I remember creating only one childhood science-fair project; plotting the growth difference between corn seeds planted in potting soil and ordinary backyard dirt. While I don’t remember any other science projects, I do remember the hardest part of any school project was coming up with a good idea. As an adult, I constantly conceive new creations or investigations, and do my best to at least remember some of them and write them down :). Here’s a simple but significant investigation from last summer that costs very little and requires no special equipment.
Water is more than H2O. You’ve heard that from bottled water companies, water filter salesmen, and probably countless cautionary chain emails. All natural water contains dissolved solids, has varying pH (acidity), and various amounts of other suspended materials and dissolved elements. Water from different sources exhibit different chemical signatures because of the differing amounts of dissolved materials. That means streams or springs may have different acidity and different concentrations of dissolved solids such as calcium or iron. I wondered if measuring and comparing the water chemistry of nearby streams may reveal noticeable and interesting differences.
I purchased a simple jar of pool water testing strips at Home Depot. These are made for swimming pools and spas, but test strips geared toward the science industry are available from other sources. I chose the pool test strips because they are relatively inexpensive and readily available. But, because they are designed for pool water analysis, the only indicators useful for natural water are pH, alkalinity, and total hardness. Other test strips have indicators for iron, nitrates, and many other dissolved solids common in natural water. But for the sake of seeing basic differences between water sources, the pool test strips were sufficient.
I followed the instructions on the container of test strips. This involved dunking the test strip in water and immediately removing, waiting a specified period of time, and comparing the indicator colors with the chart on the side of the container. In some locations, I tested the water twice for quality control purposes. In all cases of duplicate tests, the results were identical and I only recorded the results once. I recorded the test results in a notebook, along with the time, date, and location, and any observations that may influence the results, such as weather or streamflow rate. I chose sampling locations at places where I expected different results, or where results would be more significant, such as in a stream near a tributary confluence. I tested water from three streams and one lake within a relatively small geographical area, near Payson, Arizona
A table of results is listed below. If the indicator color appeared between the colors on the indicator chart, I recorded both the value above and below the indicator color. If the value was greater than the highest number on the chart, I recorded that the value was greater than the highest number. (Click on the table to make it large enough to read 😦 Some day, I will find a theme with narrower margins.)
A few interesting things stand out:
1) Unexpectedly, the water in Woods Canyon lake tested positive for chlorine. I tested the lake water several times from several locations along the shore and each time received a positive chlorine result. I’m not sure what this means. Perhaps the indicator is sensitive to another analyte and no chlorine was actually present. Or, perhaps there is chlorine in the lake water as a result of pollution. Winter road salt from a nearby highway could be a potential source. I need to test other lakes within the region but further from the highway to see if there are differences.
2) Two nearby streams had different chemistry, Tonto Creek and the East Verde River. Tonto Creek had a much lower pH, alkalinity, and total hardness. Because both streams are fed primarily from groundwater discharge from springs and have similar vegetation and climate, this water chemistry difference could mean the two streams are fed by two different groundwater aquifers, or chemically different layers within the same aquifer
3) Two tests of the same stream showed the same results before and after a rainstorm that increased both discharge and turbidity. This surprised me. Before the rainstorm, streamflow was almost entirely groundwater discharge from springs. The rainstorm added a runoff component to the flow, but the pH and the concentration of dissolved solids remained nearly constant, at least within the testing limits of the indicator strips. A more sensitive measurement method would probably reveal different results.
4) The East Verde River and its tributary, Ellison Creek, had nearly identical chemical signatures, at least within the precision of the indicator strips. As both streams are fed by springs, it likely means the springs that feed each stream come from the same aquifer and aquifer layer.
5) The hydraulically disconnected pothole near Ellison Creek had very different chemistry than the creek. This means the pothole was filled with rainwater and not water from the creek.
This is an easy experiment that would make a suitable science project for middle or high school students, or as a class project. Testing more water bodies or over the course of a longer time span would certainly yield more interesting conclusions regarding water sources and the origins of chemical water signatures.
A special thanks to Payton Taylor for help with this project.