If you happened to be hiking, biking or boating in the Wissahickon Creek area recently or watched the local news you may have thought you were imaging things. It wasn’t St. Patrick’s Day, but the creek was green!
Wissahickon Creek is a tributary of the Schuylkill River that flows through Philadelphia and Montgomery counties. Environmental scientists from the Academy of Natural Sciences and Temple University turned the water green in order to conduct an experiment to study the health of the stream ecosystem.
It’s something they do periodically.
Here to explain the process are the project leaders: Marie Kurz, PhD, Academy environmental geochemist and assistant research professor in Drexel University’s Department of Biodiversity, Earth and Environmental Science, and Sarah Ledford, PhD, postdoctoral fellow in Temple University’s Department of Earth and Environmental Science.
We added non-toxic, colored dye to the creek and tracked how that dye signal traveled downstream. The dyes we used are used commonly in environmental research and elsewhere (ex. dying the Chicago River green for St. Patrick’s Day).
The experiment was conducted in consultation with the state Department of Environmental Protection and was funded through grants from the National Science Foundation and the William Penn Foundation.
We injected two dyes: One, a bright green color, is non-reactive and tells us something about how water flows through the stream, as in how much goes straight down the main channel versus how much lingers in slow flowing areas, like pools.
The other, a purple color, is reactive, changing color and chemistry when it comes into contact with a living, metabolizing cell, such as algae and bacteria. The degree to which the purple dye changes during the tracer test tells us how metabolically active the stream ecosystem is.
By combining the two tracers, we gain a better understanding about what areas and flow paths within the stream are more or less metabolically active. Understanding what controls the metabolism of urban stream ecosystems helps us and other practitioners to more effectively manage and improve the health of these systems.
Academy scientists have monitored stream, river and lake ecosystems for many years. One major project is the Delaware River Watershed Initiative, which aims to protect our drinking water. For more information on that project, visit our web page.
Post by Carolyn Belardo