Carbon Storage in Wetlands of the United States: 2011-2016
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Wetland soils contain some of the densest stores of carbon in the biosphere. However, there is little understanding of the quantity and distribution of carbon stored across US wetlands, or how these stocks change over time. Soil carbon was measured using the same protocol to a maximum depth ranging from 90 to 120 cm at approximately 1000 probabilistically selected wetland sites in each of the 2011 and 2016 National Wetland Condition Assessment (NWCA); 195 of these sites were sampled for carbon in both survey years. Preliminary analyses of the resampled sites show no difference in carbon density in the top 10 cm between years but indicate a decrease in carbon density in deeper layers over the 5-year period. We hypothesize that temporal decreases in soil carbon density deeper in the soil profile are due to human disturbance or climate change, as human disturbance was correlated to lower carbon densities in the deepest (60–90 cm and 90–120 cm) soil layers in the 2011 NWCA data (Nahlik & Fennessy, 2016, NatComm:13835). We explore human disturbance and other mechanisms that may be impacting carbon stores over time. These data provide the first empirical, unbiased estimates of change in soil carbon for wetlands of the United States and demonstrate the power of probabilistic surveys for upscaling data collected at a limited number of sites to regional and national scales. Understanding wetland carbon storage at large scales provides critical insight for the effective management of carbon stocks for climate regulation.