New Zealand Journal of Marine and Freshwater Research abstracts

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Water and sediment chemistry of Sutton Salt Lake, east Otago, New Zealand

D. Craw
S. Beckett

Geology Department
University of Otago
P.O. Box 56
Dunedin, New Zealand
email: dave.craw@stonebow.otago.ac.nz

Abstract  The Sutton Salt Lake is the only saline lake in New Zealand, and has formed in a windy cool-temperate maritime climate. Consequently, the lake is distinctly different from most of the world’s saline lakes that form in arid continental settings. Sutton Salt Lake forms annually in a shallow (5 m) bedrock-floored depression c. 50 km from the nearest coast. The site receives c. 500 mm/year rainfall compared with coastal rainfall of near 1000 mm/year because of a minor rain-shadow effect of coastal hills. Surface evaporation rate is high (c. 700 mm/year) because of frequent strong winds. Sediments on the lake floor are derived by rain and wind erosion of the surrounding quartzofeldspathic schist bedrock, with a contribution from organic sources, particularly ostracods, and evaporative halite. The sediments have a higher proportion of phyllosilicates (muscovite, kaolinite, and chlorite) than the source rocks because of differential transport of these minerals into the lake depression. Lake water is entirely derived from rain, rather than groundwater, and the lake waters have had minimal chemical interaction with bedrock. Lake water pH is near 9 and pH of pore waters in drying lake sediments is near 8, compared with a pH near 7 for regional surface and ground waters. When full, the lake has salinity about one quarter to one third of that of sea-water, and ion ratios are similar to sea-water. The lake salinity is derived from marine aerosols in rainwater concentrated by c. 20 000 evaporation and refilling cycles in the lake depression.

Keywords  saline lake; geochemistry; marine aerosol; evaporite

M03094; Received 10 December 2003; accepted 5 April 2004; Online publication date 8 June 2004
New Zealand Journal of Marine and Freshwater Research, 2004, Vol. 38: 315-328
0028-8330/04/3802-0315 © The Royal Society of New Zealand 2004

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