To what extent are dissolved oxygen levels in the Otter Creek waterway in Vermont affected by flow rate?
Background
This lab focused on environmental science, and more specifically water quality, in
Vermont rivers. This related to the environmental issue of human development and its effect on waterways. Flow rate is one major determining factor in dissolved oxygen levels, with lowered flow rates acting as a leading cause of lower dissolved oxygen levels. Faster moving water tends to more efficiently aerate the water, allowing for the higher dissolved oxygen contents that many organisms need in order to thrive. (Fondriest, 1) Having the correct levels of dissolved oxygen is critical as it allows for the continuing functionality of ecosystems, protecting fish, insects, and plants. (USGS) The research question that was investigated was ‘To what extent are dissolved oxygen levels in the Otter Creek waterway in Vermont affected by flow rate?’
Answering this question would allow for better knowledge of the effect that certain types of development could have on riverway health. Many kinds of development involve changing the flow rate of waterways through techniques such as diverting water, installing dams, siphoning water, etc. Further research of the connection between the two factors could allow for more accurate environmental impact assessments and better protection of ecosystems. The hypothesis that was investigated was ‘if a body of water has a quicker flow rate then it will have a higher dissolved oxygen content because the quicker flow will assist with aeration.’
Materials and Procedure
The materials used in this lab were:
1. a LabQuest
2. a dissolved oxygen detector
3. a flow rate sensor
4. a bucket with a rope attached
5. distilled water
6. pipettes
7. graph paper and a pencil
8. paper towels to dry the DO probe
Once these materials are gathered those conducting the experiment will travel to the first location that is being tested. The dissolved oxygen of the location will be tested using the dissolved oxygen probe to conduct five trials. The probe will first be calibrated as per the process described by the Vernier Dissolved Oxygen Probe instructions. To begin, filling solution will be added to the probe which is connected to a LabQuest. After ten minutes the dissolved oxygen value of a sodium sulfite solution and saturated water will be found. The trials will then be conducted using river water, cleaning the probe with distilled water after each test. (Vernier, 1) Five flow rate trials will be conducted in each location, which involves putting the pieces of the flow rate sensor together and placing the end in the water so that the spinner is free to turn. These processes will be repeated for the next four locations that are being measured, except for the calibration of the dissolved oxygen sensor which does not need to be recalculated in the subsequent locations as the values will be saved on the LabQuest. (Vernier, 1)
The locations that will be sampled include a variety of different conditions. Location one was on the banks of a large, calm lake. Location two was in a stagnant pond with no inflow or outflow. Location three was in a faster portion of the river, with quick water flowing down a mountain from the lake that was measured in location one. Location four was a very fast portion of that same river, directly inside of a mini waterfall. Location five was even further down the river, after it had slowed down to a more calm, steady flow. The five locations that were tested were at different points along the same river in order to control as many variables as possible. However, there were still several factors that could not be controlled, such as the body of water that was tested in. Several trials were done in lakes that fed into a river, and several trials were conducted in the river. Control of air temperature and sunlight level was controlled as much as possible by scheduling the trials to be conducted as close together in time of day as possible.
In order to ensure the accuracy of the data that was collected, five trials of both dissolved oxygen and flow rate will be found in each location, for a total of 50 data points. This will allow any outliers to be discovered, and data to be as consistent with the flow rates and dissolved oxygen levels of the areas as possible.
The most significant possible safety issue that could have been associated with this lab is the disturbance of natural areas while testing. Trials were conducted along different parts of a river where animals, plants and funguses were living. Thus these systems run the risk of being crushed while water from the river is being collected in the bucket, or while those conducting the lab are walking on the river bank. In addition, small organisms could be unintentionally caught in the bucket and disrupted by the testing process. Lastly, there is the possible threat that those conducting the experiment could accidentally fall in the river while testing and hurt themselves.
