Protecting stranded biodiversity using groundwater pumps and surface water engineering at Lake Toolibin, Western Australia

Abstract

Dryland salinity has claimed 8% of the Toolibin Lake catchment and approximately 24% is at risk. As a result, the native fauna and flora of the ephemeral lake, a 300 ha Ramsar Wetland of International Importance, face salinisation. This is a fate that has already befallen over one million hectares of farmland, wetlands and lakes (e.g nearby 830 ha Lake Taarblin) in the Western Australian Wheatbelt. Surface water management and groundwater pumping have been undertaken on the western edge of the lakebed at Toolibin since 1997 to manage the spread of salinity, which first developed in the mid 1970s. In 2001, the pumping system was upgraded when a second series of higher yielding groundwater pumps was commissioned on the eastern half of the lake. Results to date indicate the surface water management has been successful in diverting approximately 5000 tonnes of salt from the lake. The combined effects of low rainfall and pumping (660 kL/d) have lowered groundwater levels ∼3–4 m beneath the lake. Quantifying their individual effects has been difficult. Root zone soil salinities (measured with ground EM) remain high across the majority of the lake, except around older western pumps that are reducing in soil salinity, and the vegetation is recovering. The efficiency of pumping in this terrain is impacted by the low permeability of the eastern floor sediments, iron biofouling and the high operating costs. The eventual fate of the lake and its vegetation are dependent on the sustained effectiveness of the pumps, managed flooding and subsequent leaching By reviewing the effectiveness of the pumping system and surface water management structures, the forecasts for salinisation in the catchment can also be reviewed, which may impact the Toolibin Lake Recovery Plan