Control Options

Nutrient Control

Nutrient import into wetlands on the Swan Coastal Plain is facilitated by overland flow from the catchment, usually through stormwater drains, or through enriched groundwater. Consequently, even if external inputs such as stormwater are reduced, groundwater can still constitute an important source of nutrients. Currently, there are no viable means to control nutrients entering via groundwater with the exception of lining the wetland. Where groundwater is enriched, lining should be considered during the design phase of constructed wetlands..

Remediation of nutrients in purpose-built wetlands is an approach that is used in Australia and elsewhere in the world. Constraints to the success of such systems on the Swan Coastal Plain include:

Close proximity of groundwater to the surface in many areas provides a challenge when siting nutrient remediation wetlands unless they are lined. Wetlands in connection with the groundwater may export nutrients to the groundwater or receive inputs of nutrients.
High concentrations of dissolved organic carbon (DOC) which are drained into stormwater outlets from newly developed urban areas may limit the growth of biofilms which are an important biological uptake mechanism in remediation wetlands (Lund 2001).
The sandy soils of the Swan Coastal Plain have a low phosphorus retention index resulting in high concentrations of phosphorus leaching into the groundwater.

Despite these constraints, the potential exists to use remediation wetlands to treat nutrient- rich water on the Swan Coastal Plain. In a purpose built wetland at Henley Brook, a removal efficiency of up to 10% was obtained for filterable reactive phosphorus (FRP) (Lund et al. 2001). Ecomax is a company that constructs the Storm Max nutrient removal system. This system uses amended soils to remove nutrients and can be designed for various site conditions, flow rates and volumes. The manufacturer claims a 19.3% reduction in the concentration of nitrogen and a 51.4% reduction in the concentration of total phosphorus with its use. However, there is no information available on any independent assessments of these claims. Further research into the effective design of systems specifically for conditions on the Swan Coastal Plain and investigation of techniques such as the Storm Max system should yield practical guidance for treating nutrient rich water entering natural and constructed wetlands.

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Updated : 23 June, 2009