Effects of Pulpmill Effluent on Phytoplankton Production in Coastal Marine Waters of British Columbia

Abstract

Phytoplankton production adjacent to two kraft pulpmills in Howe Sound, British Columbia, was considerably lower than daily rates at control stations removed from the zone of influence. Average daily production at the Port Mellon mill was 29 and 24 mg C∙m−2∙day−1 in 1973 and 1974, in contrast with 332 and 367, in respective years at the control. Less difference in production was seen between Woodfibre mill and its control, because this mill is situated in a more actively flushed location. Howe Sound studies showed little qualitative or quantitative difference between chlorophyll a levels or phytoplankton assemblages among mill and control stations. Skeletonema costatum and Thalassiosira spp. were dominant phytoplankton species. Light attenuation and selective absorption of 400–500 nm wavelength light by kraft mill effluent was considered the major factor responsible for reduced production in the zone of influence. Axenic culture studies with marine phytoplankton showed that phytotoxicity occurs only at high effluent concentrations. Our laboratory experiments suggest that, given sufficient time, it is possible for phytoplankton to adapt to relatively high effluent concentrations, if pH remains normal.