water as an environment light water movements part 3
TRANSCRIPT
Water as an EnvironmentWater as an Environment
LightLightWater MovementsWater Movements
Part 3Part 3
Light and Primary Production•The depth of primary production in lakes is dependent on light penetration• k is used to determine the compensation depth (1% of subsurface light)
Compensation depth
Payne, 1986
•Phytoplankton circulates vertically through the mixed layer.
•The thickness of the euphotic zone (Zeu) in relation to the thickness of the mixing layer (Zmix)has a large effect on primary production. •If zeu:zmix is low, phytoplankton will be spending much of their time below the compensation depth.Irradiance and mixing depth change with the seasons, which helps to explain seasonal patterns of primary production.
Light and Predation
DMV: Diel (daily) vertical migration
Vertical Mixing and Nutrient Cycles
Nutrient concentrations (N and P) increase after spring thaw due to tributary input and isothermal mixing (whole lake in contact with sediments)
Nutrient concentrations in epilimnion decline over summer because
Tributary inputs decline (less external loading) Surface waters are not in contact with sediments
(less internal loading) Nutrient concentrations in epilimnion increase
after fall turnover
Phytoplankton growth cycles (Typical temperate-zone lake)
Phytoplankton Growth Cycle are the product of
Seasonal Temperature Cycles Light Nutrients
JanJan JuneJune Dec DecNut
rient
s in
Epi
limni
on
Nut
rient
s in
Epi
limni
on
Ice-outIce-out TurnoverTurnover
JanJan JuneJune Dec Dec
Ligh
tLi
ght
Ice-outIce-outTurnoverTurnover
Light available to organisms in the lake changes over the seasons Low light under snow/ice cover Increased light as snow melts and ice thins. Very low light during spring isothermal period (high turbidity, deep
mixing) Light in epilimnion increases after stratification (longer daylength,
increased clarity) Light levels decline at fall turnover
Light
JanJan JuneJune Dec Dec
Tem
pera
ture
Tem
pera
ture
Ice-outIce-outTurnoverTurnover
Temperature of the epilimnion follows a regular seasonal pattern
Temperature
Tem
pera
ture
Tem
pera
ture Ice-outIce-out
TurnoverTurnover
Combine all three factors
Ligh
tLi
ght
JanJan JuneJune Dec Dec
Nut
rient
sN
utrie
nts
For phytoplankton growth in the epilimnion
1. During spring mixing, conditions are poor – very low light
2. Following spring stratificaton conditions are excellent. (high light, high nutrients, cool temperature)
3. Nutrient depletion in epilimnion, High temperature causes high sinking rates. OK conditions
4. Higher nutrients as hypolimnion begins to mix with epilimnion. Good conditions
5. Poor conditions due to low light
11 22 33 44 55
Annual Phytoplankton Growth Cycle
JanJan JuneJune Dec DecPh
yto
pla
nkto
n G
row
thP
hyt
opl
ank
ton
Gro
wth
Ice-outIce-outTurnoverTurnover
11
22
5533
44
Water MovementsWater Movements
Gravity WavesGravity Waves SeichesSeiches Internal wavesInternal waves Laminar flow vs. turbulent flowLaminar flow vs. turbulent flow
Gravity (Surface) wavesGravity (Surface) waves Characterized by wavelength (L), height (h), and period Water molecules mainly move up and down, not sideways Wave amplitude (height) attenuates with depth Maximum wave height in a lake is proportional to fetch
H = 0.105 (x)1
/
2
SeichesSeiches Strong, sustained winds cause water to “slosh” to the far end of the lake When wind stops, the water sloshes back and forth several times. Seiche may have one or more nodes Seiche period can be calculated by T= 2L/(n(gh)1/2)
L=lake length, n=# of nodes, g=gravity, h=depth of lake
Lake Erie seiche period is about 14 hours.
Internal wavesInternal waves A surface seiche can cause internal waves in a stratified lake between the epilimnion and hypolimnion. Internal waves typicallly have many nodes and continue for long after the surface seiche ends. Internal waves cause limited mixing between the l
Nutrients from the hypolimnion can be mixed into the epilimnionIncrease in epilmnion phytoplankton productivity
http://www.youtube.com/watch?v=oljinlD2yho&feature=fvsr
Turbulent vs Laminar Flow At low speeds and small scales, water flow is laminar,
adjacent layers of water do not mix with each other At higher speeds and larger scales, laminar flow breaks
down and flow becomes turbulent (chaotic). Laminar and turbulent characteristics are important for
nutrient dynamics of phytoplankton and feeding of zooplankton
http://www.youtube.com/watch?v=p08_KlTKP50&feature=related