HR: 0800h
AN: B11A-0066    [Abstracts]
TI: Bioavailability, Composition and Fate of Dissolved Organic Matter in the Swan-Canning Catchment, South-Western Australia
AU: * Petrone, K C
EM: kevin.petrone@csiro.au
AF: CSIRO-Ensis, CSIRO Centre for Environment and Life Sciences, Wembley, WA 6913, Australia
AU: Hughes, C S
EM: hughec01@student.uwa.edu.au
AF: University of Western Australia, Ecosystems Research Group, School of Plant Biology, Crawley, WA 6009, Australia
AU: Norris, J R
EM: norrij01@student.uwa.edu.au
AF: University of Western Australia, Ecosystems Research Group, School of Plant Biology, Crawley, WA 6009, Australia
AU: Grierson, P F
EM: pfgblue@cyllene.uwa.edu.au
AF: University of Western Australia, Ecosystems Research Group, School of Plant Biology, Crawley, WA 6009, Australia
AB: Dissolved organic nitrogen (DON) comprises the bulk of the total nitrogen load to the N-limited Swan-Canning river and estuary that bisects Perth, WA, yet its ecological role is largely unknown. Our objective was to assess the bioavailability and composition of dissolved organic matter (DOM), particularly its DON component, and the potential of DOM to supply dissolved inorganic nitrogen (DIN) to the estuary during the summer months when algal blooms are common. We compared water samples from 10 sub-catchments of the Swan-Canning that vary in land-use: eucalypt forests on the Darling Scarp most distant from the estuary, mixed (agriculture/ residential) catchments on the metropolitan perimeter, and urban catchments on the Swan Coastal Plain near Perth CBD. We inoculated water samples with a common bacterial inoculum and measured changes in DOC, DON and DIN over time. We found that 2 to 17 per cent of DOC and 18 to 44 per cent of the DON was consumed during the experiment and DIN was produced in 8 of 10 catchments. DOC and DON consumption were linearly related to concentration across sites and were greatest in the urban catchments. However, DOC and DON consumption were not significantly related, suggesting that C and N are concentrated in different fractions of DOM. Using resin fractionation techniques, we found that DOC was concentrated in the hydrophobic fraction, followed by transphilics, and lesser amounts of charged and neutral hydrophilics. Ongoing analyses will examine the N content of resin fractions and the amino acid composition of streams to determine how N composition relates to DOM decomposition. We are currently examining organic matter leached from native plants (Corymbia, Melaleuca) in coastal plain wetlands in order to characterize allochthonous DOM. Further examination of algal- derived DOM and point sources will enable us to determine the bioavailability and composition of in-stream and anthropogenic sources. These studies provide much needed information to target catchment management and may improve the accuracy of estuarine hydrochemical models by incorporating DOM decomposition as a dynamic parameter.
DE: 0470 Nutrients and nutrient cycling (4845, 4850)
DE: 0493 Urban systems
DE: 0496 Water quality
DE: 1804 Catchment
DE: 1806 Chemistry of fresh water
SC: Biogeosciences [B]
MN: 2007 Fall Meeting