Macrozoobenthos of Lakes Beloe and Kolyvanskoe (Northwestern Altai) and the main ecological factors of its formation

. In comparison with the large volume of work on lakes located in lowland territories, only scattered information about their ecosystems was available for lakes located in foothill (low-mountain) areas, both in Russia and worldwide. Foothill lakes differ significantly from high-mountain and lowland lakes in both physical and biological properties. In May, July and September 2022, the current state of Lakes Beloe and Kolyvanskoe was studied in the north-west of Altai (Russia). The composition and structure of macrozoobenthos, as well as the main ecological factors of its formation (morphometric, physical and hydrochemical) are revealed. A total of 90 species of benthic invertebrates from 8 classes were found in the zoobenthos. Zoobenthos species of Lake Beloe represented the most diverse compare to Lake Kolyvanskoe. In terms of zoobenthos biomass, the lakes corresponded to mesotrophic lakes. Most of the bioindication indices characterized the water of the studied lakes as "very clean" and "clean". The greatest influence on the level of macrozoobenthos development in the low-mountain lakes Beloe and Kolyvanskoe is exerted by factors that determine salinity, the content of organic matter and their decomposition products in water, as well as the features of the soil.


Introduction
Ecosystems of mountain and foothill lakes are most sensitive to anthropogenic impact and climate change, which is due, among other things, to the predominance of highly sensitive hydrobionts in their population.The main factor of pollution of the natural environment of foothill lakes, traditionally used for tourist purposes, is a high recreational load.In accordance with the development strategy of the Siberian Federal District of Russia, the tourism and recreation industry in southern Siberia is becoming one of the priority areas of economic activity.Therefore, in this region, the problems of rational use of water bodies in the" recreation industry" are becoming more and more relevant.The study of the current state of ecosystems of foothill lakes in the Altai Krai is based on an ecosystem approach.This includes the analysis of the composition, structure, and functioning of bottom communities in combination with the analysis of the influence of abiotic factors.The most convenient and indicative method for assessing the ecological state of water pollution is bioindication based on the composition and structural indicators of zoobenthos [1].We should note the long-term experience of different countries in using bioindication [2,3,4].The advantage of this method is its greater reliability and objectivity.The state of the biota is determined by the cumulative effect of the environment and clearly reacts to negative impacts of any origin, regardless of their accounting and degree of study.Benthic organisms meet many requirements for bioindicators, including: ubiquitous occurrence, sufficiently high abundance, relatively large size, easy collection and processing, a combination of being confined to a biotope with a certain mobility, and a sufficiently long life span to accumulate pollutants over a long period.In the conditions of climate change and anthropogenic impact, it is especially important to study the composition and structure of macroinvertebrate communities in foothill lakes, since it is the best bioindicator of chronic pollution of water bodies [5].

