Investigation into the Ecology of a small stream in Tillingbourne.

Investigation into the Ecology of a small stream in Tillingbourne

Ecology is the scientific study of the interactions between organisms and their environment. Invertebrates are interesting organisms to investigate because they represent an enormous diversity of body shapes, survival strategies, and adaptations. Many invertebrates require clear, cool water, adequate oxygen, stable flows, and a steady source of food in order to complete their life cycles.

My aims are to investigate the abundance and distribution of freshwater invertebrates in the stream, and to measure abiotic factors such as oxygen levels, in the stream.

Prediction

I predict that there will be a higher number of organisms at the edge of the stream, than in the middle.

Introduction

I make this prediction as there is increased vegetation at the edge of the river meaning that more oxygen is released as the plants photosynthesise, from which organisms can respire. The vegetation also provides food for herbivores and detritivores, and shelter from light, predators, and the current. Therefore the edge of the river is generally a more desirable place for organisms to live, so theoretically more should be found there, than in the middle of the stream.

The Location

The stream in which I carried out my investigation on the 18th October 2001 was part of the River Tillingbourne at Abinger Hammer, located south of the Hackhurst Downs.

The factors I measured were the water temperature, velocity, dissolved oxygen and the organisms in a particular area of the stream.

Apparatus

1 pond net
1 tray
2 pots
3 teaspoons
1 flow meter
1 oxygen meter
1 stopwatch
1 one-litre water bottle
1 pipette
disinfectant

Fair Test

One person should do both kicking samples and try to kick in the same way

both times.

Both kicking samples should last 30 seconds.
More than one person should identify and count the organisms.
The flow and oxygen meters should be held at the same height, and the

temperature measured at the same depth.

All measurements and samples should be collected from the same location in the

stream.

Safety

I should wear rubber gloves and wellington boots to protect my hands and feet from

the fresh water.

I should disinfect my hands after the experiment to eliminate any bacteria I may

have accumulated from the water.

Methods

I will use biotic and abiotic methods in my experiment.

Biotic: Kick Sampling

Collect all equipment needed (listed above), and choose a location in which to

conduct the experiment.

Wade into the middle of the stream with the pond net.
Place the pond net on the bed of the stream, facing downstream.
Begin kicking the riverbed enough to disturb it, and simultaneously start the

stopwatch.

After 30 seconds stop kicking.
Fill the tray ...

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have accumulated from the water.

Methods

I will use biotic and abiotic methods in my experiment.

Biotic: Kick Sampling

Collect all equipment needed (listed above), and choose a location in which to

conduct the experiment.

Wade into the middle of the stream with the pond net.
Place the pond net on the bed of the stream, facing downstream.
Begin kicking the riverbed enough to disturb it, and simultaneously start the

stopwatch.

After 30 seconds stop kicking.
Fill the tray with a random sample from the stream, and empty the contents of your

net into it.

Tip the organisms with as little water as possible, into the pot labelled ‘Middle of the

stream’.

Repeat this experiment at the edge of the stream, and pour the contents of the tray

into the pot labelled ‘Edge of the stream’.

Abiotic: Hydro Prop

Twist the rotation fan to the end of the metal screw.
Wade into the middle of the stream, and place the flow prop 2cm above the riverbed

facing upstream.

Start the stopwatch, and when the fan twists down to the other end of the pole, stop

the stopwatch.

Repeat this experiment at the edge of the stream.

Oxygen and Temperature:

1. Use an oxygen and temperature probe to measure the oxygen levels and

temperature of the water, at both locations of the stream (in the middle and at the

edge). Record these results.

Freshwater invertebrate recording sheet to show the abiotic factors in the River Billinghurst

Analysis

My results did not illustrate a clear trend. I did not pinpoint any clear anomalies in my results, but there being no obvious pattern made it difficult to spot them. The velocity of the current in the middle of the stream was faster (by 0.159 m/s) than at the edge which was predicted, but the temperature and the amount of dissolved oxygen were the same in both areas of the stream. This does not correspond with the explanation of my prediction, that there would be higher volume of oxygen at the edge due to the vegetation there, making it more attractive as a habitat.

My results and graph demonstrate that there were more organisms in the middle of the stream than at the edge; 860 in the middle, 652 at the edge. This does not support my prediction, that there are more organisms at the edge of the river due to more oxygen present and shelter.

