HELCOM Baltic Sea Environment Fact Sheets for 2010

As the environmental focal point for the Baltic Sea, HELCOM, has been assessing the sources and inputs of nutrients and hazardous substances and their effects on ecosystems in the Baltic Sea for almost 30 years. The resulting fact sheets presented here are based on scientific research carried out around the Baltic Sea under the HELCOM PLC, COMBINE and MORS monitoring programmes. Since 2002 years, HELCOM Baltic Sea Environment Fact Sheets (previously called indicator fact sheets ¹) have been compiled by responsible institutions around the Baltic and approved by the HELCOM Monitoring and Assessment Group for publication. 

Note that HELCOM is developing a "core set" of indicators for assessing the progress towards reaching the goals and objectives of the HELCOM Baltic Sea Action Plan. So far a demonstration set of core eutrophication indicators has been adopted, and work is on-going under the HELCOM CORESET project to develop indicators for hazardous substances and biodiversity.

Changing seasons

After a continuous increase in the annual sea surface temperatures average, in 2009 the sea surface temperature decreased. The year of 2009 was characterized by comparatively warm months from January until May in far parts of the Baltic Sea. The heating phase normally observed in June in the southern and central Baltic Sea did not occur, but the Bothnian Sea was comparatively warm. August was the warmest month and in September long lasting westerly winds led to strong upwelling of cold water along the Swedish east coast. In December the south-western Baltic Sea cooled down, but in the northern Baltic Sea the sea surface temperature was above the long-term average.

The ice season of 2009-2010 was average in terms of ice extent. The largest ice cover – 244,000 km² – was reached almost two weeks earlier than average on the 17^th of February. The ice winter was in the Bay of Bothnia over a month shorter than normal. In the Quark, the season was two weeks longer than normal and in the Gulf of Finland the ice winter was from a week to more than month longer than normal. On the 31^st May the Baltic Sea was ice free.

The wave climate in the Baltic Sea was calmer that usual during the first four months of 2009. During the summer months the mean significant wave height was close to the long term mean values, except in June, when the wave climate was clearly rougher than usual in the Western Baltic Proper. The autumn season was characterised by a September that was rougher and a December that was calmer than usual.

Life pulsates according to water inflows

The present state of the Baltic Sea is not only the result of anthropogenic pressures but is also influenced by meteorological conditions and hydrographic forces such as water exchange between the Baltic Sea and the North Sea. The inflow of waters from the Kattegat into the Baltic Sea during 2002-2003 terminated the stagnation period in the Baltic deep water which lasted since 1995. The period afterwards has been characterized by low inflow activities and except for in the southern Baltic, the stagnation period lasting since 2004/2005 has resulted in a continuous increase in hydrogen sulphide concentrations in the central basins. is  A baroclinic inflow in summer 2006, followed by small barotropic inflows in 2007 and 2009 caused high temperatures observed in the central Baltic deepwater. As a result of the minor but frequent barotropic and baroclinic inflow activity, no hydrogen sulphide was found in the Bornholm Basin in 2008, 2009, and in the first half of 2010.

This stagnation period has resulted in poor oxygen conditions in the deep basins of the central Baltic. The area of the central Baltic affected by hypoxia (oxygen deficiency) and anoxia (absence of oxygen) remains very high, although a slight improvement (reduction) in the anoxic area has occurred in the last three years. Deep water salinity remains high in the Baltic Proper, which hampers vertical mixing. Hydrogen Sulphide is present in the deep water of the East Gotland Basin, the Northern Baltic Proper and West Gotland Basin.

Meteorological conditions, including wind patterns and precipitation affect the inflow of water from the catchment area and the deposition of pollutants directly onto the sea. The total runoff to the Baltic Sea area shows no long-term trend for the period 1950 – 2009, although this time period is characterised by dry and wet periods lasting for between a couple of years and a decade. In the last 12 years, the total inflow to the Baltic Sea has decreased from a top flow rate of over 17,500 m³/s in 1998 to less than 11,000 in 2003. In 2009 the runoff was below the mean value, and since 2003, only 2008 has seen runoff above the mean value. Both the Gulf of Finland and Gulf of Riga had a above average runoff during 2009, but for the Baltic Proper and Gulf of Bothnia the runoff was below the mean value. When looking at the entire Baltic Sea, the difference from the mean value was -4%.

