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While the study found areas where human activity may affect the color of some rivers, these changes may not be permanent.
After examining about 235,000 satellite images taken by Landset between 1984 and 2018, a joint program between NASA and the US Geological Survey, a team of scientists has established that a significant change in color has been observed over a third of rivers in the United States. The last three and a half decades, living science reports.
According to the media outlet, more than half of the images in question rivers were “impressively yellow”, a third of the images were “mostly green”, and only 8 percent of the pictures in the river turned out to be “mostly blue”. “.
“Most rivers are slowly changing and are not significant to the human eye,” said John Gardner, a postdoctoral researcher at the Global Hydrology Lab at the University of North Carolina and lead author of the study. “But areas that change the fastest are more likely to be man-made.”
During their study, the research team collected “16 million measurements” over a period of 34 years on about 108,000 kilometers of rivers with a width of about 60,000 meters in the United States.
Usually the color of a river is determined by “suspended silt, algae, pollution or organic matter in the water”, the media outlet notes that river water produces more algae, or when water carries less silt. “While the yellow color potentially means that the river carries more silt.
“The big trend of yellow or green can be worrisome,” Gardner commented, “depending on the individual river”.
The study also established that about 55 percent of these rivers differ in color, but without showing any clear trend and in a third of the rivers their color has changed; The 12 per cent color of the rivers in question has remained constant.
While satellite images are displayed in areas where human activity, such as “dams, reservoirs, agriculture and urban development” may affect the color of some rivers, such changes may not be permanent, the media outlet adds.
“You can see these trends going in the other direction,” Gardner explained, “especially if the change is due to local mismanagement that is easily corrected.”