Open Cut » Environment
Saline pit lakes formed in flooded open cut voids, are likely to become saline due to a lack of surface outflows and through evaporation. Preparing saline pit lakes for closure is difficult because there is little data available on saline pit lake ecosystems and their rehabilitation. This project builds on project C27043 and aims to continue the baseline monitoring and research on a series of saline pit lakes across the Bowen Basin and Hunter Valley with a focus on biodiversity. In addition, the project investigated organic matter breakdown, addition of organic matter, and floating islands for biodiversity. The findings of this project were used to develop a Design Manual for the closure of Saline Pit lakes.
A scientifically robust and comprehensive pit lake monitoring system for both physico-chemical, water chemistry and biodiversity assessment has been developed. Our system (detailed in the methods) is designed to be easy to implement in pit lakes around operational requirements of the mine.
Pit lakes exist on a sliding scale from 'easy' to rehabilitate to 'more difficult.' The saline pit lakes in this study are at the 'easier' end of the rehabilitation scale as they have generally good water qualities. The main limitations to rehabilitating the pit lakes in this study are likely physical and related to the creation of littoral and riparian areas and developing strategies to enhance natural ecological successional processes. Results suggest that the lack of habitat and the lakes morphology are an important constraint for the development of biodiversity within these lakes. These ideas are explored more fully in the Design Manual for Closure of Saline Pit Lakes which is included.
The biodiversity in the lakes was low compared to natural systems, with benthic diatoms, zooplankton not always present in the samples. All taxa presented were dominated by tolerant and cosmopolitan species with low richness and abundance. No clear evidence was found that biodiversity had improved in the lakes since 2019 - 2021.
THE DESIGN MANUAL FOR PIT LAKES IS INCLUDED AS AN ATTACHMENT FILE.