main affecting factors in different peatland land use types. The highest DOC concentrations in groundwater were found in Scots pine forests and active peat extraction sites, with values of 113.7 mg L−1 and 109.7 mg L−1, respectively, and the lowest in silver birch forests and croplands, at 51.9 mg L−1 and 18.6 mg L−1, respectively. There were statistically significant correlations, including a strong negative correlation between DOC concentrations and several groundwater chemical properties, such as pH, electrical conductivity (EC), Ca, Mg, and K concentrations. The concentrations of DOC in the groundwater of drained peatland showed significant variation between different land use types. The highest annual DOC efflux was observed in active peat extraction sites, at 513.1 kg ha−1 y−1, while the lowest was in grasslands, at 61.9 kg ha−1 y−1, where Ca and Mg concentrations, as well as EC, were the highest. Continuous monitoring of these concentration patterns is essential. [ABSTRACT FROM AUTHOR]

Peatland hydrology plays an important role in preserving or changing the record in any consideration of past atmospheric deposition records in peat bogs. The Šijec bog, located on the Pokljuka plateau in Slovenia, is one of the largest ombrotrophic peatlands. We sampled the surface pools, pore water, drainage from the peatland, and karst streams not connected to the peatland. Additionally, we sampled the precipitation, as ombrotrophic peatlands receive mineral matter solely from the atmosphere. The results of the evaluation of the chemical and isotopic composition indicated different origins of dissolved mineral matter in different water types. The components originating from the bedrock and surrounding soils (Ca, Mg, Al, Si, Sr) predominated in the streams. The chemical composition of the peatland drainage water revealed the significant removal of major components from the peatland, particularly elements like Al, Fe, and REE, and metals that are readily dissolved in an acidic environment or mobile in their reduced state. Despite their solubility, concentrations of metals (As, Cr, Cu, Fe, Ni, Pb, Ti) and REE in surface pools remained higher than in the drainage due to incomplete elimination from the peatland. The composition of pore water reflects variations among the W and E parts of the peatland, indicating a heterogenous hydrological structure with different dynamics, such as an additional source of water at approximately 90 cm depth in the NW part. The chemical composition and isotope signature (18O and 2H) of pore water additionally indicated a heterogeneous recharge with residence times of less than a year. The overall analysis indicated a predominantly ombrotrophic type and a small part in the NW area of the peatland as a minerotrophic type of peat. [ABSTRACT FROM AUTHOR]

High-resolution paleoclimate records from tropical continental settings are greatly needed to advance understanding of global climate dynamics. The International Continental Scientific Drilling Program (ICDP) project DeepCHALLA recovered a 214.8 m long sediment sequence from Lake Chala, a deep and permanently stratified (meromictic) crater lake in eastern equatorial Africa, covering the past ca. 250 000 years (250 kyr) of continuous lacustrine deposition since the earliest phase of lake-basin development. Lipid biomarker analyses on the sediments of Lake Chala can provide quantitative records of past variation in temperature and moisture balance from this poorly documented region. However, the degree to which climate proxies derived from aquatically produced biomarkers are affected by aspects of lake developmental history is rarely considered, even though it may critically influence their ability to consistently register a particular climate variable through time. Modern-system studies of Lake Chala revealed crucial information about the mechanisms underpinning relationships between proxies based on isoprenoid (iso-) and branched (br-) glycerol dialkyl glycerol tetraethers (GDGTs) and the targeted climate variables, but the persistence of these relationships in the past remains unclear. Here we assess the reliability of long-term climate signals registered in the sediments of Lake Chala by comparing downcore variations in GDGT distributions with major phases in lake-system evolution as reflected by independent proxies of lake depth, mixing regime and nutrient dynamics: seismic reflection data, lithology and fossil diatom assemblages. Together, these records suggest that during early lake history (before ca. 180–200 ka) the distinct mixing-related depth zones with which specific GDGT producers are associated in the modern-day lake were not yet formed, likely due to more open lake hydrology and absence of chemical water-column stratification. Consequently absolute GDGT concentrations dating to this period are relatively low, proxies sensitive to water-column stratification (e.g., branched versus isoprenoid tetraether (BIT) index) display highly irregular temporal variability, and correlations between proxies are dissimilar to expectations based on modern-system understanding. A sequence of lake-system changes between ca. 180–200 and ca. 80 ka first established and then strengthened the chemical density gradient, promoting meromictic conditions despite the overall decrease in lake depth due to the basin gradually being filled up with sediments. From ca. 180 ka onward some GDGTs and derived proxies (e.g., crenarchaeol concentration, BIT index and Ipage2878R6Me) display strong ∼ 23 kyr periodicity, likely reflecting the predominantly precession-driven insolation forcing of Quaternary climate variability in low-latitude regions. Our results suggest that GDGT-based temperature and moisture-balance proxies in Lake Chala sediments reflect the climate history of eastern equatorial Africa from at least ca. 160 ka onwards, i.e., covering the complete last glacial–interglacial cycle and the penultimate glacial maximum. This work confirms the potential of lacustrine GDGTs for elucidating the climate history of tropical regions at Quaternary timescales, provided they are applied to suitably high-quality sediment archives. Additionally, their interpretation should incorporate a broader understanding of the extent to which lake-system evolution limits the extrapolation back in time of proxy-climate relationships established in the modern system. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are bacterial lipids that have been widely used as environmental proxies in continental paleorecords. Another group of related lipids, branched glycerol monoalkyl glycerol tetraethers (brGMGTs), has recently been proposed as a potential paleotemperature proxy. Nevertheless, the sources and environmental dependencies of both brGDGTs and brGMGTs along the river–sea continuum are still poorly understood, complicating their application as paleoenvironmental proxies in some aquatic settings. In this study, the sources of brGDGTs and brGMGTs and the potential factors controlling their distributions are explored across the Seine River basin (NW France), which encompasses the freshwater-to-seawater continuum. BrGDGTs and brGMGTs were analyzed in soils, suspended particulate matter (SPM), and sediments (n=237) collected along the land–sea continuum of the Seine basin. Both types of compounds (i.e., brGDGTs and brGMGTs) are shown to be produced in situ, in freshwater and saltwater, based on their high concentrations and distinct distributions in aquatic settings (SPM and sediments) vs. soils. Redundancy analysis further shows that both salinity and nitrogen dominantly control the brGDGT distributions. Furthermore, the relative abundance of 6-methyl vs. that of 5-methyl brGDGTs (the IR 6Me ratio), the total nitrogen (TN), the δ15 N, and the chlorophyll a concentration co-vary in a specific geographical zone with low salinity, suggesting that 6-methyl brGDGTs are preferentially produced under low-salinity and high-productivity conditions. In contrast to brGDGTs, the brGMGT distribution appears to be primarily regulated by salinity, with a distinct influence on the individual homologues. Salinity is positively correlated with homologues H1020a and H1020b and negatively correlated with compounds H1020c and H1034b in SPM. This suggests that bacteria living in freshwater preferentially produce compounds H1020c and H1034b, whereas bacteria that primarily grow in saltwater appear to be predominantly responsible for the production of homologues H1020a and H1020b. Based on the abundance ratio of the freshwater-derived compounds (H1020c and H1034b) vs. their saltwater-derived homologues (H1020a and H1020b), a novel proxy, the Riverine IndeX (RIX), is proposed to trace riverine organic matter inputs, with high values (>0.5) indicating a higher riverine contribution. We successfully applied RIX to the Godavari River basin (India) and a paleorecord across the upper Paleocene and lower Eocene from the Arctic Coring Expedition at Lomonosov Ridge, showing its potential applicability to both modern samples and paleorecords. [ABSTRACT FROM AUTHOR]

