OF THE ENVIRONMENTAL STATE OF THE BILEĆKO JEZERO LAKE

Abstract The research refers to the physical, chemical and microbiological parameters of the Bilećko Jezero Lake water quality. The monitoring of physical and chemical parameters and their interaction with other parameters helps estimate the water quality and any possible changes. Some parameter values and their alteration directly affect the water life. The research was performed at three sites: the Grančarevo watergate, the Trebisnjica River fountain and Orah in the period 2006-2009, and the results of conducted physical and chemical analyses indicate that the water quality was satisfactory, albeit with certain deviations. Bacteriological analyses showed that the water of Bileća accumulation, especially at the Izvor site, was burdened with fecal material.


INTRODUCTION
The Bilećko Jezero Lake artificial accumulation is formed in the Trebisnjica River valley, 18 km upstream from the Grančarevo watergate.The highest water level is reached during the autumn floods and in spring as the snow melts.During summer, the water level is low due to poor precipitation in the river basin.When the lake water reaches its maximum, the level at the Trebisnjica River fountain is around 70 m and along the Grančarevo watergate it is approximately 104 m.The karst out-crop of the basin is characterized by a network of undersurface circulation, rapid infiltration, saturation of crops, swift changes of the river flow speed through the karst canals and oscillations of the undersurface water level.
The Bilećko Jezero Ly production and drinking.Up to now, the Lake had been endangered by wastewaters from both factories and households of the town of Bileća and its suburbs as a consequence of unattended sewerage and water refinement systems.From 2006 to 2009, detailed analyses were carried out so as to estimate the physical, chemical and microbiological status of the lake water.The monitoring of physical and chemical parameters and their interaction with other parameters helps estimate the water quality and any possible changes.Some parameter values and their alteration directly affect the water life.Independent physical and chemical measurements do not provide a clear picture of the water quality (Cvijan, 2000;Dalmacija, 2000;Maletin et al., 1996).A more general picture of water quality is obtained by comparative analysis of physical and chemical and microbiological parameters.On the basis of the bacteriological state and quality indicators, it is possible to specify the nature and intensity of pollution, and the level of saprobity and eutrophication.

MATERIALS AND METHODS
The water samples were collected into sterile canisters under aseptic conditions following the prescribed procedure (Karakašević, 1967;Škunca-Milovanović et al., 1990).There was a spot-check of water and air temperature, pH values, current conduction, soluble oxygen concentration, water oxygen saturation, turbidity and transparency (Dalmacija, 2000;Dalmacija et al., 2004).The samples were then transported on ice at a +4˚C.The physical and chemical and microbiological water analyses were conducted within 12 h from the moment the water was collected, according to the standard procedures of the Regulation of Water Clasification and Waterstream Categorization (RS Official Gazette 43/01) and the Book of Rules of Drinking Water Regularity (RS Official Gazette 40/03).The research was performed at three sites: the Grančarevo watergate, the Trebisnjica River fountain (Izvor) and Orah.During the period 2006-2009, 27 physical and chemical and 5 microbiological parameters were observed.At the Grančarevo watergate site, samples were collected 26 times, at the Izvor site they were collected 15 times, and, finally, 18 times at the Orah site.There were no microbiological analyses performed in 2007.

