Ap Environmental Science- Water Use

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APES
3/22/12
One consequence of human use of water is the wasted water resulted from inefficient irrigation. Less than half of the freshwater we use for irrigation is actually absorbed by crops. Wasteful practices like “flood and furrow” irrigation, which involve liberally flood fields with water, use up water unnecessarily because it may evaporate from standing pools in the field. This kind accounts for 90% of worldwide irrigation. Overirrigation leads to waterlogging and salinization, which ultimately affects 20% of worldwide farmland and loses $11 billion in farming income. Another consequence is the depletion of groundwater. In the past 60 years, humans have taken more and more groundwater, at a faster rate than what can be restored. As extraction increases, water tables drop. Around the world, the complete depletion of ground water is eminent; such places include parts of Mexico, India, China, and the Middle East. Overpumping of groundwater leads to salt-water contamination and can make water undrinkable; this has happened in Florida, Turkey, and Bangkok. As aquifers lose water, their substrate can become weaker and less capable of supporting overlying strata, and the land surface above may subside. For this reason, cities from Venice to Bangkok to Beijing are slowly sinking. Mexico City’s downtown has sunk over 10 m (33 ft) since the time of Spanish arrival; streets are buckled, old buildings lean at angles, and underground pipes break so often that 30% of the system’s water is lost to leaks. Sometimes subsidence can occur suddenly in the form of sinkholes, areas where the ground gives way with little warning, occasionally swallowing people’s homes. Once the ground subsides, soil becomes compacted, losing the porosity that enabled it to hold water. Another consequence of human use of water is the drying up of rivers’ natural courses and of lakes and seas. Humans divert water from rivers for their own use in farms, cities, etc., but this leads to only a...
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