Investigation into the relationship between the density of fresh water shrimps in fleet brook and the flow rate of water brook Essay Example

Investigation into the relationship between the density of fresh water shrimps in fleet brook and the flow rate of water brook Essay Fresh water shrimps (gammarus pulex) are crustacean living in many rivers and streams of this country. They prefer to live in flowing fresh water environments which often has better oxygenated waters that still water environments.2 Aim The aim of my investigation will be to determine the relationship, if any, between the gammarus pulex (fresh water shrimp) population density (the number of shrimps) and the rate of water flow at particular sites of Shir Burn Brook. Preliminary work We will write a custom essay sample on Investigation into the relationship between the density of fresh water shrimps in fleet brook and the flow rate of water brook specifically for you for only $16.38 $13.9/page Order now We will write a custom essay sample on Investigation into the relationship between the density of fresh water shrimps in fleet brook and the flow rate of water brook specifically for you FOR ONLY $16.38 $13.9/page Hire Writer We will write a custom essay sample on Investigation into the relationship between the density of fresh water shrimps in fleet brook and the flow rate of water brook specifically for you FOR ONLY $16.38 $13.9/page Hire Writer For my preliminary work, a variety of sampling techniques were carried out to collect samples of freshwater organisms in Shir Burn Brook. The methods include the kick sampling technique and the prodding sampling technique. The range of the flow rate of water in Shir Burn Brook was found to be 0.05m/s-0.25m/s. The samples collected also enabled me to correctly classify and thus allowing me to recognize gammarus pulex. Samples were also collected in a static water environment to enable me to differentiate between the species gammarus pulex and its static water relatives, grangonyx pseudogracilis. Kick samples were taken at different site in the brook. The numbers of freshwater shrimps found at each of these sites are 20, 35, 60, 15, 24. This shows me the range of the number gammarus pulex I should expect. These figures gave me a rough guide on the range of the numbers of gammarus pulex living in the brook. This means that I have a rough estimate of the numbers of shrimps I expect to find during my investigation. Hypothesis: There will be higher densities of gammarus pulex present in areas of faster water flow. The results should show a positive relationship between the rate of flow at a site in the stream and the number of shrimps found at the site. I believe this will be due to the variation in oxygenation of the water. As the water flows faster, the movement will mean that more oxygen can be dissolved into the water, creating a higher dissolved oxygen level in the water. The increased amount of oxygen will allow larger numbers of shrimps to thrive. Null hypothesis 1. There will be no relationship between the population density of gammarus pulex and the water flow rates of sites in Shir Burn Brook where the gammarus pulex are collected. 2. There is no correlation between the dissolved oxygen level of the water of the different sites of Shir Burn Brook and the rate of flow of water at these sites. Background information to explain hypothesis Site The Fleet is a man-made brook by diversion of Shir Burn Brook (TM075314) in the 19th century. The purpose of the Fleet was to deliver water to be used by the steam turbines in the near by railway station down stream.1 It runs through a clearing in woodlands. It is relatively unpolluted with nitrates and phosphate levels within the normal guidelines. As with any flowing fresh water habitat, there are large numbers of freshwater shrimp dwelling there.1 Gammarus pulex Gammarus pulex is a species of freshwater shrimps. Fresh water shrimps belong to the order of the amphipoda. A typical amphipod crustacean is flattened from side to side, and the body when at rest is curved round to form an arch. Gammarus pulex is found swimming on its side. When it is moving the hind parts of its body straightens out, only to contract again suddenly into its normal curved position as soon as the creature stops. They are often found under stones or on the soft surface of the mud, and when disturbed scud rapidly away to shelter. The male is about 25mm in length and the females slightly smaller. Their colour is usually lightish brown. Fresh water shrimps are largely scavengers, feeding on decaying organic matter, but they are also known to devour other smaller creatures. Gammarus pulex are found abundantly in freshwater habitats in the British Isles. Care should be taken during classification to differentiate between the species gammarus pulex and grangonyx pseudogracilis which are usually found in static water environments.2 Flow rate of water Velocity of water varies throughout streams. This is due to the friction between the water and the stream bed. It is therefore expected that deeper parts of the stream will have higher rates of water flow since the surface in contact with stream bed-water volume area is smaller, meaning less friction. Depth is therefore a good indication of the flow rate at any site in the stream. Slower flow rates