Dissolved Oxygen Flashcards
(22 cards)
Why study dissolved oxygen (DO) levels?
Essential to metabolism
Affects solubility of some elements at the sediment-water interface
Alters trace metal solubility
Determines community structure & available habitat
How is dissolved oxygen (DO) expressed?
Concentration (mg O₂ L⁻¹ or ppm)
% Saturation
How do phytoplankton, benthic algae, and submerged macrophytes affect DO levels?
They add DO to the euphotic zone (photosynthesis»_space; respiration).
How do plant, animal, and bacterial respiration and decomposition affect DO?
They remove DO from the aphotic zone (photosynthesis «_space;respiration).
What are the three main regions of productivity in aquatic ecosystems?
Lowest in open-water region
Intermediate in catchment
Greatest between land and water
What is the difference between DOM and POM?
DOM (Dissolved Organic Matter) is about 10 times greater than POM (Particulate Organic Matter).
How does oxygen solubility vary in freshwater?
Temperature: ↑ Temp = ↓ Solubility
Pressure: ↑ Pressure = ↑ Solubility
Salinity: ↑ Salinity = ↓ Solubility
(Saline waters hold 20% less DO)
What are the primary sources and sinks of DO in aquatic ecosystems?
Sources: Photosynthesis, atmospheric diffusion (wind), water inflow
Sinks: Respiration (all organisms), decomposition (bacteria), photochemical oxidation, water outflow
What are some barriers to DO exchange?
Reduced turbulence
Thermocline
Sediments
Where and when might supersaturation of DO occur?
Sensitive to time of day and light conditions
What is the difference between anoxic and hypoxic conditions in terms of DO?
Anoxic: DO < 1 mg O₂ L⁻¹ (Very stressful)
Hypoxic: DO ~2-3 mg O₂ L⁻¹
What factors influence the loss of DO in the hypolimnion once stratified?
Amount of organic matter entering the hypolimnion
Time since onset of stratification
Volume of hypolimnion
Water temperature
What are the different DO profiles in lakes?
Orthograde: DO higher in the hypolimnion
Clinograde: DO levels decline with depth
What can modify DO patterns near the thermocline?
Heterograde: Elevated photosynthesis in the metalimnion leads to DO max
Heterograde negative: Metalimnetic DO min, due to bacterial or zooplankton respiration
What spatial differences in DO can be found in lakes?
Aquatic macrophytes (littoral zone)
Rapid decomposition of organic matter
Between basin differences
River inflows or sewage inputs
Ice/snow cover variability
What DO profile would you expect in a humic lake (dark water)?
Expect a Clinograde profile with lower DO in the hypolimnion due to the dark water limiting light penetration for photosynthesis.
What is hypoxia?
Hypoxia is a state of low oxygen in water, typically affecting aquatic ecosystems.
What causes hypoxia in freshwater bodies?
Hypoxia occurs when the water column stratifies, causing oxygen to accumulate in the warmer upper layers, while the colder lower regions (hypolimnion) remain poorly oxygenated.
How does decomposition contribute to hypoxia?
Decomposers at the bottom of the water consume oxygen, which can further reduce oxygen levels in the hypolimnion, especially when organic matter accumulates.
How does pollution exacerbate hypoxia?
Pollution, particularly nutrient enrichment, can promote algae blooms. As algae die and decompose, it increases oxygen consumption at the bottom, worsening hypoxia.
What happens to zooplankton in hypoxic conditions?
Zooplankton, which are important for controlling algae, may die in hypoxic conditions, leading to more unchecked algae growth and more decomposition, further reducing oxygen levels.
What are the four key questions to ask when predicting hypoxia?
Is the water being mixed?
Is there an algae bloom?
Is the algae bloom being consumed by small animals?
Are there too many nutrients (e.g., from pollution)?
