Editor's comment

Ya. Topalova             3-6

Sediment microbial community profile in upper part of Iskar River

Yovana Todorova, Ivaylo Yotinov, Dayana Todorova, Yana Topalova            7-15

New data on the Chironomidae (Diptera) fauna from the upper Iskar River catchment (Bulgaria) – spatial distribution and ecological notes

Dimitriy Dashinov            16-21

Heavy metal content and element composition of plankton and fish from Iskar Reservoir and its ecotone

Galerida Raikova-Petrova, Milena Stefanova, Dimitar Kozuharov, Ralitsa Vаlcheva, Desislava Rozdina, Marieta Stanachkova, Ivan Petrov            22-31

Ecological status of upper part of Iskar River catchment according Regulation N4 based on macrozoobenthos and fish fauna

Lyubomir Kenderov, Dimitriy Dashinov, Emil Kanev, Lyubomira Lyubomirova, Eliza Uzunova                32-38

Community structure of zooplankton as key factor for self-purification capacity of Iskar Reservoir

Marieta Stanachkova, Milena Stefanova, Dimitar Kozuharov, Galerida Raikova-Petrova, Eleonora Fikovska                39-46

Assessment of contamination with opportunistic pathogenic bacteria from family Enterobacteriaceae in sediments of Iskar River

Ivaylo Yotinov, Yovana Todorova, Lyubomir Kenderov, Yana Topalova                47-55

Age-size structure and growth rate of the European chub (Squalius cephalus L.) in Lesnovska River, Bulgaria

Galerida Raikova-Petrova, Desislava Rozdina, Margarita Kamenova                56-65

Comparative assessment of Denitrification / Nitrification processes in water treatment technologies in WWTP “Sadinata” and WWTP “Kubratovo”

Irina Schneider, Nora Dinova, Ivaylo Yotinov, Elmira Daskalova, Nikolay Savov, Yana Topalova                66-75

Adaptive Mechanisms of the Biofilm Communities in Technologies with Gradually and Shock Concentration Increase of Xenobiotic Pollutants – Functional and FISH analysis

Mihaela Belоuhova, Ivaylo Yotinov, Yana Topalova                76-86

Development of a bio-indicative control system of the technologies for biogas production

Nora Dinova, Mihaela Belouhova, Irina Schneider, Yana Topalova            87-95

New record of thick shelled river mussel Unio Crassus (Unionidae, Bivalvia) from Palakaria River, Bulgaria

Lyubomir Kenderov, Yonko Sashov            96-99

Yovana Todorova, Ivaylo Yotinov, Dayana Todorova, Yana Topalova

Abstract: Iskar River and its reservoir are the water sources in Bulgaria with the most important economical and social meaning because of their role for drinking water supply of Sofia. In this study, we focus on the sediment microbial community in upper part of Iskar River subcatchment as functional diversity related to main self-purification processes and as a risk factor for water quality. Microbial communities in freshwater sediments and their associated metabolic activity have fundamental role in ecology and metabolism of river ecosystems. The functional profile of sediment microbial communities was studied over a period of 8 years. The obtained results show that the microbial groups participating in organic carbon transformation and specific indicators (bacteria from g. Pseudomonas and coliforms) have higher quantitative parameters in sediments near to discharge of WWTP Samokov. The data for high ecological and chemical state of river sector confirm that the impact of WWTP discharge is in the frames of self-purification capacity of ecosystem and do not disturb significantly the water quality. In sediments of Palakaria River, the bacteria from nitrogen cycle are detected in permanently high number. These data are related to significant nitrogen loading identified in the river and present an adequate response of microbial community structure to this type of disturbance. The modeling of ecosystem response to risk situation of overloading with nutrients and organics confirms the high self-purification capacity of Iskar River. The importance of studied subcatchment for formation of water quality in Iskar Reservoir and literature data for sediment function as depot for coliforms in other rivers enforces the extension of existing monitoring program with regular assessment of this indicator in the sediment component of the ecosystem.

