An integrative analysis of the role of atmospheric deposition and land management practices on nitrogen in the US agricultural sector

Satellite observations for monitoring atmospheric NO2 in correlation with the existing pollution sources under arid environment

Monitoring of air pollutants using satellite data has been largely improved over the past few decades, which can provide deeper insights into the effects of anthropogenic activities on the air quality. The observations and measurements of atmospheric NO₂ are poorly investigated in North Africa, therefore, the current study applied a multi-proxy approach to better understand of the ambient environment. This approach is based on satellite observations, chemical and biological analyses, and investigative information during fieldworks. The Aura satellite provides the basic data for the current study with fine resolution of atmospheric NO₂ and O₃ concentrations. The obtained results reveal noticeable increases of atmospheric NO₂ values since the 2011, where its emission reaches the peak during summer season that is characterized by high anthropogenic activities. The study area has many sources for NO₂ emissions, such as the urban region, traffic, as well as the NH₃ emission that is in turn converted to NO_2. Although the discharged and spreading wastewater (80,000 m³/day in summer) has a limited role in NO₂ emissions, it represents an indicator of the anthropogenic activities. The wastewater analyses confirm the occurrence of nitrate (NO₃⁻), nitrite (NO₂⁻), and ammonia (NH₄⁺), which provide an appropriate condition for NO₂ release. The analyses of multi-climate datasets (previous records and the expected scenarios) reveal an increase of temperature accompanied by decrease of precipitation which confirmed the existence of climate change. Therefore, the study presents a set of suggestions to mitigate the release of NOx gases and achieve Net-Zero emissions.

Wet deposition of atmospheric nitrogen contributes to nitrogen loading in the surface waters of Lake Tanganyika, East Africa: a case study of the Kigoma region

Lake Tanganyika, an African Great Lake, is a complex tropical ecosystem that has been subjected to extreme climate-related changes in the last century, including seasonal changes in temperature and rainfall, decreased overall annual rainfall, and greater frequency of rainstorms. Atmospheric nitrogen (N) is an important component of the lake's N loading, but how long-term and seasonal changes in precipitation affect this loading still needs clarification. This study aimed to improve our understanding of the seasonal features of N deposition in the lake, by monitoring atmospheric N deposition concentrations and fluxes from March 2013 to February 2014. There was a significant temporal variation in wet N depositions in the study area. The distribution of the annual rainfall into major (March-May 299.8 mm) and minor (October-December 343.2 mm) rainy seasons translated into 20 and 30% of N deposition. In September and January-February, there was 10 and 12% precipitation, representing 43 and 7% of N deposition in the lake. Nitrogen deposition was highest in September due to farmlands' burning during the dry season (June-August), leading to N accumulation in the atmosphere. In conclusion, the pattern of N deposition appears to be driven by the unique climatic characteristics of the lake basin and to be closely associated with local anthropogenic activities.

Ammonia in the atmosphere: a review on emission sources, atmospheric chemistry and deposition on terrestrial bodies

Gaseous ammonia (NH3) is the most abundant alkaline gas in the atmosphere. In addition, it is a major component of total reactive nitrogen. The largest source of NH3 emissions is agriculture, including animal husbandry and NH3-based fertilizer applications. Other sources of NH3 include industrial processes, vehicular emissions and volatilization from soils and oceans. Recent studies have indicated that NH3 emissions have been increasing over the last few decades on a global scale. This is a concern because NH3 plays a significant role in the formation of atmospheric particulate matter, visibility degradation and atmospheric deposition of nitrogen to sensitive ecosystems. Thus, the increase in NH3 emissions negatively influences environmental and public health as well as climate change. For these reasons, it is important to have a clear understanding of the sources, deposition and atmospheric behaviour of NH3. Over the last two decades, a number of research papers have addressed pertinent issues related to NH3 emissions into the atmosphere at global, regional and local scales. This review article integrates the knowledge available on atmospheric NH3 from the literature in a systematic manner, describes the environmental implications of unabated NH3 emissions and provides a scientific basis for developing effective control strategies for NH3.

Nitrogen multitemporal monitoring through mosses in urban areas affected by mud volcanoes around Mt. Etna, Italy

Nitrogen emissions were assessed by using mosses as bioindicators in a densely inhabited area affected by mud volcanoes. Such volcanoes, locally called Salinelle, are phenomena that occur around Mt. Etna (Sicily, Italy), and are interpreted as the surface outflow of a hydrothermal system located below Mt. Etna, which releases sedimentary fluids (hydrocarbons and Na-Cl brines) along with magmatic gases (mainly CO2 and He). To date, N emissions from such mud volcanoes have been only quantitatively assessed, and no biomonitoring campaigns are reported about the cumulative effects of these emissions. This study analyzed N concentrations in moss, water and soil samples, collected in a 4-year monitoring campaign. The bryophyte Bryum argenteum, a species widely adopted in surveys of atmospheric pollution, was used as a biological indicator. N concentrations in biomonitors showed relatively low values in the study sites. However, the results of this study suggest that N emissions from Salinelle may have an impact on surrounding ecosystems because N values in moss and water showed a significant correlation. N oxides, in particular, contribute to acidification of ecosystems, thus multitemporal biomonitoring is recommended, especially in those areas where N emitting sources are anthropogenic and natural.

