Material and methods

The material of this work consists of the results collected in the permanent monitoring programme and complementary hydrographical and hyrdobiological studies carried out in the marine environment of the Loviisa nuclear power plant since 1970. STUK has been responsible not only for implementing the monitoring programme, but also for designing and developing it, and for sampling and other field work connected with the monitoring.

The sampling and analysis methods used have been described in detail in the Annual Reports of the monitoring programme, which have been written in Finnish (Ilus 1980 … Mattila and Ilus 2007, Appendix 1), but some of them have also been described in English (eg. Ilus & Keskitalo 1986, 1987, 2008). The objective has been to follow as far as possible the same methods throughout the 40 years, so that the comparability of the results would endure in the long time-series. In such cases when the methods had to be modified or changed due to a

Fig. 4. Location of the transects for surveying littoral vegetation at Loviisa.

general development in sampling or analysis techniques, the comparability of the results was confirmed by intercomparison of the old and new methods.

Position finding

The permanent sampling stations were marked with surface buoys in spring.

Benchmarks on the shore, an echo sounder and GPS were used when installing the buoys. The samples were regularly collected within a radius of 5 – 10 m of the buoy.

Taking the water samples

The water samples were taken with Ruttner or Limnos samplers. The height of the samplers varied between 32 and 62 cm and the volumes between 2 and 4.2 L. The marks on the hoisting wire were measured from the bottom plate of the sampler. In general, water samples were taken at depths of 0, 2 and 5 metres, and after that at intervals of five metres. The samples from the near-bottom water were taken so that the near-bottom of the sampler was 50 cm above the seabed.

The sub-samples were already separated in the boat as soon as possible into the sample bottles, with the oxygen, plankton and primary production samples being taken first. In particular, the samples for oxygen and primary production measurements were kept sheltered from sunlight in the boat. The sub-samples for pH measurements were separated later in the field laboratory from the salinity samples. In principle, the methods used followed the recommendations given by Mäkelä et al. (1992).

Temperature

The temperature of the water in the sampler was read with a mercury thermometer (accuracy 0.1 °C) immediately after drawing up. The accuracy of the thermometer was checked at the beginning of the sampling period.

Transparency

During the open water period, the transparency of the water was measured from the shady side of the boat with a white, Ø 20-cm Secchi disc. In winter, transparency was measured from the cover plate of the water sampler through the hole in the ice.

salinity

The samples were put into 250 ml glass or plastic bottles provided by the Finnish Institute of Marine Research (FIMR). The salinity was analysed at FIMR in accordance with its standard method using a salinometer. The method is

described in Grasshoff et al. (1999). The samples were kept cool before analysis.

The results were given to two decimal places.

pH

The pH of the water samples was measured in the field laboratory immediately after the sampling trip. The measurements were made with portable Orion Research 401 or Orion Research 420A pH meters from temperature-adjusted samples according to the instruction manuals of the devices. Before the measurements the instrumentation was calibrated with buffer solutions of pH 7.00 and 10.00. The results were given to two decimal places.

oxygen

The standard method of FIMR was used in the taking of oxygen samples and in carrying out their analysis (Koroleff 1979). The method was a modified Winkler method, in which the samples were put into 50 ml bottles (the volume of each bottle being individually determined), and the reagents (MnCl solution and alkalinic iodide solution) were added to the samples immediately after sampling before closing the ground-glass bung. The titration was done in the field laboratory as soon as possible after the sampling trip. The 0.015 N sodium thiosulphate solution used in the titration was changed twice during a sampling period. Solubility values from International Oceanographic Tables Vol. 2 were used in calculating the degree of saturation of oxygen.

Total phosphorus and total nitrogen

The samples were analysed at FIMR in accordance with its standard methods.

The samples were kept cool before analysis. A manual method for total phosphorus and total nitrogen analyses was used until 1981 (Koroleff 1979), after which continuous-flow analysers and the methods described in Koroleff (1983) were used. The FIMR laboratory is the test facility T040 (EN ISO/IEC 17025) appraised by FINAS (Finnish Accreditation Service).

Primary production

Primary production was measured in situ with Steemann Nielsen’s radiocarbon method (1952) in accordance with the Finnish SFS standard 3049 and the recommendations given by Lassig & Niemi (1972) and Gargas (1975).

The sampling was started in April – May and was continued until October – November at 1 – 3 week intervals in spring and 2 – 4 week intervals in summer and autumn. The samples were taken and the incubation was started in the morning, generally before 10 o’clock. The measurement depths were 0, 1, 2, 3, 5, 7.5 and 10 m (the lowest depth being 12 m in Hudöfjärden from 1967 to 1973).

The total depth is 11.5 m at permanent sampling station 2 in Hästholmsfjärden, and 17 m at sampling station 8 in Hudöfjärden. In the first few years, a measurement set consisted of one light and one darkened bottle at each depth.

The employment of two parallel light samples was started in 1976, and in 1978 – 1981 parallel light samples were used regularly at each depth. From 1982 onwards, the measurement set regularly consisted of two light bottles at depths of 0, 1, 2 and 3 m; mean values of the parallel samples were used in reporting the results. Single light bottles were used at 5, 7.5 and 10 m. Dark fixation was measured at depths of 0, 2, 5, 7.5 and 10 m.

One ml of NaH¹⁴CO₃ solution was added to 110 ml (volume of the bottles) of sample water, after which the sample bottles were put back as soon as possible into the sea and incubated for 24 h at their own depths in clear and darkened Jena glass bottles. Stout black plastic sheets were used in the light-shielding of the dark fixation bottles. From 1976 onwards, the NaH¹⁴CO₃ solution was prepared and the activity was verified at STUK (Salonen 1979). Before that, the solution was prepared at Tracer Tekniikka Oy, Finland. The incubation was finished by adding 0.5 ml of conc. formalin (i.e., 0.2 ml of formaldehyde) to the sample. The samples were filtered through 0.45 μm cellulose-acetate filters in the field laboratory soon after drawing up the bottles from the water.

