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UBC Theses and Dissertations

An investigation of possible phytoplankton seeding in the Strait of Georgia from Nanoose Bay Ianson, Debby


This thesis investigates the possibility of bays providing the seed population for the spring phytoplankton bloom to larger adjacent bodies of water via advective transport. The study area was Nanoose Bay, Vancouver Island and the adjacent region of the Strait of Georgia. In 1992 and 1993 data were collected 2-3 times weekly and a mooring with an array of 5 current meters was placed at the mouth of the bay during the 1992 study. Interannual variability was tremendous. In 1992 seeding from Nanoose Bay was not possible as the net transport was into the bay at the surface and middle depths. The influence of the Fraser River seemed to dominate as low density water with high silicate concentrations was present at the surface and density profiles were generally well stratified. Although nutrients were not limiting and light availability appeared high, phytoplankton concentrations were low until March 5 when they began to increase and a bloom occurred. It is suggested that horizontal advection and flushing of the bay were responsible for suppressing a bloom prior to March 5 in 1992. In 1993 phytoplankton concentrations were high inside the bay from the beginning of February onward. In the Strait no periods of high phytoplankton concentration occurred although there were two small increases which appear to be due to advective transport, although it is possible that the first was due to reduced wind mixing. It is suggested that seeding of the Strait from Nanoose Bay was possible in this year, although it is also possible that seeding occurred from other locations depending on time and conditions. The conservation equation for a scalar was used to investigate advective transport as balanced by biological sources and sinks. With no current measurements available in 1993, estimates were made from the above equation and compared to wind direction in the Strait and density changes at the mouth of the bay. In 1993 profiles were well mixed with respect to 1992 and overall salinity was higher. It is suggested that light was usually limiting to phytoplankton growth in the Strait due to vertical mixing throughout the study, while in the bay the depth of the water column limited vertical mixing thus allowing phytoplankton to bloom. To continue experiments of this type it is suggested that daily sampling be done as temporal changes can occur quickly. As evidenced from the 1993 data, spatial resolution is also valuable. Current measurements are necessary and their absence in the 1993 data set was unfortunate. It is suggested that drogues may be useful for measuring currents. They could be used to attempt to track phytoplankton when concentrations begin to increase.

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