Freshwater lakes already emit a quarter of global CO2, say researchers

The carbon cycle [credit: laurencenet.net]

This seems to be underlining the futility of pretending that humans could somehow control or manage nature’s carbon cycle, to satisfy a strange ‘greenhouse gas’ obsession.

Lakes and ponds are the final resting place for many of the Earth’s plants. Rivers collect much of the planet’s dead organic matter, transporting it to rest in calmer waters, says Phys.org.

But on a microscopic scale, lakes are anything but calm. An invisible metropolis of microbes feeds on these logs and leaves, producing greenhouse gases as a byproduct.

As a result, lakes may be responsible for as much as a quarter of the carbon in the atmosphere—and rising.

New research conducted with my colleagues in Cambridge, Germany and Canada suggests that emissions from freshwater lakes could double in the coming decades because of climate change.

All known life on Earth is made of carbon. When plants and animals reach the end of their lives, microorganisms such as bacteria and fungi come to feast. They feed on the carbon-based remains of other organisms and their waste products—collectively known as organic matter.

As a byproduct of this never-ending feast, microbes release gases such as carbon dioxide and methane into the environment. While each individual microbe releases a minuscule amount of gas, they are the most abundant organisms on Earth, so it adds up.

Energy from sunlight can also break the chemical bonds between molecules of organic matter, releasing smaller molecules, such as carbon dioxide, into the environment.

Some of this degradation happens on the forest floor. But much of the organic matter that falls to the ground ends up in the water. Winds, rain and snow transport it into lakes, or more often into the rivers that feed them.

The amount of greenhouse gases released from lakes by microbes and sunlight is huge. Initial estimates were about 9% of the net carbon released from the Earth’s surface to the atmosphere—that is, the amount released over and above the Earth’s carbon-storing processes.

But, thanks to improved measurements, recent research has revised the figure to as high as 25%. These numbers are substantial given that that lakes only comprise about 4% of the global land surface.

In the coming years, lakes will receive more and more organic matter for microbes to digest. A warming climate will bring more forest cover around lakes and a greater proportion of broad-leaved trees, such as maples and oaks, as compared to needle-leaved trees, such as pines.

Carbon in a thousand forms

To understand how changes to forests will alter the role that lakes play in the carbon cycle, we performed an experiment in two Canadian lakes.

Continued here.