Novel phosphate monitoring technology from OTT Hydrometry is helping the South Cumbria Rivers Trust (SCRT) to improve water quality during a project to restore a lake in the north of England.
Funded by United Utilities, the Elterwater Remediation Project has been created to improve water quality by increasing water flow and dramatically lowering residency time through the lake, which is also a Site of Special Scientific Interest.
Between 1974 and 1999 United Utilities operated a wastewater treatment works serving the Elterwater village within the consents of the day. However this and other sources left a legacy of phosphorus-enriched sediments in the inner and middle basins of the lake - Soluble Reactive Phosphate (SRP) released from the sediment accumulates over time. This has caused eutrophic and hyper-eutrophic conditions leading to algal blooms, anoxia and poor water quality.
A study commissioned in United Utilities AMP5 business plan for April 2010 to March 2015 identified the key issues and options for resolution. The options included improving the lake’s water quality by dredging to remove the phosphorus rich sediments or diverting two local becks to improve water turnover and prevent the conditions necessary for phosphorus release and the creation of algal blooms.
The preferred solution is to divert the becks - dredging would permanently remove the phosphorus rich sediments but could cause significant environmental damage particularly in the disposal of the enriched sediments. A continuous remote phosphate analyser is keeping a check on progress.
Phosphate in the lake sediment is clearly the cause of the lake’s ongoing water quality problems, so 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.
Background phosphate monitoring commenced in August 2014 with samplesbeing been taken at 2 week intervals for laboratory analysis. However, continuous monitoring is always preferable, when possible, because spot sampling risks missing pollution incidents.
Traditional continuous phosphate monitors employ colorimetry and generally require mains power, which is often not available at remote sites. However, the ‘Cycle-P’ from OTT Hydrometry is battery powered and able to operate unattended in the field, running over 1,000 tests before a field service is necessary to change the reagents.
When combined with telemetry, the instrument delivers almost real-time data at user-selectable intervals - typically 1 to 4 hours.
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 SCRT’s Technical Officer Dr Mike Sturt’s mobile phone. The Environment Agency has also installed a water quality monitor (DO, pH, EC, turbidity) at the same location which also has a text alarm system.Commenting on the results to date, Dr. Sturt said:
“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. It is still early days, but we are seeing a marked improvement in waterquality, which is very pleasing.”