Altered greenhouse gas emissions in shallow lakes invaded by common carp ( Cyprinus carpio )

Methane emissions along biomethane and biogas supply chains are underestimated

Vegetation loss and plant diversity decline in wetlands affect carbon and nitrogen cycling and consequently influence gas fluxes. Although extensive grazing by livestock and climate change have caused significant physical degradation of wetlands on the Qinghai-Tibet Plateau (QTP), and created a clear drainage gradient, the impact on greenhouse gas (GHG) emissions associated with this change has rarely been reported. A 3-year study (2013–2015) was conducted to examine the effect of vegetation change and seasonality on ecosystem respiration, methane (CH4) and nitrous oxide (N2O) fluxes in four classes of wetlands with distinct magnitudes of vegetation degradation: healthy vegetation (HV), slightly degraded (SD), moderately degraded, and heavily degraded (HD). We used the dark static chamber-chromatography method to measure the gas fluxes. Highly degraded wetlands were larger C and GHG sources than HV, despite lower methane emissions, due to the loss of gross primary production. SD and HD exhibited the highest cumulative mean annual ecosystem respiration and N2O emissions, respectively. Ecosystem respiration and CH4 fluxes were much higher during the growing seasons than in the non-growing seasons. Ecosystem respiration and N2O fluxes were positively correlated with soil and air temperatures. This points at a potential effect of global warming on GHG emissions from the QTP wetlands. Top soil (0–20 cm) moisture content significantly correlated positively with CH4 fluxes. Vegetation loss led to a reduced C uptake and increased global warming potential. Therefore, we recommend soil conservation measures and reduced livestock grazing in the wetlands in order to conserve their role as carbon sinks.

Aquatic ecosystems play a crucial role in the global carbon cycle, serving as both significant carbon sinks and as sources of greenhouse gases (GHGs). Dynamic redox fluctuations, driven by factors such as changes in water levels and periodic flooding, facilitate interactions among reduced substances, metal-bearing minerals, and oxygen (Nielsen et al., 2010). These interactions shape microbial communities and influence the dynamics of soil organic carbon (Lalonde et al., 2012;Xiao et al., 2023). While redox fluctuations impact carbon cycling processes driven by microorganisms, further research is needed to elucidate the specific mechanisms through which microbial species, metabolic pathways, and microbial residues affect soil carbon cycling (Hu et al., 2024;Luo et al., 2019). This Special Issue invites research on GHG emissions and carbon sequestration in areas characterized by dry-wet cycling, with a focus on microbial processes and their ecological impact on the carbon cycle. Topics of interest include innovative technologies for GHG mitigation and carbon storage, microbial adaptations to environmental changes affecting GHG emissions, mechanisms of microbial carbon fixation, and interactions between microbes, minerals, and carbon in aquatic ecosystems. The goal is to enhance our understanding of sustainable solutions for managing carbon dynamics in regions with moisture fluctuations.In this Special Issue, the research topics encompass a variety of ecosystems, including wetlands, lakes, agricultural soils, estuarine intertidal zones, grasslands, and saltmarshes. The studies investigate the effects of plants, inorganic substances (e.g., inorganic nitrogen), drought, organic matter (e.g., phenolic compounds), iron-bearing minerals, precipitation, salinity and heavy metals on greenhouse gas (GHG) emissions, microbial metabolism, enzyme activities, and other relevant environmental factors.Li and Ge et al. highlight the importance of soil enzymes in wetland carbon and nutrient cycling and their varied responses to drought. A meta-analysis of 55 studies shows that while most enzyme activities remain stable, phosphorus-related enzyme activity increases by 38% under drought conditions, possibly due to their greater resilience to phenolic biotoxicity. Long-term experiments confirm that drought-driven plant shifts lead to phenolic accumulation, limiting enzyme activity, with phosphorus-related enzymes being an exception. These findings highlight wetland ecosystems' adaptive responses to drought, offering insights for assessing drought impacts and guiding restoration efforts. Jiang et al. demonstrate that the invasive plant Spartina alterniflora significantly affects GHG production in tidal wetland sediments. The presence of this species increases the production rates of CH₄ and CO₂, as well as the levels of organic matter and the abundance of microbial genes in invaded areas. These effects vary with spatial and seasonal dynamics, showing higher GHG production in surface sediments (0-10 cm) during the summer months. This study underscores how the invasion of S. alterniflora modifies GHG dynamics in coastal wetlands, offering valuable insights into emissions and carbon storage potential. Similarly, Zhang et al. examine the impact of varying precipitation levels on soil CO₂ emissions in a saltmarsh within the Yellow River Delta, China. Over a seven-year period, the results indicate that a 40% increase in precipitation enhances soil CO₂ production potential by 66.2%, with the highest soil respiration rates occurring under these conditions. Additionally, the quantity and quality of soil organic carbon positively correlate with CO₂ production, although microbial diversity remains unaffected by changes in precipitation. These findings suggest that moderate increases in precipitation may enhance CO₂ emissions, thereby influencing the carbon sink function of these blue carbon ecosystems. Looking ahead, the importance of aquatic ecosystems in the global carbon cycle is becoming increasingly prominent. As climate change and human activities intensify their impact on the environment, in-depth studies of the dynamics of microbial processes in ecosystems such as wetlands, lakes, and paddy fields will become crucial. Future research should focus on the effects of dynamic redox fluctuations on microbial communities and soil organic carbon, exploring the specific mechanisms through which different microbial species, metabolic pathways, and microbial residues influence soil carbon cycling. Additionally, developing innovative technologies to reduce GHG emissions and promote carbon storage will be key to achieving sustainable development.Research should also examine biological adaptations to environmental changes, particularly in regions characterized by dry-wet cycles, to enhance the functionality of carbon sinks. As our understanding of heavy metals in soil environments and their effects on microbial metabolism deepens, future management strategies will become more targeted to address the challenges posed by metal pollution. In summary, future research will contribute valuable scientific knowledge for combating climate change and provide feasible solutions for the conservation and restoration of aquatic ecosystems.