The Baltic Sea continues to suffer the impacts of human activities

Baltic Sea habitats and species are threatened by eutrophication and elevated amounts of hazardous substances as a result of decades of human activities in the sea and its surrounding catchment area.

The inputs of some hazardous substances to the Baltic Sea have reduced considerably over the past 20 to 30 years, in particular discharges of heavy metals. In 2006, the reported waterborne loads of mercury. lead and cadmium entering the Baltic Sea were 10.8 tonnes, 274 tonnes and 47.5 tonnes, respectively. During the period 1994-2006 riverine annual heavy metal loads (notably cadmium and lead) seem to have decreased for most of Contracting Parties. 

Annual emissions of heavy metals to the air from HELCOM countries have decreased during the period from 1990 to 2008 by 47% for cadmium, 52% for mercury, and 86% for lead. During the same period, the amount of cadmium, mercury and lead deposited on the Baltic Sea via the atmosphere has decreased by 44%, 26%, and 71% respectively.

Annual emissions of dioxins and furans have decreased in HELCOM countries during the period 1990-2008 by 22%. In 2008 total annual PCDD/F emissions of HELCOM countries amounted to 1.4 kg TEQ. Among the HELCOM countries the largest contributions to the total annual PCDD/F emission of HELCOM countries belong to Russia (58%) followed by Poland (28%) and Germany (5%) .In the same period, the annual atmospheric deposition fluxes of PCDD/Fs over the Baltic Sea have decreased by 50%. The most significant change in PCDD/F atmospheric deposition can be noted for the Kattegat (57%) and the Baltic Proper (54%).

A range of anthropogenic activities contribute to the significant inputs of nutrient to the sea, which enter the sea via runoff, riverine input, through direct waterborne discharges or via atmospheric deposition. Although nutrient inputs from point sources such as industries and municipalities have been cut significantly, the total input of nitrogen to the Baltic Sea is still almost 837,500 tonnes per year, of which approximately 25% enters as atmospheric deposition on the Baltic Sea and 75% as waterborne inputs. The total input of phosphorus to the Baltic Sea in 2006 was ca 28,000 tonnes and entered the Baltic Sea mainly as waterborne input with the contribution of atmospheric deposition being only 1-5 % of the total. The main source of nutrient loads to the Baltic Sea is agriculture.

When comparing the 2006 waterborne nutrient loades to the 10 year average (1997-2006), waterborne nitrogen input load has decreased by about 5%, and phosphorus by almost 15%. The riverine, coastal and point source flow in 2006 was 11% lower than the 10-year flow average suggesting that a large part of the nitrogen and phosphorus reductions are due to hydrological variations. Total waterborne phosphorus inputs have clearly decreased suggesting positive effects of the implementation of load reduction measures in catchment area. It is known that the load reduction measures are particularly efficient for phosphorus in municipal wastewater treatment plants.

For most of the HELCOM countries, there was a decline in the annual emissions of nitrogen to the air during the period 1995 – 2007. The opposite trend can be noticed for ammonia emissions from Finland and Lithuania and nitrogen oxides emissions from Latvia and especially Russia. Emissions from outside the Baltic Sea region add to the airborne nitrogen loads entering the Baltic, as do emissions from shipping. The emission levels of Baltic Sea shipping have decreased in general, carbon monoxide emissions being an exception to this rule. The decrease of NO_x, SO_x and PM2.5 compared to 2008 were -2 %, -3.7 % and -2.6 %, respectively. Energy consumption, fuel consumption and CO₂ emissions have all decreased by 1.8 %. Summer months dominate the emissions and also the number of ships peak during June, July and August when the passenger traffic most intensive.

Mainly because of interannual changes in meteorological conditions, annual nitrogen depostion to the Baltic Sea and its sub-basins varies significantly from one year to another in the period 1995 - 2008. Annual depositons of oxidised, reduced and total nitrogen in 2008 are respectively 2.6%, 2.3% and 2.5%  lower than in 1995.

Eutrophication intensifies phytoplankton blooms

Eutrophication is the result of excessive nutrient inputs to the ecosystem and is an issue of major concern almost everywhere around the Baltic Sea area. The excess nutrients have resulted in an increased average biomass production by a factor of 2.5, leading to decreased water clarity*, exceptionally intense algal blooms, more extensive areas of oxygen-depleted sea beds as well as degraded habitats and changes in species abundance and distribution.**

A decrease in water clarity* has been observed in all Baltic Sea sub-regions over the last one hundred years, with it being most pronounced in the Northern Baltic Proper and the Gulf of Finland. An increase in water transparency during the last 20 years has been detected in the Bornholm and Arkona Seas and in Kattegat and the Eastern Gotland Basin the decreasing trend has ceased during the past 10 to 15 years with the water transparency remaining at about the same level.

