Global Water Cycle Essay

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Global Water Cycle The water cycle contains the largest chemical flux on earth. Water distributes heat around the globe and thus creates climate, and water is the single most important factor regulating land-plant productivity worldwide. Without water life would not exist (perhaps on ANY planet), and despite the fact that 70% of the earth's surface is covered with water, that water is salty and can't be used for drinking, agriculture, or industry. Only about 0.014% of the water at earth's surface is useable by plants, humans, and other animals. In attempting to understand element cycles as part of the major functioning of ecosystems, it is useful to follow a specific "approach". This general approach was followed in the previous lecture on the carbon cycle, and it can be used to help understand any element cycle. It consists of 3 parts and is formally outlined below: 1st - Accounting: Accounting tells you "where things are", or the distribution of the element in different pools within the ecosystem. 2nd - Cycling: Cycling tells you "where things are going", and how fast they are moving from different pools in the ecosystem. 3rd - Controls: Determining the controls tells you "how does the system function, and what factors drive the cycling". Using this approach of gaining knowledge about each of these three components enables you to answer the question of "How will things change?". Gaining this kind of a predictive understanding of ecosystems, or of communities or populations, is the most important goal in basic scientific research. So, let's start with the Accounting in our examination of the global water cycle. Figure 1. The Laurentian Great Lakes. Accounting for Water (distribution of water in km3 x 106) Rocks (not usable) 25,000 Oceans (97.4% of usable water) 1,350 Ice 27.5 Groundwater 8.2 Lakes and Rivers

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