Temporal changes in the composition of macrophyte communities and environmental factors governing the distribution of aquatic plants in an unregulated lowland river (Emajõgi, Estonia)

The species composition and dominating species were determined in five 25-m river reaches every week or every second week during the vegetation period of three consecutive years (2006–2008). The number of species and the composition of macrophytes at each site differed from year to year. A total of 33 taxa of vascular plants were identified. Butomus umbellatus, Glyceria maxima, and Sagittaria sagittifolia were registered at all sites each year. The number of constant species was low and we identified a large number of occasional taxa. The dominant species varied during the vegetation period. According to CCA, year was a statistically important parameter for determining the composition of the macrophyte community. The hydrological parameters (discharge, water level, water temperature) had an effect on the distribution of the aquatic plants. Among hydrochemical parameters conductivity, O2, O2 saturation, and sulphate content were statistically significant parameters governing the distribution of the macrophyte taxa.