In 2008, the concentrations of dissolved surface nutrients** near the surface increased until March-April in the Gulf of Finland and until February in the Northern Baltic Proper and the Bornholm Sea. This is considerably later than during the previous two years.

The spatial distribution of inorganic (primary bio-available) nutrients (in surface waters, during winter) highlights problem areas, and shows the availability of nutrients for the spring bloom. Changes in the spatial distribution may indicate changes in the hydrography or the effect of remedial works. Dissolved inorganic nitrogen (DIN) levels in 2009/2010 remain well below the 1993 – 2002 average, except in some nearshore areas. Winter levels of dissolved inorganic phosphorus (DIP) remain above the 1993 - 2002 average in the surface waters of the Baltic Proper and the eastern Bothnian Sea.

The spring bloom biomass (phytoplankton biomass) was higher than usually in the Southern and Northern Baltic Proper, but lower and longer in the Gulf of Finland due to strong mixing in March. The invasive alien dinoflagellate Prorocentrum minimum was very abundant in late August and September in the Northern Baltic Proper.

Cyanobacterial blooms in the Baltic Sea during the summer of 2010 were restricted to the first three weeks of July and mostly affected the southeastern parts of the Baltic Proper. Blooms were frequently observed in the northern Baltic Proper, the outer parts of the Gulf of Finland and in the Hanö Bight. However, after three weeks the blooms scattered and only minor surface blooms where detected in August. As in previous years, blooms occurred in the central and eastern Bothnian Sea during the second half of August, but the surface accumulations were less prominent. This year's bloom was normal in an initial comparison with previous years.

The cyanobacteria bloom index** shows, that in 2007 the toxic Nodularia spumigena rank based abundance was highest ever recorded and twice as high as in the previous year, while Aphanizomenon flos-aquae showed slightly higher values in the year 1999.

The satellite-derived chlorophyll-like pigments** in the Baltic Sea are clearly higher than in the Skagerrak and North Sea. The chlorophyll a concentration** exceeded 3mg m^-3 for more than 60% of the days during the summer period 2006 (June-September) in the Arkona, Bornholm, Easter Gotland and Northern Gotland Basins and Gulf of Riga and Finland.

Bacterioplankton growth rate  is an indicator of the decomposition of organic matter, and thus indicates the rate of oxygen consumption that may lead to oxygen deficiency in the water column. Bacterioplankton accounts for half of the pelagic oxygen consumption. The bacterioplankton growth rate indicates good trophic status in the off-shore Bothnian Bay and Bothnian Sea. Deep water growth rates were only 50% higher than at corresponding depths in the Atlantic Ocean, lacking excess enrichment. The bacterial growth has been stable for the past 15 years, suggesting a balanced nutrient supply to and organic production in the two basins. Declining bacterioplankton growth, and thereby trophic status, has occurred for the past 10 years in the southern Bothnian Sea.

Annual sedimentation dynamics*** in the Central Baltic can be separated into three distinct periods which can be allocated to different drivers of pelagic biomass production. Winter surface accumulated nutrients are used by spring bloom algae**, summer mixed layer biomass production is governed by nitrogen fixing cyanobacteria and  increased water mass convection in autumn finds its response in an autumn bloom of a mixed algal community. All three surface production peaks are reflected in respective transport events of organic matter to the sediment. Annual integrated rates for sedimentation of organic matter*** in the Gotland Sea have not show significant trends between 1995 and 2003 although the major Baltic inflow event in January 2003 exerted a pronounced effect on both surface biomass production and mode of vertical particle transport resulting in an overall increase of organic carbon supply to the sediment by a factor of four.

Hazardous substances still persistent in the marine environment

Despite the considerable reductions in the inputs of some hazardous substances to the Baltic Sea, the concentrations of heavy metals and organic pollutants in sea water are still several times higher in the Baltic Sea compared to waters of the North Atlantic. 

