Soil Emissions Research Articles

Effects of returning peach branch waste to fields on soil carbon cycle mediated by soil microbial communities.

In recent years, the rise in greenhouse gas emissions from agriculture has worsened climate change. Efficiently utilizing agricultural waste can significantly mitigate these effects. This study investigated the ecological benefits of returning peach branch waste to fields (RPBF) through three innovative strategies: (1) application of peach branch organic fertilizer (OF), (2) mushroom cultivation using peach branches as a substrate (MC), and (3) surface mulching with peach branches (SM). Conducted within a peach orchard ecosystem, our research aimed to assess these resource utilization strategies' effects on soil properties, microbial community, and carbon cycle, thereby contributing to sustainable agricultural practices. Our findings indicated that all RPBF treatments enhance soil nutrient content, enriching beneficial microorganisms, such as Humicola, Rhizobiales, and Bacillus. Moreover, soil AP and AK were observed to regulate the soil carbon cycle by altering the compositions and functions of microbial communities. Notably, OF and MC treatments were found to boost autotrophic microorganism abundance, thereby augmenting the potential for soil carbon sequestration and emission reduction. Interestingly, in peach orchard soil, fungal communities were found to contribute more greatly to SOC content than bacterial communities. However, SM treatment resulted in an increase in the presence of bacterial communities, thereby enhancing carbon emissions. Overall, this study illustrated the fundamental pathways by which RPBF treatment affects the soil carbon cycle, providing novel insights into the rational resource utilization of peach branch waste and the advancement of ecological agriculture.

Pengaruh Lumpur Laut pada Tanah Gambut untuk Media Tanam Kedelai terhadap Sifat Kimia Tanah dan Emisi CO2

This study aimed to determine the effect of coastal sediment on peat soil for soybean planting medium to soil chemical properties and CO2 emissions. The research lasted for 3 months starting from preparation to presentation of the results. This research was conducted at the Laboratory of Soil Quality and Health, Laboratory of Chemistry and Soil Fertility and in the Faculty of Agriculture experimental garden Tanjungpura University. The method used is experiment with a completely randomized design (CRD), which consists of 5 treatments and 4 replications. Each polybag contained 1 plant sample. So the number of plants altogether 20 units of the plant. Treatment as follows: LL0 : Without treatment coastal sediment, LL1 : coastal sediment 25.2 tonnes/ha equivalent to 180 g/polybag, LL2 : coastal sediment 33.6 tonnes/ha equivalent to 240 g/polybag, LL3 : coastal sediment 42 ton / ha equivalent to 300 grams/polybag, LL4 : coastal sediment 50.4 tonnes/ha equivalent to 360 g/polybag. The variables observed in this study are soil pH, cation exchange capacity (CEC), Base Saturation, C/N, CO2 emissions and the dry weight of soybean. The results showed that application of coastal sediment with various doses on peat soil can increase soil pH, Base Saturation and C/N ratio, with decreasing CEC. There is just a little correlation of costal sediment on CO2 emissions of soil (R2=0.0009). Coastal sediment 33.6 tonnes/ha equivalent to 240 grams/polybag was resulted dry weight of soybean to maximum vegetative phase.

Synergistic effects of warming and humic substances on driving arsenic reduction and methanogenesis in flooded paddy soil

Microbially-driven arsenic reduction and methane emissions in anaerobic soils are regulated by widespread humic substances (HS), while how this effect responds to climate change remains unknown. We investigated potential synergistic effects of HS in response to temperature changes in arsenic-contaminated paddy soils treated with humic acid (HA) and fulvic acid (FA) at temperatures ranging from 15 to 45 °C. Our results reveal a significant increase in arsenic reduction (5.6 times) and methane emissions (178 times) driven by HS, which can be exponentially stimulated at 45 °C. Acting as a electron shuttle, HS determines microbial arsenic reduction, further stimulated by warming. The top three sensitive genera are Geobacter, Anaeromyxobacter, and Gaiella which are responsible for enhanced arsenic reduction, as well as for the reduction of iron and HS with their functional genes; arrA and Geobacter spp. The top three sensitive methanogens are Methanosarsina, Methanocella, and Methanoculleus. Our study suggests notable synergistic effects between HS and warming in stimulating arsenic reduction and methanogenesis in paddy soils. Overall, the findings of this work highlight the high sensitivity of HS-mediated microbial arsenic transformation and methanogenesis in response to warming, which add potential value in predicting the biogeochemical cycling of arsenic and methane in soil under the context of climate change.

