RELATIONSHIP BETWEEN IRON MINERALS AND CARBON IN MARSH-FORESTED TRANSITIONS
Date
2025-05
Authors
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Journal ISSN
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Publisher
University of Delaware
Abstract
Marsh-forested transitions, or interfaces between upland forest systems and
tidal creeks, are dynamic coastal systems that play an important role in carbon
sequestration and mineral cycling. As the Delmarva Peninsula experiences increased
rates of relative sea level rise, it is increasingly urgent to understand biogeochemical
cycling within these critical areas. In this study, we investigated variability and
relationships of crystalline iron (Fe) oxides, short-range order Fe oxides, and water extractable organic carbon (WEOC) along three marsh-forested transitions located in
Delaware, Maryland, and Virginia. To assess Fe mineral concentrations in soils, we
used acid ammonium oxalate extractions for short-range order Fe oxides and citrate dithionite-bicarbonate to extract crystalline Fe oxides. For carbon in soils, we used
water extractions to determine WEOC concentrations and CHNS combustion analysis
to quantify total carbon. We observed variability in Fe oxide and WEOC
concentrations at site, subsite, and depth. In contrast with previous literature indicating
positive relationships between short-range order Fe oxides and carbon concentrations,
our results showed no statistically significant relationships. We did, however, see
significant negative relationships between crystalline Fe oxides and carbon at upland
forest subsites. The lack of correlation between short-range order Fe oxides and
carbon concentrations may be influenced by the dynamic redox conditions of marsh forested systems, which can prevent formation of Fe-organic complexes. Negative
relationships between crystalline Fe oxides and carbon indicate limited carbon
sequestration abilities of upland forests. These findings highlight the complex nature
of biogeochemical cycling along marsh-forested transitions and demonstrate the
influence that site-specific factors like redox conditions, salinity, and microbial
communities could have on these cycles. Our research had limited scale due to
sampling regime. Future research should emphasize additional sampling at the spatial
and temporal scale to fully understand Fe-carbon interactions and carbon cycling in
these critical systems.