Rivers, lakes, and other inland waters are an underappreciated source of natural greenhouse gas emissions. PHOTO/U.S. National Park Service.
By SPECIAL CORRESPONDENT
Inland waters are important emitters of the greenhouse gasses (GHGs) carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) to the atmosphere, new studies say.
In a new pair of studies, a global team of scientists reassessed greenhouse gas emissions stemming from rivers, streams, lakes, and reservoirs.
The studies published by the Global Biogeochemical Cycles in a publication Advancing Earth and Space Science (AGU) update previous estimates of greenhouse gas emissions from inland water sources at a global scale.
One decade ago, the Regional Carbon Cycle Assessment and Processes initiative (RECCAP-1) reported that these water bodies could emit as much as 7.7 petagrams of carbon dioxide (CO2) each year. Recently, in a pair of papers by Lauerwald et al., the team introduced the inland water chapter of RECCAP-2. This latest effort synthesizes recent emissions estimates to include two additional greenhouse gases: methane (CH4) and nitrous oxide (N2O).
The first piece reviews state-of-the-art estimates of greenhouse gas emissions from inland waters. The second pairs those estimates with global inland water surface maps to provide regionalized estimates of greenhouse gas emissions.
EOS says the study authors found that inland waters contribute 5.5 petagrams of CO2 per year, of which one third emanates from South American rivers. Meanwhile, inland waters emit 82–135 teragrams of CH4 annually, one third of which comes from North American and Russian lakes.
N2O emissions were comparatively small at 248–590 gigagrams N2O per year, and a quarter of N2O emissions stem from North American inland waters.
Inland waters could represent approximately 20% of the total global CH4 emissions, the authors found. In contrast, the contributions of inland waters to the global CO2 and N2O budgets are relatively minor.
These estimates are conservative because they do not include ephemeral water bodies, small wetlands, and water bodies smaller than 0.1 square kilometer, the authors say. Nevertheless, the results will improve climate models and global greenhouse gas budgets while spotlighting natural systems’ roles in climate change.