How Does Oxygen Concentration of Pond Water Affect the Abundance of Phantom Midge Larvae (Genus Chaoborus)?
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Submitted By lgreening Words 2630 Pages 11
Hypothesis
I will investigate whether the concentration of oxygen in pond water will affect the abundance of Phantom Midge Larvae (Genus Chaoborus) by comparing a pond that has a higher oxygen concentration with a pond that has a lower oxygen concentration.
Alternative Hypothesis: The lower the oxygen concentration, the higher the abundance of Phantom Midge Larvae.
Null Hypothesis: There will be no significant difference between the oxygen concentration and the abundance of Phantom Midge Larvae. Any difference is due to chance.
Research
The Phantom Midge Larvae (Genus Chaoborus)
A phantom Midge Larvae (Genus Chaoborus) otherwise known as a ‘glassworm’ due to its transparent appearance is a form of Midge Larva which are very abundant in static water such as ponds and lakes. The body is in distinct segments with small hairs and the last segment has a number of stiff hairs which acts as a rudder. They breathe through the end of their abdomen and have two small eyes on the front of their body. They can survive is polluted waters with little oxygen. Unlike other air filled invertebrates, the Phantom Midge Larvae has two visible black air sacs either side of their body which allows them to migrate up and down in static water. They can be found in waters as deep as 70m where there is little oxygen and they are able to avoid predators which are found in shallower waters.
Phantom Midge Larvae are consumed by other aquatic predators such as puffers, young cichlids and bumblebee gobies and by small birds. In order to avoid their main predator, which is fish, the Phantom Midge Larvae migrate from the bottom of the pond during the day and surface nocturnally to feed. This suggests that during the day, the majority of Phantom Midge Larvae will remain in deeper water, where the oxygen concentration is lower. However, this behavioural response to light intensity could vary, depending on whether fish are present in the pond. Phantom Midge Larvae are a predaceous species and have a prehensile antennae that is modified to catch their prey. Their diet consists of Copepods, Cladocerans and Culicidae, however, the Phantom Midge Larvae are not known for chasing prey, therefore they tend to select whatever prey enters its strike zone.2
Factors affecting the oxygen concentration in water
There are many different factors that can affect the oxygen content in water. Temperature has the greatest effect on oxygen levels. As the temperature increases, the oxygen concentration decreases. For example at 10oC, the maximum oxygen content is 11.28 mg/litre whereas at 20oC, the maximum oxygen content is 9.08 mg/litre. Additionally, the greater the abundance of aquatic life, the greater the oxygen demand is. Pond treatments such as TretaPond, MediFin or the TretaMedica Range can also reduce oxygen concentration. Lastly, oxygenating plants can cause the oxygen level to fluctuate. During the day, the plants photosynthesize and produce oxygen, however, at night, the plants stop photosynthesising and continue to respire, using up oxygen and causing oxygen levels to decrease until light intensity increases again.
Depth is also a contributing factor to the concentration of oxygen. Dissolved oxygen enters the water through the air or as a plant by-product. The air from the surrounding atmosphere diffuses across the surface of the water or mixed in by aeration via wind or waves. Less photosynthesis occurs in deeper due to the low light intensity suggesting oxygen concentration is lower. Furthermore, the greater abundance of decomposing organic debris at the bottom of the pond uses up dissolved oxygen to respire, decreasing oxygen levels in deeper water. Lastly, if the water at the surface is not mixed with deeper water the water becomes stratified and there is a lack of new dissolved oxygen in the deep water. Therefore, as the water becomes deeper, the concentration of oxygen decreases.
Rationale:
Phantom Midge Larvae can tolerate high water pollution and low oxygen concentration, suggesting they can be used as an indicator species. The larva breathes through its body surface, but its air sacs allow it to stay in the low-oxygen conditions on the pond’s floor which is the reasoning for my hypothesis. If a high abundance of Phantom Midge Larvae are found, this would suggest high pollution and low oxygen concentration. This shows that the pond is not well maintained.
