The development of an algal bioassay procedure using Stigeoclonium subsecundum and the demonstration of the effect of intermittent chlorination on an attached filamentous alga

Abstract

A continuous flow algal bioassay system using the filamentous alga Stigeoclonium subsecundum attached to removable substrates (stigeocloniometers) was used to determine the effects of intermittent chlorination on an attached alga. Preliminary experiments were conducted to determine 1) the best conditions for attaching the algal cells to the stigeocloniometers 2) the best method for increasing the algal biomass on each stigeocloniometer prior to testing and 3) the determination of the mathematical relationship between the pigment extract and the dry weight biomass. The term 'minimal resistant biomass' (MRB) was coined to describe the reaction of various levels of algal biomass to a given chlorine dosage. An MRB of 2.22 mg dry weight/3 in² survived 0.5 ppm peak free chlorine at intervals of six hours but biomass values below this were destroyed. The MRB for 0.25 ppm peak free chlorine at six hours intervals was 0.95 mg dry weight/3 in². Zoospore production was also drastically reduced in the algae receiving intermittent chlorination. The apparent cause of the minimal resistant biomass phenomenon was the morphological change which occurred in the algae surviving intermittent chlorination. This change was of two types. When sufficient algae was present to withstand chlorination, the mat became much more compact and dense. When all but a few cells were killed by the first 96 hr, a hemispherical or dome shaped colony composed of highly branched filaments was produced. Both changes produced such compact algal mats that the water amongst the filaments was somewhat isolated from the water above the mat and hence did not receive the full impact of chlorination.