Heterogeneity of atmospheric ammonia at the landscape scale and consequences for environmental impact assessment

Pollinator-mediated effects of landscape-scale land use on grassland plant community composition and ecosystem functioning - seven hypotheses

Environmental change is disrupting mutualisms between organisms worldwide. Reported declines in insect populations and changes in pollinator community compositions in response to land use and other environmental drivers have put the spotlight on the need to conserve pollinators. While this is often motivated by their role in supporting crop yields, the role of pollinators for reproduction and resulting taxonomic and functional assembly in wild plant communities has received less attention. Recent findings suggest that observed and experimental gradients in pollinator availability can affect plant community composition, but we know little about when such shifts are to be expected, or the impact they have on ecosystem functioning. Correlations between plant traits related to pollination and plant traits related to other important ecosystem functions, such as productivity, nitrogen uptake or palatability to herbivores, lead us to expect non-random shifts in ecosystem functioning in response to changes in pollinator communities. At the same time, ecological and evolutionary processes may counteract these effects of pollinator declines, limiting changes in plant community composition, and in ecosystem functioning. Despite calls to investigate community- and ecosystem-level impacts of reduced pollination, the study of pollinator effects on plants has largely been confined to impacts on plant individuals or single-species populations. With this review we aim to break new ground by bringing together aspects of landscape ecology, ecological and evolutionary plant-insect interactions, and biodiversity-ecosystem functioning research, to generate new ideas and hypotheses about the ecosystem-level consequences of pollinator declines in response to land-use change, using grasslands as a focal system. Based on an integrated set of seven hypotheses, we call for more research investigating the putative pollinator-mediated links between landscape-scale land use and ecosystem functioning. In particular, future research should use combinations of experimental and observational approaches to assess the effects of changes in pollinator communities over multiple years and across species on plant communities and on trait distributions both within and among species.

2011-2020 trends of urban and regional ammonia in and around Barcelona, NE Spain

It is well established that in environments where NH₃ abundance is limiting in secondary PM_2.5 generation, a reduction of NH₃ emissions can result in an important contribution to air quality control. However, as deduced from open data published by the European Environmental Agency, the availability of measurements of NH₃ concentrations is very scarce, with very few countries in Europe reporting data consistently for extensive periods, this being especially true for urban background sites. In this framework, simultaneous multi-site measurements were carried out in NE (Northeast) Spain from 2011 to 2020, using diffusion tubes. The highest NH₃ concentrations were recorded at the traffic site (5.3 μgm^-3 on average), followed by those measured at the urban background site (2.1 μgm^-3). Mean concentrations at the mountain site were 1.6 μgm^-3, while the lowest concentrations were recorded at the regional site (0.9 μgm^-3). This comparison highlights traffic emissions as an important source of NH₃. A statistically significant time trend of this pollutant was observed at the urban background site, increasing by 9.4% per year. A season-separated analysis also revealed a significant increasing trend at the mountain site during summer periods, probably related with increasing emissions from agricultural/livestock activities. These increases in NH₃ concentrations were hypothesized to be responsible for the lack of a decreasing trend of NO₃^- concentrations at the monitoring sites, in spite of a markedly reduction of NO₂ during the period, especially at the urban background. Thus, this would in turn affect the effectiveness of current action plans to abate fine aerosols, largely made up of secondary compounds. Actions to reduce NH₃ concentrations at urban backgrounds are challenging though, as predicting NH₃ is subjected to a high uncertainty and complexity due to its dependence on a variety of factors. This complexity was clearly indicated by the application of a decision tree algorithm to find the parameters better predicting NH₃ at the urban background under study. O₃, NO, NO₂, CO, SO₂ and OM + EC concentrations, together with meteorological indicators, were used as independent variables, obtaining no combination of parameters evidently able to predict significant differences in NH₃ concentrations, with a coefficient of determination between real and predicted measurements lower than 0.50. This emphasizes the need for highly temporally and spatially resolved NH₃ measurements for an accurate design of abatement actions.

Mapping Portuguese Natura 2000 sites in risk of biodiversity change caused by atmospheric nitrogen pollution

In this paper, we assess and map the risk that atmospheric nitrogen (atN) pollution poses to biodiversity in Natura 2000 sites in mainland Portugal. We first review the ecological impacts of atN pollution on terrestrial ecosystems, focusing on the biodiversity of Natura 2000 sites. These nature protection sites, especially those located within the Mediterranean Basin, are under-characterized regarding the risk posed by atN pollution. We focus on ammonia (NH3) because this N form is mostly associated with agriculture, which co-occurs at or in the immediate vicinity of most areas of conservation interest in Portugal. We produce a risk map integrating NH3 emissions and the susceptibility of Natura 2000 sites to atN pollution, ranking habitat sensitivity to atN pollution using expert knowledge from a panel of Portuguese ecological and habitat experts. Peats, mires, bogs, and similar acidic and oligotrophic habitats within Natura 2000 sites (most located in the northern mountains) were assessed to have the highest relative risk of biodiversity change due to atN pollution, whereas Natura 2000 sites in the Atlantic and Mediterranean climate zone (coastal, tidal, and scrubland habitats) were deemed the least sensitive. Overall, results allowed us to rank all Natura 2000 sites in mainland Portugal in order of evaluated risk posed by atN pollution. The approach is of great relevance for stakeholders in different countries to help prioritize site protection and to define research priorities. This is especially relevant in countries with a lack of expertise to assess the impacts of nitrogen on biodiversity and can represent an important step up from current knowledge in such countries.

