WATER AS A RESOURCE GE: 340 (NOTES)

TOPIC 1: WATER AS A RESOURCE GE: 340 (NOTES)

Distribution of water on earth

•      Saline and fresh water distribution

•      Hydrological cycle

•      Reasons for uneven distribution of water

•      Water covers about 70% of Earth’s surface (Shakhashiri,2009).

 The Earth is often referred to as the "blue planet" because when viewed from space it appears blue

 

•      This blue color is caused by reflection from the oceans which contain the bulk of water.

Water is widely distributed on Earth as freshwater and salt water in the oceans. Water is contained in the ocean, atmosphere, icecaps, glaciers, underground sources, rivers and lakes.

•       Other small amount of water in the atmosphere, and inside the body of living organisms. (Your body is made up of 60% water)

•      According to the earth system models all these areas that contain water are the hydrological interconnected systems.

•      This fact of interconnectivity among the areas that contain water can be explained by the so called Hydrological cycle.

•      The global hydrological cycle explains the distribution of water as it moves as either a liquid, solid or vapor between the ocean, the atmosphere and the land.

•      The total amount of water in the cycle is always the same; no water is added or lost (The principle of mass/matter conservation).

 This is a good example of a closed system.

•      The hydrological cycle is powered by solar energy. The sun heats water from the ocean, lakes, rivers and the Earth’s surface. This water then evaporates into the atmosphere (Evaporation)

•       Additional water is drawn from the soil by plants, and is then evaporated into the atmosphere from leaves and stems   (transpiration).

•      As the air rises and the temperature drops, the moisture-laden air condenses (Condensation) forming clouds and eventually resulting in precipitation in the form of rain or snow.

•       Surface run-off makes its way back to the ocean via rivers. Other water seeps into the soil. This process is called infiltration

•      If the rock below the soil is permeable, then the water percolates the rock and is stored as groundwater.

•      As water passes through the hydrological cycle it is naturally cleaned through the following processes.

•       Distillation: happens when water evaporates, leaving impurities behind

•      Crystallization: occurs when ocean water freezes and creates pure water ice. Again, impurities are removed from the water naturally.

•      Filtration: The ground itself works as a filtering agent. When water moves through particles of sand or rock, larger contaminants get left behind.

•      Dilution: is when contaminants in water are made less dangerous by the addition of pure water. For example, a small pond with undrinkable water will be cleaner after a large amount of precipitation increases its pure water content.

•      Oxidation: in water breaks down organic materials, such as dead plants, animals and their waste products, into simple molecules.

 

UNEVEN DISTRIBUTION OF WATER ON THE EARTH’S SURFACE

Uneven distribution of water is caused by

•      The nature of rainfall of an area

•      The nature of surface bedrock which has an effect on the rate of infiltration

•      The nature of landscape.

•      Availability of water bodies. Water bodies normally help to speed up the rate of evaporation

•      Economic development and technological development.

 

GROUP QUESTIONS

1.If water is constantly being cleaned and recycled through the earth’s water cycle, why do we need to conserve it?

2.Using examples elaborate the contention that “water is unevenly distributed in time, space, quantity and quality in Tanzania”.

3.If 70% of the earth’s surface is covered by water. Do you think there is any need to conserve water? Why?