What process causes the bottom layer of water in a reservoir to lose oxygen due to decomposition?

The process that causes the bottom layer of water in a reservoir to lose oxygen due to decomposition is anaerobic decomposition. In this process, organic matter, such as plant and animal remains, is broken down by microorganisms in the absence of oxygen. This typically occurs in deep or stagnant waters where oxygen levels are low, leading to conditions suitable for anaerobic bacteria to thrive.

As these anaerobic bacteria decompose the organic matter, they consume the limited oxygen present in the water. This can result in a significant decrease in oxygen levels at the bottom layer of the reservoir, which can negatively affect aquatic life that requires oxygen to survive.

In contrast, aerobic decomposition requires oxygen and occurs in well-oxygenated waters, where microorganisms break down organic matter using the available oxygen. Facultative processes can involve both aerobic and anaerobic processes depending on the available conditions but do not specifically characterize the loss of oxygen in deep water due to decomposition. The term speculative does not relate to a biological or chemical process in this context.