Chemical composition of lake water

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Chemical composition of lake water

• Inorganic ions, salinity
• pH
• Organic ions
• Dissolved gases (CO2 and O2)
• Nutrients

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Important inorganic ions (in order of decreasing
abundance)

• anions- HCO3-, SO42-, Cl-
• cations- Ca2, Mg2, Na, K
• Salinity total concentration of all ions
• Usually measured by electrical conductivity
• (limestone) CaCO3 H2O CO2 -gt Ca2 2HCO3-
• (dolomite) CaMg(CO3)2 2H2O 2CO2 -gt Ca2
  Mg2 4HCO3-

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Things affected by salinity

• density
• mixing (more saline more stable)
• pH
• CaCO3 (marl) H2O CO2 -gt Ca2 2H CO32-

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Naturally saline lakes- Mono Lake, CA
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Simple food web in saline Mono Lake, California
Homo californicus
Brine shrimp Artemia
Wilsons phalarope
Alkali fly
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Salinity is increasing in streams (mostly due to
chlorine from road salt)Kaushal et al. 2005 PNAS
102 13517
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Salinity causes physiological stress

• Most freshwater organisms are hypertonic (saltier
  than their environment)
• Have adaptations to excrete water, absorb ions
• Not adaptated to absorb water, excrete ions

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Low salinity (particularly Ca) can also cause
problemsJeziorski 2008 Science
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More on calcium declines Jeziorski 2008 Science
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Calcium limits the spread of invasive
musselsJones and Ricciardi 2005 Canadian Journal
of Fisheries and Aquatic Sciences
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Naturally saline lakes and their weird
inhabitantsPavilion Lake, B.C.Some of the
first photosynthetic microbes, known only from
fossils and a few weird places
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pH

• determined by
• geology, salinity
• biology (humic substances, decomposing
  vegetation)
• atmospheric CO2
• acid rain, from fossil fuel burning
• SO2 O3 (ozone) -gt SO3 O2, SO3 H2O -gt H2SO4
  -gt H HSO4-
• 3NO2 H2O -gt HNO3 NO -gt H NO3- NO
• buffering
• CaCO3 (marl) H2O CO2 -gt Ca2 2HCO3- -gt Ca2
  2H 2CO32-

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pH and CO2

• CO2 H2O -gt H HCO3-
• CO2 rising in atmosphere
• Degrades calcifying organisms (corals, urchins)
  by dissolving their carbonate skeletons

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Ocean pH, Ca and calcifying organismsOrr et al.
2005 Nature 437 681
pteropod
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Ocean pH, Ca and calcifying organismsOrr et al.
2005 Nature 437 681
pteropod
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pH and lake chemistryYan et al. 2004 Ecology
Letters 7452
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Little Rock Lake experimentFrost et al. 1999
Limnology and Oceanography 44784
Split lake with a curtain, added acid to one side
(Treatment Basin) left other side (Reference
Basin) as control
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Interactions between pH and other sources of
biological stress-1 Metals
acidified basin
reference basin
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Interactions between pH and other sources of
biological stress-2 UV Williamson et al. 1996
Limnology and Oceanography 411024
acidified basin
depth where UVB is 1 of surface
reference basin
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Compensation in zooplankton Frost et al. 1999
Limnology and Oceanography 44784
Acid-tolerant species compensated for the loss of
acid-sensitive ones
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Contrasts with slow recovery in Ontario LakesYan
et al. 2004 Ecology Letters 7452
neutralized
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All stressed out and nowhere to goVinebrooke
2004 Oikos
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Acidification of lakes

• Consequences
• low pH
• high metals
• low DOC, high UVB
• few species
• same biomass
• Calcium depletion

• Causes
• CO2
• CO2H2O-gtHCO3-H
• NOx and SOx

• Mitigating factors
• buffering by Ca

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Organic Ions (DOC)

• Come from detritus, leaked by living cells
• labile or refractory
• Can be eaten by bacteria
• Lower pH
• Stain lakes, protect from UV, decrease light
  penetration

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Organic Ions (DOC)

• Have different optical properties (absorb
  different wavelengths of light)
• Vary greatly as quality of food for bacteria
• Connect the living and dead parts of food web

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Divergent effects of benthic and pelagic fish on
DOCHarmon, Matthews, Des Roches et al. 2009
Nature
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different kinds of fish lead to different kinds
of DOC, change light environment
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(No Transcript)
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Role of allocthonous subsidies of nutrients and
energy in lakes Prairie, Bird and Cole 2002
Limnology and Oceanography 47316
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Dissolved Gases- O2 and CO2

• Obeying or breaking Henrys Law
• CsKsPt
• Reflect processes working in different directions
• Exchange with atmosphere
• goes up with wind energy
• goes down with temperature
• Respiration and photosynthesis
• both go up with temperature
• photosynthesis goes up with light
• respiration goes up with photosynthesis and DOC

exchange with atmosphere
respiration
O2
CO2
photosynthesis
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Vertical distribution

• Depends on temperature biological activity
  (photosynthesis and respiration) in stratified
  lakes
• Physical processes dominate in oligotrophic lakes

Oligotrophic lakes
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Vertical distribution

• Depends on temperature biological activity
  (photosynthesis and respiration) in stratified
  lakes
• Physical processes dominate in oligotrophic lakes
• Biological activity dominates in eutrophic lakes

Oligotrophic lakes
Eutrophic lakes
O2
depth
CO2
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Daily cycles
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Daily cycles
day
night
O2 concentration
oligotrophic lakes
eutrophic lakes
respiration photosynthesis exchange
respiration exchange
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Daily cycles
day
night
saturation (Henrys law)
O2 concentration
oligotrophic lakes
eutrophic lakes
respiration photosynthesis exchange
respiration exchange
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Low O2 under ice can trigger fish kills
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Role of allocthonous subsidies of nutrients and
energy in lakes Prairie, Bird and Cole 2002
Limnology and Oceanography 47316
P gt R
RgtP