of water will allow small sediments of mud to develop on the bed of the stream. In faster sites, however only larger substrates such as pebbles are allowed to deposit while substrates that are too small are carried off by the water. The stony bed of the stream are especially suited for the gammarus pulex as there legs will allow them to cling on to rocks, this would be less possible with a muddy substrate.3 Some species of fresh water fauna are in a similar niche to the gammarus pulex will not all be designed to with stand the turbulence of the water. Therefore, at sites with higher water speeds, the diversity of species present there will be less. This means that there will be less interspecies competition for all the essentials which the gammarus requires (e.g. planktonic foodstuffs, oxygen, space for shelter).4 Dissolved oxygen and temperature. The solubility of oxygen from air, at normal atmospheric pressure, in pure fresh water is related to the temperature of the water by the equation: Cs = 475à ¯Ã‚ ¿Ã‚ ½(33.5 + t ) 5 Where Cs is the solubility of O2 in water in mg/l and t is the temperature. It is obvious that if more oxygen is dissolved in the water, there will be more of it available for the respiration of fresh water fauna living in the stream. Respiration provides energy in the form of ATP allowing the metabolisms in the animals bodies to occur.6 The oxygen concentration in the streams is expected to be higher in concentration compared to static aquatic environment. The distribution of oxygen is also expected to be more even than static water habitats. This is all due to the movement of the water in streams allowing more oxygen to dissolve and subsequently mixing the oxygen evenly. Nitrates and phosphates Nitrogen and phosphorus are basic elements in all living matter. Nitrates and phosphates therefore are not unexpected to be found dissolved in Nitrate is an essential provider of nitrogenous elements for living organisms. Nitrogen is essential for the synthesis of protein and nucleotides in most living things. Nitrogen is recycled through the biosphere by the nitrogen cycle.7 Dead and decaying organic materials (in this case dead leaves) are broken down by denitrifying bacteria inhabiting the water. The nitrogenous molecules are converted into nitrates Nitrate and phosphates are regulators of organic growth. The free flowing algae and small planktonic forms are affected directly. High levels of nitrates and phosphates often stimulate their growth. Gammarus feed on these. Therefore if more plankton are in the stream due to the nitrate and phosphates, the number of gammarus will increase also. The problem with nitrate and phosphates is that when excessive amounts are present (often due to soil leaching, effluent produced by farms, and human effluent) algal growth is intensified leading to eventual deoxygenation of the water eventually causing eutrophication. Thus there will be a decrease in the number of gammarus found in the water. 8 Variables and Key variables Explain Independent, the different rates of flow of the Dependent Factor / Variable Effect on the project Control method Density of fresh water shrimps This is what is tested Flow rate of river This is the key variable of the investigation. It is expected that a higher flow rate of water will lead to higher gammarus population densities, and lower water flow rate will lead to smaller gammarus populations. Dissolve oxygen level of water For all aerobic organisms, oxygen is essential for their survival. Thus, a higher concentration of dissolved will enable a larger population of gammarus to exist in an area providing other factors are not limiting. Control variables Nitrate levels in water This will increase the algal populations in the water. Though sustainable amount of nitrates in the stream will lead to more foodstuffs for the gammarus and thus increase their population, high levels of nitrates caused primarily by pollution will lead to diminished shrimp population as the result to the effects of eutrophication. This variable is sampled at each site so that it is ensured that the nitrate level throughout the stream is constant. It is expected to be constant since the movement of the water will mix any dissolved nitrates till it is in equilibrium in the water. Phosphate levels in water Like the nitrate levels, this abiotic factor will cause fluctuating levels of micro organisms in the stream. The phosphate level in the water is tested at every site. This again ensures that the phosphate concentration is constant throughout all of the tested sites as expected. The phosphate compound is expected to be distributed evenly in the water due to the movement of the currents. Water temperature There will be an optimal temperature range at which gammarus will like to live. If a section of the river is out of this range, the number of gammarus found there will be lower than other sites. The water temperature is monitored at every site. This again ensures that the temperature of the water is constant throughout every site. The water of the brook should be of very similar temperatures since the flowing water currents will distribute the heat evenly throughout the river. Where the water temperature is significantly different from the other sites tested, another site with a more acceptable water temperature