Relationship Between Carbon and Amorphous Iron Oxides in Marsh-Forested Transitions

• Tara Metters, Environmental Science, University of Delaware

• Angelia Seyfferth, Plant and Soil Science, University of Delaware

The coastal critical zone, which includes marsh-forested transitions, is a biogeochemically diverse area that provides valuable ecosystem services, such as carbon sequestration. Marsh sediments store and sequester more carbon per unit area than terrestrial ecosystems. This sequestered carbon, also known as Blue Carbon, has entered conversations regarding climate change mitigation. Iron-mineral associations are one of the primary ways dissolved organic carbon is sequestered in the environment. When carbon is sorbed to iron minerals, it is considered less likely to undergo mineralization, remaining in soils rather than being released as CO2 gas. However, marshes and transition zones that become inundated with salt water undergo redox oscillations that can change the state of iron minerals and destabilize these associations. Understanding how carbon in these associations is affected as our coasts change is imperative as we plan for sea level rise and increased storm surge events.  

For this project, I analyzed soil cores collected from three marsh-forested field sites along the Delmarva peninsula. At each field site, there were four distinct subsites along these transitions: high forest, mid forest, low forest, and phragmites marsh. For each of these sites and their respective subsites I performed acid ammonium oxalate extractions to target amorphous iron oxides present in the soils, and combustion analysis for the total carbon content of the soils. The resulting data shows no significant relationship between amorphous iron and total carbon content of the soils across the three sites. This indicates that another factor is at play regarding iron-carbon interactions in these soils, such as the impact of crystalline iron oxides. Future research such as a citrate-bicarbonate-dithionite extraction on these soils would give further insight into how crystalline iron oxides impact carbon fluxes in these dynamic ecosystems.