Longitudinal trends in river functioning: Patterns of nutrient and carbon processing in three Australian rivers

Authors

  • Wade L. Hadwen,

    Corresponding author
    1. eWater Cooperative Research Centre, Canberra, Australia
    2. Australian Rivers Institute, Griffith School of Environment, Griffith University, Nathan Campus, Nathan, Queensland 4111, Australia
    • Australian Rivers Institute, Griffith School of Environment, Griffith University, Nathan Campus, Nathan, Queensland 4111, Australia.
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  • Christine S. Fellows,

    1. eWater Cooperative Research Centre, Canberra, Australia
    2. Australian Rivers Institute, Griffith School of Environment, Griffith University, Nathan Campus, Nathan, Queensland 4111, Australia
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  • Douglas P. Westhorpe,

    1. eWater Cooperative Research Centre, Canberra, Australia
    2. New South Wales Department of Water and Energy, Aquatic Sciences Unit, Water Management Division, P.O. Box U245, Armidale, New South Wales 2351, Australia
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  • Gavin N. Rees,

    1. eWater Cooperative Research Centre, Canberra, Australia
    2. Murray-Darling Freshwater Research Centre, Commonwealth Scientific and Industrial Research Organisation, University Drive, P.O. Box 991, Wodonga, Victoria 3689, Australia
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  • Simon M. Mitrovic,

    1. eWater Cooperative Research Centre, Canberra, Australia
    2. New South Wales Department of Water and Energy, Aquatic Sciences Unit, Water Management Division, P.O. Box U245, Armidale, New South Wales 2351, Australia
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  • Brett Taylor,

    1. eWater Cooperative Research Centre, Canberra, Australia
    2. Australian Rivers Institute, Griffith School of Environment, Griffith University, Nathan Campus, Nathan, Queensland 4111, Australia
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  • Darren S. Baldwin,

    1. eWater Cooperative Research Centre, Canberra, Australia
    2. Murray-Darling Freshwater Research Centre, Commonwealth Scientific and Industrial Research Organisation, University Drive, P.O. Box 991, Wodonga, Victoria 3689, Australia
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  • Ewen Silvester,

    1. eWater Cooperative Research Centre, Canberra, Australia
    2. Department of Environmental Management and Ecology, La Trobe University, P.O. Box 821, Wodonga, Victoria 3689, Australia
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  • Roger Croome

    1. eWater Cooperative Research Centre, Canberra, Australia
    2. Department of Environmental Management and Ecology, La Trobe University, P.O. Box 821, Wodonga, Victoria 3689, Australia
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Abstract

Understanding longitudinal trends in the processing of carbon in rivers represents a much conceptualised, but infrequently tested, issue in aquatic ecology. In this study, we conducted concurrent longitudinal examinations of three very different rivers in eastern Australia to determine whether general principles in river functioning exist across broad geographic and hydrologic scales. Specifically, we examined trends in ambient basic water chemistry, nutrient concentrations, dissolved organic carbon (DOC), extracellular enzymes and food web structure and functioning and conducted bioassays to examine the degree to which DOC and nutrients limit heterotrophic bacterial respiration. These parameters revealed striking similarities across all sites. For metazoan communities, stable isotope analysis showed that algal carbon was the dominant basal resource utilised by consumers in all three rivers, suggesting that in-stream primary producers strongly underpin trophic pathways regardless of the position within a catchment or catchment condition. Analyses of extracellular enzymes revealed that microbial communities are actively utilising DOC at all sites. In fact, heterotrophic microbial respiration was strongly limited by DOC at all sites, with nutrient additions resulting in only relatively minor increases in respiration. Ultimately, this study demonstrates that DOC and algal carbon are critically important drivers of ecosystem processes in Australian riverine ecosystems. Furthermore, across all of our sites and rivers, ambient nutrient concentrations did not influence carbon processing. The consistent longitudinal trends in river function identified in this study provide useful insights for catchment managers and modellers with respect to identifiying key principles that underpin ecosystem functioning in Australian rivers. Copyright © 2009 John Wiley & Sons, Ltd.

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