Hydrological, geomorphological, and chemical effects of Hurricane Andrew on coastal marshes of Louisiana

Hydrological conditions are reported for the hurricane-induced storm surge at marsh sites in Terrebonne and Barataria Basins. There was a 6 hour or greater delay in the arrival of the storm surge at interior marsh sites compared to coastal locations. A water surge of about 1.5 m with a salinity of 10–15‰ was recorded at an intermediate salinity marsh site in Terrebonne Basin where significant geomorphological changes occurred with lateral movement and stacking of marsh vegetation and sediment, erosion, and the conversion of wetlands to open water. A residual salt wedge attributed to the storm surge was detected in sediments at this intermediate marsh site about 55 days after the hurricane. In the pore water, at 30 cm in depth, there were increases in alkalinity, ammonia, phosphate, and manganese, but not iron or sulfide, although there was a significant depletion of sulfur with respect to chloride. The increases in concentration of these species in the pore water suggests that there was an increase in organic matter decomposition. Although increases in sulfide phytotoxicity were not obvious, the residual salinity of pore water may influence wetland loss through longer-term impacts on macrophyte production. Storm-induced sediment deposition, which will help ameliorate wetland loss, was observed at a salt marsh site in Terrebonne Basin.