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Hypoxia (environmental)

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**Types of Hypoxia:**
– Atmospheric Hypoxia:
– Occurs naturally at high altitudes
– Total atmospheric pressure decreases with altitude
– Lower partial pressure of oxygen at high altitudes
Oxygen remains at 20.9% of the total gas mixture
– Basis of altitude training for elite athletes
– Aquatic Hypoxia:
– Anoxic aquatic systems lack dissolved oxygen
Oxygen levels in water are approximately 7 ppm
– Hypoxic conditions are required by many organisms
– Most fish cannot live below 30% oxygen saturation
– Healthy aquatic environments should rarely have less than 80% oxygen saturation

**Causes and Effects of Hypoxia:**
– Causes of Hypoxia:
Oxygen depletion can result from natural factors
– Pollution and eutrophication are common causes
– Phytoplankton blooms can lead to oxygen depletion
– Dead zones can be created in estuaries
– Hypoxic coastal zones are a global concern
– Seasonal Kill:
– Hypolimnetic oxygen depletion leads to summer and winter kills
– Summer kills occur due to extreme oxygen depletion
– Winter kills happen when ice cover reduces oxygen exchange
– Anaerobic organisms can die in winter kills
– Hypoxia can extend throughout the water column

**Phytoplankton and Oxygen Consumption:**
– Phytoplankton Breakdown:
– Phytoplankton breakdown consumes oxygen
Oxygen presence affects breakdown rate
– Rate of breakdown can be represented by an equation
Oxygen is used up quickly in the breakdown process
– Breakdown releases dissolved carbon into the environment

**Environmental Impact and Concerns:**
– Algal blooms
– Anoxic event
– Dead zone (ecology)
– Cyanobacterial bloom
– Denitrification
– Declining oxygen in the global ocean and coastal waters
– Ocean time series observations of changing marine ecosystems
– Spreading Dead Zones and Consequences for Marine Ecosystems
– Aquatic Hypoxia Is an Endocrine Disruptor and Impairs Fish Reproduction
– Characterization of Hypoxia: Topic 1 Report for the Integrated Assessment on Hypoxia in the Gulf of Mexico

**Research and Studies on Hypoxia:**
– Dissolved Oxygen
– Encyclopedia of Puget Sound: Hypoxia
– Modeling the biodegradation of multicomponent organic matter in an aquatic environment
– Dynamics and impact of ocean acidification and hypoxia
– Oceanography: Dead in the water
– Environmental conditions in burrows of two species of African mole-rat
– Limnology: Lake and river ecosystems
– Eutrophication: An Overview of Status, Trends, Policies, and Strategies
– Dead Zone Causing a Wave of Death Off Oregon Coast
– Kinetics of phytoplankton decay during simulated sedimentation
– In situ Investigations on Respiration and Behaviour of Stickleback and the Eelpout During Low Oxygen Stress
– In situ investigations on the respiration and behaviour of the eelpout under short term hypoxia

Hypoxia refers to low oxygen conditions. For air-breathing organisms, hypoxia is problematic but for many anaerobic organisms, hypoxia is essential. Hypoxia applies to many situations, but usually refers to the atmosphere and natural waters.

Global map of low and declining oxygen levels in the open ocean and coastal waters, 2009. The map indicates coastal sites where anthropogenic nutrients have exacerbated or caused oxygen declines to <2 mg/L (<63 μmol/L) (red dots), as well as ocean oxygen minimum zones at 300 m (blue shaded regions).
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