Biogeochemical Cycle - 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 waste 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 vapour.

The Water Cycle

1. Evaporation:

The water cycle starts with evaporation. This happens when the Sun heats up water from oceans, lakes, rivers, and even plants. The heat turns the water into water vapor, which is an invisible gas. This water vapor rises up into the air because it is lighter than liquid water.

2. Condensation:

As water vapor rises into the atmosphere, it cools and, when cool enough, transforms back into tiny droplets of liquid water, forming clouds through condensation, which are composed of millions of these tiny droplets or ice crystals.

3. Precipitation:

Cloudwater droplets become too heavy to stay in the air, causing them to fall back to Earth as precipitation. Precipitation can be rain, snow, sleet, or hail, depending on atmospheric temperature and conditions.

4. Infiltration and Collection

 Infiltration: (Water soaking into the ground and moving downward)

Infiltration is the process where rain or snow soaks into the ground, replenishing underground groundwater supplies. It is crucial for maintaining soil moisture and providing water for plants.

Collection: (Gathering of water in any location, whether it’s on the surface or underground)

Precipitation causes water to accumulate on Earth, flowing into rivers, streams, oceans, and lakes. Some seeps into the ground, becoming groundwater. 

Infiltration and collection both are crucial for maintaining soil moisture and providing water for plants.

5. Transpiration:

Transpiration is a special part of the water cycle that happens in plants. Plants take in water from the soil and use it to grow. They release some of this water into the air through tiny openings in their leaves as water vapor, which then rises into the atmosphere just like in evaporation.

6. Runoff:

Rainfall on land causes runoff, which flows over the ground, filling rivers and lakes, and eventually returning to the oceans. It can also transport water to underground reservoirs.