Light, physics and mixing of water

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Light, physics and mixing of water

• Hydrology, how does water get into and out of
  lakes?
• Mixing, how does water move around in lakes?
• Light, how is energy distributed?

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Drainage ratio Catchment area lake area
Big drainage ratio
Small drainage ratio
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Endorheic vs. ectorheic

• Endorheic- evaporation gt runoff
• salty
• Ectorheic- runoff lt evaporation
• fresh

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Laminar vs. turbulent flow

• Determined by Reynolds number (Re)
• Reinertial/viscous forces
• RedeltalU/mu
• delta density of fluid
• l length of object or surface
• U speed of movement
• mu viscosity of medium

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Surface Gravity Waves
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Seiche
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Zooplankton mix up Saanich InletKunze et al.
2006 Science 313 1768
zooplankton (krill, mostly) density
turbulent mixing
A classic case of bioturbation
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Distribution of light

• controls
• temperature
• energy for photosynthesis
• UV damage
• ability to hunt or avoid predators

light
IzIoe-kz
depth
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What is the relationship between light and
temperature?

• controlled by
• extinction coefficient
• wind mixing and thermal resistance to mixing
• density

If there were no mixing, light and temperature
would follow the same distributions
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Annual cycle of stratification in Lake Kinneret
(Red Sea, Israel)
Turnover
Turnover
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Annual cycles of stratification

• Monomictic- dont freeze over, mix in winter,
  stratify in summer
• Dimictic- freeze in winter (no mixing under ice),
  mix in spring and fall, stratified in summer
  (many temperate zone lakes)
• Polymictic- mix many times during year, may
  stratify daily
• Meromictic- always stratified (many tropical lakes

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Marine lakes marine islands
OTM
Palau
CLM
TLM
Lagoon
David Doubilet
?
?
?
envt
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Stratification depth varies among Scottish lakes
epilimnion
metalimnion
hypolimnion
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What determines mixing depth and degree of
stratification (temperature difference between
top and bottom)
not so windy
windy
Answer 1 Fetch (related to surface area)
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What determines mixing depth and degree of
stratification (mixing depth)
Answer 2 Water transparency
New Zealand
windy
not so windy
Africa
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Fish affect mixing depthMazumder et al. 1990
Science 247312
Trophic cascades fish increase phytoplankton,
decrease water transparency
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Consequences of stratificationLake Nyos, Cameroon
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Consequences of stratificationLake Nyos, Cameroon
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Consequences of stratificationLake Nyos, Cameroon
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Biological consequences of stratification

light
light
Euphotic zone
temperature

Depth
temperature
Aphotic zone
Phytoplankton in lakes with deeper mixing get
less light
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Lakes with deep mixing have less phytoplankton on
average
Eutrophic
Oligotrophic
Phytoplankton in lakes with deep epilimnions get
less light
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Biological consequences of stratification- deep
chlorophyll maxima
Newstead Lake, Vancouver Island
light
nutrients
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Deep chlorophyll and nutrients in the
ocean Huisman et al. 2006 Nature 439322
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Why are most phytoplankton down deep?
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Why are most phytoplankton down deep?

• Things that change with depth
• light
• nutrients
• temperature
• animals

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Our friend the sun-more light means more
lifeKarlsson et al. 2009 Nature 460 506
dissolved organic carbon (DOC)
primary production
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Our friend the sun-more light means more
lifeKarlsson et al. 2009 Nature 460 506
A measure of primary production
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The dark side of light

• sunburn of the deep

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Organisms adaptations to UVsunscreen of the deep
Pigmentation Behaviour (migration) Repair
mechanisms
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UV is increasing due to ozone loss in
atmosphereKerr and McElroy 1993 Science 262
1032
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UV inhibits periphyton growth (when grazers are
absent)Bothwell et al. 1994 Science 26597
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UV increases periphyton growth when grazers are
presentBothwell et al. 1994 Science 26597
no chironomids
no UV
PAR
UV
PAR UVB
no UV
UV
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Effects of UVA and UVB on larval amphibian
survival Palen et al. 2005 Proceedings of
the Royal Society 2721227
Cascades frog

• Exposure to UVB decreases survival
• Exposure to UVA increases survival when UVB is
  present
• Effects vary among species

Pacific treefrog
with UVA
no UVA
Long-toed salamander
Northwest salamander
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Sensitive species lay eggs at low UVB
with UVA
no UVA
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Copepods tradeoff threat from UV damage vs. fish
predatorsL.A. Hansson 2004 Ecology 851005
lotsa fish
not so many fish
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Copepods tradeoff threat from UV damage vs. fish
predatorsL.A. Hansson 2004 Ecology 851005
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Pigments are plastic- decrease in the presence of
fish
fish absent
fish present
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UV and DOC (dissolved organic carbon)
Williamson et al. 1996 Limnology and Oceanography
411024
depth where UVB is 1 of surface
IzIoe-kz
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Concepts to know

• Hydrology
• Catchment ratio
• Drainage vs. seepage lakes
• Endorheic vs. ectorheic
• Flow
• Laminar vs. turbulent
• Reynolds number
• Surface Gravity Waves
• Langmuir cells
• Upwelling
• Bioturbation

• Stratification
• Extinction coefficient
• Thermal resistance to mixing
• Seasonal cycles
• Thermocline
• Epilimnion, metalimnion, hypolimnion
• Euphotic vs. aphotic
• Turnover