Temporal and spatial variations in primary productivity, phytoplankton assemblages and dissolved nutrient concentrations in Saanich Inlet, a British Columbia fjord




Grundle, Damian Shaun

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The present study investigated the temporal and spatial dynamics of primary productivity, total and size-fractionated chlorophyll a, phytoplankton taxonomic composition, dissolved nutrients, and temperature and salinity in the euphotic zone of Saanich Inlet. Seawater sampling was carried out monthly from May 2005 to November 2006 at the mouth and head of Saanich Inlet. Physical and chemical data indicated that spring/neap tidal cycles supplied nutrients to the head as well as to the mouth region of Saanich Inlet. Of the three nutrients (N03-, Si(OH)4 and P043) measured, N03- was identified as the potentially limiting nutrient for phytoplankton growth. During the growing season, three major phytoplankton bloom periods were observed in Saanich Inlet: a spring. a summer and a fall bloom, and phytoplankton assemblages were consistently dominated by micro-phytoplankton (mainly diatoms). During both the 2005 and 2006 growing season, rates of primary production and phytoplankton biomass were highest during the summer blooms, and results suggest that these blooms were triggered by peak freshwater discharge from the Fraser River. The estimated annual rate of total primary production in Saanich Inlet was 461 g C m-2 year-l. On average primary productivity was 1.5 times higher at the mouth than at the head of Saanich Inlet during the growing season. Results indicated that this difference was caused by a combination of lower NO3- concentrations and lower micro-phytoplankton biomass at the head of Saanich Inlet in comparison to the mouth. Throughout the 2005 and 2006 growing season, micro-phytoplankton contributed significantly to primary productivity in Saanich Inlet, indicating that a substantial portion of primary production was based on new primary productivity. This was confirmed by measurements of new primary production from May to October 2006. During this period, new primary production was responsible for 53 and 57% of total primary production at the head and mouth of Saanich Inlet, respectively. The results reported in this study have significantly improved our understanding of the factors that control the temporal and spatial variability of primary productivity in Saanich Inlet.



Marine phytoplankton, Primary productivity, Saanich Inlet, B.C.