RESULTS
The results of the conducted physical and chemical analyses are given in the Tables, wherein we provided the mean values of certain parameters at the time of analyses, with maximum and minimum values.The values of the monitored physical and chemical parameters of the Bilećko Jezero Lake, according to site locations, are provided in Tables 1, 2, and 3. Table 1 shows the mean values: minimums and maximums of the parameters per year of monitoring.The average annual water temperature at the Grančarevo watergate site was relatively high over the monitored period since the samples were collected each month during the summer and once during the other seasons.The lowest mean annual temperature was measured in 2009 and it was established to be 17.52˚C.Mean values of most parameters exhibited a high fit on the annual level, and they were in accordance with the Regulation of Water Classification and Waterstream Categorization as they matched the 1 st class surface waters (RS Official Gazette, 43/01).
In 2007, there were higher values of water turbidity with an average value of 3.76°NTU and maximum value of 6.29°NTU (RS Official Gazette 40/03).These high values of turbidity surpass the recommended values for water used for household supplies.In 2009, the water turbidity was also higher than usual and the average annual value was 1.78°NTU.During the monitored period, the water oxygen saturation was high, which indicated water of a 2 nd and 3 rd quality class.Based on the mean annual values in 2006 and 2009, the water was 2 nd class and in 2007 and 2008 it was of a 3 rd class quality, whereas the maximum saturation values over the whole monitored period indicated that the water at this site was of the 3 rd class quality.The average water transparency in 2007 and 2009 was poor and matched to 3 rd class water, but in 2006 and 2008 it matched to 2 nd class water.In the summer of 2007, there were multiple transparency measurements that indicated the water transparency of only 1.3 meters, which was probably the consequence of intensive phytoplankton production.
The mean, minimum and maximum values of the monitored physical and chemical parameters at the Izvor site over the research period are presented in Table 2. On the basis of the results, we can conclude that most of these parameters of water quality had favorable values.At the same time, some of the monitored parameters displayed certain deviations that indicate a water quality of 2 nd and 3 rd class.Regarding the mean values of O 2 saturation, these deviations were observed in 2006, 2007 and 2009, and the water quality was of 2 nd class quality.Furthermore, this parameter value displayed a 3 rd class of water quality in 2008.Still, the maximum values over all the years of the monitored period were of 3 rd class quality.There were also significant deviations regarding the water color since in 2009 the mean values were increased, as was the maximum value.Water transparency is yet another parameter on the basis of which it is possible to estimate the existence of 2 nd and 3 rd class quality in compliance with the Regulation of Water Classification and Waterstream Categorization (RS Official Gazette 43/01).
The results of the monitored physical and chemical parameters at the Orah site, i.e. the mean, minimum and maximum annual values, are given in Table 3.As with the previous two sites (Grančarevo and Izvor), on the basis of most of the parameters here we can mark the water quality as of being 1 st class.

Microbiological analyses of water quality in the Bilećko Jezero Lake
Bacteriological analyses of the Bileća accumulation lake were performed in the period 2006-2009.We estimated the parameters with reference to the sanitary aspect of water quality and its household usage.These parameters could indicate fecal material presence and permanent pollution.The samples were collected at the three locations, Grančarevo watergate, Izvor and Orah, under aseptic conditions from the surface layer at 30 cm depth.They were then analyzed for the basic bacteriological parameters using indirect breeding methods.The samples at the Grančarevo site were collected six times: in April (spring), November (autumn) and during the critical warm months when the samples were collected monthly.At the Izvor and Orah sites, the samples were collected seasonally.Based on the results, we calculated the medians of the monitored parameters for each year.The values we reached are given in Table 4.The total number of coliform bacteria at the Grančarevo watergate site was below 20 colonies/100 ml throughout the monitored years, which matches a 1 st class of surface water.Neither potentially pathogenic fecal coliforms nor streptococcus of fecal origin or sulfate-reducing anaerobic bacteria were isolated, which indicates that water at this site was not polluted with fecal materials and was health-friendly.Aerobic mesophilic bacteria were few and within the limits acceptable for an open-space water source.
At the Izvor site, there was a constant presence of coliform bacteria, among which we isolated fecal coliforms.It was only in 2008 that the number of total coliforms matched the 1 st class of surface water, whereas in 2006 and 2009 it matched the 2 nd class.At the same time, there were sulfate-reducing anaerobic bacteria whose presence in the drinking water was rather concerning since this type of bacteria is difficult to remove by conventional refinement methods.The number of aerobic mesophilic bacteria increased annually so that in 2009 there were 1000 colonies per cm 3 .
We isolated fecal coliform bacteria from the water at the Orah site in 2006, which indicates that the water at this site was in close contact with fecal materials.The 2008 analyses showed a permanent presence of fecal streptococcus, but fecal coliforms were not isolated in great number.This kind of bacterioplankton distribution signifies that there was no fresh fecal pollution in the water since there were only fecal streptococci that survive in water even when there are fewer nutrients.In 2009, no bacteria indicating fecal pollution were isolated from the water.There was only a significant presence of the total coliform and aerobic mesophilic bacteria.Despite the fact that these are potential disease triggers, they do not necessarily have to be pathogenic.
By comparing the three sites/locations of the Bileća water accumulation at which the samples were collected, we can infer that the water at the Izvor site was mostly exposed to fecal pollution since from nearly all the samples some potentially pathogenic bacteria were isolated.The best water quality was at the Grančarevo watergate site, whereas at the Orah site, year after year, we isolated less and less bacteria indicating the presence of fecal pollution, but there was still a great number of potentially pathogenic bacteria.

