Phytoplankton crops, bacterial metabolism and oxygen in saanich inlet, a fjord in Vancouver Island, British Columbia

Abstract

Phytoplankton crops in Saanich Inlet were characterized by their content of photosynthetic pigments and by their taxonomic compositions, from early April to mid-December, 1981. Crop sizes were correlated to particle volumes, bacterial activities, and oxygen concentrations at all depths to test the hypothesis that the degradation of sinking phytoplankton debris by bacterial production results in anoxia. Particles produced during the spring bloom were rich in chlorophyll a and pheopigments, which disappeared as particles sank deeper in the water column. The volume of particles, with sizes ranging from 2.0 to 40 μm, was dominated by those with a mean size of about 32 μm. Qualitatively, many of the particles were frustules of the two diatom genera, Thalassiosira and Chaetoceros, which dominated crops in the euphotic zone. No temporal changes in either qualities or quantities of photosynthetic pigments were observed in anoxic sediments. A positive correlation between particle volume and bacterial production was observed. However, no correlation between production and changes in dissolved O 2 was seen in the deep water prior to mid-June. Further observations were masked by flushing that occurred in August and may have begun as early as mid-June.