Changes in Plankton Abundance, Biomass, and Chemical Composition under the Influence of the Cooling System of the Beloyarsk Nuclear Power Plant

Key words: phytoplankton, zooplankton, abundance, biomass, radionuclides, the Beloyarsk reservoir.

The Beloyarsk reservoir, which supplies cooling water to the Beloyarsk Nuclear Power Plant (NPP) in Sverdlovsk oblast, is an object of multifaceted investi- gation (Guseva and Chebotina, 1988, 1989; Kulikov, 1982; Trapeznikov et al., 1992; Chebotina et al., 1992). To date, however, the influence of the cooling system of the Beloyarsk NPP on phytoplanktonic and zooplank- tonic organisms has not been studied in detail. The available data concern mainly the Konakovo, Kos- troma, and other thermal power stations and are rather contradictory. Some studies indicate the absence of any influence of the cooling system on planktonic organ- isms, whereas other studies demonstrate a stimulating or inhibitory effect. The latter may be related to the fact that investigations are usually performed in the zone of heated water discharge, where conditions are favorable for the restoration of abundance of organisms passing through the cooling systems (Devyatkin, 1975; Elag- ina, 1975; Mamaeva, 1975; Mordukhai-Boltovskoi, 1975; Riv'er, 1975). For this reason, we took samples of plankton immediately at the outlet of the cooling system. Water from the water intake canal supplying it to the cooling system of the NPP was used as a control. The purpose of this study was to analyze changes in the species composition, abundance, biomass, and chem- ical composition of the plankton in the course of its pas- sage through the cooling system of the Beloyarsk NPP.


In the years 1986-1991, in July, plankton samples were taken immediately at the inlet (the water intake canal) and the outlet of the cooling system (the water dis- charge canal). The phytoplankton was sampled 11 times, and the zooplankton, six times.

To determine species composition, abundance, and biomass of the phytoplankton, samples were taken from both canals simultaneously in two replications, using a water bottle. The samples were preserved, concentrated, and analyzed using a standard hemocytometer chamber under an MBI-15 microscope. Zooplankton was col- lected using a special dip net made of bolting cloth no. 70 and equipped with a bucket. After preservation, the samples were examined in a Bogorov chamber under a binocular microscope. Methods for identifying plank- tonic organisms and determining their abundance and biomass are described in detail in handbooks (Vasil'eva, 1987; Gollerbakh et al., 1953; Zabelina et al., 1951; Kiselev, 1954; Kratkii opredelitel', 1977; Komarenko and Vasil'eva, 1978; Metodika izucheniya, 1975; Metod- icheskie rekomendatsii, 1984). To determine the content of radionuclides and stable chemical elements in the plankton, the latter was collected by special dip nets made of bolting cloth no. 70. As it was impossible to sep- arate phyto- and zooplankton at this stage of investiga- tion, the total plankton was analyzed. The samples were dried in a drying oven at 105~ incinerated in a muffle furnace at 450~ and weighed. The content of 9~ was determined radiochemically; those of 6~ and 137Cs, by gamma-spectrometric methods using an AI-256 multi- channel amplitude analyzer with a Lemon NaJ(T1) scin- tillation detector with a statistical error of no more than 15-29%. The chemical composition of the plankton was determined using a Labtest apparatus.


Table 1 presents the data generally characterizing the species composition, abundance, and biomass of the phytoplankton in the investigated canals. During the period of observations, 61 species of phytoplank- tonic organisms were recorded, with chlorococcous algae (belonging to the Chlorophyta) remaining preva- lent and accounting, on an average, for 38% of the total number of phytoplanktonic species. Blue-green algae prevailed in terms of abundance (80-100%). The most common species of this group included Aphanizome- non flos-aquae, Microcystis aeruginosa, M. pulverea, and Merismopedia tenuissima, Among green algae, Oocystis submarina was relatively abundant.

In terms of biomass, the Cyanophyta, Pyrrophyta, diatoms, and chlorococcous algae proved to be domi- nant in different periods of observation. According to the averaged data, however, the biomass of Cyanophyta clearly prevailed over that of other algae, accounting for approximately 70% of the total average for the phy- toplankton.