Keywords: microbial community profile, sediments, Upper Iskar, self-purification, transformation processes

Dimitriy Dashinov

Abstract: The Chironomid composition was studied in 23 sites from 12 rivers along the upper part of the Iskar River catchment (Danube basin). Samples were gathered using Surber sampler in the summer period of 2015-2016. A total of 54 taxa (from 39 genera and 5 subfamilies) were identified from which 33 taxa were new for the upper Iskar River catchment.  Two species were new for Bulgaria: Potthastia montium (Edwards, 1929) and Symbiocladius rhithrogenae (Zavrel, 1924). Two taxa belonged to genera not reported for the Bulgarian fauna – Cryptotendipes sp. and Sympotthastia sp. For most of the rivers the chiro abundance was relatively low with a mean of 60 ind.m^-2, which is about 12% of the marozoobenthos community.

Key words: Chironomidae, Iskar, Potthastia montium, Symbiocladius rhithrogenae, new records

Galerida Raikova-Petrova, Milena Stefanova, Dimitar Kozuharov, Ralitsa Vаlcheva, Desislava Rozdina, Marieta Stanachkova, Ivan Petrov

Abstract: The present work includes part of the first studies of element composition and metals concentrations in the plankton and fish tissues and organs from Iskar Reservoir, Bulgaria, determined by x-ray fluorescent  analysis. The levels of heavy metals varied significantly among fish species and organs. The results showed that the mean concentrations of heavy metals were higher in internal organs and gills than muscles of fish. The samples for the plankton analysis were executed at different stations in the ecotone zone between Iskar River and Iskar Reservoir and in the middle of the reservoir. The results show substantial spatial heterogeneity. The highest concentrations of heavy metals in plankton were registered in the upper ecotone.

Key words: heavy metals, plankton, fish, Irkar Reservoir, ecotone 

Lyubomir Kenderov, Dimitriy Dashinov, Emil Kanev, Lyubomira Lyubomirova, Eliza Uzunova

Abstract: Recent information about the ecological status of upper part of Iskar River and some tributaries was given. Ecological assessment according WFD and national water legalisation (Regulation N4) was applied. For estimation of fish based indices (BRI and TRI) the following ichthyologic parameters were used: total abundance and biomass of ichthyofauna, abundance and biomass of Salmo trutta, occurrence of introduced species, sensitive and migrants. For calculation of BI and TTN indices were used taxa composition of the macroinvertebrate fauna. Ecological situation of Iskar River and tributaries was assessed as “high” according macroinvertebrate based indices and “moderate” to “bad” according fish based indices. Deterioration of ecological quality of lower river sites was recorded.

Keywords: ecological status, fishes, macrozoobenthos, Iskar River

Marieta Stanachkova, Milena Stefanova, Dimitar Kozuharov, Galerida Raikova-Petrova, Eleonora Fikovska

Abstract: Iskar Reservoir provides more than 2/3 of the water supply for the city of Sofia. According to 2016 data, the city has a population of 1 304 772. Therefore information regarding the quality of the water from the reservoir is extremely important. The processes of self-purification of the reservoir were assessed using a biological quality component with special emphasis on the inhabiting zooplankton community. In the article some new data for dominant complex, related to environmental conditions was provided. The processes of self-purification of the Iskar River-Iskar Reservoir system according to RCC index can be described in two stages. In the stage of increasing: the RCC index increased by 125% from a sampling point in the ecotone zone between the river and the reservoir to a sampling point in the pelagic part of the reservoir. The role of rotifers in the destruction of organic matter is significant in the ecotone zone. The results can be useful for all consumers of high quality drinking water. The reserves of zooplankton filter feeders maintain the filtration activity at а level providing a sufficiently high quality of water.

