Open access publications in the SLU publication database

Potential ecosystem effects caused by the effluent cooling water from the Simpevarp
nuclear power plant, close to Oskarshamn on the Swedish coast of the Baltic
Proper, are monitored in yearly surveys. Gillnets and fyke nets are used at several
sites in a coastal gradient, starting at the location of the emitted cooling water, and
in a reference area unaffected by the recipient. Soft bottom macrofauna and macrovegetation
are monitored both in the gradient and in the reference area. In addition,
fish mortality due to impingement in the cooling water system and to commercial
landings is monitored to assess possible effects on the local fishery.
The emitted cooling water is normally 10–12 °C warmer than the incoming water.
The emitted water from reactor O3 exceeded 25 °C during 28 days 2013 which was
a longer period than usual. Absence of heating during the main part of the year from
reactor O2 and cooler incoming water to reactor O1, however, resulted in cooler
outgoing water overall than before. Overall, during April through November, the
average temperature in the recipient bay Hamnefjärden was 0.6–3 °C higher than in
comparable reference areas. This temperature elevation was lower than in recent
years.
A transition to deep cooling water intake began in the fall of 2011 because of the
planned effect increases on reactor O2 in 2015. The purpose is to access cooler water
to the intake and to reduce high temperatures of the discharged water. After the
transition, the losses of herring (Clupea harengus) and small fishes decreased in the
water intake to reactor O2. In reactor O1 the transition took place in late June 2013
and decreased losses of especially three-spined stickleback (Gasterosteus aculeatus),
but also of larger fishes, were recorded. Influences on the population level are estimated
to be low, although local effects cannot be ruled out.
Total catches of fish caught with gillnets increased in the surveys in Hamnefjärden.
Perch (Perca fluviatilis), silver bream (Blicca bjoerkna), roach (Rutilus rutilus) and
Aqua reports 2014:4
rudd (Scardinius erythrophthalmus) dominated the catch. Catches of perch and
rudd have increased over time in Hamnefjärden as well as in the archipelago south
of the power plant. Catches of roach and rudd have decreased over time at the inner
location in the reference area. At the outer location there were still large catches of
perch, but no trends to be found. Perch in Simpevarp tend to be younger than in the
reference area.
Abnormal gonads, previously observed at high frequencies in perch and roach in
Hamnefjärden, have rarely been observed in recent years. In the 2013 sampling, the
frequency of abnormal gonads were 2.5 percent in Hamnefjärden and zero in the
reference area. No abnormalities in roach gonads were found in either area.
The trend in abundance of perch fry in the recipient was negative, due to very low
abundances both in 2012 and 2013. The average length of the fry has increased in
the long run but did not differ between the two areas in 2013.
Fyke net catch of yellow eel (Anguilla anguilla) was still quite low in the recipient
in 2013, but there was an increase in the catch of small yellow eel since year 2000.
The prevalence of swim bladder parasites (Anguillicoloides sp.) has been constant
at 50–60 percent since the parasite was established in Hamnefjärden in the late
1980's.
Gillnet surveys are performed in the spring on the open coast at the power plant to
study effects on herring and other marine species, normally appearing at relatively
low water temperatures. Interferences from grey seals (Halichoerus grypus) were
recorded in 25 percent of the fishing effort. The increase of herring that has been
observed in recent years did not continue in 2013, likely due to very low water
temperatures. The abundances of the other long term dominants such as cod (Gadus
morhua), sea scorpion (Myoxocephalus scorpius), European flounder (Platichtys
flesus) and eelpout (Zoarces viviparus) showed moderate changes.
Aqua reports 2014:4
Silver eel (Anguilla anguilla) catches increased in the reference area from 1972 until
silver eel fishing ceased in 2001. The catches decreased in the local fishery near
Simpevarp during the same period. The development in silver eel abundance since
the bottom year 1996 has, however, been positive in Simpevarp.
Species richness in soft bottom macrofauna increased strongly between 1962 and
2013 in Simpevarp as well as in the reference area. The increase was particularly
sharp in the shallow sites where total abundance also had a positive trend. In the
shallow site in Simpevarp and the deep site in the reference area, abundance was
dominated by polychaetes Marenzelleria sp. which has been introduced to the Baltic
Sea. At the two other sites, Baltic clam (Macoma balthica) was the most common
species.
Vegetation on hard bottoms is monitored on three sites in the coastal gradient of
cooling water. The coverage of filamentous green algae increased 2013 while both
coverage and spread of bladder wrack (Fucus vesiculosus) decreased when data
from the three sites were merged compared to 2012. The algal communities are
considered to have good ecological status and the studied sites are among the richest
in the