Physical and Biological Alterations Following Dredging in Two Beach Nourishment Borrow Areas in South Carolina's Coastal Zone

Dredging of nearshore subtidal sand deposits as a source for beach fill is a common practice in the SE United States, but the long-term effects of this practice on benthic environments are not well documented. Two borrow areas used to nourish the shoreface of Folly Beach, South Carolina, in 2005 (borrow area A) and 2007 (borrow area B) were sampled for sediment characteristics (silt and clay, calcium carbonate, total organic matter content, and sand phi size) and macrobenthic infaunal community composition using a before-after, control-impact design over periods of 8 and 6 years postdredging, respectively. Following dredging, surficial sediment characteristics within both borrow pits shifted toward finer materials and showed little evidence of recovering 8 and 6 years after impact. Changes in the benthic community occurred with respect to faunal density, number of species, and changes in composition at the species level, largely reflecting recolonization by opportunistic taxa within the disturbed seafloor. Benthic community changes consisted largely of the loss of species associated with coarser sands and shell and recolonization by species associated with finer sands and silt and clay. The similar responses of two nearby borrow areas dredged 2 years apart may be partly because of their location and the depth they were dredged below the seafloor. Borrow site location and the depth at which sediments are mined below grade may be important considerations for improving the sustainable reuse of limited sand resources in many areas and avoiding long-term changes in benthic infaunal community composition.