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How Oxic Decomposition Impacts Organic Carbon Preservation At Big Cypress National Preserve, South Florida !"#$%&'()!*$+, )./01(+)23)4&("'/&, )5&(06$")7/("# 8 ) ) 9$:(*;1$";)0<)=$0%0#&'(%)2'&$"'$+)>"&?$*+&;@)0<)A%0*&B(,)=(&"$+?&%%$,)AC) Methodology Conclusions and Future Outlook References Introduction Data and Results Wetlands ("Blue Carbon" habitats) have been shown to be vital in the sequestration of CO 2 from the atmosphere and thus, understanding their role in global carbon preservation is critical. The wetlands of Big Cypress National Preserve, Florida (BICY) serve as an ideal location to examine the effects of water level on organic carbon (OC) preservation. ThirtyThree percent of BICY is estimated to be covered with cypress trees, many of which are found in "cypress domes," which are circular depressions that show a systematic spatial geomorphological and vegetational pattern. Oxic decomposition is well known to be more efficient in the breakdown of organic matter than anoxic decomposition. These wetlands experience high variability in water levels over time which is linked with oxygen availability in sediments. Thus, OC preservation should be impacted by changes in oxygen availability in sediment. Here, we examine the carbon (C) and nitrogen (N) concentrations and stable isotope ratios (! 13 C) in sediment cores to analyze the organic carbon distribution and preservation in wet (three TR sites) versus dry sites (three RP sites) within three distinct geologic formations. At each site, three cores were taken to represent the different environments at each cypress dome. At each site, 3 cores (center, intermediate, edge) were taken to represent the different environments at each cypress dome. All cores were subsampled, freeze dried and ground. Carbon (C) and Nitrogen (N) concentrations and stable carbon isotope ratios ( 13 C/ 12 C) were measured at the University of Florida (UF). Radiocarbon analyses on sediments were prepared at UF and analyzed by accelerator mass spectrometry at NOSAMS (National Ocean Sciences Accelerator Mass Spectrometry Facility, Woods Hole, MA) Both TR and RP sites showed greater abundance of organic carbon at centers than at edges likely due to greater aboveground biomass and better preservation of OC at centers. Both TR and RP surface sediments have vegetation alterations from C3 sources to more mixed C4 sources from center to edge. This is likely due to the greater water saturation exhibited at the center than at edge. !13C at TR centers showed greater shifts at certain depths that indicated possible OC source shift from C3 to more C4 sources throughout historical time while RP centers showed more stability down-core. Biomarkers (fatty acids) will be used to test the shifts in vegetation at the center as demonstrated by downcore !13 records. Utilizing plant end-members to compare current data and help support findings. ) 1. Hedges JI, Keil RG, Benner R (1997) What happens to terrestrial organic matter in the ocean? Organ Geochem 27:195-21 2. Huang, P.M., Yuncong Li, and M.E. Sumner. Handbook of Soil Sciences. Boca Raton, FL: CRC, 2012. Print. 3. Hulthe Gustaf Stefan Hulth and Per O.j Hall. "Effect of Oxygen on Degradation Rate of Refractory and Labile Organic Matter in Continental Margin Sediments." Geochimica Et Cosmochimica Acta 62.8 (1998): 1319-328. Web. 4. Reddy KR, Delaune RD (2008) Biogeochemistry of Wetlands: Science and Applications. CRC/Taylor & Francis, Boca Raton, FL, USA. Print. 5. Watts, Adam C., Danielle L. Watts, Matthew J. Cohen, James B. Heffernan, Daniel L. Mclaughlin Jonathan B. Martin, David A. Kaplan, Todd Z. Osborne, and Leda N. Kobziar "Evidence of Biogeomorphic Patterning in a Low-relief Karst Landscape." Earth Surface Processes and Landforms 39.15 (2014): 2027-037. Web. Hypothesis Values showed an enrichment trend from center to edge in both TR and RP surface sediments; this supports the vegetation alterations from mixed terrestrial C4 plant types (generally -6 to -15) to more algal-derived C3 (generally -24 to -34) sources. Figures 7-8. Organic carbon and bulk density are inversely proportional as organic-rich areas show less density. Figure 1. 13 C at TR had increased variability, indicating possible OC source shift from algal to cypress trees from past to present times. The C:N molar ratio also exhibits a change mid-depth that supports the vegetation shift seen through the 13 C analysis. Similar trends followed for TR2 and TR3 ( Figures 2-3. ) Figure 2. TR2 Figure 3. TR3 Figure 4. RP3 Figure 5. RP2 Figure 6. RP1 Figure 1. TR1 Figure 6. It is notable that 13 C at RP centers were relatively stable with depth. 13 C edges are more enriched than center and intermediate indicating either a shift in vegetation or possibly the preferential uptake of light isotopes by bacteria (Carbon-12 taken more readily than Carbon-13.) This pattern in shift is also observed in RP2 and RP3 ( Figures 4-5. ) Figure 7. Figure 8. Figure 9. Figure 9. In general, OC content at the surface decreased from center to edge, demonstrating the spatial vegetation differences in cypress domes. H 1 : The abundance of organic carbon in wetland sediments of Big Cypress Swamp, will be greater in sites that experience more frequent water inundation than those having more dry periods where oxygen exposure times are greater. Sub-H 1 : Areas exposed to recurring water saturation will have a relatively greater abundance of algal-derived organic matter in surface soils than at the drier sites.
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