High frequency fluorescence monitoring reveals new insights into organic matter dynamics of an urban river, Birmingham, UK

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Natural organic matter (NOM) is fundamental to many biogeochemical processes in river ecosystems. Currently,however, we have limited knowledge of NOM dynamics across the spectrum offlow conditions as previous stud-ies have focused largely on storm events. Field deployablefluorescence technology offers new opportunities toexplore both stochastic and predictable diel NOM dynamics atfiner time-steps and for longer periods thanwas hitherto possible, thus yielding new insight into NOM sources, processing, and pathways. Hourlyfluores-cence data (humic-likefluorescence [Peak C] and tryptophan-likefluorescence [Peak T]) and a suite of hydro-climatological variables were collected from an urban river (Birmingham, UK). We explored monthlyconcentration-discharge (C-Q) patterns using segmented regression and assessed hysteretic andflushing behav-iour for Peak C, T and turbidity to infer source zone activation. Diel patterns were assessed during lowflow pe-riods. Wavelet analysis identified strong diurnal variations in Peak C with early morning peaks while no dieldynamics were apparent for Peak T. Using generalised linear modelling relationships between Peak C periodicityand both solar radiation and time since previous storm/scouring event were identified. Breakpoints and positiveslopes for C-Q relationship highlighted chemodynamic behaviour for NOM over most of the monitoring period,with Peak T mobilised more relative to Peak C during high Q. Hysteresis patterns were highly variable butflush-ing behaviour of Peak T and C suggested exhaustion of humic compounds during long duration events and fol-lowing successive rainfall events. Peak Tflushing was correlated with Q magnitude highlighting the potentialfor combined sewer overflows to act as important NOM sources despite significant dilution potential. This re-search highlights the potential of real-time,field deployablefluorescence spectroscopy as a viable method forproviding insight into diel and transport driven NOM dynamics.


Original languageEnglish
Article number135668
JournalScience of the Total Environment
Publication statusPublished - 22 Nov 2019