Critical levels (CLEs) of atmospheric ammonia based on biodiversity changes have been mostly calculated using small-scale single-source approaches, to avoid interference by other factors, which also influence biodiversity. Thus, it is questionable whether these CLEs are valid at larger spatial scales, in a multi- disturbances context. To test so, we sampled lichen diversity and ammonia at 80 sites across a region with a complex land-cover including industrial and urban areas. At a regional scale, confounding factors such as industrial pollutants prevailed, masking the CLEs. We propose and use a new tool to calculate CLEs by stratifying ammonia concentrations into classes, and focusing on the highest diversity values. Based on the significant correlations between ammonia and biodiversity, we found the CLE of ammonia for Mediterranean evergreen woodlands to be 0.69 μg m−3, below the previously accepted value of 1.9 μg m−3, and below the currently accepted pan-European CLE of 1.0 μg m−3.

Highways are major sources of nitrogen dioxide (NO2) and ammonia (NH3). In this study, springtime NO2 and NH3 concentrations were measured at 17 Ontario Forest Biomonitoring Network (OFBN) plots using passive samplers. Average springtime NO2 concentrations were between 1.3 μg m−3 and 27 μg m−3, and NH3 concentrations were between 0.2 μg m−3 and 1.7 μg m−3, although concentrations measured in May (before leaf out) were typically twice as high as values recorded in June. Average NO2 concentrations, and to a lesser extent NH3, could be predicted by road density at all radii (around the plot) tested (500 m, 1000 m, 1500 m). Springtime NO2 concentrations were predicted for a further 50 OFBN sites. Normalized plant/lichen N concentrations were positively correlated with estimated springtime NO2 and NH3 concentrations. Epiphytic foliose lichen richness decreased with increasing NO2 and NH3, but vascular plant richness was positively related to estimated springtime NO2 and NH3.

Ammonia (NH3) empirical critical levels for Europe were re-evaluated in 2009, based mainly on the ecological responses of lichen communities without acknowledging the physiological differences between oligotrophic and nitrophytic species. Here, we compare a nitrogen sensitive lichen (Evernia prunastri) with a nitrogen tolerant one (Xanthoria parietina), focussing on their physiological response (Fv/Fm) to short-term NH3 exposure and their frequency of occurrence along an NH3 field gradient. Both frequency and Fv/Fm of E. prunastri decreased abruptly above 3 μg m−3 NH3 suggesting direct adverse effects of NH3 on its photosynthetic performance. By contrast, X. parietina increased its frequency with NH3, despite showing decreased capacity of photosystem II above 50 μg m−3 NH3, suggesting that the ecological success of X. parietina at ammonia-rich sites might be related to indirect effects of increased nitrogen (NH3) availability. These results highlight the need to establish NH3 critical levels based on oligotrophic lichen species.

Phase 1 of the TIE method was applied to samples of elutriates from sediments of the Itajaí-Açu estuary and adjacent coastal region in southern Brazil. Embryo-larval toxicity assays were used with the sea urchin Arbacia lixula in samples of raw elutriate, and treated with Ulva fasciata, EDTA and sodium thiosulfate. Inside the estuary, ammonia was responsible for more than 40% of the toxicity in both the dredged and undredged regions. A toxicity gradient was observed, between the estuary and the coastal region, with an increase in the importance of metals for the latter. Temporally, there is strong evidence of the influence of dredging and disposal of sediments in the contamination of the coastal dumping site. The results indicating that this area presents limitations in its saturation capacity. Chemical analysis indicated the metal Cu is probably responsible for the toxicity of the sediments observed, without the interference of ammonia.

Anthropogenic nitrogen (N) discharges has caused eutrophication in coastal zones. Ammonia-oxidizing bacteria (AOB) convert ammonia to nitrite and play important roles in N transformation. Here, we used pyrosequencing based on the amoA gene to investigate the response of the sediment AOB community to an N pollution gradient in the East China Sea. The results showed that AOB assemblages were primarily affiliated with Nitrosospira-like lineages, and only 0.4% of those belonged to Nitrosomonas-like lineage. The Nitrosospira-like lineage was separated into four clusters that were most similar to the sediment AOB communities detected in adjacent marine regions. Additionally, one clade was out grouped from the AOB lineages, which shared the high similarities with pmoA gene. The AOB community structures substantially changed along the pollution gradient, which were primarily shaped by NH4+–N, NO3−–N, SO42−–S, TP and Eh. These results demonstrated that coastal pollution could dramatically influence AOB communities, which, in turn, may change ecosystem function.

A literature review on the effects of high ammonium concentrations on the growth of 6 classes of microalgae suggests the following rankings. Mean optimal ammonium concentrations were 7600, 2500, 1400, 340, 260, 100μM for Chlorophyceae, Cyanophyceae, Prymnesiophyceae, Diatomophyceae, Raphidophyceae, and Dinophyceae respectively and their tolerance to high toxic ammonium levels was 39,000, 13,000, 2300, 3600, 2500, 1200μM respectively. Field ammonium concentrations <100μM would not likely reduce the growth rate of most microalgae. Chlorophytes were significantly more tolerant to high ammonium than diatoms, prymnesiophytes, dinoflagellates, and raphidophytes. Cyanophytes were significantly more tolerant than dinoflagellates which were the least tolerant. A smaller but more complete data set was used to estimate ammonium EC50 values, and the ranking was: Chlorophyceae>Cyanophyceae, Dinophyceae, Diatomophyceae, and Raphidophyceae. Ammonia toxicity is mainly attributed to NH3 at pHs >9 and at pHs <8, toxicity is likely associated with the ammonium ion rather than ammonia.