will be chosen to be sampled. pH of water There again will be a range of pH of water outside of which few gammarus will survive. Sites whose water pH is too low or high will not contain many gammarus. The pH of the water is tested at every site. This is to make sure that every site tested all have the same pH. Sites whose pH is significantly different from all of the other sites are not chosen to take samples from. The pH is expected to remain fairly consistent throughout the stream. Leaf coverage of the sky above the brook If a section of the brook is covered by leaves, the chance of a dead leave falling into the brook is greatly increased. Since gammarus pulex feeds primarily on decaying plant material, the populations of freshwater shrimp in these regions will be expected to be greater than regions with no leaf cover. The percentage leaf coverage is recorded at the sites where samples are taken. It is made sure that the leaf coverages at all these sites are similar. This shall not prove to be difficult since the brook runs through a wooded area. Seasonal variations Due to the life cycle of the fresh water shrimps, there will be times in the year were there will be small amounts of the gammarus making sampling difficult. This is over come by taking all of the samples in a day. The investigation is conducted in summer when there is sufficient numbers of shrimps in the river. 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 Spearmans 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. Use of apparatus Apparatus available Apparatus Chosen Reason for choice Effect on precision and reliability To measure flow rate of rive at different sites Pooh stick method Impellor method Impellor method The impellor will enable me to determine the rate of water flow at the bed of the stream. Whereas the Pooh stick method will only tell me the surface flow rate. The impellor and flow rate counter will give the speed of water flow to the nearest 0.1m/s. it also eliminates any human error To measure water temperatures Mercury thermometer Digital thermometer Digital thermometer It is more accurate if the thermometer is always left in the water when the temperature reading is taken. The level of the stream is on a very low level, making the accurate reading of the mercury thermometer very difficult. Furthermore, the digital thermometer will record the temperature to the nearest 0.1oC, whereas the accuracy of the spirit thermometer is at best à ¯Ã‚ ¿Ã‚ ½0.25oC. The digital will give us the temperature of the water to a greater degree of accuracy (à ¯Ã‚ ¿Ã‚ ½0.05oC). This reduces the precision error from the mercury thermometer by ten fold. Human error is eliminated by not having to take a reading of the temperature at the correct eye level. There is no longer need to estimate when the reading lies between two graduation marks. To measure water pH level Digital pH meter Universal indicator Digital pH meter The digital pH meter will give an accurate qualitative pH reading to two decimal places. The universal indictor will allow me to estimate the pH by matching the colour of the test solution with a colour chart. This is extremely prone to errors in that it is often very difficult to obtain test solutions with exact matching colours as the chart. The digital meter gives the pH to a far greater degree of accuracy. There is no comparison with colour charts needed. Care should be taken to ensure that the pH meter is properly calibrated before use. To measure dissolved oxygen concentrations of water. Diaphragm dissolved oxygen meter Diaphragm dissolved oxygen meter (0.0-19.9mg/l) This will give the dissolved oxygen level of the water. There is not another method that is both as accurate and as easily performed as this, making it ideal for project work in the wild. This is the only applicable method of testing the oxygen content of the water in the stream. It is also the most accurate method that could be used. The dissolved oxygen concentration of the water will have to be tested on site rather than on samples taken back to the laboratory. This is because that some oxygen will enter or leave the water in the sample bottles during transporting to the laboratory. To obtain dissolved nitrate concentrations of water. Reflectometer Indicator strips Reflectometer The reflectometer gives the nitrate concentration quantitatively rather than a qualitative result from the indicator strips. It gives the concentration of nitrate in water in units of mg/l. Reflectometry allows the conversion of a single nitrate presence test in to a qualitative nitrate concentration analysis. As the name suggests, the test is conducted by reflection light on an indicator strip which will undergoes a colour change in the presence of nitrate. The strip changes colour in proportion to the concentration of nitrate in the water. The reflectometer is calibrated to detect the degree of this change and convert it into a quantitative concentration of nitrates. To obtain dissolved phosphate concentrations of water. Reflectometer Indicator strips Reflectometer (for high phosphate levels) Indicator strip and reagents kit (for low phosphate levels: 3.0mg/l Similar to the nitrate concentration test, the reflectometer gives the concentration of phosphate in the water quantitatively. One difference between testing for phosphate