Response of communities of aquatic organisms to the anthropogenically-driven changes in water mineralization of a small stream (the White Sea basin, Republic of Karelia, Russia)

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Response of communities of aquatic organisms to the anthropogenically-driven changes in water mineralization of a small stream (the White Sea basin, Republic of Karelia, Russia)

Hydrobiological studies on the freshwater tributaries of the White Sea began much later than the first researches performed in the sea itself. This was due to the lack of large-scale economic activities of the local population, whose density has always been low. Nowadays, only 72 thousand people live on the territory of the Karelian coast, which is 67100 km2, i.e. slightly more than 1 person per km2; 76% of population live in four regional centers (Kem', Belomorsk, Loukhi, and Kalevala). In general, high urbanization with a low population density in the rest of the territory is also typical for the entire Republic of Karelia. The state of the environment in the region has been assessed as stable in recent years (Gosudarstvennyi Doklad..., 2020). Cases of extremely high pollution of watercourses, leading to a noticeable decrease in water quality and mass mortality of aquatic organisms, were not registered. This is due to the fact that most of the large settlements with developed industry are located along the shores of the White Sea. Therefore, all river ecosystems, except the Kem' River, are exposed to anthropogenic impact only in the estuaries.

The research in the White Sea watershed area has become regular only from late 1970s; in particular, these were the studies in the Kem' River and its main tributary, the Kenti River (Vliyanie..., 1995; Sostoyanie..., 2007). This was due to the construction of the Kostomuksha mining and processing plant (GOK) in the upper reaches of the Kenti River. This plant is the largest in the north-west of Russia; along with the city of Kostomuksha, it is still the main source of anthropogenic impact in the region today. However, the structure of natural communities, except that of phytoperiphyton (Komulaynen, 1995, 2019), has been mainly studied in the lakes belonging to the Kenti River stream.

Chemical analysis of water in drainage lakes evidences that the upstream system of the Kenti River is exposed to anthropogenic impact (Lozovik and Galakhina, 2017). However, the lakes belonging to the Kenti River system differ markedly in their morphometry. The largest of the lakes, Lake Kento, has an area of 28.1 km2, a water volume of 0.103 km3, and a maximum depth of 23.5 m. The smallest Lake Okunevoe has an area of 0.3 km2, a water volume of about 0.001 km3, and a maximum depth of 5.6 m. Undoubtedly, such differences affect structure of aquatic biocoenoses. Meantime, the formation of communities of aquatic organisms in the watercourses full of rapids occurs under similar conditions (depth, flow rate, and substrate). We suggest that searching for the influence of anthropogenic factors may be much easier here than in other types of water bodies.

The study aims:

(1) to assess the influence of anthropogenic increase in mineralization on the structure of aquatic biocoenoses and to search for the peculiarities of their formation;

(2) to obtain data on the indicator significance of the communities of aquatic organisms;

(3) to analyze the ability of river ecosystems to recover after disturbances caused by this type of anthropogenic impact (i.e., water mineralization).

Materials and methods

aquatic organisms water mineralization

The watershed area of the Kenti River locates on the Karelian (western) coast of the White Sea; it is a swampy plain (the so-called Belomorskaya Lowland) with relative heights of up to 20 m, one of the most climatically unfavorable regions of the Republic of Karelia with a long winter and a short growing season.

Hydrobiological and hydrochemical studies were carried out in August 2019. At the Kenti River, two sites were studied. The first site (station no. 1) is located 100 m downstream from the runoff from the tailing dump of the Kostomuksha GOK, the second site (station no. 2), 10 km downstream, in 100 m from the confluence of the river into the Lake Koyvas. In order to obtain comparative data, simultaneous studies were carried out in the Lakhna River (station no. 3), where no economic activity has being performed currently.

The headstream of the Kenti River is located in the northeastern part of the Lake Kostomukshskoe (N 64°42'09" E 30°53'34") with an area of 5.4 km2, converted into a tailing pond; the river flows into the Lake Yulijдrvi (N 65°02'02" E 31°07'57"). The headstream of the Lakhna River is located 8 km from the headstream of the Kenti River (N 64°39'09" E 31°03'11"); it flows into the Lake Pushtos'-Jдrvi (N 64°46'34" E 31°58'05"). The catchments of both rivers have a mostly flat, sometimes swampy relief. The main characteristics of rivers and their catchments are given in Table 1.

When controlling the chemical composition of water, indirect parameters of the organic matter content (CW - color of water; PV - permanganate value) and the content of biogenic elements (BE) were determined, as well as the electrical conductivity (ж) and pH of water (Rukovodstvo..., 2009).

Sampling of phytoplankton, phytoperiphyton, zooplankton, and zoobenthos, their processing in the laboratory and analysis of the qualitative composition and quantitative development of particular species were carried out according to the methods worked out by the authors (Komulaynen et al., 1989; Komulaynen, 2003; Rukovodstvo..., 1983). Species, which relative abundance exceeded 10%, were classified as dominants. The ecological group of algae was defined according to S.S. Barinova et al. (2006).

