The kinetics of nitrate(N0, ) uptake, the maximum uptake velocity (V,) and the half-saturation constant (K,), were determined for 18 species of batch-cultured freshwater algae grown without nitrogen limitation. Values of K, ranged from 0.25 to 6.94 p M 1 for Chlorella pyrenoidosa Chick, and Navicula pelliculosa (Breb.) Hilse, respectively. Values of V, ranged from 0.51 to 5.07 p M 1-' h-I for Anabaena A7214 and Nitzschia W-32 O'Kelley, respectively. The mean positive values of K, for Chlorophyta, Cyanophyta and Chrysophyta were 1.89,3.67 and 4.07 p M 1-I, respectively. The mean values of V, for the same phyla were 1.6 1, 1.02 and 2.97 p M 1 h ' lo5 cells1, respectively. The ranges of these kinetic parameters encompass values of kinetic parameters for marine and freshwater species in batch culture, for freshwater algae grown in N-limited chemostats and for natural populations of freshwater phytoplankton. Thus, in spite of variability between species, uptake parameters for both marine and freshwater algae are identical.

Lakes may be acid because of natural ecological conditions or because of anthropogenic activities. Apparently there has been a recent increase in acidity of many lakes in the northeastern United States. Factors that may be contributing to this increase include the use by utilities of precipitators, sulfur scrubbers, and tall stacks; the use of petroleum; and methods of combustion of fossil fuels.