Anoxic (no oxygen) Conditions in Lakes and Wetlands

Anoxic conditions in wetlands refer to the lack of molecular oxygen (O2) in wetlands and lakes.  They can arise under a number of conditions.  Most organisms are stressed or killed

Flowers of Silver Maple floating on the water.

The decaying leaves and plants in this floodplain forest can lead to anoxic conditions in the wetland soils.

under anoxic conditions, but there are some bacteria that require anoxic conditions to survive.  Anoxic conditions lead to anaerobic processes (those chemical reactions that occur in the absence of molecular oxygen)

How Anoxic Conditions Arise

I most cases organisms are the cause of anoxic conditions.  They take in oxygen for cellular respiration and release CO2 as part of the chemical process that makes energy for the cell.

One ways anoxia occurs is the overabundance of algae.  It’s true that algae produce oxygen during the daylight hours, but when the sun dips below the horizon these same algae need oxygen to use the energy they created by photosynthesis during the day.  In elementary school it is drilled in our heads that plants produce oxygen and animals use oxygen.  This is really half a lie, because oxygen is just as important to plants as it is to animals, and some plants like Indian Pipe produce zero oxygen.

Anoxia can result quickly in sediments or in other places where there is little or no movement of water, such as in the bottom of deep lakes.  In these stagnant situations it can take 7 hours to diffuse 1 cm.

Many organisms that live in lakes and wetlands have developed adaptations that allow them to survive near anoxic, or fully anoxic conditions temporarily.  Some organisms, shut down their functions for short periods.  Emergent plants will pump oxygen down into their roots, where conditions in the sediment are usually anoxic.  Some fish have the ability to gulp air at the water’s surface.  Many of these adaptations require energy, put them at risk of predation or have some other negative impact to the organism, so anoxia is usually avoided if at all possible.

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