The Effects of Tropical Storms and Hurricanes on Phytoplankton and Nutrient Concentrations in Wetland-Estuary Transition Zones along the Gulf Coast

Abstract

Two consecutive storms made landfall along the Northern Gulf of Mexico on June and August 2012 (Tropical Storm Debby, 06/26/2012; Isaac, 08/28/2012, Category (Cat) 1 Saffir-Simpson Hurricane Scale). Each storm passed within 48 to 273 km of one of seven wetland-estuary transition zone sampling sites, and indirect storm effects associated with changes in freshwater discharge and an inflow of inorganic nutrients were observed at five of the seven sites. To assess the impacts of the 2012 hurricanes on hydrology, nutrient concentrations, and phytoplankton concentrations at transition zones along the Gulf Coast, a within-sites analysis along with a seasonal analysis were conducted to differentiate between seasonality and any deviations caused by storm effects at that particular site. Along with the within-sites analysis, a between-site analysis was also conducted to distinguish any trends among sites that were collective after the passing of a storm. Finally, to better understand the status of nutrient limitation at each site, enrichment experiments were conducted, with an emphasis on phosphorous and nitrogen, to determine the limiting nutrient. The results of the before-and-after nutrient analysis were generally consistent, with nitrate, phosphate, silicate, and ammonium levels decreasing, and chlorophyll concentrations increasing, thus suggesting that the storm stimulated nutrient uptake and phytoplankton growth. At some sites low post-storm nutrient concentrations appeared to be part of a seasonal pattern of declining nutrient concentrations rather than the result of phytoplankton uptake stimulated by passage of the storm.