AN INVESTIGATION TO SEE THE EFFECT OF AN ABIOTIC FACTOR ON THE FREQUENCY AND DISTRIBUTION OF A FRESHWATER INVERTEBRATE

2. Abiotic factors are different from biotic factors in that they don't involve other organisms. This means that anything, which affects an organism in its ecosystem that is not living, is classed as an abiotic factor. Popular examples of abiotic factors include the climate and water currents. It has to be accepted that different organisms will respond in different ways to the same abiotic factor. It will be important to remember this throughout the course of the investigation.

Now that these key terms have been clarified the title can be fully understood and a scientific investigation can be planned.

A good starting point is to decide upon the abiotic factor and freshwater organism that will be investigated. Hence it is important to construct a list of possible biotic factors, this essentially will be a list of any organisms that may be found in the studied ecosystem. In a similar fashion a list of abiotic factors must also be determined.

The data for the investigation will be collected some along the course of Upper Gordale Beck, a tributary of the river Aire close to Malham. Having studied similar mountainous streams on previous occasions it is possible to work out what Upper Gordale Beck will be like.

Possible organisms which may inhabit the Upper Gordale Beck ecosystem:

Trueworm

4

Cranefly lava

2

River limpet

5

Non-biting midge

3

Freshwater shrimp

6

Biting midge

4

Freshwater mite

7

Diving beetle

5

Swimming mayfly nymph

8

Riffle beetle

6

Flat mayfly nymph

9

Black water beetle

7

Burrowing mayfly nymph

20

Dragonfly nymph

8

Stonefly nymph

21

Alderfly nymph

9

Lesser water boatman

22

Damselfly nymph

0

Cased caddis (stones)

23

Whirligig beetle

1

Cased caddis (vegetation)

24

Snail

2

Caseless caddis

25

Leech

3

Blackfly lava

26

Water fly

Although 26 aquatic organisms have been identified above, it is highly possible that throughout the data collection other organisms will be encountered. These must not be ignored and can be easily added to the bottom of the list above if need be.

A similar list can be drawn up of abiotic data.

Abiotic factors that could affect the organisms of Upper Gordale Beck

Flow rate

9

Turbidity of water

2

Air temperature

0

Vegetation - percentage cover

3

Water temperature

1

Bed rock - percentage cover

4

pH of water

2

Stones - percentage cover

5

Percentage oxygen

3

Mud - percentage cover

6

Amount of nitrate

4

Shade - percentage cover

7

Amount of phosphate

5

Stream depth

8

Amount of ammonium

6

Stream width

7

Cross-sectional area of stream

To construct a list like the one above requires a great deal of scientific knowledge. The inclusion of each of the abiotic factors can be justified.

Flow rate. This may not affect large organisms that can withstand stream currents; likewise it may not affect organisms which hide themselves under rocks. However organisms which are more fragile may not be able to inhabit sections of the stream where the rate of flow is high.

Air and water temperature. Different organisms enjoy different amounts of warmth at different times of the day and at different times of the year. The local temperature at a particular site of a stream could easily decide which organisms thrive there.

pH of the water. Surprisingly this could change quite considerably along just a small length of stream. Differing pHs can be caused by the chemicals farmers put on their land getting into the water. Hence anywhere downstream of a farm may have an unsuitable pH for the normal organisms to live.

Percentage of oxygen. This will of course only affect those organisms that breathe using oxygen from the water. However some of the listed organisms do breathe in this way, and it would be a fair assumption to say that these organisms should be more frequent where the oxygen content of the water is higher.

Amount of phosphate/nitrate/ammonium. Like pH the amounts of these compounds can change considerably along just a short length of stream.

Now that these lists have been drawn up, an abiotic factor can be chosen as the one whose effect should be investigated. Also one particular organism must be selected.

Choices

Abiotic factor = Flow rate

Freshwater organism = Swimming mayfly nymph

If upon investigation either of these two do not provide suitable results for experimental writeup, it will be very simple to change the investigation to involve a different abiotic factor or organism.