The Water Cycle

Water is essential for all living things. It is constantly entering and exiting organisms in many ways as it moves through the ecosystem.

Water is constantly transforming from a liquid to a gas (water vapor) and sometimes a solid.
- Molecules can diffuse from the surface of bodies of water into the air and vice versa
- Many organisms drink water as a liquid and breathe it out as water vapor
Changes in the water cycle can have drastic effects on living things

Water Movement

The mass of all living things is mostly made up of water. It moves from the environment through organisms and back again.

Bodies of water are the biggest abiotic reservoirs
Water evaporates into the atmosphere
- It condenses to form water droplets in clouds
- Then it can fall as some form of precipitation (rain, snow, sleet, etc)
Precipitation can fall in one of two places
- back in bodies of water (cycle complete)
- on land
Water on land can either
- runoff into bodies of water (cycle complete)
- soak into the soil (infiltration)
Water in the soil is taken up by plants through root uptake
- it can also sink into aquifers (underground bodies of water in porous rock)
Plants use water for photosynthesis, but excess is given off through transpiration.
- Transpiration is the evaporation of water from a plant back into the atmosphere (cycle complete)

Humans disturb the water cycle in many ways.

Irrigation for crops can take too much water from rivers, lakes and aquifers.
- That increases transpiration and the wind carries the water away from that ecosystem
Clear cutting forests or removing too many plants increases runoff because roots don't hold the soil.
- Too much runoff causes soil erosion which makes it more difficult to regrow the plants