Article Index

Nutrient and organic loading 

Nutrient and organic loading to the Swan Canning river system is a priority issue for the waterway that has impacts on water quality, ecological health and community benefit.

Nutrients are elements or compounds including nitrogen, phosphorus and organic carbon. They enter the rivers from the catchments through drains, surface runoff and groundwater. The most common sources of nutrients entering our rivers include fertilisers, plant matter (e.g. grass clippings, leaves), detergents, sewage and animal waste.

Nutrients are essential for plant growth, including algae, but excess nutrients fuel algal blooms and can promote harmful algae.

Data from 2009 hydrological and nutrient modelling of Swan Canning sub-catchments (8.96MB) show that an estimated 26 tonnes of phosphorus and 251 tonnes of nitrogen flow into the Swan Canning river system each year. Subsequent modelling of the Avon Catchment (11.52MB) in 2015 estimated that 5 tonnes of phosphorus and 213 tonnes of nitrogen flow from the Avon each year.

Swan Canning Water Quality Improvement Plan

In 2006 the Australian Government identified the Swan Canning river system as a coastal 'hot spot' and funding was provided to coordinate a water quality improvement plan for the region. The Swan Canning Water Quality Improvement Plan (4.71MB) (SCWQIP) was released in December 2009.

Modelling undertaken as part of the SCWQIP was used to map water quality conditions in 30 sub-catchments in the Swan Canning Catchment. Based on that predictive modelling the maximum acceptable load to the Swan and Canning rivers per year is 128 tonnes of total nitrogen and 14 tonnes of total phosphorus. The SCWQIP aims to reduce the nitrogen load by 123 tonnes (49%), and phosphorus load by 12 tonnes (46%) annually.

The plan guides investment until the end of June 2017, identifying the most cost-effective management actions to address sources of land-based nitrogen and phosphorus and improve estuarine and coastal water quality.

Swan Canning Water Quality Improvement Plan publications

Local water quality improvement plans

Parks and Wildlife have developed and invested in 10 local water quality improvement plans (WQIPs) for priority catchments, providing local councils and communities with guidance to improve water quality. The WQIPs were developed as a joint project between local government regional and sub-regional natural resource management groups, community groups, State Government agencies and the Water Corporation.

Each plan uses a five-step process to trace nutrient and pollutant pathways through catchments from the source to point of discharge. Each plan identifies existing ecological condition, water quality and pollutant loads, identifies environmental values of water bodies and water quality objectives to protect those values, and identifies and commits to a set of cost-effective management measures to achieve and maintain those values and objectives. The WQIPs have attracted substantial funding which has enabled the implementation of a number of projects including on-ground works, community education and working with local government and industry to facilitate best practice.

Local water quality improvement plans

Tackling nutrients through drainage and nutrient intervention

The Drainage and Nutrient Intervention Program (DNIP) facilitates on-ground works to improve water quality in priority urban and rural drains, tributaries and catchments, influences policy and practice through innovation, project evaluation and demonstration, and guides investment and identifies the most cost-effective management actions to address sources of land-based nutrients, through initiatives such as the Swan Canning Water Quality Improvement Plan.

DNIP works include drain restoration, re-establishment of tributary vegetation, wetland creation and use of nutrient retentive materials. DNIP also trials and operates new nutrient intervention technologies, engages stakeholders and monitors and evaluates drainage restoration works.

DNIP demonstration projects include:

Environmental guidelines for the establishment and maintenance of turf grass areas

The Environmental Guidelines for the establishment and maintenance of turf and grassed areas (3.81MB) were originally published in 2001 and are an important resource for the turf and irrigation industry. The guidelines were reviewed in 2014 by the Fertiliser Partnership Urban Users Working Group, which is chaired by Parks and Wildlife. The reviewed document provides industry best management practice for turf grass areas in Western Australia for the protection of the environment.

How can you help?

  1. Fertilise wise. Limit fertiliser application, and when needed, apply a river-friendly variety in spring or early autumn. Never over-water.
  2. Wash your car on the lawn to keep detergents out of the stormwater drainage system.
  3. Grow local native plants which need less water and fertiliser.
  4. Take your rubbish home when you are out enjoying the rivers.
  5. Pick up your dog's waste and put it in a bin or worm farm. It's full of nutrients that can contribute to the overall nutrient loading of the system.
  6. Check with your local council where to dispose of paint, oil and chemicals. They can end up in the rivers if tipped down the drain.
  7. Use phosphorus-free detergents when washing clothes or dishes. Phosphorus is one of the main nutrients that feed algal blooms.
  8. Compost your leaves and grass clippings – don't let them be washed or blown into the drain.
  9. Register and attend a free Great Gardens workshop.
  10. Become a River Guardian.