Comparison of freshwater biofilms grown on polycarbonate substrata in Lake Velence (Hungary) and Lake Mogan (Turkey)

Freshwater biofilms grown on polycarbonate substrata in Lake Velence (Hungary) and Lake Mogan (Turkey) were studied by applying total reflection X-ray fluorescence spectrometry and taxonomical techniques. Concentration of calcium, which stabilizes the structure of the exopolymer matrix, was identical in the biofilms, independently of the fact that its concentration in the lake waters differs by a factor of 2.5. Enrichment factors calculated as concentration ratios of elements (Ca, K, Fe, Mn, Zn, and Sr) measured in biofilm and water varied from 3×104 to 1.5×102. The highest enrichment factors were observed for micronutrients of manganese and iron. Although the dominant alga species were different in the Hungarian and Turkish biofilms, the enrichment factors for these two elements differ only slightly. These results demonstrate that the accumulation of these micronutrients is similar within the diatom species. The lowest enrichment factors were measured for potassium.