A study of Lake Wyara, an episodically filled saline lake in southwest Queensland, Australia

Abstract

Lake Wyara lies on a tertiary fault, but is much modified geomorphologically by wind and subsequent wave action from the west, so that the eastern shore is smoothed and lined by beaches at various levels, but there is no lunette. When full and overflowing, which has occurred 4–5 times in the last 108 years, it is 3400 ha in area and ca 6m in depth. Most overflows are due to floodwaters from the adjacent Paroo catchment entering the lake via its outflow and then returning again back to the river. During 1987–96, it completely filled and dried once, salinity varying from 2.8 to 350 g L⁻¹. Water was clear, alkaline and strongly dominated by Na and Cl-ions. Macrophytes grew abundantly offshore at lower to moderate salinities, fish were few in variety and limited to low salinities, and waterbirds were usually both diverse and numerous. During the 10 years of study, only 13 zooplankter species and 23 species of littoral inverbebrates (with 3 ostracods common to both lists) were encountered; most lived at lower salinities (<30 g L⁻¹) and none was found >60 g L⁻¹. Dominants were mainly crustaceans and includedBoeckella triarticulata andDaphnia angulata when hyposaline, andDaphniopsis queenslandensis, Moina baylyi, Diacypris spp., andMytilocypris splendida at higher salinities. Insects were generally limited to hyposaline conditions, butMicronecta sp., andTanytarsus barbitarsis were euryhaline. Overall, the invertebrate fauna is depauperate by comparison with saline lakes elsewhere in Australia, but similar to that in other large saline lakes in the semi-arid and arid zones of central and eastern Australia. This is related to the lake's episode nature which provides an unreliable and unpredictable habitat and therefore not encouraging speciation and also to a relatively homogenous habitat throughout the lake due to strong wind action smoothing shorelines vertically and horizontally