Exchange of gaseous nitrogen compounds between agricultural systems and the atmosphere

Crop and livestock agricultural production systems are important contributors to local, regional and global budgets of NH₃, NO_x (NO + NO₂) and N₂O. Emissions of NH₃ and NO_x (which are biologically and chemically active) into the atmosphere serve to redistribute fixed N to local and regional aquatic and terrestrial ecosystems that may otherwise be disconnected from the sources of the N gases. The emissions of NO_x also contribute to local elevated ozone concentrations while N₂O emissions contribute to global greenhouse gas accumulation and to stratospheric ozone depletion.Ammonia is the major gaseous base in the atmosphere and serves to neutralize about 30% of the hydrogen ions in the atmosphere. Fifty to 75% of the 55 Tg N yr^–1 NH₃ from terrestrial systems is emitted from animal and crop-based agriculture from animal excreta and synthetic fertilizer application. About half of the 50 Tg N yr^–1 of NO_x emitted from the earth surface annually arises from fossil fuel combustion and the remainder from biomass burning and emissions from soil. The NO_x emitted, principally as nitric oxide (NO), reacts rapidly in the atmosphere and in a complex cycle with light, ozone and hydrocarbons, and produces nitric acid and particulate nitrate. These materials can interact with plants and the soil locally or be transported form the site and interact with atmospheric particulate to form aerosols. These salts and aerosols return to fertilize terrestrial and aquatic systems in wet and dry deposition. A small fraction of this N may be biologically converted to N₂O. About 5% of the total atmospheric greenhouse effect is attributed to N₂O from which 70% of the annual global anthropogenic emissions come from animal and crop production.The coupling of increased population with a move of a large sector of the world population to diets that require more energy and N input, will lead to continued increases in anthropogenic input into the global N cycle. This scenario suggests that emissions of NH₃, NO_x and N₂O from agricultural systems will continue to increase and impact global terrestrial and aquatic systems, even those far removed from agricultural production, to an ever growing extent, unless N resources are used more efficiently or food consumption trends change.     

The role of the atmosphere in nitrogen cycling

In this work an analysis of the sources, atmospheric concentration, chemical reactions and sinks of the principal atmospheric nitrogen compounds is made. Atmospheric emissions of N₂O and NH₃ are almost entirely due to biological activity on the continents and in the oceans. The combustion of fossil fuels and biomass is the principal source of NO_x. The only relevant chemical transformations in the troposphere are the oxidation of NO_x to NO₃ ^? and the formation of ammonium salts. Only 10% of the NH₃ emitted is oxidized. Washout of NH₄ ⁺ and NO₃ ^? by rainfall is the principal mechanism for removing nitrogen compounds from the atmosphere. Part of the N₂O enters the stratosphere and part must be removed in the biosphere by processes not yet established. NO_x produced in the atmosphere by the burning of fossil fuels and biomass and by lightning represents between 30 and 40% of the total nitrogen fixed. A complete nitrogen balance for the troposphere is presented. Since the photochemical oxidation of NO_x is rapid and atmospheric transport is relatively slow with respect to the cycling of water in the troposphere, nitrogen compounds return to the earth's surface close to where they were emitted. Fixed-nitrogen inputs to the continents and oceans due to biological and industrial fixation are slightly greater than those due to rain water. However, since rain falls everywhere, input from this source is only important on soils not subject to intensive agriculture.     

Association between Traffic-Related Air Pollution,Subclinical Inflammation and Impaired Glucose Metabolism: Results from the SALIA Study

Background

Environmental and lifestyle factors regulate the expression and release of immune mediators. It has been hypothesised that ambient air pollution may be such an external factor and that the association between air pollution and impaired glucose metabolism may be attributable to inflammatory processes. Therefore, we assessed the associations between air pollution, circulating immune mediators and impaired glucose metabolism.

Methods

We analysed concentrations of 14 pro- and anti-inflammatory immune mediators as well as fasting glucose and insulin levels in plasma of 363 women from the Study on the influence of Air pollution on Lung function, Inflammation and Aging (SALIA, Germany). Exposure data for a group of pollutants such as nitrogen oxides (NO₂, NO_x) and different fractions of particulate matter were available for the participants'' residences. We calculated the association between the pollutants and impaired glucose metabolism by multiple regression models.

