Finland's coastal areas are burdened by nutrient loading from agriculture, forestry, and wastewater

In the Baltic Sea, the coastal areas of Finland are particularly burdened by loading from agriculture, forestry, sewage treatment plants, and areas of dispersed settlement. However, there are many differences in the nutrient loading of coastal areas, depending on their geographical location.

On the southern and southwestern coasts, agriculture is by far the largest source of nutrient loading. Exceptions to this are found in the sea areas off the coasts of the major cities and at the mouth of the Kymijoki River. Off the coasts of both Turku City and the Helsinki metropolitan area, nutrients entering the sea from rivers come more from agriculture than the treated wastewater from urban areas.

Although only a small portion of the total land area consists of arable fields in the catchment area of the Bay of Bothnia, it is mainly located in an area of low-lying coastal rivers. By contrast, the amount of farmland relative to the land area in the catchment area of the Archipelago Sea is large and there are few lakes. Also, the soil there is both nutrient-rich and sensitive to erosion.

The Gulf of Finland is one of the most nutrient loaded areas of the Baltic Sea

The catchment areas along the Gulf of Finland are densely populated and largely cultivated. The eutrophication of coastal waters is caused by nutrient loading from wastewater treatment plants, as well as from agriculture and forestry. In addition, the nutrient load is increased by inadequately treated wastewater from sparsely populated areas.

The city of St. Petersburg has a great influence on the state of the Gulf of Finland

In terms of surface area, the Eastern Gulf of Finland is one of the most heavily loaded areas of the Baltic Sea. The status of the Gulf of Finland is heavily impacted by the Neva River flowing into the eastern reaches of the Gulf, as well as the city of St. Petersburg, which is situated at the river’s mouth. The increase in efficiency of wastewater treatment in St. Petersburg has improved the general status of the Gulf of Finland and its coastal waters.

The Kymijoki River transports a huge nutrient load to the Baltic Sea

In the Eastern Gulf of Finland, the quality of the waters off the coast is most influenced by rivers draining from their own catchment area. Of these, the Kymijoki River is the largest single source of nutrient loading.

In winter, the impacts of diffuse pollution on the quality of river water are minimal. At this time, the waters of the Kymijoki River spread long distances away from the river mouth under the ice, as a layer of surface water. At present, they are significantly less nutrient-rich than the coastal waters of the Eastern Gulf of Finland, particularly in terms of phosphorus, so in this respect, they dilute the phosphorus content of the surrounding seawater.

Nutrient loading from rivers does not explain the eutrophication of the outer coastal waters and the open sea

In particular, domestic nutrient loads cause eutrophication in estuaries, as well as in both inner and middle archipelago zones. However, they do not explain the eutrophication observed in outer coastal waters. This is particularly true off the coast of western Uusimaa, where the local nutrient load is relatively low.

Similarly, in the Gulf of Finland, the waters of the open sea areas are relatively rich in nutrients. Currents from these areas continue to transport nutrients to eutrophication-sensitive coastal waters. Eutrophication is strongest in the island-dotted coastline and shallow coastal waters on the western side of the Porkkalanniemi Peninsula. By contrast, the level of eutrophication in the open coastal waters off the Hanko Peninsula is clearly lower.

Compared to the inner zones of the Archipelago Sea, local agriculture is less clear as a cause of eutrophication in the Gulf of Finland. Nevertheless, it is still a significant source of nutrients.

Eutrophication is unevenly distributed in the Archipelago Sea

Eutrophication in the innermost areas of the Archipelago Sea has been mainly influenced by urban wastewater and agriculture.

 Rye breads.

Agriculture causes loading in the Archipelago Sea

The nutrient load produced by agriculture has not been reduced as expected by the implemented water protection measures. The fields in the catchment area are sensitive to erosion and rivers can carry a lot of nitrogen and phosphorus relative to their currents.

The phosphorus load in municipal wastewater decreased sharply already in the 1970s and has continued to decline since. By comparison, nitrogen loading was not significantly reduced until the 2000s, as nitrogen removal became more efficient. The greatest source of nutrient loading in the middle archipelago zones is fish farming. This loading effect was at its peak in the late 1980s and has been decreasing ever since.

The outer archipelago has also suffered from eutrophication

The eutrophication of the outer zones of the Archipelago Sea accelerated in the 1970s. This trend has continued until the 2000s.

The Archipelago Sea is very fragmented, which means that the impact of the sources of loading is unevenly distributed. The impact of local loading sources is strongest in the inner parts of the Archipelago Sea, while the proportion of total atmospheric deposition is largest in the outer archipelago.

The nutrients carried in water currents coming from the Gulf of Finland particularly affect the southeastern and southern parts of the Archipelago Sea.

Nutrient emissions have been successfully reduced on the shores of the Bay of Bothnia

Although several rivers which are heavily loaded with nutrients from agriculture drain into the coastal waters of the Bothnian Sea, there are relatively few water areas there that are clearly eutrophicated. Due to its open coastline, the eutrophic coastal zone in the Bothnian Sea is much narrower than its counterpart in the Archipelago Sea.

The heavy eutrophication observed off the Kokemäenjoki River is due not only to agriculture but also to nutrient emissions from both settlements and industry. The Kokemäenjoki River carries about 80% of the nutrient load from the catchment areas to the shores of the province of Satakunta.

Perämeren rannikolla on onnistuttu vähentämään ravinnepäästöjä

The phosphorus load in the Bay of Bothnia has decreased. This is largely due to the development of industrial processes and an increase in the efficiency of wastewater treatment.

Santapankki, Bay of Bothnia.

Conversely, nitrogen loading has increased since the mid-1990s in the Bay of Bothnia. This is thought to be due in particular to the strengthening of agriculture and the growth in urban settlement, but also to the increase of river flows. Despite many measures, the nitrogen loads carried to the sea in rivers have continued to increase.

Unlike other areas of the Baltic Sea, point source loading increased in the Bay of Bothnia after the mid-1980s. A point source load is an identifiable source of loading from a single point. One reason for this was that an ever-increasing number of households were connected to the municipal wastewater treatment.

This trend levelled off in the late 1990s, when sewage treatment plants were merged, and wastewater treatment became more efficient. At the same time, nutrient emissions from pulp and paper mills also decreased.