Despite decades of research, the influence of climate on the export of dissolved organic carbon (DOC) from soil remains poorly constrained, adding uncertainty to global carbon models. The limited temporal range of contemporary monitoring data, ongoing climate reorganisation and confounding anthropogenic activities muddy the waters further. Here, we reconstruct DOC leaching over the last ~14,000 years using alpine environmental archives (two speleothems and one lake sediment core) across 4° of latitude from Te Waipounamu/South Island of Aotearoa New Zealand. We selected broadly comparable palaeoenvironmental archives in mountainous catchments, free of anthropogenically-induced landscape changes prior to ~1200 C.E. We show that warmer temperatures resulted in increased allochthonous DOC export through the Holocene, most notably during the Holocene Climatic Optimum (HCO), which was some 1.5–2.5 °C warmer than the late pre-industrial period— then decreased during the cooler mid-Holocene. We propose that temperature exerted the key control on the observed doubling to tripling of soil DOC export during the HCO, presumably via temperature-mediated changes in vegetative soil C inputs and microbial degradation rates. Future warming may accelerate DOC export from mountainous catchments, with implications for the global carbon cycle and water quality. [ABSTRACT FROM AUTHOR]

Mangroves, as the key blue carbon ecosystem, are considered 'potential sinks' for microplastics (MPs) in the land-ocean interface zones. However, there is limited understanding of enrichment patterns of MPs in mangrove blue carbon ecosystem, particularly in relation to human activities. This study explored the abundance, composition, and diversity of MPs in mangrove and non-mangrove sediments in Zhanjiang Bay (ZJB) to investigate the effects of human activities on MPs enrichment patterns in the blue carbon system. The results showed that MPs were widely prevalent in all sediment samples, and the abundance of MPs was significantly higher in all mangrove sediments than in non-mangrove sediments (P < 0.05). Furthermore, the average abundance of MPs was found to be 263.67 ± 85.25 items/kg in non-mangrove sediment samples, whereas in mangrove sediment samples, it was 618.17 ± 71.75 items/kg. The average abundance of MPs in mangroves was about 1.6 times higher than that in non-mangroves, indicating that mangroves have an interception effect on MPs, and human activities are the key factor leading to the difference in MPs enrichment patterns between mangroves and non-mangroves. Furthermore, the predominant MPs shapes in both mangroves and non-mangroves are fragments, with multicolor and green being the most common colors and most MPs sizes ranging between 100 and 330 µm. Besides, there was no significant relationship found between MPs abundance and particulate organic carbon (P > 0.05), indicating that MPs pollution didn't significantly alter the natural POC pool in ZJB. Overall, this study provided important baseline information on MPs pollution in the mangrove blue carbon ecosystems in ZJB, which was implications for future mitigation of MPs pollution and the management of mangrove ecosystem. [ABSTRACT FROM AUTHOR]

Mercury (Hg) is a pollutant that bioaccumulates in the food web, leading to health issues in humans and other fauna. Although anthropogenic Hg deposition has decreased over the past 20 years, our watersheds continue to be sources of Hg to downstream communities. Wetlands, especially peatlands in the Boreal Region of the globe, play a vital role in the formation of bioaccumulative methylmercury (MeHg). Few studies have assessed how increases in temperatures such as those that have already occurred and those predicted will influence the hydrologic transport of Hg to downstream communities or the net fluxes of gaseous Hg. The results indicate that peatland pore water concentrations of MeHg are increasing with ecosystem warming, and to some degree with elevated carbon dioxide (eCO2) in the Spruce and Peatland Responses Under Changing Environments (SPRUCE) experiment at the Marcell Experimental Forest (MEF) in northern Minnesota, USA. Similar to SPRUCE, in the Biological Response to A Changing Environment (BRACE) experiment in Canada, mesocosm pore water MeHg concentrations increased with soil warming. However, long-term peatland watershed streamflow fluxes of MeHg at the MEF indicate that the competing effects of climate warming and decreased atmospheric deposition have led to overall decreases in watershed MeHg transport. Mesocosm studies in the PEATCOSM experiment in Upper Michigan, USA, indicate that simulated fluctuating water tables led to higher concentrations of MeHg in peatland pore water that is available for downstream transport when water tables rise and the next runoff event occurs. Results from a winter peatland soil freeze/thaw simulation from large mesocosm cores from Jennie's Bog at the MEF indicate higher total Hg (THg) upon soil thawing but lower MeHg, likely a result of cold temperatures limiting methylation during thawing. Although there are lower MeHg concentrations after thawing, more THg is available for methylation once soils warm. Results from PEATCOSM and the literature also suggest that plant community changes that result in higher densities of sedges also lead to elevated MeHg in pore water. From a climate warming perspective, it appears that two complementary mechanisms, both related to decomposition, are at play that lead to increased pore water MeHg concentrations with warming. First, warming increases decomposition rates, leading to a higher availability of many ions, including Hg (and sulfur) species. Higher decomposition rates also lead to increases in soluble carbon which complexes with Hg species and assists in downstream hydrologic transport. However, if streamflow is decreasing with climate change as a result of landscape-level changes in evapotranspiration as suggested at MEF, the combination of less direct watershed Hg deposition and lower streamflow results in decreases in the watershed transport of MeHg. Given changes already occurring in extreme events and the rewetting and restoration of hydrology during peatland restoration, it is likely that methylation and pore water MeHg concentrations will increase. However, the landscape-level hydrologic cycle will be key to understanding the connection to downstream aquatic communities. Finally, gaseous Hg fluxes increase with warming and lead to decreases in peatland pools of Hg that may influence future availability for downstream transport. [ABSTRACT FROM AUTHOR]

