Baltic Sea Fish Kill Blamed on Nutrient Runoff

BRUSSELS, Belgium, September 18, 2003 (ENS) - The dramatic loss of marine wildlife recorded last year in the Western Baltic Sea between Denmark, Germany and Sweden is largely the result of extreme weather conditions and an increase in nutrients resulting from human activities, according to the findings of a new report released by the Helsinki Commission (HELCOM).

Last fall, HELCOM and European Commission joined forces to investigate exceptional oxygen depletion in the Western Baltic that had led to hundreds of dead fish being washed ashore along the east coast of Jutland, Denmark.

Widespread and long lasting severe oxygen depletion was observed in the Kattegat, the Sound and the Baltic Sea in late summer and autumn 2002, some of the worst ever recorded.

In several areas, extreme oxygen deficiency led to the release of highly toxic hydrogen sulfide from marine sediments. As a result, creatures living near the bottom of the sea died and, in October 2002, the Jutland coast was littered with fish carcasses.


Algae bloom in the Baltic Sea due to eutrophication (Photo courtesy Helskinki Commission)
The report reveals that the oxygen deficiency was caused in part by heavy rain and snow, leading to the runoff of higher than usual levels of nutrients from agriculture, urban wastewater and air pollution into the sea.

In addition, low wind levels and high air pressure minimized exchanges between different water levels in the Baltic. The report recommends stricter controls on nutrients reaching this inland sea to prevent future oxygen depletion.

In the European Union, intensive agricultural methods make farmland a major source of waterborne nutrient pollution.

Research Commissioner Philippe Busquin said, “We must do more to reduce the level of man-made nutrients polluting the Baltic Sea and the destruction of its precious ecology. We cannot ignore nature's alarm calls, and must ensure that our research findings help shape appropriate international policies.”

The Baltic Sea is ecologically unique, being generally shallow and almost stagnant, the Commission explains. It is dominated by a substantial input of freshwater from many rivers and as well as rain and snow, and by the limited exchange of more saline water over the shallow entrances to the North Sea.

Scientists have found that the Baltic is particularly sensitive to the impact of pollution and overexploitation. It is also under pressure from the housing, agriculture, industry, traffic, energy generation, fishery and shipping needs of over 85 million people within its large drainage area.

A preliminary version of the Helsinki Commission report was used in the preparatory work for the HELCOM Ministerial Meeting, which took place on June 25 in Bremen, Germany. Environment Commissioner Margot Wallstrom participated at this meeting where a package of measures for the protection of the Baltic marine environment was agreed.

The ministers agreed to make agriculture more environmentally sustainable by improving agricultural practices to ensure efficient use of nutrients while minimizing any adverse impact on the environment.

European Union laws such as the Nitrate and Urban Waste Water Directives must be fully implemented, the ministers agreed.

Following the initiative of the HELCOM Monitoring and Assessment Group, an expert group was set up with Denmark, Germany, Sweden and the European Commission to analyze the development and causes of this situation using information gathered from marine biology, oceanography, and satellite remote monitoring.


Heike Herata chairs the HELCOM Monitoring and Assessment Group (Photo courtesy HELCOM)
The experts found that eutrophication, a condition in which the waters are extremely rich in nutrients such as fertilizer components, is still a major problem in the Baltic Sea.

The symptomatic problems of eutrophication include serious oxygen deficiency, extensive algal blooms and floating mats of decaying seaweed in coastal waters. The condition is still common, in spite of substantial efforts to reduce nutrient inputs over a wide area.

Comparisons between recent years marked by specific weather events in the area revealed the key roles of snow, rain, and wind and air pressure in the oxygen balance of marine bottom waters.

The amount of snow and rain controls the nutrient loading of surrounding rivers by soil erosion. Unseasonably late rains, combined with sunlight can also indirectly enhance marine plant production in surface waters, the expert group said. Wind and air pressure acts on the local supply of oxygen through water exchanges with the oxygen rich waters of the Skagerrak.

While weather conditions were the main trigger of the 2002 event, investigations revealed that the Baltic Sea is particularly vulnerable to oxygen depletion. Permanent separation of water strata, minimal reaction with the sea bottom, restricted flow patterns resulting from semi-enclosed bays and estuaries and shallow bowl shapes in the sea bottom all favour the isolation of bottom water masses and therefore limit reoxygenation, the scientists said.

The Baltic Sea region is one of the most naturally sensitive to oxygen deficiency in Europe. Some confined regions such as the Little Belt were already experiencing oxygen deficiencies 100 years ago, when nutrient discharges were relatively low. For several decades the main original cause of extended oxygen deficiency has been the nutrient supply in surface marine waters.

The Commission contribution indicates that the Belt Sea area has a very limited capacity to digest the organic matter and, indirectly, to assimilate any additional supply of nutrients. Further efforts are necessary to meet the 50 percent nutrient reduction target set by HELCOM.

But, the Commission said, even this might turn out to be insufficient to drastically reduce the likelihood of severe oxygen depletion in terms of geographical coverage and duration in the Western Baltic.

HELCOM is the governing body of the Convention on the Protection of the Marine Environment of the Baltic Sea Area, known as the Helsinki Convention, originally signed in 1974. Through intergovernmental co-operation between all the countries bordering the Baltic - Denmark, Estonia, Finland, Germany, Latvia, Lithuania, Poland, Russia and Sweden - and the EU, HELCOM works to protect the marine environment from all sources of pollution and to take appropriate measures to counter and prevent pollution to save the environment in a sustainable way.

The convention was updated in 1992, when the European Union became a member, and the updated convention came into force on January 17, 2000. It covers the whole of the Baltic Sea area, including inland waters as well as the water of the sea itself and the seabed. Measures are also taken in the whole catchment area to reduce land based pollution.