WHAT CAUSES FOAM IN STREAMS AND LAKES?
Jeffrey C. Davis, Aquatic
The Aquatic Restoration and Research Institute
Alaska Clean Water Action Grant No. 05-02
Foam often is seen accumulating against logs or on the banks of
streams, or along the shores of lakes on windy days. When it first
appears, foam can be white, but generally turns brown over time.
The development of foam occurs due to changes in the water surface
tension and the physical introduction of air. There is a slight
tension on the surface of water caused by the chemical attraction
among water molecules. This tension is what allows some insects
to move along the water surface and what causes water to “bead
up” on your car during a rain storm. Certain molecules interact
with the water reducing the surface tension. These molecules are
called surface active agents or surfactants. Foam is produced as
air, introduced in the turbulence of stream riffles, below waterfalls,
or as waves break upon the shore, bubbles to the water surface.
There are many natural and synthetic (human produced) surfactant
molecules. Synthetically produced surfactants are an ingredient
of most household cleaning products such as detergents, shampoos,
toothpaste, and cosmetics. Early detergents, developed after the
Second World War, were non-biodegradable, that is they could not
be broken down by bacteria. This resulted in large accumulations
of persistent foam particularly below sewage treatment plants and
other points where these surfactants were released into waterways.
These early detergents also contained phosphorus which softened
the water by binding with calcium and magnesium. However, this phosphorus
also contributed to blooms or prolific growths of algae and other
aquatic plants. Due to these problems, the chemical structure of
synthetic surfactants was modified to a biodegradable form that
contains sulfates instead of phosphates. The most widely used synthetic
surfactants today are linear alkylbenzenesulfonates (LAS) listed
on most products as sodium or ammonium laureth or lauryl sulfate.
Naturally produced organic surfactants are released from algae and
plants when they die and begin to decompose but also in lesser amount
when living. These organic surfactants are part of a large variety
of plant material that when dissolved in water is referred to as
dissolved organic carbon (DOC). The breakdown of large algal blooms
in ocean waters can lead to the accumulation of foam on beaches
up to 3 feet deep. The primary source of DOC in lakes and streams
is from the surrounding watershed soils. Bogs and wetlands deliver
large amounts of DOC to streams and lakes because they are very
productive and the breakdown of plant material within wetlands is
slow. The presence of DOC in lakes and streams is why they are dark
in color and often referred to as “brown-water streams.”
Foam often is seen in our brown-water streams in the spring as snowmelt
carries DOC to adjacent streams and lakes or during fall rain storms
after the leaves have fallen and begun to decompose. In addition
to causing foam, DOC provides energy and performs many additional
functions important to aquatic ecosystems. Although natural, human
activities that cause an increase in algae or aquatic plant growth
like the introduction of nitrogen or phosphorus fertilizers can
cause plant and algae blooms and an increase in foam production
along with the removal of oxygen as these plants decompose. The
foam is not toxic; however, removal of oxygen can cause fish kills.
Foam from plant produced surfactants will occur at many locations
along a stream accumulating on against the bank, or on logs or other
material in the stream. It may be white at first, but will turn
brown over time as sediment particles build up in the foam. The
foam will persist for some time gradually diminishing in size. Increases
in foam abundance will often follow rainstorms that transport the
surfactants to the stream or along lake shores on windy days.
Foam from detergents
and other synthetic surfactants generally will accumulate near the
source and should not occur over large distances. The foam will
be white and sweet smelling or scented. The foam will not persist,
and will dissipate quickly once the source is removed. Foam accumulations
from synthetic surfactants will generally not be related to rain
storms or windy conditions on lakes.
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occurrence of foam on lakes and streams. Great Lakes Environmental
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