Comparative major ion geochemistry of Piedmont streams in the Atlanta, Georgia region: possible effects of urbanization

Abstract

The major ion stream chemistry for an urbanized basin (Peachtree Creek) in the Atlanta (Georgia, USA) metropolitan region was analyzed and compared upon a time-series basis with the stream chemistry of a nearby, but far less developed basin (Sweetwater Creek). The major ion chemistry from both streams indicated that all parameters fell below safe drinking water standards as would be expected in watersheds underlain by low-solubility aluminosilicate bedrock. Base flow TDS concentrations for the urbanized basin (Peachtree Creek) were 30% greater than Sweetwater Creek and were characterized by elevated concentrations of base cations (Ca, Mg, Na), alkalinity, sulfate, and chloride. The less-urbanized Sweetwater Creek basin is underlain by a higher percentage of more soluble amphibolite and, therefore, the higher concentration of solutes within the urban base flow can not readily be explained by differential mineral weathering. The increased inorganic solute loads might have resulted from pollution input (leaky underground sewer lines?) and/or evaporative concentration; however, these explanations are presently speculative. Major ion concentrations within the urban Peachtree Creek basin were diluted by an average of 50% compared with only 25% in the Sweetwater Creek basin as a result of the increased contribution of direct surface runoff. The regression correlation coefficients for the ions that evolve through mineral weathering (Ca, Mg, Na, and HCO 3 ) are much higher in urban stream flow than in Sweetwater Creek waters. This might indicate that storm waters in the urban basin are more closely derived from a two end member mixture (groundwater and street runoff) than waters from Sweetwater Creek, which represent a more complex mixture.

Regional Hydrogeochemical Mapping for Environmental Studies in the Mineralized Lom Basin, East Cameroon: A Pre-industrial Mining Survey

“…-can be ascribed to the weathering of alumino-silicate minerals [21][22] or the formation of carbonic acid when CO 2 resulting from the decay of organic matter combines with rainwater. The levels of NO 3 -in the samples were generally low (< 2 mg/L) and constituted 3% of the total anions.…”

Urbanization Effects on Watershed Hydrology and In-Stream Processes in the Southern United States

“…Similarly, Rose (2002Rose ( , 2007 showed that groundwater discharging into a local urban stream was characterized by high levels of chloride, sulfate, calcium carbonate, and total dissolved solids (TDS) [66,107]. The author speculated that shallow groundwater chemistry in the region may have been influenced by effluent contamination originating from numerous septic tank systems and leaky underground sewer pipes.…”

Geochemical Eccentricity of Ground Water Allied to Weathering of Basalts from the Deccan Volcanic Province, India: Insinuation on CO2 Consumption

“…Datta and Tyagi (1996) consider higher proportion of HCO 3 to other anions, diagnostic of its naissance related to weathering of primary silicate minerals dominated by alkaline earths. Rose (2002) also considers HCO 3 [ SO 4 + Cl as indicator of rock weathering as the chief source rather than pollutant input from atmosphere and/or soils. Elevated values of Ca + Mg in the groundwater from Upper Panjhara basin support this inference.…”