Floating Azolla as an Evaporation Cover
The floating fern Azolla forms a low-profile surface cover that cut evaporation ~26% in a study — and up to ~46% paired with a chemical monolayer.
What it is
Azolla is a small floating aquatic fern that spreads into a continuous mat over still water. Like duckweed, it works as a living surface cover — shading the water and partly sealing the surface — but it sits especially low and flat, which keeps its transpiration penalty relatively small (see what is evaporation).
How well it works
A study of flooded water surfaces found an Azolla cover reduced loss by ~26% on its own, rising to ~46% when combined with a chemical monolayer (Wetlands, 2020). The combination result is a useful illustration that natural and chemical approaches can stack: the floating mat handles shading and the surface barrier while the monolayer helps seal the gaps between fronds.
As with any living cover, part of the suppressed evaporation returns as transpiration — but Azolla’s low profile makes that penalty smaller than for tall emergent plants.
Trade-offs
- Ecology. Azolla can be invasive and needs containment; a decaying mat depletes oxygen and degrades water quality.
- Co-benefit. It fixes nitrogen, which is valued in rice paddies and integrated farming — sometimes the primary reason it is grown.
- Robustness. It drifts and breaks up in wind and waves, so it suits calm, contained water rather than open reservoirs.
Where it fits
Azolla is most defensible on rice paddies, small irrigation ponds and integrated aquaculture systems where its nitrogen fixing adds value and the water is calm and contained. For larger or windier sites, compare duckweed, palm fronds and the full methods comparison.