On the methane paradox: Transport from shallow water zones rather than in situ methanogenesis is the major source of CH_4 in the open surface water of lakes

摘要

Estimates of global methane (CH_4) emissions from lakes and the contributions of different pathways are currently under debate. In situ methanogenesis linked to algae growth was recently suggested to be the major source of CH_4 fluxes from aquatic systems. However, based on our very large data set on CH_4 distributions within lakes, we demonstrate here that methane-enriched water from shallow water zones is the most likely source of the basin-wide mean CH_4 concentrations in the surface water of lakes. Consistently, the mean surface CH_4 concentrations are significantly correlated with the ratio between the surface area of the shallow water zone and the entire lake, fA,s/t, but not with the total surface area. The categorization of CH_4 fluxes according to fA,s/t may therefore improve global estimates of CH_4 emissions from lakes. Furthermore, CH_4 concentrations increase substantially with water temperature, indicating that seasonally resolved data are required to accurately estimate annual CH_4 emissions.