However, my hypothesis was fairly general and did not focus on specific invertebrates. There are explanations for why certain invertebrates were found in the locations they were, even though the findings did not support my hypothesis:

According to my results, there were 7 more flatworms in the middle than at the edge. This may have been because they are adapted for swimming in the middle of the stream where the velocity is faster and more rapid, by being flattened and having bodies able to expand and contract. Their elongated and bilaterally symmetrical bodies are mostly elongated allow them to move and steer themselves more easily.

My results also showed there to be 14 more leeches at the side than in the middle. A reason for this could be because leeches coil and are not streamlined, and therefore not suited for the faster flow rate in the middle of the stream. They also have a sucking disc on their undersurface so it is easier for them to latch onto other organisms if the water is flowing more slowly.

More snails were found to be in the middle; 10 at the edge, while in the middle there were only 4. This may be because they can use the vegetation for extra shelter from their predators which include fish, waterfowl and leeches. It would also be more convenient for them to live by the plants at the edge, as they feed by scraping algae and organic debris from leaves and other substrates, and this would make their source of food closer by and easily accessible.

Over 100 more freshwater shrimps were found at the edge of the stream than the middle. The reason for this is likely to be that when they are young, they are weak swimmers so it is more appropriate for them to live in an area where the water flow is slower, so that they can move around with ease.

There were 39 more flattened mayfly nymphs in the middle of the stream than the side. This is because they are strong swimmers and have more than one tail to help them manoeuvre through a faster flow.

Almost twice the number of swimming mayfly nymphs were found in the middle of the stream (middle= 238, edge= 127). This may have been because they are streamlined, and being sucker shaped allows them to cling to the river bed, so they are adapted for living in the middle.

Almost twice as many caseless caddis larvae were caught at the side than in the middle. The reason for this is that they spin nets to capture their prey, and the stream edge is a more strategic location for them to build their nets as they can efficiently latch onto the side or vegetation.

(, www.wildkids.org.uk, www.seanet.com/~leska/online/guide.html)

Evaluation

There were many factors which could have affected the accuracy of my experiment, explaining why my results did not support my hypothesis.

Design errors:

A limitation on my investigation was the shortage of time. The whole experiment had to be fit into just a couple of hours, so results obtained from it would have not been as reliable as if we had done the full investigation.

My results did not take into consideration seasonal variations, as I only carried out the experiments once. This is not reliable as the climate and time of year would affect the number of certain invertebrates living in parts of the stream. For example in winter there is likely to be less vegetation at the edge of the stream, meaning a smaller difference in the amount of organisms found in the middle and at the side. Repeating my investigation at intervals throughout the year and comparing my results, would consider more affecting factors so would produce more accurate results.

Also, due to the shortage of time I did not take into account the width and depth of the stream which would have affected the amount of organisms living in particular area, or the sunlight which affects the amount of vegetation at the edge and therefore the organisms living there. Deeper water is likely to contain more invertebrates than shallow water as there is a larger area, which may have affected the results.

Although I tried to carry out my experiments in the same location, it was not possible to be exact.

Operator errors:

I am not an expert at identifying and classifying organisms and I was not supervised while doing this, so I may have miscounted or misinterpreted creatures, for example there was a case where I initially misconstrued a damselfly with a group of mayfly nymphs. The shortage of time to identify every organism in the tray meant that if there were too many of one species to be counted, the number had to be estimated and obviously that is not accurate. Also some very small invertebrates may have been missed although a microscope was used, so were not recorded.

When kick sampling, it was impossible to carry it out the same way using the same effort, which is not a fair test. Also, it was impossible to carry out the kick sampling in exactly the same location each time, and this could have affected the number of invertebrates that were collected by the net.

Also, there were other groups conducting experiments in the stream at the same time, which may have slightly disturbed the flow of the stream, lessening the accuracy of the results I obtained.

Instrument errors:

My results may have been more reliable had I used more reliable equipment.

The hydroprop used had a tendency to become stuck; lubrication could have helped the propeller move more easily, but a digital flow prop is ideal as it would have improved the quality of the results.

The method in which the samples of organisms were collected was not very accurate, as organisms had a chance of escaping the net through the fairly large holes, so we may have counted a lower number of invertebrates than were initially caught.

The degree of accuracy of the procedure was not very high, so I do not think my results are accurate enough to draw up a firm conclusion as there were many factors of my experiment which made it an unfair test. Although the amount of some of organisms found in the two locations could be scientifically supported, as my results did not support my prediction or show a clear trend, they are reliable.