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Carbon Storage in US Wetlands.
Nahlik, A. AND S. Fennessy. Carbon Storage in US Wetlands. Ecological Society of America, Portland, Oregon, August 06 - 11, 2017.
This presentation will discuss some of the major results from an analysis of carbon storage in US wetlands, the data of which originated from the 2011 National Wetland Condition Assessment (NWCA) and results of which were recently published in Nature Communications (Nahlik & Fennessy 2016 "Carbon Storage in US Wetlands" Nature Communications Article Number 13835). The broad audience of the Ecological Society of America's annual meeting is an ideal forum to showcase these results and to highlight the importance of national surveys, such as the NWCA. This interaction will likely increase interest in the USEPA's National Aquatic Resource Surveys and contribute to wetland science by increasing the number of scientists who will read the NWCA reports and use the data from the survey in additional analysis and research efforts.
Background/Question/Methods Wetland soils contain some of the highest stores of soil carbon in the biosphere. However, there is little understanding of the quantity and distribution of carbon stored in US wetlands or of the potential effects of human disturbance on these stocks. We provide unbiased estimates of soil carbon stocks for wetlands at regional and national scales and describe how soil carbon stocks vary by anthropogenic disturbance to the wetland. To estimate the quantity and distribution of carbon stocks in wetlands of the conterminous US, we used data gathered in the field as part of the 2011 National Wetland Condition Assessment (NWCA) conducted by USEPA. During the growing season, field crews collected soil samples by horizon from 120-cm deep soil pits at 967 randomly selected wetland sites. Soil samples were analyzed for bulk density and organic carbon. We applied site carbon stock averages by soil depth back to the national population of wetlands and to several subpopulations, including five geographic areas and anthropogenic disturbance level. Disturbance levels were categorized by the NWCA as least, intermediately, or most disturbed using a priori defined physical, chemical, and biological indicators that were observable at the time of the site visit.Results/Conclusions We find that wetlands in the conterminous US store a total of 11.52 PgC – roughly equivalent to four years of annual carbon emissions by the US, with the greatest soil carbon densities in the Eastern Mountains and Upper Midwest region, averaging 478±58 tC ha-1. Furthermore, our data suggest a relationship between carbon stocks and anthropogenic disturbance, with more carbon being stored in least disturbed wetlands (407±51 tC ha-1) than in most disturbed wetlands (236±47 tC ha-1). These data provide the first empirical, unbiased estimates of soil carbon for targeted populations of wetlands at the national scale. This is also the first time the relationship between human disturbance and wetland carbon stocks has been demonstrated on a national scale. This effort exemplifies the power of collecting national data, and the results of this research further support indicator development efforts by USEPA for future NWCA surveys. The data we provide here are necessary to effectively identify characteristics of wetlands or types of wetlands in particular geographic areas that contain disproportionately large carbon stores – critical information if we are to implement policies related to climate protection targeted to where they can have the most positive effect.