water cycle and energy balance Flashcards
what are the properties of water
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
cohesion and adhesion?
B/c water is polar:
Cohesion: holding together of like substances
Adhesion: holding together of unlike substances
water flow in a terrestrial system: input, absorption, infiltration, output
Input – precipitation
Absorption – uptake by plants
Infiltration and Percolation – baseflow
Output – evapotranspiration and runoff
Infiltration – amount of water in the soil
what is the main input of water
- Main input is precip
interception?
- 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
describe throughfall and stem flow
- 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
when is infiltration lower?
Wet OR Clay soil – lower water
infiltration
describe groundwater
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
what is the water cycle coupled with?
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
why do Different biomes have different latent heat energy and sensible heat flux?
They lose heat with vaporization at different rates because confiner loose more than deciduous.
why do different plants have different rooting depth?
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)
what is water potential?
Water potential ( ψ ) – the capacity of water to do work, amount of free energy in wate
How does water move from soil to plants?
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
pure water potential? what is the typical water potential?
Pure water at soil surface has potential of zero
- Water potential is generally negative
when is water potential more stable? what does water movement depend on?
More stable at lower concentration
- Water movement into the soil depends on soil particle size and matric forces (adhesion+
cohesion)
what 3 things affect water potential
- Pressure potential ( Ψp)
- Osmotic potential ( Ψs)
Matric forces (Ψ m)
describe pressure potential
Pressure potential ( Ψp) – reduction in pressure potential generated by
evapotranspiration. Creates a water vapor pressure deficit and negative pressure is
exerted on water
describe osmotic potential
Osmotic potential ( Ψs) – reduction in water potential due to dissolved solutes (harder
to pull water with salty water)
describe matric forces
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
Rate of water movement through soil or plant = Js . what is the driving force? resistance to movement?
Driving force à ∆Ψ = water potential gradient
Resistance to movement à Ls = hydraulic conductivity
I = path length
what is hydraulic conductivity? affected by?
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)
how can hydraulic productivity be enhanced?
Enhance productivity by:
Increase hydraulic (easier to move water) = rate of water increases
Sand – higher hydraulic conductivity
Clay – significant smaller hydraulic conductivity
water vapor pressure? how does it change?
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
Measured against saturation water vapour pressure?
apour pressure deficit (VPD) = saturation water vapour pressure – water vapour pressure
how is the water content of air measured?
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
how does water move in the air (VPD)? dry vs humid?
Water moves from high to low water vapour pressure
Increased VPD = Drier = Increased evapotranspiration
Decreased VPD = Humid = Decreased evapotranspiration (b/c of deficit
what is evotranspiration
Evapotranspiration – transpiration + evaporation
describe how transpiration occurs. moist vs dry soil?
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
what is stoma controlled by
Stoma (water moving from leaves to atm) controlled by:
1. Vapour pressure deficit
2. Soil water supply
3. Stomatal conductance
describe the threshold effect
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%
photosynthesis pattern day vs night?
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
key factor water cycle is dependent on?
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
main water inputs and outputs ecosystem
input - precip
ecosystem - storage
outputs - evapotranspiration and run off `
how is run off calculated
Runoff (R) = P – (ET + ∆𝑆)
P = precipitation
ET = evapotranspiration
∆𝑆= change in ecosystem
what is runoff affected by?
. 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)
how do human activities effect the cycle
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
