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

Abstract

Abstract. Blooms of noxious N 2 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 reemergence of cyanobacterial blooms.

Downstream Transport of Geosmin Based on Harmful Cyanobacterial Outbreak Upstream in a Reservoir Cascade

“…This might occur during the water-level drawdown, decrease (e.g., discharge), and increase (e.g., impoundment) stages. This is achieved by the interaction between the water and sediment layers and is a more dominant survival strategy during water-level drawdowns and low water levels [ 64 , 65 , 66 , 67 ]. When the water level of a reservoir is reduced or maintained at low levels, the water bodies are vulnerable to pollution.…”

Watching the tide roll away – contested interpretations of the nature of the Lower Lakes of the Murray Darling Basin

“…The Cyclotella group has a wide environmental tolerance, but only eight species have been found in saline waters (Olvia et al 2008) including those in the C. striata complex. C. striata sensu stricto has been described as being prevalent in brackish, marine, estuarine and inland saline lakes (Bradbury et al 1981;Jiang et al 1997;Saunders et al 2008;Cook et al 2016). It was regarded by Roetzel et al (2006) as being allochthonous euryhaline (able to adapt to a wide range of salinities).…”

Using sedimentary prokaryotic communities to assess historical changes in the Gippsland Lakes

“…The Gippsland Lakes is the largest estuarine system in Australia, consisting of a complex network of channels and water bodies interconnecting five major rivers, which flow into three main lakes—Lake King (LK), Lake Victoria (LV), and Lake Wellington (LW; Figure 1). This system hosts a diversity of wetlands with high conservation value included in the Ramsar Convention (Cook et al, 2016; Saunders et al, 2007). However, over the last 2 centuries, this unique system has suffered substantial modifications mostly associated with anthropogenic impact.…”

“…The permanent entrance of seawater has generated several environmental problems over the years, resulting in an immediate change in water levels and chronic salinisation of a formerly fresh or brackish‐water system, and affecting the local biodiversity at all ecological levels (Boon et al, 2016; Day et al, 2011; Komoroske et al, 2016; Saunders et al, 2008). Their hydric balance is regulated mostly by the entrance of freshwater, which causes low salinity periods in winter and spring and leads to blooms of diatom and dinoflagellates, and, since 1987, periodic cyanobacterial blooms ( Nodularia spumigena ) (Cook et al, 2016; Cook & Holland, 2012).…”

“…Previous studies have attempted to identify the impact of these historical human activities on the waterway health of the Gippsland Lakes. For example, Cook et al (2016) determined the historic occurrence of eutrophication periods and cyanobacterial blooms in the Gippsland lakes during pre‐ and post‐European arrival periods, using stable isotopes and pigment biomarkers in dated cores. These findings allowed the authors to establish a relationship between bloom events with anthropogenic impacts, providing important conservation measures (Cook et al, 2016).…”