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publications > paper > groundwater control of mangrove surface elevation: shrink and swell varies with soil depth > introduction
In a 3-yr study of a coastal mangrove forest along Shark River, Everglades National Park, Florida, soil surface elevation was found to vary linearly (R2 = 0.38) with surface water stage 15-30 d prior to sampling (Smith and Cahoon 2003). The investigation was limited in that the benchmarks used to measure soil elevation extended just 4 m into the soil and stopped approximately 2 m above the limestone bedrock. Processes occurring below the 4-m deep benchmark were not included in the elevation readings. The influence of processes within the active root zone (e.g., root growth and decomposition or shrink and swell) on soil elevation could not be determined because the benchmarks integrated processes over the entire 4-m soil column. Because of these limitations we added sampling devices that allowed us to measure the shallow active root zone (0-0.35 m) and the deeper soil zone (4-6 m).
We present here a study of soil elevation dynamics in the lower Shark River drainage basin that includes the entire soil profile and distinguishes between three depths within the soil profile; 0-0.35, 0-4, and 0-6 m. Our main objective was to investigate the relationship among changes in soil surface elevation and changes in the hydrological parameters of river stage and groundwater piezometric head pressure at the site over the three depths. We wanted to determine the relative contribution to soil elevation by each of the four components of the soil profile: surface (i.e., accretion), shallow zone (active root zone, 0-0.35 m), middle zone (0.35-4 m), and bottom zone (4-6 m).
A comprehensive understanding of the influences
of hydrology on the soil profile at this site is of
considerable importance. The site is located in the
Shark River estuary downstream of the Shark River
Slough, receives freshwater inputs from the Greater
Everglades drainage, and is under the influence of
upstream water management practices of the
Greater Everglades. The Everglades drainage is
currently undergoing an ecosystem restoration
concentrating on modifying water deliveries to
mimic predrainage flows. In addition to the
changing freshwater flows linked to restoration, this
mangrove forest is affected by sea level rise.
Determining how hydrology influences the specific
soil zones and surface elevation will allow managers
to make more informed decisions regarding these
two opposing hydrological processes.
U.S. Department of the Interior, U.S. Geological Survey
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