Research vessel Muikku has spent two weeks at sea surveying the sea bottom off the coast of Helsinki in a mission organized by the City of Helsinki Environment Centre.

“The sea bottom is in an alarmingly poor state in places, although overall the state of the sea bottom is tolerable,” says researcher Emil Vahtera of the Environment Centre.

Approximately 40 percent of the sea bottom in surveyed areas was found to be anoxic (depleted of dissolved oxygen), leading to disruptions in sea-bottom processes. A healthy sea bottom binds nutrients. But when the bottom becomes depleted of oxygen, which is a result of eutrophication (excessive plant growth due to excess nutrients in a water body), the flow of nutrients is reversed and nutrients are released, resulting in further deterioration of the water body.

Detailed results available in the autumn

The sea-bottom survey suggests that the internal load – load originating from the sea itself – is a major problem in the waters off Helsinki. “The internal load would seem to be significantly higher than the external load,” Vahtera says. This means that the effects of water protection measures aimed at curbing diffuse loading (loading from agriculture and scattered settlements) will have a longer time lag.

The samples collected during the survey are also used to study how phosphorus is chemically bound in the sediment. Normally, phosphorus bound in the sediment is released into the water under oxygen-depleted conditions, which increases the internal nutrient load. However, phosphorus may also be bound in forms not affected by low oxygen levels.

More detailed information on the scope of the internal load and on how phosphorus is bound will become available during the autumn, after laboratory analyses are completed.

A videoblog on Muikku’s mission is available on demand at www.helsinkikanava.fi (in Finnish).

Baltic Sea Challenge to protect the sea

The mission on Muikku was carried out from 30 July to 9 August 2012 in the waters off Helsinki, Sipoo and Espoo. The furthest sampling stations were located at some 20km from shore and the nearest right off it. The mission was a joint venture of the City of Helsinki Environment Centre, the Finnish Environment Institute and the Baltic Sea Challenge.

The Baltic Sea Challenge is a campaign declared by the Cities of Helsinki and Turku to protect the Baltic Sea. The cities seek to improve the state of their coastal water regions, as well as the entire Baltic Sea. The cities have defined action plans for themselves and challenge other communities and players to join the campaign and define their own action plans for Baltic Sea protection. Today, the campaign has more than 190 participants.