Fluxes of greenhouse gases from incubated soils using different lid-closure times

Tree species influence the soil through stemflow and throughfall water, leaf litter and the root system. Little is known about the effects of tree roots on the C and N dynamics of the soil and the gas exchange with the atmosphere. In the present study, the effects of European beech (<i>Fagus sylvatica</i>) and Common ash (<i>Fraxinus excelsior</i> L.) saplings, as important European broad-leaved tree species, on C and N fluxes in the soil of a species-rich temperate forest were investigated under constant climatic conditions. The main objective was to identify root-induced changes in the greenhouse gas fluxes of CO₂, CH₄, and N₂O between soil and atmosphere. A stepwise experimental approach was used to extend the knowledge about rhizosphere effects on soil biogeochemistry. In the first step, the effects of simple C and N alteration by KNO₃ (equivalent to 200 kg N ha^-1 yr^-1) and glucose addition (equivalent to 9419 kg C kg ha^-1 yr^-1) on the fluxes of CO₂, CH₄, and N₂O were investigated for a basic understanding of the C and N dynamics in the incubated forest soil (Chapters 2 and 3). In the next step, the changes due to C and N alteration were compared with the putatively complex effects of ash roots on CO₂ and N₂O emissions in soil columns (Chapter 4). Finally, species-specific effects of the roots of beech and ash saplings on the C and N cycling of the soil were analysed in soil columns and novel double-split-root rhizotrons (Chapters 4, 5, and 6). The experimental investigation of the effects of NO₃^- and glucose addition on the greenhouse gas exchange (Chapter 2) revealed a large reduction in net CH₄ uptake due to increased N availability and saturating doses of C (reductions up to 86% and 83%, respectively). Moreover, addition of NO₃^- and glucose increased the N₂O emissions by factors of 8 and 39, respectively, whereas the CO₂ efflux remained constant after N addition and increased dramatically up to 11-fold after C addition (Chapter 3). A synergistic effect of C and N addition on all three investigated gas fluxes could be shown. The results of the simple C and N addition experiments suggest that the effect of the large C addition on all three investigated greenhouse gases, including the measured N emissions, was larger than the effect of elevated N availability, which might be important under a variable climate. The comparison of the effects of N addition and the presence of ash roots on CO₂ and N₂O emissions showed that the ash roots greatly reduced the N₂O emissions by up to 98%, whereas N addition increased the N₂O emissions just by 54% (Chapter 4). These results indicate that the effect of ash saplings on N₂O might not be exclusively explained by the N uptake of the roots, and that plant species effects of the rhizosphere changes should achieve a higher attention in future studies on the greenhouse gas balance of forest soils. As in the soil columns, the rhizotron experiment showed a large reduction of N₂O emissions by ash roots (Chapter 5). In contrast, the reduction of N₂O release in presence of beech saplings was only slight or not visible in the rhizotrons and the soil columns (Chapters 4 and 5). The CO₂ emissions from soil planted with ash tended to be higher than, or were similar to, the emissions from soil planted with beech (Chapters 4 and 5). Due to the higher relative contribution of root respiration to total soil respiration in ash rhizotrons (35.5 ± 8.5 vs. 9.0 ± 2.7 %, Chapter 5), we assume that a higher activity of saprotrophic fungi and a larger microbial-specific respiration was responsible for the similar CO₂ effluxes from soil under beech and ash (Chapter 6). In the rhizotron approach, the CH₄ uptake was significantly increased under ash compared to the control soil (Chapter 5), while beech saplings did not significantly affect the CH₄ uptake. In contrast to the observed changes in greenhouse gas fluxes, the C and N stocks of soil under beech and ash were only slightly different. In conclusion, the gas fluxes from the soil to the atmosphere can be used as sensitive indicators of even small changes in the biogeochemical processes of forests. Despite the higher CO₂ efflux from soil under ash, the greenhouse gas balance calculated as the sum of CO₂, CH₄, and N₂O fluxes tended to be more favourable for soil under ash than for soil under beech saplings in all experiments, which indicates a mitigating influence of European ash on the greenhouse gas balance of temperate forest soils. Further field and laboratory research on the relation between root systems and greenhouse gas fluxes from the soil are needed for realistic predictions of the future greenhouse gas balance under changing climatic conditions.

