Mina Aljibori
"Assessing Human Impact on the American River using Macroinvertebrates as Bioindicators"
Introduction:
The American River Parkway is a staple ecosystem in the Sacramento region, due to its biological importance, and because it provides many resources to the urban communities surrounding it. However, as climate change increases it has made our environment vulnerable. Especially environments that are close to us which we frequently interact with. This experiment was conducted to test whether the interactions between humans and areas such as the American River Parkway usually have an impact on the ecosystem’s biodiversity and overall organism’s abundance. In this experiment we will be replicating a small portion of the Magbanua et al. (2010) study, which looked at the impact of different farming techniques on the taxonomic and trait composition of macroinvertebrate communities and on-stream ecosystem functionality. We used two samples to assess the effect that increased nutrition has on macroinvertebrates; a control aquarium and a treatment aquarium. The treatment aquarium will have fertilizer added to it and the control aquarium will stay natural. Our hypothesis is that the addition of fertilizer to the treatment aquarium will negatively affect the overall abundance of the macroinvertebrate population due to the high toxicity levels from the fertilizer.
Methods:
To assess the impact of fertilizer on the American River Parkway, we began our experiment by obtaining two sample tanks, a control and a treatment tank, which we filled with 5 gallons of water each. In the first part of our experiment, which we called “Week 1”, we observed the abundancy of macroinvertebrates within the two aquariums. Then, at the end of the first part, our instructor applied a selected dose of fertilizer to the treatment aquarium to mimic the Magbanua et al. (2010) findings. The second part of the experiment, which we called “Week 4”, we evaluated the impacts of fertilizer on macroinvertebrates in the treatment tank compared to the control tank.
Each lab bench sent one member to insert a 200-mL glass jar below the water surface in control tank to collect a sample of debris while the instructor mixes the top 1 cm of the sediments in the aquariums with a small stick-like tool. After filling one jar, each bench sieved the 200-mL sample using a nylon stocking to spread the collected debris into three fingerplates. We then used the provided dichotomous key to identify which macroinvertebrates were collected. After we identified the macroinvertebrates within the sample, we replaced the collected sample in their respective aquarium. We then repeated the same procedure with the treatment aquarium.
In the second part of the experiment (Week 4), we repeated the same steps from the previous part for both the control and treatment tanks. However, we also assessed the potential change of algal growth, and the possible effects on aquatic macroinvertebrates that might be connected to eutrophication. We did so by collecting approximately 10 mL from the 200-mL glass jars and measuring the level of absorbance Chlorophyll a by using a spectrophotometer.
After the students identified and recorded the macroinvertebrates in the treatment and control tank for both week 1 and week 4, the instructor logged the total number of macroinvertebrates for two separate lab classes for both weeks on an Excel spreadsheet. After all the data was logged in, we were able to access the total number of macroinvertebrates for the treatment and control samples in each of the classes and weeks. Then we calculated the mean number of organisms, standard deviations and conducted t-tests, which allowed us to compare the mean number of organisms in the control and treatment tanks in both week 1 and 4 by obtaining their P-values.
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Results:
The mean number of macroinvertebrates in the control sample for Week 1 was 1.875 and the mean number of macroinvertebrates in the treatment sample for Week 1 was 1.688. The mean number of macroinvertebrates in the control sample for Week 4 was 9.467 and the mean number of macroinvertebrates in the treatment sample for Week 4 was 1.267. The standard deviation for control tank in Week 1 was 3.160. The standard deviation for treatment tank in Week 1 was 1.852. The standard deviation for control tank in Week 4 was 7.736. The standard deviation for treatment tank in W eek 4 was 1.907. (Figure 1). The mean for the Chlorophyll a absorption for the control tank was 0.17375 and the mean for the treatment tank was 0.0475. The P-value for means of the treatment and control tanks in Week 1 was 0.839, and the P-value for means of the control and treatment tanks in Week 4 was 0.000436.
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Figure 1. Mean abundance of macroinvertebrates in the control and treatment tanks for both week 1 and week 4. The error bars represent standard deviation.
Discussion:
The mean abundance of the macroinvertebrate population in the control tank increased from Week 1 to Week 4, unlike the treatment tank which decreased from Week 1 to Week 4. The decrease in the abundance of macroinvertebrates in the treatment tank supported our hypothesis that the addition of fertilizer to the treatment aquarium will negatively affect the overall abundance of the macroinvertebrate population due to the high toxicity levels from the fertilizer. Our hypothesis was also supported by the P-values that found after conducting the
t-tests. The P-value that was observed for Week 1 was significantly larger than 0.05, which indicated that there were no external factors that affected macroinvertebrate population beside the ones they had already adapted too, such as light, bubbles and change in temperature. The P-value that was observed for Week 4 was significantly lower than 0.05, this shows that the probability that the result is due to chance is less than 5% so there is a high degree of confidence that the result was due to the factors being tested, therefore we reject the null hypothesis. Another form of support was shown through the spectrophotometer data, the control tank had higher absorbance readings than the treatment tank which indicated greater algal growth in the control tank. A samples errors that might have occurred during this lab that could have affected the results of the experiment were high levels of lights that the tanks received which might have increased the water temperature. This idea can be supported by the results of the Brown et al. (2007) study, which researched and tested the relationship between macroinvertebrates and meltwater. The results of the study demonstrated that reduced meltwater contributions were associated with lower suspended sediment concentration, and higher water temperature, pH and electric conductivity. Another sample error that might have occurred was during the experiment, we might have lost some macroinvertebrates while we were filtering the water. This might have caused miscalculations of the macroinvertebrate abundancy within the two tanks. Therefore, we cannot infer that the control tank had more macroinvertebrates than the treatment tank.
Literature Review:
Brown, L., David, H., & Milner, A. (2007). Vulnerability of alpine stream biodiversity to shrinking glaciers and snowpacks. Global Change Biology, 13(5), pp.958-966. doi: 10.1111/j.1365-2486.2007.01341.x
Magbauna, F., Townsend, C., Blackwell, G., Phillips, N., & Matthaei, C. (2010). Responses of stream macroinvertebrates and ecosystem function to conventional, integrated and organic farming. Journal of Applied Ecology, 47(5), pp.1014-1025. doi: 10.1111/j.1365-2664.2010.01859.x