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Gippsland Lakes Algal Blooms Brochure


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A summary; The ecology of algal blooms in the Gippsland Lakes

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Gippsland Lakes Algal Blooms Brochure

  1. 1. Algal blooms in theGippsland LakesThe Gippsland Lakes are a series of linked waterways in south- Impactseastern Victoria fed by rivers and streams flowing from the Great The Taskforce has overseen a number of programs to reduce theDividing Range. loss of nutrients from farm lands. First it tackled high run-off zones,The lakes receive fresh water from several rivers and marine water such as irrigation areas, and now it is moving to address targetedfrom tides and storm surges pushing in through the man-made dryland catchments. In urban areas, authorities have improvedchannel to the sea at Lakes Entrance. The upper lakes (such the management of sewage systems and the Taskforce hasas Lake Wellington) are brackish, while the lakes closer to the worked with industrial and commercial enterprises to reduce theirentrance are more saline. Evaporation also increases their contribution of nutrients to the Lakes. Programs have also beensalinity levels. undertaken to reduce the erosion of riverbanks and lake shores,In recent times, an increase in algal blooms has indicated a which are both sources of nutrients into the waterways.decline in water quality. Algal blooms may be toxic to people,animals and fish, and therefore have a detrimental effect on the More informationsystem’s environmental and recreational value. In response, the A more detailed description of the ecology of algal blooms isGippsland Lakes & Catchment Taskforce was formed to improve presented in, ‘The ecology of algal blooms in the Gippslandwater quality and so tackle the problem of algal blooms. Lakes’. For copies of the report and the research it draws on, see NICHOL RResearch funded by the Taskforce has provided a clearer MITC TAMBO RIVER RIVE HELL RIVE R SON Bairnsdaleunderstanding of the complex interactions that determine whether Map of the Gippslandan algal bloom will occur in the Lakes and the species most likely Lakes LAKE Lakes Entranceto thrive in different situations. This is essential knowledge for JONES KING (DSE, 2011) BAYcombating future algal outbreaks. ERThe work reinforces the need to continually improve the PERRY RIVmanagement of the Lakes to reduce nutrient inputs, as it is hard, if AVON RIV ER LAKE VICTORIAnot impossible, to manage the Lakes to overcome problems once LAKEthe inflows have occurred. WELLINGTON BASS STRAIT OBE LA TR R RIVE LAKEThis brochure presents a summary of the research about the REEVEdrivers of algal blooms in the Gippsland Lakes. 0 5 10 KilometresPhotograph: Cathrine Sutherland
  2. 2. Types of algaeMicro-Algae are tiny aquatic organisms powered by sunlight. Theyinclude some of the oldest life-forms on earth, and their ancestorsdate back more than three billion years.Algae contain the green pigment chlorophyll which enables them touse the sun’s energy to turn carbon dioxide and water into organiccompounds and oxygen; known as photosynthesis. This ability,coupled with their abundance, means they generate massive Nodularia spumigena. Photo: Jonathan Smith, SEAProamounts of oxygen as well as being the foundation of aquatic food-webs.Many micro-algae are single-celled organisms, but some linktogether to form colonies that range in shape from filaments, tospheres or sheets.The main types of algae in the Gippsland Lakes are:• Green algae (mainly dinoflagellates), the ancestors of flowering plants.• Diatoms, whose cell walls are made of silica (the same chemical found in sand and glass). Calothrix parasitica. Photo: Jonathan Smith, SEAPro• Blue-green algae, or ‘cyanobacteria’. Bacteria containing chlorophyll and many species can also ‘fix’ nitrogen from the water.The blue-green algae found in the Gippsland Lakes include: • Synechococcus – unicellular and colonial forms. They are• Nodularia – a filamentous, nitrogen-fixing form, known to often marine and, though there are freshwater species, they produce thin toxic scums. It can occur in fresh water, but is do better in saline waters. Synechococcus can use dissolved more common in brackish environments. nitrogen and thrive in high-nutrient environments.• Anabaena – a filamentous, nitrogen-fixing form, known to • Calothrix parasitica – a fimalentous, non-toxic and bottom- produce toxic blooms. dwelling alga.• Microcystis – small irregular, nitrogen-fixing colonies; often found in fresh water where they can also produce toxic blooms.
