Large amounts of carbon dioxide equivalents taken up by plants on land are returned to the atmosphere from aquatic environments. This according to a study carried out by two master's students at Linkoping University.

Emissions of carbon dioxide equivalents - such as methane and carbon dioxide - from lakes, ponds, rivers, open wells, reservoirs, springs, and canals correspond to on an average 42 % of the expected natural carbon sink in India.

These are the findings of the study by master's students Bala Panneer Selvam and Sivakiruthika Natchimuthu, students at the Science for Sustainable Development master's programme. They have done a thorough investigation of greenhouse gas emissions from many types of inland waters in India under supervision of Dr Lakshmanan Arunachalam, Tamil Nadu Agricultural University, India, and Dr David Bastviken, Linkoping University, Sweden.

"This carbon sink may therefore be smaller than expected, illustrating that we do not have full knowledge of the natural greenhouse gas balance," says Dr Bastviken. "Hence, it may be better to try to reduce fossil carbon emissions rather than hoping that natural environments have a large capacity to take up emitted carbon."

Methane accounted for 71% of the emitted aquatic CO2 equivalents and this opens up possibilities to reduce these emissions by reducing the water pollution in terms of nutrients and organic material.

"It is important to point out that these findings are not specific for India - all countries should consider aquatic emissions in their greenhouse gas balances."

The study also illustrates how student projects can contribute to science that attracts global interest. It was recently published in the scientific journal Global Change Biology, with the title Methane and carbon dioxide emissions from inland waters in India - Implications for large scale greenhouse gas balances.