Hydrosphere

Water is all around us and is the molecule that makes life on Earth possible; we depend on water daily to hydrate us. The entirety of the planet's water is called the hydrosphere; amazingly, only a fraction of this is available for us to drink. This is because only 2.5% of the hydrosphere is freshwater, with the rest being saltwater in the oceans. Of this 2.5%, only a tiny fraction is available to humans, most stored in ice sheets, glaciers, or deep underground aquifers.

The definition of the hydrosphere

The hydrosphere encompasses all the water in the Earth's system; this includes water in the liquid, solid, and gas phases. Here are where you find water in each state:

• Liquid: water found in oceans, lakes, rivers, and estuaries is in a liquid state. Groundwater in aquifers and Soils is also in the liquid phase, and so is precipitation.

• Solid: icebergs, ice sheets, glaciers, snow, and hail are all water in the solid phase, that being ice. The entirety of the planet's ice is called the cryosphere.

• Gas: water in the gaseous phase refers to water vapour in The Atmosphere. Water vapour can form mist, fog, and clouds; sometimes, it is invisible in the air.

All these different forms of water can be described as reservoirs of the hydrosphere, with the most abundant reservoirs being oceans and water vapour in The Atmosphere.

Formation of the hydrosphere

Climate researchers have various theories about how the Earth gained water; most believe that asteroid impacts brought water to the Earth (these asteroids often contained vast amounts of ice that would have melted with increasing temperatures).

Other theories include water released from reactions between minerals in the Earth's crust and the consistent outgassing of this water into the atmosphere as water vapour (this would have taken much longer than asteroid impacts). Most scientists agree that a combination of these events caused the formation of the hydrosphere.

The characteristic of the hydrosphere

Here are some essential characteristics of the hydrosphere that you should know:

• Solar energy from sunlight provides the power for water molecules to transition between different states.

• The hydrosphere surrounds the Earth as water vapour.

• The density of water changes with heat and salinity.

• Freshwater from melting ice will reduce the density of salty waters.

• Temperature decreases at higher latitudes as there are fewer particles at lower pressures (see hint).

• The hydrosphere is an essential part of the Earth's system that sustains life.

• Water is consistently cycling between the Lithosphere, biosphere, and atmosphere.

The water cycle

The water cycle is the circulation of water between the atmosphere, Lithosphere, and biosphere. This circulation of the planet's water maintains the hydrosphere and makes water available to ecosystems and human populations. Here are the various stages of the water cycle.

Interaction between the hydrosphere and atmosphere

The first two stages of the water cycle, evaporation and condensation, involve interactions between the Earth's hydrosphere and atmosphere.

Evaporation

Infrared radiation (solar energy) from the sun warms water molecules and causes them to move around faster and gain more energy. Once they have sufficient energy, the intermolecular forces between them will break, and they will transition to the gaseous phase forming water vapour, which then rises into the atmosphere. Evapotranspiration concerns all the water vapour evaporated from Soils and the stomata of plant leaves in transpiration.

Condensation

Water vapour molecules will rise to cooler regions of the atmosphere (they are less dense than air) and form clouds. These clouds will move around the atmosphere with winds and air currents. Once the water vapour molecules become cold enough, they will not have sufficient energy to remain as gaseous molecules. They will be forced to develop intermolecular bonds with the molecules around them and form water droplets. Once these droplets are heavy enough to overcome the cloud's updraft, they will transform into precipitation.

Interactions between the hydrosphere and the biosphere

Precipitation, infiltration, and runoff involve interactions between the Earth's hydrosphere and biosphere.

Precipitation and infiltration

Condensed water droplets will fall as rain and seep into grounds and soils. This process is called infiltration and is much more efficient in porous materials like mud and soils. Water that runs far into the ground will be stored in aquifers that eventually rise to the surface to form springs.

Runoff

Runoff is the natural process by which water travels downwards to sea level. Gravitational forces are the driving mechanisms behind runoff. Water transportation by runoff is essential in most biogeochemical cycles in transporting nutrients from the lithosphere to the hydrosphere.

Figure 1: The Water Cycle, via Wikimedia Commons

Human impacts on the hydrosphere

The stability of the hydrosphere is pivotal in providing a consistent freshwater source for the human population. However, human activity is having a significant effect on the hydrosphere. Here's how:

Agriculture

Global agriculture is constantly expanding. With an ever-growing global population and increasing demands for food with higher consumption rates, reliable agricultural output is essential. To provide this, farmers will employ intensive methods that require massive amounts of water for heavy machinery and complex temperature regulation.

Land use and exploitation

Figure 2: Dams block water flow and disrupt aquatic ecosystems. via Wikimedia Commons

Pollution

Industrial and urban runoff is a massive threat to water bodies. The discharge will contain many poisonous chemicals.

Climate change

Human-induced climate change is another way we are negatively impacting the hydrosphere. The release of carbon dioxide and other Greenhouse Gases from:

• fossil fuel combustion,

• agriculture,

• deforestation,

• and mass production.

This is adding to the greenhouse effect and warming the Earth's system.

Water vapour is a greenhouse gas, too, so it amplifies this effect and causes more global warming and evaporation in a positive feedback mechanism.