The current state of the Southern Bug River mouth ecosystem

The article considers the pre-war conditions main components of the Southern Bug mouth ecosystem. The results of sediments samples study have shown transformation of lagoonal accumulation, appearance of reducing condition spots in sediments, presence of exceeding MAP for lead. An estuarine water analysis given an idea about hydrochemical features mouth section of river, namely: high concentration of suspended solids – on an average 11,4 mg/dm3; increasable concentration BOD5 – an indicator of easily oxidized organic substances content; periodic significant exceeding MAC of ammonium and nitrite nitrogen. Hydrobiological changes primarily concern a decrease in primary productivity due to a decline in phytoplankton biodiversity; there was also a reduction of zooplankton. The current state of the Southern Bug River mouth ecosystem is formed predominantly under the periodic dredging of shipping channels followed by the formation silt dumps. The post-war revitalization of the Southern Bug estuary ecosystem should include measures to mitigate the negative effects of anthropogenic activity especially the consequences of hydraulic engineering works.


Introduction
The Southern Bug is one of the largest rivers of Ukraine, which constantly experiences significant anthropogenic pressure due to the high regulation of the river, large-scale ploughing of coastal areas, dense settlement load.At the same time, the Southern Bug plays a very essential economic and social role in the functioning of the Black Sea region of Ukraine -it is a transport artery, a source of drinking water and food, a place of recreation, etc.If you look at this range of ecosystem services, especially in the context of global climate change, it is impossible to overestimate the importance of the Southern Bug River in the socio-economic development of the southern part of Ukraine [1].However, now, since the beginning Russia's full-fledged military aggression, the territory the Southern Bug River mouth is under catastrophic influence due to bombing and shelling.
The current state of the Southern Bug mouth ecosystem is formed under the influence of the multi-purpose usage of the river; one of the most powerful factors affecting the estuary part of the river is shipping and the associated periodic dredging of shipping channels.The Bug-Dnipro-estuary Canal (BDEC) serves as the entrance for the ships to Mykolaiv Port and a number of ports in the estuary.In addition, the lower part of the Southern Bug is intensively used for economic purposes: hydrotechnical (water intakes, discharges), fisheries, irrigation, etc. [2].Periodic hydrotechnical dredging measures have a significant impact on the functional capacity of the river ecosystem and its biota.The key goal of the presented research was to characterize the pre-war state of the Southern Bug River mouth ecosystem using a wide range of indicators, including lithological, hydrochemical and hydrobiological ones.
In order to achieve the above goal, expeditionary research of the Southern Bug River mouth, laboratory and desktop processing of the results was carried out.Moreover, comparative assessment of the obtained results with the results of own previous research and literature data was fulfilled; the features of the obtained indicators in the context of anthropogenic activity are characterized and possible ways of mitigating environmental problems are considered.

Materials and methods
The presented materials are based on the research data of the Southern Bug lower part in the spring and summer of 2021, analysis of research data of 2012 and analysis of literature.The research area is the Southern Bug River mouth, which is part of the Dnieper-Bug estuary (figure 1).The study of modern sediments of the lower part of the Southern Bug River has been carried out.The sampling points were located along profiles that crossed an investigation object.We researched samples from two profiles: first -near the port Olvia, second -across the Southern Bug (between villages Parutyne -Lymany).
The Southern Bug River research area was conducted at the lower reaches, below the Mykolaiv city; 18 samples of sediment and 27 samples of water were selected.Samples of sediments were taken with the special cylindrical equipment.The thickness of the sediment layer selected for analysis was 0.1-0.25 m.After drying, the selected samples were subjected to averaging at the points of selection.
The sediment samples analysis included the description of sediments, determination of their granulometric composition and density; definition of physical and chemical indicators: pH, Eh, electrical conductivity.The chemical composition study of the samples consisted in the pollutant elements determination, the water-soluble salts content and iron oxides.
The water samples analysis included the determination of the chemical indicators, namely: pH, total salts, dissolved oxygen, suspended substances, chlorides, sulphates, biological oxygen consumption (BOD 5 ), the content of ammonium, nitrite, nitrate and total phosphorus.All indicators in the water were determined by standard methods.
Hydrobiological studies consisted in general assessments of phytoplankton and phytobenthos, zooplankton and zoobenthos, and characterization of higher aquatic vegetation involved.The samples of phytoplankton were taken and processed through standard hydrobiological procedures [3,4].Both qualitative and quantitative characteristics of phytoplankton in performing ecological analysis were used.

