A new study has found that one of the three major American rivers has changed color since 1984, with many bodies of water slowly turning yellow and green – and scientists have told Salon that this could mean something bad for humans. . Health.
Analyzing about 1.9.9 million satellite images taken over a period of more than three decades, researchers at Chapel Hill University of North Carolina, University of Pittsburgh and Colorado State University found that 108,000 kilometers (at least 67,000 miles) of rivers Meters (197 feet) wide have been studied across the country, with 56% appearing primarily yellow and 38% predominantly green. While rivers often change color depending on the flow and flow regime, scientists discovered in 1984 that one-third of rivers experienced long-term “significant color changes” between 1984 and 2018. (If you want to see what happened to your local river, here’s a handy interactive map.)
“One thing to remember is that rivers do not necessarily turn ‘yellow’ or ‘green’,” said co-author of the study, Dr. John Gardner (which was published in Geophysical Research Letters earlier this month), wrote to Salon. “If you recall the visible light spectrum RoyGBIV (red, orange, yellow, green, blue, violet), a significant ‘red-shift’ trend means a trend towards the red-yellow edge of the spectrum, which could mean In the same way that a river changes from green-blue to green, the ‘blue-shift’ trend means that the river is turning towards the blue / green end of the spectrum, which could mean that the river changes from yellow-orange to yellow. Or green-yellow to green. “
As Gardner points out, there are many factors that can cause this visible color shift. When a river appears yellow, the potential culprit is suspended; When it appears greenish, the probable cause is algae; And if a river is blue … well, as the clichચી goes, chances are you’re dealing with “relatively clear water.”
The end result is that “if a river turns from green to yellow, it is probably due to a combination of less algae and more suspended silt. The potential drivers of such a change are numerous, the river water itself changes and how the whole landscapes change. Gardner observed that increasing construction due to urbanization could increase river flows and increase agricultural stagnant silt and make the river look more yellow, while a decrease in nutrients and light could reduce algae and make the river look less green.
Dr. Temlin Powellsky, who co-authored a paper with Gardner and worked with Gardner at the Global Hydrology Institute, said, “The rapidly softening that is rapidly turning yellow is close to the upstream of the reservoirs.” He cited the Colorado River as an example of the flow over the lake plains, which he said had changed color due to the presence of silt in the reservoirs, creating a “delta” and moving the river into the reservoir. When that happens. We are relatively blue / We convert the green atmosphere (reservoir) into a relatively yellow atmosphere (river).
He added, “It’s a little less clear why some rivers are turning green. It could be that they carry less sediment; there’s evidence that this is the case in U.S. rivers, and we’re working on a detailed analysis using satellite. Doing. Imagination. It could also be because they are experiencing the growth of algae or both. “
Both scientists warned to draw specific conclusions about whether this color change poses a threat to human health, noting that numerous variations could cause rivers to change color, as color changes indicate danger and why the feature is so specific. Depends on. The river has changed its color.
“Color change can be difficult in terms of the risks to human health, as color integrates many different signals,” explains Pewelsky, listing organic matter dissolved with algae and silt as possible causes of river color change. “In general, however, some rivers that are becoming greener may experience increasing algal growth, which can sometimes be detrimental to humans.” He also said that rivers that are turning yellow “may increase how much sediment they carry, which could be a sign of further erosion of land from the upper areas or other changes in river characteristics due to human activities.” Such as connected to dams and reservoirs.
“I don’t believe there are any immediate risks to human health (due to the long-term changes in the color of the river),” Gardner told the salon echoing the observations. However, nature has already placed organic matter, silt and algae in most rivers, “more or less (depending on the river) can be harmful to the ecosystem and human health.” He pointed to the Ohio River in 2015 as an example of a situation in which algae peacocks “can reduce the concentration of oxygen that fish need to breathe and can also produce toxins.” Conversely, “many pollutants (such as mercury) are associated with suspended silt, but in large rivers generally included in our study, there are very few suspended sediments that have the problem of seawater for the need for river silt to keep pace with the sea surface. “
“We only measured the color, which is the combined effect of silt, algae and dissolved organic matter on how water looks in the human eye. So, we can’t say exactly what the river is changing color and if it’s problematic Is human (or ecosystem health). “
Salon also reached out to meteorologists, who said the findings of the new study could, in some cases, be linked to man-made global warming.
Dr. Michael E., Distinguished Professor of Atmospheric Sciences, Penn State University. “A lot of human influences are leading to this,” Mann told the salon via email. “Pollution in the form of agricultural fertilizers can cause eagle peacocks (usually cyanobacteria) that turn the water yellow, green or red. But climate change is also a factor. Hot water leads to anoxic conditions that favor algae peacocks. .So in short, the reports that are changing here are the result of many of the consequences of environmental degradation by human activities, including climate change. “
A distinguished senior scientist from the Department of Climate Analysis at the National Center for Atmospheric Research at the University Corporation Corporation for Atmospheric Research, Dr. Kevin Trenbert made a similar point to the salon, writing that “a source of influence in a change is more relevant. In more places people do more things” such as changing how they use land, building dams and interfering with the flow of nutrients into rivers. Change. “There is no doubt about the effects of climate change, but the amount is probably a little less,” he said, citing changes in rainfall patterns, increased melting intensity and wildfires, for example.