Peat fires in the northern high latitudes have the potential to burn vast amounts of carbon-rich organic soil, releasing large quantities of long-term stored carbon to the atmosphere. Due to anthropogenic activities and climate change, peat fires are increasing in frequency and intensity across the high latitudes. However, at present they are not explicitly included in most fire models. Here we detail the development of INFERNO-peat, the first parameterization of peat fires in the JULES-INFERNO (Joint UK Land Environment Simulator INteractive Fire and Emission algoRithm for Natural envirOnments) fire model. INFERNO-peat utilizes knowledge from lab and field-based studies on peat fire ignition and spread to be able to model peat burnt area, burn depth, and carbon emissions, based on data of the moisture content, inorganic content, bulk density, soil temperature, and water table depth of peat. INFERNO-peat improves the representation of burnt area in the high latitudes, with peat fires simulating on average an additional 0.305×106 km 2 of burn area each year, emitting 224.10 Tg of carbon. Compared to Global Fire Emissions Database version 5 (GFED5), INFERNO-peat captures ∼ 20 % more burnt area, whereas INFERNO underestimated burning by 50 %. Additionally, INFERNO-peat substantially improves the representation of interannual variability in burnt area and subsequent carbon emissions across the high latitudes. The coefficient of variation in carbon emissions is increased from 0.071 in INFERNO to 0.127 in INFERNO-peat, an almost 80 % increase. Therefore, explicitly modelling peat fires shows a substantial improvement in the fire modelling capabilities of JULES-INFERNO, highlighting the importance of representing peatland systems in fire models. [ABSTRACT FROM AUTHOR]

In this study, we analyzed the content of chemical elements in rainwater and investigated the influence of forest cover on the composition of precipitation. The results obtained showed that the concentration of some elements in the rainwater collected under the forest canopy was higher than that in the open area. As part of the work, we calculated the enrichment factor and examined the sources of chemical elements in rainwater. We found that all macro-elements had increased values of the enrichment factors compared to the supporting elements of the Earth's crust. Ca had the highest value. The values of the remaining elements (Sr, Pb, Mn, Cr, Ba, V, Fe) indicated their lithogenic and anthropogenic origins. We noted that the enrichment factor under the forest canopy was significantly lower than in the open area, indicating the dilution of these elements during water passage through the canopy. Elements such as Zn, Co, Cu, and Ni also had high enrichment factors, which indicate their anthropogenic origin. In the open area, most elements had an inverse relationship with pH, except for the alkali metals Na, Mg, and Ca, which had a positive relationship with the pH value. The concentration of K was not dependent on pH. In rainwater that had passed through the forest canopy, the concentrations of Na, Mg, and Ca were also not dependent on pH, while the concentration of K had an inverse relationship with pH. As the concentration of heavy metals in rainwater increases, the role of Na, Mg, and Ca in the process of water neutralization decreases. [ABSTRACT FROM AUTHOR]

Greenhouse gas (GHGs) emissions from peatlands contribute significantly to ongoing climate change because of human land use. To develop reliable and comprehensive estimates and predictions of GHG emissions from peatlands, it is necessary to have GHG observations, including carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O), that cover different peatland types globally. We synthesize published peatland studies with field GHG flux measurements to identify gaps in observations and suggest directions for future research. Although GHG flux measurements have been conducted at numerous sites globally, substantial gaps remain in current observations, encompassing various peatland types, regions and GHGs. Generally, there is a pressing need for additional GHG observations in Africa, Latin America and the Caribbean regions. Despite widespread measurements of CO2 and CH4, studies quantifying N2O emissions from peatlands are scarce, particularly in natural ecosystems. To expand the global coverage of peatland data, it is crucial to conduct more eddy covariance observations for long-term monitoring. Automated chambers are preferable for plot-scale observations to produce high temporal resolution data; however, traditional field campaigns with manual chamber measurements remain necessary, particularly in remote areas. To ensure that the data can be further used for modeling purposes, we suggest that chamber campaigns should be conducted at least monthly for a minimum duration of one year with no fewer than three replicates and measure key environmental variables. In addition, further studies are needed in restored peatlands, focusing on identifying the most effective restoration approaches for different ecosystem types, conditions, climates, and land use histories. [ABSTRACT FROM AUTHOR]