High water pollution can have other affects other than low oxygen concentration such phosphate, nitrate and pH fluctuation. Whilst the Phantom Midge Larvae is adapted to live in polluted environments, other species are not, suggesting that high pollution will interrupt with the food chain. For example, the larva feed on water fleas which are commonly found in nutrient rich water and are also an important source of food for other aquatic invertebrates. From this, we can infer that in polluted waters the aquatic invertebrates such as the Phantom Midge Larvae may have less prey, increasing competition between predator species resulting in predator species becoming endangered due to lack of prey or prey species becoming endangered due to an increase of demand. The Phantom Midge Larvae is also a secondary consumer and is consumed by other species such as birds, fish, the great diving beetle and large insect larvae. This suggests that the abundance of Midge Larvae will also affect species further up the food chain. Predators who only live nutrient rich water such as fish may have a lower abundance of Phantom Midge Larvae which could also lead to an increase in demand. Therefore, indicator species such as Phantom Midge Larvae are important to monitor the pollution of water in how it could affect other species.
Risk Assessment:
Risk Likelihood of Occurrence Severity of Outcome Total Management
Slips, trips and falls 2 1 3 Wear suitable footwear
Tread with caution
Weils disease 1 3 3 Wear clothes
Wash hands
Insect bites and stings 2 1 2 Wear suitable clothing
Use insect repellent
Drowning 1 3 3 Tread with caution
Weather 1 3 3 Wear suitable clothing
Equipment breaking 1 1 1 Be careful with equipment
The likelihood and severity of the hazards are rated using a 3-point Likert scale, in which 1 is unlikely or not severe and 3 is likely or very severe.
Ethics of Using Aquatic Species
Preliminary Trial
In order to investigate whether my experiment would work I carried out a preliminary trial. This proved helpful as initially I planned on look at the Mayfly nymph, however I after my preliminary trial I decided to change to Phantom Midge Larvae as there was a much greater abundance in both ponds. Furthermore, there was a greater difference in Phantom Midge Larvae in the two ponds which increases significance.
Initial Questions to Answer
• How will I collect my samples?
• At what depth will I collect my samples?
• How many water samples will I collect?
• How many times will I sweep the net back and forth?
• Which other abiotic factors could affect my results?
The Two Ponds
In my preliminary trial, I assessed two ponds to see if they would be suitable to use in my investigation. Two ponds were bought to my attention, including the ‘staff pond’ which had relatively clear water, surrounded by aquatic plants and away from public access. The clear water allowed me to easily count the abundance of species when using a net and tray to give accurate results.
The second pond I chose to investigate was known as the ‘black pond’ which had black, muggy water with less aquatic plants. It was open to the public, however off a public footpath so there was not much interference from the public. Whilst the dark water made the counting the abundance of aquatic species harder, I noticed a difference in the abundance of species and oxygen concentration between the two ponds which would allow me to carry out my investigation.
Method:
1. Take all necessary equipment to first pond and apply gloves.
2. Lay out tape measure across the width of the pond.
3. Use a random sampling method to select three points on the width of the pond and select the pond samples.
4. Fill a tray of water from the first point, deep enough to allow organisms to be comfortable in the tray.
5. Using a pond net, take 3 sweeps going from left to right and repeating in the opposite direction, each sweep approximately 1 metre each. Do this at the bottom of the pond by touching the pond bed with the net and lifting it slightly.
6. Carefully place the net over the tray filled with pond water and tip out the contents of the net. Dip the net into the water until as much of the contents as possible is put into the tray.
7. Wait for the sample collected to settle before counting each Phantom Midge Larvae. Record all data.
8. Pour the contents of the tray back into the pond, making sure that no organisms are left in the tray.
9. Repeat steps (4-8) at each point in the pond.
10. Collect water samples in a sample pot for testing of oxygen, phosphates and nitrates. Collect other abiotic factors including pH, temperature and light intensity. Record all data.
