A dynamical systems approach to modeling mercury contamination in aquatic food webs

McFadyen, Catherine (2008) A dynamical systems approach to modeling mercury contamination in aquatic food webs. Masters thesis, Memorial University of Newfoundland.

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Unacceptable mercury levels have frequently been observed in the fish of Boreal forest lake systems. Because of this, fish consumers are at risk for mercury exposure through fish consumption. Populations relying heavily on dietary fish are particularly at risk. The Innu population in Labrador is one such group of people. They catch fish year-round from a variety of lakes in Labrador. Some species of fish harvested by the Innu have been shown to accumulate high levels of mercury that surpass consumption guidelines. This is of great concern because mercury is a neurotoxicant and can have adverse health effects including reproductive impairment, growth inhibition, developmental abnormalities, and altered behavioural responses. -- We have developed a dynamical systems model to predict the effect that certain environmental changes have on the mercury content of food fish in lake systems. We model the aquatic system using a system of ordinary differential equations which relate the biomass of fish in the highest trophic levels with the amount of methyl mercury in these fish populations and in the environment. We look at factors such as harvesting rates, intrinsic growth rates of populations, mercury absorption rate, and rate that mercury is introduced to the lake environment. We also examine the effect that seasonal temperatures and spring snow melt has on the system. -- Dynamical systems models are often used in biology but have rarely been used to examine situations involving contamination of aquatic environments. The models described here are original models; to our knowledge, these are the first dynamical systems models developed to model an aquatic contaminant that is not lethal to the population. -- The model predicts that when mercury enters the lake at a constant rate a stable equilibrium state will be reached eventually. The time taken to reach this equilibrium will vary depending on rate of mercury input. Using parameter values applicable to Boreal forest lakes, the time taken to reach equilibrium is predicted to be approximately 15-20 years, and the final mercury concentration is predicted to be 0.4 ppm for prey fish and 0.655 ppm for top predator fish. When the seasonal effect of colder temperatures and spring snow melt is considered, the lake system exhibits yearly cyclical behaviour. This model predicts fish mercury concentrations very similar to the nonseasonal model. The models described here were shown to be sensitive to methyl mercury input to the lake, methyl mercury output from the lake, and predator functional response.

Item Type: Thesis (Masters)
URI: http://research.library.mun.ca/id/eprint/8639
Item ID: 8639
Additional Information: Includes bibliographical references (leaves 95-103)
Department(s): Science, Faculty of > Environmental Science
Date: 2008
Date Type: Submission
Library of Congress Subject Heading: Aquatic ecology--Mathematical models; Fish as food--Contamination; Fishes--Mercury content; Food chains (Ecology)--Mathematical models

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