The Baltic Sea is confronted with serious challenges. The sea has been utilised intensively by humans for centuries and is suffering from eutrophication, climate change, waste-pollution, traffic and declining fish stocks. Does the recipe for the recovery of the territorial sea lie on land?
"Excessive nutrient inputs cause a body of water to tip over. I think we know that from the garden. And unfortunately our Baltic Sea is no different."
Prof. Dr. Oliver Zielinski is the Director of the Leibniz Institute for Baltic Sea Research Warnemünde and Professor of Earth System Research at the University of Rostock.
The human impact on the ecosystem of the Baltic Sea can now be measured and seen everywhere: warmer surface water, blue-green algae plagues in summer and, thus, resulting oxygen-free zones in the depths, declining fish stocks, a disappearing coastal fishery.
The Baltic Sea is special. Because many large rivers drain into this marginal sea, it is a brackish sea with low biodiversity. It has no tides and there are only small straits for water exchange with the Atlantic. It warms up much faster than other coastal regions. All these aspects make the Baltic Sea an ideal study area for observing the consequences of climate change and eutrophication on territorial seas and, thus, recognising what other territorial seas will face in the future.
Take nutrient pollution, for example: two thirds of nutrients in the entire Baltic Sea stem from agriculture. In Germany, however, the largest proportion - more than 50 per cent - comes from the atmosphere. Nitrogen primarily enters the sea as a result of combustion processes, such as those occurring in power plants or diesel engines. The second major source is agriculture with fertilisers, and the third largest source industrial and domestic wastewater. However, it is not just a question of limiting further inputs, but also of how the existing nutrients can be removed from the sea. Even if the nutrient input were to dry up completely immediately, it would take at least 30 years for the nutrient loads to be noticeably reduced. Until a few years ago, nutrients were taken from the sea in the form of fish. Now, the stocks are so small that no significant quantities are harvested.
“The problem originates on land, you have to solve it there too. If it's in the Baltic Sea, it's actually already too late.”
Dr. Uwe Krumme is Deputy Director of the Thünen Institute of Baltic Sea Fisheries. He heads the Living Marine Resources department.
The guests in this episode, Prof. Dr. Oliver Zielinski and Dr. Uwe Krumme, see their research object outside their window every day. In this episode, the scientists approach a possible solution for the ailing ecosystem of the Baltic Sea. It is clear to both of them that the solution for the recovery of the Baltic Sea - and for all other territorial seas around the world - lies on land. The Baltic Sea is a permanent sink for all inputs it receives from its vast catchment area, due to the extensive river network that drains into the sea. Therefore, it can only be saved by overcoming the sea-land boundary in thought and action.
Further links and literature:
- Thünen explains why the herring in the western Baltic Sea is producing less offspring. (in German)
- Potential futures of coastal fishing in Germany are discussed in the podcast episode ‘For the museum only? - The future of coastal fisheries in Germany’ of the Thünen Podcast. (partially in German)
- The Thünen podcast episode ‘Can the eel still be saved?’ provides insights into the pros and cons of a ban on catching eels. (partially in German)
- Scientists have researched the global importance of mangrove forests for fish populations in coastal seas. Also the shallow water habitats along our coasts, such as the Greifswalder Bodden are important nurseries for juvenile fish.
- The effects of warmer and longer summers on food webs and thus on cod in the Baltic Sea have been investigated jointly by the Thünen Institute and the IOW.
- Scientists from the Carl von Ossietzky University of Oldenburg, the German Research Centre for Artificial Intelligence and the Leibniz Institute for Baltic Sea Research Warnemünde investigated how AI can support the monitoring of marine pollution and developed their own system to monitor it.
- The Thünen topic Seas contains a wide range of information on what harms the Baltic Sea and what protects it.
- The Thünen topic Fisheries explains how bycatch occurs and how it can be avoided.
- You can explore the depths of the Baltic Sea for yourself in NABU's Baltic Sea Life virtual reality dive.
Prof. Dr. Oliver Zielinski is the Director of the Leibniz Institute for Baltic Sea Research Warnemünde and Professor of Earth System Research at the University of Rostock.
Dr. Uwe Krumme is Deputy Director of the Thünen Institute of Baltic Sea Fisheries. He heads the Living Marine Resources department.
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