NSP2 route with V2 - Line A
7.6 Climate and air
The climate and air quality in the Baltic region is an important factor that influences the environ-ment and living conditions for the associated fauna and flora, as well as for humans. Therefore, climate and air quality is considered an important receptor. In this section, the present and fu-ture climate and the factors affecting air quality are presented.
Current climate
Meteorological forces together with hydrographical processes, have a strong influence on the en-vironmental conditions of the Baltic Sea. These processes influence the water temperature and ice conditions, the regional river run-off, and the atmospheric deposition of pollutants on the sea sur-face. Moreover, they also govern water exchange with the North Sea and between the sub-basins, as well as the transport and mixing of water within the various sub-regions of the Baltic Sea /127/.
The Baltic Sea is located in the temperate climate zone, which is characterised by large seasonal contrasts. The climate is influenced by major air-pressure systems, particularly the North Atlantic Oscillation during wintertime, which affects atmospheric circulation and precipitation in the Baltic Sea basin.
Within the Danish EEZ, the combination of the proposed NSP2 route with either the NSP2 route V1 or the NSP2 route V2 will extend east and south of Bornholm. Measurements during the period 1985-2005 at two stations on Bornholm have shown a temperature variation from 1.5 °C as the average for January to 17.4 °C as the average for August. The average yearly temperature is 8.5
°C /152/.
Although average precipitation in general is higher over land than at sea, the precipitation at Born-holm can be considered representative of conditions for the pipeline section in the Danish EEZ.
Measurements during the period 1985-2005 at three stations on Bornholm showed an average yearly precipitation of 655 mm. The average monthly precipitation varied from a minimum of 36 mm in April to a maximum of 76 mm in September /152/.
The Baltic Sea is located within the west-wind zone, where low-pressure weather systems coming from the west or south-west dominate the weather scene. Cyclones from a more southerly direction can enter the region periodically. Winds are closely related to the cyclones and pressure gradients around these wind systems. Winds of storm force, i.e. at least 25 m/s, are almost exclusively connected to deep cyclones that form west of Scandinavia and occur mainly from September to
March. The winds in the Bornholm area are dominated by easterly winds in spring, although west-erly winds are also common. During the rest of the year, winds from the west prevail /152/.
In the Baltic Sea, ice can appear as fast ice or as drift ice. Fast ice is smooth and stationary and can be attached to islands, islets and shallow reefs. Fast ice usually appears at a water depth of up to 15 m /153/. In deeper waters in the open sea, ice is more dynamically formed, consisting of drift ice that moves along with the currents and winds. On stormy days, drift ice can move 20-30 km. Drift ice and deformed ice can easily get packed against one another or other obstacles, which can result in pack ice or vast ice ridges /153/.
In the areas where the proposed NSP2 route, the NSP2 route V1 and the NSP2 route V2 cross the Danish EEZ, the probability of ice formation is 10-25%, which is relatively low compared with other parts of the Baltic Sea. In Danish waters, ice extends to the proposed NSP2 route, NSP2 route V1 and NSP2 route V2 only during severe winters, and the maximum annual ice thickness is less than 10 cm in the waters around Bornholm /154/.
Atlas Map CL-01 shows the extent of ice cover during three recent winters: 2010-2011 (severe winter), 2012-2013 (average winter), and 2014-2015 (mild winter).
Future climate
The annual mean sea surface temperature has increased by up to 1°C per decade from 1990 to 2008. At the same time, the annual maximum ice extent of the Baltic Sea has decreased about 20% over the past 100 years, and the length of the ice season has decreased by about 18 days/cen-tury in the Bothnian Bay and 41 days/cendays/cen-tury in the eastern Gulf of Finland /111/. The purpose of this section is to describe how the forecasted global climate changes can be expected to affect the Baltic Sea region during the NSP2 lifetime.
