Biologisk recipientkontroll vid Ringhals kärnkraftverk: årsrapport för 2011

The cooling system of the Ringhals nuclear power plant affects the fish community in two steps. In the first step, seawater is used to cool the system in the nuclear power plant. Fish eggs, larvae and small juveniles are carried by the incoming water and are exposed to risk of damage or mortality. In the second step the heated water is released back into the sea, where the fish is affected by the increase in temperature. Reactor 1 and reactor 3 at Ringhals nuclear power plant produced electricity during the major part of the year 2011, with exceptions for the annual audits, and shorter stops in production. Reactor 2 only operated between January and April, due to a fire which led to a shutdown and a thorough remediation work during the rest of the year. Reactor 4 was producing electricity from January to June, but was later shutdown due to a prolonged annual audit until November. Fish eggs and fish larvae are sampled in the incoming cooling water using a modified Bongo net to monitor losses of eggs and larvae in the nuclear power plant. The abundance of shorthorn sculpin larvae (Myoxocephalus scorpius) has decreased since the sampling period started, although it is still the most abundant larvae. Also the abundance of rock gunnel larvae (Pholis gunnellus) has decreased over the years. To sample juvenile fish a modified Isaacs-Kidd midwater-trawl is used. This sampling is mainly focused on glass eels (Anguilla anguilla). The abundance of glass eels have declined strongly since the beginning of the 1980's, but a minor increase was observed in 2011. The decline of the glass eel abundance is most probably due to a general decrease in recruitment and not to a local effect caused by the nuclear power plant. The effects of the heated water released into the sea are monitored by fykenet surveys in the recipient as well as in a reference area. These two areas are monitored in two seasons to compare differences between the two areas in naturally cold and warm water of the two seasons. There was a different development in the diversity of fish between the two areas in the cold season, where the recipient showed a decreasing trend in diversity and the reference area was stable with no trend. This is possibly an effect of the warm water emissions. Species which prefer warm water have been observed to concentrate in the recipient area. Eel and shore crabs (Carcinus maenas) are good examples, showing either stable or increasing catches in the area. Species which prefer cold water, as cod (Gadus morhua), shorthorn sculpin (Myoxocephalus scorpius) and eelpout (Zoarches viviparous) were less abundant in the recipient. No new findings for Swedish water of marine alien species were made in a scuba diving survey in four shallow areas near the outlet of cooling water from Ringhals (Ringhals udde, Båtafjorden, Norra Horta and Vendelsö). Four species already established on the Swedish west coast were found however, the japanese oyster (Crassostrea gigas), two species of red algae Dasya baillouviana, Bonnemaisonia hamifera and one brown algae, the japanese wireweed (Sargassum muticum).