, 92:9 | Cite as

Changes in the chemistry of sedimentary organic matter within the Coorong over space and time

  • Evelyn Krull
  • Deborah Haynes
  • Sébastien Lamontagne
  • Peter Gell
  • David McKirdy
  • Gary Hancock
  • Janine McGowan
  • Ronald Smernik
Original Paper


Like many other coastal systems across the world, the Coorong lagoonal ecosystem (South Australia) has degraded over the last 100 years; in this case as a result of extensive regulation and diversions of water across the Murray-Darling Basin following European settlement. To evaluate whether the sources of organic matter (OM) supporting its food-web have changed since the inception of water management and barrage construction, sedimentary OM was characterised in cores spanning the Coorong’s salinity gradient at depths representative of the last 100 years over which the management alterations to river and estuarine flow were most marked. Detailed 210Pb, 137Cs and Pu dating in conjunction with palaeolimnological data (Pinus pollen) allowed for the reconstruction of the timing of substantial changes observed in the composition of the OM, most of which occur during the early 1950s, concurrent with management-related variations in water flow and salinity. Negative shifts in δ13C of up to 8.3‰ in the 2–10 and <2 μm fractions after the 1950s suggest a pronounced alteration in biogeochemical cycling or in the origin of OM. Elemental ratios and δ13C values of potential sources are inconclusive as to the cause of these biogeochemical changes. However, 13C-NMR spectra of the sediments suggest that degraded phytoplankton constitutes a large proportion of today’s OM and also reveal that an OM source rich in lignin was present prior to the 1950s. The high δ13C (−18.3‰) and low C/N (7.5) signatures of the lignin-bearing sediments are inconsistent with a C3 terrestrial OM source and instead suggest that the lignin-bearing seagrass Ruppia megacarpa13C of −13‰) contributed to a large degree to the sediment of the North Lagoon. R. megacarpa once was abundant in the North Lagoon but today has all but vanished from the system. Thus, only through a combination of isotopic and spectroscopic techniques was it possible to effectively decipher the changes in the composition of OM deposited throughout the Coorong over space and time. These results have important implications for research in estuarine OM dynamics in other geographic locations. Specifically, utilising complementary analytical techniques may sometimes be essential in reliably determining OM sources and processes in estuaries and lagoons.


Coorong Carbon isotopes Organic matter 13C-NMR 137Cs 210Pb 



We thank Mike Geddes for his assistance during the fieldwork component of this project. Jeff Baldock provided advice and guidance in the application of the molecular mixing model, while John Tibby, Matt Forbes and Kris Broos helped with data interpretation and by providing reviews of an earlier version of the manuscript. We thank Jenny Dick for kindly providing us access to R megacarpa samples. Finally, we thank the CSIRO Water for a Healthy Country Flagship Program for its financial assistance of this project. We would like to acknowledge the financial assistance of an ARC Linkage grant to P. Gell, D. McKirdy and J. Tibby.


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Copyright information

© Springer Science+Business Media B.V. 2008

Authors and Affiliations

  • Evelyn Krull
    • 1
  • Deborah Haynes
    • 2
  • Sébastien Lamontagne
    • 1
  • Peter Gell
    • 3
    • 4
  • David McKirdy
    • 2
  • Gary Hancock
    • 5
  • Janine McGowan
    • 1
  • Ronald Smernik
    • 2
  1. 1.CSIRO Land and WaterGlen OsmondAustralia
  2. 2.School of Earth and Environmental SciencesUniversity of AdelaideAdelaideAustralia
  3. 3.School of Humanities and Social SciencesUniversity of AdelaideAdelaideAustralia
  4. 4.School of Science and EngineeringUniversity of BallaratBallaratAustralia
  5. 5.CSIRO Land and WaterCanberraAustralia

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