An oceanographic study published by the Swedish Meteorological and Hydrological Institute (SMHI) in 2007 shows that average sea surface temperatures for the entire Baltic Sea could increase by some 2-4ºC by the end of the 21st century /156/. Ice extent in the sea would also decrease by 50-80%. Increased freshwater inflow and increased mean wind speeds may cause the Baltic Sea to reach a new steady state with significantly lower salinity. In the southern Baltic Sea, oxygen con-centrations may decrease and phosphate concon-centrations may increase, thereby resulting in in-creased phytoplankton biomass. A report issued by HELCOM in 2013 largely confirmed these find-ings /155/ and concluded that the summer sea surface temperature is likely to increase by 2-4°C by the end of this century, and that there will be a drastic decrease in sea-ice cover in the Baltic Sea. In a recent report from HELCOM, it is noted that long-term changes in surface water salinity and temperature occur in response to climate change and increased input of freshwater. Further-more, increased levels of carbon dioxide in the atmosphere are expected to cause acidification, with a decreasing pH in the long term /111/.
Air quality
The air quality in the Baltic Sea is influenced by a combination of global, regional and local emis-sions. Industrialisation of the coastal and inshore areas around the Baltic Sea has led to increased levels of air pollutants in these areas, which decrease with distance from shore. Shipping is con-sidered the major source of atmospheric pollution offshore.
The Baltic Sea constitutes one of the most intensely trafficked seas in the world and accounts for approximately 15% of the world’s cargo transportation, see section 7.15. There is considerable traffic density in the central Baltic Sea and west of Gotland, which amounts to approximately 57,000 vessel passages annually. Twenty percent of this volume is comprised of tankers of lengths in excess of 150 m.
Pollutants originating from the combustion of fuel on ships can be divided into the following com-pound groups:
• Carbon dioxide (CO2);
• Nitrogen oxides (NOX), a term covering both NO and NO2;
• Sulphur oxides (SOX), particularly sulphur dioxide (SO2);
• Carbon monoxide (CO);
• Particulate matter (PM);
• Hydrocarbons (HC).
CO2 is emitted due to the carbon content in the fuel, whereas NOX is emitted due to the nitrogen gas (N2) content of atmospheric air. The amount of NOX formed depends on the combustion pro-cess. Sulphur is naturally present in fuels. Combustion therefore gives rise to emissions of SO2 or SOX and PM, including primary soot particles and secondary inorganic sulphate particles formed as a result of atmospheric oxidation of sulphur dioxide. The remaining compounds are a result of incomplete combustion and impurities in the fuel.
CO2 is an important GHG, i.e. the emission of CO2 contributes to the greenhouse effect. The ma-jority of the global emission of CO2 originates from burning of fossil fuels such as coal, oil, gas and natural gas used in power plants, dwellings, industry and transport. Furthermore, increasing CO2
levels in the atmosphere may contribute to lower pH in water bodies when dissolved in water. The other GHGs, such as methane (CH4) and nitrous oxide (N2O), are not products of fuel combustion.
NOX is a term covering NO and NO2. It is formed during the combustion of fuel in gas and diesel engines due to the oxidation of nitrogen in the combustion air and in the fuel. Emissions of NOX
contribute to acidification, which can cause effects on ecosystems in both terrestrial and marine environments. Furthermore, NOX emissions contribute to eutrophication, where high nutrient con-centrations stimulate growth and thereby affect the natural state of ecosystems in both in terres-trial and marine environments. On a local scale, NOX emissions are able to contribute to the for-mation of ground-level ozone and impact human health. It is estimated that about 15% of anthro-pogenic NOX emissions are due to shipping /157/.
Sulphur is naturally present in fuels. It is emitted from the burning of coal and oil at power plants and mobile sources such as the shipping industry. Continuous tightening of the allowed sulphur content in fuels has gradually reduced the SO2 emissions from ships. SO2 contributes to acidification and can impact human health and cause degradation of buildings on a local scale. It is estimated that approximately 7% of the anthropogenic SO2 emissions are due to shipping /157/. The Baltic Sea has status as a Sulphur Emission Control Area (SECA), meaning that ships must use low-sulphur fuel or have a delow-sulphurisation system on board.
