Discussion

A visual analysis suggests that silica is the most important nutrient, followed by nitrogen, and then phosphorus when predicting primary productivity.   However, Mackas and Harrison (1997) suggest the Strait of Georgia is often nitrogen limited in the summer.  Throughout the spring and summer there is generally a succession of different times of phytoplankton over time.  Large diatoms with fast growth rates are the first to bloom, followed by other species such as dinoflagellates later in the summer.  Since diatoms have a unique silica requirement in order to form the frustules, this silica limitation may result from high diatom biomass in June.

Chl-a is commonly used as proxy for phytoplankton biomass in oceanography.  Although Chl-a is a good proxy since Chl-a is found in nearly all species of phytoplankton and forms the reaction center, it should be recognized that there is not a perfect correlation between Chl-a concentrations and phytoplankton biomass.

Obtaining data was one of the greatest challenges when working on this project.  Nutrient concentrations are not routinely monitored in the Strait of Georgia or with diverse spatial coverage.  Due to limited spatial data, the concentrations were extrapolated slightly beyond the distribution of the data points.  We suggest that the trends shown in this project should be considered exploratory, rather than conclusive.  Further research based on a greater number of data points and with greater spatial distribution would be helpful in confirming the results from this study.  It would also be interesting to analyze how different nutrient limitation may change over time throughout the summer.  An analysis based on July or August may have shown nitrogen as the main limiting nutrient, since the phytoplankton community composition may shift from diatom dominated to dinoflagellate dominated over time.

Overall, understanding nutrient limitation in the Strait of Georgia will further our ability to predict primary production, and to implement management policies to prevent harmful algal blooms and maximize human benefits from natural ecosystems.