Water Cycle and Human Impacts PDF

BIOL 123 z Water Cycle and Human impacts by: L. Francis z OBJECTIVES ▪ State the percentage of water available for human use and the source from which it is drawn ▪ Describe the water cycle ▪ Explain...

BIOL 123 z Water Cycle and Human impacts by: L. Francis z OBJECTIVES ▪ State the percentage of water available for human use and the source from which it is drawn ▪ Describe the water cycle ▪ Explain the human impacts on the water cycle z ▪ It is fundamental to life ▪ Covers 75% of the Earth’s surface ▪ 97.5 % of the volume is saltwater of oceans and seas ▪ 2.5% is fresh water ( has a salt content of less than 0.1%) z Fresh Water ▪ Two thirds is bound in the polar ice caps and glaciers ▪ 0.77% → lakes, wetlands , rivers, ground water, biota, soil, atmosphere ▪ Evaporation from oceans combines with precipitation to continually resupply ie hydrologic cycle ▪ Represent ecosystem good and services / capital ▪ Provides drinking water, water for industries and water to irrigate crops z Bodies of Water Provides: ▪ Energy through hydroelectric power ▪ Control flooding by absorbing excess water ▪ Transportation ▪ Recreation ▪ Waste processing ▪ Habitats for aquatic plants and animals z WATER CYCLE / HYDROLOGIC CYCLE ▪ Evaporation ( liquid to gas state) ▪ Transpiration ( loss of water vapor from soil through green plants via leaf pores) ▪ Condensation ( gas state to liquid state) ▪ Precipitation ( rain , sleet, snow, hail) ▪ * green water – water in vapor form ▪ * blue water- liquid water wherever it may occur z z Evaporation ( liquid to gas state} ▪ Weak hydrogen bonds hold water molecules together ( H2O) ▪ Below 32 F (0 C) = low kinetic energy → bond held together = solid form ( ice) ▪ Above freezing but below boiling ( 212 F or 100C) → hydrogen bonds keep breaking and reforming = liquid form ( liquid water ) ▪ Energy absorbed from sunlight or artificial light → increase in kinetic energy → breaking of hydrogen bonds = gas form (water vapour) z Condensation ( gas state to liquid state) ▪ Opposite of evaporation ▪ Droplets formed in the atmosphere =fog and clouds ▪ Droplets formed on cool surfaces of vegetation = dew ▪ Facilitated by aerosols ( microscopic liquid or solid particles from land and water surfaces ), provides sites that attracts water vapor and promotes formation of droplets of moisture z *Purification ▪ Water is separated from the solutes and particles it contains ▪ Occurs naturally in evaporation and condensation Example ▪ water evaporation from the ocean: only the water molecules leave the surface( purified water vapor) , the dissolved salts and other solids remain behind. When condensed again it is purified except for the pollutants and other aersols it may pick up from the air z Transpiration ▪ loss of water vapor from soil through green plants via leaf pores z Precipitation ▪ Warm air encounters lower atmospheric pressure at increasing altitudes = gradually cools as it expands ( adiabatic cooling) ▪ 100% relative humidity + continued cooling = condensation and clouds forming ▪ Condensation intensifies → water droplets become enough to fall ( precipitation) z HUMAN IMPACTS ON THE HYDROLOGIC CYCLE 1. Changes to the surface of the Earth ▪ Loss of vegetation ▪ Taming rivers and wetlands ▪ Building impervious surfaces ( eg roads , buildings etc) ▪ Dams ▪ Moving water to the ocean ( decrease the amounts going to ground water and increases the chances of flood, droughts and erosion) 2. Climate change 3. Atmospheric particles 4. Withdrawal for human use z ▪ BIOL123 Lecturer's Notes ▪ Environmental Science Toward a Sustainable Future by RT Wright and DF Boorse 12 ed