Results
The modern sediments of the mouth Southern Bug River mouth represent mainly silt.Sands develop in some places in the form of narrow coastal strips, as well as on beaches and capes.Shell rocks occur in the form of small spots on beaches and spits that cannot be mapped.
Due to the solid runoff from the Southern Bug River, estuarine deposits are covered with a thin layer of modern sediments in the Dnieper-Bug estuary, in the Bug part area of the shipping channel and the water areas of the ports.The role of solid runoff from the Southern Bug River and the Inhul River is small in the formation of depth topography and silting of the shipping channels of the Dnieper-Bug estuary.The origin of sandy coastal strips and spits does not depend so much on the flow of rivers, with the erosion of the shores composed of fine sand.The maximum discharge of suspended sediments is observed at the rise of the spring flood, the minimum -during the winter low tide.
Extracted sediment, which is picked up due to permanent dredging works in the Southern Bug River mouth is transported to local soil dumps, where it forms continuous silt deposits.Sediments of the Southern Bug mouth, at the present stage, along the route of the Bug-Dnieperestuary Canal (BDEC) are represented by: sandy silts with inclusions of fine sand, loamy silts, flowing clay silts [5].
The results of the sediments granulometric composition of the Southern Bug River mouth testify to the transformation of lagoonal sediment accumulation (table 1, figure 2).The data obtained from the Parutyne -Lymany profile shows a predominance of psammite.While the material taken upstream (in the area of the port of Olvia) has a siltstone-psammite composition of the samples near the shore and a pelitic composition in the central part of the river, in the direction of the Bug-Dnieper-estuary Canal.
The data listed in Table 1 shows a significant variation in grain size and at the same time make it possible to identify a tendency to the increase of pelitic fraction in sediments.Areas along the shipping channel have sediments represented mainly by pelity.Finely dispersed material is constantly stirred by ships and dispersed over a long distance.In addition, shipping channel sections contain a large amount of industrial waste.
Technogenic sediments are widely developed in the studied area.Moreover, they are most widespread in the coastal part of the land and much smaller in open water areas.In the water area, the Southern Bug mouth man-made formations were discovered by a number of drilling wells in the form of different area spots, mostly not far from the ports.In the water area of the estuary, the fields of technogenic sediments occur near landfills of raised soil from the estuary depth during passage, deepening and periodic cleaning of shipping channels, capital dredging and during other dredging works [5].
Bottom soil, during research in 2021, was characterized by thick creamy consistency of almost black colour in the area of the port of Olvia with a noticeable smell of hydrogen sulphide in two plots.In the area of the Parutyne -Lymany profile, the sediments were brown with black  interspersed and had a weak marine smell.
According to the research results, the density of the sediment in the Parutyne -Lymany profile varied from 2.23 to 2.47 g/cm 3 ; the density of the port Olvia profile sediment was lower and ranged from 1.52 to 1.69 g/cm 3 .Density indicators of sediment samples correlate strongly with its particle size composition.
Chemical analysis of sediment samples made it possible to obtain the following data on chemical elements-pollutants (table 2).Research results show that with the exception of one sample, the content of elements-pollutants in all profile's samples did not exceed the MAC for soils.Comparing the data obtained by us with the data given in [5], we can note that the data on cadmium and lead are within the measurement error limits and are comparable (table 3), while the composition of zinc and copper in our studies is on average 10 times lower.It should be noted that the content of water-soluble salts in the sediments depends on their sorption capacity, which, in turn, depends on the grain composition of the sediments.Accordingly, finely dispersed sediment (especially in dumping areas) has a greater sorption capacity and is more saline.However, of course, water salinity determines the content of watersoluble salts in the sediments.The salinity of the water at the Southern Bug mouth is on average 2.3-3.5‰, the maximum being 10-11‰.During the period of spring observations, water salinity in the area Parutyne -Lymany profile was 3.5‰, and the port Olvia profile was 3.1‰.Mixing of two different waters: fresh river water and salty seawaters play a special role in the formation of the hydrochemical regime of the Dnieper-Bug estuary water.Fresh river water and salty seawaters determine the special chemical composition of the water of the Southern Bug mouth.However, the main source of biogenic substances entering the river is river runoff, hydrobionts, sediments and wastewater.
