Ammonia (NH₃) volatilized from soils plays an important role in N cycle and air pollution, thus it is important to trace the emission source and predict source contributions to development strategies mitigating the environmental harmful of soil NH₃ volatilization. The measurements of ¹⁵N natural abundance (δ¹⁵N) could be used as a complementary tool for apportioning emissions sources to resolve the contribution of multiple NH₃ emission sources to air NH₃ pollution. However, information of the changes of δ¹⁵N–NH₃ values during the whole volatilization process under different N application rates are currently lacking. Hence, to fill this gap, we conducted a 15-day incubation experiment included different urea-N application rates to determine δ¹⁵N values of NH₃ during volatilization process. Results showed that volatilization process depleted ¹⁵N in NH₃. The average δ¹⁵N value of NH₃ volatilized from the 0, 20, 180, and 360 kg N ha⁻¹ treatment was −16.2 ± 7.3‰, −26.0 ± 5.4‰, −34.8 ± 4.8‰, and −40.6 ± 5.7‰. Overall, δ¹⁵N–NH₃ values ranged from −46.0‰ to −4.7‰ during the whole volatilization process, with lower in higher urea-N application treatments than those in control. δ¹⁵N–NH₃ values during the NH₃ volatilization process were much lower than those of the primary sources, soil (−3.4 ± 0.1‰) and urea (−3.6 ± 0.1‰). Therefore, large isotopic fractionation may occur during soil volatilization process. Moreover, negative relationships between soil NH₄⁺-N and NH₃ volatilization rate and δ¹⁵N–NH₃ values were observed in this study. Our results could be used as evidences of NH₃ source apportionments and N cycle.

Decision-making related to nitrogen (N) fertilization is a crucial step in agronomic practices because of its direct interactions with agronomic productivity and environmental risk. Here, we hypothesized that soil apparent N balance could be used as an indicator to determine the thresholds of N input through analyzing the responses of the yield and N loss to N balance. Based on the observations from 951 field experiments conducted in rice (Oryza sativa L.) cropping systems of China, we established the relationships between N balance and ammonia (NH₃) volatilization, yield increase ratio, and N application rate, respectively. Dramatical increase of NH₃ volatilizations and stagnant increase of the rice yields were observed when the N surplus exceeded certain levels. Using a piecewise regression method, the seasonal upper limits of N surplus were determined as 44.3 and 90.9 kg N ha⁻¹ under straw-return and straw-removal scenarios, respectively, derived from the responses of NH₃ volatilization, and were determined as 53.0–74.9 and 97.9–112.0 kg N ha⁻¹ under straw-return and straw-removal scenarios, respectively, derived from the maximum-yield consideration. Based on the upper limits of N surplus, the thresholds of N application rate suggested to be applied in single, middle-MLYR, middle-SW, early, and late rice types ranged 179.0–214.9 kg N ha⁻¹ in order to restrict the NH₃ volatilization, and ranged 193.3–249.8 kg N ha⁻¹ in order to achieve the maximum yields. If rice straw was returned to fields, on average, the thresholds of N application rate could be theoretically decreased by 17.5 kg N ha⁻¹. This study provides a robust reference for restricting the N surplus and the synthetic fertilizer N input in rice fields, which will guide yield goals and environmental protection.

