Site Descriptions
Furze Ground – The water here was flowing very slowly in a narrow (~50cm) shallow (~10cm) stream and so there was not much water. The site was surrounded by woodland and there were flies flying around the water.
Pyrles Brook – The River here was steep-sided and it was wider and deeper but still fairly shallow (~20cm) and narrow (~120cm). There was a lot of plant growth on the side of the river. There was quite a lot of litter inside the river e.g. carrier bags and bottles. The river was situated in the middle of a residential area. There ware trees on one side of the river and a road and housing on the other.
Debdon Brook – The River was still fairly shallow (~20cm) but slightly wider (~150cm). The banks were not as steep s Pyrles Brook either but they were still quite steep. Housing and a recreational ground surrounded one side and trees on the other providing shade.
River Roding Upstream – Here the River was deeper (~40cm), wider (~350cm) and fast flowing. The water was fairly clear and also we could see some small fishes. The sight was situated in-between recreational ground and farming as were the next two sights as well.
River Roding Middle Stream – The River was slightly deeper (~50cm), wider (~400cm) and slower but still was fairly fast.
River Roding Down stream – The river here was the same depth as Middle stream but was slightly wider (~500cm) and slightly less fast. This was the shallow riffle section.
Calculations
Using the raw data results I calculated a BWMP Score for each sight. This is a scoring system that uses the type of invertebrates (if they can or cannot tolerate low oxygen levels) in the water to obtain water quality score. The higher the score is the better the water quality. I used an adapted version of the BMWP scoring system. I included the scores in the results table.
Conclusion
I have interpreted my results into charts and graphs from which I can conclude by looking at the trends and relationships between graphs. The bar chart that shows the number of invertebrates and the BMWP scores of each site suggests that the most inhabited with the best water quality was River Roding Midstream and the least was Furze Ground. The chart shows a relationship between the numbers of invertebrates and the BMWP scores as they have the same trends. This is because both use all the invertebrates in calculating their score.
The pie chart showing the nitrate content of each site states that River Roding Downstream and River Roding Midstream contain the most nitrates and Furze Ground the least. The pie chart showing the phosphate content of each site states that River Roding Midstream has the most and Furze Ground the least. The sites on the River Roding have a higher nitrate and phosphate level because of fertilisers, which may contain nitrates and phosphates and may have run into the water from farms beside the sites. The site at Furze Ground does not contain much because the area is surrounded by woodland and it is near the source of the river. Therefore the water is unlikely to get much organic pollution. Also Pyrles Brook and Debdon Brook Downstream have housing nearby and so should get a bit of pollution. However the pollution may be non-biodegradable litter and chemical pollution which may not be recorded with the tests that I carried out. The pie chart showing the oxygen level states that Furze Ground has the least dissolved oxygen and River Roding Midstream the most.
From the graph showing how the nitrate content affects the oxygen level I can conclude that the more nitrates in the water the more dissolved oxygen because there is a good correlation of results. The graph with phosphates instead of nitrates also gave a similar but awkward correlation of results. However these correlations do not support my scientific background where I found that a high nitrate or phosphate level should give a low oxygen level because eutrophication takes place. This must have occurred because when there is a high nitrate and phosphate content there is an increase in algae and other plants because they are nutrients. These plants give out oxygen during photosynthesis, which increases the oxygen level initially. This must be when the tests were carried out giving high oxygen readings. This means the process of eutrophication has not been fully completed.
From the graph showing how oxygen affects the number of invertebrates I also obtained a correlation. It showed that the more dissolved oxygen the greater number of invertebrates which supports my scientific background knowledge. The graph showing the effect of oxygen on the BMWP score states that an increase in oxygen gives a greater BMWP score. This means that the site with the worst quality water was Furze Ground and the best was River Roding Midstream and Downstream as the BMWP score is a measure of water quality. These two graphs also gave a similar correlation to each other. This is because both use all the invertebrates found in the river. The reason why the number of invertebrates increasing as the dissolved oxygen content increased was because some invertebrates cannot tolerate low oxygen level. Therefore when the oxygen is high there are more species that can tolerate the conditions giving higher numbers of invertebrates. Also a high oxygen content gives the invertebrates more energy and so they breed which again increases the number of invertebrates. The BMWP increases because the species that cannot tolerate high oxygen levels have higher points and so when they are present the score increases. The simple key results were also a score of the cleanliness of the water. However from this I have not gained very good scores as Furze Ground was given a “C” and the rest of the sites “B”. This key was not very accurate in distinguishing between the sites but can just be used as a general score.
The temperature readings for Furze Ground, Pyrles Brook and Debdon Brook were very similar and the temperature readings for all the sites on the River Roding were similar. This was because the readings for the first three sites were taken in the morning and the other three in the afternoon and so the temperature was slightly higher in the River Roding sites.
