Date of Award

1996

Document Type

Thesis

Publisher

Edith Cowan University

Degree Name

Bachelor of Science Honours

Faculty

Faculty of Science, Technology and Engineering

First Supervisor

Adrianne Kinnear

Abstract

Lake Joondalup is one of the largest remaining permanent lakes of the Swan Coastal Plain. Despite increasing urbanisation, it supports highly diverse terrestrial and riparian communities, and an abundant and diverse aquatic fauna. However, like other wetlands of the Swan Coastal Plain, Lake Joondalup is increasingly threatened by eutrophication and degradation. The aims of this study were to describe the patterns in selected physical, chemical parameters, microcrustacean abundance and biomass of Daphnia carinata in Beenyup Swamp and the adjacent sections of Lake Joondalup; to identify the likely factors determining the patterns of phytoplankton biomass in these wetlands; and to suggest the most effective management strategies to aid in the control of eutrophication in Lake Joondalup. Sampling was carried out on a fortnightly basis from the period March to August, 1996. The appropriate measurements and collections were made at four randomly chosen replicate sites, within each study area, to allow the necessary physical, chemical and biological analysis. Results of the study reveal that Lake Joondalup continues to receive excessive input of phosphorus (as orthophosphate) in water flow from the south-east, as it has for the past two decades. This excessive nutrient enrichment of the main waterbody of Lake Joondalup is causing prolonged and substantial algal blooms. Furthermore, expansion of tile tunnel that connects the southern wetlands to the main waterbody is likely to result in further nutrient enrichment, thereby intensifying the eutrophy. In coutrast, the production of gilvin in Beenyup Swamp, and the resulting reduction in pH, has caused the inhibition of phytoplankton growth despite excessive nutrient enrichment. Surface water connection between Becnyup Swamp and Lake Joondalup (south) has resulted in similar inhibitory effects on phytoplankton growth. Grazing by D. carinata did not appear to significantly influence or control phytoplankton biomass in any of the wetland sites. It is suggested that the most appropriate management strategies to control eutrophication of Lake Joondalup are to reduce the input of phosphorus in the main waterbody through reducing the flow of water from the Wallubumup/Beenyup Swamp System, and through reducing nutrient flow from areas surrounding these wetlands. In addition, rehabilitation of riparian vegetation around these wetlands is essential as it will provide a sink for nutrient input, and a natural source of gilvin. Implementation of these management strategies will require further investigation regarding exact sources of phosphorus, and are crucial if the biological diversity and conservation value of these wetland ecosystems are to be retained.

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