Concentrations of contaminants in fish vary according to substance, species and location. Although there is no consistant trend in mercury concentrations*, the concentrations of lead* and PCBs have decreased significantly as a result of measures taken to reduce discharges of of these contaminant to the environment. Recent levels of cadmium* in herring are not significantly lower compared to the concentrations measured at the beginning of the 1980s, despite measures taken to reduce discharges of cadmium to the environment.

The concentrations of TCDD-equivalents (dioxins) in guillemot eggs show an overall significant decreasing trend, however, not during the recent 15 years. Only one decreasing trend could be observed in herring muscle from the Baltic and the Swedish west coast. TCDD-equivalents show declining trends on most localities due to measures taken to reduce emissions between 1969 and 1985 but after that, this decline has ceased, contrary to e.g. PCBs. As for the concentrations of flame retardants HBCD, a significant increase of about 3% per year can be observed in Guillemot eggs while a decreasing trend of about 10% can be seen for HBCD in herring muscle from the same area during the monitored time period, 1999-2008. No significant trend can be found at the other monitored localities.

The levels of perfluorooctane sulfonate (PFOS) in Guillemot eggs show a significant increase of 7-10% for the whole time period, which is equal to 25-30 times higher levels in the early 2000s than in the late 1960s. No trend can be observed during the last ten year, but, due to the long environmental half-live of PFOS it cannot be expected that levels will decrease rapidly.

Overall the levels of radioactivity in the Baltic Sea water and biota have shown declining trends since the Chernobyl accident in 1986, which caused significant fallout over the area.  In general, the discharges of radionuclides from local nuclear power plants into the Baltic Sea have shown decreasing trends during the last decade and contribute less than 1% of total inputs of radioactivity into the Baltic Sea. Radioactivity is now slowly transported from the Baltic Sea to the North Sea via Kattegat. The amount of caesium-137 in Baltic Sea sediments however has remained largely unchanged, with highest concentrations in the Bothnian Sea and the Gulf of Finland.

Impacts of shipping on the marine environment

A decreasing trend in the number of observed illegal oil discharges, despite rapidly growing density of shipping, increased frequency of the surveillance flights and improved usage of remote sensing equipment, is illustrating the positive results of the complex set of measures known as the Baltic Strategy, implemented by the HELCOM Contracting Parties. Furthermore, emissions of nitrogen oxides from shipping contribute to the eutrophication of Baltic Sea.

Ecosystem effects

The biodiversity of the Baltic Sea is affected by a wide range of anthropogenic as well as natural pressures. Variables such as climate-induced changes in temperature and salinity, fishing pressure, as well as variations in bottom water oxygen conditions (climate and eutrophication induced) all have significant impacts on ecosystem structure.**

As phytoplankton is an important component of the ecosystem, changes in phytoplankton events represent changes in the ecosystem. After the atypical range expansion of marine diatoms to the south-eastern part of the Baltic Sea some of them still occur in phytoplankton, while others disappeared. In 2003-2006 a new marine diatom species appeared in Polish and Lithuanian waters which now often dominate in autumn phytoplankton community. During winter and spring 2007–2008 an unusual increase in a haptophyte* belonging to the genus Chrysochromulina was observed in several parts of the Baltic Sea. Although the reasons for the exceptional and prolonged development of this species are still unknown, monitoring data show that temperature, salinity and PO₄ were higher and DIN lower than average.  If the observed species is C. polylepis, a more regular occurrence of this potentially toxic species might be expected.

Macrobenthic communities*** have also been severely degraded by the increased eutrophication throughout the Baltic Proper and the Gulf of Finland and are below the long-term averages. Populations of the amphipod Monoporeia affinis have crashed in the Gulf of Bothnia and the invasive polychaete Marenzelleria viridis has spread.Despite a lack of consistency, high water temperatures during growth seasons in recent years have possibly affected coastal fish communities** in Bothnian Sea. This is reflected as an increased recruitment success and/or increased individual growth rate of dominating, warm water dwelling, species, e.g. perch (Perca fluviatilis) and roach (Rutilus rutilus). Furthermore, the effects of changes in fishing pressure were observed in Gulf of Riga and in southern Baltic Proper. In the Gulf of Riga a high exploitation rate of piscivorous fish during mid 1990’s was clearly recognised and in the Baltic Proper, flounder (Platichthys flesus), has increased during the period possibly due to population recovery after a previous high exploitation rate.