Table 1. Characteristics of the studied rivers and their catchments. L is the length of the river; S, the catchment area; SWL, swampiness; SL, lake percentage (Resursy..., 1972).

The quality of river water was assessed by the composition of indicator species in accordance to the Pantle-Buck saprobity index (P&B) as modified by Slвdecek (Slвdecek, 1967); in addition, the diatom index (TDI) was calculated for phytoperiphyton (Kelly and Whitton, 1995).

The concentration of heavy metals in water, sediments, filamentous algae, and mollusks was determined by atomic absorption spectrometry with flame atomization (AA-7000 Shimadzu spectrophotometer, Japan) using equipment from the “Analytical Laboratory” Center for Collective Use of the Forest Research Institute, Karelian Research Centre, Russian Academy of Sciences.

Results and discussion

The wastewater releases from the tailing dump, on average 13.1 million m3/year, had the greatest impact on the chemical composition of water in the Kenti River. Their influx into the river led to an increase in mineralization, in particular, in the content of potassium, sulfates, and nitrates (Lozovik and Galakhina, 2017). There were two trends found in accordance to the obtained hydrochemical information (Table 2).

• when moving from station no. 1 to station no. 2, there is a decrease in the total mineralization in terms of electrical conductivity, the content of hydrocarbonates and chlorides, as well as of the pH value. This is due to the gradual dilution of highly mineralized man-made waters of Karelskiy Okatysh JSC coming from the tailing dump to the Kenti River. A simultaneous decrease in the concentration of total nitrogen present in the industrial waters due to the large amount of nitrates also occurs as a result of natural dilution.

• the water is being enriched with allochthonous organic matter coming from the catchment area. As a result, there is an increase in both CW and PV. The low content of total phosphorus (7-9 ^g/L) corresponds to the natural oligotrophic state of water bodies of the lake-river system of the Kenti River.

Table 2. Results of chemical analysis of the water samples from the Kenti River (stations nos. 1 and 2) and the Lakhna River (station no. 3).

At the station no. 3, low mineralization of water, high concentration of organic matter, weakly acidic reaction, and high CW in the Lakhna River are preconditioned by the high swampiness of its catchment area (Lozovik, 2013).

The algae flora of plankton in the studied areas of the Kenti and Lakhna rivers comprise 46 taxa, and 6 more forms are identified down to the genus level. Diatoms and green algae are the most diverse groups, comprising together 78.3% of the total number of species (Table 3). In general, this is a characteristic feature of the phytoplankton communities of the rivers of the Republic of Karelia (Komulaynen et al., 2006).

Table 3. Species composition of phytoplankton of the Kenti River (stations nos. 1 and 2) and the Lakhna River (station no. 3). Dn is the species dominating by abundance, Db, by biomass.

Table 4. The main indicators of phytoplankton of the Kenti River (stations nos. 1 and 2) and the Lakhna River (station no. 3). Sp is the number of species; N, abundance; B, biomass.

Planktonic diatoms (Aulacoseira islandica), along with Dinophyta (Peridiniopsis penardii, Peridinium cinctum, and P. inconspicuum) and green algae (Phacotus lenticularis), dominate by biomass (Table 4). In terms of abundance, the dominant complex includes also diatoms (Aulacoseira islandica and Eunotia pectinalis) and green algae (Botryococcus neglectus) in addition to the listed species. The average abundance and biomass of planktonic algae in the Kenti and Lakhna rivers are generally close to those previously noted in other watercourses of the Karelian coast (Komulaynen et al., 2006).

Eurybiont species prevail (83-94%) in all studied phytoplankton communities. The pH-indifferent species are the most diverse group (40-47%), followed by acidophiles (20-26%). The presence of latter is a consequence of the inflow of bog waters from the catchment into watercourses.

Algae flora of riverine periphyton (65 species in total) is also mainly represented by diatoms (39 species); euperiphyton forms of the genera Tabellaria, Eunotia, and Achnanthes have been found the most frequently. This complex of dominant species usually determines the structure of algal fouling in rivers. Green algae, represented by Bulbochaete sp., Zygnema sp. and Mougeotia sp., have been the main species forming the coenose. Red algae are represented by only one taxon (Batrachospermum gelatinosum); however, it is presented fairly constant and dominates in all studied areas.

The species dominating by abundance are represented by 13.3% of the total number of species. However, the structure of phytoperiphyton in rivers is determined by an even more limited number of species, contributing each more than 10% of the total abundance and biomass of phytoperiphyton at certain stations (Table 5).

Table 5. Species composition of phytoperiphyton of the Kenti River (stations nos. 1 and 2) and the Lakhna River (station no. 3). Dn is the species dominating by abundance, Db, by biomass.

