Indirect Hurricane Effects on Resource Availability and Microbial Communities in a Subtropical Wetland-Estuary Transition Zone |
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| Authors: | Clayton J Williams Joseph N Boyer Frank J Jochem |
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| Institution: | (1) Marine Biology Program, Florida International University, 3000 N.E. 151st Street, North Miami, FL 33181, USA;(2) Southeast Environmental Research Center, Florida International University, Miami, FL 33199, USA; |
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| Abstract: | Three sequential hurricanes made landfall over the South Florida peninsula in August and September 2004. The storm systems
passed north of the Everglades wetlands and northeastern Florida Bay, but indirect storm effects associated with changes in
freshwater discharge during an otherwise drought year occurred across the wetland–estuary transition area. To assess the impacts
of the 2004 hurricane series on hydrology, nutrients, and microbial communities in the Everglades wetlands to Florida Bay
transition area, results are presented in the context of a seasonal cycle without hurricane activity (2003). Tropical activity
in 2004 increased rainfall over South Florida and the study area, thereby temporarily relieving drought conditions. Not so
much actual rainfall levels at the study site but more so water management practices in preparation of the hurricane threats,
which include draining of an extensive freshwater canal system into the coastal ocean to mitigate inland flooding, rapidly
reversed hypersalinity in the wetlands-estuary study area. Although annual discharge was comparable in both years, freshwater
discharge in 2004 occurred predominantly during the late wet season, whereas discharge was distributed evenly over the 2003
wet season. Total organic carbon (TOC), ammonium (
\operatornameNH + 4 \operatorname{NH} ^{ + }_{4} ), and soluble reactive phosphorus (SRP) concentrations increased during the hurricane series to concentrations two to five
times higher than long-term median concentrations in eastern Florida Bay. Spatiotemporal patterns in these resource enrichments
suggest that TOC and SRP originated from the Everglades mangrove ecotone, while
\operatornameNH + 4 \operatorname{NH} ^{ + }_{4} originated from the bay. Phytoplankton biomass in the bay increased significantly during storm-related freshwater discharge,
but declined at the same time in the wetland mangrove ecotone from bloom conditions during the preceding drought. In the bay,
these changes were associated with increased nanophytoplankton and decreased picophytoplankton biomass. Heterotrophic bacterial
production increased in response to freshwater discharge, whereas bacterial abundance decreased. Hydrochemical and microbial
changes were short-lived, and the wetland–bay transition area reverted to more typical oligotrophic conditions within 3 months
after the hurricanes. These results suggest that changes in freshwater discharge after drought conditions and during the hurricane
series forced the productivity and P-enriched characteristics of the wetland’s mangrove ecotone, although only briefly, to
the south into Florida Bay. |
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