Alberta’s oil sands tailings ponds are suspected to be a source of fugitive emissions of polycyclic aromatic compounds (PACs) to the atmosphere. Here we report, for the first time, fluxes of 6 parent and 21 alkylated PACs based on the measured co-located air and water concentrations using a two-film fugacity-based model (FUG), an inverse dispersion model (DISP) and a simple box model (BOX). Air samples were collected at the Suncor Tailings Pond 2/3 using a high volume air sampler from the “pond” and towards the pond (“non-pond”) directions separately. Mean ∑₂₇PACs in air from the “pond” direction was greater than the “non-pond” direction by a factor of 17. Water-air fugacity ratio of 20 PACs quantifiable in water indicated net volatilization from water. Dispersion and box model results also indicated upward fluxes of 22 PACs. Correlation between the estimated flux results of BOX and DISP model was statistically significant (r = 0.99 and p < 0.05), and correlation between FUG and DISP results ranged from 0.54 to 0.85. In this first-ever assessment of PAC fluxes from tailings pond, the three models confirmed volatilization fluxes of PACs indicating Suncor Tailings Pond 2/3 is a source of PAC emissions to the atmosphere. This study addressed a key data gap identified in the Joint Oil Sands Monitoring Emissions Inventory Compilation Report (Government of Alberta and Canada, 2016) which is the lack of consistent real-world tailings pond fugitive emission monitoring of organic chemicals. Our findings highlight the need for measurements from other tailings ponds to determine their overall contribution in releasing PACs to the atmosphere. This paper presents a practical method for estimating PAC emissions from other tailings ponds, which can provide a better understanding of these fugitive emissions, and thereby help to improve the overall characterization of emissions in the oil sands region.

The combined application of organic and synthetic nitrogen (N) fertilizers is being widely recommended in China’s vegetable systems to reduce reliance on synthetic N fertilizer. However, the effect of substituting synthetic fertilizer with organic fertilizer on vegetable productivity (yield, N uptake and nitrogen use efficiency) and reactive nitrogen (Nr) losses (N₂O emission, N leaching and NH₃ volatilization) remains unclear. A meta-analysis was performed using peer-reviewed papers published from 2000 to 2019 to comprehensively assess the effects of combined application of organic and synthetic N fertilizers. The results indicate that overall, the vegetable yield, N₂O emission and NH₃ volatilization were not significantly changed, whereas N leaching was reduced by 44.6% and soil organic carbon (SOC) concentration increased by 12.5% compared to synthetic N fertilizer alone. Specifically, when synthetic N substitution rates (SRs) were ≤70%, vegetable yields and SOC concentration were increased by 5.5%–5.6% and 13.1–18.0%, and N leaching was reduced by 41.6%–48.1%. At the high substitution rate (SR>70%), vegetable yield was reduced by 13.6%, N₂O emission was reduced by 14.3%, and SOC concentration increased by 16.4%. Mixed animal-plant sources of organic N preferentially increased vegetable yield and SOC concentration, and reduced N₂O emission and N leaching compared with single sources of organic-N. Greenhouse gas (GHG) emission was decreased by 28.4%–34.9% by combined applications of organic and synthetic N sources, relative to synthetic N fertilizer alone. We conclude that appropriate rates (SR ≤ 70%) of combined applications of organic and synthetic N fertilizers could improve vegetable yields, decrease Nr and GHG emission, and facilitate sustainable development of coupled vegetable-livestock systems.

Livestock manure has been widely used in agriculture to improve soil productivity and quality. However, intensive application can significantly enhance soil nitrogen (N) availability and facilitate ammonia (NH₃) volatilization during rice cultivation. The effects of different rates of manure application on the NH₃ volatilization rate, its mechanism, and their relationships have not been comprehensively investigated. In this study, field trials were conducted to investigate NH₃ volatilization in rice paddy soils amended with different livestock manure, cattle manure (CM), and swine manure (SM), at a rate of 0 (NPK), 10, 20, and 40 Mg ha⁻¹ during cultivation. Moreover, the soil physicochemical and biological properties and rice N uptake were investigated. Ultra-fine particulate matter (PM₂.₅) was measured quantitatively and qualitatively. Manure application significantly increased NH₃ emissions compared to the control. Much higher volatilization rates were observed in the SM soils than in the CM soils, even when the same amount of N was applied. This is mainly related to the higher labile NH₄⁺ concentration and urease activity in SM soils. With increasing application levels, NH₃ emission rates proportionally increased in the SM, but there was no significant difference in the CM. Livestock manure application significantly increased NH₃ volatilization, particularly during the initial manure application and additional fertilization stages during rice cultivation. The results showed that the application of livestock manure significantly increased NH₃ volatilization. Moreover, the biochemical properties of manure composts, including labile N and urease activity, mainly affected NH₃ dynamics in rice paddies during cultivation rather than their type. Irrespective of manure application, PM₂.₅, did not show a significant difference at the initial stage of cultivation. NH₃ volatilization was not significantly correlated with the formation of PM₂.₅. It is necessary to develop effective strategies for mitigating NH₃ volatilization and maintaining soil quality without decreasing rice productivity in paddy ecosystems.

