Mitigation of Natural Background Interference with Fluorometric Dye Measurements in Natural Waters

摘要

The potential sensitivity of the fluorometric measurement of the concentration of the tracer dye Rhodamine WT, using existing state of the art fluorometers equipped with the best optical filters, is + or - 0.001 ppb of dye. Temporal fluctuations in the natural background readings in some areas of the Chesapeake Bay have degraded this sensitivity, such that the effectiveness of the use of Rhodamine dyes as tracers of water movement and mixing in these areas is threatened. Using optical filters which were in common use at the start of this study, background fluctuations corresponding to uncertainties in dye concentration of + or - 0.2 ppb were observed in irregularly distributed patches, which in some cases were shown to correspond with patches of high phytoplankton concentrations.