Water in Nature: Oceans, Rivers, and the Water Cycle
Water in Nature
Saltwater: Oceans and Seas
Most of the planet’s water (97.21%) is saltwater found in seas and oceans.
- An ocean is a vast body of water separating continents. The major oceans are the Pacific, Atlantic, and Indian Oceans. Together, they form the Southern Ocean surrounding Antarctica. The Pacific and North Atlantic connect to form the Arctic Ocean.
- Seas are extensions of the oceans closer to continents, like the Cantabrian Sea or the Caribbean Sea, which are part of the Atlantic Ocean.
Freshwater: Lakes and Rivers
Freshwater comprises only 2.79% of the total water on Earth. It’s distributed among lakes and rivers (0.02%), groundwater and soil moisture (0.62%), ice caps and glaciers (2.14%), and the atmosphere (0.01%).
Lakes are permanent bodies of water in depressions, fed by rain and rivers.
Rivers are continuous streams of water originating from wells, springs, rain, or melting snow. The amount of water a river carries is called its flow, which depends on the characteristics of its basin (the land area draining into the river). River flow changes throughout the year, creating a river regime:
- Rivers with a pluvial regime are primarily fed by rainfall. Their flow depends on the size of the basin and the amount and regularity of rainfall.
- Rivers in basins with consistent rainfall throughout the year will have abundant and regular flow.
- Rivers in basins with irregular rainfall will experience floods during the wet season and droughts during the dry season.
- Rivers with a nival regime are mainly fed by melting snow. These rivers have higher flow in spring and early summer and lower flow in winter.
The Work of Rivers
The force of moving water and the materials carried by streams and rivers gradually shape the landscape by eroding mountains and filling valleys and depressions. This process can take millions of years.
Rivers perform different tasks along their course, from their source (headwaters) to their mouth:
- Upper course: Erosion
- Middle course: Transportation
- Lower course: Sedimentation
The Water Problem
Water Scarcity
Only 2.79% of Earth’s water is freshwater, and most of it is locked up in glaciers and ice caps. Only 0.64% is readily available as drinking water (groundwater or surface water).
Water is a scarce resource, and demand is increasing. Since 1900, the world population has doubled, but water consumption has increased sixfold. Agriculture and industry are the biggest water consumers.
Uneven Water Consumption
It’s estimated that 65% of freshwater consumption goes to agriculture, 25% to industry, and only 10% to domestic use.
Developed countries have high per capita water consumption, while countries in Africa and Western Asia face water scarcity.
Due to pollution, a significant portion of available freshwater is contaminated. Water must be treated to become potable (safe for drinking).
Water on the Planet
Most of the Earth’s surface is covered by seas and oceans.
Continents and large islands divide the Earth’s major water bodies into five oceans: Pacific, Atlantic, Indian, Arctic, and Antarctic.
Movements of Seas and Oceans
Waves, Tides, and Currents
The waters of oceans and seas are constantly moving due to waves, tides, and currents.
Waves are ripples created by wind disturbing the surface of the water.
Tides are the periodic rise and fall of sea level caused primarily by the Moon’s gravitational pull on the oceans.
Ocean currents are like vast rivers flowing through the oceans.
The Sea’s Impact on the Coast
The action of water, especially waves and tides, shapes coastlines by eroding cliffs and causing them to recede.
River sediments carried to the sea are transported by coastal currents and deposited in sheltered areas, forming beaches, lagoons, and other coastal features.
Rivers of Europe
Rivers in Spain
In the Iberian Peninsula rivers are grouped into three areas,
as the sea or ocean in which flow:
Rivers of Cantabria. The rivers of this watershed are
are short and strong currents.
Rivers of the Atlantic. It is long rivers, with
numerous tributaries flowing.
Rivers in the Mediterranean area. Except in the case of the Ebro,
rivers are short, low and irregular flow