Results

The study participants had a mean age of 74.1 (SD 2.6) years and 48% showed impaired glucose metabolism based on impaired fasting glucose or previously diagnosed type 2 diabetes. Only long-term exposure NO₂ and NO_x concentrations showed positive associations (NO₂: OR 1.465, 95% CI 1.049-2.046, NO_x: OR 1.409, 95% CI 1.010-1.967) per increased interquartile range of NO₂ (14.65 µg/m³) or NO_x (43.16 µg/m³), respectively, but statistical significance was lost after correction for multiple comparisons. Additional adjustment for circulating immune mediators or the use of anti-inflammatory medication had hardly any impact on the observed ORs.

Conclusions

Our results suggest that exposure to nitrogen oxides may contribute to impaired glucose metabolism, but the associations did not reach statistical significance so that further studies with larger sample sizes are required to substantiate our findings. Our data do not preclude a role of inflammatory mechanisms in adipose or other tissues which may not be reflected by immune mediators in plasma.     

Contemporary and pre-industrial global reactive nitrogen budgets

Increases and expansion of anthropogenic emissions of both oxidized nitrogen compounds, NO_x, and a reduced nitrogen compound, NH₃, have driven an increase in nitrogen deposition. We estimate global NO_x and NH₃ emissions and use a model of the global troposphere, MOGUNTIA, to examine the pre-industrial and contemporary quantities and spatial patterns of wet and dry NO_y and NH_x deposition. Pre-industrial wet plus dry NO_x and NH_x deposition was greatest for tropical ecosystems, related to soil emissions, biomass burning and lightning emissions. Contemporary NO_y+NH_x wet and dry deposition onto Northern Hemisphere (NH) temperate ecosystems averages more than four times that of preindustrial N deposition and far exceeds contemporary tropical N deposition. All temperate and tropical biomes receive more N via deposition today than pre-industrially. Comparison of contemporary wet deposition model estimates to measurements of wet deposition reveal that modeled and measured wet deposition for both NO ₃ ^– and NH ₄ ⁺ were quite similar over the U.S. Over Western Europe, the model tended to underestimate wet deposition of NO ₃ ^– and NH ₄ ⁺ but bulk deposition measurements were comparable to modeled total deposition. For the U.S. and Western Europe, we also estimated N emission and deposition budgets. In the U.S., estimated emissions exceed interpolated total deposition by 3-6 Tg N, suggesting that substantial N is transported offshore and/or the remote and rural location of the sites may fail to capture the deposition of urban emissions. In Europe, by contrast, interpolated total N deposition balances estimated emissions within the uncertainty of each.Abbreviations EMEP European Monitoring and Evaluation Program - GEIA Global Emissions Inventory Activity - NADP/NTN National Atmospheric Deposition Program/National Trends Network in the US - NH Northern Hemisphere - NH_x=NH₃+NH ₊ ⁴ NO_x=NO+NO₂ NO_y total odd nitrogen=NO_x+HNO₃+HONO+HO₂NO₂+NO₃+radical (NO₃ ^.)+Peroxyacetyl nitrates+N₂O₅+organic nitrates - SH Southern Hemisphere - Gg 10⁹ g - Tg 10¹² g     

Nitrogen–climate interactions in US agriculture

Agriculture in the United States (US) cycles large quantities of nitrogen (N) to produce food, fuel, and fiber and is a major source of excess reactive nitrogen (Nr) in the environment. Nitrogen lost from cropping systems and animal operations moves to waterways, groundwater, and the atmosphere. Changes in climate and climate variability may further affect the ability of agricultural systems to conserve N. The N that escapes affects climate directly through the emissions of nitrous oxide (N₂O), and indirectly through the loss of nitrate (NO₃ ^?), nitrogen oxides (NO _x ) and ammonia to downstream and downwind ecosystems that then emit some of the N received as N₂O and NO _x . Emissions of NO _x lead to the formation of tropospheric ozone, a greenhouse gas that can also harm crops directly. There are many opportunities to mitigate the impact of agricultural N on climate and the impact of climate on agricultural N. Some are available today; many need further research; and all await effective incentives to become adopted. Research needs can be grouped into four major categories: (1) an improved understanding of agricultural N cycle responses to changing climate; (2) a systems-level understanding of important crop and animal systems sufficient to identify key interactions and feedbacks; (3) the further development and testing of quantitative models capable of predicting N-climate interactions with confidence across a wide variety of crop-soil-climate combinations; and (4) socioecological research to better understand the incentives necessary to achieve meaningful deployment of realistic solutions.     

