Climate change making Earth's lakes murkier and a hotbed for pathogens, scientists say

Climate change-induced organic runoff surrounding the Earth's water bodies are making them murkier and blocking the penetration of the sun's UV rays that have a disinfectant-like effect on them. This is causing a rise in waterborne pathogens, climate scientists from New York's Rensselaer Polytechnic Institute said.

This effect, also called "browning" of waters, has been studied for a while now, but its findings were published for the first time in the journal Scientific Reports, noted Phys.org. A new study carried out by the Miami University in Ohio involved the collection and study of water samples based on previous models created by the National Center for Atmospheric Research (NCAR).

This first-time study set out to find the impact of dissolved organic matter in water and the role that the sun's UV radiation plays in getting rid of pathogens.

The presence of organic matter dissolved in water reportedly works in a way that not only makes it difficult for the sun to 'clean' water bodies, but also for water treatment plants to process water and make it useable, said Craig Williamson, a Miami University ecologist.

The report also went on to mention that 12 to 19 million people are affected by waterborne diseases annually.

The World Health Organisation (WHO), in its 2009 report, found that waterborne diseases are the world's leading killer, with about 4,000 children across the globe dying every day directly because of water-based diseases.

Kevin Rose, a researcher from Rensselaer who was responsible for the collection of most of the samples used in this study, said, "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."

Water samples were collected from lakes all over the world, including countries like the US, New Zealand and Chile. The idea was to measure the total dissolved organic matter as well as the wavelengths of light (including UV light) that water absorbed.

Scientists also calculated the refraction and reflection rates of the lakes to determine how much UV light could penetrate the surface, and if it did, how deep it could go.

With this data, they created a "solar inactivation potential" or SIP, a scale that measures "the expected disinfecting power of UV light in a particular body of water" where a higher score denotes better disinfection by UV rays.

Using the SIP, water was studied in different parts of the lakes as well as in different times of the year. One of the lakes studied in Pennsylvania, which is known to have undergone significant browning, was found to have dropped its summer time SIP by half in a span of a little more than a decade – from 1994 to 2015.

It was found that California's Lake Tahoe showed vastly different levels of SIP at its centre, which the report noted as being pristine, and its edges, which were brown due to a lot of human activity. The SIP score at the centre was found to be 10 times greater than at its banks.

It is not clear at this time whether the study will be extended to lakes in other continents as well.