Assessment of the relevance of the effect of cooling water of a planned coal power plant in Lubmin
Herring in the western Baltic Sea spawns especially in the Greifswalder Bodden, a shallow bay area in the vicinity of the island of Rügen, Germany. Would a planned new coal power plant impair the spawning success of herring? We answered that question in an expert’s report.
The State Agency for Nature and Environment Mecklenburg-Vorpommern commissioned the Thünen Institute for Baltic Sea Fisheries to do an expert’s report: we should assess whether planned new power plants near Lubmin might cause any negative impact on commercial fish stocks, especially the western Baltic spring spawning herring stock, in the Greifswalder Bodden (GWB). As the GWB is the main spawning area of the western spring spawning herring stock, we should clarify whether the reproduction of herring could be negatively affected by the cooling water of the power plants and if so, whether this also would have significant negative effects on international fisheries on this herring stock.
We investigated the spawning of herring in the GWB in spring 2009. The field investigations were supplemented by an intensive review of available literature.
Macrophytes are the major spawning substrate for herring, laying its eggs on sea grass and macroalgae. The eggs stick to the surface, as long as it is clean. To asses any potential negative effects, we therefore measured the distribution of macrophytae in the area of the potential cooling water flume as well as in the whole GWB. Only by comparing potentially affected areas with the total area of the GWB, we were able to assess quantitively whether the cooling water affects the spawning.
We wanted to answer the following questions:
The fastest and most cost efficient method to measure occurrence and extension of macrophytes in the GWB were high resolution air photography. Experts from Rostock University analysed these images using GIS techniques. Ground truthing of the information collected via air photography about potential spawning substrates was carried out by divers, in parallel. During the diving spawning habitats were classified (living/dead eggs, single/multiple spawning, development stages, etc).
By using underwater video, we filmed the sea floor on elected transects to verify air images by a second method and to cover deeper areas that could not be assessed by air photography. Air images and video transects were geo-referenced and combined to get the full picture about the distribution of macrophytes over all depths.
Two near-field areas were defined as those areas where at least over 10% of all days in March 2002 (impact area 1) and over at least 3.5 days in a row (impact area 2) the bottom temperature would be increased by at least 1°C by the cooling water flumes.
In the near field areas of cooling water flumes we identified extended areas with macrophytes and two important spawning areas of herring that are especially important for the spawning of herring. We did not expect direct negative effects by the power plants on fisheries. However, when combining the area assumes as realistically affected with a ‘worst case scenario’ of negative effects by stress factions, we were able to assess the overall impact on the herring stock and thus on the international fisheries on this stock. Thus, we concluded that fisheries must consider economic loss. Inflow of cooling water would mainly impact the recruitment of western Baltic spring spawning herring. In the worst case, production of offspring would be reduced by 4 to 7%. Compared to the high natural variability such a reduction would be significant, but neither catastrophic nor irreversible. While the results of our study did not produce any reasons to directly reject the construction of the planned power plant, it resulted in recommendations how the potential impact of the inflow of cooling water on herring spawn and larval development could be minimized during a narrow time period.
The many results of our studies were published.
3.2009 - 8.2009
Project status: finished