Effects of untreated sewage effluent on the ecology and metabolism of intertidal flora on rocky shores adjacent to shoreline-discharging sewage outfalls
Date
1973
Authors
Coon, Lowell Michael
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
An initial survey indicated that the response of the intertidal macroalgal community to the presence of sewage effluent could be related to the volume and means of discharge as well as the rate of dilution and dissemination of the sewage fi eld. Species characteristic of the lower intertidal and upper subtidal regions were the ones most sensitive to the presence of sewage effluent. Thus, the continuous discharge of effluent at Clover Point has resulted in a depression of the Phyllospadix and red algal zones. The Phyllospadix population at Macaulay Point showed signs of recovery in 1972 following the cessation of discharge from the shoreline outfall in 1971. Only three species of macro-Phaeophyte algae were present intertidally at Macaulay Point in 1971. By the spring of 1972 six additional species of macro-Phaeophyte algae had established intertidal populations at that site; of these, five had significantly higher upper limits than corresponding populations at Clover Point. With the techniques employed, no significant differences in growth rate were apparent between test populations of Laminaria groenlandica, Egregia menziesii and Nereocystis luetkeana at Clover Point and control populations at Albert Head.
The freshwater component of sewage effluent was largely responsible for the significant depression of net photosynthesis of Laminaria groenlandica at high concentrations of effluent and tapwater. The
depression is believed due to the inability of the osmoregulatory mechanisms to cope with osmotic stress at low salinities. Some component of sewage effluent other than freshwater was active in further depressing the rate of net photosynthesis. The dark respiration rate of Laminaria groenlandica was generally unaffected by reduced salinity but was affected by reduced oxygen supply in effluent-diluted seawater.
An attempt was made to explain the upper limit depressions of whole zonal associations and of individual macro-Phaeophyte species, in terms of net production as controlled by temperature and salinity.