Articles | Volume 13, issue 12
Biogeosciences, 13, 3677–3686, 2016
Biogeosciences, 13, 3677–3686, 2016

Research article 22 Jun 2016

Research article | 22 Jun 2016

Blooms of cyanobacteria in a temperate Australian lagoon system post and prior to European settlement

Perran L. M. Cook1, Miles Jennings1, Daryl P. Holland1, John Beardall2, Christy Briles3, Atun Zawadzki4, Phuong Doan5,a, Keely Mills5,6, and Peter Gell5 Perran L. M. Cook et al.
  • 1Water Studies Centre, School of Chemistry, Monash University, Clayton, VIC 3800, Australia
  • 2School of Biological Sciences, Monash University, Clayton, VIC 3800, Australia
  • 3Geography and Environmental Sciences, University of Colorado, Denver, CO 80217-3364, USA
  • 4ANSTO Institute for Environmental Research, Lucas Heights, NSW 2232, Australia
  • 5Water Research Network, Federation University Australia, Ballarat, VIC 3350, Australia
  • 6British Geological Survey, Keyworth, Nottingham, NG12 5GG, UK
  • anow at: Faculty of Biology – Environment, The University of Da Nang, Đa Nǎng, Vietnam

Abstract. Blooms of noxious N2 fixing cyanobacteria such as Nodularia spumigena are a recurring problem in some estuaries; however, the historic occurrence of such blooms in unclear in many cases. Here we report the results of a palaeoecological study on a temperate Australian lagoon system (the Gippsland Lakes) where we used stable isotopes and pigment biomarkers in dated cores as proxies for eutrophication and blooms of cyanobacteria. Pigment proxies show a clear signal, with an increase in cyanobacterial pigments (echinenone, canthaxanthin and zeaxanthin) in the period coinciding with recent blooms. Another excursion in these proxies was observed prior to the opening of an artificial entrance to the lakes in 1889, which markedly increased the salinity of the Gippsland Lakes. A coincident increase in the sediment organic-carbon content in the period prior to the opening of the artificial entrance suggests that the bottom waters of the lakes were more stratified and hypoxic, which would have led to an increase in the recycling of phosphorus. After the opening of the artificial entrance, there was a  ∼  60-year period with low values for the cyanobacterial proxies as well as a low sediment organic-carbon content suggesting a period of low bloom activity associated with the increased salinity of the lakes. During the 1940s, the current period of re-eutrophication commenced, as indicated by a steadily increasing sediment organic-carbon content and cyanobacterial pigments. We suggest that increasing nitrogen inputs from the catchment led to the return of hypoxia and increased phosphorus release from the sediment, which drove the re-emergence of cyanobacterial blooms.

Short summary
The Gippsland Lakes, Australia, have suffered from periodic blooms of cyanobacteria (blue green algae) since the mid 1980s. Prior to this, little is known about the history of cyanobacterial blooms in this system. We investigated the history of cyanobacterial blooms using a sediment core taken from the Gippsland Lakes which had each layer dated using lead isotopes. The results showed that surprising blooms of cyanobacteria were also prevalent prior to European settlement
Final-revised paper