By David Wartinbee, for the Redoubt Reporter
A few weeks ago, a friend asked me if I knew about the pollution going on in a particular stream. He had seen patches of foam and an endless stream of bubbles in a variety of places along the edge of the stream. There were masses of foam floating on the surface and large accumulations of discolored foam trapped behind a couple logs. He was certain something bad was getting into that stream.
About the same time, when launching my boat at Lower Skilak Lake Campground, I saw the entire northern shoreline outlined with a thick mass of pure white foam. The 2-inch-thick foam was blown up on shore in a swath almost a foot wide. It looked like someone spilled a giant bottle of bubble-bath soap into the water. Were these piles of bubbles the result of some untoward act, too?
The answer is simple. No pollution activity is indicated by either of these situations. Masses of bubbles floating on the surface of lakes and streams are perfectly natural. Interestingly, the natural processes that caused these bubbles to form are almost identical to those required to make soap.
People have been making and using soaps for more than 4,000 years. The needed materials haven’t changed much through the years and are relatively simple. First, there needs to be a source of fatty acids. American colonists commonly used fat (tallow or lard), but fish oils or even vegetable oils will do. Caustic lye, an alkaline solution made from wood ashes, was used to cause the fatty acids to combine with sodium or potassium ions. The resulting molecules had a nonpolar end and a polar end, which means that part of the molecule would combine with water and one part would not. These molecules change the surface tension of the water, and that causes foam or bubbles.
Lakes and streams are surrounded by living organisms, and many organisms live within the water itself. Both plants and animals produce lipids like simple fats — three fatty acids combined with a glycerol molecule. When any of these organisms die, they release fats, proteins, sugars and other molecules into the water. Nonpolar molecules like lipids float since they have a lower specific gravity than water and will not mix with water. As fats and other lipids break down, the released fatty acids also float to the surface.
Thus, the surface of the water often has a thin, completely transparent layer of lipids on it. Through reactions similar to those used to make soap, the resulting molecules change the surface tension and, just like soap, they cause bubbles to form.
Agitation of the surface layer of lipids causes bubbles to form. The thick layer of foam I saw at Skilak Lake surely resulted from the heavy wave action the day before. The associated wind then drove the foam up onto the shore where is showed up so distinctly on one side of the lake. In streams, foam collects in backwater areas and gets trapped behind floating obstacles like tree branches or emergent vegetation. As the material oxidizes and debris collects in the foam, it can take on ominous colorations. Lots of floating objects and even microorganisms get trapped within these foam masses.
The fact that foam acts as a floating debris collector has been put to good use by many different scientists. The floating pupal cast skins I use to identify Chironomids can be found by the thousands in these foam collections. My wife jokes that as a graduate student, I could recognize foam in a stream at 60 miles per hour, and then we needed to stop and collect a sample.
Other insects, like caddisflies and mayflies, can leave their pupal skins in these foam masses, too. Those who work with aquatic fungi commonly use foam collections to find representative spores. As well, within these foam masses one can find pollen, seeds, algae, moss spores, minute insects called collembola, and a variety of other minute animal, plant and fungal remains.
It has been shown that some environmentally degrading activities can cause foam to occur in streams and lakes. For example, high concentrations of detergents or faulty sewage treatment facilities are known to cause excess foam creation. Some mining activities like washing gravels or adding materials to lakes can cause extraordinary amounts of foam to be created. The foam itself is not usually the polluting activity, but rather the foam is an indication that something is going on.
Perhaps excess amounts of foam or unusual odors might raise a suspicion of human activity. Seeing lots of dead fish mixed in with the foam certainly indicates that it’s time to notify the authorities. Unfortunately, it is very difficult to separate naturally occurring foam from pollution-related foam.
While huge masses of foam in a stream or around our lakes could signal a pollution situation, the vast majority of foam we see is from perfectly normal biological processes.
David Wartinbee, Ph.D, J.D., is a biology professor at Kenai Peninsula College’s Kenai River Campus. He is writing a series of columns on the ecology of the Kenai River and Cook Inlet watershed.