Climate change may double greenhouse gas emissions from freshwater lakes: Study

Climate change may cause the levels of greenhouse gases emitted by freshwater northern lakes to increase by between 1.5 and 2.7 times, according to a study.

Researchers from the University of Cambridge in the UK noted that every drop of fresh water contains thousands of different organic molecules that have previously gone unnoticed. Small shallow lakes dominate the world's freshwater area, and the sediments within them already produce at least one-quarter of all carbon-dioxide, and more than two-thirds of all methane released from lakes into our atmosphere, they said.

"What we've traditionally called 'carbon' in freshwater turns out to be a super-diverse mixture of different carbon-based organic molecules," said Andrew Tanentzap from Cambridge, who led the research published in the journal PNAS. "We've been measuring 'carbon' in freshwater as a proxy for everything from water quality to the productivity of freshwater ecosystems. Now we've realised that it's the diversity of this invisible world of organic molecules that's important," Tanentzap said in a statement.

As the climate warms, vegetation cover is increasing in forests of the northern latitudes, the researchers said. By simulating this effect in two lakes in Ontario, Canada, the study found an increased diversity of organic molecules -- molecules containing carbon within their structure - entering the water in the matter shed by nearby plants and trees. Organic molecules are a food source for microbes in the lake sediments, which break them down and release carbon dioxide and methane as by-products.

Increasing levels of organic molecules can therefore enhance microbial activity and produce more greenhouse gases. Since the same microbes can make greenhouse gases from many different organic molecules, the diversity of organic molecules was shown to be more closely linked with levels of greenhouse gas concentrations than the diversity of the microbes. An elevated diversity of organic molecules may elevate greenhouse gas concentrations in waters because there are more molecules that can be broken down by sunlight penetrating the water.

To conduct the research, containers were filled with varying ratios of rocks and organic material - consisting of deciduous and coniferous litter from nearby forests -and submerged in the shallow waters of the two lakes.