Scientists Eye Leaf Litter in Lakes as Greenhouse Gas Source

(Kenny Goldberg photo for Courthouse News Service)

(CN) – A new study finds that one of the many effects of climate change is an increase of microscopic organic matter in rivers and lakes which will in turn boost greenhouse gas emissions from those waters.

The study, published Monday by PNAS, the official journal of the National Academy of Sciences, builds on the idea that as the climate warms and northern forests spread, more plant matter will drop into lakes and rivers. As the organic matter in the water increases through decomposition of the vegetation, the chemical composition of the water is subtly changed.

More organic matter in the water also darkens the water itself, allowing less sunlight to penetrate to deeper areas. This, too, alters the chemical processes occurring in the natural waterways and lakes.

Fresh water contains hundreds of different organic compounds, but science doesn’t yet fully understand the biological significance of the way that organic material interacts with the chemistry of the water. As substances break down and microorganisms work to decompose them, many pathways and species are impacted by the process.

In the study released by scientists from the University of Cambridge, Laurentian University and the Carl von Ossietzky University, researchers filled containers with varying ratios of artificial sediment and organic material and submerged the containers in the shallow waters of two Canadian lakes that naturally vary in clarity.

When researchers analyzed the contained water for chemical and microbial diversity two months later, they found higher concentrations of carbon dioxide and methane in the contained water, which in turn could increase greenhouse gas emissions.

According to the study’s findings, the increase of organic litter into natural waterways could increase greenhouse gas emissions by a factor of 1.5 to 2.7, with implications for the global carbon cycle.

Freshwater ecosystems such as those surrounding the lakes and rivers covered in this study constitute a small fraction of our planet but play a disproportionately large role in the global carbon cycle. Recent studies have suggested that the amount of carbon that inland waters emit is comparable to the net amount of carbon absorbed by living organisms on Earth’s land surface and in its oceans, and that bodies of fresh water bury more carbon in sediments each year than the entire ocean floor.

The researchers behind Monday’s study hope to open a door to new avenues of research in aquatic ecosystems by exposing connections between chemical and microbial diversity and their implications for the global carbon cycle.

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