Investigating the effects of climate change and anthropogenic activities on SOC storage and cumulative CO2 emissions in forest soils across altitudinal gradients using the century model

This study investigated the impact of climate change, grazing, manure application, and liming on soil organic carbon (SOC) stock and cumulative carbon dioxide (CO2) emissions in forest soils across different altitudes. Despite similar soil texture, acidity, and salinity across elevations, SOC stock significantly increased with altitude due to cooler temperatures and higher precipitation. The highest SOC stock (97.46 t ha−1) was observed at 2000–2500 m, compared to the lowest (44.23 t ha−1) at 500–1000 m. The Century C Model accurately predicted SOC stock, with correlation and determination coefficients exceeding 0.98. A climate change scenario projecting decreased precipitation (2.15 mm per decade) and increased temperature (0.4 °C) revealed potential SOC stock losses ranging from 28.36 to 36.35 %, particularly at higher altitudes. Grazing further decreased SOC stock, with a more pronounced effect at higher elevations. However, manure application (40 t ha−1 every four years) and liming (7–10 t ha−1 every three years) had positive effects on SOC stock, again amplified at higher altitudes and with an increase in lime application rate. In scenarios combining climate change with manure application and climate change with liming, manure application and liming mitigated some negative impacts of climate change, but could not fully offset them, resulting in 1.49–5.42 % and 0.39–4.07 % decreases respectively. Simulations of cumulative CO2 emissions mirrored the distribution of SOC stock, with higher emissions observed at higher altitudes and with management practices that increased SOC stock. This study emphasizes the critical role of conserving high-altitude forest soils and implementing optimal forest management strategies to combat climate change by minimizing SOC losses.

Gypsum Application and Straw Incorporation Interact to Alleviate Methane Emissions in Coastal Saline-Alkali Rice Soils

Gypsum Application and Straw Incorporation Interact to Alleviate Methane Emissions in Coastal Saline-Alkali Rice Soils

Effects of biodegradable microplastics and straw addition on soil greenhouse gas emissions

Large pieces of plastic are transformed into microplastic particles through weathering, abrasion, and ultraviolet radiation, significantly impacting the soil ecosystem. However, studies on biodegradable microplastics replacing traditional microplastics as agricultural mulching films to drive the biogeochemical processes influenced by GHG are still in their initial stages, with limited relevant reports available. This study sought to investigate the effects of microplastic and straw addition on CO2 and N2O emissions in different soils. Herein, yellow-brown soil (S1) and fluvo-aquic soil (S2) were utilized, each treated with three different concentrations of PLA (polylactic acid) microplastics (0.25%, 2%, and 7% w/w) at 25 °C for 35 days, with and without straw addition. The results showed that straw (1% w/w) significantly increased soil CO2 by 4.1-fold and 3.2-fold, respectively, and N2O by 1.8-fold and 1.8-fold, respectively, in cumulative emissions in S1 and S2 compared with the control. PLA microplastics significantly increased CO2 emissions by 71.5% and 99.0% and decreased N2O emissions by 30.1% and 24.7% at a high concentration (7% w/w, PLA3) in S1 and S2 compared with the control, respectively. The same trend was observed with the addition of straw and microplastics together. Structural equation modeling and redundancy analysis confirmed that soil physiochemical parameters, enzyme and microbial activities are key factors regulating CO2 and N2O emissions. The addition of microplastics is equivalent to the addition of carbon sources, which can significantly affect DOC, MBC, SOC and the abundance of carbon-associated bacteria (CbbL), thereby increasing soil CO2 emissions. The addition of microplastics alone inhibited the activity of nitrogen cycling enzymes (urease activity), increasing the abundance of denitrifying microbes. However, adding a high amount of microplastics and straw together released plastic additives, inhibiting microbial abundance and reducing the nitrogen cycle. These effects decreased NH4+-N and increased NO3−-N, resulting in decreased N2O emissions. This study indicates that biodegradable microplastics could reduce soil plastic residue pollution through degradation. However, their use could also increase CO2 emissions and decrease N2O emissions. Consequently, this research lays the groundwork for further investigation into the implications of utilizing biodegradable microplastics as agricultural mulch, particularly concerning soil geochemistry and GHG emissions.

