Water Cycle

The global water cycle is one of the major drivers and reservoirs for other geochemical cycles on the Earth. The water cycle describes the sum of processes operative in the hydrosphere, a dynamic mass of liquid continuously on the move between the different reservoirs on land and in the oceans and atmosphere. The hydrosphere includes all the water in oceans, lakes, streams, glaciers, atmosphere, and groundwa-ter, although most water is in the oceans. The hydro-logic, or water, cycle encompasses all of the changes, both long- and short-term, in the Earth's hydrosphere. Heat from the Sun powers the hydrologic cycle, causing water to change its state through evaporation and transpiration. Water is both a means of transport for other chemical components and a reactive agent that removes these other elements from rocks and soils on the continents and moves them into other reservoirs in the oceans.

The water cycle can be thought of as beginning in the ocean, where energy from the sun causes surface waters to evaporate, changing from the liquid to the gaseous states. Evaporation takes heat from the ocean and transfers this heat into the atmosphere. An estimated 102 cubic miles (425 cubic km3) of water evaporate from the ocean each year, leaving the salts behind in the ocean. The water vapor then condenses into water droplets in clouds and eventually falls back to the Earth as precipitation. Most (92 cubic miles; 383 cubic km3) falls directly back into the ocean, but about 26 cubic miles (108 km3) of precipitation falls as rain or snow on the continents, transforming salty water of the oceans into freshwater on the land. Nearly three-fourths of this water (17 cubic miles, or 71 cubic km/yr) evaporates back to the atmosphere or is aided by the transpiration from plants, returning the water back to the atmosphere. The other estimated 10 cubic miles (42 km3) per year of water runs across the surface, some merging together to form streams and rivers that flow eventually back into the ocean, and other parts seeping into the ground to recharge the groundwater system. Humans now intercept approximately half of the fresh surface water for drinking, agriculture, and other uses and make a significant impact on the natural hydrological cycle. Water that seeps into the groundwater system is said to infiltrate, whereas water that flows across the surface is called runoff.

Water in the atmosphere is one of the major greenhouse gases that help to regulate global temperature and climate. Changes in the water content in the atmosphere can change the erosion rate of different chemical elements on land, the evaporation rate from the ocean, and the balance between many other geochemical cycles.

Continue reading here: SODIUM cycle

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  • ashleigh
    What is plate tectonics in relation to water cycle?
    3 years ago
  • valdemar
    How water from plant's is returned back to the surface through plate tectonics?
    4 years ago