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(Journalist)
– A bird’s eye view of American rivers shows that about 1 in 3 have changed color in the past three decades, reports Live Science. Specifically, they’ve gone from blue to shades of yellow or green since 1984, according to a comprehensive analysis of satellite imagery presented in a new study. The researchers don’t present this as a catastrophic report because so many variables are involved, but they say their relatively simple metric may be one more tool for assessing the health of rivers. In general, rivers turn yellow from excess sediment and green from excess algae, while blue suggests “clean and healthy water systems”, for example. Smithsonian. According to the new report’s tally, which analyzed more than 235,000 images from 1984 to 2018, more than half of America’s rivers were yellow, about a third were green, and 8% were blue. See this interactive map.
“Most rivers change gradually and can’t be seen with the naked eye,” senior author John Gardner of the University of North Carolina tells Live Science. “But the areas that change the fastest are more likely to be human-made.” Think of dams, reservoirs and increased development, all of which can alter “nutrient flows” in rivers, a scientist from the University Corporation for Atmospheric Research explains in Salon. An atmospheric science professor at Penn State adds that climate change could also be a factor because warmer temperatures would generally increase algae levels. Still, “I don’t think there are any immediate threats to human health” because of the changing colors, Gardner says. While rivers may change color seasonally due to factors such as snowmelt, the figure of 1 in 3 reflects rivers that have undergone long-term changes. (Read more stories on the river.)
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