An important share of the greenhouse gas (GHG) emissions of many European and South-East Asian countries is originating from degraded peatlands. However, only the GHG balances of a few sites can be measured directly, as these measurements are both cost- and labour-intensive. Therefore, reliable methods for upscaling peatland GHG balances to a larger scale are necessary. Ideally, such upscaling methods use readily available data and also allow for the assessment of scenarios and implemented restoration measures.In this study, we focused on unused and extensively used bogs in Germany and collected a dataset of published annual balances of carbon dioxide (CO2) and methane (CH4) from bogs within Germany and the surrounding temperate Europe. Each site was assigned to one of eight vegetation types, which are based on a clustering of the German federal biotope type classification to enable later upscaling based on this data. The relationships of the annual CO2 and CH4-balances to vegetation type, mean annual water level and temperature were then analysed with mixed effects modelling.As expected, wet extensive grassland had relatively high CO2 and low methane emissions, while semi-natural bogs showed a small CO2-uptake but higher methane emissions. Most degeneration stages showed an intermediate behaviour. Noteworthy are the comparatively low CH4 emissions of recently rewetted sites with sparse vegetation and of wet unused forested areas. Due to very little available data, the uncertainties of GHG emissions from some vegetation types are large. For very wet vegetation types such as semi-natural Sphagnum-dominated sites, water levels did not improve the GHG emission estimates compared to solely using vegetation data. For dryer sites such as wet extensive grassland, incorporating water levels significantly improved the estimation of both CO2 and CH4 fluxes.The results are broadly in line with previous findings and provide a basis for future upscaling to a German-wide estimation. In some cases, knowledge on water levels after having taking restoration measures will still improve the estimation of GHG exchange. The most severe data shortage occurred for recently rewetted sites with sparse vegetation and wet unused forested bogs as well as subalpine and alpine peatlands.

Climate warming has the potential to alter carbon (C) and nitrogen (N) cycling affecting greenhouse gas (GHG) emissions and a range of other ecosystem functioning in grasslands. This will be particularly important for the sustainability of agricultural ecosystems due to its role in global food security and soil C sequestration. The interaction between climate warming and grassland management is highly important and needs to be addressed as it may change the direction and strength of the effects on GHG emissions by changing plant productivity (either above and/or below-ground) and plant-soil properties. Plant species composition also plays a key role affecting the nutrient cycling thus GHG emissions in grasslands. The aim of this thesis is to understand how grassland management will influence C and N cycling under future climate change. The interactive effect of climate warming and grassland management is investigated in a field experiment over two growing seasons with varied microclimate effects, and the effect of plant composition manipulation in a controlled temperature mesocosm experiment. Overall, interactions between warming and management significantly affected GHG fluxes and plant-soil properties with important single treatment effects. The role that below-ground components plays on GHG emissions was less evident, becoming unclear the mechanisms related to gas releases to the atmosphere. Increases in legume proportions in grass-legume mixtures reduced ecosystem respiration in fertilised soils, with no effects in unfertilised soils. N cycling was not affected by increases in legume proportions. Plant productivity including above- and below-ground biomass had a non-linear relationship with relative legume proportion. Either grassland management or different plant species compositions approach may improve C sequestration and reduce GHG emissions.

