About the Lake
Project Summary
Aim
To reduce the phosphorus loading within the lake.
Site Context
Laguna Niguel Lake (Sulfur Creek Reservoir) was built in 1966. The lake is primarily used for scenic recreation and local fishing, however it also is an important sanctuary for waterfowl. Recent issues with poor water quality, foul odours, declining fishery and outbreaks of avian botulism prompted the need for water quality management.
Why Treatment Was Needed
Although nutrient inputs from the inlet creek and surface runoff contribute to the annual load of phosphorus into the lake, monitoring of the water quality and lake sediments in recent years suggested internal phosphorus loading as a significant contributor to the water quality issues.
Phoslock Application
29 April - 2 May 2013
The application was carried out over a period of 4 days in 2013.
Custom mixing chamber
Phoslock was mixed with lake water in a custom mixing chamber and injected to the lake surface.
GPS-guided treatment zones
GPS technology was used on the boat to assure uniform application in the 4 treatment zones of the lake.
Phoslock dosing in each zone was based on surface area, water depth, sediment characteristics and phosphorus concentrations.
How Performance Was Evaluated
Water quality analysis was conducted from lake samples collected at 3 fixed locations in the lake in 2012 and 2013. Post-treatment water sample collection and analysis continued through September 2013.
Benthic macroinvertebrate sampling and assessment were conducted both upstream and downstream of the lake immediately before treatment on 4/29/2013 and four days after Phoslock application completion on 5/6/2013.
Sediment samples were collected from 3 sites in the lake using a threaded stainless steel coring apparatus. Sediment samples were taken prior to the Phoslock application on 4/29/2013 and again 3 and 6 months post-treatment on 8/7/2013 and 12/4/2013. The top 5 cm layer of sediments from each sample location was sent to the laboratory for analysis. Sequential extraction was used to determine relevant phosphorus fractions and compare concentrations of available and stable phosphorus forms prior to and following treatment.
Measured Water Quality Response
No significant changes were measured in pH, turbidity, conductivity and alkalinity throughout the study.
However, Phoslock rapidly, in less than 2 weeks, and significantly decreased total phosphorus by more than 80% and free reactive phosphorus by more than 95% in the water column.
It was also documented to bind the potentially releasable sediment phosphorus fractions to form stable fractions post-treatment.
The monitoring also documented no significant composition or diversity alteration to the benthic macroinvertebrate community after the Phoslock application.
Outcome
- Phoslock significantly decreased and sustained lower concentrations of phosphorus in the water column.
- The application shifted sediment phosphorus fractions to highly stable forms compared to pre-treatment concentrations.
- No significant composition or diversity alteration to the benthic macroinvertebrate community was documented after treatment.
- Phoslock provided water resource managers at Laguna Niguel Lake with an ecologically sound in situ solution to address phosphorus pollution and restore water quality.
Reference: Bishop, W.M., McNabb, T., Cormican, I., Willis, B.E., and Hyde, S. 2014. Operational Evaluation of Phoslock Phosphorus Locking Technology in Laguna Niguel Lake, California. Water, Air Soil & Pollution, 225 (7), 1 - 11.
