Water Quality of the Bočac Reservoir and the Vrbas River Downstream of the Dam

Irena Zarić1, Marija Nikolić1

 

1 Institute for Water. Miloša Obilića 51, 76300 Bijeljina, Republic of Srpska, Bosnia and Herzegovina; E-mail: This e-mail address is being protected from spambots. You need JavaScript enabled to view it

 

Abstract

In this paper the results of biological investigations of water in the Bočac Reservoir and the Vrbas River, downstream of the dam, during the period from 2013 to 2016 are presented. Tests were carried out in four series from February to December. Analyzed parameters included physico-chemical parameters and biological parameters, including pH, conductivity, dissolved oxygen, dissolved oxygen percent saturation, water transparency, nitrogen and phosphorus compounds, COD, BOD5, composition and dynamics of the phytoplankton community in the Bočac Reservoir and the Vrbas River, downstream of the dam, as well as the concentration of chlorophyll-a and macroinvertebrate community investigations.

Keywords: Phytoplankton, water quality, monitoring, macroinvertebrate.

Introduction

 

Basic biological components of an aquatic ecosystem are made up of producers (algae, macrophytes), consumers (zooplankton, macroinvertebrates, fishes, amphibians, reptiles, birds) and reducers (bacteria). All of them are a part of the water body quality, natural state and in a certain way, they contribute to basic characteristics of a water body, because, indirectly and directly, they affect their environment.

The algae communities of the open water of lakes and large streams, the phytoplankton, consist of the diverse assemblage of almost all major taxonomic groups. Many of these forms have different physiological requirements and vary in response to physical and chemical parameters, such as lights, temperature and nutrient regimen. Despite these diversities, both in taxonomic and physiological terms, many algal and cyanobacterial species coexist in the same water volume. However, dominant genera in algal groupings, change not only spatially (vertically and horizontally within the lake) but seasonally, as physical, chemical and biological conditions change in the water body. (Wetzel, 2001)

Macroinvertebrates represent a community of aquatic organisms of macroscopic dimensions and inhabit mainly the bottom of aquatic ecosystems throughout their lives or part of their life cycle. These are: leeches, individual groups of worms, shells, snails, crayfish, larvae of water insects, etc. Abiotic factors in the aquatic ecosystem, expressed through hydro-morphological and physical-chemical characteristics of aquatic habitats, significantly affect the structure of communities of benthic macroinvertebrates. Of the physical-chemical factors, the temperature, the concentration of dissolved oxygen, the concentration of oxygen saturation, the pH of water, the concentration of organic matter and others are of the highest importance. The most important factors are the hydro-morphological parameters, the substrate type, the flow rate and the water regime. All of these parameters work synergistically on macroinvertebrates and each species has an ecological valency within the limits of its survival. All listed factors determine the composition and structure of the macroinvertebrate community of a water ecosystem. (Status of surface waters of Serbia: Analysis and elements for monitoring design. 2015)

 

fig01
Figure 1: The Bočac Resevoir (Zarić, I.)

 

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Figure 2: The Bočac Resevoir (Zarić, I.)

 

The Research Area

The Vrbas River is the right tributary of the Sava River, and it flows into the Sava at the 434th km. With a river basin area of 6386 km2, the Vrbas is the smallest main tributary of the Sava in Bosnia and Herzegovina. The Vrbas River springs at the base of Zec Mountain, at 1715 m above sea level. The total difference in altitude from the source to the mouth is 1627 m. The main tributaries are the Pliva and the Crna Rijeka. The Vrbas River Basin has a moderate continental climate. There are three different parts of the watercourse of the Vrbas River: upper, middle and lower watercourse. The Bočac Reservoir was created after the construction of the dam in the middle watercourse of the Vrbas River and it is located in the Republic of Srpska, near the village of Bočac as shown in figures 1, 2. The dam has a height of 66 m and a length of 220 m. The overall length of the lake is 20 km, the surface is 2.33 million m2 and the total volume is about 52.7 million m3.

The reservoir is located between the Manjača and Čemernica mountains. (Water district of the River Danube, part B, 2004)

Sampling was performed on the following profiles, as also shown in figures 3 and 4:

  • Bočac Reservoir – profile B-5 – depth about
  • 45 m, located close in front of the dam;
  • Vrbas River – profile downstream of the Bočac Reservoir.

