The urban environmental gradient: Anthropogenic influences on the spatial and temporal distributions of lead and zinc in sediments

Urban settings are a focal point for environmental contamination due to emi ssions from industrial and municipal activities and the widespread use of m otor vehicles. As part of the National Water-Quality Assessment: Program of the U.S. Geological Survey, streambed-sediment and dated reservoir;sedimen t samples were collected from the Chattahoochee River Basin and analyzed fo r total lead (Pb) and zinc (Zn) concentrations. The sampling transect exten ds;from northern Georgia, through Atlanta, to the Gulf of Mexico and reflec ts a steep gradient in population density from nearly 1000 people/ km(2) in the Atlanta Metropolitan Area to fewer than 50 people/ km(2) in rural area s of southern Georgia and northern Florida. Correlations among population d ensity, traffic density, and total and anthropogenic Pb and Zn concentratio ns indicate that population density is strongly related to traffic density and is a predictor of Pb and Zn concentrations in the environment derived f rom anthropogenic activities. Differences in the distributions of total Pb and Zn concentrations along the urban-suburban-rural gradient from Atlanta to the Florida Panhandle are related to temporal and spatial processes. Tha t is, with the removal of leaded gasoline starting in-the late 1970s, peak Pb concentrations have decreased to the present Conversely, increased vehic ular usage has kept Zn concentrations elevated in runoff from population ce nters, which is reflected in the continued enrichment of Zn in aquatic sedi ments. Sediments from rural areas also contain elevated concentrations of Z n, possibly in response to substantial power plant emissions for the region , as well as vehicular traffic.