Comparing Oxygen and Visibility Levels in the Upper and Lower Streams of Salish Creek

Abstract

Dissolved oxygen and visibility levels are important abiotic factors in the freshwater streams that salmon reproduce and undergo early development in. We compared these two factors between the upper and lower streams of Salish Creek by measuring oxygen levels using an oxygen probe and water visibility using a colorimeter. We found that the lower stream had significantly greater oxygen levels with 10.4 ± 0.8 mg/L than the upper stream with 9.5 ± 0.4 mg/L (p < 0.0001). This may be because oxygen has a higher solubility at lower altitudes, recent rehabilitation efforts undergone at the lower stream to make it more suitable for salmon, and the close proximity of the upper stream to urbanization. The colorimeter measured high visibility levels with 100% transmittance at all samples at both sites. As a result, we did not find a difference in visibility between the two sites. Samples were taken during moderate rainfall and from the surface of the stream, potentially affecting visibility. Oxygen levels were above the minimum required levels for salmon and visibility was high at both sites, indicating these two factors are appropriate for salmon but the lower stream’s significantly higher oxygen levels indicate it may be a better site for salmon. Further studies should use a more sensitive device, like an optical attenuator, to measure visibility instead.