The indicator of the acid-base state (pH) of the water in the Southern Bug mouth is quite variable and ranges from 6.9 to 8.9 units, depending on the growing season.Most hydrobionts can usually tolerate a pH range of 5 to 9. Nevertheless, the change in pH to the alkaline side, which is observed during the "water bloom", can lead to an increase in free ammonia in the water, into which ammonium ions pass because of the increase in pH.Both ammonium ions and ammonia can be present in water within pH 8-9.
An important factor influencing the process of forming a chemogenic and biogenic complex of bottom sediments is the saturation of the water object with oxygen.Bottom sediments of natural water flow relate to the balanced aerobic-anaerobic system type.However, there are the shifts of aerobic-anaerobic balance toward anaerobic, which, in its turn, leads to the formation of another chemogenic complex and partial or total destruction of conventional ecotypes.One of the indicators of aerobic-anaerobic shift in balance toward reduction can be displacement of the ratio in the bottom sediments of iron oxides, namely the predominance of FeO over Fe 2 O 3 .In a number of works [6][7][8], the dynamics of accumulation and distribution features of a number of metals, including iron oxides, in river sediments have been analysed.The authors note that with the increase in the volume of organic matter runoff, whose rate of biodegradation does not keep up with the rate of its arrival, the development of anaerobic conditions is possible, which is reflected in the ratio of metal oxides.
Determining the ratio k (Fe 2 O 3 /FeO) shows fluctuations in river redox conditions.In the bottom layer of Parutyne -Lymany profile k (Fe 2 O 3 /FeO)>1, therefore the oxidationreduction conditions can be defined as transient with a non-constant aerobic-anaerobic balance or oxidative.While in the Port Olvia profile in the bottom layer k (Fe 2 O 3 /FeO)<1 on average, indicating the formation reducing conditions.
Thus, the study has shown that there is recently been a general tendency to silting rivers, especially in their lower reaches.This leads to a shift in the natural aerobic-anaerobic balance to the reducing side, which negatively affects the hydroecosystem in general.An indicator of this process can be the ratio of iron oxides (k Fe 2 O 3 /FeO) and the value <1 [6].
The average concentration of dissolved oxygen in water during the research period was at the level of 5.1 mg O 2 /dm 3 .However, the values of this indicator differed significantly: in the surface water -in the range of 6.5 -8.0 mg O 2 /dm 3 and in the bottom layer -0-3.5 mg O 2 /dm 3 .In the profile Parutyne -Lymany, the oxygen content was higher than in the profile of the port of Olvia.At two sites in the port Olvia profile, oxygen in the bottom layer of water was not determined, and Eh of the sediment had negative values.
Relating our data to the information provided by the Laboratory of Analytical Control of the State Administration of Ecological Resources in Vinnytsia Oblast, we can note that the data are comparable.So, the water quality in the Southern Bug River in 2003-2008, was characterized with the satisfactory oxygen regime (the content of dissolved oxygen was within the range of 7.1 to 10.8 mg O 2 /dm 3 [2]; water hardness average being 3.6-8.0mg-eq/dm 3 . The concentration of total phosphorus, according to our research, in the water area of the port Olvia profile varied in the range of 1.4-3.2mg/dm 3 ; ammonium nitrogen -0.1-0.25 mg/dm 3 ; nitrate concentration was determined within the range of 11.0-14.3mg/dm 3 ; the nitrite content being 0.005-0.04mg/dm 3 .The degree of surface waters pollution in Ukraine is regulated by the established maximum allowable concentrations (MAC).Most of the standards were approved during the Soviet era, and have since then expired.However, new standards have not yet been adopted in Ukraine, so State sanitary rules 4630-88 dated 04.07.1988 are used for comparisons.According to the state sanitary rules, the presented indicators of nitrogen content do not exceed the norms.
The turbidity and colour of the water depend on many factors and fluctuate significantly in the estuary of the Southern Bug throughout the year.The main natural factors of water turbidity are the amount of solid runoff and the mass of phytoplankton (especially the development of microalgae in the summer months).However, significant turbidity in certain areas is caused by anthropogenic factors: dredging, shipping and dumping.Thus, the concentration of suspended particles in the port Olvia profile water that we measured, ranged from 7.6 to 12.6 mg/dm 3 (under the conditions of the MAC of 0.75 mg/dm 3 ).According to [5], during the operation of a dredger, the water turbidity can reach 70 mg/dm 3 and spread in the radius of 50 to 150 m, depending on the speed of the current.Undoubtedly, the decrease in water transparency is reflected at all levels of the trophic chain of the hydroecosystem.