and nitrate is that there is going to be much less phosphate expected to be dissolved in the water than nitrate. If the nitrate concentration is smaller than 3.0mg/l, this reflectormeter will register the concentration only as low. Under these circumstances, another technique is used. In this technique, 5cm3 of water sample is used and a series of two reagents are added to it. The colour change underwent is compared to the colour changes on a chart. This gives the phosphate concentration to à ¯Ã‚ ¿Ã‚ ½0.25mg/l accuracy. The reasons are similar to those for testing the nitrate concentrations of water. The phosphate low concentration test will present a range of five distinctive colour changes. These will correspond to the concentrations of 0.0mg/l, 0.5mg/l, 1.0mg/l, 1.5mg/l, 2.0mg/l, and 2.5mg/l. This give the phosphate level to a greater degree of accuracy the reflectometers for higher concentrations of phosphates, although the over all precision error will remain similar (0.5à ¯Ã‚ ¿Ã‚ ½2.5 = 1.0 à ¯Ã‚ ¿Ã‚ ½ 5.0) To measure the depth of brook at different sites. Meter rule Meter rule The meter rule will be most suitable as only a rough guide for the depth of the brook is to be obtained. The waster will leave a mark on the ruler from which the depth can be taken. The meter rule will give the depth of the brook to à ¯Ã‚ ¿Ã‚ ½1mm. This is of an acceptable accuracy as only a rough guide of the depth of the stream at the sampling site is requires. To collect sample kicked up. 0.50 meter net width. 0.25 meter net width. 0.5mm holes. 1mm holes. 0.50m wide net with 1mm holes in the netting material with 2m handle. As kick sampling is preferred, as net of the biggest width should be used to ensure that all organisms disturbed by the kick sampling is collected. As gammarus pulex are larger than 1mm, the pores in the net will allow substrate to filter through while retaining the gammarus to be sampled. The biggest possible net is used to ensure that most of the sample kicked up from the stream bed is collected. A net with 1mm pores is used to allow mud particles to pass through the net. Less mud will be transferred to the vessel in which the gammarus pulex are counted. This means the water in the vessel will be clearer which means any gammarus pulex present can be spotted more easily. To mark out site of sample taking. 0.50m by 0.50m quadrants 1.00m by 1.00m quadrants. 0.50 x 0.50m quadrant. A suitably large area of the stream will be marked out by this quadrant for sampling. At the same time the quadrant is not so big so that the speed of water flow does not vary within the area enclosed by the quadrant. A good sized quadrant will allow a site to be marked out for sampling. The quadrant chosen will increase the reliability of the test by allowing a large enough area with the same flow rate to be sampled. Apparatus required to classify and count the numbers of gammarus pulex in each sample. White enamel tray Pipette Plastic spoon. White enamel tray Pipette Plastic spoon. A white enamel tray will offer a light background to contrast the darker colours of the gammarus pulex so that they can be easily spotted. Pipette and plastic spoons will allow gammarus to be removed from enamel tray once they are counted. This avoids one gammarus being counted more than one time. 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 1. Set test 261 on reflectonmeter. 2. Dip NO3- indicator strip in water sample. 3. Start 60 second count down. 4. The indicator strip should change to a purple colour if nitrates are present. 5. Insert the strip in to the reflectonmeter after 55 seconds. 6. Record the nitrated concentration displayed (mg/l) Phosphate 1. Put 5ml of water sample in to a small bottle. 2. Add in with it 10 drops of H2SO4 (care corrosive). Shake to mix. 3. Select test 124 on reflectonmeter. 4. Start 90 sec countdown. 5. Dip indicator strip in sample. 6. There will not be any colour change if low amounts of phosphate are present. 7. 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. 2. Add in with it 5 drops of H2SO4 (care corrosive). 3. Add 1 measure of Reagent 2 then shake for 2min to mix. 4. 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 Spearmans 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 Spearmans 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 spearmans rank correlation coefficient to support the null hypothesis. Below are examples of how I carried out the statistical analysis. Spearmans rank coefficient Flow rate of water /m/s Density of gammarus pulex R1 R2 d d2 7 8 13 22 14 16 12 7 19 13 ? 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 streams 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. * 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.9 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 * Uneven kicking 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. * Not all shrimps sampled 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. * 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 à ¯Ã‚ ¿Ã‚ ½0.5mm ; Flow meter à ¯Ã‚ ¿Ã‚ ½0.01m/s ; Oxygen meter à ¯Ã‚ ¿Ã‚ ½ 1.5% of total scale of 0.0 19.9mg/l ; Reflectometer à ¯Ã‚ ¿Ã‚ ½0.5mg/l ; Digital thermometer à ¯Ã‚ ¿Ã‚ ½0.3 ; Digital pH meter à ¯Ã‚ ¿Ã‚ ½0.2 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 * 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.