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| = Background =
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| == Influence of Development on Waterbody Health ==
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| One of the biggest impacts of development is the washing away of top soil during rain events. If top soil enters waterways it increases the turbidity of waterways which is harmful to aquatic life. Top soil is more likely to be mobilised if underlying soils are sodic (sodic soils readily disperse in water if grass and plants are removed and the soil is directly exposed to rain events).
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| Top soil also contains nutrients. When nutrients are released into waterways they can result in algal blooms or the growth of thick carpets of Azolla and other aquatic plants. Both algae and Azolla use nutrients to grow summer, however during winter when these plants die, they fall to the bottom of the lake and decompose. The decomposition process by bacteria removes oxygen from the water and can trigger an anoxic event (water severely depleted of oxygen). Fish and other aquatic animals that depend on oxygen in the water may die. Mass fish deaths are often the consequence.
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| == Development History at Laurimar Park wetlands ==
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| Aerial photo of Laurimar Park wetlands. Lake water is brown in colour. This is indicative of high levels of turbidity caused by clay and topsoil. High levels of turbidity is harmful to aquatic wildlife. High levels of turbidity is also associated with high levels of nutrients inputs. Even at this early stage in the development, plant growth (algae or Azolla) can be seen in the Eastern pond (right hand side) around the edges of the lake. This is suggestive of high nutrient levels present in the lake.
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| [[File:Laurimar Park wetlands Doreen aerial 22 Dec 2010.PNG | 900px]]
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| Aerial photos of Laurimar Park wetlands 18 April 2011. Show very high levels of turbidity in the lake. Top soils in the development are not being managed correctly. The wetland is however protecting the Plenty river catchment, however it would be better for the turbidity to remain low in this waterbody.
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| [[File:Laurimar Park wetlands Doreen aerial 18 April 2011.PNG | 900px]]
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| Lake body showing extensive growth in both waterbodies (Western and Eastern waterbodies) 16 Dec 2015. First time observed. This indicates that sediment and nutrients initially confined to the eastern waterbody have now migrated into both waterbodies. At this stage the eastern waterbody should be desilted. Azolla could also be removed from the waterbody using special harvesting machinery that floats on the surface of the waterbody and skims off the plant material (Aquatic Technologies and other consultants provide these services).
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| [[File:Laurimar Park wetlands Doreen aerial 16 Dec 2015.PNG | 900px]]
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| Significant amount of surface vegetation growth 22 Dec 2016. Algae or Azolla. Covers both waterbodies. This is becoming a yearly occurence indicating that nutrient levels in both lakes are elevated. If organic material and nutrients are not removed from the lake this cycle will repeat itself each year.
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| [[File:Laurimar Park wetlands Doreen 22 Dec 2016.PNG | 900px]]
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| Thick blanked of Azolla (identified by a red colour when growth has matured) on the surface of the eastern waterbody 25 Aug 2018. This thick film was not removed and will naturally die and sink to the bottom of the lake.
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| [[File:Laurimar Park wetlands Doreen 25 Aug 2018.PNG | 900px]]
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| Most recent photo taken 24 Dec 2021. Shows Azolla covering most of surface of both waterbodies. Confirmation of Azolla during inspection on 7 Feb 2022.
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| [[File:Laurimar Park wetlands Doreen 24 Dec 2021.PNG | 900px]]
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| == Fish deaths ==
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| On Sunday 6 Feb 2022 there was a social media posting on the Doreen Community Voice page about a large number of dead carp floating on the surface of Laurimar Park wetlands (also known as Lauries Field).
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| [[File:Doreen Community voice social media posting fish deaths 6 Feb 2022.jpg | 900px]]
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| Photo of Laurimar Park wetlands taken of the western lake from the southern bank 7 Feb 2022. Shows extensive coverage of Azolla on the surface of the water and many large dead fish floating on the surface. It was estimated that there were approximately 20-30 large dead fish.
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| [[File:Laurimar Park wetlands western pond showing fish and Azolla in water 7 Feb 2022.JPG | 900px]]
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| Photo of Laurimar Park wetlands taken from far western bank 7 Feb 2022. Shows large accummulation of Azolla on the surface of the water. Dead fish are mid water and not visible in this photo.
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| [[File:Laurimar Park wetlands far west bank showing Azolla 7 Feb 2022.JPG | 900px]]
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| Photo of Laurimar Park wetlands eastern pond showing blanket coverage of Azolla 7 Feb 2022. Ducks swimming in water.
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| [[File:Laurimar Park wetlands eastern pond showing Azolla covering water 7 Feb 2022.JPG | 900px]]
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| == EPA Investigation ==
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| The EPA was notified about the 20-30 fish deaths by local government on 7 Feb 2022. Officers with expertise of fish deaths were also notified at Agri-Bio (located within La Trobe University precinct). EPA concluded that:
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| * Large fish die-offs are most likely the result of anoxic conditions in the lake.
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| * The high amount of plant material and successive years of die-off result in a large store of decaying organic material in the lake body.
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| * As water temperatures increase (as in summer), this can result in a high rate of organic material degradation by bacteria in the water. The activity of the bacteria reduces dissolved oxygen levels in the water. If low owygen levels are sustained for a significant period of time this results in fish deaths.
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| * The EPA concluded that the release of a chemical (eg. insecticide) was unlikely to have resulted in the fish deaths because the catchment is urban only (no industrial or commerical sites in catchment). Testing for chemicals is also very expensive and time consuming because you need to know what chemical you are testing for.
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| * EPA did not issue any directives because there was no significant risk of harm (to people or property) identified at the site.
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| * The EPA Pollution report details PRI-00013055
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| == Future Actions ==
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| A list of actions is presented to help reduce the risk of fish deaths in the future:
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| * Immediate removal of dead fish and other animals from the lake
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| * Removal of surface growth of Azolla using mechanical harvesting techniques. Azolla is high in nitrogen and can be composted on site. It cannot be used on native gardens due to high nitrogen levels. The compost will also need to be tested for other contaminants before disposal.
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| * Addition of solar powere aeration pumps to both water bodies to improve dissolved oxygen levels
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| * Addition of water quality sensors, especially with temperature and dissolved oxygen sensors
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| ** Temperature sensor used to monitor any elevated water temperatures that could cause accelerated degradation of organica material.
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| ** Dissolved oxygen sensor to detect anoxic events.
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| * Desilting of the eastern lake.
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| * Educating the local community about the importance of top soil management and erosion.
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| * Possible evaluation for the presence of sodic soils in the catchment.
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