The effect of water column nutrient enrichment and water regime on vegetation in shallow, ephemeral, freshwater lakes.

Adrian R Clements

    Research output: ThesisDoctoral Thesis

    91 Downloads (Pure)


    Shallow, ephemeral, freshwater lakes are a common landscape feature in temperate regions of the world. Often modified for water storage, these lakes also provide habitat for a range of flora and fauna. Alterations to the water regime and nutrient concentrations are two drivers that affect vegetation composition, ultimately changing the ecological status.
    The principal objective of this study was to identify the response of macrophyte, and microphyte (phytoplankton, algae, and cyanobacteria) community composition, and the response to changes in water regime and water column nutrient concentrations. Three shallow, ephemeral, freshwater lakes of inland New South Wales in eastern Australia were investigated, with emphasis made on Lake Brewster, a naturally occurring lake that has undergone modifications to its structure and water regime in the effort to improve water quality for downstream agricultural and domestic use.
    To test the hypotheses that I) Variable water regime increases species diversity and abundance of macrophyte and microphyte communities in shallow, ephemeral, freshwater lakes and II) Increased water column nutrients reduces macrophyte species diversity but increases abundance of macrophytes and microphytes in shallow, ephemeral, freshwater lakes, a field study was conducted over a 2 year period. This involved macrophyte surveys, seedbank composition tests, microphyte composition and abundance analysis (i.e. concentrations of Chlorophyll a, b and c) and water column nutrient analysis (Total Nitrogen (TN) and Total Phosphorus (TP)). Additionally, changes in the macrophyte seedbank germination, biomass and abundance were investigated in more detail in mesocosm experiments where water column nutrient levels were manipulated.
    Substantial evidence was found in field studies to support the first hypothesis, with sites with variable water regime garnering a more diverse macrophyte community than those with stable water regime, in line with published literature.
    Mesocosm experiments found water column nutrient concentrations directly affected the macrophyte seedbank germination with fewer species germinating in the high nutrient treatment (consisting of 4.07 mg L-1 TN and 0.70 mg L-1 TP), supporting the second hypothesis, however no effect on biomass or the total number of seedlings was detected. Additionally, field studies did not find any correlation between TN and microphyte concentration and composition, however a weak positive correlation (r2 = 0.290, p = 0.021) was found between TP and Chlorophyll a concentration.
    Conceptual models were developed outlining the role of both water regime and water column nutrients in determining the vegetation composition and dominance of shallow ephemeral, freshwater lakes. The models show how vegetation composition is affected by water regime and suggests how land use practices (such as lakebed cropping) can have further implications for the macrophyte composition of a shallow lake upon rewetting. The models also project the impact of increased water column nutrient levels on a recently wet lake which has sufficient terrestrial vegetation cover to minimise sediment induced turbidity.
    The conceptual models and findings from this study provide water managers with a better understanding of the functioning of shallow ephemeral freshwater lakes, and how they can be manipulated to alter the composition and dominance of the macrophyte and microphyte communities.
    Original languageEnglish
    QualificationDoctor of Philosophy
    Awarding Institution
    • Charles Sturt University
    • Finlayson, Max, Principal Supervisor
    • Nielsen, Daryl, Co-Supervisor
    Award date01 Mar 2017
    Publication statusPublished - 20 Mar 2018


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