Air signals

Despite significant reductions in nitrogen emissions in Europe over the last three decades, eutrophication remains an environmental concern in the Baltic Sea basin. The waterborne input of nitrogen (mainly through river inflow) generally outweighs its airborne deposition; however, the latter occurs at the surface, where phytoplankton activity is greatest, and therefore particularly encourages plankton growth. Atmospheric nitrogen deposition remains a significant issue in the Baltic Sea.

Reducing atmospheric nitrogen deposition will be key to bringing the Baltic Sea’s total nitrogen levels under the maximum allowable input, a threshold set by the Baltic Marine Environment Protection Commission (Helcom).

Trends and main sectors contributing to airborne nitrogen deposition

Between 2000 and 2020, ammonia and nitrogen oxide emissions in the EU-27 decreased by 13% and 52%, respectively (EEA, 2022). Airborne nitrogen deposition to the Baltic Sea also decreased during the same general period, by around 25% (Gauss et al., 2021).

Impacts of eutrophication

Intensive algal blooms have become increasingly frequent in recent years as a result of a combination of excess nutrients and the increase in temperature in Baltic and Finnish coastal waters. In the Baltic Sea, there are two annual blooms: the spring bloom and the cyanobacterial bloom in late summer. In the southern Baltic Sea, autumnal blooms occur regularly. Additionally, exceptional blooms can occur locally (European Space Agency, 2022).

Massive algal and cyanobacterial blooms, caused by excess nutrients, can lead to ‘dead zones’ — areas where oxygen levels are too low for marine organisms to live. To combat this, Helcom recommends total maximum input limits for nitrogen. These limits clarify the maximum nitrogen level that the Baltic Sea sub-basins specifically can absorb; the target is 792,000 tonnes of nitrogen per year (Helcom, 2013).

Algal blooms along the Baltic coast also result in significant losses for the aquaculture industry. Summer cyanobacterial blooms in the Baltic Sea create foul bathing water and poor-quality beaches. This has an impact on tourism and raises health concerns, as some cyanobacteria produce toxins (Karlson et al., 2021).

Ground-level ozone is formed in the atmosphere when the air pollutants nitrogen oxides, methane and non-methane volatile organic compounds combine with sunlight. While the levels of these air pollutants have decreased over the last few decades, ozone is still one of the most prominent air pollution problems in Europe because of its effects on crops and natural ecosystems (EEA, 2022).

Ground-level ozone polluting the air damages vegetation. Ozone enters the plant leaf and reduces photosynthesis, slowing the plant’s growth and increasing its vulnerability to pests and disease. At the ecosystem level, high levels of ground-level ozone can drive species diversity loss and lead to changes to ecosystem structure and habitat quality.

Ground-level ozone also damages agricultural crops and timber, affecting the quality and yield of production and entailing significant economic losses for the sector. For example, in 2019, losses in wheat yields due to exposure to ozone were 9% in Greece, with losses of between 8% and 9% seen in Albania, Cyprus, Czechia and Portugal. In 17 European countries, the wheat yield loss due to ground-level ozone exposure exceeded 5%.

The countries most affected by economic losses from ground-level ozone’s impact on wheat yields are those with high overall wheat production (see Figure 1). Losses in wheat yields were highest in France, reaching €350 million, followed by €280 million in Germany and €140 million in Poland. Most countries faced losses worth several millions of euros (ETC/ATNI, 2021).