GAMBUSIA AND SYSTEMS THINKING

ABSTRACT

The team challenge involved performing fieldwork to obtain data related to daily fluctuations in dissolved oxygen levels within a natural system (Long Pond at Drew University). Once these patterns were discerned, the team designed and conducted laboratory experiments for estimating oxygen production and consumption by certain biotic factors. The main subjects of these tests were Gambusia affinis, mosquito fish, and Elodea densa, common aquarium plants. The focus of these experiments resulted in estimates of the amount of oxygen taken in or produced per gram of organism per hour both in light and dark conditions. With this information, the computer program Stella modeled a "break even" system, which represented a perfect environment. Ultimately, the team wanted to suggest the proper ratios required to design a miniature closed system in which Gambusia could be sustained for extended periods of time.
It was determined that Long Pond was not a productive system during the trial period. Obtained lab data suggests that Gambusia consume more oxygen, or respire more, in the presence of light. Also, the results of the test conducted showed that dissolved oxygen levels peaked at midday. Following this, levels began to steadily decline, reaching lowest amounts during early morning hours (4:30). It was also determined that Gambusia do not directly obtain oxygen from the atmosphere. Laboratory results suggested that the proposed equilibrium for the Stella model use 0.38 grams of Gambusia with 3.4 grams of Elodea to maintain a sustained system with respect to dissolved oxygen.

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