A study into the influence of invasive aquatic weed, the Mexican waterlily (Nymphaea Mexicana) on ecology and water quality of the lower Vasse River has been completed.
The study, funded through the Revitalising Geographe Waterways program, was initiated in response to community concern of the rapid expansion of the waterlily over recent years, which is estimated to cover about a quarter of the Lower Vasse River.
The study found that the waterlilies have both positive and negative impacts on the ecology and water quality of the river. Benefits included reducing the incidence of blue green algal blooms within and between patches of waterlilies. Waterlilies were also found to support more macroinvertebrates than other parts of the river, owing to the vegetative habitat they create. The greatest diversity was found at the edges of waterlily patches, where oxygen levels are higher.
The waterlilies also had negative impacts on the water quality with much lower dissolved oxygen below waterlily patches. The main concern, however is the loss of open water habitat in the river, which is likely to impact on water birds, and aesthetics of the river.
City of Busselton’s Senior Sustainability and Environment Officer, Robyn Paice said that the lilies will continue to spread throughout the Lower Vasse and need to be controlled to prevent further loss of open water. “However, we also need to consider the benefits of the waterlilies in reducing algal blooms”, she said.
The City will undertake strategic control of the waterlily in the Lover Vasse River, to progressively reclaim open waters between patches of waterlily. This will involve the use herbicides that are approved for use in waterways and will not persist in the ecosystem. Effectiveness, impacts and bird activity will be monitored closely.
Large scale removal of the lilies in a short time period presents a risk because rapid plant die-off and sediment disturbance can cause deoxygenation of the water and nutrient release. This could harm aquatic fauna and worsen algae blooms.
A Factsheet containing information on waterlilies in the lower Vasse River has been published, along with a scientific report and both are available on the Revitalising Geographe Waterways website https://rgw.dwer.wa.gov.au/rgw-publications/ .
For more information or copies of the factsheet, visit the City of Busselton administration building or contact Robyn Paice via email robyn.paice@busselton.wa.gov.au or phone 9781 0457.
The Revitalising Geographe Waterways program is supported by the State Government to improve water quality, waterway health and management of Geographe waterways.