Gaseous nitrogen emmissions from undisturbed terrestrial ecosystems: An assessment of their impacts on local and global nitrogen budgets

There is increasing interest in the importance of nitrogen gas emissions from natural (non-agricultural) ecosystems with respect to local as well as global nitrogen budgets and with respect to the effects of nitrogen oxides on atmospheric ozone levels and global warming. The volatile forms of nitrogen of common interest are ammonia (NH₃), nitrous oxide, (N₂O), dinitrogen (N₂), and NO_x (principally NO + NO₂). It is often difficult to attribute emissions of these compounds from soils to a single process because they are produced by a variety of common biogeochemical mechanisms. Although environmental conditions in the soil often appear to favor nitrogen gas emissions, the potential nitrogen gas emission rate from undisturbed ecosystems is rarely approached. The best estimates to date suggest that nitrogen gas emission rates from undisturbed ecosystems typically range from > 1 to perhaps 10 or 20 kg N ha^-1 yr^-1. Under certain conditions, however, emission rates may be much higher. For example, excreta from animals in grasslands may elevate ammonia volatilization up to 100 kg N ha^-1 yr^-1 depending on grazer density; tidal input of nutrients to coastal wetlands may support denitrification rates of several hundred kg N ha^-1 yr^-1 . Excepting such cases, gaseous nitrogen losses are probably a small component of the local nitrogen budget in most undisturbed ecosystems. However, emissions from undisturbed soils are an important component of the global source strengths for (N₂O + N₂), N₂O and NO_x (50%, 21%, and 10% respectively). Emission rates of N₂O from natural ecosystems are higher than assumed previously by perhaps 10 times. Large-scale disturbance may have a stimulatory effect on nitrogen emission rates which could have important effects on global nitrogen budgets. There is a need for more sophisticated methods to account for natural temporal and spatial variations of emissions rates, to more accurately and precisely assess their global source strengths.     

Atmospheric deposition of nutrients to the North Atlantic Basin

Atmospheric chemical models are used to estimate the deposition rate of various inorganic oxides of nitrogen (NO_y), reduced nitrogen species (NH_x) and mineral dust to the North Atlantic Ocean (NAO). The estimated deposition of NO_y to the NAO (excluding the coastal ocean) and the Caribbean is 360 × 10⁹ Moles-N m^–2 yr^–1 (5.0 Tg N); this is equivalent to about 13% of the estimated global emission rate (natural and anthropogenic) and a quarter of the emission rate from sources in North America and Europe. In the case of NH_x, 258 Moles-N m^–2 yr^–1 (3.6 Tg N) are deposited to the NAO and the Caribbean; this is about 6% of the global continental emissions. There is relatively little data on the deposition rate of organic nitrogen species; nonetheless, this evidence suggests that concentrations and deposition rates are comparable to those for inorganic nitrogen.Because of anthropogenic emissions, the present-day deposition rate of NO_y to the NAO is about five times greater than pre-industrial times largely due to emissions from energy production and biomass burning. The present-day emissions of NH_x from continental anthropogenic sources are about four-to-five times greater than natural sources, mostly due to the impact of emissions from animal wastes associated with food production. Indeed, present-day emissions of NH_x from animal waste are estimated to be about 10 times greater than the pre-human era. The deposition rate of mineral dust to the NAO is about 170 Tg yr^–1; deposited with the dust (assuming average crustal abundances) is about 6 Tg yr^–1 of Fe and 0.2 Tg yr^–1 of P. Dust deposition in the NAO is almost completely attributable to transport from North African sources; a substantial fraction of the dust over the NAO is probably mobilized as a consequence of land use practices in arid regions and, consequently, it should be regarded as a pollutant.     

