Lagoon argument is ecological nonsense
Seems like a lot of nonsense around the Waituna Lagoon.
I trudged along the gravel bar recently and was delighted to see the new opening.
The water level had been allowed to rise much too high, threatening the road and bridge and killing the eels, trout and water plants in the noxious soup.
I find it astonishing that horse’s mane weed, or ruppia, is regarded as the indicator of lagoon health. It thrives in warm, brackish and dirty water whereas so many other species there prefer clean, tidal seawater – eel grass, saltmarsh plants, crabs and migrant wading birds, for example.
This is a soft shoreline that is constantly changing; in the absence of solid rock, the gravel bar erodes and builds up rapidly.
At different times the Waituna Lagoon has been a lake, a bog and a river mouth – an ice-skating pond in the ice age and nothing at all when the waves crashed against the cliff there at a time when the sea level was much higher. So who is to say what the “right” state of the lagoon is?
Sometimes the lagoon has been fully tidal for years, and at other times the opening has closed after a few days of flushing.
We want a healthy lagoon ecosystem, but relying only on natural openings is not possible now because of the buildup of nutrients from farmland which could tip the lagoon into an anaerobic state.
Some sort of intervention plan is essential, but a high-waterlevel-triggered opening regime allows the water to become increasingly contaminated and drowns important shoreline ecosystems.
The best option is a sensible, low-level and quite frequent opening which allows the lagoon to become tidal and flushed for a time, preserves the bridge, lets trout and eels thrive, and allows saltmarsh plants to get a foothold.
The ruppia beds would then establish up the brackish waterways feeding the lagoon as they have done in the New River Estuary.
Again, I see the awful suggestion that the outlet could be blocked artificially to preserve the “right” ecology at the expense of the “wrong” ecology.
That’s illegal and it’s going to have a hard time getting past the Environment Court.
Lloyd Esler, Invercargill