Ecology Report on Manly Dam

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A qualitative and quantitative examination of the limnology of Manly Reservoir Catchment Word Count: 3,916

Limnology of the Manly Reservoir Catchment was undertaken to assess the trophic status of the lentic system in the catchment area. Manly Dam is surrounded by urban development and bushland. It is of extreme importance as both a water supply for domestic and commercial use and as a site for a diverse range of flora and fauna. It has a large area of bushland which is an important ecological site. The whole catchment incorporates this bushland, urban areas (including recreational areas) and commercial developments. The extent of the urban development is increasing which is in turn applying pressure to this ecosystem. The status of the water system can be established into three trophic classes, eutrophic, mesotrophic and oligotrophic. This status was observed at a number of different sites within the catchment area, at varying closeness to human population and the dam itself. The sites were tested under a number of parameters such as light intensity, temperature, conductivity, turbidity, pH, Dissolved oxygen, nutrients and present species. All of these measurements can be indicative of the trophic status of a lentic water system and used together can be used as an index of the systems overall health and biodiversity. It was found that there was little difference in the sites regarding dissolved oxygen. However site 3 which was a water body within the golf course showed significant increase in pH. While sites 3 and 4 both sites furthest from the dam showed higher levels of phosphates, turbidity and nitrates, corresponding with less total species showing a high chance of Eutrophication occuring. The sites closest to the dam ie the lake shore and the damn wall showed the lowest readings of nitrate and were within the guidelines of the ANZECC (1992). There is a strong indication that the status of the water bodies closer to urban development had was less healthy than those at the damn and was attributed to a number of factors such as recent flooding, urban runoff including household waste and sewerage, and due to horticultural practices of the golf course (which had a huge impact on the water body in its grounds). Introduction

An understanding of the physical, chemical and biological factors and how they interact with each other is essential knowledge that is required to assess the limnology and trophic status of a lentic system. Trophic status can be separated into three classes: a eutrophic system is nutrient rich and has high primary productivity thus resulting in low oxygen levels; a mesotrophic system has an intermediate trophic status; and an oligotrophic system is nutrient poor and has low primary productivity resulting in high oxygen levels. These statuses are determined by the surrounding catchment, landform and geology (Carlson and Simpson 1996). Light intensity, temperature, conductivity, turbidity, thermal stratification, pH, dissolved ions (e.g. Dissolved Oxygen, DO) and gases, nutrients (insoluble and soluble), toxicants, and organic matter (photosynthesis of algae and macrophytes, and population dynamics) are all mechanisms that play important roles in the understanding of a lentic system (UTS 2012). This study was carried out to qualitatively and quantitatively examine the functioning of a lentic system through a number of measurements and sample collections at four different sites in the reservoir catchment of Manly Dam. The Manly Dam catchment or Manly reservoir catchment has an area of 375 hectares comprising of bushland (providing a safe and tranquil environment for visitors and important habitats for native flora and fauna) and urban areas (Warringah Council). The Manly Reservoir catchment contains 7 streams and 42% of the total area is covered by bushland (UTS 2012). A Catchment is defined...
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