CO is a colourless, odourless gas emitted from combustion processes. Nationally, and particularly in urban areas, the majority of CO emissions to ambient air come from mobile sources, e.g.
transport. CO can cause harmful health effects by reducing oxygen delivery to the body's organs (including the heart and brain) and tissues.
Combustion of fuels gives rise to the emission of particulate matter, e.g. soot particles (primary particles). However, the majority of particles with regard to air pollution originate from pollution
“born” as gases and transported over long distances, e.g. inorganic sulphate particles formed as a result of atmospheric oxidation of sulphur dioxide. Particulate matter can be transported long dis-tances and may have impacts on human health. Particulate matter is usually handled as PM10
(particles <10 µm) and PM2.5 (particles <2.5 µm), respectively.
HCs belong to a larger group of chemicals known as volatile organic compounds (VOCs). HCs are compounds of hydrogen and carbon only, while VOCs may contain other elements. They are pro-duced by incomplete combustion of hydrocarbon fuels and also by their evaporation. Because there are many hundreds of different compounds, HCs and VOCs display a wide range of properties.
Some, such as benzene, are carcinogenic; some are toxic and others are harmless to health.
When pollutants are emitted to the atmosphere, they can cause impacts of local, regional and global range. Emissions of the four main polluting compounds, CO2, NOX, SOX and PM, are pre-sented in the following.
In 2016, the total annual Danish emissions of CO2, NOX, SOX and PM caused by shipping (national and international) were approximately 2,596,000 t of CO2, 58,687 t of NOx, 1,636 t of SOx, and 1,497 t of PM, respectively /328/.
Looking at emissions from all vessels sailing in the Baltic Sea, the total emissions (2015) amounted to 15,900,000 t of CO2, 342,000 t of NOX, 10,000 t of SOX and 10,000 t of PM /158/.
7.7 Plankton
Zoo- and phytoplankton constitute important components of the food chain in the Baltic Sea, and are thus considered an important receptor despite not being protected species.
Phytoplankton
Phytoplankton is a group of microscopic photosynthetic organisms (e.g. diatoms, dinoflagellates and cyanobacteria). They are the main source of primary production in the Baltic Sea and form the basis of the marine food chain.
7.7.1.1 Phytoplankton in the Baltic Sea
Phytoplankton grow photosynthetically (by using light as an energy source). Growth is therefore limited to roughly the upper 20 m of the water column, where sufficient light is present (photic zone). One of the key roles of phytoplankton is to provide the basis for the secondary production of higher trophic levels (zooplankton, fish, etc.). Phytoplankton also play a vital role in the bioge-ochemical cycles of many important chemical elements, e.g. the carbon cycle of the ocean.
Phytoplankton populations are highly dynamic and vary spatially in response to e.g. light condi-tions, nutrient concentracondi-tions, climatic conditions and currents. Phytoplankton also exhibit signifi-cant cyclical changes in response to seasonal variations in sunlight and temperature. For example, in the winter, the surface water is rich in nutrients, but phytoplankton biomass remains low because of the lack of light.
There are typically three annual blooms in the southern Baltic Sea /150//159//160//162//163/:
• In spring, when nutrients and light become available, the biomass of phytoplankton increases.
The spring bloom typically consists mostly of diatoms and/or dinoflagellates. When the dis-solved nitrogen is depleted, the algal biomass in the upper part of the water column decreases.
• In summer, recurrent blooms of cyanobacteria usually dominate the coastal areas and surface waters /150/. Cyanobacteria blooms depend on the available amounts of phosphate in the surface water and favourable weather conditions during the summer. Some cyanobacteria are capable of nitrogen fixation, i.e. uptake of nitrogen from the atmosphere, and can form massive visible surface accumulations of several weeks’ duration throughout large parts of the Baltic Sea /162/. One of the bloom-forming cyanobacteria, Nitzschia spumigena, can produce nodu-larin, a hepatotoxic toxin that can result in liver damage.