The climate impact from the useof peat for energy production in Sweden hasbeen evaluated in terms of contribution toatmospheric radiative forcing. This wasdone by attempting to answer the question`What will be the climate impact if onewould use 1 m2 of mire for peatextraction during 20 years?'. Two differentmethods of after-treatment were studied:afforestation and restoration of wetland.The climate impact from a peatland –wetland scenario and a peatland –forestation – bioenergy scenario wascompared to the climate impact from coal,natural gas and forest residues.Sensitivity analyses were performed toevaluate which parameters that areimportant to take into consideration inorder to minimize the climate impact frompeat utilisation. In a `multiple generationscenario' we investigate the climate impactif 1 Mega Joule (MJ) of energy is produced every yearfor 300 years from peat compared to otherenergy sources.The main conclusions from the study are:•The accumulated radiative forcing from the peatland – forestation – bioenergy scenario over a long time perspective (300 years) is estimated to be 1.35 mJ/m2/m2 extraction area assuming a medium-high forest growth rate and medium original methane emissions from the virgin mire. This is below the corresponding values for coal 3.13 mJ/ m2/ m2 extraction area and natural gas, 1.71 mJ/ m2/ m2 extraction area, but higher than the value for forest residues, 0.42 mJ/ m2/ m2 extraction area. A `best-best-case' scenario, i.e. with high forest growth rate combined with high `avoided' methane (CH4) emissions, will generate accumulated radiative forcing comparable to using forest residues for energy production. A `worst-worst-case' scenario, with low growth rate and low `avoided' CH4 emissions, will generate radiative forcing somewhere in between natural gas and coal.•The accumulated radiative forcing from the peatland – wetland scenario over a 300-year perspective is estimated to be 0.73 –1.80 mJ/ m2/ m2 extraction area depending on the assumed carbon (C) uptake rates for the wetland and assuming a medium-high methane emissions from a restored wetland. The corresponding values for coal is 1.88 mJ/ m2/ m2 extraction area, for natural gas 1.06 mJ/ m2/ m2 extraction area and for forest residues 0.10 mJ/ m2/ m2 extraction area. A `best-best-case' scenario (i.e. with high carbon dioxide CO2-uptake combined with high `avoided' CH4 emissions and low methane emissions from the restored wetland) will generate accumulated radiative forcing that decreases and reaches zero after 240 years. A `worst-worst-case' (i.e. with low CO2-uptake combined with low `avoided' CH4 emissions and high methane emissions from the restored wetland) will generate radiative forcing higher than coal over the entire time period.•The accumulated radiative forcing in the `multiple generations' – scenarios over a 300-year perspective producing 1 MJ/year is estimated to be 0.089 mJ/ m2 for the scenario `Peat forestation – bioenergy', 0.097 mJ/ m2 for the scenario `Peat wetland with high CO2-uptake' and 0.140 mJ/ m2 for the scenario `Peat wetland with low CO2-uptake'. Corresponding values for coal is 0.160 mJ/ m2, for natural gas 0.083 mJ/ m2 and for forest residues 0.015 mJ/ m2. Using a longer time perspective than 300 years will result in lower accumulated radiative forcing from the scenario `Peat wetland with high CO2-uptake'. This is due to the negative instantaneous forcing that occurs after 200 years for each added generation.•It is important to consider CH4 emissions from the virgin mire when choosing mires for utilization. Low original methane emissions give significantly higher total climate impact than high original emissions do.•Afforestation on areas previously used for peat extraction should be performed in a way that gives a high forest growth rate, both for the extraction area and the surrounding area. A high forest growth rate gives lower climate impact than a low forest growth rate.•There are great uncertainties related to the data used for emissions and uptake of greenhouse gases in restored wetlands. The mechanisms affecting these emissions and uptake should be studied further.

Effect of pre-main-post diesel injection strategy on greenhouse gas and nitrogen oxide emissions of natural gas/diesel dual-fuel engine at high load conditions

