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One-Third of All US Rivers Have Turned Yellow or Green in Less Than 40 Years

Image credits: Reuters.

Image credits: Reuters.

Researchers explained that rivers are among the most endangered ecosystems in the world and still we do not have a large scale understanding of their changing ecology because most are rarely sampled.

Over the years, you must have come across multiple news reports on rivers changing colours, sometimes yellow, sometimes green. Now scientists in America have come together to study this phenomena which has taken place in the country.

A recent research published in the journal Geophysical Research Letters studies this issue in the USA, where a third of the country's rivers have changed colour over the last 36 years from blue to yellow or green. Researchers John Gardner, Xiao Yang, Simon Topp, Matthew Ross, Elizabeth Altenau and Tamlin Pavelsky came together to prepare an interactive map that traced the changing of river colours over the years.

The six scientists analysed over 235,000 satellite images, taken over a 34-year period between 1984 and 2018 — from the National Aeronautics and Space Administration (NASA) and the US Geological Survey (USGS) Landsat program.

Researchers explained that rivers are among the most endangered ecosystems in the world and still we do not have a large scale understanding of their changing ecology because most are rarely sampled. Changing water colour is also an integrative factor that determines the quality of water.

Lead author of the paper, Gardner, who is also a postdoctoral researcher in the global hydrology lab at University of North Carolina, explained that the colour of rivers can be blue, green, yellow, and brown which indicates its quality. The colour can also be an indication of presence of sediment, algae, and dissolved organic carbon. Researchers mentioned that the human eye can work as an instrument that differentiates the quality of water based on its colour.

Explaining the need for this research, scientists mentioned that although various studies have shown how some rivers are not suitable for human consumption because of their poor quality, the colour of river has not been investigated much when it comes to its gradual change over time. Hence, using data provided by satellites that have kept an eye on this change in colour of rivers, scientists found that rivers have a distinct seasonal pattern in color that changes with its flow.

Their study also found that the dominant color in one‐third of the rivers has significantly changed. Scientists mentioned that the change in water colour of rivers also points out a fast environmental change. Speaking to Live Science, Gardner said that most of the rivers are changing gradually and the change is not noticeable to the human eye. However, he said that the areas that are the fastest changing are more likely to be man-made.

first published:December 31, 2020, 15:26 IST