Spatial-Temporal Carbon Assessment within the St. Johns River Basin.

Rising levels of greenhouse gas concentrations in the atmosphere have raised concern that human actions are altering the world’s climate.   Land use change may be a significant contributor to this problem, but also might provide a way to re-capture carbon into terrestrial systems.  The world soil carbon reservoir is approximately four times greater than the atmospheric carbon reservoir and five times greater than the biotic reservoir; as a result, relatively small changes in the terrestrial carbon pool could have a large impact on the climate.
The objectives of this project were intended to  i) assess and compare current and historic soil carbon stocks; ii) quantify estimates of terrestrial carbon (both soil carbon and aboveground biomass carbon); and iii) investigate relationships between soil carbon stocks and environmental properties (such as land-cover/land-use, biomass, and soil types) and stressors (such as temperature or land-use change).  This study was conducted in the St. Johns River Basin (22,251 km²) in Florida that has seen significant land-use change.  Three different soil organic carbon datasets were used: i) Florida Soil Characterization Database (1965 – 1996); ii) Soil Data Mart (Natural Resource Conservation Service) (1961 – 2004); and new site observations (2008/2009) with 144 locations. Ordinary and block kriging were used to interpolate site-specific observations across the basin.   Geoprocessing techniques were used to calculate soil carbon and biomass carbon, soil carbon sequestration rates, and to assess how soil carbon properties interact with environmental properties and stressors.  Our study indicated that major amounts of soil carbon are stored in wetlands, swamps and marsh systems that cover approximately 30% of the study area, whereas major proportions of aboveground carbon is bound in biomass with 15.7% pinelands and 6.5% xeric upland forest.  Spodosols with 30.8% coverage and Histosols with 9.8% coverage contributed the largest amount to the soil carbon budget.