Sex On The Sea Essay

1189 WordsOct 7, 20095 Pages
E5 Dissolved Oxygen in Water 1) Outline the importance of dissolved oxygen in water. DO means Dissolved Oxygen, and it accounts for all the oxygen that is dissolved in a water body. DO is measured in the units of mg/l. All organisms need oxygen in order to survive, whether they live on the land or in the water. The oxygen in the water is dissolved and it is in the form of bubbles of oxygen. As the water travels past their gills, the bubbles of oxygen are taken in by the fishes, and then the oxygen is transferred to their blood. It is important that the DO is at a level in which the organisms can survive. If the DO level is too low, some organisms won’t be able to attain the oxygen required to function and die. Different aquatic animals have different minimum DO levels with which they can survive. Fishes that live in the waters with environments with high-level DO (e.g. whitewater stream) can not survive in waters with low-level DO (e.g. bayou). However fishes originally from low-level DO can sustain a life in high-level DO waters. There is no maximum limit for DO. Figure #1: Diagram illustrating the DO limits for fishes (reference: http://islandwood.org/kids/stream_health/Data/DO_Ranges?.html) 2) Outline biological oxygen demand (BOD) as a measure of oxygen-demanding wastes in water. The BOD, which stands for Biochemical Oxygen Demand, measures the amount of oxygen consumed by aerobic bacteria when decomposing organic matter present in the water body. These aerobic bacteria require oxygen just like the other aquatic organisms (e.g. fishes). When there are a lot of these microorganisms in the water, the BOD increases, as these bacteria use up a lot of the oxygen. That means that there is less oxygen available in the water and the level of DO decreases. A low-level of DO can be harmful for some of the organisms in the water. BOD is determined by

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