The dominant complex of species in fouling algal coenoses is presented mostly by both obligate and facultative rheophiles. In relation to the total mineralization of water, most of the species are oligohalobes. The pH-indifferent species prevail, which is common for humified waters, but the group of acidophiles is also quite numerous. In fouling algal coenoses, they are represented by diatoms of the genus Eunotia and green algae of the order Desmidiales.

A sufficiently high similarity of taxonomic composition at different stations is accompanied by the differences in the structure of the dominant complex and noticeable fluctuations in the abundance of the formed groups (Table 6).

Table 6. The main indicators of phytoperiphyton of the Kenti River (stations nos. 1 and 2) and the Lakhna River (station no. 3). Sp is the number of species; N, abundance; B, biomass.

In total, 26 species of planktonic crustaceans and rotifers are identified in the zooplankton communities of the studied sites (Table 7).

The zooplankton abundance and biomass in the studied sites differ markedly, which may be explained not only by the influence of runoff from the drainage lakes, but also by a change in the level of anthropogenic load. There are only five zooplankton species dominating by abundance and biomass at some study sites (Table 8).

Table 7. Species composition of zooplankton the Kenti River (stations nos. 1 and 2) and the Lakhna River (station no. 3). Dn is the species dominating by abundance, Db, by biomass.

Table 8. The main indicators of zooplankton of the Kenti River (stations nos. 1 and 2) and the Lakhna River (station no. 3). Sp is the number of species; N, abundance; B, biomass.

Table 9. Species composition of macrozoobenthos in the Kenti River (stations nos. 1 and 2) and the Lakhna River (station no. 3). Dn is the species dominating by abundance, Db, by biomass.

The macrozoobenthos is presented by 58 taxa of macroinvertebrates, 77% of them are insects (Table 9).

The representatives of Oligochaeta, Bivalvia, Ephemeroptera, Trichoptera, Plecoptera, and Diptera form the basis of macrozoobenthos community. The quantitative characteristics of benthic communities generally correspond to those previously identified in the rivers of the northern part of the Republic of Karelia (Baryshev, 2015; Baryshev and Khrennikov, 2016). Despite high species richness and taxonomic diversity, the composition of the dominant complex is quite stable and includes species that are typical for litreophilous biotopes of the Karelian rivers (Table 10).

Table 10. The main indicators of zoobenthos of the Kenti River (stations nos. 1 and 2) and the Lakhna River (station no. 3). Sp is the number of species; N, abundance; B, biomass.

Table 11. Indicator species in the studied communities of aquatic organisms. x - xenosaprobic species; xo - xeno-oligosaprobic; Я - betamezosaprobic; o-Я - oligo-beta-mesosaprobic; o - oligosaprobic; a-Я - alphabetamezosaprobic; a - alphamesosaprobic species.

In total, 112 saprobity indicator species are found in the studied communities of aquatic organisms. The most diverse are Я-mesosaprobes and oligosaprobes (Table 11). That is why the values of the Pantle - Buck index calculated for phytoplankton, phytoperiphyton, zooplankton, and zoobenthos of the Kenti and Lakh- na rivers are characteristic of the oligosaprobic zone (Table 12), these values are lower comparing that in the polluted rivers of the Northern European Russia (Komulaynen, 2002, 2004b).

Therefore, the structure of all studied communities and the list of dominant species are typical for river ecosystems in the Republic of Karelia (Biotic diversity of Karelia..., 2003). They are preconditioned by geographic location, landscape and topography of river catchments. All the identified species are present in various proportions in the groups of aquatic organisms in the watercourses of the region. However, in the upper reaches of the Kenti River (station no. 1), a number of specific features, which cannot be explained by natural factors only, are noted in the structure of communities.

It is natural that an increase of the density of the precipitated mineral matter on the surface of a solid substrate in the upper reaches of the Kenti River (station no. 1) reduces the possibility for the formation of a “real” periphyton (Komulaynen, 2004a) and leads to an increase in the abundance and diversity of benthic forms typical of microphytobenthos (Algal ecology..., 1996). Here, mesohalobes and halophiles are the most diverse groups in plankton and periphyton, i.e. the species preferring waters with increased mineralization. In phytoplankton, the dominance of small-sized species of green algae (up to 70%) is observed, which explains the maximum values of the total abundance. Meantime, the number of zooplankton and macrozoobenthos species decreases.

A comparison of aquatic biocoenoses of the Kenti and Lakhna rivers also brings indicative results. The phytoplankton and phytoperiphyton of the Lakhna River are characterized by a greater diversity and abundance of acidophilic forms, characteristic of water bodies with swampy catchments, and by the absence of halophilic species, which are common in the algae flora of the Kenti River, especially in its upper reaches. These differences, as well as the general impoverishment of the species composition and simplification of the structure of algal coenoses of the periphyton of the Kenti River, can only be explained by the increased water mineralization, s...