The study aimed to investigate the physico-chemical properties as well as phytoplankton and bacterial community diversity of Bovan Lake reservoir in Serbia to gain insight into the seasonal dynamic of water quality. All analyses were performed at three localities and water depths in spring, summer, autumn, and winter 2019. Seven phytoplankton phyla comprising 139 taxa were detected at all three localities (Chlorophyta 58%, Bacillariophyta 14%, Cyanobacteria 9%, Chrysophyta 5%, Dinophyta 5%, Euglenophyta 5%, and Cryptophyta 4%). Winter 2019 was characterized by the presence of 36 unique species in all phyla except Euglenophyta. Bacterial diversity analyses showed that Proteobacteria, Actinobacteria, Bacteroidetes, Cyanobacteria, and Verrucomicrobia dominated the water intake locality at all three water depths (0.5, 10, and 20 m below the surface). In general, the physico-chemical parameters, phytoplankton, and bacterial community composition depended on the season and the water depth and showed that Bovan Lake was of satisfactory ecological status and water quality at all localities, and meets the needs for all intended purposes.

Sediment is a special realm in aquatic environments and has high microbial diversity. Addition of organic electron donors to sediments stimulated heterotrophic activity. Bacteria utilize the more available fractions of the organic detritus in their own metabolism, leaving indigestible residues known as marine humus. Input of nitrogen and carbon from vegetated regions into freshwater sediments also stimulate aerobic, anaerobic and chemolithotrophic sediment microbes. Because bacteria respond dramatically to changes in their chemical environment, can be predicted rapid responses by the aquatic sediment microbial community to any change in plant species that affects sediment porewater chemistry. Temperature and rainfall can affect the some microorganisms growth and permanence such as E. coli and Enterococcus spp. The increase of pollutants load (e.g. Pb and Zn) in water can be expected with the reduction of flow, whereby the decrease of pathogens concentration can be due to high concentrations of metals (e.g. Hg and Pb) discharges in rivers. The enrichment of metals and nutrients concentration in sediments, especially in those with the fine texture, highlights that the adsorption process is the prevailing self-purification mechanism. Investigations of short-term variations of microbiological and chemical parameters in the water column have implied that, despite seasonal and daily variations, microbial standing stock biomass and activity in one and the same body of water do not change drastically from one day to the other. Marine sediments contain as much as 18 per cent organic matter and bacteria in bottom deposits may grow and multiply. Enteric bacteria may be concentrated in bottom sediments of rivers as a result of sedimentation of bacteria-bound particles. Although it has been demonstrated that microbial communities can affect chemical pollutants, the presence of toxicants can also affect microbial community structure.

The Gradašnica River originates on the Ozren Mountain, in the Landscape of exceptional features “Ozrenske meadows“ area. After approximately 6 kilometers it flows into the Sokobanjska Moravica as a left tributary. Along the stream, areas of fast and slow flow alternate. The invertebrate fauna is moderately rich, with the probable presence of another 10-20 species. Quantitatively, individuals from the genus Gammarus and the orders Ephemeroptera and Trichoptera dominate, with the subdominant species Gerris lacustris in calmer areas. A total of 14 taxa were recorded, from which some without possibilty of precise identification.

The pond is located on the northern slope of Ozren Mountain and has no visible surface sources of recharge. The water in it is maintained at approximately the same level and probably originates from seepage from the Ozren terrace. Fourteen taxa were found, and fauna diversity can be evaluated as moderate.

At this moment, in the world as well as in Serbia, due to climate change, there is an increase in the occurrence of fires and large material damages as a result. One of the major problems in this process is the insufficient number of water surfaces where water can be captured and transported to the point of impact at the lowest cost. This paper analyses the possibility of development of a decentralized network of fire-fighting water ponds in Serbia, with two typical capacities: 300 m³ and 1,000 m³. In particular, an investment program of 140 smaller and 30 larger reservoirs, with a total usable reserve of 72,000 m³, is being considered. In addition to construction and hydraulic indicators, a scenario analysis of savings in water transport was carried out if the average intake distance was reduced from 20 km to 5 km. 5,000 fires per year are used as a reference scenario, which is a conservative planning assumption in relation to the actual number of fire events in Serbia.