10.5: Review and Additional Resources

Review

Review and assess your learning. Start with the "Important Terms and Concepts" to ensure you know the terminology related to the topic of the chapter and concepts discussed. Move on to the "Review Questions" to answer critical thinking questions about concepts and processes discussed in the chapter. Finally, test your overall understanding by taking the "Self-assessment quiz".

Important Terms and Concepts

• hydrosphere

  often called the "water sphere" as it includes all the earth's water found in the oceans, glaciers, streams, lakes, the soil, groundwater, and in the air.

• hydrologic cycle

  aka water cycle. the cycling of water through the earth system. It is a cycle of energy as well.

• soil water

  the water that is immediately available to plants.

• groundwater

  occupies the zone of saturation. Found in aquifers and replenished by percolation of water from the zone of aeration downward to the zone of saturation, or in the recharge zone of a confined aquifer.

• evaporation

  the phase change of liquid water into a vapor (gas)

• latent energy

  "locked up" in the water molecule when water undergoes the phase change from a liquid to a gas.

• precipitation

  droplets of water that fall from the clouds to the earth

• interception

  Precipitation that collects on the leaves or stems of plants

• infiltration

  refers to water that penetrates into the surface of soil.

• zone of aeration

  aka "unsaturated zone", includes soil water zone. See image under "zone of saturation"

• zone of saturation

  includes ground water

  

• groundwater zone

  included in zone of saturation. See image under "zone of saturation"

• water table

  divides the zone of aeration from the zone of saturation. The height of the water table will fluctuate with precipitation, increasing in elevation during wet periods and decreasing during dry.

• hygroscopic water

  a microscopic film of water surrounding soil particles

• capillary water

  held by cohesive forces between the films of hygroscopic water

• wilting point

  At this point the plant cannot pull water from the plant-rooting zone and it wilts

• gravity water

  water moved through the soil by the force of gravity

• field capacity

  The amount of water held in the soil after excess water has drained

• available water

  The difference between the wilting point and the field capacity

• percolation

  the movement of water downward through the soil

• seepage

  water that moves downward through the soil toward a stream channel of large body of water

• aquifer

  bodies of earth material that have the ability to hold and transmit water

• aquiclude

  dense impermeable layers of earth material

• hydraulic gradient

  the difference in elevation between two points on the water table divided by the horizontal distance between them

• groundwater flow rate

  permeability X hydraulic gradient

• runoff

  precipitation that moves across the surface

• unconfined flow

  moves across the surface in broad sheets of water often creating sheet erosion

• confined flow

  water confined to channels

• depression storage

  Water that became trapped in depressions

• stream discharge

  the volume of water passing through a particular cross-section of a stream in a unit of time

• stream hydrograph

  illustrates the relationship between discharge and runoff

• water balance

  an accounting of the inputs and outputs of water

• precipitation

  makes up the primarily supply of water to the surface.

• actual evapotranspiration

  the amount of water delivered to the air from evaporation and transpiration

• evaporation

  the phase change from a liquid to a gas releasing water from a wet surface into the air above

• transpiration

  represents a phase change when water is released into the air by plants

• evapotranspiration

  combined transfer of water into the air by evaporation and transpiration

• potential evapotranspiration

  the amount of water that would be evaporated under an optimal set of conditions, among which is an unlimited supply of water

• soil moisture storage

  the amount of water held in the soil at any particular time

• change in soil moisture storage

  the amount of water that is being added to or removed from what is stored

• deficit

  demand for water exceeds that which is actually available; when potential evapotranspiration exceeds actual evapotranspiration (PE>AE)

• surplus

  when P exceeds PE and the soil is at its field capacity (saturated); we have more water than we actually need to use given the environmental conditions at a place

• soil moisture recharge

  Precipitation satisfies the need for water with water left over and begins to replenish the soil moisture

• soil moisture utilization

  precipitation is no longer is able to meet the demands of potential evapotranspiration. Plants must extract water that is stored in the soil from the previous months

Review Questions \(\PageIndex{1}\)

Briefly describe what the hydrologic cycle is.

Answer

The hydrologic cycle or water cycle is the pathway through which water moves in the Earth system. It is a cycle of energy as well as moisture.

Compare and contrast soil water and groundwater.

