Oxygen and Redox Potential Flashcards
Name two ways to measure DO
Winkler titration and YSI probe
How much DO can 0 degree water hold?
14.6 mg/L
How much DO can 25 degree water hold?
8.3 mg/L
Do waters at higher elevations hold more oxygen?
No, there is less 02 at higher elevations.
Does salt water hold as much DO as freshwater?
No salt water holds 25% less DO then freshwater.
What is the typical DO profile of a oligotrophic lake?
Orthograde
What is a typical profile of a eutrophic lake?
Clinograde
What defines a Orthograde profile?
O2 increases with depth indicating lack of respiration. Can saturate water depending on temp
What defines a Clinograde profile?
Decrease of DO, respiration occurs in the hypolimnion. As 02 depletes hypoxia occurs and if it is totally depleted anoxia occurs.
What is a Diurnal Cycle?
This is a 24 hr cycle, In the day time photosynthesis occurs and creates 02. At sunset photosynthesis shuts off but respiration is still occurring and can deplete the DO levels in a lake. This is more pronounced in eutrophic lakes and in the literal zone where biomass is higher.
Where are diurnal cycles most extreme?
The litoral zone
Why does summer kill occur?
In hyper eutrophic lakes cyanobacteria can form massive blankets on the surface. This blocks oxygen for other photosynthesizers below. At night if the blankets are unbroken by wind respiration occurs and can cause anoxia which results in fish kills literally overnight.
What DO profile would you expect Anoxia sediments to have?
Clinograde with a sharp depletion of 02
What is redox potential?
Redox potential measures the availability of free electrons for chemical reactions in water. it affects potential energy costs for chemical reactions.
Describe High redox potential
High redox potential occurs in the presence of oxygen (oxidizing environment) and favours nitrification where ammonium is converted to nitrate. O2 is high and there are few free electrons.
Describe Low redox potential
Low redox potential occurs when oxygen is limited and there are many free electrons.( reducing environment)
What is a positive heterograde profile?
This is essentially a clinograde profile with a sharp sudden increase in 02 at depth. This is caused when algae adapted to metalimnetic conditions are present at depth.
What is a negative heterograde profile?
This is a clinograde profile with a sharp sudden decrease in 02 then a slow decrease. This occurs when ground water saturated with organic material settles in that part of the water column. Then retiring bacteria go to work breaking it down.
