Biofilm on the sandstone substrata of the bridge 'Brankov most' and on the granite substrata of the 'Monument of the Unknown Hero' contains a complex consortia of cyanobacteria, algae, and fungi. Coccoid and filamentous cyanobacteria, green algae and diatoms make up the photosynthetic part of the biofilm while hyphal fragments, chlamydospores, fruiting bodies and spores take part as fungal components. These structures make a dense layer by intertwining and overlapping the stone surface. Five cyanobacterial, 11 algal and 23 fungal taxa were found. The interaction of the biofilm's constituents results in the bioweathering of the stone substrata through mechanical penetration, acid corrosion and the production of secondary mycogenic biominerals. .

Aerophytic phototrophs, colonizers of different substrates exposed to air, among which are rock substrates in cave habitats, are in general not sufficiently investigated and studied. From the ecological point of view, seasonal/temporal variations and parameters that influence aerophytic phototrophic communities through seasons still remain largely unknown. Seasonal analysis of phototrophic microorganisms from biofilms developed at entrances of Samar and Jezava caves in Eastern Serbia was performed four times a year. All identified phototrophic representatives were assigned to a certain division or group. The relationship between documented groups and different measured, determined and observed ecological parameters was illustrated using principal component analysis (PCA). A high diversity of cyanobacteria and algae was observed as a result of seasonal sampling: 141 taxa in Samar and 61 taxa in Jezava Cave. Cyanobacteria were dominant in both caves (coccoid forms prevailing) and were followed by Bacillariophyta. Bacillariophyta were positively correlated with light intensity and sites where seeping water was present, and cyanobacteria with water content in biofilm, Chl a and relative air humidity. Higher diversity of phototrophs was documented in December and March, and lower in May and August in both caves with Chl a values having the same trend as the diversity of phototrophic microorganisms. This was especially the case with biofilms in which diversity was more prone to seasonal changes and where Cyanobacteria dominated. Only 24 taxa were documented during all four seasons in Samar Cave (Cyanobacteria, Bacillariophyta and Chlorophyta representatives) and three in Jezava Cave (Cyanobacteria only).

The main objective of this study was to assess the ecological status of the Mlava River based on epilithic diatoms and to test the use of diatom indices as a tool for estimating the quality of flowing waters in Serbia. Quantitative analysis showed that in AprilAchnanthidium minutissimumwas dominant at each site, except at the fifth site, whereAmphora pediculuswas dominant. In July and September,Achnanthidium minutissimum, Achnanthidium pyrenaicum,Amphora pediculus,Denticula tenuis,Diatoma vulgaris,Gomphonema elegantissimum,Cocconeis pseudolineataandCocconeis placentulavar.lineatadominated. Detrended correspondence analysis (DCA) was used to detect the major patterns of variation in species composition. The first DCA axis summarizes the distribution of the diatom community, mainly through temperature, conductivity, oxygen and water hardness gradient. The second DCA axis was weakly correlated with few variables. Based on the average values of the pollution sensitivity index (IPS), commission for economical community metric (CEE) and biological diatom index (IBD), the water of the Mlava River belonged to water class I during all three seasons. Values of the diatom-based eutrophication/pollution index (EPI-D) indicated class II water quality. According to calculated trophic diatom index (TDI) values, water of the Mlava River was characterized by intermediate nutrient concentrations during three seasons. Principal components analysis was used to represent the correlation between diatom indices, and the highest correlation among the selected diatom indices is seen between EPI-D, IPS and IBD.