Towards closure of potentially saline pit lakes: understanding biophysical processes for condition assessment and remediation options

This project aimed to conduct baseline monitoring and research on a series of saline pit lakes across the Bowen Basin and Hunter Valley with a focus on biodiversity. As a potential rehabilitation technique, an on-site tank experiment was conducted to determine the effect of organic matter additions on biodiversity development in saline pit lake water.

The objectives of the project were to:

• Address and understand salinity issues in terms of pit lake closure.

• Improve upon and implement a simple and low-cost monitoring strategy for both physicochemical and biological parameters in pit lakes.

• Extend a key hypothesis (developed in previous ACARP projects for acidic and metalliferous pit lakes) that addition of organic materials potentially enhances biodiversity in saline pit lakes with circumneutral pH.

• Implement the ‘sliding scale’ of pit lake assessment, whereby pit lakes are ‘graded’ on their relative difficulty to rehabilitate.

This report presents data collected at mines in from four pit lakes.

In an earlier project the idea was promoted that pit lakes exist on a sliding scale from easy to rehabilitate to more difficult. The saline pit lakes in this project are at the easier end of the rehabilitation scale as they have generally good water quality, the main limitations are likely to be physical ones related to the creation of littoral and riparian areas and developing strategies to enhance natural successional processes.