Drought legacy regulates the stability of greenhouse gases emissions of aquatic sediments

Abstract

Abstract Although climate change models predict more frequent and severe climatic events such as droughts, the effects of drought on greenhouse gas (GHG) emissions from lentic ecosystems are still poorly understood. Moreover, little is known of the extent to which drought effects on GHG emissions depends on the occurrence and intensity of previous droughts (legacy effect). Here, we examined the temporal stability of methane (CH4) and carbon dioxide (CO2) emissions during rewetting after a drought, and how drought legacy modulates this response. Laboratory microcosms containing sediments from natural lentic ecosystems were pre-exposed to drying-rewetting treatments (hereafter “D-RW event”) that differed by the durations of both the drying and rewetting periods. Then, we analyzed the resistance and the recovery rates of CH4 and CO2 emissions following a second drying-rewetting event equally established in all treatments. Water column was kept constant in controls. We found a pulse of CH4 and CO2 emissions upon the second dry-rewetting event, followed by a progressive recovery toward control emissions. This response was regulated by the drought legacy effect: the recovery of GHG emissions was faster in microcosms that had been subjected to a previous drought. For CO2 emissions, the drought legacy effect was stronger (faster recovery) where previous drought was longer. We therefore emphasize the incorporation of GHG emissions during D-RW events into GHG emission estimates, especially because climate models predict scenarios of drought intensification. While contemporary climate should be the dominant driver of GHGs from lentic ecosystems, previous drought can also regulate their response to D-RW events.