Dissolved Oxygen Saturation Lab Report

An experiment was conducted to determine the dissolved oxygen, phosphate and nitrate in Freshwater Creek on 22nd February 2016 at 10:46 am. The same tests were done by students previously however in this report only the recent 2 years results will be taken into consideration for comparing trends, anomalies and interrelationships.

The recommended levels of dissolved oxygen saturation is 85%. The dissolved oxygen saturation last year was 85% at water temperature 22.9° and 2 years ago being 92% at water temperature being 23.1°. However this years it was recorded to be 80% at water temperature of 27.2° (see appendix 1 for the raw data table and calculations of Dissolved Oxygen). All three results are in the recommended levels which means there

However there has been a decrease in dissolved oxygen compared to the levels recorded 2 years decreasing yearly at the rate of 5-8%. Inferencing from this trend/rate, it seems the dissolved oxygen will decrease and would be lower than the recommended dissolved oxygen level of 85%. The decrease in dissolved oxygen could be because of the water-falls or dam nearby Freshwater Creek, dams are known to reduce dissolved oxygen by decreasing aeriation of water to prevent more oxygen from the atmosphere to diffuse with the water. However it looks like the main cause of reduction in dissolved oxygen is due to the increase of dissolved phosphate and nitrates in Freshwater Creek. The dissolved phosphate of last two years were 0mg/l and 0.0568mg/l and this year’s dissolved phosphate in average was 0.24mg/l ° (see appendix 3 for the raw data table and calculations of dissolved phosphate). However there was an outlier of 0.15mg/l, this could be due to a mistake made during the testing method or possibly a very few concentration of phosphate in the location of where the sampling was collected. The recommended levels for dissolved phosphate in fresh water is 0mg/l.

This is not a huge number however it shows that the amount of dissolved phosphate in Freshwater Creek is slowly increasing. Simultaneously, the dissolved nitrate has also increased. The recommended levels of dissolved nitrate in Freshwater Creek is 0mg/l. In the past 2 years the dissolved nitrate levels were 0mg/l which was in the recommended levels however this year’s average measure shows an increased level of 0.33mg/l (see appendix 4 for the raw data table and calculations of dissolved nitrate). Reasons as to why dissolved phosphate and nitrate have increased cannot be found accurately however there is a possibility it may be due to fertilizers. The most prevalent fertilizer used in Cairns is urea and single superphosphate, it contains high concentration of phosphate and nitrates and it is used to grow plants. When the soil is watered, the fertilizer will naturally cause the fertilizer to run-off and possibly accumulate in Freshwater Creek. Another way dissolved phosphates and nitrate could have increased is by detergent run-off and sewage used by homes. Detergent contain phosphate and nitrates and waste such as feces contain ammonia,