Abstract
Relationships of bacterial, picocyanobacterial, eucaryotic picoplankton, nano-flagellate and ciliate abundances to each other and to chlorophyll α (Chl.α) (total and > 10, 2-10 and <2 μm fractions), total phosphorus (TP), total nitrogen (TN) and TN : TP ratio in 34 epilimnetic waters during the warm season in 1994 were investigated. Linear regressions on TP and Chl.α accounted for 51% and 34% of the variability in bacterial and ciliate abundances, respectively. The abundance of heterotrophic nanoflagellates was not correlated with that of bacteria. For occasions when the abundance of picocyanobacteria was greater than 104 cells⋅ml-1, the maximum abundance of picocyanobacteria in each lake was positively correlated with TP (γ=0.40, n=32, P=0.021), but negatively correlated with the TN : TP ratio (γ=-0.51, n=32, P=0.003). Eucaryotic picoplankton (spherical chlorococcales) were not observed in oligotrophic lakes with less than 7 mg⋅m-3 TP. The Chl.α contents in the <2, 2-10 and >10 μm fractions were linearly regressed on TP. Among these regressions, that for the <2 μm Chl.α fraction had the lowest slope and the highest Y intercept, indicating that the <2 μm Chl.α was larger in clear waters, but did not increase as sharply as did larger size fractions with increasing nutrient levels. The reason why the <2 μm Chl.α fraction was not correlated with picophytoplankton abundance was discussed.
