Investigation of factors affecting the distribution of Chironomus larvae in Nant Iago (James' Stream) Nr. Abergavenny, S. Wales.

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Biology Coursework

Biology

April Jane Alarcon

Title:  Investigation of factors affecting the distribution of Chironomus larvae in Nant Iago (James’ Stream) Nr. Abergavenny, S. Wales.

Method:  Biotic Data

  1. The stream was split into 14 sections and groups of 3 were each assigned to work at different sections of the stream, which began at the beginning, right at the top, and ended further down stream.
  2. The method we used for our experiment was Disturbance Sampling. This was accomplished with the aid of a Surber Sampler which we used in one riffle and one pool in our section. The Surber Sampler consisted of a net which had a 1.0mm2 mesh at the end where all the samples were collected and a quadrat which was placed over a part of the riffle or pool and gave us our area of sampling.
  3. By laying the quadrat flat on the bed, I disturbed the stream bed and washed any lying organisms into the mesh. I then washed the water through the mesh to collect any samples in the water.
  4. Once this was done the invertebrates were identified, counted and recorded

Physical Data:

  1. To accomplish my physical data, I measured the pH of the water, the Total Dissolved Solids (TDS), the dissolved oxygen, the depth and the temperature.
  2. All were measured using specialised probes which were placed in the water of the riffles or the pool. The probes gave us readings of whichever piece of data we were trying to achieve after 30 seconds. The readings were then recorded.
  3. The amount of detritus was estimated using estimation by eye, recorded and measured using a scale of 1-4:
  1. None
  1.                                      2.   Little

                                           3.   Some

                                           4. Abundant

        The pool was 4 and the riffles was 2.

  1. The substrate was also identified as to what matter was present, i.e. Riffles: gravel’s and pebbles. Pools: twigs, soil, leaves, detritus.

Null Hypothesis:   There will be no difference in the numbers of Chironomus between pools and riffles.

Alternative Hypothesis:   There will be a significantly higher number of Chironomus in the pools than in the riffles.

Which statistical test?

           I am going to use the chi square test because we do not know the normal distribution of the data and because I only have a small data sample of 14. A chi square test is used to see if observe values are different from expected values.

          X2 =   Σ (O-E)2                                            o = observed

                           E                                                 E = expected

 

My chi square value from the experiment was 243. The critical value from the table at 95% confidence showed to be 3.84 at 1 degree of freedom.

          Because my experimental chi- square value is of a much greater value than my calculated value, it leaves me with a result indicating that my Null Hypothesis is incorrect. I am 99.9% confident that it is wrong as the critical value at this point is 10.8 and my calculated critical value is 243 which is an extremely larger figure.

           Therefore I will in turn accept my alternative hypothesis which states that there will be a significantly larger number of Chironomus in pools than in the riffles. After my statistical analysis, I can see that there was significantly more Chironomus found in the pool. As my density data shows the maximum abundance of Chironomus is 800m2 in the pool, whereas the maximum number of Chironomus found in the riffles is 50m2.

     

Interpretation

 

              Our aim was to investigate the distribution of freshwater Macroinvertebrates in two microhabitats in an upland stream. A stream is formed due to gravity causing overland flow in water and there are many individual factors which affect the stream and the abundance of its inhabitants. The two different types of factors are Abiotic and Biotic.

Abiotic

The Abiotic factors, which would affect the stream and its inhabitants, are:

     

         The current in the riffles, which is significantly stronger compared to the current in the pools. It would suggest that there are either not as many organisms living in the riffles or that if there are, then they would be specially adapted organisms. Examples of this would be an organism, which is highly streamlined. This would help it be prevented from being washed off the rock. It is also adapted to living in the riffles with its ‘claws’ that help it grip and cling onto the rock to prevent it from being washed away.

          In comparison, there is evidence to indicate that there is none or very little current in the pools. This will affect the organisms living in the pools, because there is very little chance for them to be washed away, resulting in there being a higher population of organisms in the pools than there is in the riffles. The low ratings of current mean that there is also a lot of small substrate particles. This means that many other different types of organisms will inhabit the pools as there will be more prey for predators, and in turn, those which are the predators, will attract organisms which hunt for them themselves. These new predators will also inhabit the pools to consume their prey.

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         The substratum levels and content of them also affects the stream and its organisms. In the pools, there are mostly high levels of detritus as the current is extremely low and so the sediment is allowed to settle on the streambed and be built up. There are, however, lower numbers of detritus, twigs and leaves in the riffles because there is a high current running here and anything which settles here will get washed away. Therefore, there is a layer of gravel and pebbles.

          Temperature also affects the distribution of ...

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