Determination of biological oxygen demand (BOD 5 ) -is an indicator that characterizes the content of easily oxidized organic substances pollutants, contained in water -confirmed the differences between the profiles.If in the area port Olvia profile this indicator did not exceed the MAC and fluctuated in the range of 2.3-3.1 mg O 2 /dm 3 , then in the area of Parutyne -Lymany profile the values of this indicator were on average twice higher -4.7-8.2 mg O 2 /dm 3 , which in some places exceeds the MAC by one and a half times.Comparison of this indicator with [2] resulted in same data.So, pollution with organic compounds observed (biological oxygen demand (BOD 5 ) fluctuated within the range of 2.11-5.4mg O 2 /dm 3 .
The concentration of sulphates in the water slightly exceeded the MAC in the port Olvia profile.Thus, we determined sulphate concentrations within the range of 502.5 -532.5 mg/dm 3 .In the area of the Parutino-Lymany profile, on the contrary, the concentration of sulphates was lower, it did not exceed the MAC, and amounted to 315.0 -340.5 mg/dm 3 .The chloride content was high and was determined at the level of 3047.0 -3244.0mg/dm 3 .This is definitely higher than the MAC, however, the chloride concentration is mainly determined by the inflow of seawater.
In general, the hydrochemical parameters of the Southern Bug mouth water in the studied period did not differ from the average long-term values.The most threatening situation is with significant turbidity of the water and extremely low oxygen concentration in some places.
A key goal presented in aquatic biology studies is to introduce data characterizing the status of the aquatic environment with a broad range of measurable indicators including in-stream habitat, phytoplankton, zooplankton, macroinvertebrate and macrophyte assemblages.
The area of the Southern Bug mouth is a transition zone -the continuum between freshwaters and coastal marine waters.According to the EU Water Framework Directive (The Directive 2000/60/EC) are defined as "bodies of surface water in the vicinity of river mouths which are partially saline in character as a result of their proximity to coastal waters but which are substantially influenced by freshwater flows".The salinity is a major, if not the most important, natural factor structuring the algal communities and explaining their variability within these ecosystems [9][10][11].Furthermore, transitional waters have intrinsically higher productivity in comparison to open seawaters.This may be attributed to the fact that such zones are deemed to be naturally stressed systems as they work as basins for runoff from their catchments and impact of saline waters from the sea [12].Thus, in the water area of the Southern Bug low reaches (below the city of Mykolaiv), a transitional community is formed, consisting of freshwater and marine species that are on the edge of their ecological ranges.
The phytoplankton community composition of the Southern Bug estuary system fluctuates from 50 to 60 species in the context of average long-term indicators (over the past 15 years), which are represented mainly by cyanobacteria, diatoms and green algae [13,14].Diatoms (Chromista, Bacallariophyta) have a wide range of interesting morphological and physiological features and are the main component of marine and freshwater ecosystems [15].The majority of centric diatoms genera are discovered in strictly marine waters but in freshwater environments, this group is present with much less diversity [16].
The transitional zone of the Mykolaiv area with its changing salinities is offering conditions for the existence of 24 centric diatom taxa representing 11 genera.Species-indicators of eutrophication in the coastal zone of the Black Sea waters, which enter the estuary and then move upstream of the South Bug River, have been identified [17].Thus, the following taxa are resistant to pollution by organic substances: Aulacoseira subarctica, Cyclotella atomus, C. choctawhatcheeana, Cyclostephanos dubius, Melosira varians, Skeletonema subsalsum, Stephanodiscus hantzschii, S. Minutulus.
Only taxa with high euryhalinity tolerance are able to move upstream and adapt to eutrophic freshwaters.The study [17] shows that salinity is one of the most significant factors for the species composition of diatoms.The appearance of three alien marine species (Actinocyclus normanii, Skeletonema subsalsum, Thalassiosira incerta) in the lower part of the Southern Bug might be considered as the immigration of marine species into this area due to change in salinity.Therefore, the monitoring of these species is important for biodiversity conservation.
At present, freshwater and euryhaline species prevail -up to 59%.The number of halophilic representatives of phytoplankton varies from season to season (which is associated with the upward of seawaters).The optimal water salinity for phytoplankton is 0.4-5.2‰.
