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EFFECTS OF HURRICANE IVAN ON WATER QUALITY IN PENSACOLA BAY, FL USA
Citation:
HAGY, J. D., J. C. LEHRTER, AND M. C. MURRELL. EFFECTS OF HURRICANE IVAN ON WATER QUALITY IN PENSACOLA BAY, FL USA. Estuaries and Coasts. Estuarine Research Federation, Port Republic, MD, 29(6A):919-925, (2006).
Impact/Purpose:
to examine the effects of a hurricane on water quality
Description:
Pensacola Bay was in the strong NE quadrant of Hurricane Ivan when it made landfall on September 16, 2004 as a category 3 hurricane on the Saffir-Simpson scale. We present data describing the timeline and maximum height of the storm surge, the extent of flooding of coastal land, and the magnitude of the freshwater inflow pulse that followed the storm. We computed the magnitude of tidal flushing associated with the surge using a tidal prism model. We also evaluated hurricane effects on water quality using water quality surveys conducted 20 and 50 days after the storm, which we compared with a survey 14 days before landfall. We evaluated the scale of hurricane effects relative to normal variability using a 5-year monthly record. Ivan’s ~3.5 m storm surge inundated ~165 km2 of land, increasing the surface area of Pensacola Bay by ~50% and its volume by 230%. The model suggests that 60% of the Bay’s volume was flushed, initially increasing the average salinity of Bay waters from 23 to 30, lowering nutrient and chlorophyll-a concentrations, and eliminating hypoxia. Freshwater discharge from the largest river increased 20-fold during the subsequent 4 days, stimulating a modest phytoplankton bloom (chlorophyll up to ~18 ug 1-1) and re-establishing hypoxia for several months. Although the immediate physical perturbation was extreme, the water quality effects that persisted beyond the first several days were within the normal range of variability for this system. In terms of water quality and phytoplankton productivity, this ecosystem is at present more resistant to severe hurricane impacts than the human development along its coast.