On slightly more golden pond
The trial clean-up of Nelson’s Modellers’ Pond is almost over, and there is some light in the murky waters.
A report on the three-month trial came before the Nelson City Council works and infrastructure committee on Thursday, five days before the end of the trial.
While council officers were reluctant to discuss progress before receiving more details, committee chairman Stuart Walker said anecdotal results were positive.
‘‘We have a beneficial trend that is very very encouraging, but we don’t have the concrete data to support that at the moment,’’ he said.
‘‘The indication is that we’ve got wildlife in there that we never had before.
‘‘There’s tiny small fish in there; right through to herrings eating algae on the surface, schools of them I witnessed a couple of days ago; there’s eels in there, at least two were seen a couple of days ago.’’
Walker said modellers had told him they had never seen activity like it before.
The method being trialled is product called Diatomix, a mix of silica-coated nano-sized nutrient packs called flocs.
These flocs are consumed by diatoms, a type of microorganism which is a base for a food chain including insects and fish which tend not to eat the algae choking the pond.
When given the Diatomix nutrient mix – which algae cannot eat – diatoms quickly outperform the algal blooms and starve them out, resulting in a clean pond.
This method has been used successfully in Australia, and is also being looked into for Lake Ellesmere in Canterbury.
The trial’s budget doubled to $135,000 with no apparent explanation in August.
Councillor Matt Lawrey asked for an indication of how the trial was going, which prompted Walker’s response.
‘‘The trial had, as part of it, a date set up where we discussed whether or not we go further with the trial. It seems to me that when that plan was hatched we thought we would have an idea of whether the trial was being successful,’’ Lawrey said.
‘‘I don’t want to refer something up to council if it’s not bearing any fruit at this stage.’’
Council chief executive Pat Dougherty said they had ‘‘some data’’, but couldn’t make a judgement at this stage.
‘‘We don’t want to be drawn into making conclusions today when we specifically brought this report to ask for some more time to evaluate it,’’ he said.
NCC group manager of infrastructure Alec Louverdis said the committee report was a ‘‘procedural’’ one, asking for the final report to be accepted at the next full council meeting to give the trial time to be completed on November 20.
The results of the trial will be delivered to the full council on December 13.