Understanding peat soil deformation and biogenic gas dynamics across a salinity gradient in the southwestern Everglades

Abstract:

Saltwater intrusion poses a significant threat to coastal peatlands, particularly to those that have experienced anthropogenic reductions in water flow like the Florida Everglades. This salinization can affect wetland biogeochemistry and result in accelerated soil decomposition, altered carbon storage and biogeochemical cycling, and ultimately peat collapse. Peat collapse is a unique form of shallow subsidence in highly organic soils characterized by a loss of soil strength and structural integrity that leads to elevation loss below the threshold for emergent plant growth and natural recovery. Areas of peat collapse are currently observable across areas of the southwestern coastal Everglades and coincide with saltwater intrusion, yet the mechanisms behind this collapse are not well understood. In this study we use a combination of laboratory ground penetrating radar measurements (GPR), laboratory and field-based time-lapse photography, gas traps, deformation rods to investigate how salinization affects peat soils in relation to: 1) changes in production, accumulation and release of biogenic gases (e.g. CH₄ and CO₂) within the peat soil monoliths at the laboratory scale, and fixed platforms at three locations distributed across a landscape-scale salinity gradient; and 2) changes in their physical properties (i.e. porosity) and its relevance for peat matrix deformation at the laboratory and field scales in the southwestern Everglades. Field scale electrical resistivity surveys were also conducted at each platform location to image peat collapse areas and to infer potential lithological controls and changes in peat properties that may lead to peat collapse.