Differences of lake ecosystems with various trophic status

Summary

42 lakes (23 dimictic, 19 polymictic) with 20–940 μg P_tot and 3–62 N_tot/P_tot in epilimnion in summer were studied. Polymictic lakes had about twice higher (whilst dimictic — slightly lower) summer epilimnetic P_tot concentrations than spring ones, and much higher (growing to highest P_tot, concentrations) than dimictic ones, biomasses of phytoplankton. Ratio of non-predatory zooplankton to phytoplankton biomass was high (allowing probably efficient controlling of phytoplankton) as a rule only in the group of lakes of lowest trophic status, but it happened also in single lakes of hypertrophic groups.

Quotient of P_tot in epilimnion to that in bottom deposits increased with increasing trophic status. Release of PO₄-P by zooplankton increased with trophic status, but its ratio to epilimnetic P_tot decreased.

The scatter of analysed indices in analysed lake groups is high, especially in the ones of highest trophic state; some of the last ones have relatively clean water, inspite o f extremely high phosphorus concentration.