"Investigating The Distribution Of Streams Invertebrates"

3559 words - 15 pages

Method1) We investigate the distribution of Benthic invertebrates at the Nant Iago stream, which is near Abergaveng in South Wales;2) We measured a 150 m stretch of the stream, each group had a 10 m stretch meter long of stream;3) A surber sample was used, the size of the holes in the net was 1 mm2, while the size of the quadrat was 0.1 m2 (this size prevents the invertebrates from passing through the holes, but small particles of fine sand could);4) We placed the quadrats so it was flat in an area which was firstly slow flowing and then fast flowing (stony and sandy regions);5) We the disturbed the area by turning the rocks and brushed then lightly into the net so that the species were washed in by the current;6) Then we put the species that were inside of the net into a white tray and identified the species and counted them;7) At each sample site we also measured:a) Temperature by putting a thermometer in the water until it stabilised, then we recorded it;b) Dissolved Oxygen by using a probe which we stirred, for about 30 seconds, in the water encouraging the water to move, then we recorded it;c) pH by using a pH meter which was put in the water, then we recorded it;d) Depth of water by using a metal measuring tape, then we recorded it;e) Velocity by using a probe that we put in the water, then we recorded it;f) Sediment size by estimating the size and by comparing it with a card given to us with many possible sizes, then we recorded it;g) T.D.S. by using a probe which we put into the water, then we recorded it;h) The detritus amount by using a 4 part scale:i) None - 0%ii) Some - 1%-29%iii) Abundant - 30%- 59%iv) Very Abundant - >60%Null Hypothesis There is no correlation between the distribution of chironomus in the sandy and stony substrate.Alternative HypothesisThere will be a higher distribution of chironomus in the sandy substrate than in the stony substrate.v I'm going to use the ÷2 (chi) test, because the sample that I have is smaller than 30 and we don't know the exact distribution.Total number of chironomus in sandy region: 10+4+6+1+5+6+7+4+80+8+5 = 136Total number of chironomus in stony region: 5+3 = 8 Sandy Stony TotalObserved 8 136 144Expected 144 = 72 2 144 = 72 2 ÷2 Test ÷2 = Ó (O-E)2E Note:O = ObservedE = Expected Sandy StonyObserved (O) 136 8Expected (E) 144 = 72 2 144 = 72 2O - E 136 - 72 = 64 8 - 72 = -64(O - E)2 642 = 4096 -642 = 4096(O - E)2 E 4096 = 56.89 72 4096 = 56.89 72Ó(O - E)2 E 56.89 = 56.89 = 113.78 56.89 = 56.89 = 113.78 ÷2 = 113.78 Degrees of freedom = 1, because number of samples = 2.Number of data classes - 1 = Degrees of freedomTherefore in our investigation the degree of freedom equals 1, as we have 2 data classes (either sandy or stony).The critical ÷2 value from table is 3.84. That is more than 95% sure that the null hypothesis is wrong. For this we used 1 degree of freedom to measure the value of the ÷2 and also the confidence level. Therefore by looking at the degree of frequency table and at my results of the ÷2 test, which was 113.78, I am more than 95% and even 99.9% certain that the null hypothesis is wrong and that the alternative hypothesis is correct.Therefore I can validate with plenty of confidence the alternative hypothesis, which was that there are higher distributions of chironomus in the sandy substrate than in the stony substrate.Mean calculations Stony region: Number of chironomus = 5+0+0+0+0+0+0+0+0+0+0+0+0+3 = (0.1 m2 quadrat) 14 = 0.6 per 0.1 m2 quadrat Detritus rating = 3+3+2+2+2+3+2+3+3+2+1+2+2+2 =(1 to4) 14 = 2.3 Flow rate =(ms-1)0.25+0.38+0.37+0.50+0.49+0.51+0.25+0.60+0.30+0.68+0.24+0.22+0.23+0.52=14= 0.4 ms-1 pH = 8.0+8.1+8.0+8.0+8.0+8.1+7.7+8.1+8.1+8.0+8.0+8.1+8.0 =13= 8.0 Dissolved Oxygen =(% Saturation)101+102+99+101+103+105+99+103+103+104+101+103+103+102.1 =14= 102.1 % Water depth =(m)0.17+0.12+0.15+0.19+0.21+0.16+0.09+0.12+0.19+0.17+0.19+0.15+0.20+0.18= 14= 0.2 m Temperature =(0C)12.0+11.9+12.1+12.2+12.0+12.0+12.0+11.9+12.1+13.0+12.1+12.2 = 12= 12.1 0C Total dissolved solids = (Parts per million)65+65+66+66+67+67+59+66+66+60+66+63= 12= 64.7 parts per million Sandy substrate: Number of chironomus = 10+4+6+1+5+6+7+0+4+80+0+0+8+5 = (0.1 m2 quadrat) 14= 9.7 per 0.1 m2 quadrat Detritus rating = 3+3+3+4+4+3+2+2+2+4+3+2+2+3 =(1 to4) 14 = 2.9Flow rate =(ms-1)0.08+0.02+0.04+0.01+0.0+0.0+0.2+0.12+0.03+0.02+0.01+0.03+0.03+0.02 = 14= 0.04 ms-1 pH = 8.0+8.0+7.9+7.9+8.0+8.1+8.0+8.0+8.0+8.0+7.3+7.4 = 12 = 7.9Dissolved Oxygen = 99+101+98+95+93+100+98+102+99+98+101+95=(% Saturation) 12 =98.3% Water depth =(m)0.05+0.13+0.14+0.14+0.03+0.45+0.06+0.14+0.14+0.18+0.17+0.05+0.04+0.01 = 14= 0.12 m Temperature =(0C)12.2+11.9+12.1+12.1+12.6+11.9+12.1+12.1+12.1+12.0+11.9+11.7 = 12= 12.1 0CTotal dissolved solids = (Parts per million)62+67+62+67+65+66+65+66+66+69+66+68 = 12= 65.8 parts per millionsOther organisms found in my quadratv I used the following formula:Number of organisms found x 10 = Number of organisms found per m2v That's because my quadrat was 0.1 m2 therefore 10 x 0.1 m2 = 1m2 Stony region: number per m2Perlodidae 1 x 10 = 10 per m2Glossosomatidae 2 x 10 = 20 per m2Polycentropidae 4 x 10 = 40 per m2Ecdyonuridae 5 x 10 = 50 per m2Baetidae 8 x 10 = 80 per m2Gammaridae 28 x 10 = 280 per m2 Sandy region: number per m2Sericostomatidae 1 x 10 = 10 per m2Rhyacophilidae 1 x 10 = 10 per m2Ecdyonuridae 2 x 10 = 20 per m2Baetidae 3 x 10 = 30 per m2Ephemerellidae 1 x 10 = 10 per m2Chironomidae 