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Soil carbon (C) storage is a globally important ecosystem service with the potential to contribute to climate change mitigation. Wetlands are heavily researched hot spots for soil C storage. Despite the growing number of wetland soil C inventories, most studies focus only on total C quantification; there is limited application of methods that evaluate differences in C stability and vulnerability to mineralization within the C pool. Permanganate oxidizable C (POXC) is a well-established soil health indicator in agriculture shown to be sensitive to changing conditions or management regimes and may prove equally informative in wetland studies. This research quantified POXC in six diverse wetland soils that differed greatly in organic matter content and spanned both freshwater and saltwater habitats, then evaluated the relationship between POXC and basic soil C properties, microbial indicators, and physical and chemical fractionation metrics. Results showed POXC averaged ∼ 37 times greater in wetlands than upland agricultural soils, but was less robust in differentiating between individual wetlands than total C or organic matter content. Rather, the ratio of POXC to soil organic C may be a more informative metric for evaluating the proportion of slightly processed C in wetland soils. Significant correlations were found between POXC and almost all other soil properties measured, suggesting POXC could be a rapid, reliable, and economical proxy for other analyses. Overall, POXC shows potential for providing novel information about wetland soil C stability, but requires additional research to improve interpretability. Applying POXC analysis in time series data collection and before-after-control impact experiments may be particularly informative for wetland management. 

Hurricanes can alter the rates and trajectories of biogeochemical cycling in coastal wetlands. Defoliation and vegetation death can lead to increased soil temperatures, and storm surge can variously cause erosion or deposition of sediment leading to changes in soil bulk density, nutrient composition, and redox characteristics. The objective of this study was to compare the biogeochemistry of pre-storm soils and a carbonate-rich sediment layer deposited by Hurricane Irma that made landfall in southwest Florida as a category 3 storm in September 2017. We predicted that indicators of biogeochemical activity (e.g., potential soil respiration rates, microbial biomass (MBC), and extracellular enzyme activities) would be lower in the storm sediment layer because of its lower organic matter content relative to pre-storm soils. There were few differences between the storm sediment and pre-storm soils at two of the sites closest to the Gulf of Mexico (GOM). This suggests that marine deposition regularly influences soil formation at these sites and is not something that occurs only during hurricanes. At a third site, 8 km from the GOM, the pre-storm soils had much greater concentrations of organic matter, total N, total P, MBC, and higher potential respiration rates than the storm layer. At this same site, CO2 fluxes from intact soil cores containing a layer of storm sediment were 30% lower than those without it. This suggests that sediment deposition from storm surge has the potential to preserve historically sequestered carbon in coastal soils through reduced respiratory losses.