Table 1 shows that the abundance and biomass of different algae was markedly higher in the water intake canal than in the discharge canal. As averaged over the period of observations, the abundance of phytoplank- ton decreased upon the passage through the cooling systems by a factor of approximately 2, and its biomass decreased by a factor of 1.6. Table 2 demonstrates the average annual data on the total phytoplankton abun- dance and biomass, and the same parameters exist for the prevailing types of algae. In most cases, the param- eters recorded in the water discharge canal were signif- icantly lower than those in the water intake. It should be noted that the levels of abundance and biomass in the water intake and discharge canals were relatively high, compared with the corresponding aver- * Calculations performed without taking into account samples taken on July 31, 1990 at a peak of Cyanophyta abundance. age levels for the water body (Guseva et al., 1989). This is apparently explained by the fact that the cooling sys- tem receives water mainly from the surface layers, which are richer in phytoplankton than bottom layers. Hence, our data on phytoplankton abundance and bio- mass should not be extrapolated to the entire water body, as they only pertain to the aforementioned canals. The zooplankton was represented by 17 species belonging to two classes: Crustacea (nine species of the order Cladocera and four species of the Copepoda) and Rotatoria (four species). In terms of abundance and biomass, crustaceans obviously prevailed over rotifers, accounting for about 90-99% of the total zooplankton. As in the case of phytoplankton, the abundance and biomass of zooplanktonic organisms noticeably decreased after passing through the cooling installa- tions of the NPP. This was clearly observed with respect to the total average abundance and biomass of zooplankton (which decreased by factors of 3 and 2, respectively) and the corresponding parameters for individual classes and orders of zooplanktonic organ- isms. Table 4 shows that this difference between the water intake and discharge canals was revealed in dif- ferent years, with the values of zooplankton abundance and biomass decreasing by a factor of 2 to 5.

These results demonstrated that water passage through the cooling systems of the Beloyarsk NPP has an obvious damaging effect on phytoplanktonic and zooplanktonic organisms, which may be attributed to rapid water heating (by 8-9~ and traumatization of small aquatic organisms passing with cooling water through pumps and condenser tubes (Kulikov, 1978). It was interesting to estimate the proportions of undamaged and destroyed organisms in the phy- toplankton and zooplankton passing through the cool- ing system. These calculations were based on the aver- aged values of phytoplankton and zooplankton biomass in the investigated canals (Tables 1, 2) and the average monthly water volume passing through the water intake canal into the cooling system (65 x 106 m3). Table 5 shows that approximately 173 metric tons of phy- toplanktonic organisms and 11 t of zooplanktonic organ- isms per day are pumped in with water from the intake canal. Approximately 62% of phytoplanktonic and 45% of zooplanktonic organisms return to the reservoir through the water discharge canal without any apparent damage, whereas 38% of phytoplankton (65 t/day) and 55% of zooplankton (6 t/day) perish and tum into detri- tus, which is released in the cooling reservoir with heated water and, probably, is partly retained in the cooling systems.

The content of radionuclides in the plankton of the investigated canals varied in different years of observa- tions (Table 6). The increased values were obtained in 1986, when the second and third units of the NPP were functioning. In 1990 and 1991, after the second unit was put out of operation, the concentration of radionu- clides in the plankton noticeably decreased. Subse- ~0~ent observations revealed no differences between o and 137Cs concentrations in plankton samples from the water intake and water discharge canals. Regarding the plankton as a bioindicator of radioactive water con- tamination, it may be concluded that the operating third unit of the Beloyarsk NPP released no additional 6~ and 137Cs radionuclides into the reservoir through the cooling system. On the whole, radionuclide concentra- tions in the plankton of water intake and discharge canals are comparable with those in plants and grounds of the Beloyarsk reservoir (Chebotina et al., 1992). In 1985, the chemical composition of plankton before and after its passage through the cooling system was investigated (Table 7). In the water discharge canal, the plankton contained much more macro- and micro- elements than in the water intake canal. It may well be that chemical elements were adsorbed on particles and retained by dip nets in the course of plankton sampling. On the other hand, they could be absorbed by plank- tonic organisms in the course of their passage through the cooling system. In the present study, we did not determine whether these elements were stable or radio- active. In any case, when the second unit was operating (1985), they were released into the cooling reservoir and contributed to water contamination. Similar data were obtained for the cooling reservoir of the Kursk NPP (Vereshchak et al., 1996).

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