(Newser)
– A bird’s eye view of American rivers shows that approximately 1 in 3 has changed color in the last three decades, reports Live Science. Specifically, they have gone from blue to yellow or green tones since 1984, according to a complete analysis of the satellite images exposed in a new study. Researchers do not present this as a report of destruction and twilight because many variables are involved, but they say its relatively simple metric can be another tool for measuring waterway health. Rivers generally turn yellow due to excess sediment and green due to excess algae, while blue suggests “clean, healthy water systems” for Smithsonian. According to the count of the new report, which analyzed more than 235,000 images from 1984 to 2018, more than half of American rivers were yellow, about a third were green and 8% were blue. See this interactive map.
“Most rivers change gradually and are not noticeable to the human eye,” University of North Carolina lead author John Gardner tells Live Science. “But areas that change most quickly are more likely to be man-made.” Think of dams, reservoirs, and increased development, which can change “nutrient flows” in rivers, a scientist at the University Corporation for Atmospheric Research tells Salon. An atmospheric science professor at Penn State adds that climate change could also be a factor because warmer temperatures would generally raise algae levels. Still, “I don’t think there are immediate threats to human health” because of the changing colors, Gardner says. Although rivers can change colors seasonally due to factors such as melting snow, Figure 1 in 3 reflects rivers that have experienced long-term changes. (Read more river stories.)