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Aquatic vegetation harvesting

Freshwater lakes are dynamic environments and some years will see more plant growth than others. Unlike the tidal lake and canal systems found throughout the Gold Coast, the presence of aquatic plants is entirely natural in these lakes and should be expected. It is neither practical nor desirable to maintain our non-tidal waterways in a weed free condition.

Harvesting aquatic vegetation

Aquatic plants play an essential role in removal of nutrients from the water column and lake bed sediment. At present, the aquatic plants are the primary utilisers of nutrients (nitrogen and phosphorous) in the lake systems. They also provide a valuable habitat for native fauna. This includes zoo plankton and other microscopic life that graze primarily on algae.

Overzealous removal of aquatic plants can lead to an increase in the volume of water borne nutrients. This in turn, tends to increase rates of algal growth to the extent where blooms occur. This includes potentially toxic cyanobacteria blooms (blue-green algae). Systems dominated by algae are significantly more difficult to manage effectively. Under such conditions, fish kills, oxygen depletion, bird deaths and other adverse impacts can become far more common.

Monitoring lakes and waterways

To combat this and provide a more cost-effective long-term solution to managing water quality in the lakes, total vegetation removal is no longer undertaken. Instead, manual inspections of the lakes now occur on a regular basis to assess plant growth and identify areas that require necessary harvesting. Inspection based, targeted weed harvesting will allow aquatic plants to grow largely unimpeded throughout the spring and summer months. Harvesting the nutrient rich 'crop' is typically undertaken each autumn before die-off occurs. This maximises the amount of nutrient removed from the lake.

For the lakes' long-term wellbeing, a buffer zone of aquatic vegetation is required around their perimeters. This is to ensure that there is sufficient plant life in place to support fish and colonies of microorganisms necessary for control of algal growth. Retention of these buffer strips therefore assists in the mitigation of algal outbreaks by providing a refuge for native fauna during harvesting operations. The buffer zone flora also absorbs nutrients from the sediment and water column on a year round basis. Its retention assists in the gradual improvement of water quality in the lake system.

Managing aquatic vegetation

In general, the vegetation of the buffer strips in the larger lake systems are comprised of a two metre to five metre wide band of Ribbon Weed and Snow Flake Lily. Other species present include Azolla (native floating fern), Salvinia and Mexican Lily. The latter two species are both exotic pest species, which are subject to additional controls.

To find out more about the City's harvesting program, contact our Maintenance Services team on 07 5667 5974.

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