Freshwater is a precious resource that has become very limited due to increased water usage associated with global population growth and decreased supplies in many regions due to climate change. Recycling water ensures that the use of available water supplies can be maximised for anthropogenic uses and environmental purposes.

Recycled water needs to be of adequate quality to be suitable for its intended use. Before water can be reused, it is often treated. For example, wastewater is treated using a range of technologies before it may be suitable for agricultural purposes or discharged into natural waterbodies. Urban stormwater is often passed through constructed wetlands to reduce nutrients, heavy metals, and other pollutants.

The Ebro Delta in Catalonia, Spain, has extensive rice cultivation where there is intensive use of pesticides. Once the water is used in the rice paddies, it is discharged into Spain’s second largest wetland system that is protected as a Natural Park and an EU Natura site. Constructed wetlands have shown great potential in treating rice runoff before it reaches these wetlands. Constructed wetlands are also used in Melbourne, Australia, to treat urban stormwater that is discharged into local rivers and estuaries. In the past 25 years, the focus on these wetlands has been to remove nitrogen to reduce the loads of nitrogen flowing into Port Phillip Bay. Recent research has found this urban runoff to be also contaminated with heavy metals, petroleum hydrocarbons, and many pesticides, and the untreated runoff is toxic to aquatic life.

The goal of this research is to determine what level of treatment is required using constructed wetlands to ensure that the discharges from these wetlands are non-toxic to aquatic life in the receiving waters. This will be achieved by conducting laboratory and field-based ecotoxicological tests to assess whether the waters and associated sediments upstream and downstream of these wetlands are toxic to laboratory test species. They will also determine how effective these wetlands are in reducing bioavailable nutrients. This information will help determine the level of treatment required from constructed wetlands and whether they need to be augmented with other treatment devices to improve treatment to protect aquatic ecosystems.

Research group websites

• Aquatic Environmental Stress Research Group (AQUEST)
• Climate solutions and ecosystem services (CLIMES)