Greenhouse Gas Fluxes Research Articles

A First Assessment of Greenhouse Gas Emissions From Agricultural Peatlands in Canada: Evaluation of Climate Change Mitigation Potential

ABSTRACTCanada has a quarter of the world's peatlands accounting for an estimated 150 Gt of stored carbon. While over 98% of Canadian peatlands are intact, agriculture has been estimated as accounting for the greatest peatland disturbance by area. Greenhouse gas (GHG) emissions from peatland agriculture can contribute a large proportion of national anthropogenic emissions for some countries. In Canada, estimates of GHG emissions from cultivated peat soils are incomplete. Improved accounting of these GHG emissions is required to inform decisions about where to deploy ecological restoration projects and where to allow future agricultural expansion as climate warms. Compiled studies that measured GHG fluxes from agricultural peat fields in Canada resulted in mean emissions factors of 5.1 t CO2e ha−1 year−1, −0.12 kg CH4 ha−1 year−1, and 14.3 kg N2O‐N ha−1 year−1 for carbon dioxide, methane, and nitrous oxide, respectively. Combining these values with a compilation of estimates of agricultural peatland disturbance area in Canada, GHG emissions estimates in Canada arising from peatland converted to agriculture remain highly uncertain, ranging from 1.4 to 35 Mt CO2e year−1, with a median value near 18 Mt CO2e year−1. The largest contributor to this wide range of estimates is uncertainty peatland area affected, indicating an urgent need to improving mapping of organic soils under agriculture in Canada. To help guide decision‐making in Canada, we recommend a network of research stations across a range of agricultural management intensities and climate regions for monitoring hydrological conditions and GHG exchange on organic soils affected by agriculture.

The Hydration-Dependent Dynamics of Greenhouse Gas Fluxes of Epiphytic Lichens in the Permafrost-Affected Region

Recent studies actively debate oxic methane (CH4) production processes in water and terrestrial ecosystems. This previously unknown source of CH4 on a regional and global scale has the potential to alter our understanding of climate-driving processes in vulnerable ecosystems, particularly high-latitude ecosystems. Thus, the main objective of this study is to use the incubation approach to explore possible greenhouse gas (GHG) fluxes by the most widely distributed species of epiphytic lichens (ELs; Evernia mesomorpha Nyl. and Bryoria simplicior (Vain.) Brodo et D. Hawksw.) in the permafrost zone of Central Siberia. We observed CH4 production by hydrated (50%–400% of thallus water content) ELs during 2 h incubation under illumination. Moreover, in agreement with other studies, we found evidence that oxic CH4 production by Els is linked to the CO2 photoassimilation process, and the EL thallus water content regulates that relationship. Although the GHG fluxes presented here were obtained under a controlled environment and are probably not representative of actual emissions in the field, more research is needed to fully comprehend ELs’ function in the C cycle. This particular research provides a solid foundation for future studies into the role of ELs in the C cycle of permafrost forest ecosystems under ongoing climate change (as non-methanogenesis processes in oxic environments).

Optimizing residue return with soil moisture and nutrient stoichiometry reduced greenhouse gas fluxes in Alfisols

Optimum soil moisture and high crop residue return (RR) can increase the active pool of soil organic carbon and nitrogen, thus modulating the magnitude of greenhouse gas (GHG) fluxes. To determine the effect of soil moisture on the threshold level of RR for the wheat production system, we analyzed the relationship between GHG fluxes and RR at four levels, namely 0, 5, 10, and 15 Mg ha−1 (R0, R5, R10, and R15) under two soil moisture content (80% FC and 100% FC) and three levels of nutrient management (NS0: no nutrient; NS1, NS2= 3x NS1). Nutrient input (N and P) in NS1 balanced the residue C/nutrient stoichiometry to achieve 30% stabilization of the residue C input in RR (R5). All RR treatments (cf. R0) were found to significantly reduce N2O emission in moderate soil moisture content (80% FC) by 22–56% across nutrient management due to enhanced soil C mineralization, microbial biomass carbon, and N immobilization. However, averaged across nutrient management, a linear increase in N2O emission was observed with increasing RR under 100% FC soil moisture. A significant decrease in CH4 emission by ca. 46% in most RR treatments was observed in 100% FC compared with the R0. The N2O emission was negatively correlated (p = <0.001) with nutrient stoichiometry. Partial least square (PLS) regression indicated that GHG emissions were more responsive (values > 0.8) to management variables (RR rate, nitrogen (N) input rate, soil moisture, and nutrient stoichiometry of C: N) and post-incubation soil properties (SMBC and NO3-N) in Alfisols. This study demonstrated that the mechanisms responsible for RR effects on soil N2O, CH4 fluxes, and carbon mineralization depend on soil moisture and nutrient management, shifting the nutrient stoichiometry of residue C: N: P.

