| Abstract: | Algal assays were performed with unialgal cultures of Oscillatoria rubescens. Asterionella formosa, Synedra acus. Haematococcus pluvialis and Scenedesmus quadricauda. The method we used differs in some important respects from the methods described in literature on this subject and these differences are explained in detail.The agal crop, measured as μg 1−1 chlorophyll α was used to determine the productivity of the water samples tested. The following were tested: (1) untreated Wahnbach water; (2) Wahnbach water treated in a pilot plant for elimination of phosphorus and turbid materials; (3) water samples from the pre-reservoir effluent of the Wahnbach Reservoir; and (4) water samples from the Wahnbach Reservoir taken from near the dam.The fertility of the water samples decreased in all the test series in the following order: untreated Wahnbach water > pre-reservoir effluent > water from the Wahnbach reservoir > Wahnbach water treated in the pilot plant. The productivity of the water samples rich in turbid materials and algae, was higher in heat sterilized samples than those prepared by filtration. There is a clear correlation between the productivity of unfiltered sterilized water samples and their iron and total phosphorus content.Using algal assays we proved that the large decrease in productivity resulting from treating the Wahnbach, the main reservoir inflow, is chiefly due to the removal of phosphorus compounds, but also to the removal of iron and other unknown substances. There are indications that the amount of iron required for growth, as compared to that of phosphorus, varies greatly depending on the individual algal species.The significance of the algal assay and their results relating to measures for limiting eutrophication using phosphorus removal plants is discussed. |
