Impacts of Hurricanes on Wetland Phytoplankton Communities in the Gulf of Mexico
Measurements were made of inorganic nutrient and chlorophyll a (chl a) concentrations over a period of 7 months during the spring and summer of 2012 at coastal wetland sites along the northern coastline of the Gulf of Mexico. Tropical Storm Debby and Hurricane Isaac passed near several of the sampling sites during the study. Samples collected before and within a few days after passages of these storms allowed us to assess the impact of the storms on the wetland phytoplankton communities. Passages of the storms were associated with significant increases of chl a concentrations and reductions of nitrate, ammonium, and phosphate concentrations, but there were no significant changes of salinity or silicate concentrations. Much of the increase of the chl a concentrations could be explained by the reduction of dissolved inorganic nitrogen. The phytoplankton populations did not appear to be nutrient limited prior to passage of the storms, and the increases of chl a following passage of the storms appeared to reflect a reduction of zooplankton grazing pressure. Introduction of H2S into the water column via resuspension of bottom sediments may have been the cause of the reduction of zooplankton grazing activity.
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