Plan for Water Quality Monitoring

August 05, 2015

The Autumn is the best window of opportunity to begin carrying out water quality monitoring. This project will be a best practice example for others, led by the TVT and Westcountry Rivers Trust. Below is a breakdown of what the project would entail.

Sonde deployment

We will monitor water quality on the River Tale using a new portable fluorometer (SMF4) and the Tryptophan / OBA / Turbidity multi-probe. The SMF4 is a portable instrument tuned to detect tryptophan-like fluorescence. Samples are introduced to the optical chamber via a small cuvette - this allows samples to be filtered prior to analysis. The multi-probe is designed to remain in-situ and can be set to record tryptophan-like fluorescence, Optical Brightening Agents, turbidity and temperature at regular intervals, typically every 15 minutes. By collecting data using both instruments we will be able to 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. We will endeavour where possible to leave the multi-probe in situ between spot sampling visits. This will allow us to gain a greater understanding of temporal changes, whilst also helping with the accuracy and interpretation of data from the SMF4 portable fluorometer. 

 

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 watercourses. 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. 

Approach 

The Westcountry Rivers Trust has invested in a multi-probe 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, plus we also have a new portable tryptophan fluorometer (SMF4) to be used in collaboration. It is proposed that these instruments will be used at around 15 existing sites across the Tale catchment. These deployments will be made in a range of flow conditions, between October 2015 - March 2016. 

 

To ensure analytical quality control, the sensors will be calibrated before deployment and will be operated by trained members of WRT monitoring staff. At each location the fluorescence intensities and turbidity levels will be measured using both instruments, if turbidity is very high then we can filter samples prior to analysis by the SMF4 portable fluorometer. If a suitable site is found then the multi-probe will remain in place for the duration of the study, except for sampling days where it will be used at all sites in conjunction with the portable fluorometer, before being re-sited to its original location. 

Outcomes

Collected data will be analysed, interpreted and will be detailed in a short report. It is important to note that the data will be freely available in the public domain, so long as all the sampling points are public access. The relevant agencies/companies will be able to use the data should they wish to carry out their own investigations. As with all data of this kind it is limited by the duration of the study. Data collected over several years/decades is scientifically more credible than single season data. That said, the purpose of this project is to help us in further pinpointing our actions, to those areas of greatest concern. Without projects of this nature such focusing of actions wouldn’t be possible, this could also be one the building blocks for further long term monitoring and the benefits that brings.

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