A Review of Greenhouse Gas Emissions from Agricultural Soil

Greenhouse gases (GHGs) like nitrous oxide (N2O), carbon dioxide (CO2), and methane (CH4) are both emitted and removed by soils. Accurate worldwide allocations of carbon budget are essential for land use planning, global climate change, and climate-related research. Precise measurements, drivers, and mitigation strategies are necessary, given agricultural soil’s significant potential storage and emission capacities. Different agricultural management practices cause greenhouse gas (GHG) emissions into the atmosphere and contribute to anthropogenic emissions. Agricultural soils can generate 70% of the world’s manmade N2O emissions and also behave as a CO2 sink and a source of organic carbon and as producers and consumers of CH4. When it comes to agronomic management, the source and sink of all these GHGs are distinct. Therefore, several approaches to measuring GHG emissions from agricultural soils are available and can be categorized into chamber systems and remote sensing approaches. Sustainable agriculture stands out as a viable and transformative approach to increase agricultural efficiency while addressing the challenge of GHG emissions. Incorporating advanced technologies, precise data analytics, and site-specific management practices can offer a pathway to mitigate GHG emissions, thereby reducing the global warming potential (GWP). Therefore, this review paper focuses solely on the drivers influencing and involving soil emissions and on quantification approaches for GHG emissions. In addition, mitigation practices aimed at optimizing GHG emissions from agricultural soils are highlighted.

Green Manuring with Oilseed Rape (Brassica napus L.) Mitigates Methane (CH4) and Nitrous Oxide (N2O) Emissions in a Rice-Ratooning System in Central China

The use of oilseed rape (OS, Brassica napus L.) as a winter green manure is crucial for enhancing soil fertility and reducing chemical N application in paddy fields. However, the impacts of replacing varying amounts of chemical N with OS on CH4 and N2O emissions in paddy soils have not been well evaluated. In this study, GHG emissions, soil properties and OS decomposition in a rice-ratooning system with different OS-urea N replacement rates (0%, 25%, 50%, 75% and 100%) were investigated. Our results indicate that 84.7–90.7% of the initial C and 97.5–98.4% of the N were released during the 192-day decomposition process, and that the mineralization patterns of net C and net N in the OS residue were consistent with a single exponential decay model. The lowest CH4 emissions (9.97 g m−2) were observed at 0% OS, while the highest N2O emissions (0.40 g m−2) were observed at this level of substitution. Conversely, the highest CH4 emissions (20.71 g m−2) and lowest N2O emissions (0.07 g m−2) were observed at 100% OS. Compared to 0% substitution, 25% substitution significantly decreased GWP and GHGI without reducing rice grain yield. Environmental parameters such as soil redox, NH4+-N and residual N and C were shown to be significantly associated with CH4 emissions, whereas soil redox, NH4+-N and residual C were the main drivers of N2O emissions. In conclusion, 25% substitution of OS was the most cost-effective measure for balancing greenhouse gas emission and rice yield.

Analysis of the Coupling Coordinated Development of the Water-Soil-Energy-Carbon System in Northwest China

