A comparative study of the phytoplankton populations of polluted St. John's Harbour and unpolluted Aquaforte Harbour, with emphasis on eutrophication

Hydrographic and phytoplanktonic data from four sampling depths (0, 5, 10 and 22 meters) were collected during the summer and fall of 1969 and the spring and summer of 1970 from St. John's Harbour and Aquaforte Harbour, located on the south-east coast of Newfoundland. Eighty-five species and four unidentified categories (u-cells, flagellates, naviculoids and gymnodinians) were identified from seven algal classes. These were primarily boreal forms. The seasonal distribution pattern of the phytoplankton differed in the two harbours. -- It was concluded that St. John's Harbour, which receives untreated sewage from the city and suburbs, and servies a combined population of approximately 93,500, was the more eutrophicated. Evidence for the eutrophic state was especially notable in the central basin (station 1) of the harbour. Here the bottom waters were deficient in oxygen especially during the summer months. Secchi disc readings were generally lower at this station. The annual standing crop at this station was almost three times that at Aquaforte Harbour. Greater concentrations of nannoplankton were supported by the higher nutrient content. One euglenoid occurred in bloom concentrations throughout the summer months, and may possibly be considered an indicator of organically-polluted waters