Global methane and nitrous oxide emissions from inland waters and estuaries.

Inland waters (rivers, reservoirs, lakes, ponds, streams) and estuaries are significant emitters of methane (CH ) and nitrous oxide (N O) to the atmosphere, while global estimates of these emissions have been hampered due to the lack of a worldwide comprehensive data set of CH and N O flux components. Here, we synthesize 2997 in-situ flux or concentration measurements of CH and N O from 277 peer-reviewed publications to estimate global CH and N O emissions from inland waters and estuaries. Inland waters including rivers, reservoirs, lakes, and streams together release 95.18 Tg CH  year (ebullition plus diffusion) and 1.48 Tg N O year (diffusion) to the atmosphere, yielding an overall CO -equivalent emission total of 3.06 Pg CO  year . The estimate of CH and N O emissions represents roughly 60% of CO emissions (5.13 Pg CO  year ) from these four inland aquatic systems, among which lakes act as the largest emitter for both CH and N O. Ebullition showed as a dominant flux component of CH , contributing up to 62%-84% of total CH fluxes across all inland waters. Chamber-derived CH emission rates are significantly greater than those determined by diffusion model-based methods for commonly capturing of both diffusive and ebullitive fluxes. Water dissolved oxygen (DO) showed as a dominant factor among all variables to influence both CH (diffusive and ebullitive) and N O fluxes from inland waters. Our study reveals a major oversight in regional and global CH budgets from inland waters, caused by neglecting the dominant role of ebullition pathways in those emissions. The estimated indirect N O EF values suggest that a downward refinement is required in current IPCC default EF values for inland waters and estuaries. Our findings further indicate that a comprehensive understanding of the magnitude and patterns of CH and N O emissions from inland waters and estuaries is essential in defining the way of how these aquatic systems will shape our climate.