Our estuaries are under increasing pressures from reduced rainfall and flows, an increasing population and intensification of land use. Nutrient over-enrichment is a serious problem, and symptoms manifest as algal blooms, low oxygen and occasional fish deaths.
The Innovative Remediation strategy will test new technologies for nutrient management, gathering evidence to see if they can be used at a catchment-scale. This strategy will develop and trial new technologies to reduce nutrient losses to waterways from urban and rural land uses and improve soil condition for plant growth.
By wise investment to develop and test new treatment options, we can ensure that we have solutions available to achieve value-for-money outcomes for our estuaries, supporting both environmental and economic needs.
Soil amendment trials
Soil amendments are products that raise the ability of soils to retain phosphorous (phosphorus retention capacity) and reduce phosphorus losses from farms, ensuring it stays on the farm for plant growth. Numerical catchment modelling now backed by trial results has shown up to 50 per cent reduction in phosphorus losses when soil amendments are combined with good fertiliser management.
The Regional Estuaries Initiative has developed partnerships with farmers and local governments to trial soil amendments targeting high phosphorus (P) loss areas. The trials use Iron Man Gypsum (IMG), produced by Iluka Resources Ltd in Capel, which has a high capacity to retain phosphorus. Our learnings will also be transferable to other high P-retaining materials.
Four trials have been established exploring five application rates and four incorporation techniques on sites in the Peel-Harvey and Vasse-Wonnerup catchments. These include land used for dairy grazing, hay production and beneath a recreational sport ground. Soil, leached rain water, groundwater and plants are monitored to assess: environmental benefits of reducing P loss to waterways; improvements in agricultural production due to increased P retention; and any environmental risks.
Results in the first year have found that IMG treatment can reduce the amount of phosphorus lost by up to 20 kg/ha and that surface applications with slight incorporation can reduce runoff P concentrations by more than 90 per cent.
Parallel studies have also been carried out to investigate any risks of these IMG applications to beef and dairy cattle via soil or drinking water as well as to aquatic organisms that may be in downstream waterways.
Learnings from the trials will be used to establish guidelines for soil amendments on the Swan Coastal Plain.
Soil amendments are products that raise the phosphorus retention index of soils and reduce phosphorus losses from farms, ensuring it stays on the farm for plant growth. Numerical catchment modelling and cost benefit analysis has shown up to 50% reduction in phosphorus losses when soil amendments are combined with good fertiliser management.
Introducing new materials to agricultural systems takes time to build confidence with users, who may be unsure of the efficacy, risks and benefits of soil amendments. The Regional Estuaries Initiative will develop partnerships with turf farmers and other horticultural and agricultural businesses to trial soil amendments. Monitoring of demonstration sites will be used to establish guidelines for soil amendments on the Swan Coastal Plain.
In-drain treatments using soil amendments
Techniques to treat soluble phosphorus in waters entering and flowing in agricultural drains are being trialled in the Peel-Harvey catchment. A series of in-drain treatment designs incorporating soil amendments were piloted in the nutrient rich Gull Road drain in 2017 and expanded in 2018. The designs consist of a several treatment bed configurations in the base of the drains as well as swales and riffles. These are being intensively monitored to evaluate the benefits, management requirements and risks of treatments with full findings to be reported in 2020.
Water treatment techniques to reduce algal blooms in the short term may be an option to provide respite to estuarine health while longer nutrient reduction activities in the catchment are realised. By testing treatments that lock up soluble phosphorus and treat algal blooms, we will identify when and where these approaches work best.
Several new high-capacity phosphate binding clays will be trialled as in-stream dosing agents in the upper Serpentine catchment (Peel-Harvey) and for dosing large pools in the lower Vasse River (Vasse-Geographe).
Some of the clays will incorporate the benefits of nano-technology and require working with innovative partners to upscale these for field trials. Evaluation of the materials will focus on working out application regimes and techniques to maximise how these take up soluble phosphorus either in-stream or from sediments. Algal flocculating materials will also be evaluated in combination with clay applications to treat algae once these bloom in large water bodies such as the Vasse.
The Regional Estuaries Initiative is investigating the effectiveness of a newly developed clay at two sites, Punrak Drain, a tributary of the lower Serpentine River and the Lower Vasse River.