COASTAL WETLAND SURFACE ELEVATIONAL CHANGES: SALT MARSH AND MANGROVE SYSTEMS, TAMPA BAY, FLORIDA

The surface elevation of coastal wetlands can be altered through a variety of processes. These include sediment accretion, underground biomass production, subsidence, compaction, and erosion. These processes are important because they regulate the stability of salt marsh and mangrove mangal surface elevations with respect to sea level. Three coastal wetlands within Tampa Bay, west-central Florida, have been monitored for surface elevation changes using a combination of techniques, most notably the surface elevation table (SET). Though this method has been utilized in other Gulf of Mexico and Atlantic coastal regions, measurements have previously been obtained on a quarterly or semi-annual basis. In this study hourly, daily, and bi-monthly to monthly sampling has been carried out in an effort to understand short-term surface variability in coastal wetlands in response to diurnal, tidal (neap/spring), and seasonal fluctuations, as well as storm events. Preliminary data suggests that events such as the passage of a cold front, tidal stage (low/high), and spring versus neap low tide effectively alter the surface elevation on the order of 1-3cm from the "norm". Short-term surface fluctuation as a result of these random and cyclical influences occurs on the same scale of vertical change, a few centimeters, that might typically be observed over a period of a year or more in this coastal setting. Therefore, without high-frequency sampling, these few centimeters of change might incorrectly be associated with a long-term pattern in this low energy, low sediment, microtidal environment. Refinement of the SET measurement technique, higher frequency sampling, and accounting for tidal conditions is recommended in order to remove the bias of short-term influences from quarterly measurements, which have more commonly been used to characterize coastal wetland surface elevation changes through time. These refinements may be necessary for the collection of data representative of long-term trends, rather than a snap-shot of the coastal wetland surface elevation at the time of a single measurement.