MICROBIAL FOOD WEB COMPONENTS AS POTENTIAL INDICATORS OF URBAN HYDROECOSYSTEMS

Assessment of the effect of urbanisation on biodiversity and ecological impact studies are focused on plants, birds, terrestrial arthropods, and relatively few studies have been on aquatic organisms. The aim of this study was to investigate the microbial food web components as potential indicators of the trophic state of two small natural lakes (Gailezers, Bâbelîtis), two artificial lakes or reservoirs (created after excavation activities before 20 years) and the Gulf of Riga seaside Vecâki beach (littoral), all of which are located in the city of Riga or close to it. Analysis of samples was conducted from April til October 2014 by epifluorescense microscopy for pico and nano- plankton (DAPI staining), and by inverted microscopy (Lugol’s fixation) for planktonic ciliates. SYBER green for DNS staining was used to examine population structure in a qualitative way by the cytometre Facs Jazz FCM. The obtained results illustrate that the studied aquatic ecosystems have different impact of eutrophication: the mean seasonal trophic status index value was higher in Lake Bâbelîtis (5.22) than in Lake Gaiïezers (4.57), Sauriesi reservoir (4.76) and Bolderâja res- ervoir (4.22). In Bolderâja reservoir, picoplankton density reached maximum development (192 thous.cells/mL). The nanoplankton consists mainly of autotrophic flagellates, and their abundance was positively related with increasing size structure groups. During seasonal succession stages, ciliates of the size group less than 30 µ are well presented and could be analysed by flow cytome- try together with pico and nanoplankton. Bolderâja reservoir could serve as reference site against lakes Gaiïezers and Bâbelîtis due to less eutrophication impact.