Evaluation of Streamwater Quality in the Atlanta Region
Peters, Norman E.
Kandell, Stephen J.
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A water-quality index (WQI) was developed from historical data for streams in the Atlanta region. The WQI was derived from percentile ranks of individual water-quality parameter values at each stream by normalizing the constituent ranks for values from all sites in the area for the period from 1990 to 1995. WQIs were developed primarily for nutrients and nutrient-related parameters, because data for metals, organics (pesticides and herbicides), biological conditions, and suspended sediment generally were unavailable. Average WQI of the individual parameter WQIs for sites in the region ranged from 0.26 (good quality) to 0.86 (poor quality), and increased downstream of known nutrient sources. Annual average site WQI decreased at most long-term monitoring sites from 1986 to 1995. Temporal trends, in part, reflect effects of a drought in the late 1980's and normal to higher-than-normal rainfall and runoff in the 1990's. For several sites, particularly in the northern part of the region where major development is ongoing, WQI increased dramatically from 1994 to 1995. Interannual WQI variability typically was less than spatial variability. Average annual site WQI for individual parameters correlated with annual hydrologic characteristics, particularly precipitation amount and water yield, reflecting the effect of dilution on individual water-quality parameter values.