Fluorescence-Based Indicators of <i>Escherichia coli</i> and Untreated Wastewater: Turbidity Correction and Comparison of <i>In Situ</i> and Benchtop Fluorometers in a Sewage-Polluted Urban River

Fluorescence-based sensors of tryptophan (TRP) and chromophoric dissolved organic matter (CDOM) can provide real-time information on water quality. We 1) evaluate the accuracy of benchtop (Aqualog) and <i>in situ</i> (Manta) fluorometers for estimating percent untreated wastewater (pctWW) in laboratory experiments; 2) propose a correction for turbidity; 3) test for correlations between TRP or CDOM and <i>Escherichia coli</i> (<i>E. coli</i>) concentrations in river water samples; and 4) quantify the impact of stormflow on wastewater discharge and bacteria in the Tijuana River. In laboratory experiments, Aqualog TRP correlated closely with pctWW (R² > 0.98), while Manta TRP increased with pctWW up to 20-50% but then decreased thereafter. In river water samples, Aqualog TRP and CDOM had stronger correlations with <i>E. coli</i> concentrations than did Manta TRP, which correlates with <i>E. coli</i> but the relationship varies by event. Wastewater flow (m³ s^-1) increased during storm events, but much less than total storm discharge, so the percent wastewater decreased during storms. Benchtop fluorometers provide reliable estimates of wastewater percentage and bacteria concentrations, while <i>in situ</i> fluorometers indicate wastewater and bacteria presence, but may not provide reliable estimates in highly polluted waters or stormflow without further correction of turbidity, inner filter effects, and variations among storm events.