 

fig03
Figure 3: The Bočac Resevoir (Zarić, I.)

 

fig04
Figure 4: The Bočac Resevoir (Zarić, I.)

 

A problem that is present in the Bočac accumulation is floating waste (branches, pet-packaging, dead animals etc.). Floating waste, in addition to having a negative visual effect, is also a significant source of pollution of the reservoir, as shown in figures 5, 6, 7 and 8. (Water quality testing of Lake Bočac and the Vrbas River downstream from the dam, 2013 2014, 2015/16 and 2016/17). Also, plants were not removed sufficiently before the initial filling up of the reservoir.

 

fig05
Figure 5: The Bočac Resevoir (Lekić, G.)

 

fig06
Figure 6: The Bočac Resevoir (Lekić, G.)

 

fig07
Figure 7: The Bočac Resevoir (Mitrović, P.)

 

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Figure 8: The Bočac Resevoir (Mitrović, P.)

 

Materials and Methods

The water quality research was conducted in 4 series between February and November, in the period from 2013 to 2016. Regulations on Water Classification and Categorization of Watercourses ("Official Gazette of the Republic of Srpska" No. 42/01) is used for evaluating of the water quality state. Analyses of collected samples for chemical parameters, as well as methods for their preservation and conservation, have been performed in accordance with the following methods: BAS ISO 5667-2, 3, 4 i 6 and for macroinvertebrates, BAS EN ISO 10870:2014 – samples were collected with a hand net and an Ekman-Birge grab. Samples from the surface river water layer for qualitative and quantitative analysis of phytoplankton at the examined profiles were taken with a plankton net, (EFE and GB nets), made of Monodur Nytal (Nylon), pore diameter of 20 μ.

During each sampling cycle, measurements were carried out for basic physico-chemical parameters (BOD5, suspended solids, nitrogen compounds, phosphorus, metals (Fe, Cu, Cr, Hg, Ni, Pb, and Cd)) and for on-site measured parameters: water temperature, air temperature, pH, electro-conductivity, dissolved oxygen, dissolved oxygen percentage saturation and water transparency of the reservoir.

Methods of determination of composition and number of phytoplankton, concentration of chlorophyll-a, as well as saprobity index S (Pantle, Buck, 1955), are based on Standard methods, APHA-AWWA-WEF, 2005, BAS ISO 10260:2002. MSZ 12 756: 1998. Phytoplankton classification which was used in the paper, is according to Jelena Blaženčić (Algal systematics, 2000). This system of classification of algae uses 10 classifications of divisions as follows: Cyanobacteriophyta (blue-green algae), Rhodophyta (red algae), Pyrrophyta, Xanthophyta (yellow-green algae), Chrysophyta (golden algae), Bacilariophyta (siliceous algae), Pheophyta (brown algae), Euglenophytes, Chlorophyta (green algae) and Charophyta.

Beside floristic analysis, the following analyses were also performed: determining the composition and number of macroinvertebrate communities at the bottom of the tested watercourses, in addition to determining the necessary metrics: saprobity index S (Pantle, Buck, 1955) and (Zelinka & Marvan, 1961), Trent biotic index TBI (Wodwiss, 1964), BWMP/ASPT (Armitage et al., 1983), diversity index Shannon-Weaver index (1949), BBI (Flanders, 1990/2010), Chandler index (Chandler, 1970), Margalef index, (Margalef, 1958), EPT, %EPT, %D, EPT/D and taxon number. Processing of the research and the qualitative and quantitative data is carried out by using of ASTERICS-program (European AQEM stream assessment program, Version 2.3, released on April 2004).

In addition to the qualitative and quantitative composition, relative frequency of taxa was analyzed, and based on this analysis, dominant and subdominant species were determined. (Water quality testing of the Lake Bočac and the Vrbas River downstream from the dam,2013 2014, 2015/16 and 2016/17)

 

Results and Discussion

Physico-Chemical Parameters of Water Quality

Measurement and analysis of basic physico-chemical parameters that are indicative for the biological component of an aquatic system such as the Bočac reservoir, included oxygen regime, salinity, acidity, nutrients, suspended solids, COD, BOD5, metals.

