CHARACTERIZATION OF NUTRIENTS AND TRACE METALS IN THE PEEDEE SAND AND CASTLE HAYNE LIMESTONE AQUIFERS: NEW HANOVER COUNTY, SOUTHEASTERN NORTH CAROLINA

Concerns about overuse and potential contamination of major aquifers in the southeastern part of North Carolina resulted in the initiation of a subsurface water quality study in February 2001. This study was initiated to examine the variations in certain nutrients NO₃, PO₄, SO₄, Cl, NH₄) and Fe in the Cretaceous Peedee and Tertiary Castle Hayne aquifers of northeastern New Hanover County, North Carolina. Water samples are collected monthly from 17 wells located in the Porters Neck area (west of the intracoastal waterway and south of Futch Creek) and four springs located on the south side of Futch Creek. Variations in nutrient concentrations are seen not only between the two aquifers, but also within each aquifer depending upon well location and time of year. Major changes that occur in the Peedee aquifer are increases in the concentrations of PO₄ and Fe during the warmer summer months. NH₄ shows higher concentrations during early spring and later summer-early fall. In late summer to early fall, Fe, NO₃, NH₄, and PO₄ concentrations in the Castle Hayne aquifer are significantly higher than during the spring and winter months. Cl and SO₄ concentrations vary with a constant ratio in both aquifers, suggesting saltwater intrusion as a probable source. Factors considered for nutrient and trace element variance include: temperature variation, anaerobic conditions, subsurface stratigraphy/structure, recharge rates, site location and fertilization schedule. The shallower Castle Hayne aquifer is more affected by seasonal impacts than the Peedee aquifer. Increases in NO₃ and PO₄ lag slightly behind periods of high fertilization and are more prevalent downdip of a major golf course. Nutrient analyses of Futch Creek springs indicate seasonal variations with peaks during the summer.