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Salinity variation in an estuary used for oyster cultivation in Southeastern North Carolina during the passover of the eye of Hurricane Bertha

American Geophysical Union 1996 Fall Meeting, Eos, Transactions, AGU Volume 77, Number 46, November 12 1996.
By D.A. Harned, D. J. Newcomb, E.T. Hudson and J.F. Levine

Abstract

In 1995 a salinity monitor was established to help demonstrate the feasibility of oyster cultivation using floating trays and bags in Alligator Bay behind the barrier island of Topsail Island N. C. This plot is monitored on an hourly basis for specific conductance and temperature. The 2.6-square-kilometer area of Alligator Bay is bisected by the intracoastal waterway, the primary source of saline water for the Bay, and is fed by Mill Creek, a 15.4-square-kilometer freshwater drainage.

The monitor was in operation during the passover of Hurricane Bertha on July 12, 1996. The eye of Hurricane Bertha passed over Alligator Bay at approximately 5:30 p.m. with maximum sustained winds of 168 kilometers per hour. A storm surge of 3 to 4 meters caused overwash of the barrier island and rainfall of 12 to 20 cm caused extensive flooding. High-water marks on the barrier island, with land-surface elevations near 2 meters, were recorded near overwash areas at 2.5 meters.

The influx of fresh and saltwater drove rapid changes in salinity in Alligator Bay. Surficial salinity at the monitor, which bad a mean concentration of 28 parts per thousand (ppt) during the previous 3 weeks, dropped within a few hours to about 10 ppt. Daily variability also showed an increased range from 2 ppt salinity before the storm to around 7 ppt salinity. The larger volume and rapid input of fresh rainwater had a greater influence on salinity than saltwater overwash during this storm. Oysters require salinities ranging from 10 to 32 ppt to survive. An optimal range for oyster growth is about 16 to 26 ppt. The salinities recorded during Hurricane Bertha are not optimal for oyster growth or survival.

Harned, D.A., Newcomb, D.J., Hudson, E.T., and Levine, J.F.,1996, Salinity variation in an estuary used for oyster cultivation in Southeastern North Carolina during the passover of the eye of Hurricane Bertha: American Geophysical Union 1996 Fall Meeting, Eos, Transactions, AGU Volume 77, Number 46, November 12 1996.