Tillage affects atmosphere–soil greenhouse gas (GHG) flux by opening soil pore spaces releasing pockets of CO2, CH4, and N2O. Tillage may also stimulate microbes responsible for GHG biogenesis and consumption at longer time scales following a discrete tillage event. I measured soil gas flux immediately after three mechanically different tillage events (moldboard plow, rip‐plow, and disc‐till) over 2 mo within the same field. Delayed effects of tillage on soil respiration were measured; CH4 and N2O fluxes via laboratory incubations on soils were collected following tillage events compared to undisturbed soils. Moldboard plowing did not result in immediate pulses of GHG. Carbon dioxide emissions and CH4 influx to soil peaked 1 h post‐plow. Later rip‐plowing caused a more sustained pulse of CO2 and CH4 uptake over 2 h in the field. Disc‐tillage produced a CO2 production pulse‐then‐decline profile, but CH4 and N2O fluxes were highly variable after this event. Greenhouse gas flux from laboratory‐incubated alfalfa soil and fallow soil were similar to soil collected after rip‐plowing. Soils incubated after the last field tillage event produced significantly lower CO2 emissions during lab incubations compared with other undisturbed and plowed soil. These results show that instantaneous tillage effects are not uniform among GHGs, tillage alteration of soil respiration persists for months following a disturbance, and repeated tillage in the field changes microbial regulation of specific GHGs. Tillage has immediate impacts on GHG flux and has the potential for persistent effects on microbial activity that need further investigation as a GHG abatement tool.

Evaluating temporal controls on greenhouse gas (GHG) fluxes in an Arctic tundra environment: An entropy-based approach

Freshwater wetlands can contribute significantly to the global carbon budget as a net source or sink of the major greenhouse gas (GHG) fluxes such as carbon dioxide (FCO2) and methane (FCH4). The amount of GHG fluxes in the freshwater wetlands is highly variable and depends on a range of environmental drivers. These wetlands are commonly hypothesized to be net sinks (i.e., burial) of FCO2 and net sources (emission) of FCH4 at the monthly to annual scales. Understanding the environmental controls on the wetland GHG fluxes is essential for an accurate estimation of the global GHG budget, which is often used as a pivotal measure to reduce GHG emissions and enhance carbon sequestration. In this study, we analyzed FLUXNET data from 38 freshwater wetlands located across the globe to investigate the relationships of monthly-scale GHG fluxes with various climatic and ecohydrological drivers. Data analytics with multivariate pattern recognition techniques—including principal component analysis, factor analysis, and partial least squares regression— were performed to identify and quantify the dominant controls of wetland FCO2 and FCH4 fluxes. The environmental controls on the GHG fluxes in freshwater wetlands were found to highly vary based on the climatic zones. In the tropical (i.e., mega thermal) zone, the GHG fluxes were overall primarily controlled by photosynthetically active radiation (PAR), soil temperature (TS), wind speed (WS), friction velocity (USTAR), and vapor pressure deficit (VPD). However, the latent heat flux (LE) and VPD, alongside PAR, TS, and USTAR, exhibited the dominant controls on the GHG fluxes in the dry (or arid) zone wetlands. Both GHG fluxes in wetlands of the temperate (or mesothermal) zone were mainly controlled by water table depth (WL), TS, and LE. Surprisingly, PAR did not appear to be a strong driver of the monthly averaged fluxes in the temperate wetlands. In contrast, PAR, LE, TS, WS, and USTAR were the primary controlling factors of the GHG fluxes in wetlands representing continental (or microthermal) climates. However, in wetlands of the polar (alpine) region, sensible heat flux (H) had a strong linkage with the GHG fluxes, alongside the controls of PAR, TS, WS, VPD and USTAR. These findings and new knowledge can help inform wetland management and conservation strategies, particularly in the context of climate and land cover changes. Effective management and conservation of wetlands can help reduce GHG emissions, thereby contributing to the mitigation efforts on global warming.

