SILVER AND OTHER TRACE METALS IN WATER OF THE CHATTAHOOCHEE RIVER, GEORGIA: DEFINING THE IMPACT OF ATLANTA'S SEWAGE DISCHARGE

As rivers pass through urban areas, they experience a change in their water chemistry. One specific concern of potential water pollution is trace metal contamination. Metals increase as the rivers receive runoff from impervious surfaces, sewage from wastewater treatment plants, and aerial deposition. Often it is a problem is to differentiate between these several sources of trace metals. Recently, silver (Ag) has been used successfully to delineate the extent of sewage inputs in environmental settings. We used this approach to interpret the chemistry of water collected at several locations along the Chattahoochee River as it flows through the Atlanta metropolitan area, and are the first to present Ag data for this fresh water environment. Although the Ag concentrations remain low (<20ng/L), they increase more then 15-fold as the river flows through metro-Atlanta. That is within the range of increase previously observed for other trace metals which reach from 2-fold to >100-fold. However, the Ag concentrations rise further upstream, and in the upper stretch of the river faster than most other metals, suggesting an earlier impact from sewage discharge. When passing through the central area of Atlanta, the rate of increase of Ag is similar to that of other trace metals such as Pb, Cu, and Co. As the river leaves the Atlanta area, Ag values decrease, both in absolute terms as well as compared to conservative tracers such as chloride. This suggests a removal by adsorption to particles, as well as by dilution by streams with non-elevated Ag concentrations. The behavior of Ag and other dissolved trace metals correlates well with USGS-NAWQA sediment data of the Chattahoochee and some of its tributaries in the Atlanta region, corroborating the importance of metro-Atlanta's impact on the Chattahoochee's water and sediment geochemistry.