Complete question:
Fish are sensitive to many environmental variables: dissolved oxygen, light, temperature, pH, clarity of the water, food supply, presence of predators, etc. Fish will be attracted to different locations in a lake, based on its mix of variables.
Imagine you want to conduct an experiment to understand how just one of these variables differs in a local lake, depending on its depth. This lake reaches a depth of 17 meters. For this activity:
Pick a variable that might change as you go deeper in the lake on a given day.
Do a little research on that variable to determine how you might measure it in a lake.
Use the template below to outline an experiment to investigate this variable in the lake by depth. For each part, simply answer the question in parentheses to create your outline.
Type your response to each field in the space below that field:
Title: (Enter a brief, descriptive title. Hint: Sometimes it’s best to do this last.)
Purpose: (Why are you doing this experiment?)
Hypothesis: (What do you predict from this experiment and why?)
Procedure/Method: (How will you specifically carry out your experiment to test your prediction?)
Observations: (What specifically would you look for and record?)
Data analysis: (With this kind of data, what would be the best way to present it?)
Conclusion: [No need to enter anything here for now.]
References: (List any references you used to design the experiment. Note that for a full experiment write-up you’d also list any references you used while carrying out the experiment or in analyzing your results.)
Answer and Explanation:
Variable: dissolved oxygen
Title: Oxygen variation as a water quality indicator.
Purpose: To study how dissolved oxygen varies with depth
Hypothesis: The percentage of dissolved oxygen will decrease as depth increases.
Procedure/Method:
- Selection of sampling spots, according to the morphometry of the lake, different depth, water currents inputs and outputs, aquatic vegetation, and lake type of use.
- In each spot water samples will be taken using a Niskin bottle. The sample will be taken from different depth: 5 meters deep, 10 meters deep, and 15 meters deep (photic zone).
- Dissolved oxygen (DO) will be measured in each sample, by using a multiparameter sensor.
- In a field sheet to evaluate the parameter, the %DO by site and depth will be recorded.
Observations:
%DO in each site and depth will be recorded in order to analyze how it varies with depth.
Data analysis:
According to different indicators of water quality in a lake, the observed %DO will be compared and analyzed to evaluate the sanity state of the lake water. Example of valuation scale,
NORMAL index: Oxygen concentration in the water column is found to be sufficient for the fish survival
REGULAR: Decrease in oxygen concentration at greater depth, values below saturation in the background
CRITICAL: Null oxygen concentration in all or part of the column profile of water. Probable fish mortality events.
According to the taken data, observations on the study site will be taken, such as the variation in oxygen concentration as it gets deeper, until reaching hypoxia level, where fishes can not survive. Data can be presented in tables and in graphs, in both cases comparing sampling sites and depth, making a focus on the valuation scale.
Conclusion:
Association of the oxygen variation with the sanity state of the lake, microbiology decomposition processes at different depths, eutrophication state, among others.
References:
- Quality monitoring in San Roque waters. INA-CIRSA. 02/26/2013
- Quality Monitoring Program of Water from Los Molinos Reservoir. Articulation and Institutional Synergy for the Water Resources Preservation. Cossavella A, Bazan R. 2018
- Limnology course. Córdoba National University, UNC, 2018