Effects of beach nourishment on sediments and benthic assemblages

Beach nourishment (i.e. the addition of sediments transported from other source locations) is increasingly used to counteract erosion of coastal areas. We tested whether sediment descriptors (grain size structure and organic content) and macrobenthic assemblages (species composition and abundance) differed among replicated shores previously exposed to nourishment alone (N), nourishment in combination with pre-existing hard structures (N + H) or no nourishment (NoN) along about 50 km of shores of the Emilia Romagna region (North Adriatic Sea, Italy). There was large variation among shores. Two out of three N shores were nearly defaunated, while one N shore had species composition and abundances comparable to NoN shores. There were also large differences between N and N + H shores, the latter possessing higher abundances of organisms and the presence of species that do not usually occur in the nearshore surf habitats in this region. More than 50% of the variability in the benthic assemblages was related to variations in the grain size structure of the sediments among shores. The results suggest that beach nourishments may lead to modifications of sedimentary environments and inhabiting fauna, but the resulting effects may be strongly related to local conditions, which dictate the rate at which added sand is redistributed.