The intricate interplay between water resources, land resources, energy systems, and carbon emissions has emerged as a prominent discourse in academic research. Nonetheless, there remains a dearth of comprehensive research dedicated to fostering environmentally friendly and low-carbon development through systematic integration and coordination efforts. This study aimed to fill this gap by integrating the coupling mechanism of the Water-Land-Energy-Carbon (WLEC) system, thereby constructing an evaluation index framework that assesses coordinated developments in Northwest China’s WLEC system. It scrutinizes the security levels within the Water-Land-Energy (WLE) subsystem while conducting quantitative analyses on the degrees of coupling coordination within the WLEC systems, alongside their associated hindering factors. The preliminary findings were as follows: Firstly, the safety development within the WLE system demonstrates a positive trend across Northwest China, with notable advancements primarily observed in the Qinghai and Gansu provinces. In 2021, all five Northwestern provinces exhibited moderate levels of safe development, except for the Qinghai province, which transitioned from moderate to robust. Secondly, the coupling coordination degree of the WLEC system across the five provinces has consistently illustrated an upward trajectory over the years. However, as of 2021, the system remains in a state characterized by marginal disorder. Notably, the Qinghai and Gansu provinces have shown particularly encouraging upward trends, with the Shaanxi province also making notable progress. Conversely, Xinjiang has declined since 2017 due to negative interactions between the subsystems of water, soil, energy, and carbon emissions. Thirdly, spatial variations exist in the distribution patterns between the provinces regarding the influence of obstructing factors on indicators related to coupled coordinated development, such as per capita arable land area, per capita energy consumption, per capita carbon emissions, per capita construction land area, and the proportion of groundwater water in the total amount of water supply, which demonstrated an increasing trend. These findings carry significant practical implications for actively and steadily promoting carbon peaking and carbon neutrality in Northwest China.

Erosion rate of lunar soil under a landing rocket, part 1: Identifying the rate-limiting physics

Multiple nations are planning activity on the Moon's surface, and to deconflict lunar operations we must understand the sandblasting damage from rocket exhaust blowing soil. Prior research disagreed over the scaling of the erosion rate, which determines the magnitude of the damage. Reduced gravity experiments and two other lines of evidence now indicate that the erosion rate scales with the kinetic energy flux at the bottom of the laminar sublayer of the gas. Because the rocket exhaust is so fast, eroded particles lifted higher in the boundary layer do not impact the surface for kilometers (if at all; some leave the Moon entirely), so there is no saltation in the vicinity of the gas. As a result, there is little transport of gas kinetic energy from higher in the boundary layer down to the surface, so the emission of soil into the gas is a surprisingly low energy process. In low lunar gravity, a dominant source of resistance to this small energy flux turns out to be the cohesive energy density of the lunar soil, which arises primarily from particles in the 0.3 to 3 μm size range. These particles constitute only a tiny fraction of the mass of lunar soil and have been largely ignored in most studies, so they are poorly characterized.

Effect of rice hull biochar treatment on net ecosystem carbon budget and greenhouse gas emissions in Chinese cabbage cultivation on infertile soil

Biochar, with its potential to enhance soil fertility, sequester carbon, boost crop yields and reduce greenhouse gas emissions, offers a solution. Addressing the challenges posed by climate change is crucial for food security and agriculture. However, its widespread adoption in agriculture remains in its infancy. This study assessed the effects of rice hull biochar on cabbage production and greenhouse gas emissions, especially nitrous oxide (N2O). A trial, employing a randomized block design in triplicate was conducted from September 13 to November 23, 2022, where "Cheongomabi" cabbage was cultivated with N-P2O5-K2O fertilization at 32-\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$-$$\\end{document}7.8-\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$-$$\\end{document}19.8 kg 10a−1. Additional fertilizer was applied twice post-sowing. The Biochar application rates were control = 0 ton ha−1, B1 = 1 ton ha−1, B3 = 3 ton ha−1, and B5 = 5 ton ha−1. The aboveground biomass of autumn cabbage harvested 82 days after sowing was 2.40–2.70 kg plant−1 in the control and biochar treatments (B1, B3, and B5), with no significant differences (p > 0.05). Cumulative CO2 emissions during cultivation varied across treatment groups, with initial and cumulative emissions of 10.40–17.94 g m−2 day−1 and 3.63–4.43 ton ha−1, respectively. N2O emissions decreased with higher biochar application: reductions of 2.9%, 25.4%, and 41.1% in the B1, B3, and B5 treatments, respectively, compared to the control. The biochar application had no significant impact on yield but curbed soil emissions, Net ecosystem carbon balance during cabbage cultivation ranged from 0.42 to 3.41 ton ha−1 for the B1, B3, and B5 treatments, respectively, compared to control. Overall, the study underscores biochar’s role in mitigating emissions and boosting soil carbon during cabbage cultivation in fall.