Peatlands cover only 3–4% of the Earth's surface, but they store nearly 30% of global soil carbon stock. This significant carbon store is under threat as peatlands continue to be degraded at alarming rates around the world. It has prompted countries worldwide to establish regulations to conserve and reduce emissions from this carbon rich ecosystem. For example, the EU has implemented new rules that mandate sustainable management of peatlands, critical to reaching the goal of carbon neutrality by 2050. However, a lack of information on the extent and condition of peatlands has hindered the development of national policies and restoration efforts. This paper reviews the current state of knowledge on mapping and monitoring peatlands from field sites to the globe and identifies areas where further research is needed. It presents an overview of the different methodologies used to map peatlands in nine countries, which vary in definition of peat soil and peatland, mapping coverage, and mapping detail. Whereas mapping peatlands across the world with only one approach is hardly possible, the paper highlights the need for more consistent approaches within regions having comparable peatland types and climates to inform their protection and urgent restoration. The review further summarises various approaches used for monitoring peatland conditions and functions. These include monitoring at the plot scale for degree of humification and stoichiometric ratio, and proximal sensing such as gamma radiometrics and electromagnetic induction at the field to landscape scale for mapping peat thickness and identifying hotspots for greenhouse gas (GHG) emissions. Remote sensing techniques with passive and active sensors at regional to national scale can help in monitoring subsidence rate, water table, peat moisture, landslides, and GHG emissions. Although the use of water table depth as a proxy for interannual GHG emissions from peatlands has been well established, there is no single remote sensing method or data product yet that has been verified beyond local or regional scales. Broader land-use change and fire monitoring at a global scale may further assist national GHG inventory reporting. Monitoring of peatland conditions to evaluate the success of individual restoration schemes still requires field work to assess local proxies combined with remote sensing and modeling. Long-term monitoring is necessary to draw valid conclusions on revegetation outcomes and associated GHG emissions in rewetted peatlands, as their dynamics are not fully understood at the site level. Monitoring vegetation development and hydrology of restored peatlands is needed as a proxy to assess the return of water and changes in nutrient cycling and biodiversity. [ABSTRACT FROM AUTHOR]

Millennial-scale climate variations during the last glacial period, such as Dansgaard–Oeschger (DO) cycles and Heinrich events, have been extensively studied using ice core and marine proxy records. However, there is a limited understanding of the magnitude of these temperature fluctuations in continental regions, and questions remain about the seasonal signal of these climate events. This study presents a 60 000-year-long temperature reconstruction based on branched glycerol dialkyl glycerol tetraethers (brGDGTs) extracted from lake sediments from the Eifel Volcanic Field, Germany. brGDGTs are bacterial membrane-spanning lipids that are known to have a strong relationship with temperature, making them suitable for temperature reconstructions. We test several temperature calibration models on modern samples taken from soils and multiple maar lakes. We find a negative bias in brGDGT-based temperature estimates associated with water depth and anoxic conditions that can be corrected for by accounting for a brGDGT isomer that is only produced in anoxic conditions. The corrected temperature reconstruction correlates with proxy and climate model estimates of temperature spanning the same time period, validating the calibration approach we selected. However, millennial-scale variability is significantly dampened in the brGDGT record, and in contrast to other Northern Hemisphere climate records, during several Heinrich stadials, temperatures actually increase. We demonstrate that these apparent discrepancies can be explained by the unique seasonal response of the brGDGT paleothermometer to temperatures of months above freezing (TMAF). Our data support the view that warm-season temperatures in Europe varied minimally during the last glacial period and that abrupt millennial-scale events were defined by colder, longer winters. Our continuous high-resolution temperature reconstruction provides important information about the magnitude of seasonal climate variability during the last glacial period that can be used to test climate models and inform studies of paleoecological change. [ABSTRACT FROM AUTHOR]

The coastal temperate rainforests (CTRs) of Chilean Patagonia are a valuable forest biome on Earth given their prominent role in biogeochemical cycling and the ecological value and dynamics of surface processes. The Patagonian CTRs are amongst the most carbon-rich biomes on Earth. Together with frequent landscape disturbances, these forests potentially allow for episodic and massive release or sequestration of carbon into and from the atmosphere. We argue that, despite their particular biogeographic, geochemical, and ecological roles, the Patagonian CTRs in particular and the global CTRs in general are not adequately represented in the current catalog listing critical zone observatories (CZOs). Here, we present the Pumalín CZO as the first of its kind, located in Pumalín National Park in northern Chilean Patagonia. We consider our CZO a representative end-member of undisturbed ecosystem functioning of the Patagonian CTRs. We have identified four core research themes for the Pumalín CZO around which our activities circle in an integrative, quantitative, and generic approach using a range of emerging techniques. Our methodological blend includes an environmental seismology that also fills a critical spatiotemporal scale in terms of monitoring critical zone and surface processes with a minimum intervention in those pristine forests. We aim to gain quantitative understanding of these topics: (1) carbon sink functioning; (2) biota-driven landscape evolution; (3) water, biogeological, and energy fluxes; and (4) disturbance regime understanding. Our findings highlight the multitude of active functions that trees in particular and forests in general may have on the entire cascade of surface processes and the concomitant carbon cycling. This highlights the importance of an integrated approach, i.e., "one physical system", as proposed by Richter and Billings (2015), and accounts for the recent advances in pushing nature conservation along the Chilean coast. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Grassland management affects soil respiration (Rs, consists of heterotrophic respiration and autotrophic respiration) through soil micro-ecological processes, such as hydrothermal, plant root, organic carbon decomposition and microbial activity. Flooding, an irregular phenomenon in grasslands, may strongly regulate the response of soil respiration and its components to grassland management, but the regulatory mechanism remains unclear. We conducted a 3-year experiment by grassland management (fencing and grazing) and flooding conditions (no flooding (NF), short-term flooding (STF) and long-term flooding (LTF)) to study their effects on Rs and its components in a meadow steppe in the Hui River basin of Hulunbuir. We found differences in the patterns of Rs and its components under grassland management and flooding conditions. In 2021–2023, the temporal trends of Rs, heterotrophic respiration (Rh) and autotrophic respiration (Ra) were generally consistent, with peaks occurring on days 190–220, and the peaks of grazing were higher than that of fencing. In NF, Rs of grazed grassland was significantly higher than that of fenced grassland in 2021–2022 (p < 0.05). In STF and LTF, there was no significant difference in Rs between fenced and grazed grassland (p > 0.05). The dependence of Rs on soil temperature (ST) decreased with increasing flooding duration, and the dependence of Rs on ST of grazed grassland was higher than fenced grassland under NF and STF, but there was no difference between fenced grassland and grazed grassland under LTF. In addition, Rh was more sensitive to ST than Ra. This may be due to the different pathways of ST effects on Rs under grazing in different flooding conditions. Our study indicates that the effect of flooding on Rs is the key to the rational use of grassland under future climate change. To reduce regional carbon emissions, we recommend grazing on flooding grassland and fencing on no-flooding grassland. [ABSTRACT FROM AUTHOR]

