School of Geography - Theses

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    Alternative community states in reservoirs of the Central Highlands region
    Bateson, Jane Karen ( 2001)
    The occurrence of nuisance algae within reservoirs of the Central Highlands region is a problem facing Central Highlands Water and the communities they serve. Therefore, there is a need to know how to manage this threat. Management of the causal factors contributing to the development of algal blooms within the Central Highlands region, and Victoria as a whole, has tended to focus on reducing nutrient loads into the system. However, in shallow lakes nutrient control alone is often ineffective in managing the undesirable effects of eutrophication including algal blooms. The main reason for this is thought to be due to existence of alternative clear, macrophyte-dominated and turbid, phytoplankton-dominated stable states in shallow freshwater systems. This thesis presents analyses of two field studies carried out to investigate the alternative stable states hypothesis on shallow reservoirs of the Central Highlands region. First an assessment of spatial variation in chlorophyll a, macrophyte abundance and key growth regulating variables has shown that within reservoir spatial variation that is often assumed to be insignificant, is significant. Such spatial variation can lead to different conclusions being drawn regarding the application of ecological models and processes that may have caused observed patterns. Consequently, an appreciation of the effects of scale is vital to ensure ecological models, such as the theory of alternative stable states, are applied correctly and the outcomes of field experiments are not confounded by spatial variation. Second an investigation of shallow reservoirs of the Central Highlands region revealed that the presence of macrophytes is associated with low algal biomass. Parallels were drawn between study sites and the model of phase changes of shallow lakes undergoing eutrophication (Moss et al., 1996). A majority of reservoirs were characterised as potentially being within the clear, macrophyte-dominated alternative state, either in the unique clear Phase I or transitional Phase n. However, several reservoirs of the Central Highlands region did not bear a resemblance to any of the alternative states (phases) identified in the literature. Accordingly, it can be concluded that reservoirs of the Central Highlands region may support alternative states but that phase changes used to describe communities of the Northern Hemisphere lakes need to be modified to suit Australian conditions. This study emphasises the need to adopt a holistic approach to managing the undesirable effect of eutrophication such as algal blooms. Within the Central Highlands region a holistic approach should include management of the macrophyte communities, water level manipulation and potentially biomanipulation in addition to nutrient control.