HYDROSPHERE
DEFINITION
In physical geography, the term hydrosphere (Greek hydro means "water") describes
the collective mass of water found on, under, and over a planet's surface. The Earth's
hydrosphere consists chiefly of the oceans, but technically includes inland seas, lakes, rivers,
and underground waters.
The abundance of water on Earth is a unique feature that
distinguishes our "blue planet" from others in the solar system. Approximately 70.8
percent of the Earth is covered by water and only 29.2 percent is terra firma. The average
depth of the Earth's oceans is 3,794 m (12,447 ft)—more than five times the average height of
the continents. The mass of the oceans is approximately 1.35 × 1018 tons, or about 1/4400 of
the total mass of the Earth.
The hydrosphere plays a key role in the development and sustenance of life. It
is thought that the earliest living organisms probably emerged in a watery soup. In addition,
each human life begins in the watery environment of its mother's womb, our cells and tissues
are mostly water, and most of the chemical reactions that are part of life's processes take
place in water.
STATES OF WATER
Water is the only substance on Earth that is present in all three states of matter – as a
solid, liquid or gas. Along with that, Earth is the only planet where water is present in all three
states. Because of the ranges in temperature in specific locations around the planet, all three
phases may be present in a single location or in a region. The three phases are solid (ice or
snow), liquid (water), and gas (water vapor).
On Earth, liquid water exists on the surface in the form of oceans, lakes and rivers. It
also exists below ground—as groundwater, in wells and aquifers. Water vapor is most visible
as clouds and fog.
The frozen part of Earth's hydrosphere is made of ice: glaciers, ice caps and icebergs.
The frozen part of the hydrosphere has its own name, the cryosphere.
DISTRIBUTION AND QUANTITY OF EARTH’S WATERS
Earth’s oceans contain 97% of the planet’s water, so just 3% is fresh water, water with
low concentrations of salts. Most fresh water is trapped as ice in the vast glaciers and ice
sheets of Greenland. A storage location for water such as an ocean, glacier, pond, or even the
atmosphere is known as a reservoir. A water molecule may pass through a reservoir very quickly or may remain for much longer. The amount of time a molecule stays in a reservoir is
known as its residence time.
Distribution of the Earth's Water
Credit: Timothy Bralower
The distribution of water on the Earth’s surface is extremely uneven. Only 3% of water on the
surface is fresh; the remaining 97% resides in the ocean. Of freshwater,
69% resides in glaciers, 30% underground, and less than 1% is located in lakes, rivers, and
swamps. Looked at another way, only one percent of the water on the Earth’s surface is usable
by humans, and 99% of the usable quantity is situated underground.
WATER CYCLE
The water cycle, also known as the hydrologic cycle or the hydrological cycle,
describes the continuous movement of water on, above and below the surface of the Earth.
The mass of water on Earth remains fairly constant over time but the partitioning of the water
into the major reservoirs of ice, fresh water, saline water and atmospheric water is variable
depending on a wide range of climatic variables. The water moves from one reservoir to
another, such as from river to ocean, or from the ocean to the atmosphere, by the physical
processes of evaporation, condensation, precipitation, infiltration, surface runoff, and
subsurface flow. In doing so, the water goes through different forms: liquid, solid (ice)
and vapor. The water cycle involves the exchange of energy, which leads to temperature changes.
When water evaporates, it takes up energy from its surroundings and cools the environment.
When it condenses, it releases energy and warms the environment. These heat exchanges
influence climate.
The evaporative phase of the cycle purifies water which then replenishes the land with
freshwater. The flow of liquid water and ice transports minerals across the globe. It is also
involved in reshaping the geological features of the Earth, through processes
including erosion and sedimentation. The water cycle is also essential for the maintenance of
most life and ecosystems on the planet.
IMPORTANCE OF HYDROSPHERE
We rarely think about the role of the planet that keeps us alive and take hydrosphere for
granted. The major importance of hydrosphere is that water sustains various life forms and
plays an important role in ecosystems and regulating the atmosphere. Hydrosphere covers all
water present on the Earth surface. It involves saltwater, freshwater and frozen water along
with groundwater and water in the lower levels of the atmosphere.
Following are the functions of a hydrosphere.
Water is the most important part of living cells
Every cell in living organism is built up of about 75% of water, hence allows the cell to
function appropriately. Cells would not able to carry out normal functions and life cannot
exist without water. Human needs
Humans use water in many ways. Drinking water is the most obvious use, but it is also used
for domestic purpose like washing and cleaning, and in industries. Water is also utilized in
generating electricity through hydropower.
Water provides habitat
Hydrosphere provides place for many plants and animals to live. Many gasses like CO2, O2,
nutrients like ammonium and nitrite(NO–2) as well as other ions are dissolved in water. The
presence of these substances is essential for life to exist in water.
Regulate Climate
The water’s specific heat is its unique characteristics. This indicates that water takes a lot
of time to heat up and a lot of time cool down. It helps in regulating temperatures on earth as
they stay in a range which is acceptable for life on earth to exist.
THREATS OF HYDROSPHERE
It should be clear by now that the hydrosphere plays an extremely important role in the
survival of life on Earth and that the unique properties of water allow various important
chemical processes to take place which would otherwise not be possible. Unfortunately for us
however, there are a number of factors that threaten our hydrosphere and most
of these threats
are
because
of
human
activities.
We
are
going
to
focus
on
two
of
these issues: pollution and overuse and look at ways
in which these problems can possibly be overcome.
1.
Pollution
Pollution of the hydrosphere is a major problem. When we think of pollution, we
sometimes only think of things like plastic, bottles, oil and so on. But any chemical that is
present in the hydrosphere in an amount that is not what it should be is a pollutant. Animals
and plants that live in the Earth's water bodies are specially adapted to surviving within a
certain range of conditions. If these conditions are changed (e.g. through pollution), these
organisms may not be able to survive. Pollution then, can affect entire aquatic ecosystems.
The most common forms of pollution in the hydrosphere are waste products from humans
and from industries, nutrient pollution e.g. fertiliser runoff which causes eutrophication (an
excess of nutrients in the water leading to excessive plant growth) and toxic trace elements
such as aluminium, mercury and copper to name a few. Most of these elements come from
mines or from industries.
2.
Overuse of water
We mentioned earlier that only a very small percentage of the hydrosphere's water is
available as freshwater. However, despite this, humans continue to use more and more water
to the point where water consumption is fast approaching the amount of water that
is available. The situation is a serious one, particularly in countries such as South Africa which are naturally dry and where water resources are limited. It is anticipated that water
supplies in South Africa will no longer be able to meet the growing demand for water in this
country. This is partly due to population growth, but also because of the increasing needs of
industries as they expand and develop.
As populations grow, so do the demands that are placed on dwindling water resources.
While many people argue that building dams helps to solve this water-shortage problem,
there is evidence that dams are only a temporary solution and that they often end up doing far
more ecological damage than good. The only sustainable solution is to reduce the demand for
water, so that water supplies are sufficient to meet this.
It is important to realise that our hydrosphere exists in a delicate balance with other
systems and that disturbing this balance can have serious consequences for life on this planet.
