Agricultural activity enhances CO2 and CH4 emissions after sediment rewetting in a tropical semiarid reservoir

In response to climate change, prolonged droughts in semiarid regions have increased; consequently, reservoir sediments have been more frequently exposed to the atmosphere. Because of the large proportion of drawdown areas, reservoir sediments are used for agricultural activity. Agricultural intensification creates new biochemically active spots that may enhance the fluxes of carbon dioxide (CO2) and methane (CH4) after reservoir refilling. Here, we experimentally evaluated the influence of rewetting on CO2 and CH4 fluxes from the drawdown area of a Brazilian semiarid reservoir with and without agricultural activity. The observed CO2 and CH4 emissions were two and three times higher, respectively, in the sediment with agricultural activity. Higher values of organic carbon, organic matter, and nutrients in the crop-related sediment were the best predictors for the highest CO2 and CH4 emission rates. It is essential to better understand regional scenarios, such as emissions from semiarid regions, to refine the role of human-made reservoirs in the global C balance. Agricultural practices are becoming increasingly common because of extended droughts that keep reservoir sediment exposed to the atmosphere for longer periods. The response of sediments to crops suggests that land-use changes can promote positive and powerful climate feedback.