Wires crossed at Waituna

| December 7, 2018 | 0 Comments
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Seagrass. Ruppia megacarpa v R. polycarpa
By Ken Calvert
16 October 2011

It would seem to me that the authorities controlling the lagoon have got their wires crossed.

They are bemoaning that the lagoon is going to flip, seagrass is dying and algae growth and sediment are taking over.

As I understand it, the reason for declaring Waituna a RAMSAR area was for the migratory birds that pass through it.

However, 18 of the 21 odd migratory species mentioned in that original plea are wading birds that prefer tidal mud flats.

Under the present regime, Waituna lagoon is anything but tidal, being more often than not closed off.

Previously, when the water level hit the mark on Waghorns bridge, farmers were allowed to open the lagoon and reduce the flooding over their properties.

The worst period was the late forties early fifties when The Govt.Lands and Survey began land development and the lagoon nearly flipped. It took nearly two years of open tidal conditions to flush out again and recover without any extra help.

It is very easy to take pictures of cows up to their hocks and shitting in water, when you flood the farmers out!

Yes the dairy industry has quadrupled, yes it does need to improve its control of sediment and pollution, but don’t hang all the blame on them. There have been measures undertaken to change the natural habitat of the lagoon by ‘RAMSAR’ Advocates as well!

When the lagoon has been regularly opened on a much more frequent basis, sea run trout and flounder have provided sportsmen with much pleasure, eels could get out to breed, and the migratory wading birds have enjoyed their stop over in a conciliatory habitat with tidal levels held within about 300mm.

Holding the lagoon shut until the water levels become excessive and then letting it all go with a rush and then closing it off again is no way to grow seagrass and keep water levels within a satisfactory mean.

Ruppia megacarpa is the saline deep water species of seagrass that can provide food and habitat for estuarine fauna and keep the water oxygenated. That is the species that we should be encouraging rather than sickening it off in fresh water.

According to es.govt.nz/…/waituna/science:

“On top of increased nutrients and sediment in the lagoon, artificial lagoon opening also places Ruppia under stress, primarily by increasing the frequency of salinity changes and drying out periods.”

This sort of habitat sounds more like R.polycarpa than metacarpa, and as Bachelotia, The algal slime in question, according to ZipcodeZoo.com, grows in the same habitat as the shallow freshwater species of Ruppia, it would seem to me that making the lagoon more rather than less tidal would benefit.

The argument that its Ruppia polycarpa that needs to be encouraged is entirely negated by the large fluctuations in water level that create problems for all the subalpine floral species that don’t mind wet feet but don’t like being drowned.

Drown the cushion bog and what happens to those 80 species of subalpine moths that the RAMSAR was meant to protect?

Drown the salt marsh that is supposed to fringe the bog and what should you expect?

Open the lagoon a lot more often, the deep seagrass will grow better than ever and the varying saline conditions will help to control the algae.

Category: Waituna

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