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Towards a Cleaner Marine Environment 7. Bridges from coast to coastThe construction of the bridges over the Great Belt and Øresund gave cause for grave concern on behalf of the environment. The most crucial environmental requirement was the so-called "zero-solution", i.e. bridge construction that did not disturb the currents flowing into the Baltic Sea from the Great Belt and Øresund. The Great Belt and Øresund both constitute corridors between the salty Kattegat and the sweeter water of the Baltic Sea. Any reduction in water exchange would reduce the salt content, and, therefore, the oxygen content, of the Baltic Sea and would alter its ecological balance. The zero-solutions found for both of these major projects enabled us to avoid any detrimental impact on the Baltic Sea. A total of about 18 million m³ of sea-bed was dredged up, about 8 million m³ of which was needed to secure the zero-solution. Øresund also demanded the dredging of about 1.5 million m³ of sea-bed in compensation for the artificial peninsula and the artificial island at Peberholm. A total of about 7.5 million m³ of sea-bed was dredged up for the Øresund link. Local changes The environmental authorities feared that the major dredging and spillage of sea-bed material would perhaps cause permanent damage to the sea-bed close to two of the bridge constructions. That is why a requirement was set on a maximum of 5 percent spillage in the sea, of the material dredged up at the Øresund Bridge. The 5 percent requirement was satisfied and the damage done to the sea-bed was minor and of short duration. Continual monitoring of eel grass and common mussels showed that, after a general but minor decline, populations had recovered by the time the bridge was opened. Trends in bird-life were also observed. There was a minor downturn, e.g. in breeding eiders at Saltholm, during the construction period. The different bird populations have all returned to their normal sizes after completion of the Øresund Bridge. Overall, the environment paid a low price at Øresund and the Great Belt, because it was given consideration throughout the planning and construction phases of the bridges.
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