IMPACTS OF DOMESTIC SEWAGE EFFLUENT ON PHYTOPLANKTON FROM BEDFORD BASIN, EASTERN CANADA

The impact of domestic sewage effluent (SE) on the dynamics of phytopl ankton assemblages from Bedford Basin was evaluated in the laboratory, Phytoplankton production and chlorophyll a increased proportionally w ith SE enrichment. Phytoplankton species composition also changed, The potentially harmful diatoms, Pseudo-nitzschia spp., present initially in small numbers (600 cells l(-1)) in Bedford Basin seawater, and bec ame dominant (3-5x10(6) cells l(-1)) when the seawater was enriched wi th 0.5-5% untreated SE, With higher proportions of SE, other harmful s pecies such as Fragilaria spp. and Euglena spp, became dominant (7-15x 10(6) and 2.2 x 10(4) cells l(-1), respectively), Treatment of SE with UV light or activated charcoal seems to favour growth of benign speci es, such as Chaetoceros socialis, Skeletonema costatum and Thalassiosi ra spp., but not harmful species such as Pseudo-nitzschia spp. Further research on UV treatment of domestic sewage is recommended. (C) 1997 Elsevier Science Ltd. All rights reserved.