Abstract
Research on the diversity of thalli and mats built by freshwater Ulva flexuosa, as well as the impact of abiotic factors on the development and distribution of Ulva mats, was conducted from May to August 2013. The study describes the dynamics of “green tides” formation by U. flexuosa. The study assessed abiotic factors that may influence the colonization and the growth of Ulva populations in freshwater systems. The results are of major importance to the trade and industry sectors. In total, eleven environmental parameters were included in the analysis. The most important environmental parameters characterizing the Ulva sites are sodium chloride levels and conductivity. High values of pH inhibited the development of Ulva, leading to a lower percentage of mature thalli in the mats. The water depth was positively correlated with an increase in the density of thalli in the mats and the average thallus length. Significant differences were identified between the concentrations of nitrates under and outside the Ulva mats. Concentrations of nitrate under the Ulva thalli were always lower.