Net carbon dioxide exchange in a hyperseasonal cattle pasture in the northern Pantanal wetland of Brazil

Abstract

The Pantanal is the largest seasonal wetland in the world with a landscape that consists of a mosaic of permanent aquatic habitats, and floodable and non-floodable savannas, pastures and forests. Drought events are expected to occur more frequently in the Pantanal biome under future climate conditions, but the effects of land management and hydrological extremes on pastures have been poorly studied at spatial scales relevant to local livestock. In this study, we measured CO2C fluxes using eddy covariance over a hydrological year on pastures within a cattle farm in the Brazilian Pantanal that experienced seasonal flooding. Our measurements show that seasonally flooded pastures were large emitters of CO2C, contributing 337 g CO2C m−2 year−1 to the atmosphere. During flooding, when the soils were anaerobic, and soil O2 was close to zero, the flooded pasture was a net sink of -18 g CO2C m−2, while during the aerobic phase (soil O2 > 15%) the pasture was a significant CO2 source to the atmosphere (301 g CO2C m−2). Transitions to and from anaerobic conditions corresponded to 54 g CO2C m−2. Our results indicate that the seasonally flooded cattle pastures in the Brazilian Pantanal may be an important regional source of CO2C for the atmosphere. Better management, and use of drought resistant grasses, may be a way to improve soil C stocks and limit emissions, especially as global climate change is anticipated to increase heating and drying for the Pantanal biome.