11. Go to the next pond and repeat steps (1-10).
12. After all samples have been collected, take water samples to lab and test for oxygen, nitrates and phosphates. Record all data.
Changes from the Preliminary Test
My preliminary trial allowed a greater insight into the abundance of phantom midge larvae in the area and contributing factors. I found a difference in oxygen of 2.5 mg/l which confirms I will be able to use this as my abiotic variable in my investigation. I also noticed a difference in pH, therefore I will monitor pH levels and take into account how this could affect my results. To measure oxygen in my investigation I will use an oxygen metre instead of a titration method as this will improve accuracy as it allows me to measure oxygen straight from the pond rather than collecting samples in a pot as air bubbles in the water samples could decrease the accuracy of my results.
I also plan to change my sampling method in my investigation to systematic sampling. I plan to gain a greater number of samples at intervals of 1m across a 15m width of the pond as this will allow further analysis of the data and increase reliability. Furthermore, a systematic method will ensure that I do not collect samples with the same organisms twice so the validity of my investigation is increased. I shall also collect all of my samples at an arm’s length which increases the accuracy of my results. Before counting the abundance of phantom midge larvae, I will leave my sample to settle for two minutes to make the phantom midge larvae easier to count and improve accuracy of my results.
Initial Questions Answered
• How will I collect my samples?
I will use a stratified sampling method to collect both my abiotic variable (oxygen) and my biotic variable (phantom midge larvae) at 1m intervals for 15m. I have chosen this as I have accessibility for 15m across the pond so this is a suitable method.
• At what depth will I collect my samples?
I have chosen to collect samples just above the bed of the pond by raising the net slightly upwards from the bed of the pond by approximately 5cm (assuming the bottom of the ponds are level).
• How many times will I sweep the net back and forth?
I will sweep the net back and forth 3 times to ensure a good sized sample whilst keeping disruption to other organisms at a minimum.
• How many water samples will I collect?
I will collect 3 water samples to take back to the lab at random points selected using a calculator. I will also collect temperature, light intensity and pH at these points.
• Which other abiotic factors could affect my results?
The ponds differ in pH as well as oxygen concentration, whilst other abiotic factors such as temperature, light intensity phosphates and nitrates stay the same. From this, we can infer there are controls over some variables which could have some effect of the results if a difference was shown. I plan to focus my investigation on oxygen concentration however I will take into account how the difference in other factors could affect my results.
New Method:
1. Take all necessary equipment to first pond and apply gloves.
2. Lay out tape measure across the width of the pond.
3. Use a systematic sampling collecting samples at 1m intervals for 15m.
4. Fill a tray of water from the first point, deep enough to allow organisms to be comfortable in the tray. Get as little debris as possible to allow maximum viewing of the organisms for more accurate results.
5. Using a pond net, take 3 sweeps going from left to right and repeating in the opposite direction, each sweep approximately 1 metre each. Do this at the bottom of the pond by measuring the depth by placing the net at the bed of the pond and lifting it slightly. Do this gently to reduce debris disturbing organisms.
6. Carefully place the net over the tray filled with pond water and tip out the contents of the net. Dip the net into the water to make sure no organisms are left on the net.
7. Wait for the sample collected to settle before counting each Phantom Midge Larvae. Record all data.
8. Pour the contents of the tray back into the pond, making sure that no organisms are left in the tray.
9. Collect the abiotic samples second so that you do not disturb the organisms before collecting your abiotic sample. Dangle probe on the oxygen metre in the water and swirl until the figure on the screen stops and record the number.
10. Collect other abiotic samples such as temperature, pH and light intensity at three points including first interval (0m), middle interval (7.5m) and last interval (15m). Collect pots of water in same place to test for nitrates and phosphates. Record all data.
11. Repeat the same steps (4-9) at each point in the pond.
12. Go to the next pond and repeat steps (1-11).
13. After all samples have been collected, take water samples to lab and test nitrate and phosphate concentrations.
Final Investigation Results:
