Results
We statistically analyzed chlorophyll-α data in RStudio and Microsoft Excel to determine whether sediment sizes or flow regimes had an effect on benthic algal growth. Results of the Welch two-sample t-test, Kruskal-Wallis test, and linear regression analyses gave no statistically significant evidence for a cause-effect relationship.
Figures 1 : Calculated chlorophyll-a concentrations.
Figure 3: Box and Whisker Plot Depicting [Chlorophyll-É‘]/Turbulence Characteristics
Figure 4: Box and Whisker Plot Depicting [Chlorophyll-É‘]/Substrate Type
Figure 5-8: Linear Regression Analyses of [Chlorophyll-α] vs. Percent Sediment Size
Table 1: Z-score calculations for upstream and downstream subsamples and composite samples.
Discussion
Previous sampling efforts have found a statistical connection between sediment type and concentration of chlorophyll-α. However, after conducting altered methods and statistical tests on these two variables in this year’s project, no significant correlations between them were found. Samples collected from single large rocks did show greater levels of calculated chlorophyll-α than those collected from silt/clay, sand, or pebbles, although no overall significance was determined across all sediment types. Our data may be different from previous years’ due to the number of new methods and slightly modified methods we carried out. These included more accurate and extensive sediment drying and sieving for better determination of sediment subtypes, the addition of a centrifugation step, and an altered spectrophotometer testing protocol. In addition to these intentional changes, we also encountered a river scouring event in the week preceding field sampling. Scouring events can remove large amounts of sediment-bound periphyton from rivers and under-express the true daily levels of chlorophyll-α.