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.
Results of my experiment
Table to show number of Chironomus sp in the Woodland Pond
Results table
Table to show the number of Chironomus sp in the Meadow Pond
Results table
Results graph is shown in appendix 2.
Analysis
The Mann-Whitney statistical test
I’m using the mann-whitney statistical test to compare the mean of my two sets of data.
The hypothesises that will be tested are:
Ho: There is no difference in the meadow pond compared with the woodland pond of Chironomus sp.
H1: There is more Chironomus sp in the woodland pond compared to the meadow pond.
Stage 1 my two sets of data from the woodland pond and the meadow pond are laid out in a table
Stage 2 Calculate a score for woodland pond reading
Woodland pond
All of my results are 15 because all 15 of the woodland readings are a higher value Therefore my total score of my woodland pond readings are 225
Meadow pond
All of my results are 0 because all of the meadow pond readings are a lower value than the woodland pond so therefore my total score for my meadow pond readings are 0.
The smaller of the two scores will be the U-value therefore my u-value is 0
Compare my calculated U-value with the critical value in the tables at the appropriate significant level. If my value is smaller reject Ho and accept H1.
The critical value for two samples of 15 is 64 at the 5% level of significance. Since my value is 0 we accept H1 and reject Ho and conclude that there is a significant difference between the number of Chironomus sp in the woodland pond compared with the meadow pond.
My results and my statistical test both prove my hypothesis correct. This is because the woodland pond has all the factors the Chironomus sp lives in. Such as, a canopy cover, this keeps the pond warm. As it’s woodland there will be a lot of mud due to leaves falling and plants dying. This also means there will be a suitable pH and oxygen content. The meadow pond is open, which means it therefore has many plants and a small amount of mud.
The amount of pH, Light, Mud depth, Oxygen and temperature has a huge affect of the Chironomus sp.
Results of my abiotic tests
Woodland pond
Meadow Pond
Graph for these abiotic factors are shown in appendix 3.
Chironomus sp lives in warm conditions, this proves the mud acts as a good insulator, as the table above shows the mud depth in the meadow pond is 4 cm and depth in the woodland pond is 14.3 cm. Now compare this to the temperature of the woodland pond the average temperature is 13.8’C compared to the meadow pond where the temperature 12.9’C. This proves the woodland pond is an ideal place for the chironomus sp to live. From this experiment I feel the main reason the chironomus sp prefers the woodland pond is because of the thick layer of mud. The deeper the mud, the lower the pH as shown in appendix 1. A reduction in oxygen corresponds to a fall in pH although how the two are related is unknown. The Chironomus sp lives in around 15cm of mud, which is pH 6.5 to 7.2 but is absent in 30cm, which is pH 6.3. This means the woodland pond is the Chironomus sp ideal mud depth, temperature and pH. My research has proven that species like the Chironomus sp which feed on detritus and are therefore only indirectly dependant on green plants for food seem to be able to tolerate a wide range of pH.
The Chironomus sp doesn’t need much light to live as it lives in the mud, the light intensity is linked with the oxygen content as the light provides energy for the plants to photosynthesise, which produces oxygen. The Chironomus sp only needs small amounts of oxygen to survive as it contains haemoglobin which has a high affinity for oxygen in low partial pressures. All these points mean the woodland pond is the ideal habitat for the Chironomus sp.
pH
If the pH is too high or to low the Chironomus sp will not be able to survive. pH isn’t as important as the other abiotic factors, as the Chironomus sp can live in wide ranges of pH. However if something was to make the pH change dramatically this could kill the species.
Temperature
The Chironomus sp need to live in reasonably warm conditions this is why they live in the mud.
Light intensity and oxygen content
The Chironomus sp doesn’t need much light to live as it lives in the mud, The light intensity is linked with the oxygen content as the light provides energy for the plants to photosynthesise which produces oxygen. The Chironomus sp only needs small amounts of oxygen to live so therefore if there’s no light intensity the chironomus cannot survive, but if there’s too much it will produce the wrong type of habitat.
Mud depth
The Chironomus sp needs a lot of mud to burrow in, it also feeds of this so if there’s not enough mud the species could not survive.
Trends and patterns
My results show that the amount of Chironomus sp in the two ponds are frequent, they show a distinct difference in the two ponds shown in the mann-whitney test.
My results didn’t show many anomalous results, there were only two small anomalies, and these are highlighted in red on my table of results.
Meadow pond
These are my anomalous results for the meadow pond.
Woodland Pond
These are my anomalous results for the woodland pond.
These anomalies aren’t large enough to affect my results, but they do not fit in with the frequency of results, the meadow pond results are in the range of 0-3 and the woodland pond 8 – 17. As you can see the meadow pond is 2.74 away from the total average of the meadow pond, and the woodland pond is 5.92 away from the woodland average. These could be anomalous for a variety of reasons these could include, more or less chironomus sp in one particular area due to more food or better living conditions something may have scared them away.
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. if 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.
