The relationships between levels of dissolved nutrients and biotic life

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Research question

How will the levels of dissolved nutrients in the water affect amounts of aquatic biotic life?

Risk assessment

Background Information

In this scientific report I will be reporting on the relationships between levels of dissolved nutrients and biotic life in wyangan creek. (refer to Graph 1/Table 1) As we can see from the data tested and provided pond 1 and 2 have lower nitrate levels and phosphate levels whereas in pond 3 there is a sudden spike in the levels of phosphates and nitrates and then in pond 4 there is a decrease and then in pond 5 another increase.

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I believe this is caused by a fact that in pond 3 and 5 there is more runoff received compared to the other ponds. This in turn should increase the coverage percentage of plant life and algae if the pH and dissolved oxygen levels are also increasing accordingly. (refer to Graph 2/Table 2) The only anomaly in the measured data of dissolved oxygen is in pond 3which was 5.1 mg/L compared to all the other ponds which were generally in the 7 to 9 range. This anomaly can occur for many reasons, such as increased water temperature. Another reason could be an excess amount of biological oxygen demand (BOD), an example of this could be untreated sewage flow, organic discharge which uses up dissolved oxygen. The final reason is related to phosphate and nitrate levels in water. Phosphates and nitrates can allow aquatic flora to flourish which means that on cloudy days plants will consume the dissolved oxygen when they fail to photosynthesise. (refer to Graph 3/ Table 3) The only anomaly again is in pond

Whereas all the other ponds are in the 7-8 range pond 3 exceeds that range. The reason that this could occur is either through the amount of plant growth and organic matter in a body of water as a result of organic decomposition, bedrock and soil composition through which water will flow through, dumping of different types of chemicals and runoff can all be attributed to different levels of ph in the water. The main two aquatic plants we found that dominated the creeks were Nelumbo nucifera more commonly known as the Indian lotus and Salvinia minima also known as small Salvinia. Indian lotus is an introduced species to Australia from Asia; however, it doesn't do harm. Indian lotus through promising statists shows for usage in treatment for wastewater removing polluting compounds and heavy metals. It can grow in variable water conditions and in low light intensity. Various studies show the successful use of The Indian lotus to counteract water eutrophication which according to the (Merriam-Webster dictionary online) means the process by which a body of water becomes enriched in dissolved nutrients such as phosphates that stimulate the growth of aquatic plant life usually resulting in the depletion of dissolved oxygen. The leaves of the floating lotus reduce sunlight reaching the lower part of the water. This suppresses algae growth in aquatic systems that have the Indian lotus growing in them and thus, the oxygen content is up to 20% higher than in other aquatic plant systems. Due to intense agricultural practices, nitrogen and phosphorus pollution are major problems in aquatic systems. Lotus is able to assimilate a higher content of phosphorus than other aquatic plants currently used for water remediation such as water hyacinth. It also assimilates nitrogen denitrification which according to the (Merriam-Webster dictionary online) the loss or removal of nitrogen or nitrogen compounds specifically : reduction of nitrates or nitrites commonly by bacteria (as in soil) that usually results in the escape of nitrogen into the air and creates a habitat for bacterial growth in the water body.

