Range of samples and number of repeats
At least ten different sites of the stream should be sampled. This will give me a suitable amount of data to adequately perform statistical tests such as Spearman’s rank coefficient.
The range of the water flow rate of the sites will be from about 0.05m/s – 0.25m/s as I have discovered in my preliminary work. This will provide an adequate range for the above ten sites of data to be taken, e.g.:
0.05m/s 0.07m/s
0.09m/s 0.11m/s
0.13m/s 0.15m/s
0.17m/s 0.19m/s
0.21m/s 0.23m/s
In practice it will be difficult in the natural environment of to select sites with these exact flow speeds of water. Rather than findinf sites with precisely the same flow rate of the above, ten sites with suitably different flow rates and of suitable range is used to take the samples from.
At each site, the site is repeatedly sampled for ten times. This will allow me to calculate the mean of each site and to identify any anomalous samples that were taken.
Apparatus
A wide range of equipments are needed for sample collection and the monitoring of the aboitic variables of the different sites of the stream.
The possible sampling techniques are also considered here as the preference of any one of the methods will invariably affect the choices of apparatus.
Kick sampling
Prod sampling
Needs large area to take each sample,
So the sample area may not e of equal flow rate
Not much substrate at some sites. Prodding method difficult in picking up samples.
Several major measures are to be take ensure the accuracy of the investigation.
Water tamparature, oxygen concentrations, and water samples are collected before any sample is taken. This ensures that the abiotic variables of the water is not disturbed before they are measure.
Whilst sampling, always work from down stream to up stream. This means that sites up stream from where the sample is taken is not disturbed.
For each sample, the same number of kicks is done with the same hardness. From my preliminary work, kicking each spot ten times gives an adequate numbers of shrimps in each sample. It was seen that if the shrimp population density at a site is high, kicking 10 times brings up large number of gammarus pulex. At areas with low gammarus concentration however, only small numbers of gammarus are collected despite kicking ten times.
Method
1. Select 10 sites in the river with 5 suitably ranged flow rates. This can be estimated by firstly measuring the depth of the brook at that point with a meter ruler. Make sure there are no drastic differences in percentage branch cover by using a section of hose pipe.
2. Once a site is chosen, the dissolved oxygen level and the water temperature must be measured first. This means that the water is no disturbed before the measuring which could lead to anomalous results.
Water dissolved O2 levels
Submerge probe in water. Do not sub merge the electrical wires.
Move probe gently in water and wait for dissolve O2 level reading to equilibrate on digital display.
Record the dissolve oxygen level in mg/l.
Temperature
Submerge metal part of thermometer into the water.
Water for readings to equilibrate
Record the water temperature.
3. Water sample is taken with a 150ml water sample bottle. The water sample should be taken from as close to the bottom of the stream as possible as this is the immediate surrounding of the freshwater shrimps.
3. The flow rate of the water is then tested with an impellor. The impellor device is placed in to the water. When in rotates freely, the digital counter is switched on. A flow rate speed is then given after 30 seconds of testing. Wait another 30 seconds to ensure that the reading displayed is correct since the first reading could be erroneous.
4. Before taking the sample, fill a white porcelain tray with water from the brook. This will allow any fauna collected to survive while the sample is being counted.
5. A 50cm x 50cm quadrat is then placed into the brook. Collect the sample by using the kick sampling technique on areas within the quadrat. The substrate is kicked ten times with the same hardness. The disturbed substrate and organisms is then collected by the net placed down stream.
6. The sample in the net is emptied in to a porcelain tray. It is rinsed with water in the porcelain tray to ensure no life forms are stuck on to the net.
7. Any gammarus pulex identified in the sample is counted. To avoid counting the same shrimp twice, the counted shrimps are removed by a plastic spoon or pipette in to a plastic palette. Once counting is completed the shrimps are returned back in to the brook.
8. All of the remaining substrate and fauna in the porcelain tray are returned in to the river also.
9. Within the vicinity of the quadrant, choose another undisturbed site around 15cm up stream and repeat the process above. A site upstream is used to ensure that the site used is not disturbed when the previous sample is taken.
10. Ten samples should be taken altogether from a site with a certain flow rate.
11. The above is to be repeated with the other nine sites.
Testing of water samples
The pH, nitrate, and phosphate levels are tested in the laboratory due to the nature of the equipment which has to be used.
Nitrate
- Set test 261 on reflectonmeter.
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Dip NO3- indicator strip in water sample.
- Start 60 second count down.
- The indicator strip should change to a purple colour if nitrates are present.
- Insert the strip in to the reflectonmeter after 55 seconds.
