EXPLORING CONTROLS ON CARBON BURIAL IN TROPICAL FLOODPLAIN LAKES IN THE PANTANAL WETLANDS

Tropical wetlands are important ecosystems in the global carbon cycle that are highly sensitive to climate change. Therefore, understanding the dynamics of carbon burial and transformations in these settings is essential. Carbon dynamics are still understudied in the Pantanal wetlands, particularly in the relatively large floodplain lakes connected with the Paraguay River. Here, satellite image analysis is paired with direct sediment geochemical measurements (TOC, TN, δ¹³C, and δ¹⁵N) to create a more comprehensive picture of carbon deposition in six representative lake basins. Our results revealed that the open water area of these lakes expands seasonally with the arrival of monsoon rainfall and river flooding, and contracts as flooding abates in the winter months. During the wet season, the six lakes expand to cover ~910 km² in aggregate; this area retracts to ~546 km² in the dry season. As a result of the seasonal changes in morphology, dense macrophytes can colonize ~40% of the total lake area, which in turn promotes high levels of carbon burial. Carbon accumulation at the open water area is highly variable with respect to provenance and quantity within each of the Pantanal floodplain lakes. Among the lakes as a total group, surface sediment TOC concentrations range from 0.2 wt.% to 27.5 wt.%. Two distinct patterns are apparent in the data: (a) lakes that become deeper without major surface area changes, exhibiting organic matter deposition primarily in the depocenter, and (b) lakes marked by considerable lateral expansion, with low gradient lake floors and shallow swampy margins during the dry season, resulting in high-density colonization by aquatic macrophytes. Our findings highlight the importance of considering seasonal hydrological dynamics, lake morphology and the distribution and production of emergent aquatic plant life for understanding carbon burial processes in the Pantanal and provide vital information for wetland management and conservation strategies.