Temporal and spatial patterns of phytoplankton in a temperate lowland river (Emajogi, Estonia)

Abstract

For the first time, a general survey is presented of the temporal and spatial patterns of the phytoplankton community in the River Emajõgi, one of the largest Estonian rivers. The species composition of phytoplankton in the River Emajõgi resembles that of Lake Võrtsjärv from which the river arises. The cyanobacteria Limnothrix planctonica (Wołoszyńska) Meffert, Limnothrix redekei (Van Goor) Meffert and Planktolyngbya limnetica (Lemmermann) Komárková-Legnerova et Cronberg dominated the phytoplankton biomass. Phytoplankton abundance, biomass and chlorophyll a concentration showed an increasing trend from spring to late autumn. The results of principal component analysis revealed that the first and the second axes explained 43.6% and 14.5% of total variance, respectively. The first principal component was positively correlated with pH, O2, BOD5 as well as with phytoplankton parameters, and negatively correlated with water level, transparency and concentrations of nitrite and carbonate. The second principal component was positively correlated with chemical oxygen demand and negatively correlated with the concentrations of ammonium and total phosphorus. Projection of the cases on the factor plane indicated that the water of the upper reach of the river and the water of the River Pedja differed significantly from each other as well as from the waters of a majority of other rivers.