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Effects of cooling water discharge from a thermoelectric power plant on the nutrient and phytoplankton dynamics in Port Moody Arm, British Columbia, Canada Henry, Michael Francis

Abstract

This thesis examines the influence of thermoelectric generation, particularly its nutrient loading effect, on the phytoplankton dynamics in Port Moody Arm (PMA), British Columbia, Canada, a shallow tidal inlet near the city of Vancouver. Spatiotemporal trends of phytoplankton biomass and composition were investigated over a 2 (1/4) year period. These were related to 'natural' environmental factors within PMA and the influence of Burrard Generating Station (BGS), a 950 MW natural gas-fired electric utility that is permitted to withdraw 1.7xl0⁶ m3 d⁻¹ from PMA and discharge the nutrient-rich cooling water at thermally elevated temperatures of 27°C. This study determined that PMA supports some of the highest phytoplankton standing stocks in BC coastal waters; the maximum biomass concentration (1,200 mg chl a m ⁻²) was recorded during a bloom of the potentially ichthyotoxic raphidophyte, Heterosigma akashiwo. This was primarily due to its partial confinement and low light attenuance levels, which led to a highly stratified system where the seaward-flowing surface layer was contained entirely within the photic layer. Average chlorophyll a concentrations in PMA (95 mg chl a m~2 integrated over 10 m) were >3-fold higher than the contiguous waters of the Strait of Georgia and other adjacent inlets. The intake of cooling water through the BGS condenser system had profound effects on the entrained phytoplankton. Overall, -50% of the entrained phytoplankton biomass was destroyed during condenser passage, which was mainly due to in-plant cooling water chlorination. Dinoflagellates suffered the greatest mortality (55%), as compared to nanoflagellates (48%), and diatoms (34%). Since this cooling water was drawn from depth where biomass was low, and tidal flushing rates in PMA are high, this daily phytoplankton biomass loss can be considered inconsequential, amounting to

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