Coastal wetlands are globally significant carbon (C) and nitrogen (N) sinks, yet their long-term stability is threatened by climate-driven vegetation shifts and anthropogenic nutrient inputs. This dissertation investigates how mangrove encroachment, N additions, and soil physical structure regulate the stabilization, formation, and mineralization of organic matter (OM) across Florida’s marsh–mangrove ecotones. Chapter 1 examines how vegetation type, N fertilization, and hydrogeomorphic setting influence soil biogeochemical properties and the partitioning of soil organic matter (SOM) into particulate (POM) and mineral-associated (MAOM) pools. Chapter 2 uses a field-based ¹⁵N tracer experiment to examine MAOM–N stabilization in greater depth by quantify how newly added N becomes stabilized within these SOM pools over time under different vegetation and fertilization conditions. Chapter 3 extends this approach by tracing ¹⁵N incorporation through multiple physical fractions to distinguish between in vivo (microbial transformation) and ex vivo (direct sorption) SOM formation pathways, while also quantifying aboveground–belowground coupling of N cycling. Chapter 4 complements the field studies with controlled anaerobic incubations across multiple wetland sites to evaluate how soil size fractions regulate N mineralization, nutrient release, and greenhouse gas fluxes. Together, these studies integrate field and laboratory approaches to link microbial and mineral-level processes with ecosystem-scale biogeochemical outcomes. By combining isotopic tracing, fractionation, and incubation experiments, this research advances mechanistic understanding of C and N stabilization in dynamic coastal wetlands and provides key insights for predicting their resilience, nutrient retention, and greenhouse gas dynamics under accelerating environmental change.
Mercedes M. Pinzon Delgado
Dr. Lisa Chambers, Advisor
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