Unit 4: The Hydrosphere

1. Unit 4: The Hydrosphere Part 1: Structure of the Hydrosphere Part 2: Oceans Part 3: Water Quality

2. Part 1: The Structure of the Hydrosphere Objectives: Characteristics of Water The Water Cycle Reservoirs within the Hydrosphere River Basins

3. Properties of Water • Water has unique properties that impact the role it plays on the Earth. o Polarity o Cohesion o Adhesion o High surface tension o Density o High specific heat o High heat of vaporization

4. The Water Molecule • Made of 2 H atoms and 1 O atom • The atoms share valence electrons to form covalent bonds.

5. Water is Polar Covalent • However, the electrons are not shared equally. • Oxygen has a much stronger attraction for the electrons so the shared electrons get pulled closer to the oxygen. • This makes the oxygen slightly negative and the hydrogen atoms slightly positive. • This unequal sharing of electrons is called polarity.

6. Water is Polar Covalent Partially negative Partially positive Most of the properties of water are due to polarity!

8. Cohesion • Attraction of water molecules to each other.

9. Surface Tension • Cohesion cause surface tension. Molecules on the surface have no neighbors above so they pull more strongly on those beside and below them. • This forms a surface "film" which makes it more difficult to move an object through the surface than to move it when it is underwater. • This also makes water form drops because the surface molecules are pulled inward.

10. Surface Tension • Water attracts itself and pulls in to form a drop with a “film” on its surface.

11. Adhesion • Attraction of water to an unlike substance

12. Cohesion and Adhesion

13. What forms a drop? • Cohesion causes water to form drops • surface tension causes them to be nearly spherical • adhesion keeps the drops in place.

14. Interesting Polarity Facts • Polar substances stick to other polar substances. • Polar ↔ Polar = High Adhesion • Polar ↔ Nonpolar = Low Adhesion

15. Water Drop Shapes • Water coheres to itself and forms a nice, round drop. • On a nonpolar surface the drop stays round (low adhesion) • On a polar surface the drop flattens out because polar water “sticks” to the polar surface. (higher adhesion)

16. Capillary Action– water moves through narrow, porous spaces • Some of the molecules adhere to the surface of the object. • The other molecules that are cohered to them are pulled along.

17. Adhesion to surface of objectCohesion of water to water Capillary action of absorbent paper

18. Interesting Polarity Facts • “Like dissolves like” • Polar solvents dissolve polar substances. • Nonpolar solvents dissolve nonpolar substances • BUT Polar and Nonpolar don’t mix. • Water is called the universal solvent because so many things will dissolve in it.

19. Oil and water do not mix. “Like Dissolves Like” Oil is nonpolar Water is polar

20. Density of Water • Cold water is more dense than water up to the freezing point. • So cold water sinks and warm water rises. • This happens in the oceans and regulates our climate.

21. Density of Water • Solids are usually more dense than liquids. • Solid water (ice) is actually less dense then liquid water. • That means ice floats on water. • Important for lakes/ponds

22. High Specific Heat of Water • Specific Heat (or heat capacity) is the amount of heat (i.e. thermal energy) needed to raise the temperature of a substance. • High Specific Heat = lots of heat to raise the temperature = takes longer • Low Specific Heat = little heat needed to raise the temperature = quicker

23. High Specific Heat of Water • This means water can absorb a lot of heat without changing temperatures drastically. • Large bodies of water maintain a moderate temperature even when the air temperature changes drastically.

24. High Heat of Vaporization • Heat of Vaporization: amount of heat needed to vaporize a liquid • This makes evaporation a cooling process. • Water has a high heat of vaporization which means that when water evaporates it takes a lot of heat with it.

25. Water, Water Everywhere! • Water is one of the most common substances on the surface of the Earth. • Water covers about 71% of the planet • Exists as a solid (ice), liquid (water), or gas (vapor) • But less than 1% is drinkable

26. Distribution of Water on Earth Easily Accessible Fresh Water All Water Fresh Water

27. The Water Cycle • The total amount of water on Earth is constant. • But the water can move to different reservoirs and change phases. • A reservoir is a storage location for water (the atmosphere, oceans, lakes, glaciers, etc.) • Residence time is the amount of time that water stays in a given reservoir. • Energy from the sun drives the water cycle

28. The Water Cycle infiltration

29. Water Cycle • Go to http://www.hippocampus.org/Earth%20Science • Click on Environmental Science • Then choose Water Cycle

30. Hydrosphere Reservoirs: Atmosphere • Contains water vapor • Average residence time = 10 days Hydrosphere Reservoirs: Ice • Frozen water is found in the polar ice caps, glaciers, and icebergs. • The oldest ice sample identified had an estimated residence time of 900,000 years

31. Hydrosphere Reservoirs: Groundwater • Water that moves through the soil through the process of infiltration. Infiltration Water Table Saturated Zone (Permeable Layer) Impermeable Layer

32. Hydrosphere Reservoirs: Groundwater An aquifer is an underground layer of water-bearing permeable rock or unconsolidated materials (gravel, sand, or silt) from which groundwater can be extracted using a well.

33. Hydrosphere Reservoirs: Groundwater • Potential Threats to Groundwater • Overuse and depletion • Contamination • Improper wastewater management • Pharmaceutical and personal care products • Nitrates

34. Hydrosphere Reservoirs: Groundwater Hard vs. Soft Water • Hard water contains dissolved minerals (like calcium and magnesium) • Tastes good, BUT it can be damaging to plumbing and soaps don’t lather well. • Soft water contains almost no dissolved minerals (except sodium). • If it is too soft, then it doesn’t taste as good, but it is easier on the plumbing and works better for washing.

35. Hydrosphere Reservoirs: Lakes • Large bodies of surface water found on continents. Hydrosphere Reservoirs: Rivers & Streams • Account for a very small % of water, but are very important! • Carry water out to the ocean

36. Hydrosphere Reservoirs: Wetlands • Areas of land that are covered with a shallow layer of water for at least part of the year • Marshes-grassy wetlands • Swamps-wetlands that have trees and bushes • Importance: • Recharge groundwater • Filter water • Habitat for many birds and animals

37. Hydrosphere Reservoirs: Estuaries • The point where a river meets the ocean. • Contain a mix of fresh and salt water called brackish water. • Aquatic nurseries

38. Hydrosphere Reservoirs: Oceans • Salty because water (the universal solvent) dissolves chemicals from the soil and deposits them in the oceans. • Volcanoes release solid and gaseous materials that contribute. • And hydrothermal vents on the ocean floor release superheated ocean water from the earth.

39. Hydrosphere Reservoirs: Oceans • Oceans are critical to maintaining our climate • Oceans collect, mix, and circulate water, heat and carbon dioxide. • High Specific Heat, High Heat of Vaporization, and the unique density of water are critical in maintaining moderate temperatures on the Earth.

40. Average Residence Times

41. River Basins • River basins include the entire land surface drained by the various streams and creeks that flow downhill into one another, and eventually into one river. • The final destination of the water drained by a river basin is an estuary or an ocean. • A river basin sends all the water falling on the surrounding land into a central river and out to the sea.

42. River Basins • Everyone lives in river basin. • Our actions will affect water quality far from our homes because the water will travel across the land, into a river, and out to the ocean. • Topography determines the river basin. • Water flows downhill!