Globally doubled methane emissions from nutrient-enriched rivers

ABSTRACT Methane (CH4) accounts for about one-third of the current anthropogenic greenhouse gas-driven warming. Rivers, particularly those draining human-impacted landscapes, are important sources of CH4 to the atmosphere. Yet, effective mitigation of this important flux remains elusive due to the lack of accurate quantification of human-induced emissions and a poor understanding of its key aquatic drivers. Here, we demonstrate that CH4 emission rates from global nutrient-enriched rivers in human-impacted regions more than double (2.5-fold) those from pristine rivers. Importantly, a strong association is identified between CH4 flux and concentrations of total phosphorus and ammonium nitrogen in these systems. This relationship is mediated by increased autochthonous and exogenous supplies of labile organic substrates, enhanced methanogen abundance and diversity, and extended anoxia in nutrient-enriched rivers. Quantitative modeling incorporating nutrient effects estimates global CH4 emissions from nutrient-enriched rivers at 9.7 ± 1.1 Tg CH4 yr−1, of which 22%–49% could be mitigated by reducing current nutrient concentrations to levels constrained by sustainable development goals, half of their current levels, or pristine conditions. These findings highlight the substantial potential for effective mitigation of riverine CH4 emissions via coordinated riverine nutrient management at the global scale.