Microbial release of CO 2 from soils to the atmosphere reflects how environmental conditions affect the stability of soil organic matter (SOM), especially in massive organic-rich ecosystems like the peatlands and grasslands of the Qinghai–Tibetan Plateau (QTP). Radiocarbon (14 C) is an important tracer of the global carbon cycle and can be used to understand SOM dynamics through the estimation of time lags between carbon fixation and respiration, often assessed with metrics such as age and transit time. In this study, we incubated peatland and grassland soils at four temperature (5, 10, 15 and 20 °C) and two water-filled pore space (WFPS) levels (60 % and 95 %) and measured the 14 C signature of bulk soil and heterotrophic respired CO 2. We compared the relation between the Δ14 C of the bulk soil and the Δ14 CO 2 of respired carbon as a function of temperature and WFPS for the two soils. To better interpret our results, we used a mathematical model to analyse how the calculated number of pools, decomposition rates of carbon (k), transfer (α) and partitioning (γ) coefficients affect the Δ14 C bulk and Δ14 CO 2 relation, with their respective mean age and mean transit time. From our incubations, we found that 14 C values in bulk and CO 2 from peatland were significantly more depleted (old) than from grassland soil. Our results showed that changes in temperature did not affect the Δ14 C values of heterotrophic respired CO 2 in either soil. However, changes in WFPS had a small effect on the 14 CO 2 in grassland soils and a significant influence in peatland soils, where higher WFPS levels led to more depleted Δ14 CO 2. In our models, the correspondence between Δ14 C, age and transit time highly depended on the internal dynamics of the soil (k , α , γ and number of pools) as well as on model structure. We observed large differences between slow and fast cycling systems, where low values of decomposition rates modified the Δ14 C values in a non-linear pattern due to the incorporation of modern carbon (14 C bomb) in the soil. We concluded that the stability of carbon in the peatland and grassland soils of the QTP depends strongly on the direction of change in moisture and how it affects the rates of SOM decomposition, while temperature regulates the number of fluxes. Current land cover modification (desiccation) in Zoigê peatlands and climate change occurring on the QTP might largely increase CO 2 fluxes along with the release of old carbon to the atmosphere potentially shifting carbon sinks into sources. [ABSTRACT FROM AUTHOR]

Compaction is recognized as an effective method for mitigating the risk of fires by enhancing soil moisture levels. This technique involves restricting peat pore spaces through compaction, facilitating improved capillary action for water retention and rehydration. The compaction of tropical peatlands, while beneficial for fire prevention, has the potential to influence biogeochemical processes and subsequent carbon emissions. The magnitude of compaction and groundwater level are strongly coupled in such environments, making it difficult to distinguish the control of physicochemical properties. Therefore, this study seeks to understand how peat compaction affects its properties, carbon emissions, and their relationship, with a focus on geophysical processes. Intact peat samples were collected from a secondary peat swamp forest and an oil palm plantation in Selangor, Peninsular Malaysia. Compaction treatments were applied to achieve three levels of volume reduction. CO2 and CH4 emissions were measured using an automated gas analyzer, and the physicochemical properties of the peat were determined. The results revealed that mechanical compaction significantly altered the physicochemical properties of the secondary forest peat, displaying an opposite pattern to the oil palm plantation, particularly regarding total nitrogen and sulfur. Moreover, the average reduction percentage ratio of CO2 emissions (from 275.4 to 182.0 mg m-2 hr-1; 33.9%) to CH4 uptakes (from -17.8 to -5.2 µg m-2 hr-1; 70.1%) (~1:2) indicated distinct stages of decomposition and translocation of less decomposed peat to deeper layers due to compaction, predominantly in secondary peat swamp forest samples. The oil palm plantation samples were unaffected by compaction in terms of physicochemical properties and carbon emissions, indicating the ineffectiveness of this approach for reducing fire risk in already drained systems. This study underscores the necessity of understanding the effects of compaction in the absence of groundwater to accurately evaluate the widespread application of this technique. [ABSTRACT FROM AUTHOR]

The sediment-water interfaces of cold seeps play important roles in nutrient transportation between seafloor and deep-water column. Microorganisms are the key actors of biogeochemical processes in this interface. However, the knowledge of the microbiome in this interface are limited. Here we studied the microbial diversity and potential metabolic functions by 16S rRNA gene amplicon sequencing at sediment-water interface of two active cold seeps in the northern slope of South China Sea, Lingshui and Site F cold seeps. The microbial diversity and potential functions in the two cold seeps are obviously different. The microbial diversity of Lingshui interface areas, is found to be relatively low. Microbes associated with methane consumption are enriched, possibly due to the large and continuous eruptions of methane fluids. Methane consumption is mainly mediated by aerobic oxidation and denitrifying anaerobic methane oxidation (DAMO). The microbial diversity in Site F is higher than Lingshui. Fluids from seepage of Site F are mitigated by methanotrophic bacteria at the cyclical oxic-hypoxic fluctuating interface where intense redox cycling of carbon, sulfur, and nitrogen compounds occurs. The primary modes of microbial methane consumption are aerobic methane oxidation, along with DAMO, sulfate-dependent anaerobic methane oxidation (SAMO). To sum up, anaerobic oxidation of methane (AOM) may be underestimated in cold seep interface microenvironments. Our findings highlight the significance of AOM and interdependence between microorganisms and their environments in the interface microenvironments, providing insights into the biogeochemical processes that govern these unique ecological systems. [ABSTRACT FROM AUTHOR]