I have also drawn pyramids of numbers for each site. The pyramids slightly differed from each other. All the sites had many detritivores. Furze Ground had no herbivores but all the other sites did. This was probably because of the low oxygen level. All the other sites had detritivores, primary carnivores and herbivores. Pyrles Brook and Debdon Brook Downstream had more herbivores than primary carnivores, which is how it should be. However in the River Roding sites there were more primary carnivores than herbivores. This probably occurred because carnivores hunt for their food and so need a lot of energy and so they prefer high oxygen levels.
My first hypothesis “ The more dissolved oxygen in the water, the more invertebrates in the water” was supported by my results. This is shown clearly on the graph showing the effect of oxygen on the number of invertebrates. I explained the reason for this before. The second hypothesis “The more nitrates and phosphates in the water, the less invertebrates that can tolerate low oxygen levels” was not supported by my results as eutrophication had not fully taken place as I explained earlier.
The prediction “In water that contain stoneflies the biochemical oxygen demand will be 0-3mgl-1” was not supported by my results because no stoneflies were found. The second prediction “In water which has nearby agriculture, the nitrate levels will be above 5mgl-1” was supported as the three sites on the River Roding were near agriculture and had high nitrate levels. This was because fertilisers used in agriculture contain nitrates and may have got into the water in the river.
Therefore from the results I have obtained I found that Furze Ground had the worst quality water and that River Roding Midstream the best quality water according to the oxygen level of the water. However I found that the most polluted (in terms of nitrates and phosphates) was river Roding Midstream.
Evaluation
The evidence I obtained is fairly reliable because a lot of it did support my scientific background knowledge. One thing I did not expect to occur was that with high nitrates and phosphates there was high dissolved oxygen content. However I could explain why this occurred which I did in the conclusion. Otherwise the number of invertebrates and the BMWP score increasing as the oxygen level increased was expected because of my scientific background.
The method of kick sampling to collect the invertebrates was not very accurate. There are many reasons for this. Firstly when kicking it is very difficult to kick the same way and with the same effort each time. At each site the flow of the water is very different. This means that in faster flowing water it is more likely to collect more invertebrates than in slow flowing water. The depth of the water in some sites was more than for others. Water that is deeper may contain more invertebrates than shallow water because there is a larger area which also might affect the results. Also when identifying the invertebrates some very small invertebrates (probably herbivores as they are small) may not be seen and so are not recorded. If there are so many of one specie, the number had to be estimated because it would be too difficult to count them all in a short time and so would not be very accurate. The first three sites Furze Ground, Pyrles Brook and Debdon Brook Downstream were investigated in the morning and the other three on the River Roding were investigated in the afternoon. This could affect the invertebrates, as the temperature was slightly lower in the morning. This all shows that there were many other factors that have affected the results obtained but these have not been recorded for. This shows that the sites had to be investigated in a more thorough way. I did do two replicates of the kick sampling which may have made the results more accurate. However the results obtained from the replicates at each site were fairly different showing that the degree of accuracy of the procedure was not very high. Having the same time for the kick sampling and the recording made the results slightly more accurate as it made it a fair test.
The tests for nitrates, phosphates and oxygen were fairly accurate as the apparatus was specialised for that particular test. However for the nitrate and phosphate test the exact quantity could not be recorded, as I had to make a comparison with a colour chart. This gives quite a high uncertainty and so a low degree of accuracy. The oxygen readings were likely to be more accurate because the meter gave an exact percentage. The thermometer used to take the temperature was also fairly accurate. However this also has a small uncertainty.
I obtained two anomalous results. One in the nitrate results and one in the BMWP score. The nitrate anomaly is clearly shown on the graph showing the effect of nitrates on the oxygen content. This may have been due to a misreading or the test may not have been done properly in terms of timing or instructions. The BMWP anomaly is clearly shown on the graph showing the effect of oxygen on the BMWP score. This probably occurred because the BMWP score does not take in mind the number of invertebrates but just the type.
The procedure was suitable for the investigation because I was able to see and conclude how pollution affects the type and number of invertebrates in a particular area. Also it was fairly easy to carry out and used the time we had well.
The quality and accuracy of the evidence I obtained could have been improved. I could have done more replicates of kick sampling to obtain more accurate results. I could have repeated the nitrate, phosphate and oxygen tests to get more accurate results and also to be able to identify anomalous results. I could have increased the recording time after the kick sampling to obtain a more thorough set of results. I could have used a microscope when identifying the invertebrates to able to record the smaller invertebrates.
There is also a lot of further work I could carry out to extend my investigation. I could take samples from more sites along the river Roding System to show me more about the factors that cause the pollution in the river. I could carry out different tests on the water for example the pH and ammonium that also affect the invertebrates living in the water. pH tests would test for chemical pollution like acid rain. I could find the exact depth, width and speed of flow of the water as these factors may affect the distribution of invertebrates. I could find out where the sewage output into the river is to see where I should expect a lot of pollution to be.
From the evidence I obtained I was able to come to a fairly firm conclusion. However I have found many other factors that may have affected the invertebrates which if were investigated may have made the results more accurate and reliable.