DISCUSSION
The results of research on the physical and chemical water characteristics of the Bileća accumulation (based on the monitored parameters) indicate that the water is of a high quality.The values that placed the water in the 2 nd and 3 rd quality class referred to oxygen saturation and water transparency.Hence, we have to bear in mind that the concentration of soluble oxygen and water oxygen saturation changed during the day due to photosynthesis.During daylight, as a result of the light stage of photosynthesis, oxygen is released and its concentration in the water grows and reaches high values at noon (Djukic et al.. 2003;Siege et al., 2004.).Furthermore, the high concentration of soluble oxygen and oxygen saturation indicates the low intensity of organic-substance mineralization during which oxygen is absorbed.We may infer the same on the basis of the low CO 2 concentration in the water that is also released in the process of mineralization.The values of biological oxygen demand are also low, which is yet another indicator of the poor oxidation of the water.According to the values of this parameter, the Bileća water accumulation belongs to the type of oligo-beta mesosaprobic waters that are poorly inhabited (Felföldy, 1980).
The lowest values of water transparency were measured in spring and late autumn, when increases in turbidity were observed.During that period of the year, there is intensive precipitation and an increase of the undersurface water level (Gnjato, 2004).Rain brings a large amount of organic and mineral substances due to the washing-out of soil, the consequence of which is greater turbidity and poorer transparency.Natural drainage from the basin can bring certain amounts of suspended or melted materials into the water (Štefatić, 2005).During drought months, the imported particles settle and the water becomes clearer, the consequence of which are changes in water turbidity and transparency that are greater during the summer.
The water of the Bileća water accumulation is mildly alkaline, with no smell or taste.It belongs to the calcium-bicarbonate type of mean hardness.There is no massive development of phytoplankton due to the low nutrient content in the water.The water is poor in ammonia, nitrates and phosphates that are crucial for an intensive plankton development.This is the main reason for the low level of accumulation at the trophic level.Electrical conductivity is constantly low, which indicates the small amount of ions and organic substances in the water.None of the samples had either smell or taste.The concentrations of iron, manganese, ammonia, nitrates, nitrites and phosphate in the water were extremely low.Only the concentration of sulphate was somewhat higher.
In order to preserve this favorable condition, it is necessary to deal with the issue of sewerage which brings to the site not only the pathogenic bacteria that threaten health but also a large amount of organic materials that might increase the production of plankton.Phytoplankton is not produced due to the effects of dilution and auto-purification, but the increased pollution might harm the existing balance.Nevertheless, the conducted bacteriological analyses indicate that the water of the Bileća accumulation, especially at the Izvor site, is full of fecal substances since it is constantly full of bacteria that are indicators of fecal pollution and potential disease triggers.Obviously, the unattended sewerage issues of the town of Bileća greatly affect the water quality of the Bileća accumulation.Since the Lake is of great relevance to water supplies, it is crucial to undertake protection measures so as to avoid further impairment.Special attention should be paid to the presence of sulphitereducing clostridia since it is a sporogenic bacterium that is difficult to destroy using conventional chloral refinement methods.Furthermore, the breeding and multiplication of cyanobacteria would be extremely dangerous because they produce a whole range of different toxins.

Table 1 .
Physical and chemical water analyses of the Bileća accumulation at the Grančarevo watergate site

Fe
hydroelectric power-plant, 2010.Table 2. Physical and chemical analyses of the Bileća accumulation at the Izvor site

Fe
Physical and chemical analyses of the Bileća accumulation at the Orah site

Fe
Furthermore, the physical and chemical parameters of the Orah site indicate values that correspond to 2 nd and 3 rd class water.Thus, the mean values of O 2 saturation in 2006, 2007 and 2009 indicate 2 nd class quality, whereas the O 2 saturation in 2008 indicates the 3 rd class.This class was also indicated by all the maximum values.Concurrently, physical and chemical analyses were accompanied by microbiological analyses of the water quality of the Bileća accumulation in 2006, 2008 and 2009.