Date of Award

2001

Degree Type

Thesis

Degree Name

Bachelor of Science Honours

Faculty

Faculty of Communications, Health and Science

First Advisor

Dr Pierre Horwitz

Abstract

Mine dewatering is a critical part of the mining process to prevent flooding of underground or open pits, to allow for the excavation of the available resources. Groundwater is abstracted from underground pits to the surface through extraction bores. The issue of where to discharge the excess water is a major concern. The use of natural wetlands is one option for mine water discharge. Saline lakes in arid areas are ideal receiving environments for discharge options, acting as evaporation facilities for the storage and disposal of excess mine water. Mine water discharge into ephemeral lake systems modifies the volume of water in the lake on an annual basis; parts of the wetland are thus subjected to prolonged inundation. An experiment was carried out to determine whether the biotic composition was altered accordingly to the degree of seasonal inundation by mine dewatering, as well as whether the salinity of the discharge water affects the composition and assemblage of biota emerging from lake sediment. Sediments from two lakes: Lake Austin and Lake

Wownaminya, located within arid regions of Central Western Australia, were sampled to determine which invertebrates responded to dewatering regimes and to investigate the nature of biofilm. Laboratory experiments were carried out to test I he emergence of invertebrates from sediments as they responded to mimicked dewatering regimes under controlled laboratory conditions. Two hypotheses were tested. The first hypothesis tested states that the biotic composition emerging from sediments will be the same irrespective of the salinities of the mine water discharge. The second hypothesis states that there is no difference in the biotic composition (biofilm and aquatic invertebrates) in accordance to the whether or not the sediments have been previously exposed to prolonged inundation. The responses of emerging invertebrates were monitored and recorded over a four week period. The results obtained indicated that changes do occur in the assemblages and composition of the aquatic biota in accordance with the salinity of the mine water discharge. Areas that are exposed to a longer period of inundation also showed altered biotic compositions compared to areas with less frequent inundation due to mine dewatering. Statical analysis (MANN - Whitney test and ANOV A) and tho use of configuration diagrams (Dendrograms and MDS plots) were used to determine the interaction between mine water discharge and species composition. It was concluded that salinity is a major factor clearly influencing the occurrence of species in the lakes. The timing and the period of inundation is a factor that has also lead to altered compositions of species at Lake Wownaminya. Dewatering operations alter the composition and species richness in the receiving wetland environments causing some concern of the overall impacts on these lakes. Altered characteristics of wetland hydrology can be detrimental to the endemism of crustacean or molluscan forms that only occur within saline lake systems, and may lead to the extinction of local forms.

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