Great Lakes Article:

THE OCCURRENCE OF FOAM ON LAKES AND STREAMS
Doug Fuller
Tip of the Mitt Watershed Council
Posted 01/29/2003

Foam is often observed on surface waters throughout northern Michigan. It is especially prevalent in lakes on windy days, either as streaks on the surface or in windrows along the shoreline; or in streams below rapids and waterfalls. It is most commonly the result of the natural characteristics of the water.

The physical properties of water result in an exceptionally strong bonding of water molecules to each other (cohesion) at the water's surface. This is commonly referred to as surface tension. The surface tension of water is higher than that any other liquid, except mercury. Surface tension appears sort of like a tough plastic film over the water surface. Some insects, such as water striders, take advantage of surface tension to walk on the water in search of prey. Keen observers can actually see the depression made on the water's surface film by each of the insect's feet. The surface tension also presents a threat to some tiny organisms, such as microscopic zooplankton, which may become trapped in the surface film and cannot escape.

Under very still conditions, grains of sand at the water's edge can become trapped in the surface film and drift offshore. A reduction in surface tension is conducive to the formation of bubbles or foam. The surface tension of water can be greatly reduced by the addition of certain substances, mostly organic compounds. These substances are called surface active agents (or surfactants). Natural populations of algae and submerged aquatic plants secrete large quantities of organic compounds during photosynthesis, as well as during decomposition, which act as surfactants. Locally reduced surface tension near beds of aquatic plants has been observed. Strongly stained bog lakes and lakes having massive algal blooms are likely to have the greatest surface tension reduction.

In autumn, when there is a general die-back and decomposition of aquatic plants, the pulse of surfactants released often results in the most conspicuous foaming of the year. Slowly flowing streams generally develop greater surface tension reduction than more rapidly flowing waters. Although unstained lakes with low plankton productivity have relatively low surface tension reduction, foam forms even on unproductive waters such as the Great Lakes.

Seawater, which is very productive, has long been noted for its foaming properties. Wind and wave action can create parallel cells of clockwise and counterclockwise vertical currents that result in linear alternations of divergences and convergences in the upper layers of lakes. These type of currents, called Langmuir circulation, are most noticeable when the wind is strong. Where current cells converge, drifting debris and surfactants concentrate. This, coupled with the turbulence of the lake surface, generates streaks of foam which are oriented approximately parallel to the wind. Between the streaks are clearer zones of upwelling. The greater the wind speed and wave size, the wider the distance between streaks. The persistent foam blows downwind and forms windrows along windward shores. The compounds responsible for surface tension reduction can also be concentrated in downwind areas, resulting in additional foaming as waves break on the shoreline.

Soaps, detergents, and other cleaning products contain surfactants mixed with conditioning and water softening agents. Surfactants increase the wetting and cleaning power of water. In the past, synthetic surfactants were highly resistant to microbial degradation. Foaming was excessive and persistent, and often mountainous piles of foam could be found downstream from urban areas and wastewater treatment plants. In addition to being unsightly, excessive foam causes water quality problems. Light transmission and atmospheric air exchange are reduced, causing low oxygen levels. The foam may also become wind-borne, causing public health problems in areas where the water contains high levels of bacteria or other pollutants. Surfactants are now made of more degradable compounds that bacteria can utilize as a source of food.

Without laboratory analysis, it is impossible to determine whether foam observed on lakes or streams is the result of natural conditions or human activities. Foam-causing detergents or other pollutants could possibly find their way into our waterways from faulty septic systems, commercial or industrial areas, waste treatment facilities, or human activities such as car washing or in-lake bathing. However, it is unlikely that foam from these sources would be found far from its source, because it degrades relatively quickly and it becomes greatly diluted. Undoubtedly, most observed foam is the result of natural circumstances.

An increase of foaming has been observed in Northern Michigan on inland waters where zebra mussels have reached high population densities (including Burt, Charlevoix, Crooked, Mullet, and Pickerel).This relationship has also been observed in other parts of the country, particularly the Finger Lakes of New York. It seems likely that these invasive exotic organisms are either directly excreting large amounts of surfactants into the water, or affecting the foaming indirectly through the other changes they have wrought on aquatic ecosystems (such as an increase in filamentous algae growing on the bottom). In fact, researchers there have found high levels of proteins and fatty acids in the foam. Next, they will be analyzing the protein molecules and trying to correlate them somehow with the zebra mussels.

REFERENCES Hutchinson, G. E. 1975. A Treatise on Limnology, Vol. 1. John Wiley and Sons. 1015 p. Hynes, H.B.N. 1974. The Biology of Polluted Waters. U. of Toronto Press. 202 p. Maxwell, K. E. Environment of Life. Dickenson Pub. Co. 489 p. Wetzel, R. G. 1975. Limnology. W.B. Saunders Co. 743 p.