Methane (CH4) is the second most important greenhouse gas. Despite occupying only 0.58% of Earth's non-glaciated land surface, rivers play a critical role in carbon delivery and transformation within aquatic networks, rendering them a significant contributor of CH4 to the atmosphere.
Dam construction has increased since the mid-20th century driven by the growing utilization of hydropower. However, they have a potential to impede carbon transport and impact the biogeochemical cycling of CH4, leading to an uncertainty in riverine CH4 emissions.
Researchers led by Dr. Li Biao and Prof. Wu Qinglong from the Nanjing Institute of Geography and Limnology of the Chinese Academy of Sciences (NIGLAS), along with their collaborators, have carried out an extensive examination of CH4 dynamics along the river-estuary continuum of the Yangtze River.
Their findings were published in Water Research on May 20.
The stable carbon isotope signature (δ13C-CH4) along the river-estuary continuum of the Yangtze River strongly supports the persistence of hydrogenotrophic methanogenesis as the primary pathway within the study area. In order to provide further validation for this hypothesis, the researchers conducted comprehensive tests involving methanogenic community composition and substrate amendment, and ultimately confirmed the prevailing role of hydrogenotrophic methanogenesis along the river-estuary continuum of the Yangtze River.
Through field investigations, the researchers identified a robust correlation between dissolved carbon dioxide (CO2) and dissolved CH4. Based on the established predominance of hydrogenotrophic methanogenesis, they developed a process-based model. Historical CO2 data were further employed to retrospectively examine the historical fluctuations in CH4, uncovering a substantial reduction of 82.5% in CH4 emissions after the construction of the Three Gorges Dam.
"Our study provides new insights from a microbial perspective on CH4 cycling, and it is necessary to take the methanogenic pathway into account when predicting CH4 emissions from inland waters in the future," said Dr. Li.