1 x 10 = 10 per m2Gammaridae 63 x 10 = 630 per m2True worms 1 x 10 = 10 per m2Conclusion After statistically analysing the critical value of ÷2 (chi- square) that I obtained, which was 113.78, I got to the conclusion that it was much higher than the critical value (3.84). I used 1 degree of freedom to measure the value obtained (÷2 = 113.78) and also the confidence level. By analysing the value of 1 degree of freedom I became 95% to 99.9% certain that the null hypothesis was incorrect and accepted the alternative hypothesis, which says that there are a higher distribution of chironomus is sandy substrate than in stony substrate, e.g. the number of chironomus per m2 in the sandy region was 97.1 while there was only 5.7 chironomus per m2 in the stony region.Interpretation In our investigation I studied Benthic invertebrates, particularly chironomus in the Nant Iago stream in South Wales. A stream is formed due to gravitational forces that cause an overland flow of water. Many invertebrates live in the streambed creating a Benthic community. There are a number of factors that can affect the distribution of invertebrates. These factors can be divided into two groups: Abiotic and Biotic. There are six abiotic factors, which are:v Current/flow rate- The flow rate differs because of the slope, depth and degree of frictional resistance offered by the streambed.v The average substrate type/size - The size of particles deposited on the streambed is dependent on the flow/velocity, i.e. the lower the velocity the lower the kinetic energy available to move or carry particles, therefore the lower the velocity the smaller the size of the particles deposited.v Temperature - By looking at my results I observed that chironomus could survive at a temperature of 12.10C, which was the same at both sandy and stony regions. Nevertheless there is a relationship between temperature and dissolved oxygen concentration.v Dissolved oxygen - Most Benthic communities need oxygen for respiration. Chironomus have haemoglobin to transport oxygen around the body surface to their cells.v pH - pH affects chemical interactions, nutrients and toxins solubility, but also metabolic processes, e.g. enzymes activities.v Detritus rating - Many organisms are detritivores; therefore they eat dead material (detritus) so the amount of detritus affects the distribution of species.There are three biotic factors, which are:v Food availability - Prey of food particles of the correct type and size.v Predation - The probability of prey surviving decreases when predator densities are high.v Predation - From species with similar ecological niches (tolerances and requirements).Within the stream habitat we divided it into two microhabitats; sandy and stony, which differed in some of the abiotic and biotic factors mentioned before.In the stony microhabitat I found that there were larger substrate, this is because of the fast current (high kinetic energy) that swept away all the small particles, as a result this region is very ventilated (lots of oxygen in the substrate). If there is a high kinetic energy and all the small particles and detritus are swept away then there are a low number of decomposing bacteria, because they don't have a food supply as it gets carried away with the fast current.In contrast the sandy microhabitat, we found that the current flow is slow, therefore there is a low kinetic energy to sweep away the particles and detritus. This causes it to be a poor ventilated region, for the reason that water can't squeeze in between the particles, hence causing the poor ventilation. The other difference is that there are lots of decomposing bacteria in the sediments because the mall particles and detritus are deposited there, this creates a anoxic condition because the bacteria uses up the oxygen available.By considering my results, the differences between sandy and stony microhabitats and the specie being studied I came to the conclusion that chironomus is perfectly adapted to survive in the sandy region, in anoxic conditions.Chironomus possess haemoglobin, which play a vital physiological role in increasing respiratory efficiency in anoxic conditions. The haemoglobins found in chironomus have a very high affinity for oxygen, that is caused by the fact that their haemoglobin molecule it's made up on only one polypeptide chain, which contains one haem group. (Human's haemoglobin contains four polypeptide chains and each polypeptide chain contains one haem group.) This is a great advantage for the chironomus as it only has one polypeptide chain, therefore only one haem group, hence the great affinity for oxygen, so it grabs oxygen molecules very easily and well.Chironomus also have an advantage to live in anoxic conditions because of their behavioral adaptations. Chironomus, as most species in low oxygen sediments, can build tunnels and fixed tubes of sediments that are held together with their secretions, which are able to ventilate their tubes with fresh water by undulations of the body, in so doing this it facilitates oxygen diffusion during times of low concentration of dissolved oxygen in the water.They also have a great amount of food supply, detritus, as they feed on dead material. And since sandy regions are areas of low kinetic energy, detritus settles in. Also the fact that there are no competitions as other detritivores (e.g. ephemerellidae) cannot live with the lack of oxygen found in sediments. Predators are also rare in this type of sediments (e.g. caddis nymphs) as the anoxic conditions make it hard for them to survive.So chironomus is adapted to the anoxic sediments both physiologically and behaviorally and so it gains a food rich environment with little predation and little inter-specific competition. This is why chironomus was found mainly in the sandy areas.EvaluationExperimental errors: There are a number of experimental errors that can cause limitations in this investigation, such as:v The surber sample - That we used to collect species. In stony regions the surber sample didn't lie flat, as there were rocks there enabling it to lie flat, causing less accurate results because species got swept away with the current. This means that there will a lower number of species collected, as they get lost.v The current - It was also a limitation as in sandy areas there are less current; therefore organisms can swim away from the net causing a decrease in the number of species being collected.v The size of the mesh - Also contributed for less accurate results. The mesh size I used was 1 mm2, so younger (smaller) organisms got through the net.v The fact that there was no standard method of disturbing the rocks, this will vary the results from group to group, as for example, if people have bigger hands or spend more time disturbing the rocks, then they will get a higher number of results, that's is because if more disturbance happens then it is more likely that more species will get into the net, therefore increasing the number of results. This will really affect the results because in this investigation we pooled all groups' results together.v Drift problem - Groups at the end of the stream will get higher number of results, as species get drift. For this investigation we had a 150 m long of stream, we had it divided for 14 groups, the group at the beginning of the stream after collecting their species and record them, will put them back into the stream which will then flow to next group's net with the current, and so on. Therefore the group at the end of the stream will, possibly, get some of the species of all the groups behind them.v Also the groups had the choice of sandy and stony regions, this will give us less reliable results.So by looking at my results I can assume that those limitations listed above contributed to the accuracy of my results.Anomalous results In my sandy area I only got one chironomus, which is an anomalous result. There are some reasons why I think I got this anomalous result. The flies lay their eggs in a clumped way, so if the eggs were all laid at the same time then they will became flies at the same time too. If so, then my sampling may have occurred just after they became flies and left the stream. Or if the eggs had just hatched then the species will be too small so they will pass through the net, and I will not be able to detect them. This result may be explained and it may be real because of the chironomus life cycle resulting in a clumped distribution.Reliability By looking at the results of my quadrats and at the whole group results, I can detect that my results are quite reliable, taking the idea that our alternative hypothesis was correct (that there will a higher number of chironomus in the sandy region than in the stony region), and that is what my results show:· In the sandy region I got 10 chironomus per m2 while in the stony region I got 0 chironomus per m2.Nevertheless there are a number of improvements that I could have done in order to increase the reliability of my results. Such as;v A smaller mesh - That would have stop smaller organisms from passing through the net, therefore making the number of each specie collected more real result, as this investigation was not made under laboratory conditions but natural condition.v By using a standard method of disturbance, such as by using a shovel and by having a specific time of disturbance e.g. 5 minutes. This would make results more accurate as more species would be collected so it would give us a more real result, as we were under natural conditions.v An objective choice of sandy and stony regions, as it would minimize the biases of which this investigation was under. Also by having standard decisions, like if a stone was half in half out, if we would count it as in or out.v Also if the whole group worked against the current it would have solved the drifting problem, as after collecting and recording the species each group would put the species back, but if working against the current then it wouldn't end up at the next group's results.v If we had be given more time, instead of using nets we could have left trays for some time, that would have make this investigation very reliable as we would have got real results in natural conditions. Final conclusion Despite errors I still trust my results, taking into consideration the alternative hypothesis, which was:"There will be a higher distributions of chironomus in the sandy substrate than in the stony substrate." And by looking at my results and at the group's results I can say that the confidence level that I worked up with the ÷2 equaling 113.78, which means that it is 95% or even 99.9% certain that the null hypothesis was wrong, therefore that the alternative hypothesis was right.Group's results per m2:Sandy region - 97 chironomus per m2Stony region - 6 chironomus per m2My own results per m2:Sandy region - 10 chironomus per m2Stony region - 0 chironomus per m2

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