In situ tryptophan-like fluorometers: assessing turbidity and temperature effects for freshwater applications

• Published in: Environmental science--processes & impacts 2015-04, Vol.17 (4), p.740-752
• Main Authors: Khamis, K, Sorensen, J P R, Bradley, C, Hannah, D M, Lapworth, D J, Stevens, R
• Format: Article
• Language: English
• Subjects: Environmental Monitoring - methods; Fluorescence; Fresh Water - chemistry; Temperature; Tryptophan - analysis; Water Pollutants - analysis
• ISSN: 2050-7887; 2050-7895
• DOI: 10.1039/c5em00030k

Tryptophan-like fluorescence (TLF) is an indicator of human influence on water quality as TLF peaks are associated with the input of labile organic carbon (e.g. sewage or farm waste) and its microbial breakdown. Hence, real-time measurement of TLF could be particularly useful for monitoring water quality at a higher temporal resolution than available hitherto. However, current understanding of TLF quenching/interference is limited for field deployable sensors. We present results from a rigorous test of two commercially available submersible tryptophan fluorometers (ex ∼ 285, em ∼ 350). Temperature quenching and turbidity interference were quantified in the laboratory and compensation algorithms developed. Field trials were then undertaken involving: (i) an extended deployment (28 days) in a small urban stream; and, (ii) depth profiling of an urban multi-level borehole. TLF was inversely related to water temperature (regression slope range: -1.57 to -2.50). Sediment particle size was identified as an important control on the turbidity specific TLF response, with signal amplification apparent