Extreme rainfall events eliminate the response of greenhouse gas fluxes to hydrological alterations and fertilization in a riparian ecosystem

Riparian ecosystems are essential carbon dioxide (CO2) sources, which considerably promotes climate warming. However, the other greenhouse gas fluxes (GHGs), such as methane (CH4) and nitrous oxide (N2O), in the riparian ecosystems have not been well studied, and it remains unclear whether and how these GHG fluxes respond to extreme weather, fertilization and hydrological alterations associated with reservoir management. Here, we assessed the impacts of hydrological alterations (i.e., flooding frequency) and fertilization (nitrogen and/or phosphorus) induced by human activities (hydroengineering construction and agricultural activities) on GHG fluxes, and further investigated the underlying mechanisms in two contrasting years (normal vs. extreme rainfall years) in a reservoir riparian zone dominated by grasses. The significant combined effects of extreme rainfall events and human activities (hydrological alterations and fertilization) on the GHGs were observed. Continuous flooding reduced CO2 emissions by 24% but increased CH4 emissions by ∼4 times in a normal rainfall year. In addition, nitrogen fertilization promoted CO2 emissions by 37%. However, these phenomena were not observed in the year with extreme rainfall events, which made the flooding levels homogeneous across the treatments. Furthermore, we found that CO2 fluxes were driven by the soil moisture, nutrient content, aboveground biomass, and root carbon content, while CH4 and N2O fluxes were merely driven by the soil properties (pH, moisture, and nutrient content). This study provides valuable insights into the crucial role of extreme rainfall events, hydrological alteration, and fertilization in regulating GHG fluxes in riparian ecosystems, as well as supports the integration of these changes in GHG emission models.

Fluxfinder: An R Package for Reproducible Calculation and Initial Processing of Greenhouse Gas Fluxes From Static Chamber Measurements

AbstractFluxes of greenhouse gases are a critical component of the earth's natural climate, but anthropogenic emissions have created an imbalance and resulted in global climate change. Quantifying the emission of these gases is vital to our understanding of their sources and sinks, both natural and anthropogenic. The static chamber method, in which a system of interest is enclosed, and gas concentrations are measured over time, is widely used to estimate fluxes of greenhouse gases. With the development of instruments such as infrared gas analyzers (IRGAs) supporting high‐frequency concentration data, there is a growing need for open‐source workflows to calculate fluxes. Here we present fluxfinder, an R package designed to support reproducible calculations and processing of greenhouse gas fluxes measured with the static chamber method. The package includes raw data file parsing from widely used IRGAs, metadata matching, unit conversion, flux estimations, and initial quality assurance/quality control (QA/QC). Diagnostic graphical plots provide a transparent way to differentiate between measurement issues and nonlinear behavior. The package is also designed to be easily integrated with the gasfluxes package for further fitting of nonlinear concentration‐time models, allowing alternative or additional flux QA/QC. The fluxfinder package offers a flexible workflow that is easily adaptable to promote open and reproducible greenhouse gas flux estimations.

Reduction of forest soil biota impacts tree performance but not greenhouse gas fluxes

Reduction of forest soil biota impacts tree performance but not greenhouse gas fluxes

Sulfate availability affect sulfate reduction pathways and methane consumption in freshwater wetland sediments

