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An investigation into the abundance of fresh water black fly larvae, Simuliidae, between pools and riffles in Woodford meanders on the 19th September 2003.

Extracts from this document...

Introduction

An investigation into the abundance of fresh water black fly larvae, Simuliidae, between pools and riffles in Woodford meanders on the 19th September 2003. Abstract:- My investigation was to see where the black fly larvae, Simuliidae, preferred to inhabit, slower moving pools or fast moving riffles. I accomplished my results on the 19/09/03 at Woodford meanders using a "stone shake" sampling method. The results were conducted on the same day and within 3 hours from the first to the last. Readings of temperature, width, depth and impellor travel time were taken at each sample point. I plotted a graph of, pools or riffles against number of black fly larvae, Simuliidae. To analyse my results I used a Mann Whitney U significance test which showed with a 5% significance that the black fly larvae, Simuliidae, preferred the faster moving riffles or the slow moving pools. Introduction:- I accomplished my investigation at Woodford meanders (Grid reference - Sr06370638) on the 19th of September 2003. I chose to investigate the abundance of the black fly larvae, Simuliidae, whether they are in higher concentration in the slow moving pools or the fast moving riffles. I chose a freshwater dwelling species because there was a stream, Woodford meanders near to the base camp, Nettlecombe court, where we were staying, therefore it was more accessible, there was no time limit and in case of emergencies, help was only at the base camp. I chose the black fly larvae, Simuliidae, because in preliminary experiments at Woodford meanders, there was a moderate amount of the species, so comparisons could be made on the preferred dwelling for the black fly larvae, Simuliidae; Plus I was personally curious why there were large amounts of the species under trees or bushes so I decided to investigate further. Background information:- The black fly larvae, Simuliidae, is a detritivore; Detritivore, an animal that feeds on animal and plant waste or remains, sequentially reducing the particle sizes so that the true decomposers, bacteria and fungi, can break them down to their constituent chemical parts for recycling in the ecosystem. ...read more.

Middle

Repeats:- To gain a true representation of the stream, many repeats should be achieved; for this reason I have chosen to repeat the experiment 20 times for both pools and riffles. I feel that this will give an accurate representation, in the time given to me, of the concentration of black fly larvae, Simuliidae, in the river. 20 repeats is the maximum number of results I can have for a Mann-Whitney U test; having the maximum values possible will give me a precise value to compare to the critical value. Range:- I will be measuring the following factors at each site of the stream:- * The temperature of the stream, to view if the abundance of black fly larvae, Simuliidae, alters with the temperature of the water. * The width and depth of the stream, to differ from pools and riffles * The velocity of the stream, to see whether the black fly larvae, Simuliidae, are in a higher abundance in the fast riffles or the slower pools. Variables:- Independent variables Dependent variables Controlled variables * Whether it is a pool or a riffle. * Abundance of black fly larvae, Simuliidae. * Velocity. * Width. * Depth. * Temperature. * Standardise procedure. * Same climate and day. * Same chemistry of water. * Sample the same stream. * Same environment. * Same geology. In choosing a pool or riffle, the independent variable, will alter the abundance of black fly larvae, Simuliidae, the width and depth of the stream, the temperature and the velocity, the dependent variables. I will be measuring the dependent variables. In controlling some variables, I will gain more accurate results as not taking account for these factors can alter my results dramatically, In standardising my procedure, it will keep my result from showing a bias outcome, my results will then be standardised and portray a true representation of the experiment. Doing the experiment on the same day and constant climate, stops large biotic factors, such as the weather and temperature, affecting my results. ...read more.

Conclusion

To improve the accuracy I would take more readings. The metre rule measuring the depth could have not been directly on the bottom of the stream bed but sitting on stone, giving a false reading. To eliminate this error the bottom of the bed should be examined and the metre rule placed carefully away from stones. The width measurement was measured perpendicular to the current, but there was no way to be sure that it was perpendicular to the current as it was done by eye so could have given a false measurement. To remove this error a piece of thick string could be held in the current and then the tape measure be held at 90 degrees to the string. The Impellor travel time was measured parallel to the current, but there was no way to be sure that it was parallel to the current as it was done by eye so could have given a false measurement. To remove this error a piece of thick string could be held in the current and then the impellor can be held parallel to the string. The impellor travel time was taken using a stopwatch so the decision to start or stop the stopwatch was down to me so human error was introduced. To eliminate this a digital impellor could be used cutting out human error. The equipment used was dated and of poor condition, the net was worn and had small holes, but were small enough to let black fly larvae, Simuliidae, escape. This affects the true number of black fly larvae, Simuliidae, counted. The stone shake was much more efficient in collecting the black fly larvae, Simuliidae, as not so much debris went into the net as in foot sampling, so miss identification was lessened. The limit of time affected the number of readings I could take, thus affecting the accuracy of my results. If I could repeat this experiment with unlimited time I would investigate the abundance of black fly larvae, Simuliidae, at different temperatures. ...read more.

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Here's what a teacher thought of this essay

4 star(s)

Overall, this is an impressive report of an investigation into the effect of stream velocity on the abundance of black fly larvae. The writer carried out detailed research into the ecology of the larvae and used this to formulate hypothesis and predictions. Variables were discussed in some detail and the methodology used was thoroughly justified.

The overall essay could be improved by making a number of minor changes or additions as follows:

[1] At times, the report lacks conciseness being repetitive and unnecessarily long in some sections.
[2] The term 'abundance' needs to be explained more fully and a more rigid approach to measuring it undertaken when sampling the larvae.
[3] The statistical test results need a fuller explanation, enabling the reader to understand why the data supported the hypothesis.
[4] A more thorough examination of the data is needed beyond the stats tests. The fact that the graphs were not displayed in this pdf version made data analysis difficult to follow.

Overall, however, this is a thorough piece of scientific research which was, on the whole, well reported.

4 stars

Marked by teacher Ross Robertson 24/06/2013

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