FEATURE MONITORING TECHNOLOGY
MONITORING WATER QUALITY
Phosphate monitoring equipment from OTT Hydrometry is being used in a project created to improve the water quality of Elterwater lake in Cumbria
D
esignated a Site of Special Scientific Interest (SSSI), Elterwater in the
Lake District is a high amenity value lake comprised of three basins measuring 930m long and with variable widths up to 320m. However, a wastewater treatment plant operated by United Utilities until 1999, plus other sources, resulted in phosphorus enriched sediments in the inner and middle basins of the lake. These in turn caused eutrophic and hyper- eutrophic conditions – leading to algal blooms, anoxia and poor water quality. Under United Utilities’ asset
management plan for April 2010 to March 2015 (AMP5), a study was commissioned that identified the key issues and options for resolution. It was decided that while dredging
would permanently remove the phosphorus rich sediments, it could cause significant environmental damage particularly in the disposal of the enriched sediments. The preferred solution was therefore to divert two local becks. Dr Mike Sturt, technical officer at SCRT
(South Cumbria Rivers Trust), said: “Soluble Reactive Phosphate (SRP) released from the sediment accumulates over time and becomes bioavailable, resulting in a proliferation of algae and bacteria. This causes a lowering of dissolved oxygen and pH which, in turn, causes an increase in SRP desorption from the sediment. So, there is a complex cycle in play which causes thermal stratification
28 SEPTEMBER 2016 | INSTRUMENTATION
and anoxic/high turbidity conditions in the summer months. As a result, Elterwater is incapable of supporting natural, healthy, populations of fauna and flora beyond benthic invertebrates.” With phosphate the cause of the water
quality issues, the aim of the restoration project is to implement a sustainable solution that does not result in an increase in SRP within the water body. To help, background phosphate monitoring began in August 2014, with samples taken at two week intervals for laboratory analysis. However, because spot sampling risks missing pollution incidents, continuous monitoring is preferable.
THE TECHNOLOGY To meet demands, the battery powered ‘Cycle-P’ phosphate monitor from OTT Hydrometry was selected. This is an in-water total reactive phosphate analyser, capable of operating unattended in the field and running over 1000 tests before a field service is necessary to change the reagents. The instrument has an onboard logger, and the quality of the data is underpinned by QA/QC processing in conjunction with an on-board NIST standard. The Cycle-P methodology is based on US EPA standard methods, employing pre-mixed onboard colour coded cartridges for simple reagent replacement in the field. With a detection limit equal to or less than 0.0023mg/L PO4
-P, and a range of 0-0.3mg/L PO4 -P,
the Cycle-P is able to measure down to extremely low levels, which makes it ideal for the Elterwater application. However, a higher range can be specified at the time of order (0 to 1.2mg/L). Two units were initially installed, but after one year it became clear that just one was sufficient.
MONITORING The background monitoring undertaken by the Cycle-P (and lab samples) has not shown significant SRP in the water body because the release of phosphate from the sediment is quickly taken up by algae. However, the piped diversion of the Great Langdale Beck delivers around 122 litres/sec of very clean water, and the Cycle-P constantly checks that this is not causing a rise in SRP from the sediment. If alarm conditions arise, the system automatically sends a text message to Sturt’s mobile phone. The Environment Agency has also installed a water quality monitor (DO, pH, EC, turbidity) at the same location and this also has a text alarm system. Sturt added: “The clean water from Great Langdale Beck started to arrive in the inner basin during early February 2016 and at the time of writing no alarms have occurred, so we are cautiously optimistic!”
OTT Hydrometry T: 01246 573480
www.ott-hydrometry.co.uk
OTT Hydrometry’s ‘Cycle-P’ phosphate monitor, an in-water total reactive phosphate analyser, has been selected for Elterwater, a high amenity value lake
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