Chemical composition of lake water

1
Chemical composition of lake water

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

2
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-

3
Things affected by salinity

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

4
Naturally saline lakes- Mono Lake, CA
5
Simple food web in saline Mono Lake, California
Homo californicus
Brine shrimp Artemia
Wilsons phalarope
Alkali fly
6
Salinity is increasing in streams (mostly due to
chlorine from road salt)Kaushal et al. 2005 PNAS
102 13517
7
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

8
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-

9
pH and CO2

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

10
Ocean pH, Ca and calcifying organismsOrr et al.
2005 Nature 437 681
pteropod
11
pH and lake chemistryYan et al. 2004 Ecology
Letters 7452
12
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
14
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
15
Compensation in zooplankton Frost et al. 1999
Limnology and Oceanography 44784
Acid-tolerant species compensated for the loss of
acid-sensitive ones
16
Contrasts with slow recovery in Ontario LakesYan
et al. 2004 Ecology Letters 7452
neutralized
17
Acidification of lakes

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

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

• Mitigating factors
• buffering by Ca

18
Organic Ions (DOC)

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

19
Role of allocthonous subsidies of nutrients and
energy in lakes Prairie, Bird and Cole 2002
Limnology and Oceanography 47316
20
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
23
Daily cycles
24
Daily cycles
day
night
O2 concentration
oligotrophic lakes
eutrophic lakes
respiration photosynthesis exchange
respiration exchange
25
Daily cycles
day
night
saturation (Henrys law)
O2 concentration
oligotrophic lakes
eutrophic lakes
respiration photosynthesis exchange
respiration exchange
26
Low O2 under ice can trigger fish kills
27
Role of allocthonous subsidies of nutrients and
energy in lakes Prairie, Bird and Cole 2002
Limnology and Oceanography 47316
P gt R
RgtP