Understanding the critical zone processes related to groundwater flows relies on subsurface structure knowledge and its associated parameters. We propose a methodology to draw the patterns of the subsurface critical zone at the catchment scale from seismic refraction data and show its interest for hydrological modelling. The designed patterns define the structure of a physically based distributed hydrological model applied to a mountainous catchment. With that goal, we acquired 10 seismic profiles covering the different geomorphology zones of the studied catchment. We develop a methodology to analyse the geostatistical characteristics of the seismic data and interpolate them over the whole catchment. The applied geostatistical model considers the scale variability of the subsurface structures observed from the seismic data analysis. We use compressional seismic wave velocity thresholds to identify the depth of the soil and saprolite bottom boundaries. Assuming that such porous compartments host the main part of the active aquifer, their patterns are embedded in a distributed hydrological model. We examine the sensitivity of classical hydrological data (piezometric heads) and geophysical data (magnetic resonance soundings) to the applied velocity thresholds used to define the soil and saprolite boundaries. Different sets of hydrogeological parameters are used in order to distinguish general trends or specificities related to the choice of parameter values. The application of the methodology to an actual catchment illustrates the interest of seismic refraction in constraining the structure of the critical zone subsurface compartments. The sensitivity tests highlight the complementarity of the analysed hydrogeophysical data sets. [ABSTRACT FROM AUTHOR]

Dissolved organic carbon (DOC) dynamics are evolving in the rapidly changing Arctic and a comprehensive understanding of the controlling processes is urgently required. For example, the transport processes governing DOC dynamics are prone to climate-driven alteration given their strong seasonal nature. Hence, high-resolution and long-term studies are required to assess potential seasonal and interannual changes in DOC transport processes. In this study, we monitored DOC at a 30 min resolution from September 2018 to December 2022 in a headwater peatland-influenced stream in northern Finland (Pallas catchment, 68° N). Temporal variability in transport processes was assessed using multiple methods: concentration–discharge (C – Q) slope for seasonal analysis, a modified hysteresis index for event analysis, yield analysis, and random forest regression models to determine the hydroclimatic controls on transport. The findings revealed the following distinct patterns: (a) the slope of the C – Q relationship displayed a strong seasonal trend, indicating increasing transport limitation each month after snowmelt began; (b) the hysteresis index decreased post-snowmelt, signifying the influence of distal sources and DOC mobilization through slower pathways; and (c) interannual variations in these metrics were generally low, often smaller than month-to-month fluctuations. These results highlight the importance of long-term and detailed monitoring to enable separation of inter- and intra-annual variability to better understand the complexities of DOC transport. This study contributes to a broader comprehension of DOC transport dynamics in the Arctic, specifically quantifying seasonal variability and associated mechanistic drivers, which is vital for predicting how the carbon cycle is likely to change in Arctic ecosystems. [ABSTRACT FROM AUTHOR]

Studying competitive effects of microbial and light-induced degradation of dissolved organic matter (DOM) is crucially important for understanding the factors controlling aquatic carbon (C) transformation in boreal waters. However, studies addressing both DOM and trace element (TE) behavior are limited, which does not allow assessment of coupled C – TE (including macro- and micronutrients and toxicants) biogeochemical cycles in these environmentally important settings. Here we conducted a seasonally-resolved assessment on the degree of DOM and related major and TE transformation under biotic activity and sunlight using conventional incubations of humic surface waters from the European subarctic. We studied bio- and photodegradation over 2–3 weeks in an ombrotrophic peatbog continuum (subsurface water from piezometer – small peatland pool – outlet stream) during July, and in three horizons (0.5, 5 and 10 m) of deep (30 m), a stratified forest lake from the same region during June, August and September. Along the bog water continuum in July, biodegradation rate was the highest in subsurface waters collected via piezometer and the lowest in the acidic peatland pool (0.17 to 0.03 mg C L-1 d-1, respectively). Photodegradation was similar for piezometrically collected subsurface waters and the stream (about 0.3 mg C L-1 d-1), but was not detectable in the peatland pool. The waters of forest lake exhibited a strong seasonal effect of biodegradation, which was the highest in October and the lowest in June (0.04 and 0.02 mg C L-1 d-1, respectively). The photodegradation of DOM from the forest lake was observed only in June and August (0.19 and 0.07 mg C L-1 d-1, respectively). Biodegradation was capable of removing between 1 and 7 % of initial DOC, being the highest in the forest lake in October and in peatland pool in summer. The photolysis was capable of degrading a much higher proportion of the initial DOC (10–25 %), especially in the forest lake during June and the bog stream during July. The change of optical parameters confirmed the highest photodegradation occurs in June (Arctic summer) and demonstrates a decrease of chromophoric (aromatic) compounds during incubation, whereas biodegradation acted preferentially on aliphatic, low molecular weight compounds. Only a few trace metals were sizably affected by both photo- and biodegradation of DOM (Fe, Al, Ti, Nb and light REE), whereas V, Mn, Co, Cu and Ba were affected solely by biodegradation. Typical values of TE removal over a 2-week period of incubation ranged from 1 to 10 %. These effects were mostly pronounced in the less acidic forest lake compared to the bog waters. A likely mechanism of TE removal was their coprecipitation with coagulating Fe(III) hydroxides. When averaged across sites and seasons, DOM biodegradation and photodegradation processes could remove 5.3 and 10.8 mg C L-1 y-1, respectively. Compared to typical CO2 emissions from inland waters of the region, biodegradation of DOM can provide the totality of C-CO2 evasion from lake water surfaces whereas bio- and photodegradation are not sufficient to explain the observed fluxes in bog water continuum. Overall, these results demonstrated strong spatial and seasonal variability in DOM and TE complexes bio- and photodegradation, which was poorly accessed until now, and call for the need of a systematic assessment of both processes across seasons with high spatial resolution. [ABSTRACT FROM AUTHOR]

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The Canadian Fire Weather Index (FWI) system, even though originally developed and calibrated for an upland Jack pine forest, is used globally to estimate fire danger for any fire environment. However, for some environments, such as peatlands, the applicability of the FWI in its current form, is often questioned. In this study, we replaced the original moisture codes of the FWI with hydrological estimates resulting from the assimilation of satellite-based L-band passive microwave observations into a peatland-specific land surface model. In a conservative approach that maintains the integrity of the original FWI structure, the distributions of the hydrological estimates were first matched to those of the corresponding original moisture codes before replacement. The resulting adapted FWI, hereafter called FWI peat , was evaluated using satellite-based information on fire presence over boreal peatlands from 2010 through 2018. Adapting the FWI with model- and satellite-based hydrological information was found to be beneficial in estimating fire danger, especially when replacing the deeper moisture codes of the FWI. For late-season fires, further adaptations of the fine fuel moisture code show even more improvement due to the fact that late-season fires are more hydrologically driven. The proposed FWI peat should enable improved monitoring of fire risk in boreal peatlands. [ABSTRACT FROM AUTHOR]

