The sun has always been crucial to keeping Earth’s lakes clean and safe. That’s because ultraviolet (UV) sunlight acts as a natural disinfectant, penetrating down into bodies of water and killing harmful pathogens.
But this effect is dampened when organic matter runoff builds up in bodies of water, which is happening at an increased rate due to climate change.
Now, a new study has found that increased organic matter runoff in lakes and rivers clouds the water and hinders the sun’s ability to disinfect harmful waterborne pathogens.
“Water clarity is dropping in many regions due to factors such as browning, and this research demonstrates that this change is likely decreasing natural disinfection of potentially harmful pathogens,” said Kevin Rose, the Frederic R. Kolleck Career Development Chair in Freshwater Ecology at Rensselaer.
Harmful waterborne pathogens are responsible for making 12 to 19 million people sick every year, and without the natural disinfecting potential of UV rays, those numbers could increase.
For the study, the researchers gathered and analyzed water samples from lakes all around the world, including in New Zealand and Wisconsin.
In order to measure the impact of UV radiation on pathogens, the researchers first tested each sample to see how much light was absorbed by the organic matter.
This helped the research team determine how much UV radiation could penetrate the bodies of water and kill pathogens, also known as the “solar inactivation potential” (SIP).
The results showed that the disinfecting potential of UV radiation in water has significantly decreased over the years because of an increase in organic matter runoff.
For example, after a heavy rainfall where the Manitowoc River flows into Lake Michigan, an increase in organic matter caused the SIP or disinfecting ability of UV rays to drop by 22 percent.
The study shows how climate change is impacting the world’s water sources and serves as a warning of how our ponds and lakes could be compromised.