MISSISSIPPI RIVER METHODS COMPARISON STUDY - IMPLICATIONS FOR WATER-QUALITY MONITORING OF DISSOLVED TRACE-ELEMENTS

Recent reports have questioned the validity of dissolved trace element concentrations reported by the U.S. Geological Survey's National Stre am Quality Accounting Network (NASQAN) as well as by other water-quali ty monitoring programs. To address these concerns and to evaluate the NASQAN protocols, the U.S. Geological Survey undertook the Mississippi River Methods Comparison Study. We report here the major results and implications of this study. In particular, we confirm the possible ina ccuracy of previous NASQAN dissolved trace element data. The results s uggest that all steps of the NASQAN protocol (sampling, processing, an d analysis) require revision, though the sample filtration step appear s to be of particular concern.