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This article in JEQ

  1. Vol. 36 No. 4, p. 963-974
     
    Received: Aug 15, 2006


    * Corresponding author(s): Bill.Maher@canberra.edu.au
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doi:10.2134/jeq2006.0318

Riparian Plant Material Inputs to the Murray River, Australia

  1. Graeme Esslemontab,
  2. William Maher *ab,
  3. Phillip Fordac and
  4. Ian Lawrencea
  1. a Cooperative Research Centre for Freshwater Ecology, Univ. of Canberra, ACT 2601 Australia
    b Ecochemistry Lab., Institute of Applied Ecology, Univ. of Canberra, ACT 2601 Australia
    c CSIRO, Land and Water. GPO Box 1666, Canberra, ACT, 2601

Abstract

By changing riparian plants from Eucalypts to pasture and exotic deciduous trees, modern development has altered the type of carbon assimilated by Australian rivers. To investigate influences of plant litter substrates on biochemical oxygen demand, plant materials entering the Murray River were analyzed for their composition and mineralization potential. Plant materials were distinguished compositionally by two principal components, structural carbon and macronutrients, as: (i) Eucalyptus leaves, (ii) Eucalyptus bark and Casuarina cunninghamiana seed cone, (iii) grasses, (iv) macrophytes, (v) aquatic herbs, (vi) non-eucalypt leaf (Salix, Casuarina, Acacia). Ratios of C/P (1879–14524) and C/N (65–267) were relatively high in Eucalyptus bark, while mean N/P (7–60) ratios were similar among plant materials. Terrestrial weathering increased C/P and C/N ratios, while N/P ratios remained similar, due to greater loss of N and P relative to C. Aerobic decay experiments showed that nutrient supplementation accelerated decay of all organic substrates, except for grasses that decayed efficiently without supplementation. Aquatic herbs also had substantial carbon availability, macrophytes and non-eucalypt leaves had intermediate carbon availability, while eucalypt leaf and bark had intermediate to low carbon availabilities. Because biochemical oxygen demand varies with organic substrates sampled from the Murray River, and also with soluble nutrient availability, it is plausible that that modern changes to riverine plant communities and land use have influenced the biogeochemistry of this river toward faster, and more complete, processing of allochthonous carbon.

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