lect03-16-10

lect03-16-10 - Food and Other Resources 1. Water and Soil...

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Unformatted text preview: Food and Other Resources 1. Water and Soil Resources 2. Food Resources 3. Forest and Wildlife Resources Water and Soil Resources Water Resources - availability, uses, and sources of fresh water - groundwater depletion and its management - surface water scarcity and its management - dams and reservoirs Soil Resources - properties of soils - soil erosion - causes, consequences - soil conservation and reclamation - soil salinization and waterlogging Availability of Fresh Water Freshwater is only a small fraction of all water on earth Even less freshwater is readily available for human use Uses of Fresh Water Worldwide 70% agriculture (60%80% of this not used by crops) 20% energy production & industry 10% domestic & municipal use United States 41% agriculture 49% energy production (power plant cooling) & industry (38% & 11%) 10% domestic & municipal use Fresh Water Stress & Scarcity - Worldwide Fresh Water Scarcity - United States Acute shortage Shortage Adequate supply Metropolitan regions with population greater than 1 million Sources of Fresh Water Surface Water: precipitation that does not infiltrate the ground or evaporate - available as rivers, streams, lakes, ponds, and reservoirs Watershed (or Drainage Basin): region from which water drains into a water body (such as a stream) Groundwater: water that infiltrates the ground & is stored in voids between soil particles Aquifers: porous, watersaturated layers of soil or rock through which groundwater flows Recharge area: any area of land through which water passes into an aquifer Groundwater System Groundwater Hydrology Unconfined Aquifers are located below a permeable layer of rock and soil, called the zone of aeration The boundary that separates the relatively dry zone of aeration and the zone of saturation is called the water table Confined Aquifers are bounded above & below by less permeable rock As part of the Hydrologic Cycle, groundwater moves from the recharge area through an aquifer & out to a discharge area (well, spring, lake, geyser, stream, or ocean) Groundwater Use and Aquifer Depletion One-third of world's drinking water comes from groundwater Groundwater supplies about 51% of drinking water and 43% of irrigation water in the U.S. Aquifer depletion (or groundwater overdraft) occurs when water withdrawals exceed recharge Groundwater in southern Great Plains and southwestern U.S. is being withdrawn much faster than its replacement rate Aquifer depletion is also a serious concern in other parts of the world - e.g., southern Europe, Middle East, northern Africa, India, northern China Possible Consequences of Aquifer Depletion Water Scarcity Aquifer Subsidence - land sinks when water is withdrawn Saltwater Intrusion Aquifer Depletion in the U.S. The Shrinking Ogallala Aquifer Withdrawals from the world's largest aquifer exceed recharge rates by 8-10 times in many places Economics of Aquifer Depletion Large depletable aquifers are typically common-property resources Depletion may also have other negative externalities Over-exploitation occurs if users do not bear the full social cost of extraction Need for government intervention depends on extent of market failure Various policies can be designed to encourage water conservation - taxes, quotas, other guidelines and incentives Management of Surface Water Scarcity surface water scarcity may be alleviated by: modifying local water allocation laws (or doctrines) & creating incentives for conservation making regional water treaties & transfers building reservoirs and dams Surface Water Allocation Laws in U.S. Doctrine of Riparian Rights take all you need, provided enough is left for downstream users Doctrine of Prior Appropriation (or Appropriative Rights Doctrine) first-come, first-served rule use it or lose it principle ...
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