The effects of organic effluent from the seweage on the biodiversty in a freshwater stream.

What does it mean to say that the averages for two groups are statistically different? Consider the three situations shown in Figure 2. The first thing to notice about the three situations is that the difference between the means is the same in all three. But, you should also notice that the three situations don't look the same -- they tell very different stories. The top example shows a case with moderate variability of scores within each group. The second situation shows the high variability case. the third shows the case with low variability. Clearly, we would conclude that the two groups appear most different or distinct in the bottom or low-variability case. Why? Because there is relatively little overlap between the two bell-shaped curves. In the high variability case, the group difference appears least striking because the two bell-shaped distributions overlap so much.

                         Figure 2. Three scenarios for differences between means. This leads us to a very important conclusion: when we are looking at the differences between scores for two groups, we have to judge the difference between their means relative to the spread or variability of their scores. The t-test does just this.

Statistical Analysis of the t-test

The formula for the t-test is a ratio. The top part of the ratio is just the difference between the two means or averages. The bottom part is a measure of the variability or dispersion of the scores. This formula is essentially another example of the signal-to-noise metaphor  in research: the difference between the means is the signal that, in this case, we think our program or treatment introduced into the data; the bottom part of the formula is a measure of variability that is essentially noise that may make it harder to see the group difference. Figure 3 shows the formula for the t-test and how the numerator and denominator are related to the distributions.

              Figure 3. Formula for the t-test. The top part of the formula is easy to compute -- just find the difference between the means. The bottom part is called the standard error of the difference. To compute it, we take the variance <statdesc.htm> for each group and divide it by the number of people in that group minus 1. We add these two values and then take their square root. The specific formula is given in Figure 4:

       Figure 4. Formula for the Standard error of the difference between the means. Remember, that the variance is simply the square of the standard deviation

The final formula for the t-test is shown in Figure 5:

             Figure 5. Formula for the t-test. The t-value will be positive if the first mean is larger than the second and negative if it is smaller. Once you compute the t-value you have to look it up in a table of significance to test whether the ratio is large enough to say that the difference between the groups is not likely to have been a chance finding. To test the significance, you need to set a risk level (called the alpha level ). In most social research, the "rule of thumb" is to set the alpha level at .05. This means that five times out of a hundred you would find a statistically significant difference between the means even if there was none (i.e., by "chance"). You also need to determine the degrees of freedom (df) for the test. In the t-test, the degrees of freedom is the sum of the persons in both groups minus 2. Given the alpha level, the df, and the t-value, you can look the t-value up in a standard table of significance (available as an appendix in the back of most statistics texts) to determine whether the t-value is large enough to be significant. If it is, you can conclude that the difference between the means for the two groups is different (even given the variability). Fortunately, statistical computer programs routinely print the significance test results and save you the trouble of looking them up in a table.

GRAPHS:

The graphs drawn based on my hypothesis/prediction after collecting my results will have the axes as given below.

PREDICTION:

I predict that as the organic effluent from the sewage decreases down the stream many physical and chemical changes will take place in the fresh water steam.This will affect the biodiversty in several ways.The biodiversty will increase down the stream as the percentage of organic effluent present decreases.This is beacuse the BOD will decrease and the oxygen levels will rise provinding enough oxygen for most flora and fauna to survive.

Where seweage is deposited untreated in relatively small amounts of water i.e. streams the BOD may be great enough to remove entirely the dissolved oxygen. This causes death of aerobic species, including fish, leaving only anerobic ones. The BOD is offset by new oxygen being dissolved and in fast-moving, shallow, turbulent streams this is sufficient enough to prevent anaerobic conditions. Unfortunately many centres of population are situated near river estuaries where the waters are slower, deeper and less turbulent. The amount of oxygen dissolving is much less and so an untreated seweage added to these waters quickly results in them becoming anaerobic. Where untreated seweage enters a river it will create BOD which decreases further down the stream as organic material is decomposed. Part of this seweage is combined nitrogen (mostly in form of urea) which is converted to ammonia by the bacteria. Nitrifying bacteria rapidly oxidizes ammonia(a toxic gas) to nitrates.Nitrates are more soluble in water so leach out of the soil more easily and since they are important for plant growth are much more of a hazard as pollutants.

Chemical and Physical changes: brought about by seweage are accompanied by changes in the diversty of species living in the water. Where the level of seweage effluent is high, saprophytic bacteria concentrations, including sewage fungus increases as they feed on the sewage. The algal level initially falls due to sewage reducing the amount of light which penetrate the water. Further down the stream the algal levels rise above the normal because the bacterial breakdown of the sewage releases many minerals, including nitrates. These minerals which previously limited algal growth now allow it to flourish. As the minerals are used up algal population level returns to normal.

