A saline oasis

Forest and Bird, Volume 22, Issue 2, 1 May 1991, Page 5

A saline oasis

Neville Peat

A NEW SCENIC RESERVE at the southern end of the Strath Taieri Valley in Central Otago preserves a unique natural ecosystem — an inland salt lake. Sutton Salt Lake and its complement of salt-tolerant plants and invertebrate animals have long been of scientific interest. Now there is a public walkway to the lake and a series of information panels interpreting the extraordinary turns nature has taken at this place. Seasonally dry, the lake occupies a 4 ha basin in the schist-rock landscape and it fills to a depth of about half a metre. It owes its saltiness — it is half as salty as the sea — to the gradual weathering of the surrounding schist and the fact the basin has no outlet. The outcrops (tors) of schist in this area are among the most impressive in Central Otago. They form a fascinating pattern of parallel ridges, representing the rocks most resistant to weathering. Salts released from the rock are borne by surface run-off and water percolating up through the soil. The silty lake sediments show extreme alkalinity (pH 9.4). The shores of the lake are home to a range of plants more usually found by the ocean, including two native creeping herbs, Lilaeopsis novae-zelandiae and Selliera radicans. The big question is: how did they get there? One theory holds that they are derived from plants which migrated here millions of years ago when the sea encroached far into what is now Central Otago. Copepods are among the tiny salt-adapted aquatic animals found in the lake. No fish live in it. Birds likely to be seen on or near the water include paradise shelducks, shoveler and mallard ducks, black swans and whitefaced herons. Harriers and pied oystercatchers are also seen in the vicinity as well as an occasional falcon. This is good country for skinks and geckos. The large Otago skinks are sometimes found basking on the rocks on sunny days.

The reserve covers 125 ha. Formerly part of Gladbrook Station, it was acquired by the Department of Conservation last year and officially opened by Otago MP Warren Cooper in February. Conservative farm management of the block has preserved much of the natural

vegetation, including the tall blue wheat grass Elymus rectisetus, which disappears under intensive grazing. Entomologist Brian Patrick says that the presence of the southern tiger moth in the area reflects the minimal disturbance. Visitors can do a circuit of the reserve following a walkway that is marked by arrows etched on to slabs of schist. The round trip, with stops to read the information panels, takes about an hour.

Central Otago’s distinctive rock and tussock landscape is noticeably under-represented in the country’s parks and reserves system. The advent of Sutton Salt Lake Reserve gives visitors free access to this type of country and the bonus of a unique saline oasis.