Testing a Hypothesis

Is Chicopee Lake performing a water quality treatment function within the watershed?

Editor’s Note: Don Lane, Elachee Teaching Naturalist and retired environmental scientist will provide insight, each month throughout 2022, about different environs and species in, and around Chicopee Lake, located in Georgia’s Chicopee Woods Nature Preserve, in south Hall County.

Don Lanes Journal Entry: July 2022

Results of a simple water quality test conducted on waterways downstream of the Chicopee Lake dam.

Last month’s blog presented a hypothesis that Chicopee Lake may be performing a water treatment function within the watershed by allowing contaminated soil particles to fall out of the water column to the bottom. I decided to test this by doing some simple water quality tests on samples collected from the lake and from Walnut Creek immediately downstream of the dam. I used some test kits and an instrument we use at Elachee for some of our Stream Life and Lake Lanier programs. The kits consisted of a pH test kit, a Dissolved Oxygen (DO) test kit, a Phosphate test kit, a Nitrate test kit, and a conductivity meter.  

The term pH is used to indicate whether a substance is acidic, neutral, or basic (aka alkaline). The pH scale runs from 0 to 14. A pH less than 7 indicates the substance is acidic. Common household items that are acidic include citrus (orange, lemon, lime, etc.) juices, vinegar, and most carbonated beverages. The midpoint of the scale, 7, is neither an acid or a base and is referred to as neutral. Pure water is neutral. Substances with a pH greater than seven are known as bases or alkalines. Household examples of bases include dish detergent, oven cleaner, and drain cleaner.

Dissolved Oxygen, abbreviated DO, is the amount of oxygen that is present in water. Animals that live in the water and do not breath air such as frogs, and turtles, need an adequate amount of DO in the water to survive. Just as our lungs extract oxygen from the air, organisms with gills extract oxygen from the water. Just as there needs to be an adequate amount of oxygen in the air we breathe, there needs to be an adequate amount of oxygen in the water for aquatic life.

Phosphate and Nitrate are plant nutrients. Those of you that garden know that commercial fertilizer usually contains three numbers such as “10-10-20.” These numbers refer to the percentage of nitrogen, phosphorus, and potassium (NPK) in the fertilizer. Phosphate and Nitrate enter the water from sources such as animal feedlots, septic systems, and fertilizer runoff. Excessive amounts of Phosphate and Nitrate in a water body stimulates aquatic plant growth causing algae blooms. Excessive algae can knock the entire aquatic ecosystem out of balance.

Conductivity is the ability of a substance to conduct electricity. Conductance is the opposite of resistance. It is a widely held misconception that water is a good conductor of electricity. Pure water is a poor conductor. It is the impurities in water that allow electricity to flow. Measuring electrical conductivity gives us an indicator of the impurities in the water. These impurities are referred to as Total Dissolved Solids or TDS.

There are many TV commercials these days that tout products that remove TDS from tap water. The higher the conductivity, the higher the TDS. I explain TDS to students this way. Take a glass of water and add a packet of sugar to it. Stir until all the granules of sugar have completely disappeared. There is no sugar at the bottom of the glass and no granules suspended in the water. The water is clear but tastes sweet. That is an example of a dissolved solid.

The results of the tests of pH, DO, Phosphate, Nitrate, and Conductivity are tabulated below.

*“Non-Detect.” The respective tests for Phosphate and Nitrate resulted in zero. However, that does not mean there is an absence of these chemicals. There could be concentrations of Phosphate and/or Nitrate in the water but are at levels below the ability of the test kit to detect them.

To prove the hypothesis that the lake is providing a water treatment function, the water in the creek should be “better” than water in the lake. Looking at the results above, only pH and DO were better in the creek than in the lake. The DO is misleading.  Water in the lake is relatively still while water in the creek is flowing. Flowing water should have higher DO than non-flowing water because as the water flows over rocks and other solid objects in the creek it is agitated which aerates the water. This is like placing your hand in a bucket of water and trashing it around. Some of the air that is generated from this thrashing stays in the water and becomes dissolved oxygen.

The difference in the conductivity from the creek and from the lake is probably not significant.  Also, conductivity is a measure of Total Dissolved Solids (remember the glass of sugar water), and it would not be expected that the lake can do anything to “treat” TDS.

I am not ready to accept nor reject the hypothesis that the lake is proving some water treatment function, but the pH difference is encouraging. A more detailed water quality analysis involving parameters such as metals and bacteria done over the course of some months could provide a better picture of Chicopee Lake’s role in the Upper Walnut Creek watershed.