An alternative method of particulate fluorescent tracer analysis in sediments using a microplate fluorimeter

Conservative particulate fluorescent tracers (e.g. luminophores and microspheres) are commonly used in a wide range of sediment transport studies. Traditionally, their spatial redistribution is estimated by counting them in sediments under ultraviolet light (e.g. by epifluorescence microscopy), a time-consuming but effective method. While alternative methods have recently been developed (e.g. photodetection, digital image analyses), this 'classical' counting method remains the most commonly used. This article describes an alternative procedure for measuring the concentration of fluorescent tracers (here, microspheres) using a microplate fluorimeter. This technique enables simultaneous analysis of numerous samples while reducing the sediment preparation and quantification time. After a calibration step from sediment samples with known microsphere content, the method was validated by comparing results from the epifluorescence microscopy method. Different adjustments were also reported, as well as application examples. The different calibration tests showed high linear relationships between the microsphere concentration of sediment samples and the measured fluorimetric intensities (R2-0.99) with a detection limit of 6%. In comparison with the previously used method, very similar results were obtained, as illustrated in recent studies using both luminophores and microspheres. The rapid and reliable method proposed here will enable increasingly complex experiments to be performed with less time-consuming qualitative analyses.