Life Cycle Impact assessment of pollutants causing aquatic eutrophication

In life cycle impact assessment (LCIA), limited attention is generally given to a consistent inclusion of a fate analysis in the derivation of aquatic eutrophication potentials. This paper includes fate and potential effects in the calculation of aquatic eutrophication potentials of NH₃ and NO_x emitted to the ait, N and P emitted to water, and N and P emitted to soil. These characterisation factors were calculated for the Netherlands, West-Europe and the world, respectively. Implementation in current LCIA practice is further facilitated by calculating normalisation scores for the Netherlands in 1997, West-Europe in 1995 and the world in 1990. Although the results presented may be a step forward, significant improvements are still needed in the assessment of pollutants causing aquatic eutrophication. In particular, the fate factors representing transport of NO_x and NH₃, air emissions via soils to the aquatic environment should be improved. In addition, differences in the biological availability of nutrients and differences in the sensitivity of aquatic environments should be included in the calculation of effect factors for aquatic eutrophication.     

Chang impact analysis of level 3 COVID-19 alert on air pollution indicators using artificial neural network

In this study, mean monthly and diurnal variations in fine particulate matters (PM_2.5), nitrate, sulfate, and gaseous precursors were investigated during the Level 3 COVID-19 alert from May 19 to July 27 in 2021. For comparison, the historical data during the identical period in 2019 and 2020 were also provided to determine the effect of the Level 3 COVID-19 alert on aerosols and gaseous pollutants concentrations in Taichung City. A machine learning model using the artificial neural network technique coupled with a kinetic model was applied to predict NO_x, O₃, nitrate (NO₃⁻), and sulfate (SO₄²⁻) to investigate potential emission sources and chemical reaction mechanism. D during the Level 3 COVID-19 alert, a decrease in NO_x concentration due to a decrease in traffic flow under the NO_x-saturated regime was observed to enhance the secondary NO₃⁻ and O₃ formation. The present models were shown to predict 80.1, 77.0, 72.6, and 67.2% concentrations of NO_x, O₃, NO₃⁻, and SO₄²⁻, respectively, which could help decision-makers for pollutant emissions reduction policies development and air pollution control strategies. It is recommended that more long-term datasets, including water soluble inorganic salts (WIS), precursors including OH radicals, NH₃, HNO₃, and H₂SO₄, be provided by regulatory air quality monitoring stations to further improve the prediction model accuracy.     

山西北部农村区域大气活性氮沉降特征

利用DELTA系统、被动采样器和雨量器在山西省北部生态脆弱区朔州的一个监测点通过一整年的监测试验,研究了该地区农村区域大气氮素干湿沉降的月际变化。结果表明:2011年该地区大气氮素湿沉降为12.43kgN hm~(-2)a~(-1),远低于华北平原大气氮素混合沉降的平均值28.0kg N hm~(-2)a~(-1),降水中铵态氮、硝态氮和有机氮平均分别为1.24 mg N/L、1.27 mg N/L、1.26mg N/L。大气氮素湿沉降的年内分布不均,60%的沉降集中在降水较丰沛的4-10月份。试验区干沉降以氧化态氮(HNO_3NO_2和pNO_3~-)的沉降为主,氧化态氮的干沉降量是还原态氮(NH_3和pNH_4~+)的1.37倍,大气氮素干沉降总量为35.43 kg N hm~(-2)a~(-1)。总体来看,作为典型的干旱区,该地区氮的干沉降是湿沉降的3倍,氮素干湿沉降总量达到47.86kg N hm~(-2)a~(-1)。此外,硝态氮和铵态氮在雨水中呈线性相关,而在PM_(10)颗粒物中乘幂正相关;雨水中总碳和总氮呈线性正相关,而PM_(10)颗粒物中二者呈二次多项式关系。鉴于朔州地区古城镇较高的氮沉降数量,应该对该地区输入农田的氮素环境养分引起足够重视。     

