Assessing Fecal Bacteria Sources in the Wrightsville Beach, N.C. Area
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Abstract
From 2007-2009 a study was undertaken to determine the sources of fecal bacteria contamination to the marine waters adjoining the Town of Wrightsville Beach, North Carolina. Analyses included sampling for fecal coliform bacteria and Enterococcus bacteria, sampling for optical brighteners, and use of molecular bacterial source tracking techniques including polymerase chain reaction (PCR) and DNA fingerprinting. Samples were collected at nine locations on 12 occasions during the study. The human single-sample water contact standard for Enterococcus of 104 colony-forming units (CFU)/100 mL of water was exceeded on four occasions at Wynn Plaza and three occasions at sites in Lollipop Bay and near Jack Parker Boulevard. Stations with the highest geometric mean counts for the study were those three sites and a site at the Carolina Yacht Club. Optical brightener concentrations were generally low, reflecting a lack of sewage line leakage or spills. There was one exception, a doubling of optical brightener concentrations that occurred concurrent with a pulse of 1,000 fecal coliform bacteria and 925 Enterococcus/100 mL at the Jack Parker Boulevard site. The DNA fingerprint analyses revealed human fecal bacteria signals at all sites, but they occurred most frequently at boat dockage areas such as Causeway Marina, Carolina Yacht Club, Lollipop Bay, Salisbury Bridge and the Wildlife Ramp. The lack of sewer leak evidence, and the lack of septic systems in the Town points toward discharge from boat heads directly into the marine waters as a major cause of fecal bacteria pollution in this area. Action has been taken by the Town to have the US EPA declare the nearby Intracoastal Waterway and its tributaries in the area a no discharge zone, which should alleviate much of the human fecal input to the waters. The fingerprint analyses also detected various animal signals including ruminant (probably deer), rat, and avian (including signals specific for sea gulls) which would enter the water from stormwater runoff. Correlation analyses between fecal bacteria counts and rainfall also indicated a stormwater runoff problem in the Wrightsville Beach area, particularly at the Carolina Yacht Club area, Jack Parker Boulevard, Salisbury Bridge and the Wildlife Commission boat launch ramp. We recommend that the Town further investigate specific areas and animal sources of stormwater runoff to gain sufficient information to take mitigative actions to reduce the stormwater runoff pollution problem.