Methane (CH4) emissions from wetlands significantly contribute to global greenhouse gas fluxes, yet the mechanisms regulating CH4 production and oxidation in freshwater wetlands remain underexplored, particularly in the role of sulfate in the anaerobic oxidation of CH4. This study investigated the production, consumption, and release of CH4 in the sediments of the Qilihai wetland, focusing on the roles of hydrogenotrophic methanogenesis and sulfate dynamics across different seasons. CH4 concentrations ranged from 2.42 to 2290.52 μmol L⁻1, and δ13C–CH4 values became progressively more negative with depth, ranging from −87.37‰ to −57.18‰. Results indicate that hydrogenotrophic methanogenesis is the dominant pathway for CH4 production, particularly in sulfate-depleted environments, with CH4 concentrations in the sulfate-methane transition zone (SMTZ) strongly correlated with sulfate availability. Sulfate consumption through Sulfate Anaerobic Oxidation of Methane (SAOM) and Organoclastic Sulfate Reduction (OSR) demonstrated significant seasonal variation, with OSR accounting for up to 73% of sulfate consumption in the SMTZ. The SMTZ exhibited variations ranging from 2 to 40 cm in October, narrowing to 2–4 cm in July. These findings emphasize the complex interactions between sulfate availability, methanogenic pathways, and CH4 emissions in freshwater wetlands, highlighting the need for further research on sulfate dynamics and their implications for greenhouse gas emissions in the context of global climate change.

The aeration and dredging stimulate the reduction of pollution and carbon emissions in a sediment microcosm study

Sediment dredging and aeration are used as important technical measures to remediate internal loading of sediment in polluted rivers. However, previous studies have overlooked the impact of dredging and aeration on Greenhouse gases (GHGs) emission. We established three aeration rate(six different aeration intervals), one dredging treatment to investigate the effect of aeration and dredging on pollutant removals and CO2, CH4 and N2O emissions. The results indicated the pollutants and GHGs at 2.4, 3.4, 4.4 L min−1 aeration rates reached collaborative emission reduction after more than 3 h or within 1.5 h. Meanwhile, the GHGs fluxes after aeration decreased with the increasing aeration rate, with the mean CO2, CH4 and N2O fluxes of 69.74, 0.16, 7.53 mg m−2 h−1 and 33.64, 0.09, 4.17 mg m−2 h−1 before and after aeration, respectively. With respect to dredging, the pollutants and N2O reached synergic effects between reduction of pollution and carbon emissions after 1 h dredging. Specifically, the CO2 and CH4 emissions after dredging was lower than those of before dredging, but the N2O emissions was higher than those of before dredging. In addition, our analysis revealed that the dissolved oxygen (DO), oxidation-reduction potential (ORP), available potassium (AK) and ammoniacal nitrogen (NH4+-N) in the sediment influenced GHGs fluxes at the water-air interface in the aeration. Our study indicated moderate aeration and dredging can achieve the synergistic effect in reducing pollution and carbon emissions.

Greenhouse gas emissions from inland water bodies and their rejuvenation: a review

ABSTRACT Inland water bodies are observed as major sources of the emissions of greenhouse gases (GHGs) including carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). This study shows that these entities (e.g. wetlands, constructed wetlands, reservoirs, lakes, ponds, and rivers) have a major contribution in GHG flux. However, understanding of the carbon dynamics of these water bodies is not well described. It was noticed that the emissions of GHGs from inland water bodies is a result of heavy supply of organic matters into them. Approximately 2.2–3.7% of the Earth's non-glaciated land area and inland waters are having almost similar amounts of carbon emission as also observed in case of both net terrestrial productivity and net oceanic uptake. Wetlands and lakes are among the most studied water bodies. However, efforts should be made to understand the emission dynamics from ponds and rivers as recent studies say these are also among the potent sources of GHG emissions in the atmosphere. This review paper aims to highlight and give an elaborate insight into the contribution of inland waters to the global carbon cycle along possible remediative measures.

Greenhouse gas concentrations and diffusive fluxes in the middle reach of the Lancang River before and after damming

