Upper Vistula River: response of aquatic communities to pollution and impoundment. VII. Bioassay studies of water trophic state with Chlorella pyrenoidosa growth test

In the Upper Vistula River course three sections were distinguished: first, at 11 km of the river course, with low trophic level of water (mean yearly yield <30% of Chlorella pyrenoidosa Chick. control cultures), second, up to 66.2 km of the river course, with the moderate trophic level (between 30-50% yield of control), third below 115.6 km of the river course, with the high trophic level (between 50-80% of control yield). The highest water trophic level (80% of control cultures yield) was evidenced at 115.6 km of the river course, due to the input of industrial and municipal sewage. The yield of Chlorella cultures was highly significantly positively correlated with the content of organic matter, electrolytic conductivity, P-PO₄, N (as N-NH₄+N-NO₃), S-SO₄, Ca and Mg concentration in the water. In case of Cd, Cu, Pb, Mn, Zn no correlation was found.