Diurnal changes in planktonic cladoceran biomass (fresh = FW) in lake Syczyńskie in August 2006 and 2007 (sampling points abbreviations as in Fig. 1; asterisks show statistical significance in differences as compared to previous hour, *p < 0.05, **p < 0.01, SD = standard deviation, samples marked with the same letters are not significantly different − results of Tukey's post hoc test).