  3. 3. Nutrient cyclesNutrients are crucial ingredients for an algal bloom. Nitrogen and Phosphorus transformations include:phosphorus can transform as they cycle through the environment • Sorption – sediments or compounds taking in (absorption) orand the result of that depends on the form in which they are holding onto (adsorption) phosphorous.present. They may be bound up in organic molecules or liberated • Reduction – the conversion of iron to iron sulfide releasesin inorganic compounds that can then nourish living organisms phosphorus into the environment in low oxygen conditions.such as algae. The transformations are driven by microbes and Nitrogen and phosphorus may also both be subject to:chemical reactions, which are influenced by changes in theenvironment, such as oxygen levels and temperature. • Mineralisation – the decomposition of organic matter (often by microbes) into inorganic elements.For nitrogen, the key transformations are: Nutrient cycling is much faster for nitrogen than for phosphorus.• Nitrification – bacteria converting nitrogen compounds into Nitrogen that is available to organisms (known as ‘bio-available’) is more readily available forms (e.g. converting ammonium to very soluble and does not remain in sediments for long. nitrite and then nitrate). Phosphorus in sediments, however, is generally in equilibrium with• Denitrification – the conversion of nitrates into gaseous that in the water column above. As water concentrations rise so nitrogen, nitric oxide and nitrous oxide. to do the loads stored in sediments – and if water concentrations decrease, phosphorus is released from the sediments. net loss Atmosphere (1.5)Right: Simplified nitrogen cycle for the Gippsland Lakes.Source: Holland D, Cook P, Beardall J, Longmore A. (2009) ‘Gippsland Lakes Recycling Denitrification (2.5)Snapshot. Nutrient cycling and phytoplankton population dynamics.’ Water (>10)Studies Center, Monash University. Victoria. Catchment Flow (1)Note: Benthos are organisms in the sediments and on lake floors. Settling (4.5)The numbers in brackets indicate the rates of movement of nitrogen (inmmol/m2/day). Flux (2) BenthosPhotograph: Riviera Nautic
  4. 4. Algal bloomsAlgal blooms, or population explosions, may be dominated by • The low oxygen levels result in phosphorus beingseveral microscopic algae, as different species thrive in different released from the sediments and nitrogen is released toconditions, depending on nutrient availability, salinity, temperature, the atmosphere as nitrogen gas. The ratio of nitrogen tolight and oxygen levels. For example: phosphorus in the lake waters subsequently drops.• Dinoflagellates prefer high ratios of nitrogen to phosphorus; • In January to April, high temperatures and high phosphorus• Nodularia prefers lower ratios of nitrogen to phosphorus, levels are ideal for nitrogen-fixing blue-green algae (such as medium salinity and warmer temperatures; Nodularia) and blooms occur. As temperatures fall in May to June, the Nodularia dies back and the bloom ends.• Microcystis prefers lower ratios of nitrogen to phosphorus and low salinity; and This describes a typical scenario – but the script is not always followed. Conditions may become ripe for blue-green algae without• Synechococcus prefers higher nitrogen levels with higher a preceding bloom of non-nitrogen fixing algae and there may be salinities, temperatures and light. years when a winter bloom is not followed by another in summer.A ‘typical’ algal bloom scenario in the Gippsland Lakes is: For example, Synechococcus bloomed in 2007/08 following• High river flows in winter and early spring bring high levels of floods in July 2007 that brought in exceptionally high levels of nutrients, especially nitrogen, into the Lakes, enabling non- nutrients (the result of extensive bushfires in 2006/07). Although nitrogen fixing algae (diatoms and dinoflagellates) to thrive. Synechococcus is a blue-green algae it prefers high nitrogen• The algae use up the available nutrients, die off and sink to concentrations. It also likes warm, sunny conditions and can do the bottom, generally in November to January. Bacteria in well in higher salinities. The bloom persisted until early April 2008. sediments on the lake floor consume the dead algae and use up the oxygen in the water.The Gippsland Lakes & Catchment TaskforceThe Victorian Government formed the Gippsland Lakes & Catchment Taskforce in 2001 to arrest the decline in the Lakes’ water qualitythat was contributing to an increase in algal blooms.Employing an evidence-based and adaptive management approach, the Taskforce has focused on:• using science to gain a better understanding of the ecology of the Lakes;• taking targeted actions to reduce the loads of nutrients (nitrogen and phosphorus) entering the Lakes;• monitoring the ecology of the Lakes to evaluate the success of these actions; and• taking further action in response to the outcomes of monitoring work.Produced for the Gippsland Lakes & Catchment Task Taskforce by:• Peter R Day Resource Strategies (• Julian Cribb & Associates (• SUBStitution (