Salvinia on the other hand does have a detrimental effect on native species. Indigenous to native to south America and the west indies, Common Salvinia is an incredibly invasive species due to its incredibly rapid reproduction rate and its adaptiveness. Reproduction in Salvinia minima occurs asexually through fragmentation. Though sporocarps, spore-producing sacs, may be present on the leaves of this species, Common Salvinia is thought to be sterile and can only reproduce asexually. Any part of a rhizome that buds or breaks off can form another daughter plant. Since fragmentation can occur continuously, Common Salvinia often shows exponential growth. This incredible reproduction speed leads to how it can outcompete many native species of aquatic plant. When introduced to a new environment, Common Salvinia can reproduce rapidly to due it being able to reproduce asexually and form large patches on the top of waterways. Its presence and speedy reproduction can out-compete and limit the growth of native water plants. Patches of Common Salvinia can block sunlight from entering the water, which suppresses the growth of underwater plants that photosynthesize, resulting in less dissolved oxygen in the water which is a reason for why pond 1,2,4 have less algae aside from the fact that the Indian lotus. This can lead to the death of many animals most likely fish. Waterfowl species that feed on either fish or native aquatic plants can also be affected by a lack of food. In bayou and swamp areas specifically, Common Salvinia is known to out-compete the floating aquatic plant duckweed also known as Lemnoideae. Duckweed is a relatively benign plant that is rich in protein and serves as a common source of food for many fish and bird species in its ecosystem. (refer to graph 5) As seen in pond 1,2,4 there's a relative abundance of Common Salvinia and Indian lotus whereas in pond 3 there's more algae and less Salvinia and lotus which further proves the point of how either it gets outcompeted by Salvinia or the lotus will reduce the amount of sunlight reaching lower parts of the water. Again, in pond 5 there were no lotus thus there was more algae and less Salvinia which meant a larger variety of plants

Original Hypothesis

If there is a high ph, nitrate and phosphates and dissolved oxygen level there will be a larger difference in species because if how certain species require certain levels of water quality to survive.

Hypothesis (after receiving dissolved nutrient levels data)

From the current data that we have on the abiotic factors of nitrate/phosphate levels, pH levels and dissolved oxygen levels, pond 1, 2, 4, 5 will be relatively similar in the amount of species living there and percentage of plant coverage supporting relative amounts of flora and fauna however, pond 3 will not as it has incredibly low amounts of dissolved oxygen which will affect amount of biotic life.


  • Dependent: Measurements of Phosphates levels from the creeks. This data was measured by outside people thus no device was recorded however, it was measured in mg/l.
  • Dependent: Measurements of Nitrate levels from the creeks. This data was measured by outside people thus no device was recorded however, it was measured in mg/l.
  • Dependent: Measurements of Dissolved Oxygen levels from the creeks. This data was measured by outside people thus no device was recorded however, it was measured in mg/l.
  • Dependant: Measurements of pH levels from the creeks. This data was measured by outside people thus no device was recorded however, the assumption is that universal indicator was used.
  • Controlled: All samples for testing came from the same size jars.
  • Controlled: All measurements of lux levels were down twice once in shade, once not in shade.
  • Independent: percentage of plant life in ratio to area of the creek. Changed through more rains and observing different ponds at different times

Apparatus used

Ammometer, Thermometer, turbidity tube, quadrat, lux meter, sample jar, phone (for imagining)


  • Step 1: Measure the wind speed using the yellow ammometer
  • Step 2: Measure air temperature using the yellow ammometer
  • Step 3: Measure the humidity effects temperature using the yellow ammometer. Ensure that it is Celsius unless required to be in Fahrenheit
  • Step 4: Measure the Above sea level using the yellow ammometer
  • Step 5: Measure the pressure using the yellow ammometer
  • Step 6: Measure the turbidity of the water with a turbidity tube. Fill to the top with water and keep pouring out water until you can see the line on the bottom.
  • Step 7: Measure water temperature with thermometer by placing thermometer in water for approx. 10 seconds.
  • Step 8: Measure amount of species through counting.
  • Step 9: Measure lux levels in sun with the black lux meter
  • Step 10: Measure lux levels in shade with the black lux meter
  • Step 11: Fill sample jar with water from the creek for further testing
  • Step 12: repeat for all other ponds. This step may exclude step 11 if only required to fill one sample bottle.


The results were extremely well matched to the location of the ponds. Is you refer to Graph one/Table one the levels of nitrates and phosphates went up accordingly except for pond 3 and 5 which had major spikes in levels due to pond 3 receiving runoff from the housing above it and pond 5 as Somerset has a sewage pipe feeding into it. The main relationship to be discussed is the relationship between the effects of dissolved oxygen levels in water and phosphate and nitrate levels in water. When there are excess levels of phosphates and nitrates in the water it allows algae to flourish and grow rapidly often leading to algae blooms. As algae die and decompose, the process consumes oxygen. Submerged plants without sunlight die, decompose and consume more oxygen. Without enough dissolved oxygen in the water, fish and other organisms suffer and die because they can't "breathe."

