Backshore Nourishment of a Beach Degraded by Off-road Vehicles: Ecological Impacts and Benefits

Abstract

Worldwide, spoil from maintenance dredging of navigation channels is increasingly used to opportunistically nourish beaches. This is often justified on the presumption that nourishment will improve public beach amenity and restore sandy beach habitat. However, this is not necessarily the case, especially for beaches that do not have an immediate threat of significant erosion. We addressed the ecological impacts and benefits of a backshore sand nourishment project conducted along an off-road vehicle (ORV) damaged section of Blacksmiths Beach, New South Wales, Australia. Sediment, sourced from dredging the inlet of nearby Lake Macquarie, was placed on the foredune, ORVs were excluded and low-density vegetation was planted. Sampling before and after the management interventions, at the Impact (nourished) site, two Control sites (with ORVs), and two Reference sites (without ORVs), assessed ecological impacts of nourishment and the efficacy of the interventions in rehabilitating vegetation and invertebrate communities degraded by ORVs. Nourishment initially had large negative impacts on vegetation cover, as well as on invertebrate abundance and richness. Recovery to a pre-nourished state was, however, observed for vegetation cover after 9 months and invertebrate communities after 21 months. Nevertheless, by the end of our study that extended 21 months post-nourishment and ORV exclusion, there was no evidence of change in the nourished site towards the state of Reference sites. Overall, our study suggests that small-scale backshore sand nourishments of ocean beaches may have only short-term negative impacts on foredune ecosystems when accompanied with some replanting. Nevertheless, where the frequency of sand disposals is greater than the required recovery time, or cumulative effects amass, longer-term or sustained impacts may occur. Our study does not support the efficacy of sand nourishment as a tool for ecological restoration, at least in the short term, without sustained replanting and weeding efforts aimed at reinstating the vegetation community.