Oxygen and CO 2 Announcements –Openings for canoe trip? –Exams will be passed back on Monday –Project proposals due this afternoon at 5 (my office!) –Include: »Question/hypothesis & why its interesting/important »Expected results »Methods »Materials »2 pages max –The more info you include, the more feedback you will get –Think about statistics and replicate samples

Seasonal patterns associated with stratification

Seasonal patterns in O 2

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 Depth PhotosynthesisBiomass

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 ProductionDecomposition Lake A Lake B

Factors that influence O 2 availability Solubility Very slow diffusion Deviations from the theoretical amount of O 2 that can dissolve into water Depletion of O 2 during respiration/decomposition Oversaturation of O 2 during high rates of photosynthesis in dense plant beds or phytoplankton communities

Diel variations in CO 2 and O 2 For O 2, 260 µmol/L = 8.32 mg/L which is atmospheric saturation at 25 o C Northgate is supersaturated with CO 2 (atmospheric saturation is 14 µ mol/L) Cranberry shows huge diel changes in CO 2 and O 2 concentrations Note: Dystrophy: low production lake associated with high humic content (dissolved organic carbon) 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 O 2 6CO 2 + 6H 2 O  (light)  C 6 H 12 O 6 + 6O 2 Night-time respiration uses O 2 and produces CO 2 C 6 H 12 O 6 + 6O 2  6CO 2 + 6H 2 O + energy (ATP) Light rxns light ATP Dark rxns HC C H2CH2C O P OH O O-O- CO2CO2 Inorganic carbon organic carbon in a molecule of phosphoglycerate O2O2

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 Pressure gas = k h M gas K h =Henry’s Law constant M gas = molarity (moles of gas per liter of water)

Maximum solubility Compute the (maximum) solubility of O 2 in water that is in equilibrium with air at 25 o C and 1 atm (sea level). k h (O 2 ) = 780 atm/M PO 2 = 0.20 atm Solubility expressed as: M O 2 = PO 2 /k h (O 2 ) = 0.2 atm/780 atm/M = M O 2 mg/L = moles/liter*32 g O 2 /mol = 8.32 mg/L

Notice that we’ve specified 1) temperature & 2) atmospheric pressure 3) Increased salinity also reduces oxygen solubility

Biological consequences?? Less O 2 available when temperatures are high and metabolic demands are high Influences distribution of organisms for Ex: Fish oxygen tolerances –at least mg O 2 /l for epilimnetic species –at least mg O 2 /l for cold-water species –sustained hypoxia (< 2 mg O 2 /l) generally lethal

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

Biological adaptations for obtaining O2 pvbd/Moslarva.jpg images/dragonfly_nymph2.jpg members.aol.com/mkohl1/Images/ PhysellaLive300.jpg

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 Surviving winter hypoxia… Environmental biology of fishes 14(4):

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 Surviving winter hypoxia… Environmental biology of fishes 14(4): 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 O 2 –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