WISCONSIN DESMIDS .3. DESMID COMMUNITY COMPOSITION AND DISTRIBUTION IN RELATION TO LAKE TYPE AND WATER CHEMISTRY

Quantitative data on the generic composition of the euplankton and aufwuchs desmid communities of 61 Wisconsin [USA] lakes are summarized. Information with respect to the role of the various genera [Arthrodesmus, Bambusina, Closterium, Cosmarium, Desmidium, Euastrum, Gonatozygon, Hyalotheca, Micrasterias, Netrium, Penium, Phymatodocis, Pleurotaenium, Sphaerozosma, Spondylosium, Staurastrum, Tetmemorus, Triploceras, Xanthidium] in terms of frequency, density, and relative importance; the suitability of various lake types for harboring desmid communities; and the relationships between chemical parameters and desmid distribution is analyzed. The genera Staurastrum, Cosmarium and Closterium are of wide occurrence, appear to play major roles in the communities of all lake types, and are the most tolerant of varying chemical conditions. Most euplankton genera are of importance only in acid bogs, but aufwuchs genera generally are more widely distributed. Both the euplankton and the aufwuchs communities appear to be composed of 1-4 desmid assemblages, each with a differing range of importance values. Based on biological criteria, acid bogs appear to be the most suitable lake type for harboring desmid communities and calcareous spring ponds the least suitable type. High generic diversity of desmids appears to be correlated with low conductivity, Ca and alkalinity levels, pH values of 5.1-7.0, and the presence of free CO2. The evidence attending various hypotheses concerning water chemistry and desmid distribution appears contradictory, and further studies are needed to help clarify the situation.