- Record the nitrated concentration displayed (mg/l)
Phosphate
- Put 5ml of water sample in to a small bottle.
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Add in with it 10 drops of H2SO4 (care corrosive). Shake to mix.
- Select test 124 on reflectonmeter.
- Start 90 sec countdown.
- Dip indicator strip in sample.
- There will not be any colour change if low amounts of phosphate are present.
- If phosphate levels are below 3mg/l, the reflectonmeter will display LOW. If this happens, use the low phosphate test as below.
Low Phosphate
1. Put 5ml of water sample in to a small bottle.
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Add in with it 5 drops of H2SO4 (care corrosive).
- Add 1 measure of “Reagent 2” then shake for 2min to mix.
- There should be a colour change of the solution. Compare the colour change with the chart provided to ascertain phosphate level.
pH
Insert digital pH meter into water sample. Swirl around and wait till reading equilibrates. Record the pH.
Safety precautions
Make sure that there is someone around at all times, and do not work alone.
Do not sample areas in the brook which is too deep.
Wear rubber gloves while sampling to avoid infections.
Carry a mobile phone in case of an emergency.
Give mobile contact numbers to staff.
Sign in and out of the field centre so that the staffs know my whereabouts.
Analysis of results
I will calculate the standard deviation for the data collected from each site of the stream. This will tell me the diversity of the data collected at these sites.
I will plot the graph of shrimp density against water current flow. This will inform me of any correlation that may be present between the two variables.
I will carry out Spearman’s correlation to establish the strength of the correlation between the variables above.
I will plot the graph of rate of water flow against dissolve oxygen concentration. This will inform me of any correlation that may be present between the two variables.
I will carry out Spearman’s correlation to establish the strength of the correlation between the variables above.
If there seem to be a linear proportionality between any of the two pairs of variables above, I will calculate the regression line which will enable me to plot a line of best fit onto my graph. This will allow me to carry out interpolations of the data which could give me a chance to carry out further studies in the future to see whether the interpolations are reliable, thus determining the accuracy of this study.
By looking at the data for the dissolved oxygen concentration at the different sites and the rate of water flow at each site, it is obvious that there is no correlation between the two variables as I had expected. I will still plot a graph between the two variables and carry out spearman’s rank correlation coefficient to support the null hypothesis.
Below are examples of how I carried out the statistical analysis.
Spearman’s rank coefficient
Conclusion
- There is a positive correlation between the current flow rate and the density of gammarus pulex found at the site.
- The abiotic factors tested remains constant throughout the river, it is therefore assumed that the varying densities of gammarus pulex collected at different sites are not affected by these. The constant nature of abiotic factors is caused by the moving nature of the water. Any nitrate, phosphate, and oxygen will be well mixed to obtain equilibrium. The temperature of the water remained constant for the same reason.
- Contrary to my prediction, the dissolved oxygen level in the stream was indeed higher than that in still water.
- If varying oxygen levels are not the main cause for the diversity of shrimp density, the cause could be attributed to the different nature of substrates found at different sources.
- Faster sections of the stream have more small stones under which the gammarus may cling for shelter to avoid the current. The stone acts as a barrier for the gammarus against the water. Thus the numbers of gammarus in these faster, rockier sections thrive. In slower sections of the stream, more sediment is deposited. This leads to muddy sections of the river bed. Here, gammarus will have less protection from the stream’s currents. They would have to burrow under the surface of the muddy substrate. This is far difficult than hiding behind a stone. Smaller numbers of gammarus will be able to remain there, thus its density is the lowest in slower sections of the river.
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At faster sections of the stream, fewer other species of fresh water organisms will be able to survive due to them being unable to cling in to rocks and being washed away. This means there is less overlapping of the niches of organisms and thus less competition for the shrimps. This means the shrimp population is able to grow larger than areas with slower current speeds.
To be sure of the assumption above, more tests need to be carried out in site with flow rates of between 0.05-0.15m/s and <0.05m/s.
Discussion
Percentage branch cover.
Substrate quality.
I mentioned carrying out further tests to find out the accuracy of interpolations make from the available data, it is however more likely that as the flow rate of water is increased further, the increase in the number of gammarus found at these sites will not increase in the same proportions as before. A graph of this is shown below:
This is due to other limiting factors such as intra species competition.
Evaluation
Assumptions made to limit
In reality, a wide range of factors would act along with the speed of water flow to affect the gammarus population density. Assumptions were made that other factors will not vary greatly since the sampling was conducted in a single river. Although many important variables were tested to confirm that they are indeed fairly constant, there are fluctuations in the concentration of nitrate () at the different sites. This probably will have had an effect for the sample data. For example, the nitrate concentration at the site with the water flow rate of 0.18m/s is 53mg/l compared with the rest of the sites having a nitrate concentration of about 47mg/l. It is instances like this which may limit the reliabilities of the findings.