Materials and methods
In 2022, the current state of the two foothill lakes (Beloe and Kolyvanskoe) of the northwestern Altai was studied (Fig. 1).Field studies were performed three times from May to September (May 27 -June 2, July 20-28, September 05-11).The main morphometric characteristics of lakes are presented in Table 1.Morphometric (relative water level and depth -127 measurement) and physical (temperature, transparency, electrical conductivity, and Eh of water) characteristics of lakes were studied.In total 20 water samples were collected and analyzed to study hydrochemical parameters, 8 soil (bottom sediment) samples for physical and chemical properties, 55 quantitative, and 11 qualitative samples of zoobenthos.Totally, more than 4,200 macroinvertebrate specimens were collected and identified.Hydrological measurements were carried out according to standard methods used in the Russian Federal Service for Hydrometeorology and Environmental Monitoring (Roshydromet).The relative water level is measured using a hydrometric rail, and the depth is measured using a hydrological lot.Water samples for hydrochemical analysis were taken by common methods from the near-surface water layer (1.5 liters each in a plastic container).Cameral processing of hydrochemical samples and bottom sediments was performed at the Laboratory of Biogeochemistry of the IWEP SB RAS.
Qualitative samples were taken with a water net or scraper, while quantitative ones were taken with a Peterson bottom grab (0.025 m 2 mouth area).Bottom samples (boulders and pebbles) were collected using a hydrobiological net (with subsequent calculation of the area of stones by their projection in a plane), then washed through a nylon gauze with a mesh size of 350х350 μm.The animals were isolated and fixed in 70% ethanol.When taken two to three times, quantitative samples were combined into an integrated sample.For a more complete accounting of the zoobenthos composition, the samples were collected manually in various biotopes.The soil taken by a bar dredge was washed through a kapron bag with a 320-μm mesh.The samples were examined portion-wise, and the organisms found were placed in test tubes with 70% ethyl alcohol.After drying on a filter paper, we weighed the organisms on a torsion balance.When assessing the frequency of occurrence, we used the following scale: the most common species -the ones met in more than 50% of samples, frequently occurring -20-50%, infrequently occurring -1-20%, rarely occurring -less than 1%.To assess the structural organization of benthic invertebrate communities, the Shannon Index of species diversity was used; for class I (very clean), index values >3.00; class II (clean) -2.01-3.00;class III (moderately polluted) -1.51-2.00;class IV (polluted) -1.01-1.50;class V (dirty) -0.51-1.00;class VI (very dirty) -<0.50.To assess the ecological state, the following indices were used: Multimetric Macroinvertebrate Index Flanders (MMIF) [6], Goodnight and Whitley -percentage ratio of the number of oligochaetes to the number of all zoobenthos.

Hydrochemical composition of water and granulometric composition of bottom sediments
The water of the studied lakes is ultra-fresh, bicarbonate-calcium, and slightly alkaline.Due to the total phosphorus content, the lakes are oligotrophic.The concentration of nitrates and nitrites was below the detection limits.The content of organic matter in the water of both lakes is low, corresponding to clean lakes.The hydrochemical composition of the lakes is shown in Table 2.
The studied lakes were characterized by a predominance of silty soils with a low content of organic matter (Table 3).Dark gray silts prevailed in Lake Kolyvanskoe, and gray ones in Lake Beloe.

Taxonomic composition and abundance
The maximum number of benthic invertebrate species is found in Lake Beloe (81), the largest number of species is typical for insects (52), followed by water mites (10) and oligochaetes (9), gastropods (6), leeches (2), as well as crustaceans and nematodes (1 species each).Diptera (35 species, of which 30 are chironomids) predominated among insects by the number of species, caddisflies (6 species), dragonflies (4 species), mayflies (3 species), beetles (2 species), and hemiptera (2 species) were also noted.The species richness of zoobenthos was typical for lakes of this type (9.07±1.07species in the sample), the average index of species diversity in the lake was 2.12±0.13bits/ind.The lake is characterized by relatively small values of zoobenthos abundance and biomass.The maximum biomass of benthic invertebrates was recorded in May, then their gradual decrease occurred (Fig. 2).In the deep-water parts of Lake Beloe, soft silty deposits predominate, which led to the development of pelophilic communities of benthic invertebrates, represented by oligochaetes and diptera.The main contribution to abundance and biomass was made by Chaoborus (C.) flavicans (Meigen), Chironomus gr.plumosus (L.) Procladius sp. and Tubificidae.In the coastal zone, the structure of zoobenthos was conditioned by the presence of plant detritus, sandy soils, as well as small pebbles and stony soil.In this zone, more complex psammopelophilic benthic communities with elements of phytophilic fauna were formed.Crustaceans, leeches and dragonflies made a significant contribution to the biomass, and diverse water mites were represented.Beloe corresponded to the mesotrophic type of lake in terms of macrozoobenthos.The abundance in different seasons of the year varied from 0.32 to 12.2 thousand ind./m 2 , the biomass -from 0.22 to 12.5 g/m 2 .Average values of zoobenthos abundance are shown in Table 4. alpha-mesotrophic alpha-mesotrophic A total of 61 species of benthic invertebrates from seven classes were identified in the Kolyvanskoe Lake zoobenthos: Nematoda (1), Oligochaeta (10), Hirudinea (3), Bivalvia (1), Gastropoda ( 5), Arachnida (6), and Insecta (35).Diptera predominated among insects by the number of species (26 species, 21 of which were chironomids); caddisflies (5), true bugs (2), and mayflies and beetles (1 species each) was also detected.The level of development and species richness of benthic invertebrates is similar to that of Lake Beloe.The average number of species in the sample was 8.28±0.57,and the Shannon index was 2.18±0.07bits/ind.Abundance values in different seasons ranged from 0.32 to 4.96 thousand ind./m 2 , and biomass from 0.052 to 7.84 g/m 2 .The average values of biomass of zoobenthos corresponded to the mesotrophic type of the lakes.Kolyvanskoe is dominated by soft silty deposits, the dominant complex here as well as in the Beloe composition was Ch. flavicans, Ch. gr.plumosus, Procladius sp., and Tubificidae.An increase in species diversity has been observed in the coastal zone, with crustaceans, leeches, and water mites also identified.