This study investigated NH3 concentrations in and around a large–scale commercial pig farm with the so–called “gan qing fen” manure collection system near Beijing from April 2009 to August 2011. NH3 emissions from the fattening pig houses were calculated based on the heat balance method. Monthly concentrations of time–averaged NH3 in and near the pig house averaged 3 392 and 182μg m−3 and ranged from 1 044 to 7 514μg m−3 and 35.4 to 478μg m−3, respectively. Daily NH3 concentrations varied from 767 to 2 389μg m−3 in the pig house and 184 to 574μg m−3 outside. Time–averaged NH3 concentrations varied from 21.6 to 558μg m−3 within the farm while concentrations outside the farm ranged from 38.4μg m−3 at a distance of 10m to 14.0μg m−3 at a distance of 650m. Calculated average NH3 emission rates per pig were highest in summer and lowest in winter, 8.0±5.5 (average±standard deviation) and 2.0±0.4g day−1 pig−1, respectively. Average NH3 emission rates (normalized to 500kg live weight, expressed as AU) were highest during spring and summer (average 65.4±25.0 and 53.7±35.6 g day−1 AU−1) and lowest in autumn and winter (average 25.4±9.3 and 13.7±2.7g day−1 AU−1). Average NH3 emission per area (m2) from house was almost three times higher in summer (average 3.5±2.4g day−1 m−2) than in winter (average 1.1±0.3g day−1 m−2).

From April 2006 to April 2007, the geographical and seasonal variation in nitrogen content in terricolous lichen (Cladonia portentosa) and atmospheric ammonia concentrations were measured at five heathland sites. The seasonal variation in the nitrogen content of the lichen was small, even though there was a large seasonal variation in the air concentration of ammonia. A sizable local variation in the nitrogen content of the lichen was found even at the scale of a few kilometres. The nitrogen content in the lichen showed a high correlation to the yearly mean value of the measured ammonia concentration in air at the different locations. This investigation is part of a larger attempt to incorporate effects of nitrogen in the conservation status of terrestrial habitat types.

Land use specific deposition velocities of atmospheric trace gases and aerosols—particularly of reactive nitrogen compounds—are a fundamental input variable for a variety of deposition models. Although the concept is known to have shortcomings—especially with regard to bi-directional exchange—the often limited availability of concentration data and meteorological input variables make it a valuable simplification for regional modeling of deposition fluxes. In order to meet the demand for an up-to-date overview of recent publications on measurements and modeling studies, we compiled a database of ammonia (NH₃) deposition velocities published from 2004 to 2013. Observations from a total of 42 individual studies were averaged using an objective weighing scheme and classified into seven land use categories. Weighted average and median deposition velocities are 2.2 and 2.1 cm s⁻¹for coniferous forests, 1.5 and 1.2 cm s⁻¹for mixed forests, 1.1 and 0.9 cm s⁻¹for deciduous forests, 0.9 and 0.7 cm s⁻¹for semi-natural sites, 0.7 and 0.8 cm s⁻¹for urban sites, 0.7 and 0.6 cm s⁻¹for water surfaces, and 1.0 and 0.4 cm s⁻¹for agricultural sites, respectively. Thus, values presented in this compilation were considerably lower than those found in former studies (e.g., VDI 2006). Reasons for the mismatch were likely due to different land use classification, different averaging methods, choices of measurement locations, and improvements in measurement and in modeling techniques. Both data and code used for processing are made available as supplementary material to this article.

The goal of this study was to document if lakes in National Parks in Washington have exceeded critical levels of nitrogen (N) deposition, as observed in other Western States. We measured atmospheric N deposition, lake water quality, and sediment diatoms at our study lakes. Water chemistry showed that our study lakes were ultra-oligotrophic with ammonia and nitrate concentrations often at or below detection limits with low specific conductance (<100 μS/cm), and acid neutralizing capacities (<400 μeq/L). Rates of summer bulk inorganic N deposition at all our sites ranged from 0.6 to 2.4 kg N ha⁻¹ year⁻¹and were variable both within and across the parks. Diatom assemblages in a single sediment core from Hoh Lake (Olympic National Park) displayed a shift to increased relative abundances of Asterionella formosa and Fragilaria tenera beginning in the 1969–1975 timeframe, whereas these species were not found at the remaining (nine) sites. These diatom species are known to be indicative of N enrichment and were used to determine an empirical critical load of N deposition, or threshold level, where changes in diatom communities were observed at Hoh Lake. However, N deposition at the remaining nine lakes does not seem to exceed a critical load at this time. At Milk Lake, also in Olympic National Park, there was some evidence that climate change might be altering diatom communities, but more research is needed to confirm this. We used modeled precipitation for Hoh Lake and annual inorganic N concentrations from a nearby National Atmospheric Deposition Program station, to calculate elevation-corrected N deposition for 1980–2009 at Hoh Lake. An exponential fit to this data was hindcasted to the 1969–1975 time period, and we estimate a critical load of 1.0 to 1.2 kg N ha⁻¹ year⁻¹for wet deposition for this lake.