• In autumn, as temperatures decrease and winds increase, water mixing typically increases the supply of nutrients from nutrient-rich bottom water, which may lead to a third minor bloom.
7.7.1.2 Phytoplankton biomass in the Danish section
Chlorophyll-a is the most abundant photosynthetic pigment among all photosynthetic organisms.
Therefore it can be used to estimate the biomass of phytoplankton. Chlorophyll-a concentrations show considerable interannual variability, reflecting the variability in the phytoplankton.
Figure 7-27 shows the annual variation in the chlorophyll-a content of the surface water of the Danish section of the Baltic Sea in 2016, based on satellite measurements /160/.
Figure 7-27 Annual variation in the chlorophyll-a content of the surface water in the Danish section of the Baltic Sea, based on satellite measurements from 2016 /160/.
Long-term trends in the summer biomass of phytoplankton are shown for the Bornholm Basin in Figure 7-28.
Figure 7-28 Long-term trends in in-situ chlorophyll-a concentrations in summer (Jun-Sep) in the Bornholm Basin, 1970-2015. Dashed lines indicate the 5-year moving average and error bars represent the standard error /161/.
For the Bornholm Sea (north and east of Bornholm), the concentrations of surface chlorophyll-a pigments for the periods 1979-1989, 1990-1999 and 2000-2005 are shown in Figure 7-29 /160/.
The data series from 1979-1989 shows a pattern with two peaks in spring and autumn, with a maximum chlorophyll-a concentration of 2.75 mg/m3 (in November). The data series from 1990-1999 and 2000-2005 are similar, and show three peaks in spring, summer and autumn, with a maximum chlorophyll-a concentration of 5 mg/m3 (in April). More recent time series data from the Bornholm Basin for 2007-2011 /147/ and from 2010-2016 /164/ show chlorophyll-a concentrations of up to 5 µg/l, which are comparable to the values presented in Figure 7-29 /159/.
Figure 7-29 Seasonal patterns of chlorophyll-a (mg/m3, monthly mean) for 1979-1989, 1990-1999 and 2000-2005 in the Bornholm Sea east of Bornholm, based on measurements of 0-10 m depth. Figure re-drawn from /159/.
In the Arkona Basin (west of Bornholm), the chlorophyll-a concentration has been measured as part of a long-term monitoring programme from the Danish environmental authorities /165/. The chlorophyll a concentration typically varies in a similar pattern as described above, with three peaks in spring, summer and autumn, with a maximum of 6 mg/m3 /165/.
Figure 7-30 Biomass of phytoplankton (shown as carbon (C) and chlorophyll-a) in the surface layer of the open water monitoring stations in Arkona Basin. Figure redrawn from /165/.
As noted in section 7.5.3, eutrophication is a condition in an aquatic ecosystem where high nutrient concentrations stimulate growth of phytoplankton, leading to imbalanced functioning of the system.
HELCOM has presented the eutrophication status of the Baltic Sea 2007-2011, by defining the GES level for each basin in the Baltic Sea, with a chlorophyll-a average for summer (June-September).
In the areas near the proposed NSP2 route, the NSP2 route V1 and the NSP2 route V2 (Bornholm Basin), the GES level for chlorophyll-a is 1.8-2.0 µg/l (c. 1.8-2.0 mg/m3) /147//161/. The current conditions (chlorophyll-a concentrations as described above) are thus higher than the GES thresh-old.
7.7.1.3 Phytoplankton composition in the Danish section
Phytoplankton in the Baltic Sea belongs primarily to the following taxonomic groups: Cyanobacte-ria, Cryptopheceae, Dinophyceae (dinoflagellates), Bacillariophyceae (diatoms), Chryosphyceae, and Mesodiunium rubrum (a protozoan capable of photosynthesis). Though interannual variation is high, there is some consistency in the species composition /159/.
