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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

University of British Columbia

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 <1% of the total PMA phytoplankton biomass. The greatest effect of BGS on the phytoplankton dynamics of PMA was related to the discharge of elevated nutrients into the surface layer of PMA during the summer when these waters were N-limited. Seasonal phytoplankton trends in PMA were characteristic of other BC inlets as winter populations were dominated by low levels of nanoflagellates and spring and fall diatom blooms occurred each year. However, the summer community composition differed as flagellate species dominated in 1999 and diatoms in 2000. During 1999, the spring freshet was near historical levels, creating a long-lasting strongly stratified system. As well, BGS operation was <50% of 2000 levels. Consequently, nutrient inputs into the PMA surface layer during 1999 were insufficient to support diatom growth during the summer months. In contrast, BGS operated near peak capacity throughout the summer of 2000 and stratification levels in PMA were moderate, resulting in a -3-fold increase in nutrient inputs relative to 1999. This allowed diatoms, specifically Skeletonema costatum, to dominate the summer phytoplankton assemblage. BGS operation directly contributed nutrients to the PMA surface layer through its cooling water discharge. In addition, BGS operation is the primary contributor to the estuarine circulation within PMA. Consequently, BGS was likely the largest nutrient source to the summer surface waters of PMA, and was therefore the primary cause of this summer phytoplankton species shift within PMA. If these added nutrients were entirely incorporated into photosynthetic biomass, this input would replace by an order of magnitude that which was destroyed due to cooling water intake. However, it is.unlikely this would lead to eutrophication within PMA because of the strong tidal effects within the estuary and the lack of a sill at the inlet mouth. This is the first study to directly link the importance of nutrient loading from thermoelectric power generation to the phytoplankton dynamics of aquatic system.

Text

2010-01-17

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http://hdl.handle.net/2429/18541

Oceanography

University of British Columbia

UBCV

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