Globally, agriculture is directly responsible for 14% of annual greenhouse gas(GHG) emissions and induces an additional 17% through land use change, mostlyin developing countries (Vermeulen et al 2012). Agricultural intensification andexpansion in these regions is expected to catalyze the most significant relativeincreases in agricultural GHG emissions over the next decade (Smith et al 2008,Tilman et al 2011). Farms in the developing countries of sub-Saharan Africa andAsia are predominately managed by smallholders, with 80% of land holdingssmaller than ten hectares (FAO 2012). One can therefore posit that smallholderfarming significantly impacts the GHG balance of these regions today and willcontinue to do so in the near future.However, our understanding of the effect smallholder farming has on theEarth’s climate system is remarkably limited. Data quantifying existing andreduced GHG emissions and removals of smallholder production systems areavailable for only a handful of crops, livestock, and agroecosystems (Herrero et al2008, Verchot et al 2008, Palm et al 2010). For example, fewer than fifteenstudies of nitrous oxide emissions from soils have taken place in sub-SaharanAfrica, leaving the rate of emissions virtually undocumented. Due to a scarcity ofdata on GHG sources and sinks, most developing countries currently quantifyagricultural emissions and reductions using IPCC Tier 1 emissions factors.However, current Tier 1 emissions factors are either calibrated to data primarilyderived from developed countries, where agricultural production conditions aredissimilar to that in which the majority of smallholders operate, or from data thatare sparse or of mixed quality in developing countries (IPCC 2006). For the mostpart, there are insufficient emissions data characterizing smallholder agricultureto evaluate the level of accuracy or inaccuracy of current emissions estimates.Consequentially, there is no reliable information on the agricultural GHG budgetsfor developing economies. This dearth of information constrains the capacity totransition to low-carbon agricultural development, opportunities for smallholdersto capitalize on carbon markets, and the negotiating position of developingcountries in global climate policy discourse.Concerns over the poor state of information, in terms of data availability andrepresentation, have fueled appeals for new approaches to quantifying GHGemissions and removals from smallholder agriculture, for both existing conditionsand mitigation interventions (Berry and Ryan 2013, Olander et al 2013).Considering the dependence of quantification approaches on data and the currentdata deficit for smallholder systems, it is clear that in situ measurements must bea core part of initial and future strategies to improve GHG inventories and

Natural gas (NG) is a promising alternative fuel to reduce exhaust emissions of greenhouse gases (GHG), particulate matter (PM) and nitrogen oxides (NOx) from heavy-duty (HD) vehicles. Past HD NG vehicle research has focused on the fuel consumption and exhaust emission of PM and NOx. Recent global warming concerns have raised interest in methane emissions from NG vehicles. However, there is currently no model available to estimate the methane emissions from HD NG vehicles. There is also a need to project the methane emissions of HD NG vehicles in 2035.;This research developed a scenario based estimation model for methane emissions of the heavy-duty transportation sector. The methane emissions sources considered include: tailpipe; crankcase; dynamic ventilation; fueling tank; and fueling stations. The main work conducted includes (1) processing experimental data and developing model input data; (2) estimating the population scenarios of the HD transportation sector in 2035, including HD NG vehicles and NG fuel stations; (3) developing operation characteristics for each type of vehicle; (4) developing a 2035 methane emissions and fuel consumption scenario; (5) developing, coding, and demonstrating the methane emissions estimation model; (6) estimating the methane emissions of the HD transportation sector in 2035. In this research, the methane emissions and fuel consumptions measured were statistically analyzed and characterized to fuel specific methane emissions (FSME) and distance specific fuel consumption for idle activity and three driving activities noted as city, arterial, and highway operation activities. The idle activity had methane emissions and fuel consumption characterized to FSME and time specific fuel consumption. With an input of the vehicle population and operation characteristics, the model was able to estimate the total fuel consumed and total methane emissions associated with tailpipes, crankcases, dynamic ventilation, on-board fuel storage tanks, and refueling stations. The total methane emissions and fuel consumption were further processed to calculate the FSME.;The estimation model was validated using the stasis scenario developed in this research. The model was validated by comparing the estimated FSME output with the input and verifying calculations. The contribution of tailpipes, crankcases, and fuel stations to the methane emissions of HD spark ignition (SI) CNG vehicles were 33.2%, 59.4%, and 7.4%, respectively, for the stasis scenario, representing current vehicle technology. The validated model was applied to estimate the methane emissions in the HD transportation sector with the high, medium and low methane emissions and fuel consumption scenarios. It was concluded that the total methane emissions

Nitrous oxide and methane emissions from coffee agroforestry systems with different intensities of canopy closure

