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An investigation into whether varying light intensity at a stream affects the species diversity

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An investigation into whether varying light intensity at a stream affects the species diversity Introduction: Foulden common has a variety of different habitats including grassland, young woodland, ponds, swamps, fenland, set-a-side and streams which enables a diverse range of organisms to be present in an area. Life for plants and animals in any medium is a constant struggle. Besides the physical environment, predators, parasites and other competitors that have to be contended with; but compared with a terrestrial existence, fresh water offers a relatively stable environment.i The small stream that runs a long the side of Foulden common is a tributary of the River Wissey, which eventually flows into the Great Ouse. The stream is spring fed so has a fairly high chalk content and so the waters are slightly alkaline. This is good for fresh water organisms, as the majority of fresh water organisms requite chalk (limestone: CaCO3) because they either have an exoskeleton or shell, both of which contain large amounts of chalk.ii The stream is quite shallow so available light can penetrate the bottom easily however light intensity levels vary considerably along the stream due to trees and bushes which are quite dense in places, spaced well apart in other places and totally absent in other regions. Aim: The aim of my investigation is to see whether varying light intensity at a stream affects the species diversity. Light intensities will be recorded in specific zones and samples will be taken in the stream at the zones to see if a difference in light results in a change in species diversity. Background information: Rays of light falling on the surface of the water do not penetrate very far, and sedimentary matter, even organisms themselves, will absorb light. The most obvious effect of light is to promote the growth of the plants. The plants are mostly emergent plants so add little to the fresh water habitat and if anything maybe net removers of oxygen yet the plants do contribute food and shelter. ...read more.


The cut grass is taken away which removes nitrates from the area. This is a factor that should be taken into consideration as if an area by the stream has animals grazing it will have an effect in the nitrogen concentration in the stream. Excess nitrates in water cause eutrophication and a chain of effects. Algae use the nitrate that has leached into the stream for growth and there is an increase in reproduction, which leads to an algal bloom. This results in less light penetrating the water, which means that algae and other plants cannot photosynthesise and therefore die. Aerobic putrefying bacteria decompose the plants and so consequently the dissolved oxygen levels decrease and the invertebrates and fish suffocate. The nitrate levels will have an effect on the species as the oxygen levels will be decreased and also the light intensity decreased. * Sewage levels - must be monitored as this will have an effect on the species diversity. However, the stream is situated away from houses and humans and there are no signs to sewage being present at the stream. Sewage outflow into a stream results in there being a larger species diversity downstream as there is less pollution As light intensity is the factor that iam varying, it is important that cloud cover remains constant throughout the investagion to ahcieve fair results at eah zone, despite the varying light intensities. I will therfire only take readings when cloud covers the sun as when there are no clouds present the light intensitywould increase at the specific zone beign sampled. Methods involved with monitoring pH, depth of stream and flow rate of stream : Once the desired zones were marked, the light intensities recorded and the optimum number of sweeps and repeats per sample were established from the preliminary work above the pH of the zones were recorded by placing some of the stream water, from directly in front of the marker from the specific zone, into a testing point and three drops of universal indicator was added. ...read more.


Total number of Chrironomids present A Mud 336 4.24 5 B Mud 411 4.61 7 C Mud 500 3.94 4 D Gravel 637 5.00 8 E Gravel 744 4.44 5 F Sand / Gravel 1082 5.76 5 G Sand / mud 1225 6.39 26 H Sand 1377 7.83 35 I Sand / gravel 1458 6.82 39 Summary table of the total number of species collected in zones A to I: Species Total number of individuals collected Zone A B C D E F G H I Waterlouse 0 0 0 1 1 1 4 18 5 Gammarus 33 54 69 50 24 30 27 72 19 Corixa 4 3 8 5 2 4 5 31 15 Cloeon 15 15 25 25 4 17 16 42 10 Tipula 0 0 0 2 0 0 5 14 3 Stonefly 0 6 4 3 0 3 3 3 1 Watermite 18 34 35 16 18 15 37 59 42 Stickleback 0 4 2 0 7 0 1 2 14 Ephemeroptera 7 2 2 19 1 14 21 31 12 Chironomid 5 7 4 8 5 5 26 35 39 Water boatman 0 0 0 2 0 3 1 4 5 Caddisfly 0 3 2 3 1 2 2 15 3 Batracobdella 1 0 0 0 0 0 0 4 2 Polycelis tenuis 1 6 7 3 2 2 0 2 0 Halipus 0 1 4 0 0 0 0 0 0 Ecolyonorys 0 5 0 0 0 0 0 0 0 Cumbercisus varyigolus 0 2 0 0 0 0 0 0 0 i Page x; Ecology of fresh water; Leadley Brown; Heinemann Educational books limited; ii Hand out sheets at East Anglican field study centre iii Hand out sheets at East Anglican field study centre iv Page 16; Revsie A2 biology; Fosberry, Gregory, Stevens; Heinemann; 2001 v Page 3; Ecology of fresh water; Leadley Brown; Heinemann Educational books limited; vi Page 10; Ecology of fresh water; Leadley Brown; Heinemann Educational books limited; vii Page 4; Ecology of fresh water; Leadley Brown; Heinemann Educational books limited; ?? ?? ?? ?? ...read more.

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