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IntroductionPrimary production is an important part of ecosystem dynamics as it determines the total amount of carbon fixed, and therefore the amount of energy available to higher trophic levels. High nutrient concentrations are generally associated high rates of primary production, and are often associated with rich fisheries. However, too much of a good thing can be bad; excessive nutrient concentrations can lead to eutrophication and harmful effects. Studies have shown than increasing nutrients can increase the development and persistence of harmful algal blooms (Heisler et al. 2008), the development of hypoxic regions (Donner and Kucharik 2008), and cause changes in species composition, richness, and diversity, which may in turn negatively impact the benefits which people receive from ecosystems (Chapin et al. 2000, Worm et al. 2006). About 40 species of phytoplankton produce toxins which can accumulate in shellfish and pass into humans (Hallegraff 1993). The occurrence of these harmful algal blooms and hypoxic regions are deleterious to fishing industries, to ecosystem health, and to human health. Being able to predict rates of primary production is therefore integral to the work of ecologists, fisheries management, and the well-being of society. Nutrients and light are generally the two main limiting factors for marine primary productivity. Nitrogen, phosphorus, and silica can all be important limiting nutrients for phytoplankton growth. Whichever element is available in lowest supply compared to the cell demand determines the maximum biomass that can be produced. Similar to other temperate regions, primary production in the Strait of Georgia, British Columbia is generally light limited during the winter months and nutrient limited during the summer (Mackas and Harrison 1997). This project aims to predict relative rates of primary production in the Strait of Georgia during the summer, by conducting a multi-criteria analysis using a GIS, with nitrogen, phosphorus, and silica as important input parameters. |
The Strait of Georgia The Strait of Georgia(SoG) is 240 km long and 18.5 to 55km wide, and an average depth of 156m (Surface area 6,800km2). 80% of the freshwater entering the Strait of Georgia s from the Fraser River, which has a very variable flow between seasons, being ten times larger in the summer than the winter. [Wikipedia] In the summer months it is generally considered nitrogen limited. The main source of nitrogen in the Strait of Georgia is coastal upwelling providing nutrients from deep waters. Usually the concentrations of nitrogen in the Fraser River are less than those in the Straight, except at the surface during summer months. | |