The global nitrogen cycle in the twenty-first century

Global nitrogen fixation contributes 413 Tg of reactive nitrogen (N_r) to terrestrial and marine ecosystems annually of which anthropogenic activities are responsible for half, 210 Tg N. The majority of the transformations of anthropogenic N_r are on land (240 Tg N yr⁻¹) within soils and vegetation where reduced N_r contributes most of the input through the use of fertilizer nitrogen in agriculture. Leakages from the use of fertilizer N_r contribute to nitrate (NO₃⁻) in drainage waters from agricultural land and emissions of trace N_r compounds to the atmosphere. Emissions, mainly of ammonia (NH₃) from land together with combustion related emissions of nitrogen oxides (NO_x), contribute 100 Tg N yr⁻¹ to the atmosphere, which are transported between countries and processed within the atmosphere, generating secondary pollutants, including ozone and other photochemical oxidants and aerosols, especially ammonium nitrate (NH₄NO₃) and ammonium sulfate (NH₄)₂SO₄. Leaching and riverine transport of NO₃ contribute 40–70 Tg N yr⁻¹ to coastal waters and the open ocean, which together with the 30 Tg input to oceans from atmospheric deposition combine with marine biological nitrogen fixation (140 Tg N yr⁻¹) to double the ocean processing of N_r. Some of the marine N_r is buried in sediments, the remainder being denitrified back to the atmosphere as N₂ or N₂O. The marine processing is of a similar magnitude to that in terrestrial soils and vegetation, but has a larger fraction of natural origin. The lifetime of N_r in the atmosphere, with the exception of N₂O, is only a few weeks, while in terrestrial ecosystems, with the exception of peatlands (where it can be 10²–10³ years), the lifetime is a few decades. In the ocean, the lifetime of N_r is less well known but seems to be longer than in terrestrial ecosystems and may represent an important long-term source of N₂O that will respond very slowly to control measures on the sources of N_r from which it is produced.     

Disentangling the effects of acidic air pollution,atmospheric CO2, and climate change on recent growth of red spruce trees in the Central Appalachian Mountains

In the 45 years after legislation of the Clean Air Act, there has been tremendous progress in reducing acidic air pollutants in the eastern United States, yet limited evidence exists that cleaner air has improved forest health. Here, we investigate the influence of recent environmental changes on the growth and physiology of red spruce (Picea rubens Sarg.) trees, a key indicator species of forest health, spanning three locations along a 100 km transect in the Central Appalachian Mountains. We incorporated a multiproxy approach using 75‐year tree ring chronologies of basal tree growth, carbon isotope discrimination (?¹³C, a proxy for leaf gas exchange), and δ¹⁵N (a proxy for ecosystem N status) to examine tree and ecosystem level responses to environmental change. Results reveal the two most important factors driving increased tree growth since ca. 1989 are reductions in acidic sulfur pollution and increases in atmospheric CO₂, while reductions in pollutant emissions of NO_x and warmer springs played smaller, but significant roles. Tree ring ?¹³C signatures increased significantly since 1989, concurrently with significant declines in tree ring δ¹⁵N signatures. These isotope chronologies provide strong evidence that simultaneous changes in C and N cycling, including greater photosynthesis and stomatal conductance of trees and increases in ecosystem N retention, were related to recent increases in red spruce tree growth and are consequential to ecosystem recovery from acidic pollution. Intrinsic water use efficiency (iWUE) of the red spruce trees increased by ~51% across the 75‐year chronology, and was driven by changes in atmospheric CO₂ and acid pollution, but iWUE was not linked to recent increases in tree growth. This study documents the complex environmental interactions that have contributed to the recovery of red spruce forest ecosystems from pervasive acidic air pollution beginning in 1989, about 15 years after acidic pollutants started to decline in the United States.     

Nitrogen deposition induced changes in DOC : NO3‐N ratios determine the efficiency of nitrate removal from freshwaters

With a unique data set comprising 1041 boreal forested and low human impacted lakes included in three Swedish lake inventories for 1995, 2000 and 2005 and with time series for 12 of the lakes from 1988 to 2008 we show that nitrate‐nitrogen (NO₃‐N) is accumulated in freshwaters along with increasing atmospheric nitrogen deposition (N_dep). At the same time we observe decreasing DOC : NO₃‐N ratios in the water column. We suggest that NO₃‐N is accumulated in freshwaters when denitrifying bacteria are limited by their energy source rather than the availability of NO₃‐N, i.e. at low DOC : NO₃‐N ratios. We obtained further support for a close relationship between N_dep driven DOC : NO₃‐N ratios and the efficiency of nitrate removal by using a published global data set on measured nitrate removal rates in unproductive reference streams. Owing to the currently decreasing N_dep in large regions of, for instance, Northern Europe, this process is now reversed, resulting in increasing DOC : NO₃‐N ratios and more efficient nitrate removal from freshwaters. Depending on NO_x emissions, nitrogen limited regions may expand with an immediate effect on nitrate concentrations in freshwaters.     