The population levels of animal species vary according to the levels of oxygen in the water.Most tolerant of low oxygen level are animals whose heamoglobin will have a high affinity for oxygen which they will obtain at very low concentrations.These animals will therefore be likely to survive closer to the sewage outfall. Further downstream, as oxygen levels rise more organisms

will be able to survive depending upon their adaptations to the environment.

As the number of surviving species increases so will the competition between them and the better adapted will be able to survive as the biotic factors become the limiting factor for the survival of species.These organisms act as indicator species for polluted water. Where repeated additions of sewage occur at different points along the river , the water will not be anaerobic for much of its length. In addition to the death of aerobic species, these conditions will result in the build up of ammonia from decomposition of sewage.The chemicals that develop may be toxic and will result in an almost lifeless river.

Eutrophication by sewage: Eutrophication is a natural process during which the

concentration of salts builds up in bodies of streams. Salts for eutrophication in the stream comes from sewage, even when treated the sewage contains much phosphates as a result of decomposition of detergents and washing powders.Its occurance causes salts to accumulate until the equilibrium is reached where they will be exactly counterbalanced by the rate at which they are removed. The algal blooms eventually occur in eutrophic waters with high concentration of salts   and the stream water becomes densely populated with species of dense blue green bacteria. The density of these blooms increases to a point where light is unable to penetrate to any depth. The algae in the deeper regions of the lake are therefore unable to photosynthesis and die. Decomposition of these dead organisms by saprophytic bacteria creates considerable BOD resulting in deoxygenation of all but the upper layers of water. As a result the aerobic life in the lower regions dies.

As the levels of organic effluent and salts from the water decrease down the stream so does the BOD and the oxygen levels rise leading to an increased biodiversty of flaura and fauna.

Factors biotic and abiotic other then those mentioned above will also have greater effects on the biodiversty of the fresh water stream. There brief outline is given below:

BIOTIC AND ABIOTIC FACTORS:

BIOTIC:

Competetion:

Organisms will compete with each other for food, water, light, minerals. They will compete not only with members of other species-interspecific competition-but also with members of there own species -intraspecific competition.Where the two species will occupy same ecological niche(same site in the stream), interspecific competition will lead to extention of one or the other species hence determining the biodiversty.

Predation:

The distribution of species is determined by the presence or absence of the prey and the predators. The prey-predator relationship will also detremine the biodiversty of a given area according to the population size of one of them.The higher number of predators the lower number of preys and vice versa.

Human influence:

Man influences the distribution of other organisms more then any other species. As a hunter, farmer, developer and polluter. His activities dictate which organisms grow where. e.g pollution from organic effluent as mentioned in the background research.

ABIOTIC:

Light:

Ultimate source of energy.Neccesary for photosynthesis, reproduction, migration and hibernation of organisms. In a fresh water stream the high % of light leads to a greater rate of photosynthesis and hence an increased level of oxygen allowing a diverse range of animal to survive.

Temperature:

Sun is the main source of light for an ecosystem and hence the main source of heat. High

heat capacity of water effectively buffers the temperature changes in aquatic habitats.

Organic effluent from the sewage reduces this ability of water and causes high temperatures enzymes from saprophytic bacteria are denatured as the kinetic energy of molecules increases and they vibrate more leading to a breakdown of the tertiary structure of the enzymes so they are no longer able to work.These lead to high levels of carbondioxide; as oxygen is less soluble in water at high temperatures the biodiversty near the sewage may be less.

The actual temperature of each habitat may vary thugh according to the latitude, slope, degree of shading etc.these are the limiting factors in an experiment.

SAFETY AND ENVIRONMENTAL PRECAUTIONS:

Wear goggles to prevent organic effluented dirty water from entring the eyes.

Wear gloves when using the net to prevent any dirty water causing teh hands to be filthy as this can be hazardous for the skin the species may carry diseases.

Put the species back into the water where you collected them from as the conditions of those sites are neccesary for there survival.

Dont pollute the stream by throwing away rubbish as this may influence further water pollution.

Take care when handling the sensitive equipment to prevent it from being harmed or getting damaged.

IMPLEMENTATION:

SAFETY AND ENVIRONMENTAL PRECAUTIONS:

• Wear goggles to prevent organic effluent dirty water from entering the eyes.
• Wear gloves when using the net to prevent any dirty water causing the hands to be filthy, as this can be hazardous for the skin the species may bite or carry diseases.
• Put the species back into the water where you collected them from, as the conditions of those sites are necessary for their survival.
• Don’t pollute the stream by throwing away rubbish as this may influence further water pollution.
• Whilst removing the weeds for clear viewing of the species from the collected samples take care as some species may also be removed hence affecting the results being collected.
• Site selection must be done carefully taking into consideration the health and safety measures. Water banks will be too deep near some areas of the stream, places may not be tested to protect rare species, too high barks may also be a danger whilst collecting results therefore at the end of the day selection should be done finely ensuring low risk and own safety.