Bioindication
Most bioindication indices characterized the water of the studied lakes as "very clean" and "clean".The average values of the index of species diversity in Lakes Beloe and Kolyvanskoe corresponded to clean waters (Table 4).Its maximum values were recorded in the coastal zones of lakes, in Lake Beloe the index reached 3.66 bits/ind., in Lake Kolyvanskoe -2.94 bits/ind.The Multimetric Macroinvertebrate Index Flanders characterized the water quality of the Lake Beloe as good, Lake Kolyvanskoe as middling.The average values of the oligochaete index characterized the water as "very clean" and corresponded to "I class" water quality.In July, in the central zone, the index increased to 50% in Lake Beloe, up to 53% in Lake Kolyvanskoe.The level of species diversity and abundance of benthic invertebrates, the values of bioindication indices indicate good conditions for the development of macrozoobenthos in water bodies.

Influence of environmental factors
To determine the relative role of various environmental factors, we analyzed the relationship of 11 main indicators of the zoobenthos structure (the number of species in the sample, abundance and biomass in general, as well as the abundance and biomass of the main groups: oligochaetes, molluscs, chironomids and all other taxa) with 30 hydrophysical and hydrochemical indicators (depth, transparency, temperature, pH, Eh, electrical conductivity, CO3 2-, HCO -, Cl -, SO4 2-, Ca 2+ , Mg 2+ , ∑Na + +K + , NO3 -, NO2 -, NH4 + , PO4 3-, Ptotal, salinity, permanganate oxidability (PO), chemical oxygen consumption (COD), BOD5 of water, as well as granulometric composition (fractions: 1-0.25, 0.25-0.05,0.05-0.01,0.01-0.005,0.005-0.001,<0.001, <0.01 mm) and the organic carbon content (Corg.) of the soil.Analysis of these factors revealed a significant positive correlation between the hydrochemical parameters that determine the salinity of water (total salinity, Ca 2+ , and bicarbonates) and the abundance and biomass of zoobenthos, as well as with the biomass of oligochaetes (Table 5).High negative reliable values of the correlation coefficient were noted between the content of organic matter and biogenic elements, which are closely related to each other (NH4 + , Ptotal, COD, BOD5), and the following characteristics of zoobenthos: abundance and biomass of zoobenthos, MMIF (biotic index based on the species diversity of macroinvertebrates).A positive correlation was found between the biomass of chironomids and the depth of lakes.In addition, the negative influence of the proportion of small fractions of soil (silty and clay) and the positive influence of larger fractions (sand) on various characteristics of benthic invertebrates was revealed.