From 1970 to 1987 the activity concentration of ¹⁴C in algae retained on the filters was determined with a Geiger-Müller counter according to Saxén and Lehmusluoto (1979); since 1987 a liquid scintillation counter (Wallac 1414 Guardian) has been used. Wallac OptiScint HiSafe scintillation solution was added to the bottles just before measurement. When the determinations were changed to liquid scintillation counting, the old and new methods were tested against each other with a large series of parallel samples in 1988. The results obtained with the new method at Loviisa were on an average 6% higher than those obtained with the old method. The results obtained with the Geiger-Müller method, and presented in this paper, have been corrected to be comparable with those obtained with liquid scintillation counting.

The concentration of dissolved inorganic carbon was calculated from the temperature, pH and salinity of the corresponding water samples according to Buch (1945). Dark fixation of carbon was subtracted from the light fixation to obtain the final primary production results.

Primary production capacity

An incubator of the Lehmusluoto type was used in incubation of the samples.

It contains two narrow water vessels of plexiglass with two fluorescence tubes (AIRAM L18W-1XC DAYLIGHT 5000 DELUXE) between them. The luminous efficiency of the tubes at their centres was 8 800 lux, and the temperature of

the water bath, regulated by a circulation water thermostat, was 20 ± 1°C. The tubes were changed once a year before the beginning of the field season. The bottles were shaken thoroughly and transposed from the rims of the bowl to the centre and vice versa 5 – 6 times during the incubation to prevent the settling of plankton and to even out the light intensity. In the first few years, primary production capacity was measured at several depths at Stations 2 and 8, but from 1977 onwards the measurements were carried out using 0 – 2-m mixed samples. Otherwise, the methods were the same as for the in situ measurements.

In an intercomparison exercise of primary production capacity measurements, arranged by the National Board of Waters in 1983 for 15 Finnish laboratories (Vuolas & Heinonen 1984) our results were consistent with the mean values.

Benthic macrofauna

The samples were taken with an Ekman-Birge sampler at the end of May and August. Over the course of time, three different Ekman-Birge samplers were used, the area of their orifices varying from 261 to 299 cm² and their weight from 4.4 to 5.0 kg. The varying area of the orifice was taken into account when calculating the results per m². In general, five parallel samples were taken at each station. Only at Stations 51 and 52, where the sediment contained a lot of sand and gravel, did one have to be satisfied with three parallel hauls.

The parallel samples were collected into a 50 L plastic tub and mixed before sieving. However, from 2004 onwards the parallel samples were taken and handled separately. The sieving was done with a hand sieve (mesh size 0.6 mm) as soon as possible after the sampling. Before sieving, the bottom matter was thoroughly mixed with the water in the tub so that it easily passed through the sieve. The sludge produced was distributed with a plastic scoop in small batches onto the sieve so that the stay of the sludge on the sieve was as short as possible.

The sieving residue was rinsed into a plastic box, and the animals were picked from the residue in the field laboratory as soon as possible after the sampling.

Large-sized predators (Saduria, Marenzelleria, etc.) were already picked from the sample during the sieving. The sieving residue was gone through in small batches on a white plate using forceps and a light loupe.

The animals were preserved in 80% alcohol, which works better than formalin for samples that contain plenty of oligochaetes and chironomid larvae, because an exact determination of these groups generally requires the making of microscope preparates. The soft tissues of the animals become hard and less transparent in formalin. The species and biomass determinations were done from preserved samples within six months of sampling. The biomasses were weighed (accuracy 0.1 mg) species by species after the surface moisture had evaporated (less than 1 min on blotting paper). From 2004 onwards, the

parallel samples were determined separately, but the results are combined in this consideration.

littoral vegetation

Littoral vegetation was studied on permanent 100-m-long census lines by scuba diving complemented by dredging with a Luther rake (Luther 1951). The method is described in Ilus (1980), Ilus & Keskitalo (1986) and Keskitalo & Ilus (1987); it is a modification of the line census method used earlier in fish studies at Loviisa (Bagge et al. 1975). A 100-m-long floating rope with numbered stryrofoam floats at 5-m-intervals was laid out between the shoreline and a buoy anchored 100 m from the shore. The diver slowly followed the transect near the bottom from the outer end to the shore. He / she was directed with a sounding lead from a rubber dinghy proceeding along the surface rope. The boat was usually staffed by two persons, one of whom rowed, while other communicated with the diver by underwater telephone (Fig. 5). Until 1994, a wired underwater telephone (Finn-Suit SP 1) connected to a tape-recorder was used to record the observations and description of the vegetation. From 1997 onwards, a wireless telephone Aquacom SSB-2001 was used. While proceeding along the transect, the diver described the vegetation and the character of the bottom on a 2-m-broad strip (1 m on each side of the diver), while the telephone-operator in the boat recorded distances from the shoreline on the tape according to the styrofoam floats along the surface rope. The diver paid special attention to dominant species and their coverages (estimated as percentages) and noted the limits of the different vegetation belts. The diver also used numbered plastic bags carried in a string bag to collect those samples of plants that were difficult to determine during the dive. In general, an auxiliary safety diver followed by the side of the main diver and assisted him / her in the sampling. The main part of the samples were

Fig. 5. The scuba diving method used in the studies of the littoral vegetation.

determined immediately after the dive, but some of them were conserved in 5%

formalin or dried on waste paper for more exact examination.

To complete the information on the species composition, dredging was performed by the method of Luther (1951) on each transect after the dive.

The tape recording made during the dive was transcribed into written form immediately afterwards.