A Pond’s Natural Muck Accumulation Requires Periodic Cleaning

When ponds are deeper than six to eight feet, wind churns the water naturally when the water temperature is uniform. As the water warms under the summer sun, the pond stratifies with warmer water on top and cooler water below. The upper oxygen-rich layer absorbs oxygen, but the oxygen does not reach the pond bottom due to the thermal stratification.

Organic material accumulating on the pond bottom requires bacteria, worms, and other types of benthic animals to decompose. However, they consume a large amount of oxygen. When thermal stratification prevents oxygen from reaching the bottom, the beneficial critters die and are replaced by anaerobic bacteria which:

Require no oxygen
Decompose 20-30 times slower
Produce methane gas, acids, nitrite, and hydrogen sulfide resulting in a rotten egg or septic smell
Release phosphorus from the sediments that feeds new plant and algae growth

This condition reverses a pond's self-purification capability and kills aquatic animals in the lower levels. Nutrients that would normally be locked in the sediment get released into the water. The excess nutrients have the same harmful effects as those that come from the surrounding watershed. Fertilizers, animal droppings, septic tank seepage and nutrients recycled from the sediment all increase a lake's need for oxygen. Removing the pond muck do away with the gas and phosphorus source. Aerators can then be used to eliminate the thermal stratification.