After decades of imposed regulations about reducing the primary emissions of persistent organic pollutants (POPs), these pollutants are still present in the environment. Soils are important repositories of such persistent semivolatile organic contaminants (SVOCs), and it is assumed that SVOCs sequestered in these reservoirs are being re-mobilized due to anthropogenic influence. In this study, concentrations of organochlorine pesticides (OCPs), polychlorinated biphenyls (PCBs), and polybrominated diphenyl ethers (PBDEs) in soil and air, their fugacities, fluxes and the soil-air partition coefficient (KSA) were determined for three different land cover types (glacial, remote/mountainous and urban) of the Lesser Himalayan Region (LHR). The concentrations of OCPs, PCBs and PBDEs in soils and air ranged between 0.01 and 2.8, 0.81–4.8, 0.089–0.75 ng g⁻¹; 0.2–106, 0.027–182, and 0.011–7.26 pg m⁻³, respectively. The levels of SVOCs in the soil were correlated with soil organic matter (SOM) indicating that SOM is a substrate for the organic pollutants in soils. The Clausius-Clapeyron plots between ln P and inverse of temperature (1000/T) suggested that long range atmospheric transport was the major input source of PBDEs and higher chlorinated PCBs over the LHR. The uneven and wide distribution of local sources in LHR and up-slope enrichment of SVOCs explained the spatial variability and altitudinal patterns. The soils near mountain and urban lakes act as local sinks of SVOCs such as β-HCH, pp΄-DDT, CB-28, -118, −153, BDE-47, -99, and −154, with soil-air exchange fluxes tending more toward deposition. However, the soils near glacial lakes acted as local sources of more volatile congeners of α-HCH, γ-HCH, op′-DDT, pp′-DDE and lower to medium chlorinated PCBs such as CB-18, -28, −53, −42 and BDE-47, -99, with soil-air exchange tending more toward volatilization flux.

Microbial-mediated Sb volatilization is a poorly understood part of the Sb biogeochemical cycle. This is mostly due to a lack of laboratory and field-deployable methods that are capable of quantifying low-level emissions of Sb from diffuse sources. In this study, we validated two methods using a H₂O₂ -HNO₃ liquid chemotrap and an activated coconut shell charcoal solid-phase trap, achieving an absolute limit of detection of 4.6 ng and below 2.0 ng Sb, respectively. The activated charcoal solid-phase trapping method, the most easily operated method, was then applied to contaminated shooting range soils. Four treatments were tested: 1) flooded, 2) manure amended + flooded, 3) 70 % water holding capacity, and 4) manure amendment +70 % water holding capacity, since agricultural practices and flooding events may contribute to Sb volatilization. Volatile Sb was only produced from flooded microcosms and manure amendment greatly influenced the onset and amount of volatile Sb produced. The highest amount of volatile Sb produced, up to 62.1 ng kg⁻¹ d⁻¹, was from the flooded manure amended soil. This suggests that anaerobic microorganisms may potentially be drivers of Sb volatilization. Our results show that polluted shooting range soils are a source of volatile Sb under flooded conditions, which may lead to an increase in the mobility of Sb. Some of these volatile Sb species are toxic and genotoxic, highlighting the role of Sb volatilization on environmental health, especially for individuals living in contaminated areas exposed to wetlands or flooded conditions (e.g., rice paddy agriculture surrounding mining areas). This work paves way for research on Sb volatilization in the environment.

