Oxygen and CO2

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Seasonal patterns associated with stratification

Seasonal patterns in O2

Sources and sinks of oxygen

• Atmosphere• Photosynthesis

• Decomposition• Respiration

Photosynthesis distribution = specific primary production * light climate * algae biomass

Mesotrophic epilimnion (well mixed)

Eutrophic with surface bloom

Oligotrophic with max. biomass at metalimnion (positive heterograde curve)

Shallow transparent lakes with max. biomass on bottom

Dep

th

Photosynthesis Biomass

Hypolimnetic oxygen depletion rates

• Depends on

– The amount of oxygen present at the beginning of summer stratification

– Length of stratification period

– The amount of organic matter rain from the photo zone (& therefore the amount of decomposition)

– The volume of the hypolimnion

Hypolimnetic depletion rates

Production Decomposition

Lake A

Lake B

Factors that influence O2 availability

• Solubility• Very slow diffusion• Deviations from the theoretical amount of O2 that can

dissolve into water• Depletion of O2 during respiration/decomposition

• Oversaturation of O2 during high rates of photosynthesis in dense plant beds or phytoplankton communities

Diel variations in CO2 and O2

• For O2, 260 µmol/L = 8.32 mg/L which is atmospheric saturation at 25oC

• Northgate is supersaturated with CO2 (atmospheric saturation is 14 µ mol/L)

• Cranberry shows huge diel changes in CO2 and O2 concentrations

• Note: Dystrophy: low production lake associated with high humic content (dissolved organic carbon)

CO

2m

ol L

-1

O2 m

ol L-1

0

150

300

204 205 2060

150

300

Northgate (dystrophic)

0

10

20

199 200 201240

250

260

Crystal (oligotrophic)

Day of year

0

80

195 196 197180

230

280

Cranberry (mesotrophic)

CO2

O2

CO2

O2

CO2

O2

0

150

300

0

150

300

204 205 206

0

40

80

180

230

280

195 196 197

0

10

20

240

250

260

199 200 201

From a manuscript entitled “Lake metabolism: Relationships with dissolved organic carbon and chlorophyll” by Paul C. Hanson, Darren L. Bade, Stephen R. Carpenter, Timothy K. Kratz

Diel patterns…

Day-time photosynthesis produces O2

6CO2 + 6H2O (light) C6H12O6 + 6O2

Night-time respiration uses O2 and produces CO2

C6H12O6 + 6O2 6CO2 + 6H2O + energy (ATP)

Light rxns

light

ATP

Dark rxns

HCC

H2C

O

POHO

O-

CO2

Inorganic carbon

organic carbon in a molecule of phosphoglycerate

O2

Oxygen depletion or overstaturation in dense Eurasion water milfoil beds

Oxygen depletion in dense Trapa beds in the Hudson River

Solubility of gases in water

Henry’s Law: the solubility of a gas in a liquid is directly proportional to the pressure of the gas over the liquid

Partial Pressuregas = khMgas

Kh =Henry’s Law constant Mgas = molarity (moles of gas per liter of water)

Maximum solubility

Compute the (maximum) solubility of O2 in water that is in equilibrium with air at 25oC and 1 atm (sea level).

kh(O2) = 780 atm/MPO2 = 0.20 atm

Solubility expressed as: MO2 = PO2/kh(O2) = 0.2 atm/780 atm/M = 0.00026 M O2

mg/L = 0.00026 moles/liter*32 g O2/mol = 8.32 mg/L

Notice that we’ve specified 1) temperature & 2) atmospheric pressure

3) Increased salinity also reduces oxygen solubility

% of max solubility

0

20

40

60

80

100

120

-500 0 500 1000 1500 2000 2500

Altitude (m)

Perc

ent o

f max

imum

so

lubi

lity

Solubility (mg/L) at 760 mmHG pressure

0

24

68

101214

16

0 10 20 30 40

Temperature (oC)

Solu

bilit

y (m

g/L)

Biological consequences??

• Less O2 available when temperatures are high and metabolic demands are high

• Influences distribution of organismsfor Ex: Fish oxygen tolerances– at least 2 - 5 mg O2/l for epilimnetic species

– at least 5 - 9 mg O2/l for cold-water species

– sustained hypoxia (< 2 mg O2/l) generally lethal

What area of Dudley Lake is available for fishes in Early October??

Biological adaptations for obtaining O2

www.liv.ac.uk/lstm/ pvbd/Moslarva.jpg

www.ento.csiro.au/.../insects/ images/dragonfly_nymph2.jpg

members.aol.com/mkohl1/Images/ PhysellaLive300.jpg http://www.dec.state.ny.us/website/dow/stream/empfamilies.htm

europa.eu.int/comm/research/ success/images/0261a.jpg

Winterkill lakes

• Small, shallow lakes• Anoxic during ice-cover (why?)• Have distinctive fish assemblages

• Why?

Mystery Lake

inlet

See Magnuson et al. 1985. Surviving winter hypoxia… Environmental biology of fishes 14(4):241-250

Winterkill lakes• Different species had different

behaviors– Leave the lake– Move towards inlet– Move towards ice/water

interface– Breathe bubbles

• In some cases, smaller fish less tolerant

• Fish that typically winterkill (bluegill) don't exhibit these behaviors

• See Magnuson et al. 1985. Surviving winter hypoxia… Environmental biology of fishes 14(4):241-250

X

Oxygen in running waters

• At saturation in small, turbulent streams

• In areas where currents have slowed, oxygen can be altered by photosynthesis or respiration

• Seasonal inputs of organic material or nutrients can result in high decomposition rates and low O2

– Leaf-fall– Runoff with nutrients from golf-

courses, lawns, ag fields– Organic sewer (yum)

• Diel variation potentially greater in slow-flowing, nutrient enriched streams & rivers