Assessment of Modeled Indoor Air Concentrations of Particulate Matter,Gaseous Pollutants,and Volatile Organic Compounds Emitted from Candles

Candle burning is regarded as an important source of airborne pollutants in indoor environments. Indoor concentrations of aldehydes, benzo(a)pyrene, sulphur dioxide (SO₂), nitrogen oxides (NO_x), and particulate matter (PM) produced from the burning of scented candles and raw materials with different melting point/oil content (50/1, 55/9, and 65/6) were predicted using a single compartment mass balance model and compared to regulatory or guideline limits. Scented candles may be responsible for indoor acrolein concentrations that could become relevant to health only in the case of chronic exposure. Indoor concentrations of fine PM and SO₂ emitted from 65/6 wax burning under worst-case environmental and behavioral conditions were greater than their respective acute guideline limits. However, other waxes had levels of PM and SO₂ well below the recommended values. Indoor concentrations of nitrogen dioxide emitted from raw wax burning should be further investigated. The degree of pureness of raw waxes significantly affected the predicted indoor concentrations of PM and SO₂. In particular, 65/6 wax was criticized for its high content of impurities.     

The influence of rising tropospheric carbon dioxide and ozone on plant productivity

Human activities result in a wide array of pollutants being released to the atmosphere. A number of these pollutants have direct effects on plants, including carbon dioxide (CO₂), which is the substrate for photosynthesis, and ozone (O₃), a damaging oxidant. How plants respond to changes in these atmospheric air pollutants, both directly and indirectly, feeds back on atmospheric composition and climate, global net primary productivity and ecosystem service provisioning. Here we discuss the past, current and future trends in emissions of CO₂ and O₃ and synthesise the current atmospheric CO₂ and O₃ budgets, describing the important role of vegetation in determining the atmospheric burden of those pollutants. While increased atmospheric CO₂ concentration over the past 150 years has been accompanied by greater CO₂ assimilation and storage in terrestrial ecosystems, there is evidence that rising temperatures and increased drought stress may limit the ability of future terrestrial ecosystems to buffer against atmospheric emissions. Long‐term Free Air CO₂ or O₃ Enrichment (FACE) experiments provide critical experimentation about the effects of future CO₂ and O₃ on ecosystems, and highlight the important interactive effects of temperature, nutrients and water supply in determining ecosystem responses to air pollution. Long‐term experimentation in both natural and cropping systems is needed to provide critical empirical data for modelling the effects of air pollutants on plant productivity in the decades to come.     

Effects of Elevated Atmospheric CO2 Concentrations on CH4 and N2O Emission from Rice Soil: An Experiment in Controlled-environment Chambers

The effects of elevated concentrations of atmospheric CO₂ on CH₄ and N₂O emissions from rice soil were investigated in controlled-environment chambers using rice plants growing in pots. Elevated CO₂ significantly increased CH₄ emission by 58% compared with ambient CO₂. The CH₄ emitted by plant-mediated transport and ebullition–diffusion accounted for 86.7 and 13.3% of total emissions during the flooding period under ambient level, respectively; and for 88.1 and 11.9% of total emissions during the flooding period under elevated CO₂ level, respectively. No CH₄ was emitted from plant-free pots, suggesting that the main source of emitted CH₄ was root exudates or autolysis products. Most N₂O was emitted during the first 3 weeks after flooding and rice transplanting, probably through denitrification of NO₃⁻ contained in the experimental soil, and was not affected by the CO₂ concentration. Pre-harvest drainage suppressed CH₄ emission but did not cause much N₂O emission (< 10 μg N m⁻² h⁻¹) from the rice-plant pots at both CO₂ concentrations.     

