Confidence votes 4.8K. The base meanining of un pigeonnier is a dovecote (a structure where doves, or similar birds, are bred or housed). But you will also find un pigeonnier used to mean a garret-flat, or any small flat near the top of a building (especially if it is a low-rent sort of place).
Duckweed creates an anaerobic environment. When it comes to wastewater lagoons, the lack of dissolved oxygen is bad. (Read our previous article, Troubleshooting Low Lagoon Dissolved Oxygen, for an in-depth look.) Duckweed is a DO killer, blocking the oxygen-transferring interface between the surface of the lagoon and the atmosphere.
Fish and submerged plants can be killed. Because of this, duckweed infestation often contributes to poor pond health. Duckweed can tolerate a wide range pH, between 4.5 and 7.5, as well as temperatures between 68F (20C) and 86F (30C), making duckweed a challenging aquatic plant management issue worldwide.