water cycle and energy balance

Question 1

what are the properties of water

Answer 1

Polar
- Hydrogen Bonding
High specific heat: amount of energy needed to raise 1g by 1 degree Celsius
- High heat of vaporization: quantity of heat needed to convert 1g form liquid to gas

Question 2

cohesion and adhesion?

Answer 2

B/c water is polar:
Cohesion: holding together of like substances
Adhesion: holding together of unlike substances

Question 3

water flow in a terrestrial system: input, absorption, infiltration, output

Answer 3

Input – precipitation
Absorption – uptake by plants
Infiltration and Percolation – baseflow
Output – evapotranspiration and runoff
Infiltration – amount of water in the soil

Question 4

what is the main input of water

Answer 4

• Main input is precip

Question 5

interception?

Answer 5

• Interception - foggy environments - humidity in air is high enough for the water to condense onto surface - can be harvested in aired environments
  ○ Substancial (10-50%) in closed canopy forests

Question 6

describe throughfall and stem flow

Answer 6

• Throughfall and stemflow- interception of water by plants impacts the flow - stemflow = canopy draws the water down the stem - catching water and directing it so its more available to the plant
  
  • Stemflow - enhances flow by creating little spaces + stem adheres water = water goes down toward root system + help make it go deeper into the root system and less available to competition

Question 7

when is infiltration lower?

Answer 7

Wet OR Clay soil – lower water
infiltration

Question 8

describe groundwater

Answer 8

Ground water – below access of roots
-Experiences same forces (matrix and
gravitational) that water on surface
does, it is just slower due to the soil
texture found that low in the soil
profile
-Aquifers

Question 9

what is the water cycle coupled with?

Answer 9

is coupled with the energy cycle à Energy absorbed by water to vaporize it, is made from
input; a high latent heat of energy is associated with cooling through evaporation
The amount of water on earth has overall been around for millions of years = a cycle

Question 10

why do Different biomes have different latent heat energy and sensible heat flux?

Answer 10

They lose heat with vaporization at different rates because confiner loose more than deciduous.

Question 11

why do different plants have different rooting depth?

Answer 11

Regions that have dry periods – plants have long roots
Regions with short season – plants have shallow roots to get water quickly as there is a lot of
water available (snow melt, precipitation)

Question 12

what is water potential?

Answer 12

Water potential ( ψ ) – the capacity of water to do work, amount of free energy in wate

Question 13

How does water move from soil to plants?

Answer 13

Water moves from areas to high to low water potential
- Depends on its concentration in solution and various pressure
water moves from soil to plant when ψ plant < ψ soil

Question 14

pure water potential? what is the typical water potential?

Answer 14

Pure water at soil surface has potential of zero
- Water potential is generally negative

Question 15

when is water potential more stable? what does water movement depend on?

Answer 15

More stable at lower concentration
- Water movement into the soil depends on soil particle size and matric forces (adhesion+
cohesion)

Question 16

what 3 things affect water potential

Answer 16

1. Pressure potential ( Ψp)
2. Osmotic potential ( Ψs)
   Matric forces (Ψ m)

Question 17

describe pressure potential

Answer 17

Pressure potential ( Ψp) – reduction in pressure potential generated by
evapotranspiration. Creates a water vapor pressure deficit and negative pressure is
exerted on water

Question 18

describe osmotic potential

Answer 18

Osmotic potential ( Ψs) – reduction in water potential due to dissolved solutes (harder
to pull water with salty water)

Question 19

describe matric forces

Answer 19

Matric forces (Ψ m) – reduction in matric forces from absorption of water to surface of
plant cells or soil particles (water sticks to soil particles by size or texture makes it
harder to pull water out

Question 20

Rate of water movement through soil or plant = Js . what is the driving force? resistance to movement?

Answer 20

Driving force à ∆Ψ = water potential gradient
Resistance to movement à Ls = hydraulic conductivity
I = path length

Question 21

what is hydraulic conductivity? affected by?

Answer 21

the capacity to conduct water
Affected by:
1. Soil texture
2. Flow through macropores (influenced by compaction, soil organisms, roots)
3. Xylem vessel diameter (species specific)

Question 22

how can hydraulic productivity be enhanced?

