The Microcystis cyanobacteria bloom in the Swan River - February 2000

Abstract

In February 2000 the Swan-Canning estuary in Western Australia experienced a record bloom of the toxic cyanobacteria Microcystis aeruginosa. At its height, concentrations of M. aeruginosa reached integrated water column cell counts of 15,000/ml and formed bright green scums in sheltered bays, where counts of 130 million cells/ml were recorded. Due to public health concerns parts of the river were closed from 10 to 22 February 2000. Two unseasonably large summer rain events in early and late January 2000 created conditions for the bloom. Freshwater runoff, estimated at 270 GL, was enough to fill the Swan-Canning estuary five times over and brought with it high levels of nutrients, mainly nitrogen (> 2.0 mg/L TN) and phosphorus (> 0.15 mg/L TP). A number of methods to reduce bloom accumulations were tried, including an attempt to increase the salinity of the surface water above the critical 10 ppt level for Microcystis; using a bentonite clay and poly-aluminium chloride mixture to flocculate and sink the algae; and sucking up scums using oil spill equipment. Over 900 tonnes of M. aeruginosa were removed and safely disposed using sewage treatment facilities. The bloom collapsed when the freshwater flush subsided and seawater intrusion from the Indian Ocean re-established itself, raising the salinities above the tolerance of Microcystis.

Toxin-producing blooms of the cyanobacterium Microcystis aeruginosa in rainwater ponds in Saudi Arabia

“…In addition, the density of this cyanobacterium correlated with nutrient concentrations (particularly NO 3 and PO 4 ) in Saudi rainwater ponds. Thus, the results of the present study agree with those obtained by Atkins et al (2001), who report that the extent of the bloom depends largely on the availability of nitrogen and phosphorus and the salinity of the water. The growth of M. aeruginosa is limited to brackish regions and negatively correlated with the salinity in Patos Lagoon (Yunes et al 1996).…”

Toxin release in response to oxidative stress and programmed cell death in the cyanobacterium Microcystis aeruginosa

“…Salinity values surpassing this critical mark were accompanied with a reduction in total viable cell concentration and an increase in cell lysis (Atkins et al, 2000;Orr et al, 2003). Our data show nearly an 80% increase in toxin release when cells were transferred to water with a salinity of 32‰.…”

“…In an attempt to use salinity alterations as a bloom elimination strategy, specimens of M. aeruginosa were found to be viable at salt concentrations up to 9.8‰ (Atkins et al, 2000). Salinity values surpassing this critical mark were accompanied with a reduction in total viable cell concentration and an increase in cell lysis (Atkins et al, 2000;Orr et al, 2003).…”

Can mussels be used as sentinel organisms for characterization of pollution in urban water systems?

“…In the urban area, drains contain areas with and without sewers (Peters and Donohue, 2001). The Swan River estuary experienced a major toxic cyanobacterial bloom in 2000, when a large rainfall event increased nutrient concentrations and decreased salinity within the estuary (Hamilton, 2000;Atkins et al, 2001), indicating that this estuary is prone to nutrient pollution from the watershed. The Swan River estuary is influenced by mostly diurnal tides with a mean tidal range at the mouth of the estuary of 0.8 m. At the same time, the estuary is seasonally forced with a large discharge of freshwater from the tributaries during the wetter winter months (May-September), and little freshwater discharge during dry summers.…”

“…Oczkowski et al, 2008), which can lead to eutrophication. In urban estuaries, tributaries often transport high amounts of nitrogen from the watershed into the estuary, causing water-quality problems including toxic bloom development (Hamilton, 2000;Atkins et al, 2001). Nitrogen concentration gradients might develop with higher upstream and lower downstream values, where nutrients are diluted by seawater (Dähnke et al, 2010;Fry et al, 2011).…”