Insights into the abundance, expression and diversity of key denitrification genes in an ecologically managed greenhouse agricultural soil

Understanding the bacteria associated with nitrification and denitrification is crucial for comprehending the processes that lead to nitrous oxide emissions in agricultural greenhouse soils. Therefore, it is important to determine their abundance and expression to gain insight into these processes.The aim of this study was to explore the bacterial communities associated with denitrification in a greenhouse agricultural soil amended with crop residues and manure for six years. For this purpose, we proceeded to detect and quantify the genes nirK and nirS and the gene nosZ through clone library construction, sequencing, phylogenetic analysis, and quantitative polymerase chain reaction (qPCR). Sequence analysis based on the clone library revealed that many of the nirS or nirK genes detected were not closely related to known denitrifier bacteria, but some of the nosZ sequences were related to the genera such as Pseudomonas, Halomonas, and Marinobacter. Furthermore, the qPCR revealed a high abundance of DNA copies in nirK, 6.08 × 109 ± 1.16 × 109, while nirS and nosZ showed lower values, 9.05 × 106 ± 1.65 × 106 and 8.71 × 106 ± 1.44 × 106, respectively. However, the highest expression rate was observed for nirS (mRNA/DNA ratio = 3.10 × 10− 3), while nirK and nosZ showed 10-fold lower expression rates (4.4 × 10− 4 and 3.5 × 10− 4, respectively). The results of this work provide a preliminary overview of the diversity, abundance and expression of key genes associated with the denitrification process in this type of soil and are a starting point for further studies to understand how this type of soil management can influence the denitrification process.

The Impact of Agroecosystems on Nitrous Acid (HONO) Emissions during Spring and Autumn in the North China Plain.

Solar radiation triggers atmospheric nitrous acid (HONO) photolysis, producing OH radicals, thereby accelerating photochemical reactions, leading to severe secondary pollution formation. Missing daytime sources were detected in the extensive HONO budget studies carried out in the past. In the rural North China Plain, some studies attributed those to soil emissions and more recent studies to dew evaporation. To investigate the contributions of these two processes to HONO temporal variations and unknown production rates in rural areas, HONO and related field observations obtained at the Gucheng Agricultural and Ecological Meteorological Station during spring and autumn were thoroughly analyzed. Morning peaks in HONO frequently occurred simultaneously with those of ammonia (NH3) and water vapor both during spring and autumn, which were mostly caused by dew and guttation water evaporation. In spring, the unknown HONO production rate revealed pronounced afternoon peaks exceeding those in the morning. In autumn, however, the afternoon peak was barely detectable compared to the morning peak. The unknown afternoon HONO production rates were attributed to soil emissions due to their good relationship to soil temperatures, while NH3 soil emissions were not as distinctive as dew emissions. Overall, the relative daytime contribution of dew emissions was higher during autumn, while soil emissions dominated during spring. Nevertheless, dew emission remained the most dominant contributor to morning time HONO emissions in both seasons, thus being responsible for the initiation of daytime OH radical formation and activation of photochemical reactions, while soil emissions further maintained HONO and associated OH radial formation rates at a high level, especially during spring. Future studies need to thoroughly investigate the influencing factors of dew and soil emissions and establish their relationship to HONO emission rates, form reasonable parameterizations for regional and global models, and improve current underestimations in modeled atmospheric oxidation capacity.

Partial substitution of manure increases N2O emissions in the alkaline soil but not acidic soils