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Summary Trait‐based approaches evaluate ecosystem functioning under environmental change by relating traits predicting changes in species densities (response traits) to traits driving ecosystem functioning (effect traits). Stressors can, however, affect ecosystem functioning not only by altering species densities but also by directly changing species effect traits. We first identified the response traits predicting the cell density of 18 marine benthic diatom strains along gradients of two chemical stressors (a pesticide and a metal, atrazine and copper). We then tested if response traits could predict stressor‐induced changes in ecosystem functioning, i.e. changes in the effect traits driving the diatoms’ potential contribution to primary production, sediment stabilization and energy content in intertidal systems. Finally, we examined if changes in density and changes in ecosystem functioning were correlated, to assess whether species capable of growing under stressful conditions could maintain their contribution to ecosystem functioning. The relationship between response traits and stressor‐induced changes in density and ecosystem functioning was different depending on stressor type: a set of intercorrelated morphological traits predicted changes in both density and ecosystem functioning under metal stress, with large cells being more stress resistant. Changes in density and changes in ecosystem functioning were positively related: diatoms whose density was least affected by the metal were also able to sustain functioning under metal exposure. In contrast, the capacity for mixotrophic growth predicted changes in density, but not changes in ecosystem functioning under pesticide stress. Pesticide effects on density and on ecosystem functioning were negatively related for energy content and sediment stabilization, indicating a limited capacity of pesticide‐tolerant diatoms to maintain their contribution to ecosystem functioning. Synthesis. Ecosystem functioning under stress can depend on whether the response traits driving changes in species densities also predict direct stress effects on the species’ contribution to functioning. Based on our results, we expect a disproportionate loss of functioning when traits driving species densities do not allow to maintain ecosystem functioning under stress.

In the context of global climate change, carbon footprint (CF) becomes an important sustainability indicator for dairy production systems. To mitigation the CF of the dairy sector, insight into greenhouse gases (GHG) emissions from individual farms is required. The objective of this study was to determine the primary contributors to GHG emissions at the farm-gate level, expressed as a carbon dioxide equivalents (CO2-eq), to produce one kg of fat-and protein corrected milk (FPCM). Primary data about farms’ management and feeding practices were collected from twelve dairy farms that belong to Gyeonggi-do province, which represent the most important region for milk production in South Korea. Allocation of GHG emissions between meat and milk was assessed as a physical allocation, 98% allocated to milk and 2% to meat (surplus of calves and culled cows). The CF of the evaluated farms averaged to 0.61 CO2-eq/kg of FPCM and ranged from 0.49 to 0.78 CO2-eq/kg of FPCM. Results indicated that the largest source of GHG comes mostly from enteric fermentation (83%), followed by manure management (6%), manure and fertilizer land application (8%) and energy consumption (3%). By type of gas emitted, methane accounted for 86% of total emissions, originating from enteric fermentation and manure management. Nitrous oxide and carbon dioxide accounted for 11.6 % and 2.8% of total GHG emissions, respectively. Lactating cows contributed by 70% of total GHG emissions, whereas dry cows, heifers and calves contributed by 5, 22 and 3%, respectively. Differences in GHG emissions from the evaluated farms could be explained by differences in feed quality and management practices through manure and fertilizers application on cropland. This study contributes to identify the main sources of GHG production in dairy farms, which can help to define mitigation strategies towards the transition to neutral carbon emissions of the dairy sector.

Major US electric utility climate pledges have the potential to collectively reduce power sector emissions by one-third

Livestock production contributed 3.9% to the total greenhouse gas (GHG) emission from the US in 2018. Most studies to mitigate GHG from livestock are focused on enteric methane because it contributes about 70% of all livestock GHG emissions. Mitigation options can be broadly categorized into dietary and rumen manipulation. Enteric methane emissions are strongly correlated to dry matter intake and somewhat sensitive to diet composition. Dietary manipulation methods include increasing feed digestibility, such as concentrate to forage ratio, or increasing fats and oils, which are associated with lower methane emissions. These reduce digestible fiber that are positively related to methane production and more energy passing the rumen without being degraded, respectively. Rumen manipulation through feed additives can be further classified based on the mode of action: 1. rumen environment modifiers indirectly affecting emissions and 2. direct methanogenesis inhibitors. The rumen environment modifiers act on the conditions that promote methanogenesis. These include ionophores, plant bioactive compounds such as essential oils and tannins, and nitrate rich feeds that serve as alternative hydrogen sinks and directly compete with methanogens thereby reducing methane emissions. The inhibitor category include 3-nitroxypropanol and seaweeds containing halogenated compounds. The former was reported to reduce enteric methane emissions (g/d) by 39% in dairy and 22% in beef cattle. Seaweed, in particular Asparagopsis spp., reduced emissions intensity (g/kg milk) by up to 67% in dairy and emissions yield (g/kg dry matter intake) by up to 98% in beef cattle. Because inhibitors are structural analogs of methane, their mode of action is through competitive inhibition of the methyl transfer reaction catalyzed by methyl coenzyme-M reductase, the last enzyme in methanogenesis. The combination of dietary and rumen manipulation options, including feed additives, is expected to reduce enteric methane emissions by over 30% in the next decade without compromising animal productivity and health.