Physical processes associated with high primary production in Saanich Inlet, British Columbia

• Published in: Estuarine, coastal and shelf science Vol. 56; no. 5; pp. 1141 - 1156
• Main Authors: Gargett, A.E, Stucchi, D, Whitney, F
• Format: Journal Article
• Language: English
• Published: London Elsevier Ltd 01.04.2003; Elsevier
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Biological and medical sciences; box model; Brackish water ecosystems; Fundamental and applied biological sciences. Psychology; Marine; nutrient cycles; plankton production; Saanich Inlet; Synecology; turbulent exchange; Canada; British Columbia; North America; America; Canada, British Columbia; INE, Canada, British Columbia, Vancouver I., Saanich Inlet; nutrient cycles; box model; Saanich Inlet; plankton production; turbulent exchange; Brackish water environment; Oxygen; Primary productivity; Anoxia; Oceanography; Spatial variation; Inlet zone; Turbulent mixing; Coastal zone; Box model; Bloom; Nutrient; Phytoplankton
• ISSN: 0272-7714; 1096-0015
• DOI: 10.1016/S0272-7714(02)00319-0

Saanich Inlet, British Columbia, has long been known for the presence, in most years, of anoxic bottom water. One factor contributing to this anoxia is a high level of primary production, which occurs as a major spring bloom followed by sporadic ‘mini-blooms’ throughout the summer and early fall. The process(es) by which new production is refueled after nutrient exhaustion caused by the spring bloom are not well known, since Saanich is an inverse estuary and vertical mixing driven by winds and tides is low. This study presents new observational evidence that strongly suggests that the dominant mechanism of nutrient resupply during the summer months is intermittent advective exchange, driven by pressure gradients set up by strong tidal mixing in passages outside Saanich Inlet itself. A simple box model is formulated to illustrate this mechanism. When driven by annual freshwater forcing and deepwater renewal functions characteristic of the region and measured tides for 1975, the model predicts resupply of nitrate during most of the periods observed in 1975 observations (Deep-Sea Res. 24 (1977) 775). This ‘action-at-a distance’ nutrient resupply mechanism, involving strong but localized turbulent mixing and subsequent distribution of the products of mixing over large-horizontal distances by pressure-gradient-driven flow, is likely important in other coastal regions where the estuarine circulation is weak.