Date of Award

2002

Degree Type

Thesis

Degree Name

Bachelor of Science Honours

Faculty

Faculty of Communications, Health and Science

First Advisor

Dr Eddie van Etten

Abstract

Mining operations in arid regions of Western Australia are faced with many environmental management issues. One such issue is the disposal of mine water to the environment. Mine water is commonly discharged to nearby salt lakes under licence by the Department of Environmental Protection. Licence conditions dictate that the discharge water and the receiving environment be monitored to allow impacts on the environment to be detected. Salt lakes are associated with vegetation communities dominated by halophytic members of the Chenopodiaceae, While these plants are tolerant of salinity extremes, the germination stage of many species requires periods of lowered salinity. There is therefore potential for the recruitment stage of these vegetation communities to be affected by the discharge of hypersaline mine water. At Lake Austin, Big Bell Gold Operations discharge hypersaline mine water to this saline wetland system. This study has investigated whether this discharge has had an impact on the fringing vegetation of the lake. Secondly, the vegetation dynamics of the fringing vegetation have been investigated during a flood/drought cycle between 1998 and 2002 with the aim of increasing our understanding of these communities. Using an existing monitoring program established by the Centre for Ecosystem Management (CEM) in 1998, as well as twenty additional sites surveyed in 2002, soil and vegetation parameters were measured and assessed to test for evidence of an impact from the discharge of hypersaline mine water. A glasshouse experiment inundated soil samples from discharge and non-discharge zones with water of varying salinity to test for difference in seed germination between treatments and between zones. Halosarcia fimbriata, H. halocnemoides (form a), and H. pruinosa (form a) were dominant in the communities found at Lake Austin. Very few significant differences were found in changes of soil and vegetation parameters between location (discharge versus non-discharge sites) and/or time (1998, 2000 and 2002). The discharge water is linked to changes in soil pH and possibly soil salinity, however, there appears to be no impact on the vegetation. A number of explanations are given as to why an impact on the vegetation was not detected, including a lack of statistical power. The vegetation dynamics are described in relation to the flood/drought cycle experienced between 1998 and 2002. There are links between seed germination, seedling growth and subsequent structure of the Halosarcia fimbriata community and flooding frequency, depth and duration. There are three main management implications that have arisen from this study. Firstly, the sampling effort needs to be increased in order to be confident that significant differences will be detected, if indeed there are any. Secondly, further investigation of the vegetation dynamics is required to enhance impact mitigation and minimisation strategies. Finally, an engineering solution is suggested to prevent discharge water from coming into contact with fringing vegetation.

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