TEMPORAL VARIATIONS OF HEAVY METAL CONCENTRATIONS IN SEDIMENT CORES FROM BIG CREEK, A SMALL WATERSHED IN METRO ATLANTA, GA

Four 5 cm cores ranging in length from 45cm to 120cm were obtained from a point bar of Big Creek in Alpharetta,GA. The cores were systematically sampled along natural facies breaks. The sediment was washed, dried, and sieved through a 63um sieve and the clay fraction from each sampled section was homogenized before digesting it in concentrated nitric acid. Dilutions of the leacheate were prepared, spiked with Y (as an internal standard), and run on a Finnigan MAT Element2 ICP-MS for Zn, Pb, Ni, Cu, Cr, Cd. Notable variability existed between the sampled sections. A sigmoidal curve emerged denoting lower to higher to lower concentration for all heavy metals that were analyzed. The pattern observed follows closely the high flow and low flow discharge data from the USGS gauging station for this area. Increased heavy metal concentrations are thus coupled to periods of increased precipitation and run-off. The increased amount of urbanization in this area and the subsequent increase in siltation has provided the means to use short sediment cores as a proxy for determining fine scale variability of heavy metal concentration in an anthropogenically altered watershed.