Three-year monitoring results of nitrate and ammonium wet deposition in Thailand

Wet deposition is one of the important sources of nitrogen input into the ecosystem. It also contributes to rain acidity in some environments. In this study we reported the annual as well as seasonal trends of nitrogen wet deposition at three locations in Thailand: Bangkok, Chiang Mai and Nan. Comparison of nitrogen wet deposition between in rural and in the urban areas was also made. Daily rainfall was measured and monthly rainwater was collected for nitrogen analysis during 1999-2002. The average NO3- concentration in rainwater collected from the rural sites (60 km from urban area) was around 0.2-0.3 mg L(-1), while that from the urban areas of Chiang Mai and Nan cities it was 0.4-0.5 mg L(-1). NH4+ concentration in rainwater showed the similar ranges to that of NO3-, except at Nan where concentration was not significantly different between the urban and rural sites. On the other hand, the average concentrations of NO3- were higher at Bangkok site than other sites, while concentration of NH4+ was almost the same between Chiang Mai and Bangkok. Wet deposition of NO3- at the rural sites of Chiang Mai and Nan ranged from 2.1 to 3.2 kg N ha(-1) yr(-1), while at the urban sites this ranged from about 6 kg N ha(-1) yr(-1) in Chiang Mai and Nan Cities to 8.6 kg N ha(-1) yr(-1) in Bangkok. Wet deposition of NH4+ at the rural sites of Chiang Mai and Nan was about 2.4 to 3.6 kg N ha(-1) yr(-1) and at the urban sites of Chiang Mai, Nan and Bangkok this was 7.7, 4.9 and 8.1 kg N ha(-1) yr(-1), respectively. Thus, it was concluded that wet deposition of both nitrogen species was significantly higher at the urban sites than at the rural sites.

Effects of atmospheric ammonia (NH3) on terrestrial vegetation: a review

At the global scale, among all N (nitrogen) species in the atmosphere and their deposition on to terrestrial vegetation and other receptors, NH3 (ammonia) is considered to be the foremost. The major sources for atmospheric NH3 are agricultural activities and animal feedlot operations, followed by biomass burning (including forest fires) and to a lesser extent fossil fuel combustion. Close to its sources, acute exposures to NH3 can result in visible foliar injury on vegetation. NH3 is deposited rapidly within the first 4-5 km from its source. However, NH3 is also converted in the atmosphere to fine particle NH4+ (ammonium) aerosols that are a regional scale problem. Much of our current knowledge of the effects of NH3 on higher plants is predominantly derived from studies conducted in Europe. Adverse effects on vegetation occur when the rate of foliar uptake of NH3 is greater than the rate and capacity for in vivo detoxification by the plants. Most to least sensitive plant species to NH3 are native vegetation > forests > agricultural crops. There are also a number of studies on N deposition and lichens, mosses and green algae. Direct cause and effect relationships in most of those cases (exceptions being those locations very close to point sources) are confounded by other environmental factors, particularly changes in the ambient SO2 (sulfur dioxide) concentrations. In addition to direct foliar injury, adverse effects of NH3 on higher plants include alterations in: growth and productivity, tissue content of nutrients and toxic elements, drought and frost tolerance, responses to insect pests and disease causing microorganisms (pathogens), development of beneficial root symbiotic or mycorrhizal associations and inter species competition or biodiversity. In all these cases, the joint effects of NH3 with other air pollutants such as all-pervasive O3 or increasing CO2 concentrations are poorly understood. While NH3 uptake in higher plants occurs through the shoots, NH4+ uptake occurs through the shoots, roots and through both pathways. However, NH4+ is immobile in the soil and is converted to NO3- (nitrate). In agricultural systems, additions of NO3- to the soil (initially as NH3 or NH4+) and the consequent increases in the emissions of N2O (nitrous oxide, a greenhouse gas) and leaching of NO3- into the ground and surface waters are of major environmental concern. At the ecosystem level NH3 deposition cannot be viewed alone, but in the context of total N deposition. There are a number of forest ecosystems in North America that have been subjected to N saturation and the consequent negative effects. There are also heathlands and other plant communities in Europe that have been subjected to N-induced alterations. Regulatory mitigative approaches to these problems include the use of N saturation data or the concept of critical loads. Current information suggests that a critical load of 5-10 kg ha(-1) year(-1) of total N deposition (both dry and wet deposition combined of all atmospheric N species) would protect the most vulnerable terrestrial ecosystems (heaths, bogs, cryptogams) and values of 10-20 kg ha(-1) year(-1) would protect forests, depending on soil conditions. However, to derive the best analysis, the critical load concept should be coupled to the results and consequences of N saturation.