In spring, cyanobacteria, diatoms and dinophytes predominate in phytoplankton.However, the biomass of phytoplankton in spring is low, up to 1.5 g/m 3 .In summer, biomass of phytoplankton increase.Cyanobacteria play the dominant role in the formation of summer phytoplankton biomass.Many representatives of diatoms, dinophytes, and golden algae, contained in the phytoplankton of the study area are of little value in terms of nutrition.Their share in the formation of the total biomass of phytoplankton is 75%.During the vegetation period, the number of phytoplankton varies within the range of 600 -261530 cells/m 3 , and the biomass -within the range from 1.45 to 21.04 g/m 3 .The smallest phytoplankton biomass is observed in dumping areas (storage of sediment after dredging).In the areas adjacent to the port under partially anaerobic conditions, the phytoplankton biomass is minimal.
The qualitative structure of cyanobacteria has not changed significantly in recent years, which indicates the stability of the hydrobiological situation.The dominant species are: Aphanizomenon flos-aquae, Microcystis aeruginosa, Oscillatoria agardhii, Anabaena spiroides.Among diatoms Diatoma elongatum, Melosira granulata and Nitzchia tenuirostris are most frequently registered.A group of protococcus dominated by Scendesmus quadricauda forms the basis of green algae.Vegetation of other groups of algae (euglenoid, dinophytic, golden, yellow-green) is determined at a much lower level.The dominant species are: Euglena viridis, Cerratium hirundinella, Synura uvella.
As a result of the intensive hydrotechnical construction of the previous century, the conditions for the existence of hydrobionts along the entire length of the Southern Bug River have changed significantly, which was inevitably reflected in the Bug estuary ecosystem.The researched area of the river is constantly under severe stress due to anthropogenic influence, the most important factor among which is water turbidity, which limits the photosynthetic activity of algae.These waters can be considered among the most affected and endangered ecosystems.Considering that, it is difficult to exclude these impacts on the species diversity of spatial and ecological gradual boundaries between the systems; nevertheless, salinity is believed to be a prevailing stressor [18,19].
Studies of microphytobenthos have carried out upstream the city of Mykolaiv [20] show a much larger number and a greater variety of algae.Thus, data on the identification of 121 species of algae, which belong to 61 genera, 34 families, 20 orders, 6 classes and 5 divisions, are given.By the number of species, diatoms prevail (86 species or 71.07%), a much smaller number of representatives fall into the rest of the divisions.Thus, there are 20 species of green algae (16.52%), 9 species of cyanobacteria (7.43%), 3 species of euglena and chara (2.47% respectively).
The species diversity of zooplankton has almost halved over the past 30 years.At the end of the 1990-s 72 taxa were identified in zooplankton, while in the last 5 years only 36 species were identified in the water area of the Southern Bug mouth area.Wheel animalcules (Rotifera), copepods (Copepoda) and water fleas (Cladocera) form the main part of the zooplankton biomass.Freshwater and euryhaline forms dominate [13,14,21].
The number of zooplankton (average annual) does not exceed 18 th.specimens/m 3 and the biomass does not exceed 1.5 g/m 3 .Among the representatives of zooplankton 40% are wheel animalcules.In spring, water fleas (up to 70%) represent the main biomass of zooplankton.The basis of the biomass of rotifers was formed by Asplanchna priodonta.However, the numbers were formed by smaller forms of Filinia longiseta, Brachionus angularis, Keratella quadrata.
The fauna of the depth (zoobenthos) and periphyton is more diverse and rich than the aquatic fauna.At the mouth of the Southern Bug River (study area), water exchange is slowed down and salinity is increased.Oligochaetes, polychaetes, gammarids and chironomids dominate in the silt and sandy-silt bottom areas.The biomass of summer zoobenthos of silted sands is up to 26 g/m 3 .Among polychaetes Hypaniola kowalewskii and Nereis diversicolor dominate.Among gammarids Pontogammarus robustoides and Dikerogammarus haemobaphus are identified.
In some places, there are still small colonies of mollusks Dreissena bugensis, and along the spits (including the Northern Spit) there are mollusks Cerastoderma edule.Taxonomic diversity, abundance and biomass of zoobenthos of the Bug estuary are not the same in different areas.At great depths with increased salinity, low oxygen concentration and the presence (in some places) of hydrogen sulfide, the zoobenthos is taxonomically poor.Oligochaetes (24%), polychaetes (15%), molluscs (18%), and sometimes chironomids prevail in such areas not forming mass settlements.
