Leveraging Wetland Soil Carbon Data Sets to Address Spatial Representation of Wetland Carbon Stocks for the Counterminous US (CONUS)

Understanding the spatial representation of wetland soil carbon stocks is important for overall carbon cycling projections because wetlands have the capability to sequester a large amount of organic carbon relative to their area. An in-depth analysis of wetland soil data was conducted to produce a map of wetland soil organic carbon stocks for the conterminous United States and leverage these databases to explore carbon related questions. This project includes CONUS wetland sample data from the EPA National Wetland Condition Assessment (NWCA) data set, wall-to-wall organic carbon percentage data from the USDA NRCS Soil Survey Geographic Database (SSURGO) data set, coastal wetland soil carbon data from Smithsonian Coastal Carbon Research Coordination Network (CCRCN), and additional soil data from the wetlands surveyed as a part of NSF National Ecological Observatory Network (NEON) data set. Information from SSURGO was extracted as a binned frequency table using a Python script. All further analyses were carried out in R programming language, allowing for the mean and several quantiles to be compared between data sets on a region-by-region and vegetation type-by-vegetation-type basis. A broken stick linear regression technique was applied to the NWCA data on organic carbon content, to determine “mineral vs organic” model representation for soil carbon stocks to 1m depth. Both a linear least square and a quantile fit technique were explored for this analysis. Overall the results of these analyses support the position that SSURGO and NWCA datasets are cross validated at a regional scale, although there may be issues of representative sampling in some cases. This work serves as a foundational element for an ongoing USGS National Wetland Carbon Assessment and modeling project.

Impact/Purpose

There are many efforts across different governmental agencies and academic facilities to measure soil carbon across the continental United States. Carbon storage in wetlands is of particular interest to scientists because the characteristics associated with wetlands allow carbon to be stored in large quantities in these ecosystems. In an effort to map wetland soil carbon stocks across the US, scientists from the US Geological Survey and the US Environmental Protection Agency are working together to combine datasets from the National Wetland Condition Assessment (NWCA), the Soil Survey Geographic Database (SSURGO), coastal wetland carbon data from Coastal Carbon Research Coordination Network (CCRCN), and additional data from the wetlands surveyed as a part of National Ecological Observatory Network (NEON). This research effort highlights the importance of collecting probabilistic data through the NWCA and provides a foundation for future modeling efforts.

Citation

Uhran, B., L. Windham-Myers, N. Bliss, A. Nahlik, E. Sundquist, G. Richter, AND C. LaFosse Stagg. Leveraging Wetland Soil Carbon Data Sets to Address Spatial Representation of Wetland Carbon Stocks for the Counterminous US (CONUS). American Geophysical Union, San Francisco, CA, December 09 - 13, 2019.