Answer

Soil water is held in the soil moisture zone that lies in the zone of aeration. Groundwater is held in the zone of saturation. Soil water is directly available for plants to use, ground water is not.

How do plants affect the hydrologic cycle?

Answer

Plants affect the water cycle though by extracting water from the soil moisture zone and passing it to the atmosphere. Water moves as through fall through plant canopy.

What impact does soil texture have on field capacity?

Answer

The field capacity is the maximum amount of water held in the soil after it has bee drained by gravity. Field capacity is higher in fine textured soils because there is more pore space per unit volume than for coarse textured soils.

What affects the permeability of subsurface warth materials?

Answer

Permeability is the ability for water to move through earth material. The connectivity of pore spaces largely controls permeability. Large, well-connected pore space results in greater permeability. Thus, coarse soils are more permeable than fine textured soils.

How does soil texture affect available water?

Answer

Finer textured soils hold more water and thus have more available water than coarse textured soils.

Compare and contrast an aquiclude with an aquifier.

Answer

An aquifer is a body of earth material able to hold and transmit groundwater in economical amounts. An aquiclude is far less permeable and cannot transmit water through it.

Describe the effect of urbanization on a stream hydrograph.

Answer

Urbanization can decrease the lag time between maximum precipitation and runoff, and increase and steepen the recessional limb of a hydrograph.

What is potential evapotranspiration?

Answer

Evapotranspiration is the amount of water evaporated and transpired under an unlimited supply of water. Fundamentally it is determined by energy input to the environment. Evapotranspiration can be thought of as "water need”.

Under what conditions does a soil water deficit occur?

Answer

A soil water deficit occurs when potential evapotranspiration exceeds precipitation and the soil water storage is zero (dry soil).

Under what conditions does a soil water surplus occur?

Answer

A soil water surplus occurs when precipitation exceeds potential evapotranspiration and the soil is at field capacity.

Self-Assessment Quiz \(\PageIndex{1}\)

1. In soil moisture budgeting, potential evapotranspiration is largely dependent on
   1. soil texture
   2. energy input
   3. plant type
   4. all the above
2. The largest store of fresh water in the hydrosphere is
   1. the ocean
   2. glaciers
   3. the Great Lakes
   4. ground water
3. Over pumping of ground water could lead to
   1. lowered water tables
   2. land subsidence
   3. decreased aquifer permeability
   4. all the above
4. Infiltration of water into the soil
   1. is higher for coarse textured soil
   2. is higher when the soil is dry
   3. is higher for vegetated surfaces
   4. is affected by all the above
5. Which of the following soil texture classes would have the largest available water?
   1. sand
   2. silt
   3. clay
   4. loam
6. The water held that is "bound" the tightest to soil particles is
   1. hydroscopic water
   2. capillary water
   3. gravity water
   4. pore water
7. The process whereby water drips from leaf-to-leaf finally making it to the ground is called
   1. through flow
   2. stem flow
   3. through fall
   4. interception
8. The zone of saturation is the
   1. soil water zone
   2. intermediate zone
   3. aeration zone
   4. ground water zone
9. The point at which plants can no longer extract water from the soil is called the
   1. field capacity point
   2. dryness point
   3. wilting point
   4. none of the above
10. If PE is greater than AE and P, and the soil is dry, then
    1. soil water recharge is likely to occur
    2. soil water surplus is likely to occur
    3. soil water utilization is likely to occur
    4. soil water deficit is likely to occur

Answer

1. B
2. B
3. D
4. D
5. D
6. A
7. A
8. D
9. C
10. D

Additional Resources

Use these resources to further explore the world of geography

Focus on The Physical Environment: "The Rise and Fall of Africa’s Great Lake" NASA Earth Observatory

Connections: "Could California’s drought make residents sick?" NewsHour (PBS) 09/03/2016 report

Physical Geography Today: Ground Water Climate Response Network - USGS

World of Change: Evaporation of the Aral Sea (NASA Earth Observatory)

Multimedia

"The Desert Springs of Mexico's Cuatro Cienegas", (8:56)

Readings

"Defining Drought" National Drought Mitigation Center, University of Nebraska - Lincoln

Web Sites

Water Resources of the United States - United States Geological Survey

National Oceanic and Atmospheric Administration (NOAA)