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This chapter comprises the following sections: names, taxonomy, subspecies and distribution, descriptive notes, habitat, movements and home range, activity patterns, feeding ecology, reproduction and growth, behavior, parasites and diseases, status in the wild, and status in captivity.
Humans disturb bears in many ways, either directly when they encounter humans or indirectly by changing their behavior and way of life to avoid humans, human activity, and infrastructure. Here we summarize research on how brown bears normally react when encountering humans, what a human encounter may entail for a bear, and whether bears habituate or change their behavior toward humans with increased exposure. Based on this, we also discuss: (a) how our knowledge of brown bear behavior may help people to deal with their fear of bears, and not limit their use of outdoor areas with bears; (b) how human presence, activity, and infrastructure have an indirect effect on bears, that is, how bears change their movement pattern, use of terrain and vegetation, and daily activity pattern to avoid humans; (c) how human disturbance influence foraging and denning, which is crucial for brown bear growth and reproduction; and (d) apparent differences among continents in brown bear behavior toward humans and whether this may have an evolutionary cause.
The two main groups of atmospheric reactive nitrogen compounds (reduced and oxidized nitrogen) have different fates due to differences in governing processes.
Abatement strategies need to take into account these differences when assessing the impact on the sensitive ecosystems.
The chapter outlines the governing physical and chemical processes for the two main groups of reactive nitrogen compounds.
The chapter is divided into sections concerning: emissions, transformation, aerosol processes, dry deposition and wet deposition.
Key findings/state of knowledge
Reactive nitrogen compounds consist of reduced nitrogen (ammonia and its reaction product ammonium), oxidized nitrogen (nitrogen oxides) and organic nitrogen compounds.
Nitrogen oxides have little impact close to the sources since they are emitted as nitrogen monoxide and nitrogen dioxide with low dry deposition rates. These compounds need to be converted into nitric acid (about 5% per hour) before deposition is efficient.
Ammonia has a high impact near the sources due to high dry deposition rates. Ammonia may therefore have significant impact on ecosystems in areas with intense agricultural activity leading to high emissions of ammonia.
Both ammonia and gaseous nitrogen oxides lead to formation of aerosol phase compounds (ammonium and nitrate) which are transported over long distances (up to more than 1000 km).
Very little is known either quantitatively or qualitatively about organic nitrogen compounds, other than that they can contribute a significant fraction of wet-deposited N, and are present in gaseous and particulate forms in the atmosphere.
Observations of atmospheric reactive nitrogen (Nr) deposition are severely restricted in spatial extent and type. The chain of processes leading to atmospheric deposition emissions, atmospheric dispersion, chemical transformation and eventual loss from the atmosphere is extremely complex and therefore currently, observations can only address part of this chain.
Modelling provides a way of estimating atmospheric transport and deposition of Nr at the European scale. A description of the different model types is provided.
Current deposition estimates from models are compared with observations from European air chemistry monitoring networks.
The main focus of the chapter is at the European scale; however, both local variability and and intercontinental Nr transfers are also addressed.
Key findings/state of knowledge
Atmospheric deposition is a major input of Nr for European terrestrial and freshwater ecosystems as well as coastal sea areas.
Models are key tools to integrate our understanding of atmospheric chemistry and transport, and are essential for estimating the spatial distribution of deposition, and to support the formulation of air pollution control strategies.
Our knowledge of the reliability of models for deposition estimates is, however, limited, since we have so few observational constraints on many key parameters.
Total Nr deposition estimates cannot be directly assessed because of a lack of measurements, especially of the Nr dry deposition component. Differences among European regional models can be significant, however, e.g. 30% in some areas, and substantially more than this for specific locations.
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