In the last 36 years U.S. One-third of the rivers have changed significantly, from blue to yellow and green, revealing new images.
From NASA and the US Geological Survey (USGS) Landset Program – Researchers analyzed 235,000 satellite images taken over a 34-year period between 1984 and 2018. The changing hues can be seen in one Interactive map.
More than half of the satellite images featured yellow-colored rivers, while more than a third of the images were mostly green. Only 8% of the river pictures were mostly blue.
John Gardner, lead author of the postdoctoral research at the Global Hydrology Lab at the University of North Carolina, told Living Science that “most rivers change slowly and are not significant to the human eye.” “But areas that change the fastest are more likely to be man-made.”
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Rivers can be shades of blue, green, yellow, or other colors, depending on the silt, algae, pollution, or organic matter suspended in the water. As a general rule, more algae bloom or river water becomes greener when water carries less silt. Rivers turn yellow when more silt is carried.
“Both silt and algae are important, but too many or too few of them can be disruptive,” Gardner said.
Assessing trends
Altogether, the researchers found that U.S. In 1967,000 miles (108,000 kilometers) of rivers that are more than 197 feet (60 meters) wide have collected 16 million measurements over a 34-year period. This allowed them to track significant trends in color change over time.
More than half of the rivers, or 55%, vary in color over time, but there is no clear trend over time. The third color changed during that period, and only 12% of the color was consistent.
In the north and west, rivers tend to be greener, while the eastern regions of USAID tend to be yellower rivers. Major waterways such as the Ohio Basin and the Upper Mississippi Basin have also turned blue-green.
“Large trends in yellow or green can be worrisome,” Gardner said, but added that “it depends on the individual river.”
Just as autumn falls in red and golden autumn, rivers can also change color with tu due to changes in rainfall, snowfall and other factors that change river flow.
Satellite images revealed hotspots where human influences such as dams, reservoirs, agriculture and urban development could change the color of some rivers.
But these changes are not necessarily permanent.
“You can see these trends going back in another direction,” Gardner said, “especially if the change is due to local mismanagement that is easily corrected.”
Monitoring the health of the river
Although the color of the river may not give a definite number for water quality or ecosystem health, it is a great proxy for both. Thanks to satellite imaging, it is much easier for scientists to measure color than water quality.
“It’s a very simple metric, which integrates a lot of things,” Gardner said. “But it can be used to identify really fast-changing areas.”
From there, scientists can find out what caused the change, he said.
Further research is now needed to determine how accurate river color is in determining ecosystem health and what changes need to be monitored.
The researchers’ findings were published in the December 6, journal Geographical research papers.
Published on Original Living Science.