The results for the basic physico-chemical parameters for the 2013-2016 period show that during vegetation season pH values in the reservoir increased to 8.84 due to intensive photosynthetic activity. In the Vrbas River measurement profile, the pH values ranged between 7.4 and 7.9. Values of BOD5 were within the limits of 1st and 2nd water quality class, in 75% of the cases. The measured values for suspended solids for the majority of measurements (50-58.3%) were within limits of 1st or 2nd water quality class, while the other classes of soundness have different percentage participation. Oxygen regimes of the reservoir (dissolved oxygen and oxygen saturation) and of the Vrbas river have the highest percentage measurements within the limits of the 1st and 2nd classes (from 62.5 to 77.5%).

Values of nitrogen components (nitrites, nitrates, ammonia) are within limits of 1st class, while concentration of phosphorus in the Vrbas profile, for the highest number of measurements (over 50%), is within the limits of 1st class, and maximum values are between 0.068 and 0.096 g/m3. Analysis of the results, considering the average value of TSI index for transparency and chlorophyll-a, shows that the reservoir has a mesotrophic or oligotrophic status, and for the overall amount of phosphorus has an eutrophic status. According to the OECD model, the reservoir has a mesotrophic status for all the quality indexes, except for the maximum and mean value of chlorophyll concentration, for which it has an oligotrophic status, and for mean concentration of phosphorus, due to which it has an eutrophic status.

The concentration of iron, copper and chromium on all tested profiles correspond to the values prescribed for the first (87.5 to 100% of the total number of measurements), or the second class (12.5% for copper). Concentrations od mercury in 58.3 to 87.5% of cases correspond to the concentrations prescribed for first class watercourses, and in 41.7 to 100% of the cases satisfy the values prescribed for second class watercourses.

The concentration of nickel in 37.5 to 88.3% of the cases corresponds to the concentrations prescribed for second class watercourses and in 16.7 to 50% of cases correspond to the concentrations prescribed for third class watercourses, and in 5 to 12.5% of the measurements correspond to the limits prescribed for fourth class watercourses.

The highest nickel concentrations were recorded on the Bocac accumulation profile in July 2014 (2.44 mg/m3) and September 2016 (4.8 mg/m3). On the measuring profile on Vrbas, the highest concentrations for this metal were measured in June 2014 (1.81 mg/m3).

The values of lead concentrations in 12.5 to 58.3% of cases satisfy the values prescribed for the first class. In 38 to 75% of cases satisfy the values prescribed for the second class of watercourses, and in 12.5 to 14% of the measurements are within the limits prescribed for the third class of watercourses.

The values of cadmium concentration in 62.5 to 91.7% of cases satisfy the values prescribed for the first class, and in 8.3% of the cases satisfy the values prescribed for the third class of watercourses.

Of the overall 382 measurements for the purpose of the physico-chemical characteristics research of the measurement profiles in Bočac and Vrbas, during the research period, 343 measurements or 89.9% are within limits of 1st and 2nd quality class. (Water quality testing of the Lake Bočac and the Vrbas River downstream from the dam,2013 2014, 2015/16 and 2016/17)

 

Chlorophyll-a Concentration

Testing of the samples from measurement profiles in the Bočac Reservoir and the Vrbas River, for the purpose of determining of the chlorophyll-a concentration, were performed in 4 series of sampling, for each year of researching. Collecting of algae and other suspended substances from the water is done by filtration method. Spectrophotometric determination of chlorophyll-a concentration is performed in the extract. Evaluation of chlorophyll and phaeopigment concentration is based on difference of absorption at 665 nm, before and after acidification of the extract. Presence of chlorophyll is directly connected with number and respectively with mass of algal cells, considering that chlorophyll makes 1-2% of dry mass of plankton algae. This is the reason for adopting a chlorophyll concentration as an indirect indicator of quantity of an algal biomass and intensity of primary production. Obtained values of chlorophyll concentration vary depending on the month of sampling. Results of the research are shown in Table 1 (Water quality testing of the Lake Bočac and the Vrbas River downstream from the dam, 2013 2014, 2015/16 and 2016/17).

