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Saltwater intrusion driven by water extraction, coastal modifications, and climate change can potentially alter coastal wetland topography. Increased salinity and inundation can stress fresh or brackish vegetation, leading to decreased productivity and tissue death. Implications include reduced organic matter input to sediment, which slows accretion, and decreased root density, leading to soil compaction and erosion. Sulfate in seawater may accelerate microbial decomposition, reducing sediment organic matter content. We used a preserve on the Gulf Coast of Florida, where road construction isolated wetland to the north of the road from freshwater inputs it previously received, causing increased salinity, cabbage palm die-off, and decreased soil elevation evidenced by exposed tree roots. We took continuous water level and salinity measurements in saltwater-intruded areas to the north versus unaffected areas to the south. To determine whether soil organic matter cycling factors into observed soil elevation change, we measured labile and recalcitrant soil organic matter content at different depths, and decomposition rates. We found a sharp salinity increase to the north of the road, dampened tidal influence to the south, and significantly lower organic matter content to the south. Results suggest reduced organic matter content may be a factor in decreased soil elevation. |