With increasing concerns of greenhouse gas (GHG) emissions from reservoirs, the debate surrounding whether hydropower qualifies as green energy has become increasingly contentious. However, quantifying the impact of dam construction on river GHG emissions still poses challenging due to the absence of direct observational data on river GHG emissions pre- and post-damming. In the present study, the differences in GHG diffusive fluxes from pre- and post-dammed river channels in the middle reaches of the Lancang River were quantified through three field campaigns in 2016, 2018, and 2023. The results indicate that reservoir construction increases the diffusive fluxes of GHG from the natural river, the total GHG emissions (expressed as carbon dioxide equivalent: CO2eq) from post-dammed river ranged from 234.42 to 527.55 mg CO2eq m−2 d−1 and were 1.4–5.2 times higher than that from pre-dammed river. However, the GHG diffusive fluxes from the reservoirs in the Lancang River remain below the average of global reservoirs. Moreover, river damming enhances the methane (CH4) emissions, the average value of CH4/CO2 ratio (in mg m−2 d−1) was 0.003 post-dam and was 13 times higher than that of pre-dam. Our results revealed that alterations in sediment distribution following reservoir construction emerge as a pivotal factor contributing to the variations in spatial distributions of GHG diffusive fluxes in the studied river channel. Overall, the findings of the study provide a primary and direct evidence of river damming impact on GHG emissions and underscore the necessity of long-term continuous in-situ measurements of GHG fluxes in the rivers undergoing hydropower development.

The plant ecology of nature‐based solutions for people, biodiversity and climate

Abstract Integrated solutions to the climate and biodiversity crises—together with other global sustainability challenges—include the identification, design and implementation of nature‐based solutions (NbS). Living organisms mediate biogeochemical cycles and greenhouse gas fluxes from land and sea, and provide NbS to both climate change mitigation and adaptation. Plants, as the primary producers in ecosystems, lie at the heart of NbS. Plant ecology provides the foundation for developing and evaluating NbS based on an understanding of the ecological processes that underlie ecosystem service flow to people. In this Special Feature, we provide a collection of mini‐reviews that presents concise and focused analysis of the plant ecology of NbS. The mini‐reviews highlight key insights, challenges and opportunities for future research. The development of NbS that target specific ecosystem functions (e.g. carbon storage), or aim at increasing ecosystem resilience against perturbations (e.g. those associated with climate change), requires unification of ecological theory from areas such as biodiversity‐ecosystem function, plant–animal interactions, resilience and functional traits of organisms. Synthesis. Plant ecology and nature‐based solutions (NbS) research are complementary. Plant ecology can inform the design and management of effective NbS, and provide insights for the creation of novel ecosystems that provide NbS; while learning from the implementation of NbS can progress theory. To deploy NbS at the speed and scale needed to mitigate and adapt to climate change, we must rapidly integrate ecological concepts into the design of NbS. At the same time, the design and deployment of NbS in different ecological contexts provides an unprecedented opportunity to learn how performances of individual NbS sites can be explained in an integrated way, leading to the development of general concepts. Ultimately, a mechanistic understanding of how plants and their functional traits contribute to ecosystem function and service provision is critical for the design, verification of benefits from and avoidance of adverse effects of NbS.

Stronger increase of methane emissions from coastal wetlands by non‐native Spartina alterniflora than non‐native Phragmites australis

Societal Impact StatementThe invasive species S. alterniflora and P. australis are fast growing coastal wetland plants sequestering large amounts of carbon in the soil and protect coastlines against erosion and storm surges. In this global analysis, we found that Spartina and Phragmites increase methane but not nitrous oxide emissions, with Phragmites having a lesser effect. The impact of the invasive species on emissions differed greatly among different types of native plant groups, providing valuable information to managers and policymakers during coastal wetland planning and restoration efforts. Further, our estimated net emissions per wetland plant group facilitate regional and national blue carbon estimates.Summary Globally, Spartina alterniflora and Phragmites australis are among the most pervasive invasive plants in coastal wetland ecosystems. Both species sequester large amounts of atmospheric carbon dioxide (CO2) and biogenic carbon in soils but also support production and emission of methane (CH4). In this study, we investigated the magnitude of their net greenhouse gas (GHG) release from invaded and non‐invaded habitats. We conducted a meta‐analysis of GHG fluxes associated with these two species and related soil carbon content and plant biomass in invaded coastal wetlands. Our results show that both invasive species increase CH4 fluxes compared to uninvaded coastal wetlands, but they do not significantly affect CO2 and N2O fluxes. The magnitude of emissions from Spartina and Phragmites differs among native habitats. GHG fluxes, soil carbon and plant biomass of Spartina‐invaded habitats were highest compared to uninvaded mudflats and succulent forb‐dominated wetlands, while being lower compared to uninvaded mangroves (except for CH4). This meta‐analysis highlights the important role of individual plant traits as drivers of change by invasive species on plant‐mediated carbon cycles.