Comprehensive soil greenhouse gas flux dataset from a temperate old-growth forest: Effects of decade-long nitrogen addition and biological factor manipulation.

Land application of biochar reportedly provides many benefits, including reduced risk of nutrient transport, greenhouse gas (GHG) emission mitigation, and increased soil C storage, but additional field validation is needed. We evaluated the effectiveness ofbiochar in controlling the lability of nutrients in agriculturalland. This study was designed to evaluate the impacts of biochar co-applied with various N and P sources on GHG fluxes from a subtropical grassland. Nutrients (inorganic fertilizer and aerobically digested Class B biosolids) were surface applied at a rate of 160kg plant available N ha-1 yr-1 with or without biochar (applied at 20 Mg ha-1 ). Greenhouse gas (CO2 , CH4 , and N2 O) fluxes were assessed using static chambers and varied significantly, both temporally and with treatments. Greenhouse gas fluxes ranged from 1,247 to 23,160, -0.7 to 42, and -1.4 to 376mg m-2 d-1 for CO2 , N2 O, and CH4 , respectively. Results of the 3-yr field study demonstrated strong seasonal variability associated with GHG emissions. Nutrient source had no effect on soil CO2 and CH4 emissions, but annual and cumulative (3-yr) N2 O emissions increased with biosolids (8kg N2 O ha-1 yr-1 ) compared with inorganic fertilizer (5kg N2 O ha-1 yr-1 ) application. Data suggested that environmental conditions played a more important role on GHG fluxes than nutrient additions. Biochar reduced CO2 emissions modestly (<9%) but had no effects on N2 O and CH4 emissions.

Canopy soil nutrient cycling and response to elevated nutrient levels along an elevation gradient of tropical montane forests

Increase in concentrations of various greenhouse gases and their possible contributions to the global warming are becoming a serious concern. Anthropogenic activities such as cultivation of flooded rice and application of waste materials, such as sewage sludge which are rich in C and N, as soil amendments could contribute to the increase in emission of greenhouse gases such as methane (CH4) and nitrous oxide (N2O) into the atmosphere. Therefore, evaluation of flux of various greenhouse gases from soils amended with sewage sludge is essential to quantify their release into the atmosphere. Two soils with contrasting properties (Candler fine sand [CFS] from Florida, and Ogeechee loamy sand [OLS] from Savannah, GA) were amended with varying rates (0, 24.7, 49.4, 98.8, and 148.3 Mg ha− 1) of 2 types of sewage sludge (industrial [ISS] and domestic [DSS] origin. The amended soil samples were incubated in anaerobic condition at field capacity soil water content in static chamber (Qopak bottles). Gas samples were extracted immediately after amending soils and subsequently on a daily basis to evaluate the emission of CH4, CO2 and N2O. The results showed that emission rates and cumulative emission of all three gases increased with increasing rates of amendments. Cumulative emission of gases during 25-d incubation of soils amended with different types of sewage sludge decreased in the order: CO2 > N2O > CH4. The emission of gases was greater from the soils amended with DSS as compared to that with ISS. This may indicate the presence of either low C and N content or possible harmful chemicals in the ISS. The emission of gases was greater from the CFS as compared to that from the OLS. Furthermore, the results clearly depicted the inhibitory effect of acetylene in both soils by producing more N2O and CH4 emission compared to the soils that did not receive acetylene at the rate of 1 mL g− 1 soil. Enumeration of microbial population by fluorescein diacetate (FDA) and most probable number (MPN) procedure at the end of 25-d incubation demonstrated a clear relationship between microbial activity and the emission of gases. The results of this study emphasize the need to consider the emission of greenhouse gases from soils amended with organic soil amendments such as sewage sludge, especially at high rates, and their potential contribution to global warming.