This is called Biological oxygen demand or B.O.D which is the amount of oxygen required for microbial metabolism of organic compounds in water. This demand occurs over some variable period of time depending on temperature, nutrient concentrations, and the enzymes available to indigenous microbial populations. The amount of oxygen required to completely oxidize the organic compounds to carbon dioxide and water through generations of microbial growth, death, decay, and cannibalism is total biochemical oxygen demand (total BOD). Total BOD is of more significance to food webs than to water quality. Dissolved oxygen depletion is most likely to become evident during the initial aquatic microbial population explosion in response to a large amount of organic material. If the microbial population deoxygenates the water, however, that lack of oxygen imposes a limit on population growth of aerobic aquatic microbial organisms resulting in a longer term food surplus and oxygen deficit.

Most natural waters contain small quantities of organic compounds. Aquatic microorganisms have evolved to use some of these compounds as food. Microorganisms living in oxygenated waters use dissolved oxygen to oxidatively degrade the organic compounds, releasing energy which is used for growth and reproduction. Populations of these microorganisms tend to increase in proportion to the amount of food available. This microbial metabolism creates an oxygen demand proportional to the amount of organic compounds useful as food. Under some circumstances, microbial metabolism can consume dissolved oxygen faster than atmospheric oxygen can dissolve into the water or the autotrophic community primarily in our case algae can produce. Fish and aquatic insects may die when oxygen is depleted by microbial metabolism. Another variable that could affect dissolved oxygen levels which is very important is lux levels in and out of sun. As we know all plant life must rely on photosynthesis to survive. From the statement the fact is built that it doesn't matter the amount phosphates and nitrates in the water without sun there will be no plant growth. Which is why if you refer to the background research section you will be given a definition on why Indian lotus are incredibly effect at keeping algae in check. Which is why in pond 3 there is a significantly larger amount of algae growth than in any other pond as there are less obstacles for the algae to reach the sun.

The various sorts of algae play significant roles in aquatic ecology. Microscopic forms that live suspended in the water column (phytoplankton) provide the food base for most marine food chains. In very high densities (algal blooms), these algae may discolour the water and outcompete, poison, or asphyxiate other life forms. Which is why there is more life in pond 1,2,4,5 as in pond 1,2,4 there are plants that will limit the number of possible algae in the water and in pond 5 there is a larger variety of plants many of which grow far out of the water.


Problems/limitations Improvements

As we collected the data from the creeks on different days and during that time period there was rain therefor more water was in the creeks which could have changed the ratios of levels in the water As an improvement for next time a good idea would to be more prepared to ensure that the weather for the next few days are all similar as to not get large differentials in collected data

This problem is more specific however, as the collected lux level data was completed different times of day the angles of the sun would have been different which can affect the variety of measured results Prioritise steps to get the most accurate lot of data. Realise that when something could be different because of whatever reason ensure that you collect all that data on the same day

Another problem is when collecting the data for temperature there was never a time when a timer was used to equalise the amount of time for each pond which could have affected the final results Realisation that many things that require more than one device and how that certain small elements can make large difference in certain circumstances


From the collected data the hypothesis was incredibly on point. As the hypothesis stated that pond 1, 4, 5 will be relatively similar in the amount of species living there and percentage of plant coverage supporting relative amounts of flora and fauna as the levels of phosphates, nitrates , dissolved oxygen, pH levels and lux levels are all relatively on track and it stated that pond 3 would have a lower percentage of plant coverage as there is a lower level of dissolved oxygen, however, the one aspect that was wrong in the hypothesis was that pond 2 would be similar in plant coverage to pond 1,4,5 however, as it had much lower lux levels then the other ponds there wouldn't have been as much photosynthesis occurring which could lower the levels of the plant growth.

Cite this page

The relationships between levels of dissolved nutrients and biotic life. (2019, Nov 19). Retrieved from

The relationships between levels of dissolved nutrients and biotic life
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