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Does the pH to oxygen ratio vary predictably between seasons?
A correlation analysis. by C. Carrillo
Abstract
In this unit, we will explore the biological and physical parameters that control the changes in pH and oxygen at the dock of Christchurch School along the Rappahannock River. Biological parameters include the process of photosynthesis and respiration and physical parameters include temperature. During the winter, temperature is the controlling variable of pH and oxygen, by determining the solubility. During the summer, phytoplankton growth and metabolism, and heterotrophic microbial growth and metabolism control pH and oxygen through photosynthesis and respiration. Based on these assumptions we predict and find that pH and oxygen are positively correlated in the summer and negatively correlated in the winter.
Introduction and Background
Physical Hardware at the Dock
Lets first take a look at the system to understand how the data is collected. Christchurch School strives to bring the river to the classroom and one way we do this is to monitor or weather and water remotely at our dock in real time. We make the measurements available to all through he internet.
Software and Internet Interface
For a description of our internet interface please watch our screencast shown in the link below.
(Screencast of water monitoring system)
Oxygen and pH (or CO2)
Processes:Chemistry and Biology
The effect of temperature on gas solubility is predictable. As temperature decreases concentration of a gas in solution increases. Alternatively, as temperature increases, the concentration of a gas in solution decreases (General Chemistry Online). For example, as the river water cools from summer to winter, it is able to hold more oxygen. Or as the river water heats throughout the day, the oxygen concentration would decrease if temperature were the only variable controlling oxygen (engineeringtools.com )
Photosynthesis and respiration are two more processes that can change oxygen and pH. Photosynthesis, by photoautotrophs, take up CO2 and reduce it to carbohydrates with oxygen as a byproduct. Respiration, on the other hand, by heterotrophs, use oxygen to oxidize carbohydrates to CO2.
Results and Correlation Analysis
A correlation analysis is a method that helps us determine the relatedness of two variables (A simple explanation). We determine the relatedness by calculating the r-squared. We recognized the limitations of our analysis here by admitting we used excel which applies a model I linear regression when a model II would be more appropriate. For a more in depth explanation please watch the following lecture from UC Berkeley (Stats lecture from UC Berkeley ).
RESULTS
Blue = Winter Red = Summer
Water Temperature vs Oxygen Water Temperature vs pH
As you can see temperature does not really correlate with oxygen or pH during the summer or winter. The correlation of oxygen with water temperature in the summer is only 0.1 and in the winter is slight better at 0.3. pH is worse! During the summer the correlation is 0.1 and during the winter the correlation is only 0.05.
Oxygen vs pH
The best correlations are between oxygen and pH. During the summer, the correlation between oxygen and pH is 0.77 while during the winter the correlation is 0.42.
Table of Correlation Analysis
Conclusions and Ending Thoughts
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