A Case Study: The deployment of a novel in situ fluorimeter for monitoring biological contamination within the urban surface waters of Kolkata, India.&#160;
Authors: Fox Bethany , Thorn Robin , Dutta Tapan , Reynolds Darren 
Published: March 2021

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