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Scientists don’t know why a third of the rivers in the U.S. turned yellow or green



Satellite images of rivers across the United States show disturbing trends in color changes: in the past three decades, one-third of blue rivers have turned yellow or green. This discovery was made after analyzing nearly 235,000 images taken from 1984 to 2018. Among the discolored rivers, 56% of the rivers are mostly yellow, and 38% are mostly green.

Research results are published in the journal Geophysical Research Letter, Consists of a group of researchers who want to try to use the color of water to understand the health of the river. This sounds like a simple technique that even non-scientists can do, but the scientific community seems to avoid observing colors and prefer to obtain actual river samples.

If it were not such a rare sample, it would be great.

The authors wrote: “Rivers are one of the most devastated ecosystems in the world, but we don’t have a broad understanding of their changing ecosystems because most samples are rarely sampled.”

Color map of rivers throughout the United States/Japan. Gardner et al./Gardner Hydrology Lab

Therefore, the research team believes that extensive visual observation of river colors can be helpful when calculating the health of the river with very little data. Tracking colors can also enable researchers to better understand current trends, patterns, and alert areas. Moreover, nowadays, the quality of satellite images is so good that river inspection has become very easy.

“[River color] Lead author John Gardner (John Gardner) told Live Science: “This is a very simple indicator. However, it can be used to identify areas that change very quickly.”

The research team also painted the color of the river on the interactive map so that the changing sky can be seen well.

But what does the color of the river mean? Well… the scientist is not sure yet. Sometimes, the river changes its color due to the sediment flowing down when the seasonal snow melts. Sometimes the river has a period of time when a bunch of algae temporarily turns it green. Sometimes, human activities can cause environmental damage, thereby changing water quality, and thus changing color.

This actually depends on the normal condition of the river, which is why observing the color of the river is so important. The river turns blue, green, yellow or even brown, which is not unusual. However, if a sudden change occurs, it may indicate a problem.

Gardner said in an interview with “Life Science”: “Most rivers are gradually changing and invisible to the naked eye.” “But the fastest-changing areas are more likely to be man-made.”

Although more research is needed to understand exactly what color changes mean, the author insists that “watercolor can identify rivers undergoing rapid environmental changes and help understand rivers on a continental scale.”


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