Key words: Iskar Reservoir, self-purification capacity, zooplankton, RCC index, filter-feeders zoopla

Ivaylo Yotinov, Yovana Todorova, Lyubomir Kenderov, Yana Topalova

Abstract: Fecal pollution from municipal wastewater discharges is an extremely serious problem for aquatic ecosystems. This type of pollution is also found in the waters and sediments of the Iskar River in its upper and middle valley. From a microbiological point of view, an indicator of such contamination is the presence of high amounts of opportunistic pathogenic microorganisms of the family Enterobacteriaceae. An important feature is that, except in the waters where they are normally found, large amounts of these bacteria can also accumulate in sediments. The purpose of this study is to compare the contamination with opportunistic pathogenic bacteria from the Enterobacteriaceae in sediments from the upper and middle part of the Iskar River. In addition, a comparison of the quantity of entero-bacteria with the ecological state indicators was made by Regulation N-4 of 14.09.2012 on characterization of surface water.

From the results of this study, the higher amounts of entero-bacteria were found in the sediments from the middle part of the Iskar River. This is largely related to the strongly negative effect of the urbanized area of Sofia as well as the lack of functioning wastewater treatment plants in the middle of the Iskar River. The results for entero- bacteria from the Upper Iskar subcatchment, also demonstrated a significant contamination with fecal character. As a probable reason for this can be the discharge of Samokov WWTP as well as the unregulated point sources of pollution in this region. On the other hand, there is also evidence of the high self-purification potential of the river ecosystem, which is indirectly proven by the well-represented microbial consortium of aerobic heterotrophic microorganisms in the sediments of the two studied sections of the Iskar River. When comparing fecal pollution indicators with the general environmental assessment, some differences were identified, especially at Lakatnik and Prokopanik stations.

Keywords: Enterobacteriaceae, sediments, pollution, river, accumulation, fecal indicators

Adaptive Mechanisms of the Biofilm Communities in Technologies with Gradually and Shock Concentration Increase of Xenobiotic Pollutants – Functional and FISH analysis

Mihaela Belоuhova, Ivaylo Yotinov, Yana Topalova

Abstract: The main governing factors in the biodetoxification technologies are the concentration of xenobiotic pollutants in dependence of critical one as well as the way of its inflow in the system – gradually or shock loading.

The adaptive changes in two biofilm communities from lab-scale biodetoxifcation technologies were estimated and compared on the base of functional and microbiological parameters: The processes were studied in two analogous models – case studies. Case study 1 - bioremediation of sediments from Iskar river with shock phenol loading in concentration three times higher than critical one, that is about 250 mg/g sediment; Case study 2 – laboratory sand biofilter - treating amaranth polluted wastewater. The inoculation material was specially treated activated sludge, taken from Sofia WWTP (wastewater treatment plant). The biofilter was supplied with highly specialized adaptive algorithm for gradually increase of xenobiotic concentration (from 5 to 50 mg/L amaranth).

Two detoxification technologies have been compared according to: key technological and microbiological parameters, the micro-distribution and the role of unculturable microorganisms as well as the microbial relationships in genus Pseudomonas. The special attention has been paid on the analysis of the polyphosphates as an indicator for the alternative energetic sources – polyhydroxyacetate and poyhydroxybutyrate. In this study new fluorescent method was used.

The results showed that the technology with shock xenobiotic load reached the effectiveness of xenobiotic elimination 28%, while the technology with adaptive algorithm – 89%. In the same time the amount of the culturable phenol-degrading bacteria increased with 1.72 x 10⁵ CFU/g, while the amaranth-degrading bacteria decreased with 1.67 x 10⁶ CFU/g in the course of the adaptation processes. The analysis of polyphosphates (metachromatin) proved that the microbial community, functioned in the shock loading, used higher quantity of alternative energetic sources in comparison with this, governed by the adaptive algorithm.

As general conclusion the adaptation mechanisms towards xenobiotic biodegradation were different on the base of ways of inflow of the toxicants in the technology: 1/ After the shock xenobiotic loading in concentration three times higher than critical the biofilm developed the most simple mechanism – the multiplying of the microorganisms, but the biodegradation effectiveness was low; 2/ After application of the purposely constructed adaptive algorithm, microbial communities developed complex mechanisms of azo-detoxification, included the increased role of unculturable bacteria and synergistic relationships between them. This leaded to the increased effectiveness of xenobiotic detoxification.

Keywords: Detoxification, Adaptive algorithm, Pseudomonas, FISH, Polyphosphates