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摘要
The City of Atlanta, Georgia (COA) is part of the ninth largest metropolitan area in the USA and one of the fastest growing (e.g., > 24% between 2000 and 2007). Since 2003, the US Geological Survey has been operating an extensive long-term water-quantity and water-quality monitoring network for the COA. The experience gained in operating this network has provided insights into the challenges as well as some solutions associated with determining urban effects on water quality, especially in terms of estimating the annual fluxes of suspended sediment, trace/major elements, and nutrients. The majority (> 90%) of the annual fluxes of suspended sediment and discharge (> 60%) from the COA occur in conjunction with stormflow. Typically, stormflow averages a parts per thousand currency sign20% of the year. Normally, annual flux calculations employ a daily time-step; however, due to the "flashy" nature of the COA's streams, this approach can produce substantial underestimates (from 25% to 64%). Greater accuracy requires time-steps as short as every 2 to 3 h. The annual fluxes of a parts per thousand yen75% of trace elements (e.g., Cu, Pb, Zn), major elements (e.g., Fe, Al), and total P occur in association with suspended sediment; in turn, a parts per thousand yen90% of the transport of these constituents occurs in conjunction with stormflow. With the possible exception of nitrogen, baseflow sediment-associated and both baseflow and stormflow dissolved contributions represent relatively insignificant portions of the total annual load; hence, nonpoint (diffuse) sources are the dominant contributors to the fluxes of almost all of these constituents.
- 出版日期2009-8
