Land use, land use change and soil carbon sequestration in the St. Johns River Basin, Florida, USA

Land use change is widely recognized as a net source of greenhouse gas emissions at the global scale. Most of these emissions are attributed to losses from aboveground terrestrial pools such as deforestation. However, much less is known about the effects of land use change on soil carbon pools at regional scales. To address this problem, relationships between soil organic carbon (SOC), land use/land cover (LULC) classes, and LULC change were investigated at the regional scale. A legacy soil survey was used in conjunction with a new, contemporary sampling campaign to determine SOC change through time. Together, the two datasets cover an approximate 40-year time period (1965 to 2009). The greatest densities of SOC were documented in wetland classes. Specifically, soils of Hardwood Swamp, Cypress Swamp, and Mixed Urban consisted of both residential Wetland Forest contained 9.8, 9.5, and 7.8 g C m− 2. In regard to absolute storage, or SOC stocks, Hardwood Swamp, Pineland, and Urban ranked highest and contained 14.4, 13.3, and 9.9 Tg C, respectively. The effect of LULC change was mixed, and resulted in both gains and losses of SOC at the field scale. At the regional scale, median SOC increased by 16.9 g C m− 2 yr− 1. Urbanization of natural landscapes resulted in the largest rate of sequestration, which increased SOC by 37.1 g C m− 2 yr− 1. The largest losses were documented in LULC classes converted from Improved Pasture to Rangeland, which decreased SOC by 8.5 g m− 2 yr− 1.