USA: Quick Return of Beach Organisms after Nourishment, Study Says
Nags Head has completed a three-year study of the biological impacts of its 2011 beach nourishment project. The $450,000 study was a requirement of the state permit to dredge offshore sand and pump it onto 10 miles of beachfront.
The results confirm that beach organisms can re-colonize quickly after nourishment, becoming a viable biological resource and food source to surf fisheries.
The study was directed by CZR Incorporated, Wilmington NC, with independent review by scientists at Cove Labs in Maryland. It followed rigorous sampling and analysis procedures, which are prescribed for studies of this type and were in accordance with the proposed monitoring plan for the project.
Julia Kirkland Berger, CZR project director, noted that samples were collected from the offshore borrow area, where dredging occurred, as well as nearby areas where there had been no dredging.
Additionally, samples were also collected from Nags Head’s nourished beach, as well as the unnourished areas in Kitty Hawk and the Cape Hatteras National Seashore. CZR scientists collected each season before nourishment then repeated their collections at the same time of year and at the same sites in both 2012 and 2013.
“The process to sort the microscopic organisms from each sample, identify the species, and compile statistics takes hundreds of hours each year,” said Berger. “This allows us to quantify not just the numbers of tiny clams or worms in each sample, but to compare the variety of organisms present. Mole crabs feed on the worms, and fish feed on the mole crabs.”
CZR found major differences in the number of organisms from season to season. For example, winter samples showed much lower numbers than summer samples; an expected result observed on other beaches and the control beaches.
Statistics were used to determine whether any particular comparison was significantly different before and after nourishment. The questions asked were straightforward. Were there fewer organisms or a less diverse population in the borrow area after it was dredged compared with nearby undisturbed areas? What are the differences in benthic fauna in the National Seashore or Kitty Hawk compared with Nags Head the first winter after the project?
The final report shows only a few comparisons with significant differences. Two factors likely contribute to the success of the project:
– the offshore borrow area did not collect mud after dredging so the uncovered sediments in these areas remained similar to the dredged sands placed on the beach;
– Nags Head’s new sand may provide more favorable grain size habitat for organisms than the gravel-sized material found there before nourishment.
Nags Head’s results show that life goes on in the challenging and dynamic surf zone and organisms adapt quickly to change. Like a hurricane, beach nourishment can serve to “reset” the conditions for benthic organisms in the immediate or short term, but with beach nourishment projects like Nags Head’s, accurate placement of properly sized sediment on the beach seems to ensure their recovery.
Press Release, June 17, 2014