The fertilization regimes of combining manure with synthetic fertilizer are benefits for crop yields and soil fertility in cropping systems as compared to sole synthetic fertilization, but the responses of nitrous oxide (N2O) emissions to these practices are inconsistent in the literatures. We hypothesized that it is caused by different proportions of nitrogen (N) applied as manure and various soil properties. Here, we conducted a microcosm experiment, and measured the N2O emissions from control (no N) and five manure substitution treatments (supplied 100 mg N kg−1 using the combination of urea with manure) with a range of proportions of N applied as manure (0, 25%, 50%, 75%, and 100%) in three different soil types (fluvo-aquic soil, black soil, and latosol) under aerobic condition. The stimulated effect on N2O emissions was more pronounced after manure application in an alkaline soil with high nitrification rate, due to relatively rapid soil DOC depletion and N mineralization of manure. N2O emissions from partial substitution of urea with manure were significantly higher than manure-only addition under high soil pH due to abundant labile C from manure. However, there was no difference between manure substitution treatments under acid soils. Nitrification inhibitor substantially decreased N2O emissions with increasing soil pH, but it was less effective in mitigating N2O emissions with larger proportion of manure. This is likely due to the slow nitrification under low soil pH, and denitrification derived N2O increased with increasing manure application rate. Collectively, our study shows that the application of manure substitution to alkaline soils requires careful consideration, which might have rapid nitrification potential and hence trigger significant N2O emissions. The knowledge gained in this work will help the decision-makers in optimizing a sound N fertilization regime interacted with soil properties for sustainable crop production and N2O mitigation.

Dual isotopic evidence of δ15N and δ18O for priority control of vehicle emissions in a megacity of East China: Insight from measurements in summer and winter

The source apportionment and main formation pathway of nitrate aerosols in China are not yet fully understood. In this study, PM2.5 samples were collected in Shanghai in the summer and winter of 2019. Water-soluble inorganic ions and isotopic signatures of stable nitrogen (δ15N-NO3−) and stable oxygen (δ18O-NO3−) in PM2.5 were determined. The results showed that NO3− was less important in summer (NO3−/SO42− = 0.4 ± 0.8), while it became the dominant species in winter (52.1 %). The average values of δ15N-NO3− and δ18O-NO3− in summer were + 2.0 ± 6.1 ‰ and 63.3 ± 9.4 ‰ respectively, which were significantly lower than those in winter (+7.2 ± 3.4 ‰ and 88.3 ± 12.1 ‰), indicating discrepancies between NOx sources and nitrate formation pathways. Both δ15N-NO3− and δ18O-NO3− were elevated at night, demonstrating that N2O5 hydrolysis contributed to the nocturnal nitrate increase even in summer. The contribution of the OH oxidation pathway to nitrate aerosols averaged at 70.5 ± 17.0 % in summer and N2O5 hydrolysis dominated the nitrate production in winter (approximately 80 %). On average, vehicle exhaust, coal combustion, natural gas burning, and soil emission contributed 50.7 %, 21.5 %, 15.9 %, and 11.9 %, respectively, to nitrate aerosols in summer, and contributed 56.8 %, 23.9 %, 13.6 %, and 5.7 %, respectively, to nitrate production in winter. Notably, natural gas burning is a non-negligible source of nitrate aerosols in Shanghai. In contrast to an inverse correlation between δ15N-NO3− and PM2.5, the value of δ18O-NO3− was positively correlated with nitrate concentration and aerosol liquid water content (ALWC) in winter, suggesting that explosive growth of nitrate was driven by continuous accumulation of N-depleted NOx and rapid N2O5 hydrolysis under calm and humid conditions. To continuously improve air quality, priority control should be given to vehicle emissions as the dominant source of NOx and volatile organic compounds (VOCs) in Shanghai.

Microbial communities overwhelm environmental controls in explaining nitrous oxide emission in acidic soils