 

Table 1: Chlorophyll concentration research results, Bočac Reservoir and Vrbas River.
tab01

 

Qualitative Composition and Quantity of Phytoplankton Organisms Community

Phytoplankton (microalgae) are present as single cell, colonial cell and thread-like forms. Many of them are photosynthetic and they are food of zooplankton and other aquatic organisms. Algae are widespread organisms inside and outside of water, and they are significant factors of the basic biological processes, such as circulation of substances and energy flow. They are basic producers of organic substances in aquatic ecosystems and represent primary production, which is material and energetic base of overall production relations. As photosynthetic organisms, they are an inexhaustible source of oxygen which enriches atmosphere. Because of their short life cycles, species which form plankton can react fast on environmental changes. Phytoplankton community has a very strong influence on certain abiotic parameters of water quality ( for example: pH, color, taste, smell), so it practically represents a part of water quality. (Standard Methods for the Examination of Water and Wastewater, 21st Edition, 2012)

During the research period, from February to September 2013, in the Bočac Reservoir was registered presence of 43 taxa from 34 families and 5 divisions of algae: blue-green algae (Cyanobacteria) 4 taxa from 3 families (9%); golden algae (Chrysophyta) 1 taxon (2%); diatom algae (Bacillariophyta) 20 taxa from 16 families (46%); Pyrrophyta, 5 taxa from 3 families (12%); and green algae (Chlorophyta) 13 taxa from 10 families (30%), as it given in Figure 17. In the same period, in the Vrbas River was registered presence of overall 61 taxa from 37 families and also 5 divisions of algae: blue-green algae (Cyanobacteria) 6 taxa from 3 families (10%); golden algae (Chrysophyta) 1 taxon (2%); diatom algae (Bacillariophyta) 38 taxa from 21 families (62%); Pyrrophyta, 4 taxa from 2 families (6%); and green algae (Chlorophyta) 12 taxa from 12 families (20%), as it given in Figure 18.

Highest rate of diversity and quantity in the reservoir and in the Vrbas River was present among diatom algae Bacillariophyta. For the period from year 2013 to 2016 they had highest number during the year 2013. Some of the dominant diatom algae species were: Asterionella formosa, Fragillaria crotonenis, Synedra acus. Also, green algae were distinguished with 13 taxa. Within the green algae Chrysophyta, in the reservoir and in the river, were registered only Dinobryon divergens. Of the overall number of 43 taxa which were registered in the reservoir, only 2 belong to 1st class (4.7%), 36 to 2nd class (83.7%) and 5 taxa (11.6%) belong to 3rd class of water quality. In the Vrbas River, of the overall number of 61 registered taxa, 6 belong to 1st class (9.8%), 46 to 2nd class (75.4%) and 9 taxa (14.8%) belong to 3rd class of water quality. Some of the dominant species in the river are: Dinobryon divergens, Asterionella formosa, Synedra acus, Ceratium hirundinella, as shown in figures 9,10, 11, 12, 13, 14, 15, 16.

 

fig09
Figure 9: Genus Ceratium and Peridinium (Pyrrophyta), Bočac reservoir and Vrbas River (Zarić, I.)

 

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Figure 10: Genus Ceratium and Peridinium (Pyrrophyta), Bočac reservoir and Vrbas River (Zarić, I.)

 

In 2014 the research was performed from April to October. The overall number of species was 26, from 23 families: blue-green algae (Cyanobacteria) 3 species from 3 families (11.5%); golden algae (Chrysophyta) 1 specie (4%); diatom algae (Bacillariophyta) 11 species from 10 families (42%); Pyrrophyta, 5 species from 3 families (19%); Euglenophyta 1 specie (4%); and green algae (Chlorophyta) 5 species from 5 families (19%), as given in Figure 17. The presence and number of diatom algae division is not unusual for colder periods of the year, especially in a reservoir such as Bočac, with pronounced water column stratification. The significance of diatom algae is manifested in their function as basic primary producers where they are often the first link in a food chain for many aquatic invertebrates and vertebrates and they are special due to their chemical properties, because they contain vitamins, proteins and fats. Diatom algae are sensitive to chemical changes in the aquatic environment, so they are a significant biological indicator, and are also participants in the water purification process. Considering that research started during the month of April, 2014, the change of seasons, respectively increasing water temperatures, was leading to environmental changes in the reservoir, that were leading to changes in phytoplankton composition. June of 2014 characterizes a dominant presence of diatom and golden algae, but the end of July and October also characterizes the presence of Pyrrophyta and green algae. The dominant taxa are: Dinobyon divergens (Chrysophyta), Asterionella formosa, Fragillaria crotonensis, Synedra acus, (Bacillariophyta), Ceratium hirundinella, Peridinium aciculiferum (Pyrrophyta).

