Bio102-Chap10Notes - Water Resources Themes I The...

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Water Resources - Themes I. The Hydrologic Cycle II. Major Water Compartments III. IV. Water Conservation V. Water Pollution (U. S.) Water (liquid and solid) covers > 70% of world’s surface More than 370 billion billion gallons I. Hydrologic Cycle Describes the circulation of water as it: Evaporates from land, water, and transpires from plants Condenses and precipitates back to the Earth’s surfaces Moves into ground by infiltration Overland runoff into rivers, lakes, ocean Precipitation —> Recharge zone Runoff —> Stream flow - Influent vs. Effluent Aquifer Water table - Water table Solar energy drives the hydrologic cycle Solar Energy —> Evaporation —> Atmosphere (Transport) Precipitation —> Infiltration - - -> Groundwater —> Runoff Precipitation Patterns ~ 90% of water budget is within the oceans ~ 86% of evap. is from oceans ~ 10% of that is transported to land ~ 10% returns to oceans as runoff II. Major water compartments > 97% of world’s water is saline Most is in the world’s ocean (3.5% NaCl) < 2.5% of world’s water is fresh > 87% is in glaciers, ice caps, and snowfields > 12% is in groundwater < 1/2% is surface freshwater (lakes, ponds, rivers, streams)
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Groundwater Second largest reservoir of fresh water Aquifers - Porous layers of rock (sediments) holding water Artesian - Pressurized aquifer (no pumping) Recharge Zone - Area where water enters an aquifer - Recharge rate is often very slow - Groundwater is often removed faster than replenished Surface Water Supplies ~ 80% of human supply Generally renewable 2/3 is lost b/c of no effective storage Freshwater aquifers ~ 20% of human supply (~50% of drinking water) Many aquifers subject to overdrafts (used at rates >> than recharge rates) Very important in arid regions Water Use Terms: Withdrawal - Amount of water taken from a source Consumption - Water not returned to its source Degradation - Contamination making it is unsuitable for desired use Readily accessible (renewable) supplies ≈ 400,000 gal /person/year Big problem is uneven distribution Every continent has regions with scarce rainfall Natural drought cycles create temporary shortages Climatic changes (global warming) may alter supplies
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This note was uploaded on 04/14/2008 for the course BIOL 102 taught by Professor Kemp during the Fall '06 term at San Diego.

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Bio102-Chap10Notes - Water Resources Themes I The...

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