Doctoral thesis: waste heat from nuclear power plants increases eutrophication in the Baltic Sea

Changes to marine flora and fauna at cooling water discharge areas resemble those caused by climate change

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By Jorma Keskitalo
     
      Finland’s commercial nuclear reactors in Loviisa and Olkiluoto produce electricity to the national grid to the tune of more than 2,500 megawatts.
      This nevertheless equals a mere third of the total energy turned out by the reactors.
      Two thirds of the generated energy ends up in the sea as waste heat.
      The brackish water from the Baltic Sea that is used to cool down the nuclear power plants warms up in the condensers of the installations by 10-13 degrees Celsius.
      Leading expert Erkki Ilus from the Radiation and Nuclear Safety Authority Finland (STUK) studied the effects of such thermal discharges on the marine organisms of the Northern Baltic Sea.
      Simultaneously the study revealed what the effects of the impending climate change will be on the marine life.
      Ilus defended his doctoral thesis at the University of Helsinki last autumn.
     
Ilus’s study is based on an exceptionally long monitoring period of the marine environment next to the nuclear power plants.
      In Loviisa such environmental studies began in 1966 - way before Finland went nuclear - and in Eurajoki’s Olkiluoto in 1972.
      Finland entered the nuclear age only in 1977, when the first Loviisa unit was switched on. In Olkiluoto electricity production began in 1978.
      Ilus was in charge of the research project right from the start. He retired at the turn of the year.
     
The Loviisa power plant is situated on the coast of the Gulf of Finland, while the two Olkiluoto reactors sit on the Gulf of Bothnia on Finland's west coast.
      During the monitoring period, the nutrient concentrations outside of Loviisa have been nearly twice as high as those outside of Olkiluoto.
      Hence in Loviisa there can be found blue-green algae growths towards the end of the summer, and in places algae mass covers the bottom in the shore zone.
     
The effects of the cooling waters on the sea temperature have been more pronounced in the winter.
      This has served as a foretaste of the ice-free winters that the climate change is likely to bring in its wake.
      The freezing over of the sea has delayed and the melting of the ice has advanced.
      The growth season has become longer, especially at the spring end. The lack of ice cover has enabled the plant plankton to receive a lot of sunlight needed for photosynthesis.
     
The warming of the sea water accelerates the algae production, especially in environments where the lack of nutrients is not a limiting factor.
      Heat also speeds up the disintegration of dead algae mass, which easily leads to a lack of oxygen or anaerobic conditions near the bottom.
      Between 1967 and 1998 the basic production of plant plankton was doubled in the Loviisa area.
      In the first decade of the new millennium this increase of eutrophication came to a halt. Nonetheless, the production remained clearly above the original situation.
      The increased production of the plant plankton was first and foremost the result of the general eutrophication of the Gulf of Finland, which is contributed to in part by the thermal load from the nuclear power plant.
     
The most significant biological effect of the warm cooling water is the eutrophic growth of the bottom flora in the discharge area.
      The spiked water-milfoil or Eurasian water milfoil (Myriophyllum spicatum), the clasping-leaf pondweed (Potamogeton perfoliatus), the fennel pondweed ( Potamogeton pectinatus), and the thread-like top algae have all increased profusely.
      The strong eutrophication has been limited to an area of about one kilometre radius from the point of discharge, in other words to the area that remains free of ice throughout the winter.
      The bottom fauna has declined in Loviisa in the last 40 years and in places it has all but disappeared completely. A lot of organic material that consumes oxygen has accumulated on the bottom of the sea.
      The absence of oxygen speeds up the dissolving of nutrients from the bottom sediments into the water.
     
Outside Olkiluoto, there was much less eutrophication compared with the situation in Loviisa. In the Gulf of Bothnia, the sparseness of nutrients limits production.
      At Olkiluoto the bottom fauna has also remained intact.
      In Loviisa, the discharge area is a basin marked off by the mainland and various islands, connected with the rest of the archipelago only by a few narrows.
      In Olkiluoto the warm water is discharged in an area of open sea, where it is mixed with the rest of the sea water more effectively.
     
The findings indicate that the warming of the brackish water promotes eutrophication, especially if the nutrient contents are high, such as they are in Loviisa.
      It is imperative to limit the discharging of nutrients into the Baltic Sea, while efforts are put into place to avert climate change.
     
     
Helsingin Sanomat / First published in print 18.5.2010


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