Tidal Wetland Soil Organic Carbon in the Conterminous United States
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Tidal wetlands contain large reservoirs of carbon in their soils and sequester carbon dioxide (CO₂) at greater rates per unit area than nearly any ecosystem. The spatial distribution of this carbon influences climate and wetland policy. To assist with international accords such as the Paris Climate Agreement, national-level assessments such as the United States (U.S.) National Greenhouse Gas Inventory, and regional and local evaluation of CO₂ sequestration credits, I developed a geodatabase (CoBluCarb) and high-resolution maps of soil organic carbon (SOC) distribution by linking National Wetlands Inventory data with U.S. Soil Survey Geographic Database. For over 600,000 wetlands, total carbon stock and organic carbon density was calculated at 5-cm vertical resolution from 0 to 300 cm depth. There are 1,153-1,359 Tg of SOC in the upper 0-100 cm of soils across a total of 24,945.9 km² of tidal wetlands, twice as much carbon as the most recent national estimate. To assist conservation efforts and better understand the biogeochemical processes of these wetlands, I determined the statistical correlations of 45 different environmental variables and 5 different aspect factors with the distribution of this SOC. Environmental variables were divided into oceanic, terrestrial, and geographic variables to understand the array of potential influences. Geographic variables were the strongest predictors of SOC. Longitude correlated reasonably well with SOC density at the national scale (r² = 0.52), Gulf Coast (r² = 0.51), and West Coast (r² = 0.84). To determine SOC outward flux, I created current status maps showing wetland accretion, soil respiration, and remaining SOC stocks for the coastal wetlands in the conterminous United States. The calculated outward fluxes and remaining stocks were (1) from soil to the atmosphere, (2) from soil to surrounding water, and (3) the remaining recalcitrant stock of SOC. Predictive maps estimated spatial distribution of the fluxes, providing a comprehensive overview in the coastal US. Overall, regional scales may provide the most promise for predicting SOC. It is possible to use standardized values at a range of 0-100 cm of the soil profile, to provide first-order quantification and to evaluate future changes in carbon stocks in response to environmental variables.
Hinson, Audra Leigh (2017). Tidal Wetland Soil Organic Carbon in the Conterminous United States. Doctoral dissertation, Texas A & M University. Available electronically from