Managing Climate Change Impacts in karst — The Lake Cave Eco- Hydrology Recovery
Email: 1 sarahdavies@margaretriver.com
Abstract
Lake Cave, located in the Margaret River region of southwest Western Australia is renowned for its beautiful and spectacular underground lake. The cave has been visited by tourists for more than 100 years, and it continues to be a major tourism drawcard in the region, attracting more than 44,000 visitors annually. Besides its important tourism values, the cave also harbours a Subterranean Groundwater Dependent Ecosystem (SGDE) comprising aquatic subterranean invertebrates (stygofauna) recently nominated as a Threatened Ecological Community (TEC) under the Environmental Protection and Biodiversity Conservation Act (status critically endangered).
Groundwater levels in Lake Cave remained relatively stable and showed no sign of decline up until 2005, after which time there has been a progressive decline and noticeable reduction of the size of the lake in the cave. This has reduced the visual appeal for visitors, and threatened the stygofauna community. Without management intervention, at the current rate of decline (1 mm per week) the lake will be dry within two to three years.
Lake Cave is managed by the Augusta Margaret River Tourism Association (AMRTA), and its Environmental Management Plan makes a commitment to conserving natural values within the cave and its water catchment, including monitoring and maintenance of hydrology, subterranean fauna and habitats (AMRTA 2008). As part of this commitment, AMRTA initiated the Lake Cave Eco-Hydrology Recovery Project in July 2010, supported through grant funding from the W.A. Government’s Natural Resource Management Grant Scheme.
The Lake Cave Eco-Hydrology Recovery Project aims to:
- Control the water level decline in Lake Cave, by harvesting rainfall and using this to supplement recharge of the lake;
- Monitor the ecological condition of the aquatic root mat community and other stygofauna in Lake Cave;
- Develop a hydrological model of the cave and karst catchment with a view to managing water resources and dependent SGDE’s in the face of a drying climate future.
Since October 2010, AMRTA has been supplementing the natural flow of water in Lake Cave by subsoil discharge of rainwater into the cave. Initially this is a 12 month trial with assessment of the success of the trial to take place in September 2011. Baseline monitoring of water quality was undertaken during the preceding year to ensure that ongoing post-trial monitoring can detect any changes within the cave system, enabling appropriate management actions to be taken. This presentation documents baseline water quality and water levels, and the ecological condition of the aquatic root mat community and stygofauna, prior to commencing the recharge trial.
In relation to water quality, EC, pH, DO, redox and major ions were analysed for both lake water and drip water in the cave. The two water bodies exhibited different characteristics, confirming earlier indications that a portion of the lake water is of different origin from the vadose percolation waters.
In relation to stygofauna, the declining water levels and drying out of the root mat habitat in Lake Cave has resulted in a 74% decline in species richness over the past 10 years. Fourteen species with root mat associations were not recorded in 2010. Maintenance of the current water level is imperative for the conservation of the remaining stygofauna community.
The next stage (12 months) of the Project will continue monitoring of water levels, water quality and stygofauna, and undertake a detailed catchment-scale investigation to build a hydrological model of the cave and its catchment. This will be used to inform management and conservation of Lake Cave’s water resources and SGDE’s in the face of a drying climate future.