E.g.

Another site called tall house may have be ideal for the collection of data but it is too far away and has agricultural run off.

• Handle the net carefully when collecting sample as species may be left in the net when transferring into a container for accurate result purposes.
• Take care when handling the sensitive equipment (thermistor, light meters, pH meters) to prevent it from being harmed or getting damaged.
• The pH, light and temperature meters must be calibrated, as they don’t respond linearly and hence may give in accurate useless results.

 

MODIFICATIONS:

After viewing the area for the sites to obtain the results for our experiment some modifications were made to the plan in consideration to the health and safety precautions as well as the limitations and factors to be controlled.

FACTORS TO BE CONTROLLED:

From the original plan---Distance will need to be controlled. The amount of distance between the three selected areas of the water stream from the sewage will need to be equal. This is to make sure that the results obtained are more accurate and not too close so that variation between can be indicated.

Modified---The sites selected are ASHBY, LAGOON 3 AND RAISED POND. These sites will compare the species diversty within one waterway. These will vary in distance from the source of pollution however they have been selected regardless of the equal distance due to the following reasons.

• To ensure my own safety and follow the restrictions related to the sites and enable myself to get hold of a good set of results.

• The distance wouldn’t make much of a difference, as it is the organic effluent and its effects such as eutrophication we are testing not the distance and the amount of organisms. I do take into consideration the fact that the distance of the stream from the sewage will have a great impact on the results as discussed in my background research and my aim, as the stream will carry the pollutants away but that would be one of the limitations (see below for further details) affecting my experimental results.  

From the original plan ---The height also needs to be controlled using a metre stick it will be marked and it would be made sure that the streams depth is the same at the area being observed for biodiversty to ensure fair results.

Modified--- I will not be able to measure the height as some areas and their banks will be higher than the others will. Most of the organisms will be right at the bottom of the stream therefore I will have to disturb the organisms at the bottom of the stream besides the land at the bottom will be unlevelled too.

From the original plan---Temperature probes often contain a thermistor, which measures changes in electrical resistance as temperature changes. The temperature probe will need to be calibrated using water baths of known temperature, as resistance does not vary linearly with temperature.

Modified--- The temperature probe will be fully operated and calibrated by the assistant helper at the sites so that it can be handled carefully and with good analytical skill to obtain accurate results.

LIMITATIONS:

There will be several environmental and apparatus limitations when carrying out these series of experiments.

---Carrying out experiments and research on the Diversity index and BOD will be too time consuming and require appropriate analytical skill and experience and detailed knowledge about the organisms present therefore I will not be able to carry it out.

---There will be several others sites with various levels of organic waste that can also be used for the collection of results for the experiment but due to health and safety precautions that I have to follow as suggested above they will be left alone.

E.g. some may have to high banks, some may have agricultural run off or be too far away, some may contain endangered species and it will be unsuitable to disturb their habitats.

---Light sensor:  

1. Will need to be calibrated, as it doesn’t respond to changes in light intensity.
2. The scale is usually in arbitrary units so comparisons can be made but the actual light energy measurements will be difficult to obtain.  
3. Light will vary minute to minute according to the weather making accuracy very difficult and hence the results obtained may be unreliable.
4. The direction of light will be difficult to judge and will also affect the reading.

---pH meter:

1. pH is a measure of hydrogen ion concentration and pH meter will not be accurate enough to give a precise value as the water will be constantly flowing into the stream and may change the pH every instant.
2. The acidic weeds may also affect the readings as the weeds neutralise the alkaline water and may be responsible for the constantly changing of the pH readings.
3. The bank will be made of bricks and rapid leeching of the bricks may also provide unreliable pH reading.

---Temperature probes:

1. May contain silicon diodes inside which respond to temperature changes rather slowly.
2. The temperature of the organic effluent water from the stream at the sites will also depend on the weather the hotter the weather the higher the temperature hence the reading may be inaccurate.

---Oxygen solubility in water is low and varies with temperature, the lower the temperature the more oxygen dissolves. But the temperature in the environment is always fluctuating so the readings taken by the oxygen meter for oxygen may not be reliable.

---The collections of species using the net may also be different as the depths/heights of stream water from which they are obtained may vary and may not always be the same.

---The results obtained may also depend upon who collects the results first at a given site. Due to time limitations the results from other members of the class will be shared. The organisms will be disturbed once one group has collected the first set of results and the organisms may move away from the sites after realising the situation. Therefore the results obtained by some members may be anomalous.

--- The net being used may not be able to capture some of the species due to the size of holes in it. The larger holes may let some smaller species to get through. Also the removal of weeds from the net to get a clear viewing of the organisms may also lead to the removal of some organisms and hence unreliable or inaccurate results.

--- Water current may also have an effect on the number of organisms in a given area. The water current will be reduced in an area of high organic effluent and will be high in the area with low organic effluent. This may also have an impact on the number of species caught in the net. The high currents may take away most of the organisms etc.  

