Monitoring Project to be Considered for Tale

October 04, 2014

Sonde deployment

A proposal for undertaking monitoring on the River Tale using the Tryptophan / OBA probe is being considered by the TVT at present. This data will help focus future monitoring, walkover and catchment characterisation work and support the growing weight of evidence of the spatial distribution of diffuse phosphorus loads together with evidence of the likely sources.

There is increasing interest in the use of fluorometry in water quality analysis owing to its ability to provide an efficient means of tracing organic inputs to water courses. Upon excitation with an energy source, a typical river water sample will display a range of fluorescent emissions, which include protein-like (e.g. tryptophan) and fulvic/humic-like fluorescence. These emissions occur at very distinct wavelengths and are readily identifiable in emission spectra. The presence of tryptophan is related to microbial activity and the intensity of tryptophan fluorescence has been shown to correlate strongly with Biochemical Oxygen Demand (BOD), phosphate, nitrate and ammonia.  As such, the use of fluorometry can provide a useful alternative to the time consuming traditional approach to characterising BOD. In addition, there is a growing body of literature which supports the application of fluorescence techniques to identify sources of organic inputs using trypotophan/humic fluorescence ratios.

Fluorometry can also be used to detect Optical Brightening Agents (OBA). OBAs are a common component of laundry detergents and, thus, provide a useful indicator of sewage or grey water inputs to watercourses. Whereas tryptophan fluorescence is likely to be associated with both agricultural and sewage sources, OBA signatures are confined to sewage. The ability to detect both tryptophan and OBAs therefore, provides a unique opportunity to determine the source type of organic inputs. Westcountry Rivers Trust has demonstrated this approach in the River Taw catchment using tryptophan and OBA fluorescence in combination with turbidity data, with results suggesting a clear distinction between agricultural, sewage and in-channel sources.

The Trust is looking at investing in a sonde fitted with two Cyclops-7 fluorometers (for tryptophan and OBA detection) and a turbidity sensor that can be deployed as a mobile unit offering efficient real-time data. It is proposed that this sonde will be deployed at around 15 existing sites across the Tale catchment. These deployments will be made across a range of flow conditions between October 2014 - March 2015.

 

To ensure analytical quality control, the sensors will be calibrated before deployment and be operated by trained members of WRT monitoring staff. At each location the sonde will be deployed and fluorescence intensity logged at five minute intervals. Data analysis and interpretation will be detailed in a short report.

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