Answer 22

Enhance productivity by:
Increase hydraulic (easier to move water) = rate of water increases
Sand – higher hydraulic conductivity
Clay – significant smaller hydraulic conductivity

Question 23

water vapor pressure? how does it change?

Answer 23

Water vapor pressure – atmospheric pressure exerted by water molecules in the air, moving from
high to low concentrations
-changes the amount of water due to the number of water molecules
-hotter temperature has higher water vapour pressure (warmer air holds more water)
-greater water deficit, the more transpiration

Question 24

Measured against saturation water vapour pressure?

Answer 24

apour pressure deficit (VPD) = saturation water vapour pressure – water vapour pressure

Question 25

how is the water content of air measured?

Answer 25

Relative humidity (RH) = water vapour density / saturation water vapour density x 100
Decreased RH = Increased VPD
B/c the amount of water at 10 degrees it can hold 10g but at 30 degrees it can hold
3x more water = saturated water density

Question 26

how does water move in the air (VPD)? dry vs humid?

Answer 26

Water moves from high to low water vapour pressure
Increased VPD = Drier = Increased evapotranspiration
Decreased VPD = Humid = Decreased evapotranspiration (b/c of deficit

Question 27

what is evotranspiration

Answer 27

Evapotranspiration – transpiration + evaporation

Question 28

describe how transpiration occurs. moist vs dry soil?

Answer 28

evaporation on the surface of leaves
- The leaf is site of photosynthesis and CO2 exchange thus the plant
needs stomata on the surface. The stomata is also the site of gas
exchange for water vapour. Inside the stomata is saturated thus the
plant has a tendency to lose water.
- Moist soil àno problem losing water
- Dry soil à can’t lose water b/c they need to save it (store) to survive

Question 29

what is stoma controlled by

Answer 29

Stoma (water moving from leaves to atm) controlled by:
1. Vapour pressure deficit
2. Soil water supply
3. Stomatal conductance

Question 30

describe the threshold effect

Answer 30

Threshold effect – soil moisture on transpiration
- Decline in transpiration when about 80% of available water is removed from soil
rooting zone
- After field capacity, rate of transpiration hardly changes
- Threshold is around 25%

Question 31

photosynthesis pattern day vs night?

Answer 31

Daytime – photosynthesis, high transpiration
Nighttime – no photosynthesis, low transpiration b/c stomata is closed, hydraulic lift – water
moved from deep soil to higher parts of soil through roots where water is absorbed by roots at
shallow profile b/c gradient is weaker (moisture microclimate

Question 32

key factor water cycle is dependent on?

Answer 32

Water cycle is very dependent of multiple state factors, key one is climate- the amount of
precipitation and the amount of radiation (from sun) effecting rate of transpiration

Question 33

main water inputs and outputs ecosystem

Answer 33

input - precip
ecosystem - storage
outputs - evapotranspiration and run off `

Question 34

how is run off calculated

Answer 34

Runoff (R) = P – (ET + ∆𝑆)
P = precipitation
ET = evapotranspiration
∆𝑆= change in ecosystem

Question 35

what is runoff affected by?

Answer 35

. Soil texture
2. Structure of soil (compaction)
3. Water capacity – runoff is higher in saturated soils, soil with less OM and soil with little
compaction
4. Vegetation cover – increase in deforestation = stream flow increases; therefore, less trees,
less transpiration, more runoff
5. Precipitation – increase precipitation, evapotranspiration is relatively steady (slight
increase) but stream flow is directly proportional
-Hover Brooke – water shed that allowed for output to be measured because it has
complete bedrock so that all water has to runoff and cannot get absorbed (based
on geology)

Question 36

how do human activities effect the cycle

Answer 36

Human activities have substantially altered Earths hydrologic cycle
- Humans use about 50% of earths available renewable fresh water (in
terms on precipitation)
- Exceeds 100% in some dry regions
- Watershed: large spatial extent where topography and gravity suggest
the water will run to the lowest point and always to the ocean