Honors Environmental Earth Science - (Soil and Groundwater)

porosity

amount of void space or volume of empty space in rock and sediment

How can soil particles be rounded

rounded soil particles were rounded by water movement

How can soil particles be angular

angular soil particles did not come in contact with running water

"well sorted" soil

particles are all about the same size

"poorly sorted" soil

mixture of different sized particles

poorly sorted soil has….

smaller soil particles fill in the voids in between larger soil particles

sorting

distribution of grain sizes in sediment deposit

sorting index

quantitative measure used to describe the degree of sorting in soil or sediment

poorly sorted =

lower porosity

angular soil has =

lower porosity

permeability is the…

the rate at which water (or fluid) is able to flow through empty space

shape index ;

shows if particles are round or angular

higher porosity = ?

high permeability

soil porosity ;

amount of empty space within a soil

what determines how soils interact with water, roots and soils

soil porosity

soil texture ;

proportion of sand, silt, and clay, and size, shape, and connectivity of pores

soil structure ;

how particles clump together

how is porosity usually expressed?

as a percentage of total soil volume

magropores ;

large pores that drain water and allow airflow

micropores ;

small pores that store water

formula for porosity added to soil cylinder

(volume of water cm^3/volume of soil cm^3) x 100

capillary water ;

portion of water that is held in the small pores of soil by surface tension

the water that remains in the micropores forms thin films around soil particles and is available for plant roots to absorb

capillary water

what determines soils ability to hold capillary water

its texture and structure

the amount of water retained on soil particles after gravity has drained out whatever it can (in test tube) is known as :

capillary water

what is capillary water due to?

the combined effects of adhesion and cohesion

adhesion ;

when water sticks to the sides of soil particles

cohesion ;

when water sticks to itself via hydrogen bonding

formula for capillary water

((volume of water added to soil - water drained out and collected) / total volume of soil ) x 100

soil water permeability ;

measure of how easily water can move through soil pores

what determines soil water permeability?

the size of pores between soil particles and how well those pores are connected

soils with large continuous pore =

allows water to pass through quickly

soils with many tiny pores =

slow movement of water

high permeability

water drains rapidly

effects of high permeability

reduces water logging and makes soils prone to drought because they cannot hold water for long

low permeability

water infilrates slowly

effects of low permeability

causes puddling or runoff at surface which may lead to root oxygen shortages if soil becomes saturated

what factors affect soil permeability?

soil texture, structure, organic matter, content, and compaction

permeability ;

the ability of soil, sediment or rock to transmit fluid

permeability =

distance water travels / time

aquifers come in :

many shapes, sizes and "flavors"

aquifers can span :

hundreds or thousands of kilomters

aquifers may include :

multiple individual layers of rocks or sediment

aquifers can either :

total thousands of meters in thickness or be only a few kilometers and only a few meters thick

aquifers ;

geologic formation in the subsurface that can store and transmit water

adequate storage ;

requires there be sufficient void space between particles in fractures, or generated by compressing aquifers under pressure to provide usable quantities of water

adequate transmission ;

requires that the void spaces where water occurs be well enough connected that it can percolate or flow under either natural or pumping-driven conditions at a sustained rate

aquitard (confining layer, aquiclude) ;

a geologic formation (rocks or sediment) in the subsurface that doesn't transmit water effectively - acts as a barrier to groundwater flow

what are aquifers usually composed of

sediment or sedimentary rocks with grain sizes larger than fine-to medium sand or fractured rock

what are aquitards usually composed of

fine-grained sediments or sedimentary rock, where pores have been filled by mineral cements - silts, silt stones, shales, clays, cemented sandstone, or unfactured limestones

unsaturated zone (zone of moisture, vadose zone) ;

filled with air, water vapor and some liquid water bound to the surfaces of the rock

watertable ;

marks the top of groundwater system

capillary fringe ;

narrow zone of saturation immediatly above of watertable

specific yield (Sy)

the proportion of water occupying void spaces that drains under gravity

hydraulic conductivity (K) ;

a measure of the ability of a particular fluid to flow through rock or sediment

permeability (k) ;

the ability of the geologic formation (rock or sediment) alone to transmit fluid

molecular attraction ;

a thin layer of water that will always be attracted to mineral grains due to the unsatisfied ionic charge on the surface

cones of depression ;

lowering of water tables due to excess pumping

point source ;

refers to a single identifiable source of polluntants

non-point source ;

refers to a diffuse source of pollutants

water budgets ;

a relationship that exists between the amount of water entering into the ground verses the amount of water that is leaving

balanced budget ;

the amount of water entering and leaving are the same

field capacity

the amount of water remaining in the soil after gravity has drained excess water

permanent wilting point -

water is held so tightly plants can't get in

P =

precipitation

Ep

potential evapotranspiration

St

water storage

Deficit

when there is more energy for evaporation than water in the soil

surplus

when there is more water in soil than can be evaporated