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Effect of Oxygen on Gammarus Pulex

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Introduction

The Effect of the Oxygen Concentration in the River on Gammarus Pulex Rationale: Whilst doing a group study on the biodiversity of life in different parts of the river, I noticed a difference in the number of Gammerus Pulex. I thought this might be due to the difference in abiotic factors such as pH and flow rate. After doing some research on this species I discovered that they are particularly fond of more oxygenated water, thus I constructed my hypothesis to investigate this. Gammarus Pulex: This species is more commonly known as the fresh water shrimp. It is generally found in shallow fresh water rivers, although they have been known to tolerate lakes with a stream running into it for example. This is probably due to the higher oxygen levels in the water. They spend most of their time under stones in the bed of the river and feed on decomposing plant and animal material. They range from being only a couple of millimetres to up to three centimetres and can be any colour from pale orange to grey and brown. They are easy to spot by their arc shaped bodies and their distinctive movement. They propel themselves through the water by a series of contractions and relaxations and travel on their side. Although it is very difficult to see they are also constantly vibrating. This produces a constant current of water over their gills at the base of their thoracic legs. ...read more.

Middle

Stone Washing is another alternative where stones are removed from the riverbed and washed in clear water to remove any invertebrates on the stone. It is hard to measure and keep it reliable as every stone is a different size and shape. Also some invertebrates may fall off the stone as soon as it is moved which would make it inaccurate. This technique could only be used if the invertebrates being counted live on the stones. Bias could be caused by the person choosing the stones. Variables Independent Variable: River Site Dependent Variable: Abundance of gammarus pulex Other possible variables may need to be controlled or measured and taken account of when analysing the results: Abiotic Factors and how I will control or measure them: Factor What I will do about it pH of Water Measure with universal indicator Turbidity Immeasurable because of shallowness of river Speed of River Flow Measure using a flow meter Temperature of Water Measure using a thermometer Ammonia, Phosphate and Nitrate Levels in Water Measure with testing kits Light Intensity I will try to do the experiments at both sites quickly one after the other on the same day to reduce variation Anthropogenic Factors: * Distance away from fords, animal crossings etc * Pollution of water and riverbed I will have to observe and consider these anthropogenic factors and consider their importance at both sites. All these abiotic and anthropogenic factors can cause variation in the favorability of the habitat for certain species. ...read more.

Conclusion

Changes to the method As a result of my preliminary and trial experiments I have chosen to change a few parts of my method. Firstly as soon as I started to kick sample I discovered a considerable variable in the speed at which I kicked at and the strength of my kicking. A variation in either of these could mean that I would produce different amount of disturbance to the riverbed and therefore would have a not very reliable number of gammarus pulex. The speed of my kicking I can easily solve by using a stopwatch to measure the amount of kicks I do per second. I decided that a suitable rate would be two kicks a second. As for the strength of the kick, I cannot think of a way of measuring, therefore I will have to monitor this with my own judgment and try and keep it the same. In my preliminary work on the length of kicking time I decided that I would use a kicking period of forty seconds. I have decided to change the amount of samples I take to twelve samples but use the same sampling method, see plan below: 9 5 1 10 6 2 11 7 3 12 8 4 Otherwise I found that the general method worked well. Whilst working on the river I attempted to keep upstream of anyone else on the river so that their trampling did not disturb the conditions for my investigation. I also tried to keep out of their way so I did not affect their experiment, I therefore emptied my gammarus pulex downstream of them. ...read more.

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