Continuous Cultures of Natural Populations of Phytoplankton in Dilute, Treated Sewage Effluent1

Seawater diluted with secondary‐treated sewage effluent provides excellent enrichment for the maintenance of mixed natural populations of marine phytoplankton in continuous culture. Treated effluent, sampled over 1 year, was consistent in the ratios of plant nutrients and similar in its properties of plant growth stimulation and level of toxicity. The heterogeneous continuous culture system produced large quantities of plant carbon with the concomitant removal of nitrogen and phosphorus from sewage effluent. The plant species that grew in the continuous cultures were common to the typical coastal phytoplankton and the selection and elimination of species was gradual considering the chemical complexity of the sewage effluent enrichment.