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Question #1 Summarise the process that is used at the Lake Grassmere Salt works.
Question #2 What are the three optimal weather conditions for salt production at Lake Grassmere?
Question #3 At what percentage of evaporation does sodium chloride commences to deposit?
Question #4 What causes the pink colour in the summer months?
Question #5 Other than human consumtion what are four other uses for salt?
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Discover a seaside lake with large pink ponds and mounds that sparkle white against summer's light-brown, hillside pastures.
Construction of the saltworks at Lake Grassmere, Marlborough, was commenced in 1943 under wartime difficulties through the initiative of the late Mr George W Skellerup - a Christchurch businessman whose enterprise had earlier led to the formation of the Christchurch based rubber firm bearing his name.
Lake Grassmere is the only site in New Zealand to produce raw salt from seawater.
Lake Grassmere had features necessary for a solar saltworks:
• A large area of flat land, with impervious soils, located on the coast.
• A readily available area unsuitable for any other use.
• The lowest rainfall region of New Zealand.
• Marlborough is noted for its sunshine.
In addition, Lake Grassmere frequently experiences strong drying north-westerly winds during the summer months. (Sun and wind give rise to high evaporation rates).
Seawater contains just over 2.5 per cent sodium chloride, together with significant amounts of other salts. Some 60,000 – 70,000 tonnes of salt are harvested from Lake Grassmere each year. Seawater is pumped into the 688 hectare main lake continuously through the summer.
As nature does its work and evaporation increases the sea waters strength in the 50 or so ponds at Lake Grassmere.
When the brine reaches saturation point it is transferred into crystallisation ponds during the summer months. When 90% of the original seawater has evaporated, sodium chloride commences to deposit. When about half the total sodium chloride has deposited (in crystallisers) as a result of further evaporation, the concentration of the more soluble salts in the crystalliser brine has increased to a level where these commence to deposit along with the sodium chloride. Unless the brine is discarded at this point, an impure salt would be harvested, contaminated particularly by magnesium and sulphate. The brine is known as “bitterns”.
The brines at Lake Grassmere turn pink in the summer. This colour is from a bloom of micro-organisms. The predominate organisms are known as a halophilic bacteria (though they belong to the archaea class rather than bacteria). These archaea use a pink/ purple colour (bacteriorhodopsin) to absorb light for energy. Also present are single celled algae called Dunaliella Salina which use beta-carotene (orange colour in carrots) for the same purpose. These two organisms are responsible for the colour in the ponds.
The salt making season is of six months duration commencing in early October. Harvesting salt usually begins by early March and can last from four to six weeks. During this time the salt crust is lifted from the bottom of the ponds by harvesting machinery, transported to two washing plants where it is washed in brine before stacking in 20 meter high piles.
The stacks of salt can contain 100,000 tonnes of salt and are readily visible by day and night from the Blenheim-Christchurch main highway. Salt production is highly dependent on low rainfall and evaporation, so it is necessary to hold large stockpiles of salt to counter the fluctuations in annual production.
Early History of Lake Grassmere / Kapara Te Hau
The Māori name for the lake is Kapara Te Hau ("wind-blown lake"). Early whalers on the coast rendered this name “Cobblers' Hole”.
According to Māori oral tradition, the lake occupies the site of early cultivations. Kupe, the navigator, is said to have poured salt water on these cultivations, thus creating the lake.
In pre-European times it was used as a ready source of food, as it attracts a wide range of waterfowl.
In 1832–33, a year after Ngati Toa under the leadership of Te Rauparaha had defeated Ngāi Tahu at Kaiapoi and Banks Peninsula, Ngāti Toa visited the lake to take moulting ducks. A Ngāi Tahu force, having learned of this impending visit, laid an ambush. Scouts from Te Rauparaha's party found the locality apparently uninhabited and the canoes were driven ashore. On landing, the visitors were taken by surprise and sustained heavy casualties. Te Rauparaha was seized by Tūhawaiki, who was anxious to take him alive. The captive, however, after feigning resignation, was less tightly held. He then slipped out of his flax garment, swam to a canoe and made his escape.
The official name of the lake become a dual name as a result of the Ngāi Tahu Claims Settlement Act 1998.
References:
https://dominionsalt.co.nz/wp-content/uploads/2017/11/DS_LakeGrassmere_dle_v4e.pdf
https://dominionsalt.co.nz/about-us/our-locations/
https://en.wikipedia.org/wiki/Lake_Grassmere