Studies of higher aquatic plant in the mouth area of the Southern Bug River showed a depleted species composition of floristic communities [22], which form two plant complexes -coastal (helophytes) and aquatic (free-floating).The helophytes community, which is formed by border strips of different lengths and massiveness along the coastline, is represented mainly by reeds (Phragmites australis), in some places there are cattails (Typha latifolia, Typha angustifolia), sedges (Carex acuta, C. raparia, C. gracilis).
Mainly representatives of the genus Potamogeton qualify as aquatic vegetation, which forms "spots" of hydatophytes and floating pleistophytes in the water area, namely: P. crispus, P. lucens, P. pillsum, P. natans, P. perfoliatus.In addition, Myriophyllum spicatum, Ceratophyllum demersum are found in the water area.

Discussion
The specificity of the processes that take place in the Southern Bug River mouth is caused by the constant interaction of different physical and chemical properties of river and seawaters masses.The upward-downward fluctuations of water levels are a characteristic feature of the hydrological regime of the Bug estuary system.Getting through the flume of the navigable canal to the Bug estuary seawater stagnates due to very slow water exchange at the bottom.Seawater moves in the south winds and it is a constant source of increasing salinity at the mouth of the river, which fluctuates between 2-3.5‰ for most of the year.
Another feature of the Southern Bug mouth water is its considerable turbidity.Anthropogenic activity is the main cause of high concentration of suspended particles in the water.It is provoked by permanent dredging works in the Southern Bug River mouth and transporting material to local soil dumps.In 2021, the average content of suspended solids in water in the profiles below the city of Mykolaiv were 11.4±0.5 mg/dm 3 .Current sediments of the Southern Bug mouth reflect to transformation of lagoonal sediment accumulation.The role of sediment runoff from the Southern Bug River and the Inhul River in the formation of the bottom relief and siltation is insignificant.The current sediment of the Southern Bug mouth is mainly represented by pelity.
The content of pollutant elements in the sediment samples mostly does not exceed the MAC, except for lead in one sample.However, in our opinion, the presence of reducing conditions in river's bottom layers fixed some samples is much more important is a great concern.
Permanent turbidity of water leads to a decrease in the photosynthetic activity of phytoplankton, which in turn is reflected in reduced primary production.Other hydrochemical indicators, that periodically have increasable concentration in the Southern Bug mouth water, include: BOD 5 , which is characterized by periodic, sometimes significant, exceeding of MAC, ammonium and nitrite nitrogen.
Very often, transitional water is a place with increased biodiversity as the estuarine community consists of both freshwater and marine species.The Southern Bug mouth waters are considered to be among the most affected and endangered ecosystems.According to the literature review, decrease in primary productivity led to decrease in zooplankton almost by half.The composition of phytoplankton is dominated by representatives of diatoms, dinoflagellates and golden algae, which are of little value in terms of food, whose specific weight in the formation of the total biomass of phytoplankton is up to 75%.
Analysing all of the above, it should be noted that the post-war revitalization of the Southern Bug estuary ecosystem should include measures to mitigate the negative effects of anthropogenic activity, especially the consequences of hydraulic engineering works.

Consequences
The presented comprehensive research can be considered as the current pre-war state of the Southern Bug mouth ecosystem.The results of the conducted research are: assessment of the sediments features of the researched river section, assessed water conditions and characteristic of the groups of hydrobionts.
Appearance of reducing condition spots in sediments, increased turbidity, change of hydrochemical conditions, reducing of some fodder species (plankton and benthos) -these are short list of current anthropogenic transformation of Southern Bug mouth ecosystem.
The first and urgent measures to revitalize the mouth of the Southern Bug should be actions to eliminate and mitigate the consequences of hostilities.Further revitalization measures should be aimed at preserving biodiversity, which is possible under the conditions of maintaining the normal state of water and sediments in the Southern Bug, especially in the transitional estuarine zone.

Table 2 .
Chemical analysis of sediment samples in the profile port Olvia.
* -exceeding the maximum allowable concentration (MAC) of soils

Table 3 .
Concentration of chemical pollutants in the sediments samples BDEC knees (July-August 2018) [5].The values of physical and chemical parameters of the current sediments of the studied profiles are shown in table4.

Table 4 .
Physical and chemical parameters of the sediments.