TRACE METAL CONCENTRATIONS IN STREAM SEDIMENTS FROM URBAN AND LESS-URBANIZED WATERSHEDS IN THE PIEDMONT PROVINCE OF GEORGIA

Trace metal concentrations (V, Cr, Co, Ni, Cu, Zn, Pb, and Mn) were determined for stream water and suspended sediment samples from four watersheds within the Piedmont Province of Georgia. The watersheds of study were chosen to represent varying degrees of urbanization, including the highly urbanized Peachtree Creek basin (54.7 % urban land use) in the City of Atlanta and three less-urbanized watersheds. A single-step, 10 % HNO₃ trace metal extraction technique was used to release the metals adsorbed onto the sediments. Adsorbed metals are of interest from an environmental standpoint because they are attributed to anthropogenic origin. Zinc and lead, the two metals associated with specific measures of urban land use, including population and traffic density, were the most elevated within sediments from the urban (Peachtree Creek) watershed. Adsorbed concentrations of copper, lead and zinc within this watershed were 33, 76, and 198 µg/g, respectively. Elevated concentrations of adsorbed copper (36 µg/g), lead (37 µg/g), and zinc (159 µg/g) were also observed in the Sweetwater Creek watershed, which is undergoing urbanization in its eastern margin. Adsorbed zinc and lead correlated well with the square root of the percentage urbanization; however, t-tests (95% C.I.) indicated that only lead concentrations were significantly greater within the urban, Peachtree Creek watershed than in the other study basins. Calculations of trace metal distribution coefficients (K_D values) suggest that metals are well-partitioned onto the sediments in these watersheds (K_D > 10³ for all metals). All dissolved metal concentrations were well below US EPA drinking water MCL’s; however, adsorbed copper, zinc, and lead concentrations exceeded Georgia Environmental Protection Division Soil Criteria or Canadian Environmental Sediment Quality Guidelines in several cases.