Soil profile greenhouse gas concentrations and fluxes from a semiarid grassland and a cropland site in an agro-pastoral ectone of northern China

Response of soil greenhouse gas fluxes to warming: A global meta‐analysis of field studies

Coastal salt marshes play an important role in mitigating global warming by removing atmospheric carbon at a high rate. We investigated the environmental controls and emergent scaling of major greenhouse gas (GHG) fluxes such as carbon dioxide (CO2) and methane (CH4) in coastal salt marshes by conducting data analytics and empirical modeling. The underlying hypothesis is that the salt marsh GHG fluxes follow emergent scaling relationships with their environmental drivers, leading to parsimonious predictive models. CO2 and CH4 fluxes, photosynthetically active radiation (PAR), air and soil temperatures, well water level, soil moisture, and porewater pH and salinity were measured during May–October 2013 from four marshes in Waquoit Bay and adjacent estuaries, MA, USA. The salt marshes exhibited high CO2 uptake and low CH4 emission, which did not significantly vary with the nitrogen loading gradient (5–126 kg · ha−1 · year−1) among the salt marshes. Soil temperature was the strongest driver of both fluxes, representing 2 and 4–5 times higher influence than PAR and salinity, respectively. Well water level, soil moisture, and pH did not have a predictive control on the GHG fluxes, although both fluxes were significantly higher during high tides than low tides. The results were leveraged to develop emergent power law‐based parsimonious scaling models to accurately predict the salt marsh GHG fluxes from PAR, soil temperature, and salinity (Nash‐Sutcliffe Efficiency = 0.80–0.91). The scaling models are available as a user‐friendly Excel spreadsheet named Coastal Wetland GHG Model to explore scenarios of GHG fluxes in tidal marshes under a changing climate and environment.

Rivers play an important role in greenhouse gas emissions. Over the past decade, because of global urbanization trends, rapid land use changes have led to changes in river ecosystems that have had a stimulating effect on the greenhouse gas production and emissions. Presently, there is an urgent need for assessments of the greenhouse gas concentrations and emissions in watersheds. Therefore, this study was designed to evaluate river-based greenhouse gas emissions and their spatial-temporal features as well as possible impact factors in a rapidly urbanizing area. The specific objectives were to investigate how river greenhouse gas concentrations and emission fluxes are responding to urbanization in the Liangtan River, which is not only the largest sub-basin but also the most polluted one in Chongqing City. The thin layer diffusion model method was used to monitor year-round concentrations of pCO2, CH4, and N2O in September and December 2014, and March and June 2015. The pCO2 range was (23.38±34.89)-(1395.33±55.45) Pa, and the concentration ranges of CH4 and N2O were (65.09±28.09)-(6021.36±94.36) nmol·L-1 and (29.47±5.16)-(510.28±18.34) nmol·L-1, respectively. The emission fluxes of CO2, CH4, and N2O, which were calculated based on the method of wind speed model estimations, were -6.1-786.9, 0.31-27.62, and 0.06-1.08 mmol·(m2·d)-1, respectively. Moreover, the CO2 and CH4 emissions displayed significant spatial differences, and these were roughly consistent with the pollution load gradient. The greenhouse gas concentrations and fluxes of trunk streams increased and then decreased from upstream to downstream, and the highest value was detected at the middle reaches where the urbanization rate is higher than in other areas and the river is seriously polluted. As for branches, the greenhouse gas concentrations and fluxes increased significantly from the upstream agricultural areas to the downstream urban areas. The CO2 fluxes followed a seasonal pattern, with the highest CO2 emission values observed in autumn, then successively winter, summer, and spring. The CH4 fluxes were the highest in spring and the lowest in summer, while N2O flux seasonal patterns were not significant. Because of the high carbon and nitrogen loads in the basin, the CO2 products and emissions were not restricted by biogenic elements, but levels were found to be related to important biological metabolic factors such as the water temperature, pH, DO, and chlorophyll a. The carbon, nitrogen, and phosphorus content of the water combined with sewage input influenced the CH4 products and emissions. Meanwhile, N2O production and emissions were mainly found to be driven by urban sewage discharge with high N2O concentrations. Rapid urbanization accelerated greenhouse gas emissions from the urban rivers, so that in the urban reaches, CO2/CH4 fluxes were twice those of the non-urban reaches, and all over the basin N2O fluxes were at a high level. These findings illustrate how river basin urbanization can change aquatic environments and aggravate allochthonous pollution inputs such as carbon, nitrogen, and phosphorus, which in turn can dramatically stimulate river-based greenhouse gas production and emissions; meanwhile, spatial and temporal differences in greenhouse gas emissions in rivers can lead to the formation of emission hotspots.

