Lake turnover events influence dissolved oxygen by doing what?

• A. Destroys oxygen entirely
• B. Brings oxic bottom waters to the surface to re-oxygenate
• C. No effect on oxygen
• D. Creates anoxic surface layer

Answer: (B)

Turnover mixes the water column, breaking down thermal stratification so that water from different depths blends together. This mixing moves dissolved oxygen around, bringing oxygen-rich water from deeper layers upward toward the surface and redistributing it throughout the column. The result is re-oxygenation of the bottom waters that had become depleted during stratification, along with restoring higher oxygen levels near the surface. So, turnover influences dissolved oxygen by bringing oxic bottom waters toward the surface to re-oxygenate the lake. This process does not destroy oxygen, it does not leave oxygen unchanged, and it combats the formation of anoxic layers rather than creating them.