Intensively fertilized acidic soils are global hotspots of nitrous oxide (N2O) emissions, contributing to net agronomic greenhouse gas outcomes. Identifying the key drivers of soil N2O emissions is hampered by the synergistic or antagonistic effects of multiple factors. Within a framework based on the predominant role of microbial communities producing N2O, the N2O emissions are affected either by proximal regulators: temporary soil property fluctuations affect N2O production transcriptionally, or by distal regulators: persistent genetic rearrangements in local microbial communities. The proximal regulators, individually or together, may spontaneously impact distal regulators. Here, we use acidic soils from tea (Camellia sinensis L.) plantations on a broader geographic scale as a model system. Based on amplicon sequencing and properties of 195 acidic (average pH = 5.0) soils, we determined the importance of proximal and distal regulation to N2O emissions. Microbial phylogenetic diversity as a distal regulator overwhelms mineral N content as a proximal regulator in explaining high N2O emissions. Low-abundance, diverse prokaryotic communities (e.g., Acidothermu) and specialized denitrifying fungal communities (e.g., Fusarium) were associated with high N2O emissions. Revisiting the impact of proximal regulators on distal regulators revealed that soil pH is the sole proximal regulator influencing the prokaryotic rare taxa that correlated with high N2O emissions. When considering proximal regulators together (here soil properties compiled as soil fertility index), the microbial diversity were independent of soil fertility. The microbial assembly was dominated by stochastic processes. Consequently, proximal regulators have a limited impact on distal regulators of N2O emissions from acidic soils. In conclusion, the framework underscored the importance of in situ microbial communities as distal regulators in explaining high N2O emissions from acidic soils.

Sources of NH4+ in PM2.5 and Their Seasonal Variations in Urban Tianjin China: New Insights From the Seasonal δ15N Values of NH3 Source

AbstractThe stable nitrogen isotopic composition (δ15N) has been widely used to quantify sources of ammonium (NH4+) in PM2.5. However, the overlap and uncertainty in δ15N values from different NH3 sources, coupled with their seasonal variability, hinder accurate identification of NH4+ source. Here, the δ15N values of various NH3 source samples collected by the active sampler were determined. Subsequently, we measured the δ15N values of NH4+ in PM2.5, which were collected seasonally in Tianjin. We found that the combustion‐related NH3 (c‐NH3) exhibiting higher δ15N values compared to volatile NH3 (v‐NH3), but all δ15N values was fell within the range reported by previous studies. Furthermore, inconsistent seasonal variations were observed in the δ15N‐NH3 values originating from emissions of agricultural soil and human excreta. The application of the Bayesian isotope mixing model (MixSIAR model) revealed a significant increase in the contribution of v‐NH3 to NH4+ when incorporating current source data, as opposed to previous data, for δ15N of NH3 source. Notably, the contribution of v‐NH3 (53.1%) to NH4+ was almost equivalent to that of c‐NH3 (46.9%) when considering the seasonal δ15N signatures of NH3 source. Additionally, the estimated contribution of v‐NH3 to NH4+ exhibited significant seasonal variability, which is more reasonable than in the non‐seasonal scenario. This study demonstrated that v‐NH3 and c‐NH3 contributed to NH4+ in PM2.5 in Tianjin almost equally, and it is highlighted that the seasonal δ15N values of NH3 sources should be considered when estimating the contributions of different NH3 sources to NH4+ in PM2.5 by the MixSIAR model.

Insights into anthropogenic impact on atmospheric inorganic aerosols in the largest city of the Tibetan Plateau through multidimensional isotope analysis

Particulate inorganic nitrogen aerosols (PIN) significantly influence air pollution and pose health risks worldwide. Despite extensive observations on ammonium (pNH4+) and nitrate (pNO3−) aerosols in various regions, their key sources and mechanisms in the Tibetan Plateau remain poorly understood. To bridge this gap, this study conducted a sampling campaign in Lhasa, the Tibetan Plateau's largest city, with a focus on analyzing the multiple isotopic signatures (δ15N, ∆17O). These isotopes were integrated into a Bayesian mixing model to quantify the source contributions and oxidation pathways for pNH4+ and pNO3−. Our results showed that traffic was the largest contributor to pNH4+ (31.8 %), followed by livestock (25.4 %), waste (21.8 %), and fertilizer (21.0 %), underscoring the impact of vehicular emissions on urban NH3 levels in Lhasa. For pNO3−, coal combustion emerged as the largest contributor (27.3 %), succeeded by biomass burning (26.3 %), traffic emission (25.3 %), and soil emission (21.1 %). In addition, the ∆17O-based model indicated a dominant role of NO2 + OH (52.9 %) in pNO3− production in Lhasa, which was similar to previous observations. However, it should be noted that the NO3 + volatile organic component (VOC) contributed up to 18.5 % to pNO3− production, which was four times higher than the Tibetan Plateau's background regions. Taken together, the multidimensional isotope analysis performed in this study elucidates the pronounced influence of anthropogenic activities on PIN in the atmospheric environment of Lhasa.

