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Fresh water Ecology.

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Fresh water Ecology The nature of all aquatic environments depends upon the following factors which exert their effects in varying degree: i) The depth of water Has an important secondary effect by reducing the penetration of light and hence the degree of colonisation by plants. ii) Light Water absorbs light of long wavelengths, particularly the blue part of the visible spectrum. Since this would not normally be sufficient for photosynthesis, many freshwater plants possess adaptations so that light does not become a limiting factor in their growth. iii) Substrate Streams that carry a large amount of sediment in suspension (e.g. due to a muddy stream bed) may have a decreased amount of light available to submerged aquatics. A muddy stream bed may also pose problems to the attachment or respiration of animals, and can lead to a build up of semi decomposed organic matter. This can lead to a high biological oxygen demand (BOD) and the water becoming anoxic, killing off most life. iv) Temperature Water possesses certain thermal properties which make it a unique environment. In particular, it has a high specific heat, high latent heat of fusion and the highest known latent heat of evaporation. ...read more.


vii) Surface Tension Aquatic insects may use surface tension to run over the surface of the water (pond skaters), to adhere breathing tube to the water surface (e.g. water scorpions), or to enclose bubbles of air around their bodies (e.g. water boat men). viii) The chemical composition Changes in nitrate levels resulting from organic pollution may affect the ecology of a river or stream directly. The use of nitrate fertilisers, or the break down of sewage, silage can lead to an algal bloom which may cause changes to the effective substrate by trapping and creating organic matter altering the ecology and oxygen levels. Inorganic pollution such as dissolved heavy metals (e.g. copper) can have disastrous effects on fresh water ecology. In streams and rivers water flowing over calcareous rock such as chalk or limestone will tend to be 'hard' with a high pH value. Such conditions favour calcicole plants and animals with calcareous shells such as gastropod molluscs and crayfish. ix) The existence of a current The existence of a current gives rise to the following features: � The eroding impact of a current tends to wash away the smaller and lighter soil particles such as clay, also the finely divided organic matter (detritus). ...read more.


No doubt this plays some part in reducing friction against the substratum. Among animals, planarians have a slimy adhesive surface, while gastropod molluscs like the wandering snail have a muscular foot which is well supplied with mucous glands. iv) Stream lining - The stems and leaves of many aquatic plants are streamlined to some extent whilst others produce floating and submerged leaves enabling the plant to flourish in both flowing and static water. The shape of most of the animals found in streams tends to be bluntly rounded in front tapering to a narrow point behind. This is the shape that reduced the 'drag' of the water to a minimum, thus lessening the effect of the current and facilitating more rapid movement. Many animals living in mid-stream have achieved some degree of flattening as well such as the large mayfly nymphs. v) Behavioural responses - In general, stream animals face and move upstream. This facilitates the use of gills in gas exchange and also the capture of food floating towards them. Another response is a tendency to cling to any surface with which the body comes into contact. This is particularly important for small molluscs whose powers of locomotion and avoidance of an excessive current are limited. ...read more.

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