USGS Washington Water Science Center
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The Clean Water Act's objective is to restore and maintain the chemical, physical, and biological integrity of the nation's waters. For more than forty years, efforts to achieve this objective have focused on controlling municipal and industrial wastewater discharges. Discharge monitoring has driven the implementation of these controls. However, discharge monitoring does not assess the integrity of a water body. Discharge monitoring only provides a rough estimate of potential environmental effects based upon limited information on pollutant concentrations over time in relationship to variable receiving stream chemistry and flow. Storm water discharge monitoring will generate information that is certain to be inadequate for evaluating urban stream health given the large number of storm water outfalls discharging highly variable volumes containing rapidly changing pollutant concentrations. Regularly monitoring all storm water outfalls for every potential pollutant would be very expensive and generate information of limited usefulness. In addition, the detection of unknown or illegal discharges is too often left to chance resulting in a possibly serious information gap when considering stream health.
An alternative to point source measurements taken at specific times is the characterization of aquatic organism responses in streams experiencing both point and non-point sources. For example, test organisms placed in a stream would both experience a realistic environmental exposure and be able to respond to a broad spectrum of toxic chemicals. Measuring test organism responses at the molecular level using DNA transcriptional responses derived from microarray techniques would enhance knowledge of the effects on the in situ test organisms of any chemicals detected and could provide an alert if any chemicals need to be added to the analysis list. Gene microarrays applied to test organisms have the potential for an economy of scale if used routinely.