Mass extinction events can turn fresh water into toxic soup, and it already is

Aside from the global catastrophe that killed most of the dinosaurs, some experts believe that nearly every mass extinction in Earth’s history was followed by a proliferation of microbes in rivers and lakes.

After the Permian extinction 252 million years ago – the largest mass extinction in Earth’s history – there appears to have been an explosion of bacterial and algal blooms, which lasted for hundreds thousands of years.

According to the geological records of Australia, the adverse effects of climate change and climate-induced deforestation during the Permian extinction likely caused a poisonous soup to sprout in the Sydney Basin, one of the oldest known freshwater ecosystems in the world.

This is puzzling, say the authors, because human activity is leading to a similar mass extinction event today.

“We are seeing more and more toxic algal blooms in lakes and in shallow marine environments that are linked to increased temperature and changes in plant communities that lead to increased nutrient inputs to the environments. freshwater, ”says University of Connecticut geologist Tracy Frank

“So many parallels with today. Volcanism was a source of CO2 in the past, but we know that the CO2 the intake that was seen at the time was similar to the CO rate2 increases we are seeing today due to anthropogenic effects. “

Algae and bacteria are normal parts of a healthy freshwater environment, but they can sometimes grow out of control and deplete the water of oxygen, creating “dead zones”.

This tends to happen with global warming, deforestation, and the influx of soil nutrients into waterways, which can feed microbes. These three factors are at play today, which is why we are probably already seeing an increase in toxic blooms.

Considering what has happened in the past, this is a worrying sign.

According to soil, fossil and geochemical data from the Sydney Basin, researchers believe that the spread of microbes following the Permian extinction “was both a symptom of the collapse of the continental ecosystem and a cause of his delayed recovery “.

The Permian volcanic eruptions first triggered an accelerated and sustained increase in greenhouse gas emissions. This has caused higher global temperatures and sudden deforestation due to forest fires or drought.

Once the trees were gone, it didn’t take long for the soil structure to begin to erode and its nutrients to have crept into freshwater ecosystems.

For more than three million years, the Earth’s forests have struggled to recover. Rather, the Sydney Basin was littered with lowland ecosystems that “were regularly inundated by stagnant, cool / brackish water bodies harboring populations of thriving algae and bacteria,” the authors write.

In turn, these persistent dead zones have prevented the reestablishment of important carbon sinks, such as peatlands, and slowed the recovery of climate and ecosystems.

Other distant records around the world have also revealed that microbial blooms were common after extinction events caused by warming. The exception appears to be the very large asteroid event that caused the dinosaurs to become extinct 66 million years ago.

This major episode caused the rise of large amounts of dust and sulphate aerosols in the atmosphere, but compared to the volcanic activity, the meteorite caused only a modest increase in carbon dioxide and atmospheric temperature, not a sustained increase. As such, freshwater microbes only appeared to experience a short-lived explosion after the extinction event.

Unfortunately, this is very different from what happened during the Permian extinction and what is happening today.

For example, the researchers note that the “optimum temperature growth range” for these harmful algae in freshwater environments is 20 to 32 ° C (68 to 89.6 ° F). This range corresponds to the estimated summer continental surface air temperatures for the region at the beginning of the Triassic. This range is what is projected for continental surface air temperatures at mid-latitudes in 2100.

Scientists note other similarities, including an increase in forest fires and subsequent soil destabilization.

“The other big parallel is that the increase in temperature at the end of the Permian coincided with a massive increase in forest fires,” says geologist Chris Fielding, also of the University of Connecticut.

“One of the things that destroyed entire ecosystems was fire, and we’re seeing that right now in places like California. One wonders what the long term consequences of events like this are, as they become more and more widespread. “

The good news is that a lot of changes are under our control this time around. The bad news is that whatever happens next is our fault.

“The late Permian mass extinction took four million years to recover,” says Fielding. “It’s sobering.”

The study was published in Nature Communication.

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