Ecosystem Responses to Nitrogen Deposition in the Colorado Front Range

We asked whether 3–5 kg N y⁻¹ atmospheric N deposition was sufficient to have influenced natural, otherwise undisturbed, terrestrial and aquatic ecosystems of the Colorado Front Range by comparing ecosystem processes and properties east and west of the Continental Divide. The eastern side receives elevated N deposition from urban, agricultural, and industrial sources, compared with 1–2 kg N y⁻¹ on the western side. Foliage of east side old-growth Englemann spruce forests have significantly lower C:N and lignin:N ratios and greater N:Mg and N:P ratios. Soil % N is higher, and C:N ratios lower in the east side stands, and potential net N mineralization rates are greater. Lake NO₃ concentrations are significantly higher in eastern lakes than western lakes. Two east side lakes studied paleolimnologically revealed rapid changes in diatom community composition and increased biovolumes and cell concentrations. The diatom flora is now representative of increased disturbance or eutrophication. Sediment nitrogen isotopic ratios have become progressively lighter over the past 50 years, coincident with the change in algal flora, possibly from an influx of isotopically light N volatilized from agricultural fields and feedlots. Seventy-five percent of the increased east side soil N pool can be accounted for by increased N deposition commensurate with human settlement. Nitrogen emissions from fixed, mobile, and agricultural sources have increased dramatically since approximately 1950 to the east of the Colorado Front Range, as they have in many parts of the world. Our findings indicate even slight increases in atmospheric deposition lead to measurable changes in ecosystem properties. Received 16 November 1999; accepted 8 February 2000.     

Impact of novel coronavirus disease (COVID-19) lockdown on ambient air quality of Saudi Arabia

The outbreak of COVID-19 has spread globally affecting human activities but with improvement in ambient air quality. The first case of the virus in the Kingdom of Saudi Arabia was on the 2nd of March 2020. The impact of COVID-19 lockdown on the ambient air quality of the Kingdom of Saudi Arabia for the first time using data from nine cities was determined in this study. Hourly air quality data, based on concentrations of carbon monoxide (CO), particulate matter (PM₁₀), sulfur dioxide (SO₂), nitrogen dioxide (NO₂) and ozone (O₃), and meteorological conditions (atmospheric temperature, relative humidity, and wind speed) of the nine cities studied were obtained from Saudi Arabian General Authority of Meteorology and Environmental Protection (GAMEP), for the period between January 2019 to May 2020. Significant variation (p < 0.05) was recorded for the five atmospheric pollutants across the cities before and during the lockdown, with lower concentrations during the lockdown except for the concentration of O₃ in Tabuk, Al Qasim, and Haql. This can be a result of NO and O₃ reaction, causing the inability of effective O₃ depletion. The percentage changes in concentrations of CO (33.60%) and SO₂ (44.16%) were higher in Jeddah; PM₁₀ (91.12%) in Riyadh, while NO₂ (44.35%) and O₃ (18.98%) were highest in Makkah. However, even though there was a decrease in pollutants concentrations during the lockdown, the concentrations for CO, PM₁₀, SO₂, NO_2, and O₃ were still above WHO 24 h and annual mean limit levels. The COVID-19 lockdown in the Kingdom of Saudi Arabia revealed the possibility of significant atmospheric pollutant reduction by controlling traffic, activities by industries, and environmentally friendly transportation programs such as green commuting programs.     

Local vehicles add nitrogen to moss biomonitors in a low-traffic protected wilderness area as revealed by a long-term isotope study

Public use of protected areas is typically encouraged, but visitors arriving by vehicles may alter the natural areas they seek. Vehicle emissions add nitrogen oxides (NO_x) and ammonia (NH₃) to the air, which can increase the amount of plant-available (reactive) nitrogen, a limiting nutrient. Changes in ecosystem processes as a result of increases in nitrogen availability are at odds with the goals of many protected wilderness areas that are typically accessed by vehicles. In this multi-year study (2003–2019), we tested whether emissions from local vehicles entered the forest ecosystem adjacent to a highway in a protected wilderness valley near a mid-sized city (Calgary, Alberta, Canada). We examined the concentration of NO₂ in the air and the abundance of combustion-derived nitrogen isotopes (δ¹⁵N) in naturally-occurring forest moss (Hylocomium splendens and Pleurozium schreberi) within 20 m of the highway as a function of traffic levels that varied independently at two scales: along the highway and among years. Within the valley, we observed a gradient in the number of vehicles that was greatest where vehicles enter the valley, with a corresponding pattern for NO₂ concentrations in air. Traffic volume also varied among years, with the highest year having almost twice as many vehicles in the summer as the lowest year. δ¹⁵N values in forest moss displayed similar patterns as traffic both within and among years, signalling that nitrogen from vehicle emissions entered the local ecosystem corresponding to local traffic levels. Because vehicle emissions enter natural ecosystems that are intended to be conserved, vehicle use must be considered in the management of protected natural areas.