Wetlands are key ecological habitats that provide a range of important ecosystem functions and services. Invasive species are leading drivers of wetland biodiversity loss and environmental change. In Trinidad, sedge invasion has caused significant threats to wetland diversity and agriculture. The invasive sedge species (E. mutata and C. articulates) increase the frequency and intensity of seasonal wetland fires resulting in the loss of livelihoods for people depending on the goods and services the wetland provides. We focused on assessing edaphic factors as a means of explaining the increasing sedge areas in the wetland. By using geophysical imaging coupled with standard sampling approaches, we determined the major soil and water factors that influence grass and sedge zonation. Our results show that the electrical conductivity of the soil solution extract (ECe) and of the surface water (ECw) are significantly higher (P<0.05) in the sedges than in the grasses. Analysis revealed that salinity is the major factor that differentiates between plant communities and that saline intrusion enhanced by human-induced changes to wetland hydrology encourages the expansion of sedge communities.