There may be other abiotic factors which I did not have the means to measure affecting the gammarus pulex density. For example, the calcium carbonate concentration of the water is an important issue concerning the density of shrimps. Shrimps require calcium to form and repair their shells.
The assumption was made that all of the shrimps which were collected in each sample were correctly classified and tallied. The fact is that it was far from certain that every single shrimp in sample is indeed counted. The classification of the gammarus made difficult by the amount of substrate brought up along with each sample. Large numbers of shrimps in a single sample made counting difficult since they are mostly fast moving.
Difficulties caused by method
The method caused unavoidable disturbances to both the water and the substrates of the river bed other than that of the sampled area. This is due to that many groups are conductiong investigations in the stream at once. The disturbed water meant that the various abiotic variables of the river is disturbed. It also affects the speed of water flow as people standing in the river unavoibly obstructs the flow of the river.
Sources of error
Limitations of method
It is very hard to control the amount of stream bed disturbed by each kick. Although the number of kicks is kept constant, it is very hard to keep constant the area and amount of substrates and fauna sampled each time.
- Not all disturbed substrate collected
Due to the width of the net, it is impossible to collect every bit of potential sample that is kicked up.
- Equipment cross contamination
The reflectometers, pH meters which were shared between the groups could have been contaminated with the samples of other groups. Thus giving a higher NO3- level that the actual value etc.
It cannot be guaranteed that every gammarus collected in the sample will be counted. This could be caused by the size pf the gammarus, problems with identifying, and gammarus hiding below substrates brought up with the sample. The numbers of gammarus counted should be treated as a bare minimum.
- Slightly different speeds at different sites
Although several impellor readings are taken at different areas within the 0.25m2 area within the quadrat, it is more than likely that there will be areas in the site where the speed will vary.
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The dissolved O2 level meter did not work at the site. Therefore the dissolved O2 levels of the water samples collected in bottles were tested back at the lab. To avoid oxygen to be mixed in to the water while inside the bottle, the bottle was filled completely full to the brim. Due to the concave shape of the lids, some air bubbles remained in the bottle. This could have had an effect on the dissolved oxygen levels recorded.
- Other investigations taking place upstream
- There were other people conducting investigations up stream. This means that the samples I collect could contain some shrimps that have been disturbed and the carried down the stream by the current. This will increased the number of shrimps I collect in some samples.
- Errors in classifying species of shrimp
- Precision errors of apparatus
- Meter Rule ±0.5mm
- Flow meter ±0.01m/s
- Oxygen meter ± 1.5% of total scale of 0.0 – 19.9mg/l
- Reflectometer ±0.5mg/l
- Digital thermometer ±0.3
- Digital pH meter ±0.2
These contribute to the percentage errors of the results.
Anomalous results
Anomalous results are highlighted in red in the result table. These are excluded when the average for each site is calculated. This is so that it will affect the reliability of the data. The anomalies would probably have arisen due to the limitations to the method listed above.
Improvements
- Sample a larger number of sites to further establish a trend.
- Sample different rivers to see if the trend is replicated.
- Find regions in the stream where the water current is faster to see if the trend continues linearly, or whether there is a cut off point to this positive correlation.
- Retest sites which seem to give anomalous results.
- Investigate the contribution of substrate quality to shrimp density
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Reflectometers could have been contaminated with water samples of other groups. Since the equipment is shared, other groups using the reflectometer to test water samples would have their water left in the testing slot. This will results in the indictor strip changing its colour to another shade thus registering an anomalous NO3 reading.
Further work
Futher work should be conducted to investigate the relationship between the substrate quality of different sites of the stream and the number of gammarus pulex these sites contain.
- Investigate whether the diversity of fresh water fauna is linked with the speed of the water flowing at the point. This will show whether interspecies competition has a major effect on the population density gammarus pulex.
Bibliography
Freshwater Biology, L.G. Willoughby, Hutchinson & co (Publishers) Ltd, 1976
Freshwater Life, J. Clegg, Frederick Warne & Co Ltd, 1974
Collins advanced sciences: Biology, M. Boyle, K. Senior, Harper Collins Publishers Ltd, 2002.
Steve Flowerday, Flatford Mill field study centre, February 2000.
Freshwater Life, John Clegg, Fredrick Warne & Co Ltd, 1965
Adaptation of Invertebrates to life in Freshwater information sheet, Field studies council Flatford Mills
F.J.H. Mackereth, 1973. Freshwater Biological Association, Scientific Publication No. 21.
