A team of international scientists has conducted new research on greenhouse gas emissions from rivers, streams, lakes, and reservoirs, providing updated estimates on a global scale. The findings, presented in two separate studies, offer a more comprehensive understanding of greenhouse gas emissions from inland water sources.
The previous assessment, known as the Regional Carbon Cycle Assessment and Processes initiative (RECCAP-1), published ten years ago, suggested that these water bodies could release up to 7.7 petagrams of carbon dioxide (CO2) annually. However, the recent papers by Lauerwald et al in Global Biogeochemical Cycles introduce the inland water chapter of RECCAP-2, which expands the analysis to include methane (CH4) and nitrous oxide (N2O).
The first study presents updated estimates of greenhouse gas emissions from inland waters using state-of-the-art methods. The second study combines these estimates with global maps of inland water surfaces to provide regionalized emission projections.
The researchers found that inland waters contribute approximately 5.5 petagrams of CO2 per year, with one third originating from South American rivers. In terms of CH4 emissions, inland waters release 82–135 teragrams annually, with North American and Russian lakes accounting for one third of this amount. N2O emissions were relatively small at 248–590 gigagrams per year, with North American inland waters responsible for a quarter of these emissions.
The authors discovered that inland waters may represent around 20% of the total global CH4 emissions, whereas their contributions to global CO2 and N2O budgets are relatively minor.
It’s important to note that these estimates are considered conservative because they exclude ephemeral water bodies, small wetlands, and water bodies smaller than 0.1 square kilometers. Nonetheless, the results will enhance climate models and global greenhouse gas budgets, shedding light on the role of natural systems in climate change.