Greenhouse gas emissions from human-impacted lakes and rivers globally: Implications for carbon mitigation

Global lakes and rivers are significant sources of greenhouse gases (GHGs) to the atmosphere. Rapid socioeconomic development has increased nutrient loadings from various anthropogenic activities, such as agricultural practices, reclaimed water containing nutrients, and other point and non-point source pollution, into these water bodies, resulting in significant variations in GHG fluxes. However, the extent to which these human-impacted lakes and rivers contribute to GHG emissions relative to their respective global totals remains unknown, hindering the estimation of GHG emission reduction potential and the development of effective mitigation strategies. Here, we addressed this gap using meta-analyses combined with multiple models. For lakes, human-impacted lakes cover one-fifth of the total lake area yet contribute over one-third of total lake emissions, with disproportionately high emissions of CH₄ and N₂O. Within human-impacted lakes, those larger than 0.1 km² are the major contributors to GHG emissions. We speculate that global lake GHG emissions could be reduced by over one-fifth, if fluxes of human-impacted lakes are decreased to levels comparable to those of natural non-permafrost lakes through sustainable lake water quality management. For rivers draining human-impacted regions, CH₄ fluxes are significantly elevated by nutrient enrichment. Quantitative modeling accounting for nutrient effects estimates that human-impacted rivers contribute over one-third of total riverine CH₄ emissions. More than half of these emissions are attributable to anthropogenic nutrient enrichment. We speculate a one-third to half reduction potential for global human-impacted rivers under scenarios where nutrient levels are halved or reduced to natural/ semi-natural conditions. Our study highlights the critical role of anthropogenic activities in amplifying GHG emissions from global lakes and rivers, and emphasizes a “win-win” strategy: achieving both nutrient control and GHG mitigation through sustainable water quality management.