Light coloured growth shows the impact of recent spraying.
After testing spraying in the Claude Abel Lily Pond, Parks has started to control the invasive Mexican water lily in the pond. The test spraying showed no residue of glyphosate, but the Dissolved Oxygen (DO) levels did come back slightly lower than when tested before the treatment.
However, because of the naturally rotting Mexican water lily, the DO levels were already very low, and it is thought it will not start to improve until a great deal more of the water lily is removed.
The Waitakere Ranges Local Board asked that the water be tested before spraying continued: the test patch findings have minimal negative impacts on the pond environment the entire pond will be treated in patches of approximately 1/4 of the pond each control period.
It also appears the pond has naturally low DO levels as maximum DO concentrations before the glyphosate was applied was about 2.9 mg/l and. DO concentrations should be above 5 mg/l to support aquatic ecosystems but some aquatic life can survive DO concentrations of less than 0.5 mg/L. After glyphosate was applied DO concentrations generally varied between 0 to 1 mg/L. An expert in freshwater systems has advised Parks that it is likely the low water flow through the pond will be contributing towards the naturally low DO level, but the current volume of lilies naturally decomposing in the water body (not due to treatment) will also be a large factor causing low DO levels.
Consequently parks is satisfied that the impact on the pond water quality will be minor during the staged treatment and that continuing with the treatment will help improve the pond water quality in the long term.
So you can expect to see a further area sprayed before long. Notices will be posted at the park to that effect.
The plan is to control the Mexican water lily progressively, rather than spray the whole area in one go. This will enable Parks to monitor the impacts as it does the work..
The Mexican water lily was introduced some decades ago to beautify the pond but has overtaken other non-invasive water lily species, to the extent there was very little open water left.
A proposal for community hand removal was explored, but the dangers associated with the work precluded this approach. The pond is quite deep in some places and the Mexican water lily has large tubers, which can be six feet long. Previous hand removal efforts resulted in vegetation being broken off, but the tubers remaining, and regrowth was swift.