Environmental implications of the use of sulfidic back-bay sediments for dune reconstruction - Lessons learned post Hurricane Sandy

- Sulfidic back-bay sediments were dredged and used in barrier-island dune reconstruction.
- Acid-sulfate weathering of reactive iron sulfides helps cement the reconstructed dunes.
- Weathered sulfidic materials are a source of soluble acid and metals.
- Dredged bay sediments may have metal, organic, and microbial contaminants.
- Results indicate lead and other metals are below levels of human health concern.

Some barrier-island dunes damaged or destroyed by Hurricane Sandy's storm surges in October 2012 have been reconstructed using sediments dredged from back bays. These sand-, clay-, and iron sulfide-rich sediments were used to make berm-like cores for the reconstructed dunes, which were then covered by beach sand. In November 2013, we sampled and analyzed partially weathered materials collected from the cores of reconstructed dunes. There are generally low levels of metal toxicants in the reconstructed dune materials. However oxidation of reactive iron sulfides by percolating rainwater produces acid-sulfate pore waters, which evaporate during dry periods to produce efflorescent gypsum and sodium jarosite salts. The results suggest use of sulfidic sediments in dune reconstruction has both drawbacks (e.g., potential to generate acid runoff from dune cores following rainfall, enhanced corrosion of steel bulwarks) and possible benefits (e.g., efflorescent salts may enhance structural integrity).