Soil Water
Hydrologic Cycle
Water continuously moves among the earth’s biosphere, atmosphere, lithosphere, and hydrosphere; this cycling of water is called the hydrologic cycle, also known as the water cycle (Figure 7.1). The hydrologic cycle involves several reservoirs and fluxes. Reservoirs include various reservoirs such as atmosphere, oceans, lakes, rivers, soils, glaciers, snow fields, and groundwater. Fluxes (i.e., movement) of water in the hydrologic cycle include evaporation, transpiration, condensation, precipitation, runoff, infiltration, percolation, groundwater flow, sublimation, and melting. The driving force for the hydrologic cycle is the sun, which provides the energy needed for evaporation. Water changes from a liquid state to a gaseous state as it evaporates from the oceans, lakes, streams, and soil.
Fluxes
There are numerous different ways that water moves across the planet in the water cycle. All of these different types of movement are important in maintaining water levels in certain locations around the globe. Evaporation is the transfer of water from a liquid to a gas from the surface to the atmosphere. Transpiration is the evaporation of water from plants through stomata. Condensation (the opposite of evaporation) is the change of water from its gaseous form (water vapor) into liquid water. In the hydrologic cycle, transport is the movement of water through the atmosphere, specifically from over the oceans to over land. Some of the Earth’s moisture transport is visible as clouds, which themselves consist of ice crystals and/or tiny water droplets.
Click on the following topics for more information on soil water.
