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Use And Water Quality Remediation Of Acidic Coal Pit Lakes By Adjacent Aquaculture

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Published: August 11Project Number: C19018

Get ReportAuthor: Naresh Kumar, Clint McCullough, Mark Lund | Edith Cowan University

This ACARP funded project builds on the outcomes of earlier ACARP funded projects conducted in the Collie region by the authors to understand the acidic pit lakes physico-chemical and biological processes and use the knowledge to remediate pit lakes.


The present project was aimed at determining how viable the acidic pit lakes are for supporting a marron cultivation (aquaculture) facility, where the pit lake serves as both a source of water and recipient for marron wastewater discharges.


Additionally, the investigations also examine whether by receiving the marron wastewater discharges the pit lake showed improvements in lake water quality and ecological indicators such as phytoplankton, macroinvertebrates and diatoms.


This project consisted of a field monitoring program, two laboratory based experiments and one outdoor pilot scale mesocosm experiment.


The field monitoring component of the study involved sampling three different pit lakes in the Collie Lake District in south-western Western Australia. One was the treatment pit Lake WO3 which was sourcing water to the marron cultivation facility and also serving as sink for marron wastewater discharges. The other two pit lakes were chosen to serve as reference sites, these were Lake Kepwari, a river water rapid-filled pit lake and WON9, a groundwater fed pit lake.


Monitoring was carried out quarterly over a year to cover the major seasonal changes in the pit lakes physico-chemistry and ecology. For physico-chemical monitoring each sampling event included vertical profiling of the pit lakes for temperature, pH, ORP and electrical conductivity (EC). Water samples were also collected from the epilimnion and hypolimnion for metals/metalloids, nutrients and anions analyses.


In order to characterise the pit lake biota samples were collected to be analysed for phytoplankton, diatoms and macroinvertebrate community richness and abundance (where useful) in the pit lakes.


Lake Kepwari exhibited temperature based stratification during the warm summer months (December to March) whereas the other two lakes WO3 and WON9 appeared too shallow to stratify.


Lake Kepwari was moderately acidic, highly saline, contained some toxic metals, and the nutrient concentrations were very low. There were no distinct water quality changes in the Lake Kepwari during the sampling period. WON9 was the most acidic lakes of the three pit lakes studied, with elevated concentrations of metals, sulphate and very low nutrient concentrations. WON9 also did not show any significant variations between the different sampling events. Conversely, WO3 exhibited high nitrogen concentrations especially in the form of ammonia but very low phosphorus concentrations. Even though WO3 was receiving marron wastewater discharges there were no significant differences between this lake and the other two reference lakes other than the fact that marron wastewater discharges led to ammonia build-up.


The results of the present study highlighted that the marron cultivation facility adjacent to the acidic pit lake appears to be a viable option as the pit lake can serve as a long term sink for the marron wastewater. However, the important factor to consider is that the lack of phosphorus in the marron wastewater is preventing the lake from responding for any significant water quality and ecological changes. Furthermore, marron wastewater additions can be undertaken in the acidic pit lakes albeit as long as the pit lake is nutrient limited by phosphorus. Although not explicitly tested, the high uptake capacity of the sediment for phosphorus should provide some buffer against excessive algal blooms if phosphorus ends up in the lake; short -term blooms are quite likely.


Acidic pit lake water quality improvement and ecological changes towards a functioning and self-sustaining aquatic system were not evident during the course of the study. This is primarily due to the small quantities of marron wastewater discharge and the nature of the wastewater (relatively low in nutrients). Meso/micro -cosm studies did show that algal growth could be stimulated despite no measured change in water quality. This suggests that using nutrients could provide enhanced ecological values in the absence of water quality treatment for these lakes.



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