The LTAR Grazing Land Common Experiment at Platte River High Plains Aquifer.

The Long-Term Agroecosystem Research (LTAR) network of the United States Department of Agriculture (USDA) consists presently of 18 sites within the contiguous United States that are managed by the Agricultural Research Service (ARS) and its partners. The LTAR network focuses on developing national strategies for more efficient, resilient, and profitable agricultural production systems, improved environmental quality, and enhanced rural prosperity. The Platte River High Plains Aquifer (PRHPA) LTAR site is managed jointly by the University of Nebraska-Lincoln (UNL) and USDA-ARS and is one of the LTAR sites that conduct research on both integrated cropping and grazing systems. The PRHPA region encompasses multiple land resource areas and diverse agricultural production systems. The PRHPA sites, predominantly located in eastern Nebraska, are designated as an integrated system focused specifically on the region's dominant production practices of row crop (corn and soybean), managed pastures, and beef cattle production. Here, we focus on C3 cool-season smooth bromegrass (Bromus inermis Leyss.) pasture grazing systems under prevailing and alternative management practices for the region. The sites evaluate continuous and rotational grazing with and without pasture fertilization (prevailing practices). In an additional treatment, cattle are supplemented with dry distillers grains plus solubles, while manure supplies fertilization (alternative practice). Main measurements at the site evaluate plant and animal productivity, forage quality, greenhouse gas fluxes, and soil physical, chemical, and biological properties. This paper describes the regional characteristics of the PRHPA site, ongoing LTAR research related to pasture and livestock production, stakeholder engagement, and future research plans.

Greenhouse Gas Emissions Characteristics and Driving Factors Analysis in the Eutrophic Saline Lake Daihai Lake

To investigate the greenhouse gas emission characteristics and driving factors of eutrophic saline lakes in northern China, considering Daihai Lake in Inner Mongolia as an example, 10 monitoring sites were selected based on hydrological distribution characteristics in April, July, and October 2023. Using headspace gas chromatography and modeling methods, dissolved concentrations and exchange fluxes of carbon dioxide （CO2）, methane （CH4）, and nitrous oxide （N2O） were determined in the nearshore zone, open lake area, and lake center surface water. During the study period, Daihai Lake exhibited significant seasonal variations in greenhouse gas concentration and flux. The average concentrations of CO2, CH4, and N2O in surface water were （26.52 ± 17.58） μmol·L-1, （282.30 ± 172.30） nmol·L-1, and （9.09 ± 1.64） nmol·L-1, respectively. The average fluxes were （5.29 ± 11.98） mmol·（m2·d）-1, （178.24 ± 63.34） μmol·（m2·d）-1, and （-0.74 ± 1.28） μmol·（m2·d）-1, with cumulative emissions of 50 770.77, 543.52, -4.21 kg·km-2 and a global warming potential （expressed in CO2-equivalent） of 50 770.77, 15 218.49, -1 254.48 kg·km-2. Daihai Lake acted as a source of atmospheric CO2 and CH4 but a sink for N2O during the study period. Correlation and stepwise regression analyses revealed that pH and total dissolved solids （TDS） influenced CO2 concentration and flux, while the factors affecting CH4 were water temperature （WT）, water depth （WD）, wind speed （WS）, oxidation-reduction potential （ORP）, and total nitrogen （TN）. For N2O, the influencing factors were WT, WS, and TN. Additionally, Daihai Lake's eutrophication and salinity characteristics influenced the generation and emission of greenhouse gases. This study provides insights into the greenhouse gas dynamics and environmental factors in eutrophic saline lakes like Daihai Lake.