Results
[figure 3]
(Graphs unable to be uploaded in this space. I will work on uploading them as attached images) [figure 4]
Location four was excluded from the above graph in order to better display the other values. The location four flow rate values were much higher than the other flow rate values were to the extent that it hindered data readability and trend visibility.
(The following data tables are difficult to read given formatting constraints. For each calculation, values for the five trial locations are given in order from location 1 to 5. in order to aid reading of the graphs screenshots of this SAME DATA will also be attached in the photo section, formatting permitting.)
TABLE 1 CALCULATED DATA Flow Rate (m3/s)
Average
0.0058
0.0036
0.042
3.308
0.0036
Range
0.002
0.001
0.028
0.031
0.002
Standard deviation 0.00083666002 0.00054772255 0.01067707825 0.06741142336 0.00089442719
Dissolved Oxygen (mg/L) Average
7.98
1.16
6.44 7.18 4.16 Range 1.3 0.3 1.3
0.06
0.4
Standard deviation 0.4969909456 0.1140175425 0.5128352562 0.248997992 0.1673320053
Flow Rate as a Percentage of Dissolved Oxygen .000462
.000041
.0027
0.2375 .000149
TABLE TWO RAW DATA
(Apologies for the placement of this section in the middle of the report rather than appendix. This was due to submission requirements of the IBO)
flow rate trial one 0.006 0.004 0.048 0.78 0.004
trial two 0.005 0.003 0.044 0.64 0.003
trial three 0.006 0.004 0.026 0.61 0.005
trial four 0.007 0.003 0.054 0.641 0.003
trial five 0.005 0.004 0.038 0.637 0.003
Dissolved Oxygen (mg/L) trial one
8.7
1.1
5.7 6.8 4.2
trial two 8.2
1.2
6.2
7.1 3.9
trial three 7.7
1.3
6.5
7.4 4.3
trial four 7.9
1 7 7.2 4.1
trial five 7.4
1.2
6.8
7.4 4.3
Averages were calculated by adding the trials for a location and then dividing by five. For example, location one flow rate was found as follows: (.006+.005+.006+.007+.005=.029 .029)/5=.0058 Ranges were calculated by finding the difference between the largest and smallest data points in each location. For example, in location one the largest DO value was .007 mg/L and the smallest was .005 mg/L. Thus the range is .002 mg/L. The standard deviations were found by getting the mean of the trials for each location (.0058), then subtracting that value from each raw data point found in the location (.006-.0058 .005-.0058 etc). These values were then squared (4*10^(-8) etc) and the mean found of the squared value. To complete the calculation the square root of the values were found (flow rate in location one used as an example).
Variability was consistently very low for the dissolved oxygen values, with the highest ranges being 1.3 mg/L with standard deviation of .051. Given that the total Dissolved oxygen values for these measures were in the high sevens to mid sixes this demonstrates fairly little variability. The same is true for the flow rate measurements, with ranges and standard deviations very small in comparison to the values measured. The slight exception to this was in location four, which had an average flow rate of 3.308 m3/s and a range of .031 m3/s with a standard deviation of .0674 m3/s.
Analysis
The results did not substantially support the hypothesis. The most unexpected values
were collected in location four, a part of the river with a flow rate of 3.308 m3/s, which is 3.266 m3/s larger than the next highest flow rate location. The flow rates in the other locations are all fairly close together, for example .0058 m3/s and .0036 m3/s. This makes location four a very clear outlier. Location one had the largest dissolved oxygen value of 7.98 mg/L, while location four had a value of 7.18 mg/L, and location three had a similarly high value of 6.44 mg/L. According to the hypothesis, since the flow rate in location four was so much higher than in the other locations, the dissolved oxygen levels should also have shown to be considerably higher. However, this was not the case.
