Characterization of the water retention curves of Everglades wetland soils

Alterations to the natural hydrology of wetlands like the Everglades have increased the presence of unsaturated zones in typically inundated soil environments. Understanding soil moisture dynamics through numerical modeling requires a large dataset of soil hydraulic parameters (SHPs) due to the spatially variable nature of hydromorphic soils typically found in wetlands. Furthermore, the application of conventional parameterization models is challenging due to shrinkage with desaturation observed in these organic-rich soils. The objective of this work was to investigate water retention, shrinkage, and the effect of shrinkage on the SHPs of Everglades soils. This study used pressure plate extractors to determine the soil water retention curves (SWRCs) and corresponding shrinkage from triplicates for 53 sites across the Everglades. In addition, the organic content (OC), and fiber content (FC) were measured in the laboratory. An agglomerative clustering method applied to the retention and shrinkage data identified three distinct clusters: marl, mixed marl-peat and peat. Marl had higher volumetric water contents (VWCs) than marl-peat or peat particularly at higher pressures. The susceptibility of peat to shrinkage resulted in lower VWCs compared to the other two soils. When shrinkage was accounted for in the vGM model, a significantly higher alpha and lower n were observed. In addition, some deviations from typical SWRC behavior, attributed to the collapse of macro-pores, caused poor model fit. Northern marshes with predominantly fibric peat had steeper SWRCs due to the inverse relationship between FC and VWC at higher pressures. Further work is required to determine the influence of vegetation on the SWRC.