Water tracing in tropical regions, the use of fluorometric techniques in Jamaica

Abstract Fluorescent dyes have been widely used in temperate latitudes for the tracing of karst groundwater. However, a review of the literature indicates that these tracers have been much less satisfactory in tropical karst areas, and are far less successful than Lycopodium spore tracing techniques. Quantitative tests were carried out on six fluorescent tracers in a surface stream in central Jamaica. Tracer concentrations, measured using a Turner III filter fluorometer, were used in conjunction with discharge measurements to determine tracer losses under field conditions. Rhodamine WT and Lissamine FF proved to be the most successful dyes but Fluorescein also proved satisfactory under conditions with little direct sunlight. The optical brighteners Photine CU and Photine CSP showed large losses in the study reach. An underground test along a previously proven connection supported the findings of the surface tests. Two successful groundwater traces were completed in the North St. Catherine Basin, the first 30 km long using Rhodamine WT and the second over 14 km using Photine CU. The latter indicated that Photine CU was useful for the establishment of flow paths despite its relatively poor persistence. The conclusions from these studies are that selected fluorescent dyes are suitable for water tracing in tropical limestone regions provided that a sensitive fluorometer is used for the analysis. The use of activated charcoal detectors is not recommended but the effects of suspended sediment and bacteria in the stream water are not thought to be limiting factors. A detailed comparison, including costings, of dye tracing and spore methods is also given.