The health status and reproductive ability of top predators such as seals and white-tailed sea eagle also reflect the state of the Baltic environment. Although the reproductive health investigated in grey seals has improved since the middle of 1980s and the population is increasing at about 8% a year since 1990 the prevalence of intestinal ulcers has increased significantly in investigated juveniles since the mid 1980s and the mean blubber thickness has decreased significantly in investigated by-caught juveniles during the past 10 years. The reproductive health of the Baltic ringed seal females has improved since the 1970s, especially the prevalence of uterine occlusions has been steadily decreasing from 48% in the late 70’s to 30% in years 1991-2004. A majority of the health problems observed in the Baltic ringed seals have been suggested to be related to the high levels of environmental toxins such as organochlorines. A recent study indicates that PCB and DDE levels have decreased in the Baltic ringed seals and the health status of the seals has subsequently improved during the last decades.

Strong relationships have been found between white-tailed sea eagle reproductive ability*  and concentrations of DDTs and PCBs in their eggs. Reproduction in the Baltic eagle population in the 1970s was reduced to a fifth of the pre-1950 population size. Following bans of DDT and PCB during the 1970s around the Baltic, eagle productivity began to recover in the 1980s and since the mid-1990s is largely back to a pre-1950 level. The population on the Swedish Baltic coast has increased at 7.8 % per year since 1990. Nevertheless, on the Swedish coast of the Bothnian Sea, nestling brood size remains below the pre-1950 level and the occurrence of dead eggs is significantly higher than in the Baltic Proper and Bothnian Bay, indicating a possible impact from other contaminants.

The White-tailed Sea Eagle* is an example of a bird species which have severely suffered by persecution and later of contamination of the marine environment by hazardous substances. Strict conservation measures and the ban of hazardous substances allowed it to recover, however, until today anthropogenic mortality factors (especially intoxication and collisions) exert a pressure on the population development.

The Great Cormorant was exterminated as a breeding bird in several Baltic countries during the 19^th century. The persecution continued during the 20^th century, and in the early 1960s the European breeding population of the continental subspecies sinensis had declined to 4 000 breeding pairs (bp). As a result of protection measures, breeding pair numbers started to increase during the 1970s and the Cormorant has since expand its range towards the northern and eastern parts of the Baltic. Currently, the species is present in the whole Baltic Sea area, including the northern parts of the Gulf of Bothnia.

The Sandwich Tern started to expand its range to the Baltic Sea area during the first half of the 20^th century, colonising Skåne in 1911, and the Swedish east coast during the 1930s. In the second half of the 20^th century, the range expansion continued to the southern coasts of the western and central Baltic. The Baltic breeding population grew constantly and reached about 2,500 breeding pairs (bp) at the mid-1970s. Since then, despite some fluctuations and frequent shifts of breeding sites, it can be considered as more or less stable.

Several human activities such as bycatch, noise and chemical pollution, overfishing, and habitat destruction negatively influence the status of the Baltic harbour porpoise*, whose density and distribution has declined considerably during the last several decades, leading to a critically endangered status of the harbour porpoise in the Baltic Proper.

Increasing maritime traffic plays a role in the introduction of alien species into the marine environment. The American comb jelly (Mnemiopsis leidyi)* invaded the southern Baltic Sea in autumn 2006, and was thought to spread to the northern Baltic in August 2007. However, in nucleotide sequence analysis it was shown that all specimens collected from August 2008 to August 2009 were Mertensia ovum, which is an arctic comb jelly species never before reported from the Baltic Sea.

Nine species of phytoplankton have been identified as non-native for the Baltic Sea, of them only one species, the dinoflagellate Prorocentrum minimum (Pavillard) Schiller, can be categorized as an invasive species*, which is spreading and causing significant impacts on plankton community, habitat and ecosystem functioning.

 

* These Baltic Sea Environment Fact Sheets have not been updated since 2009.

**These Baltic Sea Environment Fact Sheets have not been updated since 2008.

***These Baltic Sea Environment Fact Sheets have not been updated since 2007 or earlier. 

¹ The 17^th meeting of the HELCOM Monitoring and Assessment Group (HELCOM MONAS 17/2012) decided that the "HELCOM indicator fact sheets" should be renamed as “Baltic Sea Environment Fact Sheets” (BSEFSs) to differentiate them from HELCOM Core Indicators, which are used for follow-up of the Baltic Sea Action Plan. Note: On the HELCOM website, only fact sheets published after 2009 have been renamed as Baltic Sea Environment Fact Sheets. 

 

Last updated:  15 March 2011