TEMPORAL PATTERNS OF WETLAND CONVERSION AND SOIL ORGANIC CARBON (SOC) DYNAMICS IN THE BRAZILIAN CERRADO

Despite their limited extent (6% of the Earth's surface), wetlands store a significant proportion of global soil organic carbon (SOC) (202-535 Pg C) and act as important carbon sinks or sources. Their sensitivity to environmental changes makes anthropogenic conversion a factor in carbon release, intensifying climate change. In the Brazilian Cerrado, a biome critical for national water security and under intense pressure from agriculture and livestock, wetlands represent 3.4% of the biome's area and have suffered a loss of 687,000 hectares (10% reduction) in 39 years. Understanding the vulnerability of SOC in these areas to land use change is essential. Therefore, this research investigated the relationship between the stability time of primary wetlands and changes in the SOC stock after conversion to anthropic use. Using data from MapBiomas (Collection 9) and MapBiomas Soil (Collection 2 beta), analyzed in Google Earth Engine, the study focused on primary wetlands with single conversions, categorizing stability periods in 5-year intervals (1985-2023). The SOC stock was quantified at the beginning of the series, at the end of the series, and at the time of conversion, comparing variations between converted areas with different periods of wetland stability. The results showed an average annual SOC stocks loss of 0.0059 t/ha after conversion, with peaks of over 2 t/ha/year in certain regions. The largest losses were observed in areas converted to agriculture, while silviculture and pasture showed smaller losses or localized gains. Conversions in the first 15 years of the time series showed the largest absolute losses (between -0.13 and -0.18 t/ha), while more recent conversions showed losses close to zero. However, the observed relationship between time to conversion and magnitude of SOC loss suggests that recently converted wetlands may have higher initial SOC stocks and consequently greater vulnerability to absolute loss after conversion. These results underscore the importance of Cerrado wetlands as strategic carbon reservoirs and demonstrate the significant potential for SOC loss due to deforestation and conversion to anthropogenic use, especially if early and without conservation management practices. The research reinforces the urgency of land-use history-based conservation strategies, especially in the current context of climate emergency.