How does water move from the hydrosphere to the biosphere?

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Water and the atmosphere
Water and the biosphere, hydrosphere and geosphere
Activity idea
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General nature of the cycle
How does water get to the biosphere?
How does water move from the atmosphere to the biosphere?
How does water move from geosphere to hydrosphere?
How do the hydrosphere and biosphere interact to move water through the water cycle?

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Concepts
Citizen science
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Glossary
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The Earth has a finite amount of water. The water that is here today is the same water that will be here in 20 or even 20 million years’ time. So, if all living things use water, how is it that we don’t use up all our water? The answer is that water is constantly recycled through the Earth’s system through a process called the water cycle.

The water cycle encompasses a number of processes that circulate water through the Earth’s subsystems. Water evaporates from within soils and through vegetation and from bodies of water (such as rivers, lakes and oceans). This evaporated water accumulates as water vapour in clouds and returns to the Earth as rain or snow. The returning water falls directly back into the oceans, or onto land as snow or rain. It soaks into the soil to move into the groundwater or runs off the Earth’s surface in streams, rivers and lakes, which drain back into the oceans. The water may be taken up by plants and returned to the atmosphere through processes like transpiration and photosynthesis. Water may also be returned to the atmosphere through the combustion of plants in fossil fuel.

Water and the atmosphere

Water enters the atmosphere through evaporation, transpiration, excretion and sublimation:

Transpiration is the loss of water from plants (via their leaves).
Animals excrete water by respiration and by passing urine.
Sublimation is when ice or snow transforms directly into water vapour without going through a liquid phase (i.e. they do not melt).

Water commonly occurs in the atmosphere in the form of water vapour. If it cools down, it can condense, accumulating in clouds. As the clouds grow, they become heavier and can fall back to the Earth as precipitation (rain, snow, hail or sleet) or re-evaporate back into vapour.

Water and the biosphere, hydrosphere and geosphere

When water returns to Earth, it can either enter the hydrosphere or the geosphere.

It can enter the hydrosphere by falling onto bodies of water or falling onto the ground. When it rains, water falling onto the ground can move in two ways – it can run off the surface of the ground and enter streams and rivers, or it can seep into the ground and enter the ground water. This second process is called infiltration – water moves through pore spaces between soil particles or rocks.

Once the water is in the hydrosphere or geosphere, it can be used by living things. Plants can take water from the soils, and animals can drink water from rivers and lakes or eat plants. Even microbes deep in the ground live in tiny films of water surrounding rocks. The water will then stay in the biosphere until released through evaporation, transpiration, excretion, decay, respiration and combustion and the whole process begins again.

It may stay in the hydrosphere or geosphere for a long time (such as in aquifers) or it may very quickly return to the atmosphere.

These processes that transform and transfer water within the Earth’s system occur continuously over time but at different rates in different places.

Activity idea

Water cycle models use simple materials to observe the interactions along the water cycle. It’s one of many activities featured in the interactive Learning about the water cycle.

Published 2 June 2009 Referencing Hub articles

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General nature of the cycle

The present-day water cycle at Earth’s surface is made up of several parts. Some 496,000 cubic km (about 119,000 cubic miles) of water evaporates from the land and ocean surface annually, remaining for about 10 days in the atmosphere before falling as rain or snow. The amount of solar radiation necessary to evaporate this water is half of the total solar radiation received at Earth’s surface. About one-third of the precipitation falling on land runs off to the oceans primarily in rivers, while direct groundwater discharge to the oceans accounts for only about 0.6 percent of the total discharge. A small amount of precipitation is temporarily stored in the waters of rivers and lakes. The remaining precipitation over land, 73,000 cubic km (17,500 cubic miles) per year, returns to the atmosphere by evaporation. Over the oceans, evaporation exceeds precipitation, and the net difference represents transport of water vapour over land, where it precipitates as rain or snow and returns to the oceans as river runoff and direct groundwater discharge.

The various reservoirs in the water cycle have different water residence times. Residence time is defined as the amount of water in a reservoir divided by either the rate of addition of water to the reservoir or the rate of loss from it. The oceans have a water residence time of 3,000 to 3,230 years; this long residence time reflects the large amount of water in the oceans. In the atmosphere the residence time of water vapour relative to total evaporation is only about 10 days. Lakes, rivers, ice, and groundwaters have residence times lying between these two extremes and are highly variable.

There is considerable variation in evaporation and precipitation over the globe. In order for precipitation to occur, there must be sufficient atmospheric water vapour and enough rising air to carry the vapour to an altitude where it can condense and precipitate. Precipitation and evaporation vary with latitude and their relation to the global wind belts. The trade winds, for example, are initially cool, but they warm up as they blow toward the Equator. These winds pick up moisture from the ocean, increasing ocean surface salinity and causing seawater at the surface to sink. When the trade winds reach the Equator, they rise, and the water vapour in them condenses and forms clouds. Net precipitation is high near the Equator and also in the belts of the prevailing westerlies, where there is frequent storm activity. Evaporation exceeds precipitation in the subtropics, where the air is stable, and near the poles, where the air is both stable and has a low water vapour content because of the cold. The Greenland Ice Sheet and the Antarctic Ice Sheet formed because the very low evaporation rates at the poles resulted in precipitation exceeding evaporation in these local regions.

How does water get to the biosphere?

Chemical elements and water are constantly recycled in the ecosystem through biogeochemical cycles. During the water cycle, water enters the atmosphere by evaporation and transpiration, and water returns to land by precipitation.

How does water move from the atmosphere to the biosphere?

The water cycle shows the continuous movement of water within the Earth and atmosphere. It is a complex system that includes many different processes. Liquid water evaporates into water vapor, condenses to form clouds, and precipitates back to earth in the form of rain and snow.

How does water move from geosphere to hydrosphere?

How do the hydrosphere and biosphere interact to move water through the water cycle?

For example, rain (hydrosphere) falls from clouds in the atmosphere to the lithosphere and forms streams and rivers that provide drinking water for wildlife and humans as well as water for plant growth (biosphere). River action erodes banks (lithosphere) and uproots plants (biosphere) on the riverbanks.