Saltwater encroachment

The Florida Everglades is considered as a vulnerable wetland composed primary of organic rich peat soils, experiencing saltwater intrusion. Impact of increasing salinity on the strength and deformation properties of peat is unknown. A laboratory study was undertaken to evaluate how the growing salinity level due to sea level rise may alter the compressibility behavior of the Everglades soils. Sixteen 1-dimensional oedometer tests were conducted on undisturbed Everglades peat soils in two phases. Phase I included samples from Site 1 (saltwater) and Site 3 (freshwater) without any salinity addition. Phase II consisted of soil from Site 3 (freshwater) saturated in six different levels of salinity artificially added to the samples. Compressibility properties investigated in this study include compression index (Cc), coefficient of consolidation (Cv), hydraulic conductivity (K), and the Ca/Cc ratio. In general, it was observed that the increase in salinity beyond a threshold value tends to increase the soil compressibility properties, indicating a possible reduction in soil stability with saltwater intrusion.

Saltwater intrusion is threatening coastal wetlands through alteration of the natural communities leading to native species loss. In southern Florida, the Pond Apple Slough is experiencing tidally driven saltwater intrusion, which is thought to be responsible for the invasion of a marine isopod, Sphaeroma terebrans, into the native, dominant pond apple trees. The isopod appears to be responsible for the death of pond apple trees in the site. The isopod's distribution on trees within the slough appears to be controlled by the period of inundation and distance from the source of saltwater. Restriction of tidal water entering the site may limit the isopod's distribution on the pond apple trees.