APPARATUS SELECTION:

To measure the abiotic factors the following apparatus would be used:

• a general map for the area of study
• oxygen meter- to measure the levels of oxygen at the 3 selected sites(Ashby, Lagoon 3, Raised pond)
• nitrate indicator- to determine the presence of nitrates
• light sensor - to make comparisons between sites for the presence of species due to the availability of light for photosynthesis
• pH meter- used to determine whether a site is acidic/neutral/alkaline.  
• sweep net/plankton net- to catch organisms from the stream
• Tray- to place the collected species so that biodiversty of organisms at various sites can be determined.
• Pencil and rubber- to record the results.
• Thermistor- to check out the temperature of sites contaminated with different levels of organic effluent and its effects on biodiversty.
• Secchi disk- to measure the turbidity of the water

METHOD:

1. A general map of the site will be required area selected for dipping can be found.

2. Three areas for experiment selected are raised pond, ashby, lagoon 3 to ensure the reliability of results as these have different levels of organic effluent present in them so that a general hypothesis can be made about the outcome of the results and any anomalies can be found out. Sites selected will be within one waterway varying in distance from the source of pollution. Near the sewage, in the middle of the stream and one site further away near the fresh water so that differences in biodiversty can be measured by looking at the changing effluent levels in the stream.

3. Another site at the end of the stream consisting of mostly fresh water (Raised pond) with least amount of organic effluent will be used as a control site.

4. A net will be used to collect samples from the sites top of the water and from deep within. This is because different species have different adaptations and this determines their location in the water as well as due to the organic effluent.(The algae in the deeper regions of the lake are unable to photosynthesis and die due to the organic effluent. Decomposition of these dead organisms by saprophytic bacteria creates considerable BOD resulting in deoxygenating of all but the upper layers of water. As a result the aerobic life in the lower regions dies.) See detail in: Eutrophication by sewage under prediction

5. The collected sample will be placed in a tray and observed. The results will be recorded and the table will be constructed once the sample has been observed according to the species present in the fresh water stream.

6. The biodiversty index will be drawn from the species collected to indicate the levels of pollution caused by the organic effluent from the sewage in the stream.

7. The diversty index would also have been calculated to determine whether the different levels of organic effluent from the stream have had any effect on the biodiversty of the species at a given site. However due to time limitations and the limited knowledge about the organisms in the stream this will not be carried out.

8. Checking out the abiotic factors of oxygen concentrations, light availability, and pH, nitrate levels and turbidity affecting the fresh water stream will prove the results for biotic index.

9. Oxygen concentration will be measured by using an oxygen meter at all selected site. This will allow me to make comparison between the three sites and link the results obtained with the level of organic effluent and draw a logical conclusion about how this links with the biodiversty of the organisms at those sites.

10. The bacterial breakdown of sewage releases nitrates. Nitrates are more soluble in water and since they are important for plant growth are much more of a hazard as pollutants. These may be converted into ammonia by most bacteria in the organic effluent. Ammonia is toxic and may lead to a lower biodiversty in the water stream near the sewage. Hence a nitrate indicator will be used to check for the presence of nitrates in the fresh water stream and support my hypothesis.    

12. Light sensor /meters will also be used to measure the amount of light that is received by the algae (or weeds) for photosynthesis. Single celled algae, phytoplankton, grow rapidly on the water surface leading to algal bloom. Some algae are toxic to stream life and the water contains toxins. Competition for light may lead to death of many algae, which are decayed, by aerobic bacteria. Bacteria reproduce due to high concentration of organic material. BOD increases and the species within stream decreases. The particles in raw sewage make the stream cloudy and block light reducing photosynthesis leading to lowers amount of oxygen and hence cause anaerobic conditions. This factor will be taken into account when looking at the variations between the biodiversty of the 3 selected sites.

13. pH metre will be used to test for the acidity or alkalinity of the fresh water stream as the amount of organic effluent decreases when the stream moves away from the sewage in accordance to the position of  the  3 selected sites. These conditions may cause the water and its constituents (enzymes) to become disrupted and hence change their tertiary structure and hence lead to harmful effects on the stream life. This will also affect the biodiversty of organisms in the fresh water stream.

 

14. Temperature probes will be used to determine the temperature difference between the sites and hence determining the biodiversty. Sun is the main source of light for an ecosystem and hence the main source of heat. High heat capacity of water effectively buffers the temperature changes in aquatic habitats. Organic effluent from the sewage reduces this ability of water and causes high temperatures enzymes from saprophytic bacteria are denatured as the kinetic energy of molecules increases and they vibrate more leading to a breakdown of the tertiary structure of the enzymes so they are no longer able to work. These lead to high levels of carbondioxide; as oxygen is less soluble in water at high temperatures the biodiversty near the sewage may be less.

