The environmental status of the Baltic Sea in the 1940s, today, and in the future

Abstract

In the 1940s, the Baltic Sea was a nutrient-poor sea with low biological production, clear water, and rocky shores with dense growths of the brown seaweed bladderwrack, providing food and shelter for many species, including spawning and nursery grounds for many fish. There was sufficient oxygen in the bottom water for cod to spawn in the deep areas of the Baltic Proper, except for periods of oxygen depletion in the Gotland Deep. Top consumers like seal and sea eagle were common and people living around the Baltic Sea could eat fish without risking their health. The Baltic Sea of today is different. Eutrophication and toxic substances now affect the entire Baltic Sea ecosystem, even the offshore areas. Filamentous green and brown algae shade the bladderwrack and may even totally replace it. Increased plankton blooms and organic particle production has lowered light penetration by 3 m and oxygen depletion and hydrogen sulfide formation sometimes dominate as much as one third of the total bottom area. Seals and sea eagles are slowly recovering from the effects of the large emissions of PCB and DDT during the 1960s and 1970s. To reduce the nutrient load to the levels of the 1940s, a reduction by 65% for phosphorus and 80% for nitrogen is needed. Furthermore, society's massive processing of potentially hazardous chemicals must be substantially reduced, and preferably stopped entirely. We now have adequate knowledge of how the Baltic Sea ecosystem functions, and of what is needed to restore the Baltic environment. This requires large societal changes especially in agriculture, transportation, and industry. The successful elimination of PCB and DDT emissions shows that even large-scale, negative trends can be reversed. Here, an efficient and technologically advanced industry has an important role to play. But success will be delayed, as long as political issues are given higher priority than environmental action.