Background Problems in Fluorometric Dye Measurement in Natural Water

Recent evidence points to a reduced effectiveness in dye tracer techniques in certain areas of the Chesapeake Bay system due to spacial and temporal variations in background fluorescence. The problem arises from one or both of two sources: scattering of the primary light in the fluorometer, or the fluorescence of naturally occurring pigments in the water. This background variation corresponds to an equivalent dye concentration of 0.01 ppb for low activity up to 0.30 ppb for high activity. Results of experiments which provide evidence as to the nature of the material causing the variations in background are described. Several possible solutions to the problem are presented.