Low sulphate concentrations prevent microbial sulphate reduction from reducing acidity in these lakes. However, stimulation of primary and secondary production may produce alkalinity help establish a more natural ecosystem providing a cost effective and sustainable solution to the acidity problems.
A field-scale experiment (with control) involving the treatment of in-situ macrocosms (~600 m3) with municipal mulch and phosphorus additions to enhance primary production has been established in a small southwest, Western Australian coal mine lake. Decomposition of mulch reduced nitrogen to low levels and necessitated supplementation with urea fertilizer. Phosphorus concentrations dropped rapidly after addition as it became bound to iron, organic matter and sediment. There was little difference between treatments and control for most physico-chemical parameters measured (including pH). However, a PCA of the data showed that the addition of mulch sent the macrocosms on a different trajectory to the control. This difference was reflected in observations of increased abundance and diversity of biofilms and macroinvertebrates within the treated macrocosms.
The addition of mulch and phosphorus alone was not sufficient to increase the pH of Collie mine lakes, although it does provide a number of benefits for biota in the water. We recommend that liming be used to increase pH, followed by organic matter and nutrient additions to stimulate primary production.
Associate Professor Mark Lund
Dr Clint McCullough