During all sampling series from the Vrbas River, the presence of 6 algae divisions was registered. Differences in diversity and number are present for each of the divisions, and they are related to different seasons of a year, in which the sampling and testing of phytoplankton was done. The overall number of identified species is 36, from 28 families: blue-green algae (Cyanobacteria) 4 species from 3 families (11%); golden algae (Chrysophyta) 1 specie (3%); diatom algae (Bacillariophyta) 20 species from 15 families (55%); Pyrrophyta, 2 species from 2 families (5.5%); Euglenophyta 1 specie (3%); and green algae (Chlorophyta) 7 species from 6 families (19%), as given in Figure 18. Sampling in April of 2014 was characterized by a smaller amount of all present species. Diatom and green algae were dominant. Research conducted in Jun and July of 2014 showed a large diversity within the 6 divisions of algae. Dominant species were mostly the same as the species in the reservoir. First quality class includes 3 species (12%), the second includes 20 species (80%) and the third includes 2 species (8%), as shown in figures 9, 10, 11, 12, 13, 14, 15, 16.

 

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Figure 11: Genus Ceratium and Peridinium (Pyrrophyta), zooplankton (Rotatoria), Bočac Reservoir and Vrbas River (Zarić, I.)

 

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Figure 12: Genus Ceratium and Peridinium (Pyrrophyta), zooplankton (Rotatoria), Bočac Reservoir and Vrbas River (Zarić, I.)

 

During 2015, sampling was done in 3 series. The species identified in the reservoir recorded the presence of 25 species from 23 families and 5 divisions of algae: blue-green algae (Cyanobacteria) 3 species from 2 families (12%); golden algae (Chrysophyta) 1 specie (4%); diatom algae (Bacillariophyta) 9 species from 8 families (36%); Pyrrophyta, 3 species from 3 families (12%); and green algae (Chlorophyta) 9 species from 9 families (36%), as given in Figures 17.

The first research cycle conducted by qualitative analysis of phytoplankton, identified the dominance of green algae (Chlorophyta), and the changes were registered during the second cycle. In September, diatom algae (Bacillariophyta) were becoming the dominant species: Synedra acus, Asterionella formosa. Qualitative composition of the phytoplankton community in the Vrbas River, in the profile downstream of the dam, included 5 divisions with 17 species and 16 families: blue-green algae (Cyanobacteria) 4 species and 3 families (23.5%); golden algae (Chrysophyta) 1 specie (6%); diatom algae (Bacillariophyta) 8 species and 8 families (47%); Pyrrophyta, 1 specie (6%); and green algae (Chlorophyta) 3 species and 3 families (18%) as given in Figure 18. Of the overall 25 species which were registered in the reservoir, 3 species are indicators of 1st class water quality (12%), 4 species are indicators of 2nd class (16%) and 18 species are indicators of 3rd class water quality (72%). In the profile downstream of the reservoir, 2 species are indicators of 1st class water quality (11.8%), 2 species are indicators of 2nd class (11.8%) and 13 species are indicators of 3rd class water quality (76.4%), as shown in figures 9,10, 11, 12, 13, 14, 15, 16.

 

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Figure 13: Genus Fragillaria (Bacillariophyta) and representatives of the division Chlorophyta, Bočac Reservoir and Vrbas River (Zarić, I.)

 

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Figure 14: Genus Asterionella (Bacillariophyta) and representatives of the division Chlorophyta, Bočac Reservoir and Vrbas River (Zarić, I.)

 

During the period of research from March to December 2016, presence of 15 species from 14 families and 5 divisions of algae: blue-green algae (Cyanobacteria) 1 specie (7%); golden algae (Chrysophyta) 1 specie (7%); diatom algae (Bacillariophyta) 8 species from 7 families (53%); Pyrrophyta, 1 specie from 1 family (7%); and green algae (Chlorophyta) 4 species from 4 families (27%), as shown in Figures 17 and 18.

