Water_Resources BIO 350 - Water Resources I Earth The Water Planet A 71 of the earth is covered in water 1 97.4 is salt water 2.6 is fresh 2 Of the

Water Resources I Earth: The Water Planet A 71% of the earth is covered in water. 1. 97.4% is salt water, 2.6% is fresh 2. Of the fresh water about 87% is frozen in polar caps and glaciers, about 22% is groundwater and less than 1% is surface water (lakes, rivers, soil, in living organisms) B The Water Cycle C Remember that water never disappears, it just moves around through three major loops: evapotranspiration, surface runoff, and groundwater. II Surface Water A Surface runoff forms from rain, snowmelt or groundwater springs. Water collects in streams & creeks which combine to form rivers. 1. Rivers are biologically rich ecosystems supporting many species of algae, invertebrates, fish, amphibians and mammals. Rivers are frequently surrounded by riparian forests. B In flat areas surface water may collect to form wetlands , places where the ground is saturated or plants emerge from standing water. 1. These areas are important as wildlife habitat and for reducing flooding, recharging aquifers and filtering pollutants. C Ponds and lakes form where depressions in the earth intersect with the water table, allowing for a body of open, standing water. 1. Perennial ponds and lakes also support a variety of wildlife and provide a store of water during dry seasons.

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D Uses of surface water 1. Globally, humans withdraw 34% of reliable surface runoff. Demand may double by 2025. a) 70 % of freshwater withdrawn is used for agriculture b) 20% of freshwater is used by industry c) 10% of freshwater is for municipal use III Ground Water A Water that infiltrates the soil and is not absorbed by plants becomes groundwater . B Most groundwater is stored in layers of water-saturated sand, gravel or bedrock called aquifers . 1. Unconfined aquifers a) Are near the surface and are defined by a water table. b) They are recharged by infiltration of water from the ground above. c) They can be tapped by digging wells, but the water usually must be pumped out. 2. Confined aquifers a) Are bordered by impermeable rock layers above and below, placing the water under great pressure.