AbstractsBiology & Animal Science

Periphyton communities (especially diatoms) constitute a system rich in information for environmental monitoring, placing them among important indicators of ecological conditions in lotic systems. In this thesis, field studies and laboratory experiments were conducted to elucidate the confounding effects of substrate selection, eutrophication, organic pollution, ionic strength, land-use patterns, and heavy metal pollution on benthic diatom communities. Characteristics of benthic diatom communities in relation to pollution level and type were analysed through general criteria (chlorophyll a, dry weight, ash-free dry weight, and cell densities in the case of laboratory experiments) and specific criteria (indicator value method, multivariate techniques and diatom-base indices). For field studies, epilithic, epiphytic, epipsammic and epipelic diatom communities and those growing on bricks and glasses and water quality were assessed. A gradient of decreasing water quality was observed from the agricultural/forested area to the urban area. Diatom community structure closely reflected this gradient. Upstream sites with good water quality were characterized by such species as Aulacoseira alpigena, Cymbopleura naviculiformis, Eunotia bilunaris, E. intermedia and Stauroneis phoenicenteron. Urban sites with medium to bad water quality were characterised by such species as Frustulia rhomboids, Nitzschia linearis, Cyclotella pseudostelligera, Pinnularia gibba and Achnanthidium minutissimum. Downstream urban sites with very bad water quality were characterised by such species as Luticola geoppertiana, Nitzschia palea, Sellaphora pupula, Planotidium lanceolatum and Fallacia monoculata. Common diatom species were not restricted to a single substrate, though preference was generally high for natural (especially macrophytes) compared to artificial substrates. The results of diatom-based multivariate water quality assessment based on different substrates were shown to be interchangeable. Variance in diatom data was partitioned between two sets of exploratory variables, i.e. ionic strength (26.9%), other variables, particularly eutrophication and organic pollution (23.0%), shared variance (11.3%) and unexplained variance (38.8%). Finally, 17 indices developed in other regions proved useful in providing an indication of the quality of the investigated waters. For laboratory experiments, effects of cadmium, chromium III and lead on natural periphyton community sampled from the Monjolinho River were studied. Hormesis was demonstrated with a Cd EC50 of 0.077 mg.L-1 being recorded. High metal accumulation 2 capacity (total and intracellular) by periphyton was demonstrated depending on metal concentration and exposure duration. Pb and Cr III were shown to decrease the toxicity effects of Cd on periphyton communities suggesting antagonism. Finally, combined effects of frequency, duration, recovery period, chemical type and timing of pulses with elevated Cd, Cr III and Pb concentrations on periphyton communities were assessed. The closer the…