Conclusion
The results of the experiment did not provide strong support for the hypothesis that ‘if a body of water has a quicker flow rate then it will have a higher dissolved oxygen content because the quicker flow will assist with aeration.’ The data did not show a strong correlation between the two factors, with instances like the flow rate of 3.308 m3/s being above the others by such a high margin but still having a fairly average dissolved oxygen value of 7.18 mg/L. This was further demonstrated by the wide range of flow rates as a percentage of dissolved oxygen. The percentages varied widely, from as high as .2375 in the case of location four to .000041 in the case of location two. This demonstrated a lack of solid correlation between the two factors. Given this, the issue of human development changing flow rates and thus disrupting dissolved oxygen levels and ecosystems should be considered much less of a concern than it currently is.
Reflection
The experiment was inconclusive, and did not back up the commonly accepted scientific
knowledge on the topic of flow rate and dissolved oxygen.
One problem that was encountered was the difference between the expected results and
the results that were achieved in the experiment. The experimental results were mostly inconclusive, however the established research shows a strong correlation between the two factors. (USGS, 1) This could have been due to several experimental issues, most likely related to control of variables. Many factors affect dissolved oxygen levels besides flow rate, such as water depth, certain bacteria, and time of day. (USGS, 1) All of these factors changed somewhat in the different testing locations. For example, locations two, three and four were in shaded areas with less direct access to sunlight which likely had a significant effect on factors such as bacteria growth and surface temperature. In addition, the water in locations one, two and five was much deeper than that in locations three and four. Lastly, it took some time to navigate from one testing location to another. This resulted in data that was collected from early morning to mid afternoon, which could have also been a cause of the low correlation.
One way of fixing these issues could have been to sample far more locations in an uninterrupted line from the starting point. This would not have eliminated the factors that likely caused the high variability in comparison to established research, however they would have granted a clearer picture of in what areas the dissolved oxygen values changed. By observing the conditions around these points stronger results could have been achieved.
The results of this experiment have potential application to the environmental issue of urban development and expansion of human impacted systems. When flow rate is changed by the redirection of rivers, installation of dams, etc, ecosystems can be radically altered. This has the potential to be incredibly disastrous to native species, many of whom rely on certain specific flow conditions. For example, mayfly nymphs can only survive in areas with high flow rate and dissolved oxygen (EPA, 3). Flow rate conditions are also incredibly important because they are a major determining factor of dissolved oxygen (USGS, 1). Changed flow rates, and by extension dissolved oxygen levels are often caused by human construction and the intentional shaping of natural environments to support industry and human residence. For example, increased runoff or diversion of waterways are major causes of flow rate changes. Thus it is incredibly important that flow rate is monitored as part of Environmental Impact Assessments that are conducted before major development plans are undertaken to ensure that flow rates
and by extension dissolved oxygen levels will not be altered in a negative manner. In addition, lakes and rivers should be monitored for excessive water withdrawal that can change flow rate.
Reference List
US EPA, O. (2015, November 4). Flow alteration [Collections and Lists]. https://www.epa.gov/caddis-vol2/caddis-volume-2-sources-stressors-responses-flow-alteration
Fondriest. (2011, April 1). Water Quality and Flow Rate Monitoring During Water Withdrawal. Environmental Monitor. Retrieved September 11, 2021, from https://www.fondriest.com/news/ Water-quality-and-flow-rate-monitoring-during-water-withdrawal.htm
USGS. (n.d.). Dissolved Oxygen and Water. USGS. Retrieved September 11, 2021, from https://www.usgs.gov/special-topic/water-science-school/science/ dissolved-oxygen-and-water?qt-science_center_objects=0#qt-science_center_objects
Vernier. (2021). Dissolved Oxygen Probe. Vernier. Retrieved September 11, 2021, from https://www.vernier.com/product/dissolved-oxygen-probe/
Wehmeyer, L. L., & Wagner, C. R. (2011). Relation between Flows and Dissolved Oxygen in the Roanoke
River between Roanoke Rapids Dam and Jamesville, North Carolina, 2005–2009. USGS. Retrieved
September 11, 2021, from https://pubs.usgs.gov/sir/2011/5040/pdf/sir2011-5040.pdf
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