Ammonia Emissions May Be Substantially Underestimated in China

China is a global hotspot of atmospheric ammonia (NH₃) emissions and, as a consequence, very high nitrogen (N) deposition levels are documented. However, previous estimates of total NH₃ emissions in China were much lower than inference from observed deposition values would suggest, highlighting the need for further investigation. Here, we reevaluated NH₃ emissions based on a mass balance approach, validated by N deposition monitoring and satellite observations, for China for the period of 2000 to 2015. Total NH₃ emissions in China increased from 12.1 ± 0.8 Tg N yr^-1 in 2000 to 15.6 ± 0.9 Tg N yr^-1 in 2015 at an annual rate of 1.9%, which is approximately 40% higher than existing studies suggested. This difference is mainly due to more emission sources now having been included and NH₃ emission rates from mineral fertilizer application and livestock having been underestimated previously. Our estimated NH₃ emission levels are consistent with the measured deposition of NH_x (including NH₄⁺ and NH₃) on land (11-14 Tg N yr^-1) and the substantial increases in NH₃ concentrations observed by satellite measurements over China. These findings substantially improve our understanding on NH₃ emissions, implying that future air pollution control strategies have to consider the potentials of reducing NH₃ emission in China.

Ammonia emissions from an anaerobic digestion plant estimated using atmospheric measurements and dispersion modelling

Anaerobic digestion (AD) is becoming increasingly implemented within organic waste treatment operations. The storage and processing of large volumes of organic wastes through AD has been identified as a significant source of ammonia (NH3) emissions, however the totality of ammonia emissions from an AD plant have not been previously quantified. The emissions from an AD plant processing food waste were estimated through integrating ambient NH3 concentration measurements, atmospheric dispersion modelling, and comparison with published emission factors (EFs). Two dispersion models (ADMS and a backwards Lagrangian stochastic (bLS) model) were applied to calculate emission estimates. The bLS model (WindTrax) was used to back-calculate a total (top-down) emission rate for the AD plant from a point of continuous NH3 measurement downwind from the plant. The back-calculated emission rates were then input to the ADMS forward dispersion model to make predictions of air NH3 concentrations around the site, and evaluated against weekly passive sampler NH3 measurements. As an alternative approach emission rates from individual sources within the plant were initially estimated by applying literature EFs to the available site parameters concerning the chemical composition of waste materials, room air concentrations, ventilation rates, etc. The individual emission rates were input to ADMS and later tuned by fitting the simulated ambient concentrations to the observed (passive sampler) concentration field, which gave an excellent match to measurements after an iterative process. The total emission from the AD plant thus estimated by a bottom-up approach was 16.8±1.8mgs(-1), which was significantly higher than the back-calculated top-down estimate (7.4±0.78mgs(-1)). The bottom-up approach offered a more realistic treatment of the source distribution within the plant area, while the complexity of the site was not ideally suited to the bLS method, thus the bottom-up method is believed to give a better estimate of emissions. The storage of solid digestate and the aerobic treatment of liquid effluents at the site were the greatest sources of NH3 emissions.

Urban NH3 levels and sources in six major Spanish cities

A detailed spatial and temporal assessment of urban NH3 levels and potential emission sources was made with passive samplers in six major Spanish cities (Barcelona, Madrid, A Coruña, Huelva, Santa Cruz de Tenerife and Valencia). Measurements were conducted during two different periods (winter-autumn and spring-summer) in each city. Barcelona showed the clearest spatial pattern, with the highest concentrations in the old city centre, an area characterised by a high population density and a dense urban architecture. The variability in NH3 concentrations did not follow a common seasonal pattern across the different cities. The relationship of urban NH3 with SO2 and NOX allowed concluding on the causes responsible for the variations in NH3 levels between measurement periods observed in Barcelona, Huelva and Madrid. However, the factors governing the variations in A Coruña, Valencia and Santa Cruz de Tenerife are still not fully understood. This study identified a broad variability in NH3 concentrations at the city-scale, and it confirms that NH3 sources in Spanish urban environments are vehicular traffic, biological sources (e.g. garbage containers), wastewater treatment plants, solid waste treatment plants and industry. The importance of NH3 monitoring in urban environments relies on its role as a precursor of secondary inorganic species and therefore PMX. Further research should be addressed in order to establish criteria to develop and implement mitigation strategies for cities, and to include urban NH3 sources in the emission inventories.