An investigation to compare the number of Chironomus sp in a woodland pond compared to a meadow pond

I carried out an investigation to compare the number of Chironomus sp in a woodland pond compared to a meadow pond. My hypothesis was, there would be a larger number of Chironomus sp in a woodland pond compared to a meadow pond. It is proven that Chironomus sp likes to live in areas with a high mud depth, high temperature and a low light intensity which are all factors of the woodland pond. 45 samples were taken from each pond with fishing net and a tray. The average number of Chironomus sp in the woodland equaled 11.92 while the average for the meadow pond was 1.26. The Mann-Whitney test showed a total score of 225 for the woodland pond, and 0 for the meadow pond. This meant I was able to prove my hypothesis correct.


My Experiment

I am carrying out an experiment to compare the number of Chironomus sp in a pond situated in the middle of woodland, it is covered by trees; the water is shallow with a lot of mud. Compared to a pond situated in the middle of the grassland and has many different species of plants growing from it; the water is deeper than the woodland pond and has more sunlight shining on it.


There will be a larger number of Chironomus sp found in a woodland pond compared to the meadow pond.

Null hypothesis

There will be no difference in Chironomus sp in the woodland pond compared with the meadow pond.

Background knowledge on Chironomus sp.

Chironomus sp is the Latin name for the non-biting midge larvae. Chironomus sp lives in the mud to a depth of 15cm, with a pH tolerance of 6.5 to 7.2. Mud is a zone with a high organic content in the form of detritus, and serves two important functions. It provides a source of nutrition for microorganisms, which break down detritus down to mineral salts and restore the fertility of the water above. It also serves as a home for numerous burrowing species like the Chironomus sp and acts as a good insulator. Mud, together with it detritus, thus provides an important ecological habitat for the Chironomus sp. Light is also a important abiotic factor, in areas where mud is predominant there is less vegetation due to low light intensity, which results in low oxygen availability. The oxygen content is also an important factor in the Chironomus sp living conditions as you can see from table 1.0 in appendix 1 the deeper the mud the less oxygen saturation. The Chironomus sp contains haemoglobin which has a high affinity for oxygen in low partial pressures in order for the Chironomus sp to survive the anaerobic conditions which it lives in.

Chironomus sp lives in warmer conditions preferring temperatures from 12.5 to 15. Any temperatures below this the chironomus sp cannot survive so therefore are born in the summer period, the also mud acts as a good insulator, the woodland pond is therefore an ideal place for the chironomus sp to live in due to the thick layer of mud. The deeper the mud, the lower the pH this is shown in the table in appendix 1. A reduction in oxygen corresponded to a fall in pH although how the two are related is unknown, the Chironomus sp lives in about 15cm of mud, which is pH 6.5 to 7.2 but is absent in 30cm, which is pH 6.3. My research has proves that animals like Chironomus sp which feed on detritus and therefore only indirectly dependant on green plants for food seem to be able to tolerate a wide range of pH but favouring between 6.5 and 7.5. From this I am able to predict that there will be less Chironomus sp in the meadow pond due to the lack of mud, the high oxygen conditions. The meadow pond is not the Chironomus’s sp ideal place to live as the habitat is wrong. Therefore I feel the mud is the most important factor to the Chironomus sp habitat.


Obtain all the correct equipment I will need to carry out my experiment. This includes, Fishing net to catch the Chironomus sp. A tray to place the contents of the net into. A spoon to fish out all the Chironomus sp. A stopwatch to time how long the net was in the water for. A magnifying dish to place all the Chironomus sp into so I can count them. I will be taking my first samples from the meadow pond; I will take samples from all around the pond at different locations in the open part of the pond this will make my experiment fair. My samples will be swoops with the net 1m by 1m for 1 minute, I decided to change this technique as I found swooping for 1 minute was to long, so I changed it to 10 swoops. After this I will empty the contents into the tray and fish out all the Chironomus sp with the spoon into the magnifying dish to count and record into a table. I will repeat this 3 times in each location, 15 times to get 45 samples. When I have finished this I will carry out the same procedure at the woodland pond.

There are variables, which I have to be aware of during my experiment, these include the dependant variable this is the factor I am measuring in this case it’s the number of chironomus in the two different ponds.

The independent variables are the factors I’m changing in this case it’s the two different ponds, I will be taking samples from each pond and comparing them.

There are the abiotic factors, which will change in the two different ponds that I will be measuring so I can analyse the results. The abiotic factors include, the temperature this is measured by using a digital thermometer, which you put the metal end into the water and the temperature will show. The pH, this is measured by using pH strips and a pH chart which you match the colour to the correct pH. The oxygen level is measured by using chemicals on a sample of the pond water. The light intensity is measured by a light meter, which you hold above the pond, and it tells you how much light is shining onto the pond. The depth of the mud this is measured by placing a long rod into the pond and using a measuring stick to measure where the mud comes up to on the rod.

These factors are very important to my experiment as for Chironomus sp to survive it needs the right type of living conditions. Controlled variables are variables, which I need to keep constant to make my test fair. They include my equipment if I was to change my equipment in the middle of my experiment this could vary my results thus, not achieving reliable results.

