An Algae’s Tale - Three Billion Years of Gas Bubbles,
Oxygen and, More Recently, Dog Doo

by Lake Champlain Committee Staff Scientist Mike Winslow

Perhaps one of the more unpleasant experiences one can have while exploring Lake Champlain is an encounter with a fetid mat of decaying algae right where you wanted to go swimming. If you decide to swim anyway you are likely to emerge with a layer of green slime in your hair. In early August of this year the Vermont Department of Health issued warnings that blooms of blue-green algae were likely. Even more frightening, in the summer of 1999 three dogs were killed after eating blue-green algae from the Lake. What is this stuff? Why does it have to show up right at the hottest time of the year? The answers to these questions lead to remarkable stories of persistence, catastrophe, and adaptation.

Of the algae most likely to coat the waters of Lake Champlain during the summer, one group is particularly intriguing. This group, the blue-green algae, or cyanobacteria, are similar to bacteria in that they have very small cells with no separate structures inside their cells. However, like plants and other algae they have chlorophyll and make their own food. Indeed, they were the first organisms on earth to use the energy of sunlight to combine water and carbon dioxide to produce sugars for energy.

Cyanobacteria have persisted for longer than almost any other organism. Their fossilized cells have been found in rocks over 3 billion years old, and for about 2 billion years they were the dominant life form on earth. Only in the last 0.27% of their existence have cyanobacteria coexisted with humans. For comparison, a 90 year old great-grandfather has coexisted with his 3 month old great-granddaughter only in the last 0.27% of his life. The difference is that cyanobacteria show no signs of disappearing soon.

Cyanobacteria are responsible for one of the most widespread ecological disasters in geologic history. While making sugars for themselves, blue-green algae release a waste product that is highly reactive and can be toxic to many organisms - oxygen. Though today all plants release oxygen, when cyanobacteria began doing so 3 billion years ago there was very little of it in the atmosphere. Over hundreds of millions of years, oxygen accumulated (today it accounts for about 21% of the air we breathe), and many species of bacteria that had previously lived without it went extinct. One species’ garbage is another species’ treasure, and whole new branches on the evolutionary tree sprouted to take advantage of cyanobacteria’s waste, including humans.

Over their long history, cyanobacteria have evolved elaborate defenses to avoid being eaten by grazers. Many cyanobacteria produce a slime, or mucus coating that makes them taste bad. Their most potent defenses, however, are toxic chemicals strong enough to kill livestock if sufficient quantities are drunk or eaten. There are two general categories of toxins associated with cyanobacteria: those that attack the liver and those that attack the nervous system. Liver attackers are more common and persist in water for a relatively long time. They do not seem to deteriorate as water temperature or pH changes. As a result, they can accumulate to greater concentrations before breaking down or dispersing. In cases of severe poisoning, death occurs within 36 hours. Nervous system attackers, the other category of toxins, were responsible for the 1999 dog deaths on Lake Champlain. Though generally less common and less stable than liver attackers, nervous system attackers work more quickly and livestock can die within 30 minutes. Toxins are released from cyanobacteria only when their cells break, for example, when they die or when an animal tries to graze upon them. Toxins only accumulate to detrimental levels when there are large masses of specific types of cyanobacteria.

Why do blooms of cyanobacteria only seem to occur in late summer or early fall? As lake water warms, cyanobacteria have three competitive advantages over other algae. First, cyanobacteria can get the nitrogen they need for growth directly from the air – no other algae can do this. When stream flow is low less nitrogen is carried to the lake and this element becomes limiting. Secondly as water temperatures increase, grazing increases, but cyanobacteria are less heavily grazed than other algae. In addition to their mucus and toxins, cyanobacteria have a tendency to form large mats, and size conveys some protection from predation. Thirdly, unlike other algae, cyanobacteria cells contain gas bubbles that help them stay near the surface where they use sunlight to make food. As water temperature increases, water density decreases and algae without gas bubbles sink to darker depths. Usually cyanobacteria circulate in the water column through the day by adjusting the amount of gas in their cells. If however circulation is limited (perhaps because of an absence of wind), cells near the water surface can overheat and die, and whatever toxins were in those cells are released, leading to the algae’s demise and our disgust with the green slime coating the water.

The one nutrient that cyanobacteria and other algae have the hardest time getting is phosphorus. Absence of phosphorus keeps their populations in check, but, luckily for them, humans have helped out by adding phosphorus to the Lake through a variety of avenues.

Historically, the greatest sources of phosphorus in the Lake were sewage wastes. Unlike cyanobacteria humans (and other animals) take in more phosphorus than they can utilize. What we don’t incorporate into our bodies is eliminated in the toilet, and treated in septic systems or sewage treatment plants. However, great strides have been made in updating sewage treatment plants throughout the Champlain Basin and we can no longer single out such "point" sources of pollution as the culprits. Non-point sources of phosphorus still abound however, but they are much more difficult to identify and remedy.

A significant source of non-point phosphorus is fertilizer. On land, as in the water, plant growth can be limited by an absence of phosphorus. Plants can only take advantage of certain forms of the element (water soluble), but once these forms are placed on soil they often change into unusable forms and bind to soil. If more phosphorus is added each year as fertilizer than is removed in harvest, concentrations in the soil accumulate. At some point the soil is no longer able to incorporate additional phosphorus and the excess washes off during the next rainstorm.

Phosphorus is also found in animal wastes, though not all animal wastes present a problem. One of the most common fallacious statements I hear is that phosphorus can’t be controlled because we have so many wild animals living and pooping in the woods of the Champlain Basin. Phosphorus from animal wastes only becomes a problem when the animals are so concentrated that they overwhelm the ability of the soil to recycle the nutrient, but there are examples of such conditions around the Champlain Basin. The easiest example to imagine is cows in a field, but dogs in a city also count as a significant source of untreated waste. In some ways dogs in a city are worse because they deposit their phosphorus pollution on concrete surfaces instead of soil so there is no chance for a conversion to unusable forms before it is washed off during the next storm.

Another non-point source of phosphorus pollution is failing septic systems. Household septic systems are essentially mini-sewage treatment plants. If they work properly, much of the phosphorus) from household sewage is trapped in the septic tank and the rest acts as fertilizer for the grass over the leach field. When septic systems fail, due to high water levels, inability of wastewater to percolate through soils, or any other reason, household sewage flows to the nearest water body and is eventually carried to Lake Champlain.

Finally, phosphorus is added to the Lake whenever erosion occurs. Erosion is usually caused by exposure of the top layers of soil and removal of vegetation holding these layers together. Coincidentally, the top soil layers are also where the majority of phosphorus is held. When these layers wash into rivers and then the Lake, phosphorus bound to the soil goes too.

Currently, Lake Champlain has too much phosphorus. New York, Vermont and Quebec are collaborating on ways to reduce annual inputs. It’s a formidable task, but success will mean improved lake health, and cleaner, clearer water for swimming. Failure means more ruined swimming trips and potentially, more toxic outbreaks of blue-green algae.

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Lake Look is a monthly column produced by the Lake Champlain Committee, a 2,500-member citizens’ conservation organization working in New York, Vermont and Quebec. To join, contact the Lake Champlain Committee, 106 Main Street, Suite 200, Burlington, VT 05401-8434, (802) 658-1414, lcc@lakechamplaincommittee.org.