The composition of the phytoplankton biomass in the Bornholm Sea east of Bornholm (2004 data), split into main taxonomical groups, is shown in Figure 7-31 /159/. In early February, the biomass is low and consists primarily of Cryptophyceae. Later in the month, M. rubrum starts to form a larger part of the population. The spring bloom (March-May) in the Bornholm Sea consists primarily of Mesodiunium rubrum. There is no dominance by typical spring bloom groups of the southern Baltic Sea (diatoms and/or dinoflagellates) in 2004 /159/. The species composition during the summer bloom varies, and in 2004 consisted of Cryptophyceae (Plagioselmis prolonga), cyanobac-teria (Aphanotece sp.), dinoflagellates, and other (Phacus sp.). The autumn bloom in 2004 was dominated by diatoms (Coscinodiscus granii) /159/.
Figure 7-31 Seasonal variation of phytoplankton biomass (mg chl a/m3) in the Bornholm Sea east of Born-holm in 2004, split into the main taxonomical groups. Figure redrawn from /159/.
7.7.1.4 Phytoplankton along the proposed NSP2 route, the NSP2 route V1 and the NSP2 route V2 The Peter Gaz surveys in 2005 and 2006 found that the Bacillariophyta algae were the most abundant at the stations located along the proposed NSP2 route, the NSP2 route V1 and the NSP2 route V2. The sampling was carried out in October 2005 and April/May 2006. The station numbers changed between sampling years, but are grouped in the below figure according to lo-cation.
Figure 7-32 Phytoplankton biomass at the Peter Gaz sampling stations. The lower station numbers spond to the general area of the NSP2 route V1 and the NSP2 route V2, whilst station 84/469 corre-sponds to the southern-most part of the proposed NSP2 route, see section 7.1.1.2.
7.7.1.5 Biodiversity status
In 2017, HELCOM released the integrated biodiversity status assessment for the pelagic habitats using the core indicators “Cyanobacterial bloom index” and “Chlorophyll-a” /111/. This assessment shows that in the Arkona Basin and Bornholm Basin, the integrated biodiversity status assessment for pelagic habitats is “not good” /111/.
7.7.1.6 Conservation status
The Danish Red List /166/, HELCOM Red List /167/ and EU Habitats Directive do not include phy-toplankton.
Zooplankton
Zooplankton play an important role as a food source for fish. Zooplankton taxa often have different value as prey, because of the taxa-specific variations in size, abundance, escape response and biochemical composition /161/.
7.7.2.1 Zooplankton in the Baltic Sea
The zooplankton community in the Baltic Sea consists of freshwater, brackish and marine species, which are distributed vertically and horizontally depending on their ecophysiological tolerances and the availability of food resources /150//168/.
The zooplankton of the Baltic Sea are generally dominated by calanoid copepods and cladocerans.
The thermocline and halocline in the Baltic Sea constrain the vertical distribution of zooplankton species, resulting in characteristic vertical assemblage patterns in the different layers of the water column. In the Baltic Sea, rotifers such as Keratella quadrata and copepods, e.g. the estuarine Eurytemora hirundoides, are present, as well as species from shallow coastal waters, e.g. Acartia spp. Occasionally, species of crustaceans from the North Sea, e.g. Paracalanus parvus and Oithona similis, are found, mainly below the halocline in the southern part of the Baltic Sea. Cladocerans, e.g. Evadne nordmanii, can also comprise a considerable part of the zooplankton community
/169//170/. Within the meso- and macrozooplankton, copepods Pseudocalanus spp., Temora lon-gicornis, Acartia spp., and cladocerans Evadne nordmanni are the most important taxa in the open Baltic Sea in biomass and production /150/.
Species-specific preferences often result in both seasonal and inter-annual changes in vertical abundance that, when combined with depth-specific water currents, also lead to horizontal differ-ences in spatial distribution.
Fluctuations in zooplankton populations are well-known and related to the physical environment,
Fluctuations in zooplankton populations are well-known and related to the physical environment,