Natural sinks and sources of CO<sub>2</sub> and CH<sub>4</sub> in the atmosphere of Russian regions and their contribution to climate change in the 21st century evaluated with CMIP6 model ensemble

The natural fluxes of CO2 and CH4 into the atmosphere from the territory of Russia in the 21st century have been analyzed using the results of calculations with the ensemble of global climate models of the international project CMIP6. Estimates of natural CO2 fluxes in Russian regions differ greatly for different models. Their values for the beginning of the 21st century range from –1 to 1 GtC/yr. In the 21st century the differences in model estimates of fluxes grow and at the end of the 21st century in the scenario with the largest anthropogenic impacts SSP5-8.5 range from –2.5 to 2.5 GtC/year. Estimates of natural methane emissions to the atmosphere from the territory of Russia also differ greatly for different models. Modern methane emissions are estimated in the range from 10 to 35 MtCH4/yr, with an increase in the 21st century of up to 300%. Ensemble model calculations show general trends for changes in natural greenhouse gas fluxes. Most CMIP6 ensemble models are characterized by a maximum of CO2 uptake by terrestrial ecosystems and its further reduction by the end of the 21st century, while natural methane emissions to the atmosphere for all models and scenarios of anthropogenic impacts grow throughout the 21st century. The cumulative temperature potential of natural CO2 fluxes on the territory of Russia in the 21st century is estimated, depending on the scenario of anthropogenic impacts, from –0.3 to 0.1 K, and the warming-accelerating impact of natural CH4 emissions is estimated in the range of 0.03-0.09 K.

A rough set-based model for predicting soil greenhouse gases response to biochar

Biochar application to soil is a potential climate change mitigation strategy. In addition to long-term sequestration of the carbon content of the biochar itself, its application may reduce the emissions of other greenhouse gases (GHGs) from the soil. However, the reported effects of biochar application on soil GHG fluxes exhibit inconsistent results. Prediction of such effects is an important gap that needs to be addressed in biochar research. In this study, rule-based machine learning models were developed based on rough-set theory. Data from the literature were used to generate the rules for predicting the effects of biochar application on soil GHG (CO2, N2O, and CH4) fluxes. Four rule-based models for CO2 fluxes, two rule-based models for N2O fluxes, and three rule-based models for CH4 fluxes were developed. The validity of these models was assessed based on both statistical measures and mechanistic plausibility. The final rule-based models can guide the prediction of changes in soil GHG fluxes due to biochar application, and thus serve as a decision-support tool to maximize the benefits of biochar application as a negative emission technology (NET). In particular, mechanistically plausible rules were identified that predict triggers for GHG fluxes that can offset carbon sequestration gains. This knowledge allows biochar application to be calibrated to local conditions for maximum efficacy.Graphical

Soil greenhouse gas fluxes partially reduce the net gains in carbon sequestration in mangroves of the Brazilian Amazon

There is interest in assessing the potential climate mitigation benefit of coastal wetlands based on the balance between their greenhouse gas (GHG) emissions and carbon sequestration. Here we investigated soil GHG fluxes (CO2 and CH4) on mangroves of the Brazilian Amazon coast, and across common land use impacts including shrimp farms and a pasture. We found greater methane fluxes near the Amazon River mouth (1439 to 3312 μg C m−2 h−1), which on average are equivalent to 37% of mangrove C sequestration in the region. Soil CO2 fluxes were predominant in mangrove forests to the East of the Amazon Delta. Land use change shifted mangroves from C sinks (mean sequestration of 12.2 ± 1.4 Mg CO2e ha−1 yr-1) to net GHG sources (mean loss of 8.0 ± 3.3 Mg CO2e ha−1 yr−1). Our data suggests that mangrove forests in the Amazon can aid decreasing the net annual emissions in the Brazilian forest sector in 9.7 ± 0.8 Tg CO2e yr−1 through forest conservation and avoided deforestation.

Topography‐driven variability in soil greenhouse gas emissions during potato growth season