Spatiotemporal Analysis of Soil Quality Degradation and Emissions in the State of Iowa (USA)

The concept of soil quality (SQ) is defined as the soil's capacity to function, which is commonly assessed at the field scale. Soil quality is composed of inherent (soil suitability) and dynamic (soil health, SH) SQ, which can also be analyzed using geospatial tools as a SQ continuum (SQC). This study proposes an innovative spatiotemporal analysis of SQ degradation and emissions from land developments using the state of Iowa (IA) in the United States of America (USA) as a case study. The SQ degradation was linked to anthropogenic soil (SD) and land degradation (LD) in the state. More than 88% of land in IA experienced anthropogenic LD primarily due to agriculture (93%). All six soil orders were subject to various degrees of anthropogenic LD: Entisols (75%), Inceptisols (94%), Histosols (59%), Alfisols (79%), Mollisols (93%), and Vertisols (98%). Soil and LD have primarily increased between 2001 and 2016. In addition to agricultural LD, there was also SD/LD caused by an increase in developments often through urbanization. All land developments in IA can be linked to damages to SQ, with 8385.9 km2 of developed area, causing midpoint total soil carbon (TSC) losses of 1.7 × 1011 kg of C and an associated midpoint of social cost of carbon dioxide emissions (SC-CO2) of $28.8B (where B = billion = 109, USD). More recently developed land area (398.5 km2) between 2001 and 2016 likely caused the midpoint loss of 8.0 × 109 kg of C and a corresponding midpoint of $1.3B in SC-CO2. New developments are often located near urban areas, for example, near the capital city of Des Moines, and other cities (Sioux City, Dubuque). Results of this study reveal several different kinds of SQ damage from developments: loss of potential for future C sequestration in soils, soil C loss, and “realized” soil C social costs (SC-CO2). The state of IA has very limited potential land (2.0% of the total state area) for nature-based solutions (NBS) to compensate for SD and LD. The results of this study can be used to support pending soil health-related legislation in IA and monitoring towards achieving the Sustainable Development Goals (SDGs) developed by the United Nations (UN) by providing a landscape-level perspective on LD to focus field-level initiatives to reduce soil loss and improve SQ. Future technological innovations will provide higher spatial and temporal remote sensing data that can be fused with field-level direct sensing to track SH and SQ changes.

Assessment major NOx sources to nitrate of TSP around the Danjiangkou reservoir using isotopes and a Bayesian isotope mixing model

Nitrate (NO3−) is a key component of atmospheric particulate matter. However, studies quantifying NO3− formation and sources in water source areas remain scarce. This study employs NO3− concentration, dual isotopic analyses (δ15N, δ18O), and SIAR and PSCF models to elucidate NO3− formation mechanisms and apportion sources in the Danjiangkou Reservoir area. The result showed that the concentration of NO3− (0.52 μg m−3-2.39 μg m−3), δ15N–NO3- (−2.3‰-4.2‰) and δ18O–NO3- (64.2‰–96.6‰) values varied seasonally in total suspended particulate matter (TSP). The contribution of the NO2 + ·OH pathway was the highest in summer (84%), while the main contributions came from the N2O5 + H2O and NO3 + VOCs pathways in winter (75%). The SIAR model revealed that the contributions of coal combustion and traffic emissions were 34% and 23%, respectively, indicating that fossil fuel release contributed most. Moreover, the contribution of biomass combustion sources was 31%, and soil emission sources had the least (12%). Considering liquefied petroleum gas, gasoline, and diesel vehicles as traffic emission sources, their contribution to NO3− in TSP increased to 50%. The PSCF analysis indicated that external input areas were predominantly from central Henan Province, northern Hubei Province, and central Shaanxi Province. This study quantitatively analyzed the sources of NO3− in atmospheric particulate matter in water sources for the first time, indicating that controlling the emissions of nitrogen oxides from gasoline cars, heavy-duty diesel trucks, and ships could help alleviate haze pollution and enhance air quality in the Danjiangkou reservoir area.