Indirect Hurricane Effects on Resource Availability and Microbial Communities in a Subtropical Wetland-Estuary Transition Zone

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 (NH þ 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 NH þ 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.

Groundwater-induced redox-gradients control soil properties and phosphorus availability across four headwater wetlands, New York, USA

“…The impacts of hydrochemical gradients on biogeochemical processes and soil development that we observed, however, are likely true to some extent in all wetland systems. Distinct horizontal gradients in pore-water chemistry with distance from a water source or in relation to multi-source mixing zones have been observed in riparian buffers (Duval and Hill 2007;Hill et al 2000;Vidon and Hill 2004), coastal wetlands (Bailey and Bedford 2003;Williams et al 2008), and expansive northern peatlands (Bubier 1995;Glaser et al 1997). Results from all of these studies emphasize the importance of explicitly relating plot-scaled biogeochemistry studies to local hydrologic settings.…”

Temperature, organic matter, and the control of bacterioplankton in the Neuse River and Pamlico Sound estuarine system

“…The return of these flood waters to the river probably brought in enough POM and DOM to stimulate productivity. Sediment resuspension and increased discharge from storms have been documented as being responsible for BP increases (Cotner et al 2000, Williams et al 2008. Alternatively, the flood waters may have washed in an allochthonous population of bacteria that were enhanced in the storm-impacted estuary.…”

Denitrification Dominates Sediment Nitrogen Removal and Is Enhanced by Bottom-Water Hypoxia in the Northern Gulf of Mexico

“…Together, these results suggest that hurricanes may have shifted benthic biogeochemical processes into the pelagic realm. Other studies have evaluated long-term and broad-scale impacts of hurricanes (e.g., Paerl et al 2001;Williams et al 2008), but we are not aware of other studies evaluating SWI N transformations so soon after storm passage.…”