Chapter 11

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University of Toronto Scarborough
Environmental Science
Carl Mitchell

Chapter 11Freshwater Systems and Water Resources y They fear that we will place our sovereignty at risk if we allow largescale diversions of freshwater or bulk water exports from Canadian water bodies Once bulk water exports are allowed to begin flowing to the thirsty southwestern United States they maintain they will be impossible to stop y Interbasin transfers is the transportation of water from one drainage basin to another Freshwater Systems y Freshwater is pure with dissolved salts most is in icecaps glaciers and underground aquifers y 975 of water is in ocean and 25 is fresh water Rivers and streams wind through landscapes y A small river flowing into a larger one is tributary and the area of land drained by a river and all is tributaries is that rivers drainage basin or watershed y 101 ySynthetic chemicals deplete stratospheric ozone y A pollutant in the troposphere ozone is a highly beneficial gas at altitudes of about 25 km in the lower stratosphere where it is concentrated in the stratospheric ozone layer y Ozone molecules are so effective at absorbing incoming ultraviolet radiation from the Sun that this concentration helps to protect life on Earths surface that this concentration helps to protect life on Earths surface from the damaging effects of ultraviolet UV radiation y In the 1960s atmospheric scientists began wondering why their measurements of stratospheric ozone were lower than theoretical models predicted Researchers hypothesizing that natural or artificial chemicals were depleting ozone finally pinpointed a ground of humanmade compounds derived from single hydrocarbons such as ethane and methane in which hydrogen atoms are replaced by chlorine bromine or fluorine One class of such compounds chlorofluorocarbons CFCs was being massproduced by industry at a rate of 1 million metric tons per year in the early 1970s and this rate was growing by 20 a year y In 1985 scientists announced that stratospheric ozone levels over Antarctica had declines by 4060 in the previous decade leaving a thinned ozone concentration that was soon dubbed the ozone hole There are will many questions to be resolved about ozone depletion y Scientists now believe that the ozonedepleting chemical reactions may find ideal launching sites on tiny crystals that are found only where the air is extremely cold These conditions are optimal over Antarctica where a circular wind pattern called the polar vortex traps extremely cold air over the pole y The scientists measure this ozone loss using a mobile measurement platformbasically a temperaturecontrolled box full of instruments and a
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