During thermal stratification, what happens to the bottom layer of water?

During thermal stratification, the bottom layer of water, often referred to as the hypolimnion, tends to lose oxygen and undergo anaerobic decomposition. This phenomenon occurs because the layers of water in a stratified lake or body of water are separated by temperature gradients, with the warmer, lighter water at the top (epilimnion) and the cooler, denser water below.

As thermal stratification establishes itself, the hypolimnion is isolated from the atmosphere and the upper layers, meaning it does not receive new oxygen. As organic matter settles to the bottom and decomposes, bacteria in the hypolimnion consume the oxygen present in the water. When the dissolved oxygen levels drop, anaerobic conditions prevail, leading to anaerobic decomposition processes, which can produce harmful byproducts like methane and hydrogen sulfide.

This process can negatively impact water quality in the hypolimnion, contributing to problems such as fish kills or the release of nutrients that can cause algal blooms when mixing occurs later in the season. Understanding the dynamics of thermal stratification and its effects on the bottom layer of water is crucial for effective management and protection of aquatic ecosystems.