Mutual flocculation of algae and clay: evidence and implications.

Algae-clay aggregates were formed when algal and clay suspensions were mixed in the presence of an electrolyte. The maximum ratio of clay to algae in the aggregates was 1.7, 0.2, and 0.03 milligrams of clay per milligram of algae (wet weight) for Anabaena, Chlamydomonas, and Chlorella sp., respectively. The aggregates formed at Ca(2+) concentrations higher than 5 x 10(-4)M or Na(+) concentrations higher than 2 x 10(-2). The mutualf flocculation and subsequent sedimentation have many practical and ecological implications for bodies of water.