Coastal sand dune ecosystems are essential for buffering natural and built environments from powerful storm surges and wave erosion. The geomorphology and vegetative communities of the dunes are quite dynamic as they undergo cycles of erosion, accretion, and regeneration of dune vegetation. Throughout the U.S., expensive beach re-nourishment projects often follow erosive storms to protect coastal property and support tourism. And yet, natural processes that facilitate beach and dune regeneration are often circumvented when organic shore wrack is removed or relocated for aesthetic purposes. Following Hurricane Irma in September 2017, extraordinary amounts of organic shore wrack washed in along Central Florida’s Atlantic coast. From October through December 2017, we quantified the biomass and decomposition rate of the Sargassum and seagrass-dominated wrack line that accumulated in the month following the storm. We also assessed the moisture, organic content, and Total N and P of the beach soil at 3 depths below the wrack line in front of, in the middle of and behind the wrack line. We also tracked the recruitment success of Coastal Searocket, Cakile lanceolata, an early colonizer of new dunes. Samples were collected from ten 10m transects parallel to the water at Ponce Preserve in Volusia County, Florida.
Results/Conclusions
The accumulated shore wrack averaged 7.5m wide, ranged from 20 cm deep on the front edge to 2 cm deep on the back edge, and initially contained 35.1 kg/linear meter of shoreline of dry biomass. The decomposition (loss) rate from October through December was 0.88 kg/day. Moisture content of the beach soil did not vary by depth, but did vary from the front to the back of the wrack line with the highest moisture content in the front zone (3.7%). Soil organic content was not significantly different by depth or position. Total N and P were both highest in the 0-15cm depth in the middle zone. C. lanceolata established on top of the wrack material (2.7 plants/m2) and behind it (9.3 plants/m2). However, severe erosion from winter storms in December washed out 72% of the plants from the wrack middle, and 24% of the plants from behind the wrack line. Results of this pilot study suggest that leaving shore wrack in place increases soil moisture and nutrients in beach soils that may facilitate recruitment of new dune vegetation. Prioritizing natural processes for dune regeneration as a coastal management strategy can contribute to short-term economic gains and long-term coastal resilience.