Restoring coastal wetlands that were ditched for mosquito control: A preliminary assessment of hydro-leveling as a restoration technique |
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Authors: | III" target="_blank">Thomas J SmithIII Ginger Tiling Pamela S Leasure |
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Institution: | (1) US Geological Survey, Florida Integrated Science Center, 600 Fourth Street, South, Saint Petersburg, FL 33701, USA;(2) ETI Professionals, Inc., c/o 600 Fourth Street, South, Saint Petersburg, FL 33701, USA;(3) Pinellas County Department of Environmental Management, Environmental Lands Division, 1800 Weedon Drive, NE, Saint Petersburg, FL 33702, USA |
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Abstract: | The wetlands surrounding Tampa Bay, Florida were extensively ditched for mosquito control in the 1950s. Spoil from ditch construction
was placed adjacent to the wetlands ditches creating mound-like features (spoil-mounds). These mounds represent a loss of
14% of the wetland area in Tampa Bay. Spoil mounds interfere with tidal flow and are locations for non-native plants to colonize
(e.g., Schinus terebinthifolius). Removal of the spoil mounds to eliminate exotic plants, restore native vegetation, and re-establish natural hydrology is
a restoration priority for environmental managers. Hydro-leveling, a new technique, was tested in a mangrove forest restoration
project in 2004. Hydro-leveling uses a high pressure stream of water to wash sediment from the spoil mound into the adjacent
wetland and ditch. To assess the effectiveness of this technique, we conducted vegetation surveys in areas that were hydro-leveled
and in non-hydro-leveled areas 3 years post-project. Adult Schinus were reduced but not eliminated from hydro-leveled mounds. Schinus seedlings however were absent from hydro-leveled sites. Colonization by native species was sparse. Mangrove seedlings were
essentially absent (≈2 m−2) from the centers of hydro-leveled mounds and were in low density on their edges (17 m−2) in comparison to surrounding mangrove forests (105 m−2). Hydro-leveling resulted in mortality of mangroves adjacent to the mounds being leveled. This was probably caused by burial
of pneumatophores during the hydro-leveling process. For hydro-leveling to be a useful and successful restoration technique
several requirements must be met. Spoil mounds must be lowered to the level of the surrounding wetlands. Spoil must be distributed
further into the adjacent wetland to prevent burial of nearby native vegetation. Finally, native species may need to be planted
on hydro-leveled areas to speed up the re-vegetation process. |
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Keywords: | Mangroves Salt marshes Wetlands loss Tampa Bay Florida Avicennia germinans Laguncularia racemosa Schinus terebinthifolius |
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