Chapter 12

Earth’s waters

HydrosphereThe part of the earth that includes the

oceans, seas, rivers, lakes and springs, as well as subsurface waters, ice caps and glaciers.

Fresh Waters

Seawater

Groundwater

Surface Water

Ocean and Seas

Fresh WatersFresh waters

- about 97 percent of the earth’s water are stored in the earth’s oceans. All other waters that is fit for human consumption and agriculture is called fresh water.

The basic source of fresh water is precipitation, but not all precipitation ends up as part of the freshwater supply.

Water moving across the surface is called runoff. Runoff begins as rain accumulates in thin sheets of water that move across the surface of the land.

These sheets collect into a small body of running water is called stream. A stream is defined as any body of water that is moving across the land.

Fresh waters

Runoff

Water that soaks into the ground moves down to a saturated zone where it is called groundwater.

Groundwater moves through sediments and rocks beneath the surface, slowly moving downhill.

An intermittent stream is one in which the source of groundwater is in low supply and flow only part of the time.

The amount of rainfall that becomes runoff or groundwater depends on the following factors:

1. The type of soil in the surface2. how dry the soil is

3. the amount and type of vegetation4. the slope of the land

5. if the rainfall is a long, gentle one or a cloudburst

Surface WatersThe land area drained by a stream is known as the

stream’s drainage basin or watershed.

A line called divide separated two adjacent watersheds.

A continental divide separated river systems that drain into opposite sides of a continent.

A smaller body of standing water is called a pond, and one of much larger size is called a lake.

A natural pond or lake created by building dam is called a reservoir.

watershed

reservoirsTaal lake

It is used for: 1. Water storage- A reservoir for water storage is kept as full as

possible to store water.

2. Flood control- A reservoir for flood control requires low water level in order to catch runoff, preventing waters from flooding the land.

3. Generating electricity- A reservoir used to generate electricity requires the release of water from the reservoir.

The water of streams, ponds, lakes and reservoirs are sources of fresh water and is collectively called surface water.

Groundwater

Precipitation (rain or snow) that sinks into the ground forms the groundwater reservoir.

The porosity of the soil or sediment.

Permeability of the soil.

The amount of precipitation, which makes its way into the ground, depends on two factors:

The ability of a given sample of sediment to permit water to pass through them is a measure of its permeability.

Porosity is the total amount of pore spaces in a given sample of sediments.

The amount of groundwater available in a given place depends on:

present and past climate

slope of the land

Porosity and permeability of the sediments beneath the surface.

Water from the zone of saturation is considered to be ground water.

The surface boundary between the zone of saturation and the zone above is called the water table.

A hole that is dug or drilled through the earth to the water table is called a well.

Whenever the water table reaches the surface of the ground, a body of water collects. Thus are formed the springs, lakes and swamps.

Groundwater

well.

Spring Swamp

pond

The depth of the water table differs from place to place and depends upon several factors:

1. • The thickness of the porous mantle

2. • the slope of the rock

3. • the amount of rainfall

4. • the vegetation cover.

An aquifer is a layer of sand, gravel, sandstone, or other highly permeable material beneath the surface that is capable of producing water.

Groundwater that is under such a confining pressure is in an artesian aquifer.

“Artesian” refers to the pressure and groundwater from an artesian well rises above the top of the aquifer by not necessarily to the surface.

Fresh Water as Resource

Water is a very important resource because it is used for many purposes – biological, domestic, agricultural, and industrial purposes.

Surface water contains more sediment, bacteria and possible pollutants than groundwater because it is more active and is directly exposed to the atmosphere.

This means that surface water requires filtering to remove suspended particles, treatment to kill bacteria and sometimes processing to remove pollution.

As human population grows and new industries develop, more and more demands are placed on the surface water supply, which has already been committed to other uses, and on the diminishing supply of groundwater.

Possible sources of fresh water that can answer problems of water supply is the recycling of waste water and turning to the largest supply of water in the world, the ocean.

About 90% of the water used by industries is presently dumped as waste product.

Water PollutionAny alteration in the original quality of the water brought about

by the introduction of organic substances or a change in the temperature or water is called water pollution.

PollutantsSediments -Surface waterWastes arising out of human activity (sewage waste, industrial effluents, litter, animal manure, insecticides and mine tailing)Inorganic water pollutants (mineral acids, inorganic salts and finely divided metals or metal compounds)mine drainage (sulfuric acid, soluble iron compounds)organic water pollutants (oxygen-demanding compounds from: sewage, both animal and domestic, industrial wastes from food processing plants and effluents from slaughterhouses and meatpacking plants)Synthetic organic compounds (detergents, household cleaning products, new synthetic pesticides such as DDT, dieldrin and chordane, synthetic industrial chemicals of a wide variety and waste from the manufacture of these products)

mine drainage

Water Pollution

Inorganic water pollutants

The most abundant element involved in this type of pollutant is carbon which is easily broken down or decayed by bacteria in the presence of oxygen.

 These pollutants increase the water’s acidity, salinity,

toxicity or radioactivity.

Increased acidity of water may lead to the destruction of aquatic life, damage to agricultural crops, and excessive corrosion of plumbing systems, boats, and related structures.

Sources of Salinity:industrial effluents containing inorganic salts

water used as irrigation that dissolves large amounts of minerals from soil

salt brines released from mines or oil wells, and

tidal flow from the sea

Thermal water pollution originates with the practice of using water as coolant in many industrial processes and returning it thermally enriched to the original sources.

Heat is considered a water pollutant for the following reasons:

it reduces the solubility of oxygen in water

The higher water temperature may have a direct detrimental effect in fish and aquatic life by changing their physical environment.

In organic salts such as phosphates and nitrates are plant nutrients and their enrichment in water is known as eutrophication.