Of the 15 species overall that were registered in the reservoir, 1 specie is an indicator of 1st class water quality (7%), 11 species are indicators of 2nd class (73%) and 3 species are indicators of 3rd class water quality (20%). Only 8 species from 8 families were registered in the profile downstream of the reservoir and most of them belonged to the 2nd class water quality.

The calculated values for the Saprobity index S for the phytoplankton community, (Pantle, Buck, 1955), show that all profiles are within the limits of the second class of quality in all the series and years of testing (Water quality testing of the Lake Bočac and the Vrbas River downstream from the dam, 2013, 2014, 2015/16 and 2016/17).

Analyses and evaluations of seasonal and spatial growth characteristics of phytoplankton are sometimes difficult because of the array of environmental factors involved, the individual physiological properties of each algal species, and the magnitude of change that occur in both. Clearly, the organisms and environment are both highly dynamic. Some important factors regulating growth and successions are (a) light and temperature, (b) buoyancy regulation, that is, the means of remaining within the photic zone by alterations of sinking rates, (c) inorganic nutrient factors, (d) organic micronutrient factors and interactions of organic compound with nutrient availability and biological factors of competition for available resources and predation by other organisms. Each species of algae possesses a range of tolerance to these factors and population growth proceeds most rapidly at some optimal combination of factors required for greatest growth and productivity which is probably seldom achieved under most natural conditions The competitive advantage of one species over another is relative and can change in the physical and biotic conditions that affect growth. (Wetzel, 2001)

 

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Figure 15: Genus Asterionella (Bacillariophyta), Bočac reservoir and Vrbas River (Zarić, I.)

 

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Figure 16: Genus Dinobryon (Chrysophyta) Bočac reservoir and Vrbas River (Zarić, I.)

 

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Figure 17: The diversity of the phytoplankton community, the Bočac Reservoir, 2013-2016. (Nikolić, M.)

 

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Figure 18: The diversity of the phytoplankton community, the Vrbas River, 2013-2016. (Nikolić, M.)

 

Qualitative Composition and Quantity of Benthic Animal Communities

The distribution, abundance and productivity of benthic organisms are determined by several ecological processes: (a) the historical events that have allowed or prevented species from reaching a habitat, (b) the physiological limitations of the species at all stages of the life cycle, (c) the availability of energy resources, and (d) the ability of the species to tolerate competition, predation and parasitism (Reynolds, 1983; Hutchinson, 1996).

Analyses of the complex interrelationships among the benthic animals of fresh waters have focused to a large extent on descriptions of species and their distributions within lakes and streams in relation to environmental variables. Although such analyses are essential to initial evaluations of the communities, physiological oriented experimental analyses of regulating environmental parameters have not been utilized among benthic communities to nearly the extent that they have been in studies of planktonic communities. The population, productivity, and the trophic interrelationships of the benthic fauna are poorly understood in lakes, they are better known in running waters. (Wetzel, 2001).

The advantages of using macroinvertebrates as bioindicators are: they wide spread in in all types of surface water bodies, which is the group which, from a morphoatomic point of view, includes very different organisms belonging to different taxonomic groups, by their way of life are predominantly sedentary, and therefore suitable for spatial analysis of the impact of pollutants, have long life cycles compared to other bioindicators (e.g. algae), which provides an opportunity to detect changes in the aquatic ecosystem caused by the impact of a low-intensity negative factor, and a long-term effect. (Status of surface waters of Serbia, analyses and elements for monitoring design, 2015).

By analyzing the composition and number of macroinvertebrates on the accumulation of Bočac, from a total of 3 basic types, Annelida, Mollusca and Arthropoda, 5 taxa from 5 different genera were found, as shown in table 2.

 

Table 2: Quantitative and qualitative composition of macroinvertebrates (taxon and genera) and the composition of the Insect class (Arthropoda), on the Bocac accumulation, research 2013 to 2016.
tab02

 

There were 3 types of invertebrates with a low number of indicator taxons. Species of the Mollusca type (Lymanea sp.), type Annelida (Limnodrilus sp., Tubifex sp. Oligochaeta Gen. sp.) and the type of Arthropoda, class Insecta (Chironomus sp.) are indications of highly contaminated waters and anoxic environments, loaded with organic and other pollution types. The dominant group is the genus Chironomus sp. Since the sample is taken from the lake bottom, this situation is both expected and predictable.

