Tryptophan-Like Fluorescence for Monitoring Fecal Contamination in a Marsh-Dominated Estuary

Research has revealed a positive relationship between tryptophan-like fluorescence (TLF) and fecal indicator bacteria (FIB) in freshwaters. However, TLF’s relationship with FIB in estuarine systems is less explored. This study evaluated TLF as a surrogate for FIB in a coastal setting by exploring the following objectives: (1) assess the accuracy of in situ TLF based on laboratory measurements, (2) evaluate how TLF determined with different methods correlate with FIB, and (3) identify factors that relate to the relationship between in situ TLF and FIB. Over high-frequency field campaigns spanning storm and baseflow conditions, samples were processed for Enterococci and E. coli and optical analysis. Concurrently, in situ sensor measurements were recorded via sonde. In situ TLF moderately correlated with lab-measured tryptophan-like fluorescence (Peak-T; r = 0.68), with the inaccuracy of in situ TLF most pronounced during storm conditions. While in situ TLF correlated with FIB (TLF:Enterococci r = 0.51), measurements from other sensors exhibited closer correlations with FIB. These results suggest that in situ TLF may be a more suitable FIB correlate during point-source contamination events and that TLF alone may not be a sufficient surrogate for fecal contamination in some coastal settings.