Phoslock Treatment Trial – Cox Bay North Lake

Core-bay

Project Details

The waterbody has a natural groundwater connection due to the low groundwater table. The lake is not supplied with any further groundwater via a bore system. The waterbody has a disconnected drainage network with stormwater only entering the lake on big rainfall events via one bubble-up storm water outlet. The waterbody receives stormwater from residential areas and parks runoff. The waterbody is supplied with oxygen and mixing via five aerator diffusers run by solar power. The water quality experiences ongoing sources of nutrients and is continuously eutrophic with high levels of phosphorus.

WSUD Category: Wetland/lake algae management

CriteriaInformation
Development Type:Public Open Space
Function/Driver:Water quality
Government Area:City of Mandurah
Site Context:Shallow groundwater
Year Completed:2019

Type of wetland

Constructed – Urbanised

Wetland management issue

  • The waterbody has a natural groundwater connection due to the low groundwater table. The lake is not supplied with any further groundwater via a bore system.
  • The waterbody has a disconnected drainage network with stormwater only entering the lake on big rainfall events via one bubble-up storm water outlet.
  • The waterbody receives stormwater from residential areas and parks runoff.
  • The waterbody is supplied with oxygen and mixing via five aerator diffusers run by solar power.
  • The water quality experiences ongoing sources of nutrients and is continuously eutrophic with high levels of phosphorus.

Treatment trialed

  • Name of treatment: Phoslock
  • Quantity used: 2,000 kg
  • Method of application: Mobile shore-based application equipment.
  • Is there any known scientific research supporting its effectiveness? Yes. Proposal for Phoslock treatment of Lyndhurst Place Lake Mandurah, Report, Phoslock Environmental Technologies.

Date(s) of treatment

27/05/2019 one-off application

Outcome of treatment

  • Visual observations: Water column seems clearer.
  • Have water parameters specific to the treatment claims been measured before and after application?  Yes. “Cox Bay North Lake Quarterly Health Check Report, EcoAdvise, August 2019″ (available upon request).
  • Water testing was carried out on the 12/06/2019 after the first major winter rainfall event. Further regular quarterly testing was carried out on the 8/08/2019.
  • Phoslock treatment reduced the TP concentration in the water considerably, by 73% after two weeks and by 94% after three months. Also, Phoslock treatment has helped to drop the EC or TDS levels in water and showed a 71% reduction in Biochemical Oxygen Demand (BOD) levels after 3 months, which would help to maintain the dissolved oxygen levels in the water.
  • Although the TP level dropped post Phoslock treatment, TN and TP levels remained high enough for the lake to be considered eutrophic.

 

Contact Officer:  Tanith McCaw and Dale Robinson

Email: [email protected] and [email protected]