The identification of nitrate (NO₃⁻) sources and biogeochemical transformations is critical for understanding the different nitrogen (N) pathways, and thus, for controlling diffuse pollution in groundwater affected by livestock and agricultural activities. This study combines chemical data, including environmental isotopes (δ²HH₂O, δ¹⁸OH₂O, δ¹⁵NNO₃, and δ¹⁸ONO₃), with land use/land cover data and a Bayesian isotope mixing model, with the aim of reducing the uncertainty when estimating the contributions of different pollution sources. Sampling was taken from 53 groundwater sites in Comarca Lagunera, northern Mexico, during 2018. The results revealed that the NO₃⁻ (as N) concentration ranged from 0.01 to 109 mg/L, with more than 32% of the sites exceeding the safe limit for drinking water quality established by the World Health Organization (10 mg/L). Moreover, according to the groundwater flow path, different biogeochemical transformations were observed throughout the study area: microbial nitrification was dominant in the groundwater recharge areas with elevated NO₃⁻ concentrations; in the transition zones a mixing of different transformations, such as nitrification, denitrification, and/or volatilization, were identified, associated to moderate NO₃⁻ concentrations; whereas in the discharge area the main process affecting NO₃⁻ concentrations was denitrification, resulting in low NO₃⁻ concentrations. The results of the MixSIAR isotope mixing model revealed that the application of manure from concentrated animal-feeding operations (∼48%) and urban sewage (∼43%) were the primary contributors of NO₃⁻ pollution, whereas synthetic fertilizers (∼5%), soil organic nitrogen (∼4%), and atmospheric deposition played a less important role. Finally, an estimation of an uncertainty index (UI90) of the isotope mixing results indicated that the uncertainties associated with atmospheric deposition and NO₃⁻−fertilizers were the lowest (0.05 and 0.07, respectively), while those associated with manure and sewage were the highest (0.24 and 0.20, respectively).

Understanding future climate change requires accurate estimates of the impacts of atmospheric nitrogen (N) deposition, composed of both inorganic and organic compounds, on greenhouse gas (GHG) fluxes in grassland ecosystems. However, previous studies have focused on inorganic compounds and have not considered the potential effects of organic N sources. Here, we conducted a grassland experiment that included organic, inorganic N, and a mix of them at a ratio of 4:6, with two input rates, to study N inputs induced CO₂, CH₄, and N₂O fluxes, as well as the potential abiotic and biotic mechanisms driving the fluxes. We found that N compositions significantly affected fluxes each of the three GHGs. Greater organic N decreased the impacts of N addition on CO₂ and N₂O emissions, caused primarily by low rates of increase in substrates (soil available N) for production of CO₂ and N₂O resulting from high ammonia volatilization rather than changes in microbial activity. Also, greater organic N slightly stimulated CH₄ uptake. Nitrogen composition effects on CO₂ emissions and CH₄ uptake were independent of N input rates and measurement dates, but N₂O emissions showed stronger responses to inorganic N under high N addition and in June. These results suggest that future studies should consider the source of N to improve our prediction of future climate impact of N deposition, and that management of N fertilization can help mitigate GHG emissions.

Ammonia (NH₃) volatilization is one of the main pathways of nitrogen loss from cropland, resulting not only in economic losses, but also environmental and human health impacts. The magnitude and timing of NH₃ emissions from cropland fertilizer application highly depends on agricultural practices, climate and soil factors, which previous studies have typically only considered at coarse spatio-temporal resolution. In this paper, we describe a first highly detailed empirical regression model for ammonia (ERMA) emissions based on 1443 field observations across China. This model is applied at county level by integrating data with unprecedented high spatio-temporal resolution of agricultural practices and climate and soil factors. Results showed that total NH₃ emissions from cropland fertilizer application amount to 4.3 Tg NH₃ yr⁻¹ in 2017 with an overall NH₃ emission factor of 12%. Agricultural production for vegetables, maize and rice are the three largest emitters. Compared to previous studies, more emission hotspots were found in South China and temporally, emission peaks are estimated to occur three months earlier in the year, while the total amount of emissions is estimated to be close to that calculated by previous studies. A second emission peak is identified in October, most likely related to the fertilization of the second crop in autumn. Incorporating these new findings on NH₃ emission patterns will enable a better parametrization of models and hence improve the modelling of air quality and subsequent impacts on ecosystems through reactive N deposition.