The values of the calculated indices (S, BMWP, Shannon & Weaver, Zelinka & Marvan, ASPT, TBI, BBI, CS, Margalef index, EPT, EPT%) support the above theses, because according to them, water reservoir at this sampling profile is classified into 4th class waters based on the majority of the indices used and during all four research periods. Out of the total number of calculated values for indices, 6% are in the third class, 79% in the fourth class and 17% in the fifth class of quality. Water is very organically burdened and under strong anthropogenic influence.

The composition of the bottom macroinvertebrates on the Vrbas River, downstream of the dam shows that a total of 13 different taxa from 13 genera of 3 types of invertebrates were found, as shown in table 3. These are the following types: Annelida, Mollusca and Arthropoda. The presence of larval grades of the Insect class and noticeably higher biodiversity indicates better condition of this water stream.

 

Table 3: Quantitative and qualitative composition of macroinvertebrates (taxon and genera) and the composition of the Insect class (Arthropoda), on the Vrbas river, downstream of the dam, research from 2013 to 2016.
tab03

 

The composition of the community with groups and characteristic indicator species - Oligochaeta (Oligochaeta Gen. sp., Limnodillus sp.), Hirudinea (Erpobdella octoculata, Gastropoda (Ancylus fluviatilis, Bithynia tentaculata, Lymnaea sp.), Diptera (Tanypodinae, Chironomus sp.) indicators of the class III and IV watercourses Asellus aquaticus, a Crustacea class, is also an indicator of higher organic matter loads in watercourses because this species has a fairly high tolerance of pollution. The confirmed Ephemeroptera species, which in their development require a higher presence of oxygen and are less tolerant to the existence of organic loads, present a picture of a higher ecological state. Chironomidae (Diptera) dominate and Trichoptera, Ephemeroptera and Coleoptera occur subdominantly.

The prevalence and higher numbers of Mollusca during all sampling periods indicate the presence of CaCO3 or limestone, one of the most widespread sedimentary rocks which is required by them in order to form shells. The values of the calculated indices (S, BMWP, Shannon & Weaver, Zelinka & Marvan, ASPT, TBI, BBI, CS, Margalef index, EPT, EPT%) confirm these findings.

The processing of test results and qualitative and quantitative data was made using the ASTEREM program (AQEM European stream assessment program, Version 2.3, released on April 2004).

In the investigated profiles, no species were found from the Red list of protected species of flora and fauna of the Republic of Srpska. (Water quality testing of the Lake Bočac and the Vrbas River downstream from the dam, 2013 2014, 2015/16 and 2016/17).

 

Conclusion

The results represent the research which was carried out during the period from 2013 to 2016. Each year, sampling and measurements were performed in 4 separate cycles, in order to include all seasonal aspects of the research profiles (winter, spring, summer and autumn).

The results of the physico-chemical parameters show that both profiles, statistically, are within the limits of 1st and 2nd class. TSI and OECD models for the reservoir show that the reservoir is an aquatic ecosystem which is mostly mesotrophic by all parameters, except when it comes to the phosphorus parameters, which indicate a eutrophic character. Qualitative and quantitative composition of phytoplankton shows great diversity, even though only one profile was observed, and shows great seasonal dynamic, where Bacillariophyta replace Chrysopyta, Pyrrophyta, Cyanobacteriophyta and Chlorophyta, depending on the season in which the analysis was performed. Calculated values for the Saprobity index (Pantle, Buck, 1955), show that all profiles are within the limits of the second class quality in all series and years of testing.

Qualitative and quantitative analysis of macroinvertebrates - the composition and the number of indicative taxons in the 3 types of invertebrates (Annelida, Mollusca, Arthropoda) shows that these are polluted profiles. This pollution is mainly of anthropogenic origin. The worst condition was found on the reservoir Bočac (B-5).

Indicators of existing organic pollution are present in all profiles in all sampling cycles during the years. These are larvae of the genus Chironomus sp. Living freely in sludge, sand or among aquatic plants, Oligochaeta and Hirudinea class Annelida.

 

Acknowledgements

Authors are thankful to colleagues from the Physical-Chemical Department Laboratory of the Institute for Water, and colleagues who provide assistance in field work and measurements. The results presented in this paper represent the joint work and advocacy.

 

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