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Extended Experimental Investigation | Bulimba Creek


Home | Introduction | Aim & Hypothesis | Materials | Method | Results | Discussion | Conclusion | Bibliography | Appendix

Site One: Hemmant Nature Creek Reserve

The human impact at Hemmant is obvious and easy to see. Not only is there severe erosion, but the ecosystem is suffering as well. The tiny mud crab that was dug out of the stream by the side of the railroad bridge is one example of displaced organisms of this ecosystem. With the erosion of the banks, this little crab’s shelter is unstable and unreliable, eventually exposing it to the predators seen at the reserve, such as magpies and herons/cranes. The site has been radically changed and the pre-existing mangrove ecosystem has been succeeded by an open savannah habitat with the introduction of foreign species of birds. Human activities such as clearing and building have practically destroyed this ecosystem and the lack of wildlife seen was evidence of this.
For a site that is so close to an industrialized area, the water quality is very good. The water was a bit brackish, although this could be explained by the tidal influence on this section of the creek, with salt water inflow from the Brisbane River and Moreton Bay. Of some concern was the concentration of phosphorus. Excess phosphorus in the Australian environment usually leads to the poisoning of native species that have adapted to low levels of phosphorus. As such, the safe limit for phosphorus in waterways is 0.05 mg/L. The concentration of phosphorus at Hemmant was twenty times that. A nearby sports field could account for this concentration, with excess phosphorus in lawn fertilizer leaching into the water draining into the creek. The small amount of total suspended sediment could be evidence of water impoundment upstream. Water is held for irrigation and sediment is trapped, letting water with almost no sediment to continue downstream. The result is that sediment is stripped from the creek bed and banks, leading to further erosion and loss of habitat. The small amount of TSS did not seem to relate to a higher concentration of dissolved oxygen. Instead, dissolved oxygen for Hemmant was less than for Carindale, which had a greater concentration of TSS.
The bacteria cultures that I grew yielded inconclusive results, mainly because I was not familiar with the different characteristics of the bacteria. The bacteria cultures are limited in indicating sewerage contamination as the bacteria as the indicator can occur in sources other than humans. For example, Escherichia Coli can naturally occur in paper mills.

Site two: Winstanley Street Bridge

Human activity at Carindale was also very obvious and the impact on the creek plain to see. Both sides of the creek had been radically altered, with a concrete drain carved in to the nearside bank. Drains are a source of point specific pollution where pollutants such as sediment, oils, grease, nutrients and rubbish flow into waterways. The drain was responsible for a significant decrease in water quality. Not only were there oil slicks on the surface of the water, but algal blooms were flourishing in the warm, shallow, nutrient-rich water. The drain was also a point for the entry of litter to the ecosystem. The combined effects of clearing, construction, pollution and a heavily urbanized area have also adversely affected the pre-existing ecosystem. Remnants of the ecosystem exist upstream with old stands of eucalypts and small tributaries, but at the testing site, introduced species have taken over, leading to a decrease in biodiversity. Competition for space and food means that weedy plants have been able to gain a foothold allowing introduced species to enter the ecosystem with a reliable food source at hand.
Bulimba Creek at Carindale was shown to have water of average quality. While TSS levels and dissolved oxygen concentration were quite good, the phosphorus levels in the water were phenomenal at 45 mg/L, a level 900 times the safe level. With such high human activity at the creek, the phosphorus levels are not surprising. A golf course exists just upstream, as does a park with lush green lawns, and the drain and construction sites contribute to pollution nonetheless. Golf courses require high amounts of fertilizer and water to maintain, meaning that a lot of the nutrients in the fertilizer are leached into the creek with the run-off from irrigation. While nitrogen is used up in the waterway, phosphorus is less readily needed and high amounts are toxic to native species of fish and plants. The toxic phosphorus eliminates native species and introduced species move in by secondary succession. The drain affected water quality drastically. As a source of pollution, detergents would have added to the phosphorus concentration of the water. The largest effect on water quality that it had was by increasing TSS by 30%. Sediment from the nearby construction sites and other debris on the roads washes out of the drain in to the creek, leading to an increase in turbidity. An increase in turbidity is an added stress to the ecosystem, especially in denying sunlight to aquatic plants for photosynthesis.
In growing the bacteria cultures, I found that the sample I grew from under the Winstanley Street bridge yielded a bright yellowish colony, that became dominant on the agar when incubated at 35 degrees Celsius. I am sure that this at least points to coliform bacteria and may also show that the water at Carindale was polluted with human faecal matter. What this can also point to is heavy metal contamination of the ecosystem. Heavy metals are present in sewerage. Some heavy metals such as mercury are fat soluble and have the ability to bioaccumale and biomagnify. Essentially, with heavy metal contamination in the creek, similar effects of pesticides like DDT on the ecosystem will possibly be seen in the future with the loss of top order consumers to poisoning.

Site Three: Wishart Community Park

The ecosystem at Wishart remains in better condition than at the other two sites. Lower amounts of human activity have resulted in an ecosystem that has been preserved in a better condition. The fact that verge vegetation has been left untouched except in a few places points to some of the factors that have kept the ecosystem of the creek at Wishart in good health. Lower human activity at Wishart means that run-off is relatively free of pollutants, and introduced species have less chance to gain entry to the ecosystem due to the better health of existing natives. Natural habitats are preserved and native species have greater success in breeding because of this. That being said, there is evidence of human activity at Wishart Community Park, with clearing on the opposite bank for grazing and cleared areas on the nearside for grass parks and walkways. However, the impact that this has had on the ecosystem is minimal, but may allow for greater damage to the ecosystem in the future.
The water quality at Wishart was average compared to Carindale, but poorer than Hemmant, which was surprising. The concentration of phosphorus in the water was still very high at 7 mg/L, and was the only testing site to give a reading of nitrate concentration with 4 mg/L. These nutrient levels could be attributed to the run-off from pasture land on the opposite banks. Horses were being grazed and their manure could be easily washed into the creek with run-off due to the steepness of the slope. The dissolved oxygen concentration was lower than any other testing site. Combined with the nitrate data, this could be indicative of organic decomposition in the water which has the effect of consuming oxygen and releasing nitrogen. The added vegetation cover of the creek could possibly have contributed to the organic matter in the creek.
The bacteria cultures grown from water samples at Wishart yielded interesting and complexing results. In one culture, there appeared to be a mixture of colonies that showed the yellow bacteria from Carindale as well as other pigmented bacteria strains that showed up as scarlet or blue dots. What the culture could be indicative of is a diverse selection of bacterial fauna in the creek, contributed to the higher biodiversity that exists at Wishart that is not seen at Carindale and Hemmant.

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