Groundwater control of mangrove surface elevation: Shrink and swell varies with soil depth

We measured monthly soil surface elevation change and determined its relationship to groundwater changes at a mangrove forest site along Shark River, Everglades National Park, Florida. We combined the use of an original design, surface elevation table with new rod-surface elevation tables to separately track changes in the mid zone (0-4 m), the shallow root zone (0-0.35 m), and the full sediment profile (0-6 m) in response to site hydrology (daily river stage and daily groundwater piezometric pressure). We calculated expansion and contraction for each of the four constituent soil zones (surface [accretion and erosion; above 0 m], shallow zone [0-0.35 m], middle zone [0.35-4 m], and bottom zone [4-6 m]) that comprise the entire soil column. Changes in groundwater pressure correlated strongly with changes in soil elevation for the entire profile (Adjusted R-2 = 0.90); this relationship was not proportional to the depth of the soil profile sampled. The change in thickness of the bottom soil zone accounted for the majority (R-2 = 0.63) of the entire soil profile expansion and contraction. The influence of hydrology on specific soil zones and absolute elevation change must be considered when evaluating the effect of disturbances, sea level rise, and water management decisions on coastal wetland systems.