Black-carbon-containing particles strongly absorb light, causing substantial radiative heating of the atmosphere. The climate-relevant properties of black carbon (BC) are poorly constrained in high-altitude mountain regions, where many complex interactions between BC, radiation, clouds and snow have important climate implications. This study presents 2-year measurements of BC microphysical and optical properties at the Pic du Midi (PDM) research station, a high-altitude observatory located at 2877 m above sea level in the French Pyrenees. Among the long-term monitoring sites in the world, PDM is subject to limited influence from the planetary boundary layer (PBL), making it a suitable site for characterizing the BC in the free troposphere (FT). The classification of the dominant aerosol type using aerosol spectral optical properties indicates that BC is the predominant aerosol absorption component at PDM and controls the variation in single-scattering albedo (SSA) throughout the 2 years. Single-particle soot photometer (SP2) measurements of refractory BC (rBC) show a mean mass concentration (MrBC) of 35 ngm-3 and a relatively constant rBC core mass-equivalent diameter of about 180 nm, which are typical values for remote mountain sites. Combining the MrBC with in situ absorption measurements, a rBC mass absorption cross-section (MAC rBC) of 9.2 ± 3.7 m2g-1 at λ=880 nm has been obtained, which corresponds to an absorption enhancement (Eabs) of ∼2.2 compared to that of bare rBC particles with equal rBC core size distribution. A significant reduction in the ΔMrBC/ΔCO ratio when precipitation occurred along the air mass transport suggests wet removal of rBC. However we found that the wet removal process did not affect the rBC size, resulting in unchanged Eabs. We observed a large seasonal contrast in rBC properties with higher MrBC and Eabs in summer than in winter. In winter a high diurnal variability in MrBC (Eabs) with higher (lower) values in the middle of the day was linked to the injection of rBC originating from the PBL. On the contrary, in summer, MrBC showed no diurnal variation despite more frequent PBL conditions, implying that MrBC fluctuations are rather dominated by regional and long-range transport in the FT. Combining the ΔMrBC/ΔCO ratio with air mass transport analysis, we observed additional sources from biomass burning in summer leading to an increase in MrBC and Eabs. The diurnal pattern of Eabs in summer was opposite to that observed in winter with maximum values of ∼2.9 observed at midday. We suggest that this daily variation may result from a photochemical process driving the rBC mixing state rather than a change in BC emission sources. Such direct 2-year observations of BC properties provide quantitative constraints for both regional and global climate models and have the potential to close the gap between model-predicted and observed effects of BC on the regional radiation budget and climate. The results demonstrate the complex influence of BC emission sources, transport pathways, atmospheric dynamics and chemical reactivity in driving the light absorption of BC. [ABSTRACT FROM AUTHOR]

Understanding the patterns of greenhouse gas emissions and the changes in pollution load in terrestrial freshwater systems is crucial for accurately assessing the global carbon cycle and overall greenhouse gas emissions. However, current research often focuses on wetlands and rivers, with few studies on agricultural drainage ditches, which are an important part of the agricultural ecosystem. Investigating the greenhouse gas emission patterns and pollution load changes in agricultural drainage ditches can help accurately assess the greenhouse effect of agricultural systems and improve fertilization measures in farmlands. This study explored the effects of nitrogen input and aeration on the pollution load and greenhouse gas emission processes in paddy field drainage ditches. The results showed that aeration significantly reduced the concentration of ammonium nitrogen (NH4+) in the water, decreased the emissions of nitrous oxide (N2O) and methane (CH4), and slightly increased the emission of carbon dioxide (CO2), resulting in an overall reduction of the global warming potential (GWP) by 34.02%. Nitrogen input significantly increased the concentration of ammonium nitrogen in the water, slightly reduced the emissions of N2O and CH4, and increased the CO2 emissions by 46.60%, thereby increasing the GWP by 15.24%. The drainage ditches reduced the pollution load in both the water and sediment, with the overall GWP downstream being 9.34% lower than upstream. [ABSTRACT FROM AUTHOR]

Wetland methane responses to temperature and precipitation were studied in a boreal wetland-rich region in Northern Europe using ecosystem process models. Six ecosystem models (JSBACH-HIMMELI, LPX-Bern, LPJ-GUESS, JULES, CLM4.5 and CLM5) were compared to multi-model mean of ecosystem models and atmospheric inversions from the Global Carbon Project and up-scaled eddy covariance flux results for their temperature and precipitation responses and seasonal cycles of the regional fluxes. Two models with contrasting response patterns, LPX-Bern and JSBACH-HIMMELI, were used as priors in atmospheric inversions with Carbon Tracker Europe – CH4 in order to find out how the inversion attempts to change the prior fluxes in the posterior and how this alters the interpretation of the flux responses to temperature and precipitation. The inversion attempted to move emissions of both models in posterior towards co-limitation by temperature and precipitation. In general high temperature and/or high precipitation periods often resulted in high posterior emissions. This was not the case for the warm and dry period of summer 2018. The process models showed strong temperature as well as strong precipitation responses for the region (51–91 % of the variance explained by both), and the month of maximum emissions varied from May to September. However, multi-model means, inversions and up-scaled eddy covariance flux observations agreed on the month of maximum emissions, and had rather balanced temperature and precipitation responses. The set-up of different emission components (peatland emissions, mineral land fluxes) had a significant role in building up the response patterns. Considering the significant differences among the models, it is essential to pay more attention to the magnitude, composition, annual cycle and climate driver responses of wetland emissions in different regions. [ABSTRACT FROM AUTHOR]

