Rivers draining contrasting landscapes exhibit distinct potentials to emit diffusive methane (CH4)

Abstract

Methane (CH4) is the second most important greenhouse gas, contributing approximately 17% of radiative forcing, and CH4 emissions from river networks due to intensified human activities have become a worldwide issue. However, there is a dearth of information on the CH4 emission potentials of different rivers, especially those draining contrasting watershed landscapes. Here, we examined the spatial variability of diffusive CH4 emissions and discerned the roles of environmental factors in influencing CH4 production in different river reaches (agricultural, urban, forested and mixed-landscape rivers) from the Chaohu Lake Basin in eastern China. According to our results, the urban rivers most frequently exhibited extremely high CH4 concentrations, with a mean concentration of 5.46 μmol L−1, equivalent to 4.1, 9.7, and 7.2 times those measured in the agricultural, forested, and mixed-landscape rivers, respectively. The availability of carbon sources and total phosphorus were commonly identified as the most important factors for CH4 production in agricultural and urban rivers. Dissolved oxygen and oxidation-reduction potential were separately discerned as important factors for the forested and mixed-landscape rivers, respectively. Monte Carlo flux estimations demonstrated that rivers draining contrasting landscapes exhibit distinct potentials to emit CH4. The urban rivers had the highest CH4 emissions, with a flux of 9.44 mmol m−2 d−1, which was 5.1–10.4 times higher than those of the other river reaches. Overall, our study highlighted that management actions should be specifically targeted at the river reaches with the highest emission potentials and should carefully consider the influences of different riverine environmental conditions as projected by their watershed landscapes.