15.A turbidity test will be used to measure the clearness of the water. When the water is cloudy it is called turbid. Turbidity is caused when sediment (soil and other particles that settle to the bottom) is stirred up in the water. The plants need sunlight. If they don't they will die.  We will test this by throwing a Secchi disc into the water. Lower it into water and count how many feet down you can lower the disk before it disappears.

16. Repeat the experiment 3 times for each site to ensure that the results obtained are correct and not due to chance.

RESULTS TABLE: (RAW DATA)

 

Biotic index was then calculated by dividing the total biotic score for each site by the number of species found. The results are given below:

Ashby:

41 / 11 = 3.73

Lagoon 3:

10 / 3 = 3.3

Raised pond:

70 / 16 = 4.38

RESULTS TABLE: (POOLED RESULTS)

It would’ve been impossible to repeat the results due to time limitations therefore the group results were gathered so that t-test can be carried out and the results obtained by me can be confirmed. The combined data will be helpful in reducing any errors made whilst carrying out the experiments.

Bold…indicates anomalous results.

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T-TEST (the two tailed unmatched) RESULTS:

(Quantitative confirmation of the graphs)

The following t-tests were carried out by not taking into account the anomalous results to ensure reliability of the results.

SOURCE:  Maths for Advanced Biology 

                                         By

                               Alan Cadogan

                                Robin Sutton

PUBLISHER: Nelson

Graphs:

By looking at the graphs drawn above some solid interpretations can be made. Anomalous results of the group were taken out before plotting these graphs to ensure a better understanding of the results obtained. The smooth curves provide a better understanding of the histograms, which show the spread of results and hence indicate what the standard deviations should be like. Where as the curves shows overlapping and proves the mean difference for the two sets of data in each graph. They can also be related to t-test which provides a quantitative confirmation of what the graphs show.  

Description of Graphs (trends and patterns):

Lagoon 3 Vs Raised Pond:

The first graph shows us that the means are far apart (difference of 0.4 between the two smooth curves) with a small standard deviation as the data is tightly clustered and this can be proved by the statistics of the t-test calculated above.

These graphs shows little overlap between two data sets and hence a large value of t proving that the certainty that there is a difference as t is greater then the critical value of that of the degree of freedom. Hence proving that there is a significant difference between the mean biodiversty of the two sites of varying level of organic effluent and proving the null hypothesis wrong.

Ashby Vs Raised Pond:

The means for these graphs are particularly close together(difference of  0.2 between the two smooth curves) and show that the data is widely spread hence indicating that the standard deviation is large. The greater overlapping between the two sets of data is clear from the smooth line curves hence indicating little difference between the two sets of data. But to be accurate lets look backs at the value of the t-test and relates this to our graphs. The t-test value is larger then the critical value of the degree of freedom (24 --- 2.08[0.05], 2.80 [0.01]).

The value of t is small yet larger then the value of degree of freedom hence indicating that the null hypothesis is wrong and that the significant difference in biodiversty is caused by the different levels of organic effluent at the two sites.  

Lagoon 3 Vs Ashby:

This graph shows us that the means are close together (difference of 0.2 between the two curves on the smooth line graph) with the data widely spread and the standard deviation is therefore large. The smooth line curves also show small difference between the means and also show that there is a greater overlapping between the two sets of data for both sites however just to be certain that this is not by chance we carried out the t- test.

This result is supported by the t-test above showing us greater value of t than the critical value of the degree of freedom although there is overlapping but not enough hence we can reject the null hypothesis and state that there is a significant factor responsible for this. Our results are therefore not by chance and the organic effluent is a major cause for the difference in biodiversty at both sites hence supporting our hypothesis.

CONCLUSION:

After considering the statistics and the graphs for the results obtained for the biotic index I have come to a logical conclusion that eutrophication caused by the organic effluent from the sewage leads to oxygen depletion in the fresh water and therefore to the organisms death. Raised pond our control had fresh water and low level of eutrophication and had the most organisms living in it due to less organic effluent in it. It had the highest biotic index score of 4.38. On the other hand lagoon3 being the most polluted had a low biodiversty (biotic index score of 3.3 only) due to high level of eutrophication. Whereas Ashby was moderately polluted and hence the eutrophication level was more then that of raised pond but less then lagoon 3 hence it had a moderate number of organisms surviving giving it a biotic-index score of 3.73.

N/B. The score for Biotic index can be seen from the raw data.

ANALYSIS:

      The final outcome of the investigation suggested that the fresh water of Raised pond was able to hold more diverse species. It had low level of organic effluent in it and as a result had a low eutrophication scale. This can be seen clearly from the results obtained for the biotic index score in both my raw data as well as the pooled data of the whole class used as repeats to make up for the time limitations. But the reasons for high biotic index score were also looked at in consideration to the abiotic factors to provide strong evidence for our hypothesis and look at how these conditions support or undermine the number of organisms within the site in accordance to the level of organic effluent.

