Threat of eutrophication to the Baltic Ecoregion

A widespread and persistent problem

Eutrophication is one of the most serious environmental threats facing the Baltic Sea.
Eutrophication it is a process where bodies of water, such as lakes, estuaries, or slow-moving streams, receive excess nutrients that stimulate excessive plant growth.

This enhanced plant growth, often called an algal bloom, reduces dissolved oxygen in the water. This affects the ecosystem and might change it totally.
About 80% of all nutrients in the sea come from land-based activities, including sewage, industrial and municipal waste and agricultural run-off. The rest is mainly from nitrous gasses, emitted when burning fossil fuels, from traffic, industry, power generation and heating

The Baltic Sea contains 800% more phosphorus than it did 100 years ago
There are two main nutrients causing eutrophication, nitrogen (N) and phosphorus (P). They are deposited to the sea in several different ways. In 2000, about 660,000 tonnes of nitrogen and 28,000 tonnes of phosphorus entered the Baltic Sea via rivers. The Baltic Sea now contains four times as much nitrogen and eight times as much phosphorus as it did in the early 1900s. Five large rivers – the Neva, Nemunas, Daugava,Vistula, and Oder – together account for the majority of the nutrient loads entering the Baltic Sea. Although a decline in the nutrient loading has been observed in recent years, little change in eutrophic effects has been recorded in the Baltic Sea.

The expected development of agriculture in the new EU countries around the Baltic Sea will worsen the conditions measurably if no measures are taken to reduce the harmful effects of nutrient losses.

Global warming a contributor
Global warming is also stimulating eutrophication as higher temperatures in the Baltic Sea region increases the decomposition rates of the algae, compounding the effects of the nutrients.

Ecological effects of eutrophication
The imbalance caused by the abundance of nutrients has led to numerous changes in the ecological composition and state of the Baltic Sea. Certain plants and animals thrive, enabling them to increase in number and geographic spread, frequently at the expense of other species.

Some of the negative effects of the nutrient overload of the past century are:
  • excessive growth of plants and algae – there has been an increase in primary production by 30-70%. Annuals such as green and brown filamentous algae have grown at the expense of the perennial bladder wrack, which in turn has had severe impacts on the littoral ecosystem
  • algal blooms, some of them even toxic, are a frequent phenomenon in the Baltic every summer 
  • a decrease in water transparency by 2.5-3 metres as a result of the increase in biomass, e.g. an increase in zooplankton by 25%
  • changes in fish species composition. Economically less valuable freshwater fish species are thriving and cod is severely affected
  • a decrease in numbers and spread of predatory fish, such as pike, in coastal waters.
The loss of ecological functions on land – the nutrient retention capacity of wetlands, floodplains, coastal lagoons and free-flowing rivers – has added substantially to the eutrophication problem. Up to 90% of wetlands in the southern part of the Baltic Sea region have been drained over the past century.

State support for drainage and regulation of rivers and the construction of dams have been the key reasons for loss of these natural features. The changes have been driven by demands for additional land for farming, protection from flooding and a growing demand for electricity. The lack of market or regulatory mechanisms for assigning value to wetland functions is a major root cause for the loss of ecological functions.

Limiting the negative impacts of eutrophication
Efforts have been made to limit the production of algae and reverse the development of a eutrophied Baltic. Major investments have been made in Waste water treatment plants and industrial production. But the main problems are now non-point sources – mainly run-off from agriculture.
A phytoplankton (algal) bloom fills much of the Baltic Sea. Summer 2005. / ©: ESA
A phytoplankton (algal) bloom fills much of the Baltic Sea. Summer 2005.

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