Air pollution, climate change, UV radiation and PBTs all have effects on the health of natural ecosystems and wildlife. These adverse impacts in turn affect the services provided to humans by those ecosystems, or ‘nature’s contribution to people’ (NCP) (Diaz et al. 2018).
Since the 1970s, international attention has focused on air pollution in the form of wet and dry deposition of sulphur and nitrogen, often referred to as ‘acid rain’, which led to acidification of soils and fresh water, and damage to vegetation and fish kills. In Asia and Africa, significant increases and decreases in sulphur deposition have been observed depending on location (Vet et al. 2014). In Western Europe and eastern North America, after decades of declining sulphur emissions and deposition levels, acidification is declining or slowing, and some forests and lakes are showing signs of recovery (Maas and Grennfelt eds. 2016). As sulphur emissions have decreased due to the implementation of emission controls, recent assessments have focused attention on the effect that humans have had on the global nitrogen cycle and its implications.
Human activity, mainly through combustion and fertilizer production, are responsible for as much nitrogen fixation as natural and unmanaged ecosystems, significantly altering the nitrogen cycle from its pre-industrial state (Fowler et al. 2015). Since 2000, nitrogen deposition has decreased in North America and Europe and increased in Africa and Asia, directly corresponding to decreases of NOX and increases in NH3 continent-wide emissions (Zhao et al. 2017). Nitrogen deposition exceeds critical loads over large parts of Europe and the area of exceedance has shown little change in recent decades (Hettelingh et al. 2015). High levels of nitrogen deposition contribute to the eutrophication of aquatic ecosystems and can affect terrestrial plant communities, possibly favouring dominant species, which in turn affects insects, birds and other animals. The loss of biodiversity due to excess nitrogen deposition is very likely to be occurring in many parts of the world, although the impacts have not been well quantified. Changes in climate, land use and other global changes will continue to alter the nitrogen cycle in the future, with consequences for ecosystems and human health (Fowler et al. 2015).
Marine ecosystems are also affected by air pollution, climate change and PBT pollution, for instance through the distribution of oceanic dissolved nutrients and oxygen (York 2018). Human activity is now increasing the inputs of all fixed nitrogen to the oceans by about 50 per cent (more in local hotspots near high emission regions in South-East Asia, Europe and North America) and atmospheric transport is now the dominant route contributing anthropogenic nitrogen into the open ocean beyond the continental shelf (Joint Group of Experts on the Scientific Aspects of Marine Environmental Protection [GESAMP] 2018). Harmful algal blooms in turn can contribute to respiratory health impacts through airborne transmission of aerosols (Centers for Disease Control and Prevention 2017).
Ozone exposure can affect plant growth, flowering, pollination and susceptibility to pathogens, with impacts on species composition and biodiversity (Fuhrer et al. 2016). Critical load thresholds have been identified for some terrestrial ecosystems (International Cooperative Programme on Effects of Air Pollution on Natural Vegetation and Crops 2017), but there are many ecosystems for which O3 sensitivity is poorly understood.
The full extent of PBT exposure and their biological effects on wildlife and natural ecosystems is still not well known and is an area of active research (AMAP 2017). However, given the widespread presence of PBTs in the environment, the potential exists for long-term damage to food chains and ecosystem functions especially in sensitive areas, such as the Arctic (AMAP 2011; AMAP 2016; AMAP 2017).