Out in The Woods

Stream foam near Hanson Ridge Road Rail Trail Trailhead. The newer, white foam is on the upstream section, left

Photo Credit: Kevin McKeon

Nature Brews Organic Foam

By: Kevin McKeon, Maine Master Naturalist

Enter the Rail Trail at Hanson Ridge Trailhead and look to your right near the opening to the granite box culvert — or really, look beside any woodland stream — and you’ll occasionally see a foamy mass. What is this sudsy-looking stuff? There’s a natural explanation.

Pour your brewed coffee or tea from a foot or so above your cup and it will form bubbles. Do the same with water — notice the difference in bubble persistency?

Well, nature’s brew is formed from the action of surface water mixing with dissolved organic matter from leaves, twigs, topsoil, and algae, which contain surfactants — materials that reduce surface tension in water. Hand soap does the same thing. This reduction essentially makes water “wetter” and easier to “spread”. And it also makes bubbles last longer. This action is comparable to a tea bag infusing its flavor and color into your teacup. Scientifically called dissolved organic compounds (DOC), the bubbles created from turbulent water flow stabilize and persist, collecting in stream obstructions and eddies. (Eddies are circular flows of water created by obstructions to water flow, like rocks, branches, and riverbanks.) This foam is usually white at first, turning brown as atmospheric and environmental materials are absorbed.

The waters of Deering Pond and the surrounding Hall Reserve are rich in tannins, absorbed from the landscape’s acidic, peat-forming soils. As such, you’ll notice that these waters are a bit brownish, indicating a high level of DOC’s; thus, foam is readily formed, especially during elevated turbulent flows, like after a rainfall and during snow melt.

There’s another naturally occurring foam found along shorelines and beaches. These are called foam lines, and they’re caused by similar actions. As aquatic plants and algae die and decompose, the natural oils contained in their cells are released and float to the surface. Wind and wave action combine to mix the two, both decreasing the water’s surface tension and pushing the mixture to the shore. The turbulence and wave action at the beach creates persistent bubbles that form foam lines.

So, at the seashore, seawater mixing with decaying matter from dead plankton and algae results in the beach foam we see. The sea air smell we all love is caused by bacteria eating this decay, releasing this scent.