The Significance of River Color and why it is Changing
By Dylan Gordon
Rivers are some of the most jeopardized ecosystems in modern day, as many running-water ecosystems face a severe risk of degradation. Rivers, despite seeming like a stable feature of our environment, are ever-changing. Rivers are threatened by numerous ecological challenges including changes in flow and deposition, overexploitation of natural resources, and the introduction of novel pollutants. At present, we lack an extensive understanding as to why many of these ecological challenges are occurring. Analyzing these changes can prove difficult due to a lack of sampling of the extensive networks of moving water. With this difficulty in mind, novel methods of measurement such as remote sensing have become vital to the future understanding of river and stream ecology.
John Gardner, an assistant professor here at the University of Pittsburgh, is a lead author of The Color of Rivers, a research paper focusing on the changing colors of rivers within the United States.1 Color is a unique form of measurement and is also one of the oldest methods humans have used to examine water quality. Advancements in satellite technology over recent decades now allows researchers to study river health using color without having to sample rivers on site. By examining the patterns of color with remote sensing methods, Gardner and his team of researchers were able to develop a database of surface reflectance, with satellite images from 1984 to 2018.
Now, what does color mean for river health? Gardner expressed during an interview that there are many reasons as to why a river may change color; changes in color primarily occur due to shifts in sediment, algae, or the amount of organic matter present. There is no definitive or ideal color for a river, so to understand a river’s health you need to know the historical state of the river. For instance, the Missouri Department of Conservation mentions that rivers like the Missouri are naturally muddier, with large amounts of sediment (Figure 1) - its brown color may not necessarily signify an unhealthy river.2 On the other hand, a change in color may indicate healthy seasonal changes in the river ecosystem. What a change in color means is dependent upon the river being examined. A river’s history is vital to understanding a river’s health and ecology.
Figure 1: The muddy Missouri River.3
Gardner and his team, in the paper The Color of Rivers, were able to conclude that one of every three rivers in the United States have experienced a change in color. Color is able to disclose a variety of health issues a river may encounter, but with such a significant change in color amongst rivers in the United states, what does this particular change mean? The overall significance of these large-scale changes remains unclear. As humans alter their environment, changes are expected to occur, but evidence from Gardner and his team has revealed that often, hotspots of change were proximal to urban areas and dams (Figure 2).
Rivers are changing, and the effects of human developments, such as these urban areas and dams, hint at our impact on the environment and are becoming more apparent with the growing number of data collection methods available to scientists.
Figure 2: Map of trends in river color and hotspots of change. After Gardner et al., The Color of Rivers, (2020).
As humans impact the world around them, it becomes vital to do so in a way that is sustainable and will not compromise future generations’ ability to use these resources. According to Kenneth Cummins and Margaret Wilzbach in the Encyclopedia of Ecology, the word “rehabilitation” is more practical than restoration because many polluted streams and rivers have changed beyond our capacity to restore them to their historical condition.4 Sometimes, acts of restoration will consist of restoring these systems to a state that can sustainably meet societal goals.
A great challenge for the 21st century is to rehabilitate rivers and diminish the impact we have on prominent features of our environment. These new data collection methods and insights can help guide us into learning more about river health and lead to safer and sustainable ways of interacting with our environment in the future.
Posted: March 17, 2021