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<p>With increasing pressures on water&#160;resources due to population, industrialization, agriculture, urbanization and climatic changes,&#160;improved&#160;temporal and spatial&#160;understanding&#160;of&#160;water quality&#160;is&#160;required.&#160;The&#160;development of&#160;new monitoring parameters, along with&#160;new monitoring technologies,&#160;are needed to provide real-time insight into the biogeochemical processes that underpin aquatic ecosystem health.&#160;Aquatic fluorescent organic matter (AFOM) has&#160;recently&#160;been&#160;explored&#160;for its&#160;potential&#160;to&#160;measure&#160;underpinning&#160;microbial activity within aquatic systems,&#160;which are essential in&#160;maintaining&#160;ecosystem health and function, with specific focus on the&#160;utilisation of&#160;tryptophan-like fluorescence (TLF or Peak T).&#160;<em>In situ</em>&#160;real-time portable fluorimeters&#160;have been extensively&#160;used&#160;for the identification&#160;and measurement&#160;of anthropogenic pollutants, such as polycyclic aromatic hydrocarbons (PAH) and optical brighteners.&#160;More recently, this&#160;portable&#160;fluorescence&#160;technology has been adapted&#160;for&#160;the monitoring and sensing of&#160;biological contamination, using&#160;microbially&#160;derived fluorescence signals&#160;(TLF).&#160;</p>
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<p>The principal aim of this research was to deploy, for the first time in the field, the&#160;VLux&#160;TPro&#160;sensor&#160;(Chelsea Technologies Ltd., UK)&#160;and&#160;to assess the ability of this novel&#160;fluorescence-based sensor&#160;to&#160;detect&#160;the presence of biological contamination&#160;and elevation of microbial activity.&#160;This sensor has been developed to correct&#160;<em>in&#160;situ</em>&#160;real-time sensing data for&#160;optical interferences (caused by&#160;high&#160;turbidity and absorbance), as well as to provide quantitative fluorescence data by reporting in standardised quinine sulphate units&#160;(QSU).&#160;The urban surface waters within the city of Kolkata provide an interesting&#160;challenge&#160;for water quality sensors, allowing exploration of sensor performance in a range of water bodies&#160;ranging&#160;from turbid river waters to&#160;open sewer&#160;canals.&#160;</p>
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<p>The sensor data collected demonstrates the ability of the VLux to identify waters with high bacterial loads using Peak T fluorescence. Moderate and weak positive correlations are seen for Peak T and <em>E. coli</em>&#160;or&#160;total coliform&#160;counts, R2&#160;= 0.55 and 0.38 respectively. However, a strong significant correlation is identified between Peak T and the total bacterial cell counts (R2&#160;= 0.75).&#160;This demonstrates that Peak T should not be used as a species-specific enumerator in complex surface water matrices. It does, however,&#160;demonstrate the ability of&#160;the&#160;VLux&#160;to successfully measure optically corrected and quantitative&#160;Peak T fluorescence&#160;in QSU.&#160;Therefore,&#160;data&#160;regarding the activity and fast-acting dynamics of freshwater bacterial communities, in response to pollution events,&#160;can now be reliably sensed and collected. This was demonstrated by the elevated Peak T fluorescence intensity observed when biologically contaminated water entered the main river channel, enabling identification of&#160;contamination hotspots.&#160;Sensing data has been further validated&#160;by laboratory&#160;analysis of spot samples confirming the&#160;significant correlations between Peak T and bacteria&#160;and&#160;nutrient concentrations.&#160;Further field-based research is required&#160;to determine&#160;the feasibility of long-term&#160;catchment scale sensor&#160;deployment as part of a sensing network,&#160;for the&#160;monitoring of&#160;biological activity&#160;and&#160;pollution events in freshwaters.&#160;&#160;</p>
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<p><strong>Acknowledgements:</strong> This research was supported by the NERC-DST Indo-UK Water Quality Programme NE/R003106/1 and DST/TM/INDO-UK/2K17/30. We would also like to acknowledge Chelsea Technologies Ltd. for ongoing VLux TPro sensor support.</p>
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