(N/B.Anomalous results in the tables given below are in bold)

In eutrophication the nutrients and salts e.g. nitrate from the sewage enter the fresh water. From the water quality test results for nitrates we can see the most nitrates being in Lagoon 3, the least in Raised pond and average in Ashby. The bacterial breakdown of sewage releases nitrates. Nitrates are more soluble in water and since they are important for plant growth are much more of a hazard as pollutants. These may be converted into ammonia by most bacteria in the organic effluent. Ammonia is toxic and may lead to death; a lower biodiversty in the water stream near the sewage as can be seen from the biotic index score of Lagoon 3 lowering down as the water flow takes most of the nitrates away by the time it reaches Ashby. Its less of a hazard, less ammonia made; more organisms can survive and nitrates may even be used for the benefit of the site, it may help with the growth of vegetation that supports organisms through photosynthesis by releasing oxygen. Raised pond on the other hand is right at the end and being man made contains fresh water hence low hardly any level of nitrates supporting a wide range of organisms.

 Green plants especially algae, also start to grow because of this. More algae grew where there were most nutrients meaning Lagoon 3. However the most vegetation was at Ashby due to fewer algae and the least vegetation was at Lagoon 3 due to most algae. Raised pond was our control and as expected it had an appropriate amount of vegetation out of all 3 sites with the least algae. Algae grow so fast that they cover the water surface cutting of the light to submerged plants. Lack of light causes submerged plants to die leading to a build up of detritus. Fewer plants due to increased competition for light meaning hardly any photosynthesis and lack of oxygen supply means death of organisms. The results from the collected data for Lagoon 3 (in bold below) for the light were inaccurate due to an error made by the field assistant in calibration of the equipment therefore I am relying on the scientific knowledge and the other results from the class to explain this phenomenon.

We can see from the water quality test results that the light availability is the greatest in Lagoon 3 and the lowest in Ashby. However these results are not very reliable and the value of light availability received for Lagoon 3 is an anomaly due to apparatus error it should have been lower than that of Ashby. This can be said by taking account of some facts; there were some limitations first of all, Lagoon 3 was a lot shadier due to the profile of its bank then any other site. On the other hand Ashby was more open and received much more of the light. It was raining heavily the day I went therefore the reading on the light meter couldn’t have been exactly constant.

However from the results received and taking into consideration our expectations due to the surroundings of the sites, we can draw a logical conclusion. That more availability of light to Raised pond meant its plants had the potential energy required to trigger the process of photosynthesis by splitting water and releasing oxygen as a by product. The oxygen supply determines the biodiversty amongst the three sites. However raised pond having more biodiversty than Ashby can be seen again due to high availability of light to our control because it was more open. Lagoon 3 had the least light available and without light the process of photosynthesis wasn’t a big possibility for a few plants/weeds that were present remain at Lagoon 3. Without oxygen released organisms die or don’t grow much in the first place.

Bacterial decomposition increases using up available oxygen due to detritus. Oxygen depletion may eventually lead to animal/organisms death. By carrying out % oxygen saturation test we received the following results.

There is high % of oxygen saturation for Raised pond and the lowest % of oxygen saturation for Ashby. The results received for Lagoon3 were anomalous again due to equipment error and could not have been fixed due to time limitations. This indicates that there should be more plants and hence diverse organisms in Raised pond then in Ashby. This is because more availability of oxygen means that the plant photosynthesis more in raised pond and hence provides oxygen for the biotic species within to survive. But compared to Raised pond and Ashby less vegetation in Lagoon 3 means that there is less availability of Oxygen to the species in the water and this means that species with only low oxygen requirement and adaptations can survive. As a result there is less diversity of organisms in Lagoon 3.

The temperature of the three sites can also have a major affect on the diversty of organism. Sun is the main source of light for an ecosystem and hence the main source of heat. High heat capacity of water effectively buffers the temperature changes in aquatic habitats. Organic effluent from the sewage reduces this ability of water and causes high temperatures, enzymes from saprophytic bacteria are denatured as the kinetic energy of molecules increases and they vibrate more leading to a breakdown of the tertiary structure of the enzymes so they are no longer able to work. These lead to high levels of carbondioxide; as oxygen is less soluble in water at high temperatures the biodiversty near the sewage may be less. Therefore the Lagoon 3 holds less oxygen due to high temperatures and hence has low biodiversty then the Raised pond which has the lowest temperature and as a result can hold more oxygen leading to a high biodiversty of organisms. Ashby on the other hand has temperature lower then that of Lagoon 3 yet higher then that of Raised pond, the above scientific knowledge explains that it has less diversty of organisms than that of Raised pond because of temperature and less oxygen.

