A study published in the Proceedings of the Royal Society on July 8 reports an unprecedented proliferation of green algae in high mountain lakes in the western United States. In particular, the authors argue that the phenomenon is due to the increasing influence of human activities on the environment.

Exotic and/or unprecedented ecological manifestations have multiplied rapidly in recent years. Recently, for example, there were reports of algae coating the alpine snow with a salmon pink layer or coloring the Antarctic ices with a ruby green color.

Major reorganizations in the algae ecology…

However, researchers have recently highlighted another phenomenon of the same type which is thus added to the list. Indeed, it has become evident that some elevation lakes in the western United States are turning green. The cause is the proliferation of algae – especially chlorophytes – at an unprecedented rate since at least 1850. More specifically, the amount of chlorophyta pigment has multiplied by 2 to 3 since the mid-20th century. Over the same period, the biomass of said algae doubled.

To arrive at these results, the scientists carried out sediment cores at the bottom of two isolated lakes, located a hundred kilometers from the city of Denver (Colorado). Valuable samples that helped rebuild the abundance and composition of local algae communities between the end of the Little Ice Age (1850) and 2010.

A footprint among others of Man on his environment

Although several factors contribute to the observed changes in lake ecology, all of them are directly or indirectly linked to human activities. These include the average warming of air and water or the increase in nitrogen deposits. Which promotes the growth of chlorophytes by increasing the concentration of nutrients and the ability of organisms to take advantage of them.

“Even in relatively distant lakes located in protected areas (…) the imprint of human disturbance on the Earth’s system is evident,” notes Isabella Oleksy, lead author of the study. The latter even reports that the observation made by the research team appeared as “an ecological surprise”. And for good reason, such a level of green algae is usually characteristic of water evolving in a polluted environment.

“Although we have documented these changes in two Colorado lakes, it is likely that this is not an isolated phenomenon,” said the scientist. In addition to the aesthetic aspect, it should be noted that the proliferation of algae is a significant threat to the species. Whether for those living in affected waters or those outside but coming to drink there. Ultimately, these results illustrate the indirect impacts that human activities can have on environments that are nevertheless protected.