volume of water stored in the soil that is accessible to plant roots
-a "savings account" of water that is recharged and utilized
-only water accessible to plants
is generally accessible to plant roots because it is held against the pull of gravity in the soil by hydrogen bonds between water molecules, which causes surface tension.
inaccessible to plants, molecule-thin layer that is tightly bound to each soil particle by the hydrogen bonding of water molecules.
the point at which plants are no longer able to extract moisture from the soil because the capillary water is all used up or evaporated
amount of water available for plants to use after some water drains from larger pore spaces
any water surplus in the soil body after the soil becomes saturated from a precipitation event
Water Balance Equation
Percip = ACTET + Surplus +- change in STRGE
Rock layer that is permeable to groundwater flow adequate for wells and springs.
bounded above and below by impermeable layers of rock or sediment.
has a permeable layer on top and an impermeable one beneath
a possible effect of water removal from an aquifer is that the aquifer will lose its internal support
Saltwater encroachment or intrusion is the movement of saltwater into subsurface aquifers previously occupied by freshwater. Frequently, this occurs as freshwater from coastal aquifers is displaced as a result of the shoreward movement of seawater.
Instream Use of water
use stream water in the channel without removing it: examples include navigation, wildlife and ecosystem preservation, waste dilution and removal, hydroelectric power production, fishing, and recreation
remove water from the supply, use it, then return it to the same supply.
-industry, agriculture, and steam-electric power generation.
a portion is consumed
removes water from a stream, doesn't return it
-can't be used second or third time
-ex: water vaporized in electric plants
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