The Hydrologic Cycle: Understanding Water's Role in the Earth's Systems, Essays (university) of Physics

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The Hydrologic Cycle

Chapter 6

 The Hydrosphere also known as the water sphere

includes all the earth water that is found in oceans,

lakes, rivers, groundwater and in air.

 The hydrosphere interacts with, and is influenced

by, all the other spheres of the earth, namely:-

Biosphere – the part of the Earth, including air,

land, and water within which life

occurs.

Lithosphere – includes the crust and the

uppermost mantle.

Atmosphere – is a layer of gases surrounding

the Earth that is retained by the

Earth's gravity.

The Hydrosphere

 Water follows the rule “Energy flows, matter cycles.”

 All water systems are connected through a series of processes that continuously move water around the Earth called the water cycle.

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The Water Cycle

 Evaporation is a phase change of water from a liquid form into a gas form.  Water moves from a surface body, such as a lake, to the atmosphere.

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 Condensation is the collection of water as droplets on a cold surface.

• Evaporated water condenses into clouds as it loses heat in the upper troposphere.

 Precipitation is water falling back to the ground as snow, rain, sleet, or hail.

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 When rainwater first hits dry soil, it will percolate, or move downward through spaces between soil particles.

 When soil is fully saturated, water will flow over the surface, a process called runoff.

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Runoff from a sugar cane field, Queensland, Australia.

 Canopy interception is the precipitation that is intercepted by plant foliage and eventually evaporates back to the atmosphere rather than falling to the ground.  Run-off includes the variety of ways by which water moves across the land. This includes both surface run-off and channel run-off  Percolation/Infiltration is the flow of water from the ground surface into the ground. Once infiltrated, the water becomes soil moisture or groundwater.  Subsurface Flow /Seepage is the flow of water underground , in the aquifers. Subsurface water may return to the surface (eg. as a spring or by being pumped) or eventually seep into the oceans. Groundwater tends to move slowly, and is replenished slowly, so it can remain in aquifers for thousands of years.  Sublimation is the state change directly from solid water (snow or ice) to water vapour.  Advection is the movement of water — in solid, liquid, or vapour states — through the atmosphere. Without advection, water that evaporated over the oceans could not precipitate over land.

The Hydrologic Cycle or the Water Cycle

 The majority of Earth’s water is in the oceans, and

too salty for drinking or irrigation.

 About 3% is freshwater, water that is relatively

free from salts.

• The largest accessible source of freshwater is

groundwater beneath the surface that resides

in pores in soil and rock.

• Only about 1% is surface water, such as lakes,

rivers, and ponds.

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Water Resources

 Wells that enter unconfined aquifers are called water table or groundwater wells.

 Wells that enter confined aquifers are called artesian wells.

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Groundwater well used for irrigation in Jaffna, India. Image from IWMI.org.

Oceans – 95%

Ice caps/Glaciers – 2%

Groundwater and soil water – 3%

 Soil water - water held in pore spaces between soil particles

which is partially void of water.

 Groundwater – earth material is saturated with water

throughout the year. It is also water that is flowing within

aquifers below the water table. An aquifer is an

underground formation of permeable rock or loose

material which can produce useful quantities of water when

tapped by a well.

Surface water – 0.02%

This is water in rivers , lakes or fresh water wetlands. Surface

water is naturally replenished by precipitation and naturally lost

through discharge to the oceans, evaporation, and sub-surface

seepage

Atmospheric water – 0.001%

Water Resources

 Nonpoint source pollution comes from multiple small

sources, such as cars leaking oil, fertilizer runoff from

lawns, etc.

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Algae bloom, Maumee River, Toledo, Ohio.

End

Traffic and Transport

Air pollution The transport system makes a significant contribution to air pollution. The following is a list contribution by various chemicals emitted during the consumption phase

Environmental problems caused by such emissions are:

• acidification – primarily nitrogen oxides and sulphur dioxides
• photochemical smog – hydrocarbons, nitrogen oxides and sulphur dioxides
• health problems – carbon monoxide and aerosols
• climate change – the greenhouse gas carbon dioxide

Chemical emitted Percentage (%) to total chemical emission CO 70 NOx 60 CxHy 45 CO 2 15 SO 2 15 Aerosols 30