Implications of Tryptophan-Like-Fluorescence Long-Term Monitoring for Bacterial Detection in a Mountainous Karst Aquifer

Fluorescence spectroscopy approaches like tryptophan-like-fluorescence (TLF) have been presented as a powerful tool to easily detect bacteriological contamination in groundwater used for drinking water supply in rural areas, since bacteria are able to synthetize L-Tryptophan. As commonly happens in karst springs, during flooding conditions high turbidity levels (and associated bacteria transport) are observed and thus, the exploitation of groundwater for human consumption is hindered. Hence, TLF has been considered as a potential early warning parameter to prevent polluted groundwater to reach drinking water capture points at Sierra de Ubrique carbonate karst aquifer (S Spain). The obtained results in the studied spring showed low correlation with faecal indicators (p = 0.26–0.75) and suggests the complexity in obtaining reliable continuous measurements mainly due to the multiple potential origins of tryptophan (cheese whey, bacterial activity in soil or karst conduits...) and the biochemical reactions in the soil, epikarst and karst conduits. The suitability test realized in Ubrique test site relegates TLF to a function as a biological risk indicator rather than an early warning parameter.