Discussion
A total of 90 species of zoobenthos from 8 classes of invertebrates were identified in the studied lakes: Nematoda (1), Oligochaeta (13), Hirudinea (3), Bivalvia (1), Gastropoda (6), Arachnida (10), Crustacea (1) and Insecta (55).The maximum number of species in the class of insects was found in diptera (36 species, including 30 chironomids), followed by caddisflies (6), dragonflies (4), mayflies (3), true bugs (3), and beetles (3).The lakes were dominated by chironomids and oligochaetes, which was also noted earlier for the flat lakes of western Siberia and the low-mountain lakes of the Russian Altai [7,8].The benthos of the lakes was characterized by moderate abundance and biomass during the study period from May to September.In terms of marozoobenthos biomass, the lakes corresponded to mesotrophic lakes.The maximum biomass of benthic invertebrates is recorded in May, then their slight decrease occurs.Zoobenthos was represented mainly by a chironomidoligochaete complex of species.The relative biomass of this complex was slightly affected by seasonal changes.A decrease in the biomass of benthic invertebrates in spring is associated with the presence of caddisfly larvae, and a further decrease in the biomass is associated with the flight of imago that have completed the aquatic phase of development.
The composition, structure, and abundance of macroinvertebrates communities is closely related to environmental conditions, such as temperature, hydrochemical composition, soil type, and much more [9][10][11][12][13].Correlation analysis of the influence of abiotic factors on the main characteristics of benthic communities revealed three main groups of factors: these are factors that determine the salinity of water, the content of organic matter and their decomposition products in water, and the type of the soil.The value of salinity has a significant impact on the taxonomic composition of hydrobionts in salt lakes, and as it increases, the number of species in them usually decreases.At the same time, in conditions of very low water salinity, an increase in the concentration of mineral ions has a favorable effect on bottom communities.The negative effect of concentrations of nitrates, phosphates, and their decomposition products in water on the species richness and individual taxa of benthic invertebrates has been repeatedly noted in the papers [13,14].At the same time, there is a positive effect of nitrates on the oligochaete biomass, which was also previously described [14].The type of bottom sediments is one of the dominant factors influencing the spatial distribution of macrozoobenthos, primarily its granulometric composition and the content of organic matter [15].The type of substrate affects the taxonomic diversity and abundance of zoobenthos, and these indicators increase on more stable substrates.A negative effect of the proportion of small soil fractions (silty and clay) on the total number of zoobenthos, as well as the number and biomass of chironomids, and a positive effect of larger fractions (sand) on the biomass of zoobenthos and chironomids was revealed.More often, a E3S Web of Conferences 420, 07006 (2023) https://doi.org/10.1051/e3sconf/202342007006EBWFF 2023 different trend is noted in the scientific publications: larvae of chironomids and oligochaetes are more numerous on silty soils [16].

Conclusions
Thus, 90 species from 8 classes of invertebrates were identified in the studied lakes: Nematoda (1), Oligochaeta (13), Hirudinea (3), Bivalvia (1), Gastropoda (6), Arachnida (10), Crustacea (1), and Insecta (55).The maximum number of species in the insect class was found in diptera (36, including 30 chironomids), followed by caddisflies (6), dragonflies (4), mayflies (3), true bugs (3), and beetles (3).The most diverse zoobenthos of Lake Beloe is represented.The main contribution to the abundance and biomass of zoobenthos in lakes was made by Ch. flavicans, Ch. gr.plumosus, and Procladius sp. and Tubificidae.In the coastal zone, crustaceans, leeches and dragonflies made a significant contribution to the biomass, and water mites were represented in a variety of ways.According to the bioindication indices, the waters of Lakes Beloe and Kolyvanskoe were characterized as "very clean" and "clean".Correlation analysis showed that the greatest influence on the level of zoobenthos development in the low-mountain lakes Beloe and Kolyvanskoe is exerted by factors that determine salinity, the content of organic matter and their decomposition products in water, as well as the type of the soil.

Table 1 .
Main morphometric characteristics of the studied lakes.

Table 3 .
Physical and chemical characteristics of bottom sediments of the studied lakes, 2022.

Table 4 .
Main characteristics of macrozoobenthos of the studied lakes.Notes: H -Shannon index of species diversity; MMIF -Multimetric Macroinvertebrate Index Flanders; Ko -Goodnight and Whitley oligochaete index; water quality class (Roshydromet): I -very clean; II -clean.

Table 5 .
Correlation of the main characteristics of macrozoobenthos with water and soil quality indicators of the studied lakes (r -Spearman's correlation coefficient, p -significance level).