Date of Award

2004

Degree Type

Thesis

Degree Name

Bachelor of Science Honours

Faculty

Faculty of Computing, Health and Science

First Advisor

Dr Mark Lund

Second Advisor

Clinton McCullough

Abstract

Eutrophication has become a considerable issue for managers of water bodies across Australia. Rapid urbanisation in the south-west of Western Australia is causing the eutrophication of many wetlands within the region. Lake Joondalup is a eutrophic, urban lake, located approximately 20km north of Perth city. It comprises part of the Yellagonga Regional Park, having a high conservation value. The aim of this study was to provide managers of Lake Joondalup with information on the relative importance of different nutrient sources into the lake, thus enabling the development of appropriate management strategies. Additionally, a historical examination of available water quality data was conducted to determine the lake's current trajectory in relation to nutrients. The long-term trends occurring in Lake Joondalup were inferred with the use of information collected between 1973-2001 for total phosphorus and nitrogen concentrations. Relative importance of stormwater, groundwater and surface flow from adjoining swamps was investigated through sampling that occurred between May and August of 2004. A nutrient budget was then extrapolated based on the recent sampling and the use of literature. This budget was compared to a nutrient budget constructed in the mid 1980s to determine changes. Long-term trends suggest that significant variation has occurred over the years, with nutrient concentrations increasing in the main section of the Jake and decreasing in the southern section. This was particularly prevalent for total phosphorus. However, whilst the two sections of the lake seem to be acting differently, the concentrations in the two regions are now quite similar, with both being equally polluted. This is in contrast to the 1980s, when only the southern section showed significant levels of pollution. Surface flow from Beenyup Swamp was considered the major contributor of nutrients to the Lake, as has been identified in several prior studies. Contrary to previous beliefs stormwater was not found to have a significant effect on the nutrient status of Lake Joondalup, while the complexity of groundwater movement made quantification of sub-surface impacts difficult. Nonetheless this study indicates that an old landfill site east of the Lake appears to contaminate groundwater entering the lake, yet on aggregate a net loss of nutrients from the lake was identified through groundwater flow. It is recommended that the most appropriate management strategy for Lake Joondalup is to reduce nutrient contributions through surface flows from Beenyup Swamp. Considering the importance of Beenyup Swamp to the hydrology of Lake Joondalup it would be undesirable to restrict the flow from this source. Harvesting of macrophytes may be beneficial, though a study to better understand the sources of nutrients to the swamp is required. In addition, an investigation of the relative importance of groundwater is desirable to determine the net impact of this parameter. Thus, it was concluded that whilst effects of groundwater need further investigation, reductions in nutrient input from Beenyup Swamp should be the priority and would ultimately help to ensure the conservation of Lake Joondalup.

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