Environment

7.2 Biodiversity research at Lake Carey

Sunrise Dam Gold Mine is situated on the edge of Lake Carey in Western Australia's Northern Goldfields, approximately 220 kilometres north-east of Kalgoorlie. The lake covers approximately 75,000 hectares with islands totalling 10,000 hectares spread across its surface. Like many lakes across arid and semi-arid Australia, it supports both terrestrial and aquatic ecosystems. For months at a time, Lake Carey forms a dry, hypersaline lake-bed which occasionally forms localised pools after seasonal rains.

To facilitate mining, the water table around the open pit is maintained at a level below that of the mining operations by pumping water out of a series of bores around the perimeter of the pit. This water, which is also hypersaline, is predominantly used for operational purposes, with the remainder being released into the lake. To ensure that this activity does not impact on lake ecology, mining companies operating on the edge of Lake Carey, jointly conduct research to improve their understanding of salt lake ecosystems.

During the 2003/04 wet season, three significant rainfall events had a dramatic effect on the local landscape. In November 2003, the Lake Carey catchment received over 100 millimetres of rainfall following a single storm event. Shortly afterwards, another 280 millimetres fell over the period of a month (38% of which fell in 24 hours). These combined rainfall events saturated the catchment, re-establishing numerous ephemeral freshwater and brackish wetlands and filling the 90 kilometre length of Lake Carey. This spectacular wetland feature in an otherwise arid landscape provided a magnet for wildlife and, in particular, resulted in an influx of water birds to take advantage of the favourable conditions for breeding.

Recognising the significance of this natural phenomenon, a number of studies were endorsed by the company including an ornithological survey and water/sediment quality assessments as well as investigations into invertebrate populations and microflora communities. In March 2004, an aquatic and terrestrial avifauna survey recorded 29 water bird species and 79 terrestrial species of birds. Water bird diversity was higher on the temporary wetlands (fresh and brackish), with 25 species compared to 11 species on the hypersaline Lake Carey. Ten bird species were confirmed as breeding.

The invertebrate survey was conducted on Lake Carey (five sites) and 11 surrounding wetlands. In a previous survey in 2003, 102 species were collected. During this study, an additional 14 littoral and 12 planktonic species were added to the 2003 survey results. Over time, it is anticipated that 250-plus species will be identified. So far, the freshwater wetlands have exhibited the greatest species diversity, while Lake Carey attracts a greater concentration of individual organisms.

From this study it is expected that, during the more common seasonal rainfall events when ponding on Lake Carey is hypersaline, the major aquatic species are likely to include Brine Shrimp, Fairy Shrimp, and Clam Shrimp.

The results of the recent studies on Lake Carey and its catchment suggest that the catchment wetlands provide an important ecological niche for a variety of aquatic species, which are then able to re-populate Lake Carey during periods of unusually high rainfall. The flooding of the lake could also provide a dispersal mechanism for the wider distribution of many species leading to a colonisation, or re-colonisation, of suitable habitat. This opportunistic 'migration' of species may account for the fact that a few of the invertebrates identified in the recent studies were previously unrecorded within the Lake Carey catchment.

What Lake Carey clearly demonstrates is that, even within landscapes that appear quite inhospitable to life, there can exist delicately balanced ecosystems of incredible diversity moulded by the fickle seasons of Australia's outback.