 pH metre was used to test for the acidity or alkalinity of the fresh water stream as the amount of organic effluent decreased when the stream moved away from the sewage in accordance to the position of  the  3 selected sites. The water was naturally alkaline because it was coming from river lee, which ran through, chalky bland. The acid rain also lowered the pH readings. Raised pond had the lowest of all pH due to weeds as they neutralised the alkalinity of the water. The brick material also leeched out and neutralised the acidic conditions caused by the weeds hence providing an almost neutral pH reading of the water. Lagoon 3 was strongly alkaline due to the nitrates and other salts present in the organic sewage and Ashby had slightly alkaline conditions as the distance and flow of water may have reduced the pH. These conditions may have caused the water and its constituents (enzymes) to become disrupted and changed their tertiary structure leading to extremely low biodiversty in Lagoon 3 and higher biodiversty in Ashby compared to Lagoon 3. Compared to both these sites our control Raised pond had higher biodiversty of organisms and hence less organic effluent.  

Turbidity of the 3 sites was also measured.

From the pooled results carried out for turbidity we can see a trend. The Raised pond was the least turbid whereas Ashby was the most turbid. The day we carried out our test it was raining heavily. Clarity and turbidity relate directly to rainfall and runoff. A hard, fast rain-washes a great deal of soil into the water. The high levels of turbidity can be due to run off of soil and leeching of the bricks. The turbidity reduces the amount of light that penetrates into the water, reducing the light available for algae and aquatic weeds to use in photosynthesis. High levels of turbidity may coat organisms making it difficult to breathe. Finally, the suspended material eventually settles to the bottom, where it may cover food supplies for organisms. The most biodiversty of organisms was at raised pond and our turbidity results support this fact however lagoon 3 seems to have less turbidity than Ashby. This contradicts our results for the organisms because if the scientific knowledge mentioned above is correct this shouldn’t happen. However there were some apparatus errors which could be responsible for these distorted results as well as the rainfall. Ashby also had shallow water therefore the mud already there could have been raised when the organisms were disturbed using the net providing us with the results that we did receive. On the other hand Lagoon 3 had deep water and all the mud must have sank to the bottom of the stream hence providing us with lower turbidity levels.    

The flow of a stream may also have varied by a large factor depending on the time of year. That tremendous change in volume will change the concentrations of dissolved and suspended materials in the water. The greater volume of the high stream flows dilutes all the chemicals that control pH, hardness, nutrients, and dissolved metals. However, since greater volume is due to runoff, high flows such as the ones in Ashby usually have high turbidity due to erosion of the land in the watershed. Runoff from urban areas also usually washes a large amount of metals and oils from city streets and parking lots onto streams. This is particularity true for the first part of the runoff - the "first flush" in Lagoon 3.

There were however some anomalous results in the data collected. These results were due to several factors mentioned below.

• In our method whilst we were collecting the samples from the selected sites weeds were also caught in the net and it was necessary to remove the weeds to get a better viewing of the organisms. But removing weeds also meant that we were removing some organisms with them, which led to inaccurate results.
• There could have been organisms still left in the net whilst we carried out the experiment again at another site.
• The first group to dip may have received more accurate results. Dipping again and again may have caused agitation and affected the temperature and oxygen levels. Species may have moved away or gone to deeper depths as a result once they realized that they were being disturbed.
• Cross contamination from the equipment could have caused varying unreliable readings. Such as the ones for pH they were not very precise.
• The weather had an affect on our results. Acid rain could also have had an effect as well as leeching of the bricks and the ability of weeds to neutralize the alkaline water.
• The predators could also have had an effect on the level of biodiversty for example there were ducks in Ashby to whom other organisms could have been prey.

The Order above shows biodiversty in decreasing order from raised pond to Lagoon 3 due to high organic effluent and hence a great deal of eutrophication in the water.

Basically what we are saying is that some algae produced due to nitrates are toxic to stream life and the resulting water contains toxins. Competition for light may lead to death of many algae, which are decayed, by aerobic bacteria. Bacteria reproduce due to high concentration of organic material. BOD increases and the species within stream decreases. The particles in raw sewage make the stream cloudy and block light reducing photosynthesis leading to lowers amount of oxygen and hence cause anaerobic conditions leading to death of organisms. This fact is supported by our results in the tables above and any anomalies have been explained by facts and limitations factors.

EVALUATION:

The investigation carried out by me provided me with a logical conclusion and supported my hypothesis. There were several tests carried out to provide me with evidence so that I could support or reject my null hypothesis. There were several limitations that affected my investigation an account of which is as follows:

LIMITATIONS, RELIABILITY, PRECISION:

---Carrying out experiments and research on the Diversity index was too time consuming and required appropriate analytical skill, experience and detailed knowledge about the organisms present therefore I was not able to carry it out.