This paper describes the rationale and the protocol of the first component of the third simulation round of the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP3a, http://www.isimip.org , last access: 2 November 2023) and the associated set of climate-related and direct human forcing data (CRF and DHF, respectively). The observation-based climate-related forcings for the first time include high-resolution observational climate forcings derived by orographic downscaling, monthly to hourly coastal water levels, and wind fields associated with historical tropical cyclones. The DHFs include land use patterns, population densities, information about water and agricultural management, and fishing intensities. The ISIMIP3a impact model simulations driven by these observation-based climate-related and direct human forcings are designed to test to what degree the impact models can explain observed changes in natural and human systems. In a second set of ISIMIP3a experiments the participating impact models are forced by the same DHFs but a counterfactual set of atmospheric forcings and coastal water levels where observed trends have been removed. These experiments are designed to allow for the attribution of observed changes in natural, human, and managed systems to climate change, rising CH 4 and CO 2 concentrations, and sea level rise according to the definition of the Working Group II contribution to the IPCC AR6. [ABSTRACT FROM AUTHOR]

Forests play a crucial role in global carbon cycling by absorbing and storing significant amounts of atmospheric carbon dioxide. Although boreal forests contribute to approximately 45% of the total forest carbon sink, tree growth and soil carbon sequestration are constrained by nutrient availability. Here, we examine if long-term nutrient input enhances tree productivity and whether this leads to carbon storage or whether stimulated microbial decomposition of organic matter limits soil carbon accumulation. Over six decades, nitrogen, phosphorus, and calcium were supplied to a Pinus sylvestris-dominated boreal forest. We found that nitrogen fertilization alone or together with calcium and/or phosphorus increased tree biomass production by 50% and soil carbon sequestration by 65% compared to unfertilized plots. However, the nonlinear relationship observed between tree productivity and soil carbon stock across treatments suggests microbial regulation. When phosphorus was co-applied with nitrogen, it acidified the soil, increased fungal biomass, altered microbial community composition, and enhanced biopolymer degradation capabilities. While no evidence of competition between ectomycorrhizal and saprotrophic fungi has been observed, key functional groups with the potential to reduce carbon stocks were identified. In contrast, when nitrogen was added without phosphorus, it increased soil carbon sequestration because microbial activity was likely limited by phosphorus availability. In conclusion, the addition of nitrogen to boreal forests may contribute to global warming mitigation, but this effect is context dependent., (© 2024 The Author(s). Global Change Biology published by John Wiley & Sons Ltd.)

Drained wetlands are thought to be carbon (C) source hotspots, and rewetting is advocated to restore C storage in drained wetlands for climate change mitigation. However, current assessments of wetland C balance mainly focus on vertical fluxes between the land and atmosphere, frequently neglecting lateral carbon fluxes and land-use effects. Here, we conduct a global synthesis of 893 annual net ecosystem C balance (NECB) measures that include net ecosystem exchange of CO 2 , along with C input via manure fertilization, and C removal through biomass harvest or hydrological exports of dissolved organic and inorganic carbon, across wetlands of different status and land uses. We find that elevating water table substantially reduces net ecosystem C losses, with the annual NECB decreasing from 2579 (95% interval: 1976 to 3214) kg C ha -1  year -1 in drained wetlands to -422 (-658 to -176) kg C ha -1  year -1 in natural wetlands, and to -934 (-1532 to -399) kg C ha -1  year -1 in rewetted wetlands globally. Climate, land-use history, and time since water table changes introduce variabilities, with drainage for (sub)tropical agriculture or forestry uses showing high annual C losses, while the net C losses from drained wetlands can continue to affect soil C pools for several decades. Rewetting all types of drained wetlands is needed, particularly for those formerly agriculture-used (sub)tropical wetlands where net ecosystem C losses can be largely reduced. Our findings suggest that elevating water table is an important initiative to reduce C losses in degraded wetlands, which could contribute to policy decisions for managing wetlands to enhance their C sequestration., (© 2024 John Wiley & Sons Ltd.)

Our knowledge on permafrost carbon (C) cycle is crucial for understanding its feedback to climate warming and developing nature-based solutions for mitigating climate change. To understand the characteristics of permafrost C cycle on the Tibetan Plateau, the largest alpine permafrost region around the world, we summarized recent advances including the stocks and fluxes of permafrost C and their responses to thawing, and depicted permafrost C dynamics within this century. We find that this alpine permafrost region stores approximately 14.1 Pg (1 Pg=10 15 g) of soil organic C (SOC) in the top 3 m. Both substantial gaseous emissions and lateral C transport occur across this permafrost region. Moreover, the mobilization of frozen C is expedited by permafrost thaw, especially by the formation of thermokarst landscapes, which could release significant amounts of C into the atmosphere and surrounding water bodies. This alpine permafrost region nevertheless remains an important C sink, and its capacity to sequester C will continue to increase by 2100. For future perspectives, we would suggest developing long-term in situ observation networks of C stocks and fluxes with improved temporal and spatial coverage, and exploring the mechanisms underlying the response of ecosystem C cycle to permafrost thaw. In addition, it is essential to improve the projection of permafrost C dynamics through in-depth model-data fusion on the Tibetan Plateau., (© 2024. Science China Press.)

17β-Estradiol (E2) is a novel micro-pollutant that is widely distributed in aquatic sediments and has a universal toxicological effect on aquatic organisms. However, its ecological impact on aquatic microorganisms is not yet clear. In this study, we designed a simulation system for oligotrophic water deposition in the laboratory, analyzed the impact of different concentrations of E2 pollution on the carbon metabolism activity (carbon gas emission rate) of water microorganisms. Based on high-throughput sequencing results, we revealed the impact of E2 pollution on the community structure succession and metabolic function of bacteria, archaea, and methanogens in the simulated system, explored the impact mechanism of E2 pollution on microbial carbon metabolism in water bodies. Our results suggested that E2 significantly impacts the bacterial and archaeal community rather than the methanogen community, thereby indirectly inhibiting methane production. The achievements will bridge the theoretical gap between estrogen metabolism and carbon metabolism in sedimentary environments and contribute to enriching the ecological toxicology theory of steroid estrogen., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)