Amount of time spent catching, this is a variable I will also have to keep constant, as this could vary my results also as if I spent longer catching I would probably catch more Chironomus sp. If I spent to little time catching I wouldn’t catch as much, again making my results unreliable. I made sure I kept the catching time controlled by measuring 1m by 1m and only doing 10 swoops with the net.

As well as the variables there are also risk assessments and ethical issues I have to be aware of. There are many risks associated with this experiment they include tying longhair back this is because hair could dangle into the pond. Not consuming any of the pond water as pond water contains diseases. Washing hands after the experiment this is because if any water is consumed. Make sure all equipment is washed thoroughly to avoid contamination. Not eating when doing the experiment as again diseases could be caught. The ethical issues are very important when doing experiments involving species, understanding the ecosystems is very important as killing simple specie could affect the ecosystem.

Conclusion My investigation was to find out if there was a difference in the Chironomus sp in the woodland pond compared to the meadow pond. I proved there is in fact a significant difference, proving my hypothesis correct and my null hypothesis incorrect. I feel this is due to the desirable abiotic condition in which the woodland pond possesses. These abiotic conditions include, a substantial amount of mud, because the Chironomus sp is a burrowing species the mud is essential for its habitat, the mud also provides warmth in which the Chironomus sp needs to survive.

The mud offers a source of nutrition for the species as it has high organic content in the form of detritus the Chironomus sp breaks this down into mineral salts to survive on. The mud is extremely important to the Chironomus sp therefore the woodland pond is its ideal habitat as it has an average depth of 14. 3cm of mud while the meadow pond has only 12. 6cm. Another abiotic factor is light; the Chironomus sp lives in mud which means it doesn’t need much light to survive. The amount of light and oxygen is closely linked, as the more light the faster the plants will photosynthesis resulting in a high oxygen content.

Due to the Chironomus sp containing haemoglobin which has a high affinity for oxygen in low partial pressures it is able to survive in these low oxygen conditions. The Chironomus sp is also adapted to live in a pH of around 6. 5 to 7. 5 this pH is present in 15cm, which is the ideal depth for the Chironomus sp to live in, it is also the depth of the woodland pond. As you can see from my abiotic factor results both ponds both ponds have the correct pH for the Chironomus sp to live in. This shows that pH doesn’t affect the Chironomus sp as much as the other abiotic factors.

In conclusion the woodland pond has all the ideal living conditions for the Chironomus sp, this is why I found a larger number of Chironomus so in the woodland pond compared to the meadow pond. I feel my results are reliable enough to make a valid conclusion. My results only show two slight anomalies. This can be seen highlighted in red on my table. In the meadow pond the anomaly is 4, this is higher than the other results. The other anomaly in the woodland pond is 6, this is lower than the other results. These results weren’t serious enough to affect the overall averages.

I carried my experiment out according to my method in my planning section with making only a few changes. These included, instead of swooping the net for 1 minute I changed it to just 10 swoops as I felt 1 minute was to long and I was catching to much mud and debris. I followed all my risk assessment and variables very carefully keeping them all the same. Overall I think my method was good, I got a reliable set of results, which proved my hypothesis correct. My plan was very helpful during my experiment, I read the variables and risk assessment many times to make sure I understood why I had to keep them constant.

I had a few limitations while carrying out my experiment, these included; I only had one day to carry out the whole experiment, therefore my set of results could vary from day to day, maybe when its cold there would be less Chironomus sp out. Therefore if I carried out my experiment over a year my results would be more reliable as I could see if the numbers changed throughout the different seasons. Another limitation was that I carried out my investigation in the meadow pond in the morning, and the woodland pond in the afternoon; this also could have varied my results.

Another limitation was that I could only swoop my net slightly into the mud due to; if I swooped at 15cm of mud I wouldn’t be able to see any of the Chironomus sp due to the amount of mud in my sample. How I feel I could have improved my experiment I feel to make my results more reliable; I could have measured the centre of the pond using a measuring stick each time to make sure I was receiving my sample from exactly the same depth each time. I could have also measured the pH and temperature of the mud at the bottom of the ponds, as my table in appendix 1 (‘Ecology’ W.

H. Dowdeswell) shows that as the mud get deeper the pH decreases. Therefore if I measured the pH and the temperature of mud at 15cm I could have proved this. I also could have proved that the Chironomus sp prefers the mud due to the warmth. Different experiments I could have carried out to test for the Chironomus sp. I could have tested the amount of Chironomus sp at different depths. I could have done this by measuring the depth of the pond including the mud, divide this by three and take three samples at each depth. e. g. f the mud was 15cm long, 15 divided by 3 equal 5, so therefore you take one reading at 5cm another at 10 and the third one at 15. After each reading I could have counted the amount of Chironomus sp in each sample. This would have proved the Chironomus sp prefers 15cm of mud. There would be a few problems with this though, for example, it will be very hard to count the number of Chironomus sp due to all the mud and debris. It will also be very difficult just to obtain the mud for 15cm, as you would have to scoop up some of the other mud. Therefore this experiment I feel wouldn’t have achieved reliable results.