---There were several other sites with various levels of organic waste that could also have been used for the collection of results for the experiment but due to health and safety precautions that I had to follow as suggested in my implementation they were left alone.

E.g. the banks for Lagoon 1 and 2 were too deep.

The tall house farm had agricultural run off and was too far away.

Some sites contained endangered species and it was unsuitable to disturb their habitats.

---Light varied minute to minute according to the weather making accuracy very difficult and hence the results obtained may be unreliable. The direction of light was difficult to judge and the density of water according to the amount of organic material present also affected the reading.

---pH is a measure of hydrogen ion concentration and pH meter was not accurate enough to give a precise value as the water was constantly flowing into the stream and may change the pH every instant. The acidic weeds also affected the readings as the weeds neutralised the naturally alkaline water because it came from river lee running through chalky bland and may be responsible for the constantly changing of the pH readings.

The bank was made of bricks and rapid leeching of the bricks also provided unreliable pH reading.

---The weather also had strong effect on my readings. The day I went it was raining and the acid rain could have altered the pH from its original value in normal conditions.

---Thermistors may contain silicon diodes inside which respond to temperature changes rather slowly. The temperature of the organic effluent water from the stream at the sites also depended on the weather the hotter the weather the higher the temperature hence the reading might have been inaccurate.

---Oxygen solubility in water is low and varies with temperature, the lower the temperature the more oxygen dissolves. But the temperature in the environment is always fluctuating so the readings taken by the oxygen meter for oxygen may not be reliable.

---The collections of species using the net might also be different as the depths/heights of stream water from which they were obtained varied and might not always have been the same.

---The results obtained also depend upon who collected the results first at a given site. Due to time limitations the results from other members of the class were shared. Agitation caused due to dipping might have affected the temperature and oxygen levels and lead to inaccurate results. The organisms will have been disturbed once one group had collected the first set of results and the organisms may have moved away from the sites after realising the situation. Therefore the results obtained by some members were anomalous.

--- The net being used was not able to capture some of the species due to the size of holes in it. The larger holes let some smaller species to get through. Also the removal of weeds from the net to get a clear viewing of the organisms also lead to the removal of some organisms and hence unreliable or inaccurate results.

--- Water current also had an effect on the number of organisms in a given area. The water current was reduced in areas of high organic effluent and was high in the areas with low organic effluent. This may also have had an impact on the number of species caught in the net. The high currents took away most of the organisms etc.  

---Cross contamination from the equipment may also have been responsible for unreliable results. And the apparatus error also lead to inaccurate results for the voltage of light received at the 3 selected sites in my raw data.

I used a control (Raised pond) to ensure the reliability of my results by comparing it with the other two sites and the results for their biotic index and abiotic factors.

It was impossible to carry out repeats due to time limitations but using the pooled results of the whole class made it possible to use them as the repeats. Most of them were similar supporting my hypothesis and the conclusion made. However there were some anomalies that suggested that my data was unreliable but those were caused due to the limitations (time, apparatus, environmental) and mistakes mentioned above.

By considering all the limitations, mistakes made and the results received, I can suggest that the hypothesis made was true. The evidence for this is the t-test and the graphs made from the sets of data collected for each site. This has been backed up with the scientific knowledge and I do understand that detailed knowledge and understanding of the organisms I collected for the biotic index score could have provided me with more accurate an reliable results. I came to a logical conclusion that eutrophication caused by the organic effluent from the sewage lead to oxygen depletion in the fresh water and therefore to the organisms death. Raised pond our control had fresh water and low level of eutrophication and had the most organisms living in it due to less organic effluent in it. It had the highest biotic index score of 4.38. On the other hand lagoon3 being the most polluted had a low biodiversty (biotic index score of 3.3 only) due to high level of eutrophication. Whereas Ashby was moderately polluted and hence the eutrophication level was more then that of raised pond but less then lagoon 3 hence it had a moderate number of organisms surviving giving it a biotic-index score of 3.73.

I fully agree with my hypothesis and conclusion made in the light of the results received as mentioned above. However I didn’t carry out the test for heavy metals and oil and what other substances had incorporated the organic effluent in the selected sites. So may be I ignored an important factor of where the salts, nutrients in the sewage came from and whether or not they can be reduced and even it what extent they were harmful and hence we don’t know whether my research could have just been a waste of time.

 

If was to repeat the same investigation again I will take care of the mistakes made trying to reduce anomalous results above and investigate further topics like diversty index and BOD which I was unable to do due to time limitations. Further abiotic factors would be considered over a long period of time to elaborate on how seasonal variations bring a change in the flow of water and hence in abiotic factors associated with such changes. The type and number of organisms may also change giving a different biotic index score for each site due to increased competition, predators, preys or improved vegetation etc. Limiting factors for the experiments can also be controlled if possible by getting the most precise equipment to save time, for example. This would be vital to for the improvement, reliability and accuracy of the results obtained for my research.