AbstractTopographical variations strongly influence the spatial variability of soil physicochemical properties by affecting water retention, nutrient distribution and biochemical activity. These topography‐driven differences in soil dynamics can significantly impact greenhouse gas (GHG) emissions. Understanding the variation in GHG emissions over the growing season across topographic changes can facilitate the development of targeted precision agriculture strategies to mitigate GHG emissions. The objectives of this study were to evaluate the influence of topographical variations on soil properties and to assess the spatiotemporal variations of CO2 and N2O emissions throughout the various crop‐growing stages (CGS) of the potato growing season. Moreover, the impact of topography on potato yield was also examined. The experiment was conducted at Victoria Potato Farm, Prince Edward Island, Canada. A substantial N2O flux (80 g ha−1 day−1) was emitted after fertilizer application over the early CGS, and the upper positions had the highest cumulative N2O emissions (993 g ha−1), which aligned with the higher observed soil moisture in this zone. This finding highlights the critical importance of managing fertilizer application, as well as implementing mitigation strategies based on the spatial variability of soil properties to reduce emissions following fertilization. During the mid and late CGS, the depressional positions showed the highest cumulative N2O emissions (90 and 70 g ha−1, respectively). The highest cumulative CO2 emission was observed from the upper positions during the early CGS (1580 kg ha−1); however, the highest emissions were observed in the depressional areas during the mid and late CGS (1415 and 605 kg ha−1, respectively). Overall, the total N2O emission from the three zones accounting for both the differences in each zone's GHG fluxes and the length of each CGS indicated 43% emission in the upper areas, 32% and 25% for the depressional and mid‐slope positions, respectively. These values were 32%, 36% and 32% for CO2 in the upper, depressional and mid‐slope positions. This emission pattern aligns with the elevated soil‐activated carbon (AC), biological nitrogen availability (BNA) values and soil respiration rates in upper and depressional areas. In this study, significantly higher yields were also observed in depressional areas.

Arctic Tundra Plant Dieback Can Alter Surface N2O Fluxes and Interact With Summer Warming to Increase Soil Nitrogen Retention.

In recent years, the arctic tundra has been subject to more frequent stochastic biotic or extreme weather events (causing plant dieback) and warmer summer air temperatures. However, the combined effects of these perturbations on the tundra ecosystem remain uninvestigated. We experimentally simulated plant dieback by cutting vegetation and increased summer air temperatures (ca. +2°C) by using open-top chambers (OTCs) in an arctic heath tundra, West Greenland. We quantified surface greenhouse gas fluxes, measured soil gross N transformation rates, and investigated all ecosystem compartments (plants, soils, microbial biomass) to utilize or retain nitrogen (N) upon application of stable N-15 isotope tracer. Measurements from three growing seasons showed an immediate increase in surface CH4 and N2O uptake after the plant dieback. With time, surface N2O fluxes alternated between emission and uptake, and rates in both directions were occasionally affected, which was primarily driven by soil temperatures and soil moisture conditions. Four years after plant dieback, deciduous shrubs recovered their biomass but retained significantly lower amounts of 15N, suggesting the reduced capacity of deciduous shrubs to utilize and retain N. Among four plant functional groups, summer warming only increased the biomass of deciduous shrubs and their 15N retention, while following plant dieback deciduous shrubs showed no response to warming. This suggests that deciduous shrubs may not always benefit from climate warming over other functional groups when considering plant dieback events. Soil gross N mineralization (~ -50%) and nitrification rates (~ -70%) significantly decreased under both ambient and warmed conditions, while only under warmed conditions immobilization of NO3 - significantly increased (~ +1900%). This explains that plant dieback enhanced N retention in microbial biomass and thus bulk soils under warmed conditions. This study underscores the need to consider plant dieback events alongside summer warming to better predict future ecosystem-climate feedback.

Groundwater-derived carbon stimulates headwater stream CO2 emission potential on the Qinghai-Tibet Plateau

CO2 emissions from headwater streams are a crucial component of greenhouse gas flux in inland waters. However, the influence of groundwater, a major contributor to streams in the Asian Water Tower (Qinghai-Tibet Plateau, QTP), on CO2 levels remains unclear. This study employed stable isotope analysis and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) to demonstrate that groundwater-derived dissolved inorganic carbon (DIC) significantly enhances CO2 supersaturation in the Shuiluo stream on the QTP. Specifically, the partial pressure of CO2 (pCO2), indicative of CO2 emission potential, increased more than threefold to 1,615 ± 495 μatm in groundwater-rich sites, nearly one time higher than the mean value (843 μatm) across the QTP. Groundwater-derived carbonate weathering had a significant impact of 76.6% on the increased pCO2, whereas the degradation of highly unsaturated polyphenolics with high O/C contributed to a decrease of 15.8%. The estimated inflow of groundwater-derived DIC could reach 9.59 ± 0.34 Tg C/y in total runoff across the QTP, highlighting significant CO2 sources. This study presents new findings on the effects of groundwater-derived DIC on stream CO2 emissions in weathered regions and expands our knowledge of fluvial CO2 emission on the QTP.