Disturbance effects of hurricane Hugo on a pristine coastal landscape: North Inlet, South Carolina, USA

Abstract

Despite its intensity and landfall at high tide, Hurricane Hugo (22 Sept. 1989) had only a modest impact on the geomorphology of the undeveloped coastal landscape at North Inlet, South Carolina. Pre- and post-Hugo aerial photographs (April 1987 and October 1989) showed no change in the salt-marsh creek network, nor could changes be seen in the size or shape of sand bars within the creeks. Several new, small washover fans formed on the adjacent barrier islands. These lobate fans extend 50 to 100 m from the dune line into the back barrier area and are deposited on older but recently formed fans in areas where the islands are thin and devoid of large shrubs and trees. Hugo's failure to have a more dramatic geomorphic effect was probably related to the rapid approach of the storm along a path perpendicular to the coast. This allowed minimal time for the surge to build and for wave attack to modify the shoreface. In contrast, the nearby coastal forest experienced extensive wind damage as well as tree mortality due to soil salinization by the surge. Wind damage was a function of tree species, diameter and soil type. The most severe damage occurred in mixed bottomland hardwood sites on Rutledge (sandy, silicious, thermic Typic Humaquepts) soils. Salt-induced foliage discoloration and defoliation became fully evident in the surge-inundated area by January 1990. Above-normal salt concentrations were found in shallow groundwater samples from sites up to the 3.0-m contour (MSL). Salt concentrations generally decreased inland from the forest-marsh boundary and with the passage of time. Trees standing along the forest-marsh boundary and in swales suffered the most severe salt-induced mortality. As of June 1991, new understory vegetation and pine seedlings appeared to be flourishing in the salt-affected area. Salinization also mobilized ammonium from soil storage as a result of ion exchange with seawater cations and disruption of nitrogen cycling processes. There was a virtual absence of insects and terrestrial vertebrates in the surge-affected forest immediately following Hugo. Flying insects and birds were the first to return but six months after Hugo, the abundance of reptiles and amphibians remained significantly lower than populations observed prior to the storm. Scouring and high salinity had a catastrophic effect on benthic invertebrates in the blackwater streams of the forest. Population density dropped by 97% and biomass declined from 542 mg dry mass·m −2 to only 2.0 mg dry mass·m −2. The community recovered quickly, however, as density and biomass returned to pre-storm levels in three and six months, respectively.