Reduction of dissolved oxygen levels in freshwater lakes by excess phosphorous

Katilyn Tate, Jillian Wormington, Chandler Rostochil


We predict that by adding phosphorous to a clean water source, the presence of algae will increase. As algae increases, the number of decomposers will also increase. This will leave more available algae to feed on. A decrease in dissolved oxygen is a result of this. We tested this hypothesis by treating samples of clean water. We added phosphate to one sample group, yeast was added to another group, and a combination of phosphate and yeast were added to the final sample group. We determined that fungi, a decomposer, was present within the samples which led to a decrease in dissolved oxygen when combined with the presence of another decomposer, yeast. The fungi and algae can coexist if they are balanced. However, if one dominates the other, it will lead to competition. Our results showed that there was in fact a direct impact on the dissolved oxygen levels of freshwater upon addition of yeast and fungi, verifying the occurrence of eutrophication.

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