Interactions between dissolved oxygen, pH, and temperature at Lake Merritt

Albino Guzman, Jackson Liang, Terra Mack, Anthony Majors, Kua Ngilbus, and Dario Pratt

Lake Merritt is a saltwater tidal lagoon that forms a portion of a wildlife refuge in downtown Oakland, California. In the evening, a series of lamps along its perimeter�dubbed poetically a �Necklace of Lights��illuminates the night sky. By contrast, the lake water itself is described by local residents as having a foul odor, peculiar appearance, and being full of debris. Thus,our team has investigated many areas in and around Lake Merritt in the interest of assessing Lake Merritt’s water quality. We made measurements of dissolved oxygen, pH, and temperature at twelve sites along the edge of the lake and six additional locations throughout the open waters. We then used these measurements to formulate a water quality index (WQI) using guidelines provided by the U.S. Geological Survey (U.S.G.S.). Because we focus on three measures, our water quality index is weighted differently from the U.S.G.S. index. Our index is weighted as follows: 0.5 for dissolved oxygen, 0.3 for pH, and 0.2 for temperature. The index is based on a 100 point scale that allows us to compare sites and determine the relative quality of the water. In addition, we used a special device to create digital images of columns of sampled water, which were then analyzed to determine the degree of water coloration due to dissolved material and algae content. We then used results of this analysis technique to determine the relationship between the color profile and the physical and chemical characteristic of the water. We devised this new strategy to measure water turbidity because we could not use the Secchi disc, given the shallowness of the lake. Our measurements indicated that the WQIs tend to be higher near the tidal gates, where the lake receives water from the San Francisco Bay via an inlet. These results raise the immediate concern that the water is not effectively being circulated around the entire lake.

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