Fluorescence measurements could help scientists monitor source water quality, according to a recent US Geological Survey (USGS) study of Oregon’s McKenzie River. The focus of the study was the type, amount and source of dissolved organic carbon, present in all drinking water sources. During water treatment, dissolved organic carbon reacts with chlorine to form halogenated compounds known as disinfection byproducts. Scientists from the USGS, in collaboration with Oregon’s Eugene Water and Electric Board, analyzed samples from the McKenzie River mainstream, tributaries and reservoir outflow, taking optical measurements to assess the full spectrum of fluorescence and absorption. Groundwater flows into the upper watershed of the McKenzie River in Oregon. Courtesy of Tamara Kraus, USGS. Their results showed that dissolved organic carbon and disinfection byproduct precursors originated upstream. Downstream, tributaries had higher concentrations of dissolved organic carbon, but these made up less than 5 percent of the mainstream flow, which the researchers said means that they do not significantly affect drinking water quality. There was some interference while measuring the absorbance spectra, but the study presented conclusive evidence that measuring optical properties could be a cheaper, less time-consuming and more sensitive method of water quality assessment than laboratory chemical-based analyses, the researchers found. The study was published in the November-December 2010 issue of the Journal of Environmental Quality.