Mass Extinction Events Can Turn Freshwater Into Toxic Soup, And It's Already Happening

Experts believe that almost all mass extinctions on Earth were caused by microbes living in rivers and lakes, apart from the one that decimated most dinosaurs.
The largest mass extinction in Earth history, the Permian Permian event 252,000,000 years ago, was followed by a burst of bacterial and algal blooms that lasted for hundreds of thousands years.

The geologic record of Australia suggests that the perils of climate change and climate driven deforestation during Permian extinction events likely caused toxic soup to grow in Sydney Basin, which is one of the oldest freshwater ecosystems known.

The authors find this disconcerting as humans are causing a similar mass extinction today.

"We are seeing more and more toxic algal blooms in lakes, and in shallow marine environments. This is due to temperature increases and changes in plant communities that are leading to increases of nutrient contributions in freshwater environments," Tracy Frank, University of Connecticut geologist.

There are many parallels between today and yesterday. Although volcanism was an important source of CO2 in the past, we know that it was comparable to today's CO2 increases due to anthropogenic causes.

Although bacteria and algae are part of a healthy freshwater environment they can sometimes grow out of control, causing 'dead zones'.

Global warming, deforestation and the rapid inflow of soil nutrients into waterways can all lead to this. This can feed microbes. These three factors are all present today and are likely to explain why we are already seeing an increase in toxic blooms.

This is a troubling sign considering what has happened in the past.

Researchers believe that the Permian Extinction, which saw soil, fossil and geochemical data in the Sydney Basin, was both a sign of continental ecosystem collapse and a factor in its slow recovery.

First, a sustained and rapid rise in greenhouse gas emissions was caused by volcanic eruptions in Permian. This led to higher global temperatures as well as sudden deforestation caused by drought or wildfires.

After the trees had gone, the soil structure began to erode and nutrients were absorbed into freshwater ecosystems.

Earth's forests have struggled to recover for more than three million year. Instead, the Sydney Basin was littered by lowland ecosystems that were "regularly inundated with stagnant, fresh/brackish watersbodies hosting thriving algae and bacterial populations".

These persistent dead zones also prevented the restoration of important carbon sinks like peatlands and slowed down ecosystem and climate recovery.

Deep-time records from all over the globe also show that microbial blooms occur after warming-driven events. One exception is the large asteroid impact that led to the mass extinctions of dinosaurs some 66 million years back.

Although this major episode produced large amounts of dust and sulfur aerosols, it was not comparable to volcanic activity. The meteorite caused an increase in temperature and atmospheric carbon dioxide, but only a slight one. Freshwater microbes experienced a brief, but temporary, increase in temperature and carbon dioxide after the extinction event.

This is very different to what happened during the Permian extermination and what's happening now.

Researchers note, for example, that these harmful algae in freshwater environments have a "optimal temperature range" of 20-32 C (68-89.5 F). This range corresponds to the continental summer surface temperatures that were recorded for the region in the early Triassic. This range corresponds to the projected mid-latitude continental surface air temperatures for 2100.

Scientists are also noticing similarities in other areas, such as an increase in forest fires that can lead to soil destabilization.

"The other parallel is that the Permian temperature increase coincided with huge increases in forest fires," Chris Fielding, a geologist from the University of Connecticut.

"Fire is one of the most destructive things to happen to ecosystems, as we are seeing in California right now." It is difficult to predict the long-term effects of such events as they become more common.

Good news is that many of these changes can be controlled. Unfortunately, whatever happens next is entirely our fault.

Fielding states that it took four million years for the end-Permian mass extermination event to be recovered from. It's quite alarming.

Nature Communications published the study.

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