Contribution to our Knowledge of Dutch Freshwater Algae. I

This paper, the first of an intended series on rare or otherwise interesting Dutch freshwater algae, deals with some planktonic algae observed in the waters of the Loenerveense Polder. The Loenerveense Polder is a large shallow pondlake with an average depth of about 1.5 meter. The vegetation mainly consists of Potamogeton spp. and Chara spp. with large patches of Fontinalis antipyretica L. The pH is fairly constant and ranges from 7,8 to 8,7, with highest values in summer. Colour ranges from 19 to 28; KMn04 consumption from 22 to 30 p.p.m.; chloride from 37,5 to 48,5, and bicarbonate from 86 to 118 p.p.m. Bicarbonate hardness in german degrees varies from 4,0 to 5,4. NOa is present in concentrations varying from 0 to 0,14 p.p.m. The 02 content is rather constant, with maxima in summer: 8,4 to 15,1 p.p.m. Other chemical data are not available.