The study of greenhouse gas (GHG) fluxes in terrestrial ecosystems is becoming increasingly important as the observed rise in global temperature and increased frequency of extreme weather events are attributed by the majority of climate experts to increased atmospheric GHG concentrations. Adequate and comprehensive knowledge of surface GHG fluxes is important for obtaining reliable information on CO2 and other GHG fluxes at regional and global scales, as well as for preparing reports on national GHG emissions and removals. The need to obtain accurate estimates of GHG fluxes at regional and global scales has led to the development of innovative mathematical models of varying complexity. These models can be divided into forward and inverse models. Forward algorithms provide the ability to estimate GHG fluxes when sufficient information on the structure of GHG sources and sinks is available. Inverse algorithms allow the retrieval of surface fluxes using remote sensing data. The most promising way to study high resolution fluxes over areas with complex topography and mosaic vegetation patterns is the use of unmanned aerial vehicles (UAVs).In our study, we proposed and tested a forward and inverse model for estimating GHG fluxes over an inhomogeneous underlying surface. The forward model is based on the RANS hydrodynamic model to calculate the wind velocity and turbulence coefficient, and the solution of the advection-diffusion equation to find a three-dimensional distribution of GHG concentrations. The GHG fluxes at the specified height above the ground surface are then calculated using the obtained concentration distribution and turbulence coefficient. The inverse algorithm is based on minimizing a cost functional, defined as the root mean square deviation of the modeled concentration field from the measured data. Concentration measurements at multiple (at least two) levels can be performed using UAV-based gas analyzers.Three experimental sites selected for our modeling study differ in geographic location, topography, and vegetation heterogeneity. These sites are: i) swampy and forested areas of the "Mukhrino" carbon supersite (Khanty-Mansiysk Autonomous Okrug, Russia, 60°53'20" N, 68°42'10" E), ii) the Roshni-Chu mountain forest site, which is part of the "Way Carbon" supersite (Chechen Republic, Russia, 43°2'59" N, 45°25'32" E), iii) the mixed forest experimental site "Lyali" (Komi Republic, Russia, 62°16'28" N, 50°39'54" E). For our numerical experiments we used measured data on surface topography, LAI, soil respiration, air temperature, prevailing wind direction, vertical canopy CO2 concentration profile and CO2 fluxes measured by eddy covariance technique.The model results show a rather good agreement with the measured data and could help to interpret the experimentally observed dependence of CO2 fluxes on wind direction in areas with an inhomogeneous underlying surface.

Biochar as soil amendment: Syngas recycling system is essential to create positive carbon credit

A network of carbon polygons has been established in Russia to study the emission and uptake of greenhouse gases in natural ecosystems and to develop technological solutions to control the fluxes of greenhouse gases in natural ecosystems with the aim of reducing their emission and increasing their uptake from the atmosphere. The pilot project is an important part of the low-carbon development strategy to decarbonize the Russian economy, adapt the economy to the global energy transition, reduce greenhouse gas emissions and achieve carbon neutrality in Russia by 2060. To achieve these goals, the pilot project uses an integrated approach that includes ground-based measurements of carbon balance and greenhouse gas fluxes, remote sensing data, and mathematical modeling methods. To provide observations of greenhouse gas fluxes, a wide range of experimental methods for direct and indirect measurements of greenhouse gas fluxes will be used. Direct field flux measurements include eddy covariance and chamber methods. Carbon polygons for monitoring greenhouse gas fluxes are planned to be distributed in the most representative natural terrestrial and aquatic ecosystems, allowing to assess the spatial and temporal variability of greenhouse gas emission and uptake. The territory of Armenia is a unique region in terms of diversity of climatic conditions and landscapes. The development of a system for monitoring greenhouse gas fluxes can serve as a guarantee of obtaining representative data on the emission and absorption of greenhouse gases by natural ecosystems, with the perspective of Armenia achieving carbon neutrality in the coming decades.