Studies of Gloeotrichia echinulata (Gloeo) a blue-green alga or cyanobacteria blooming in Lake Sunapee, do not hold good news for our lake. Dartmouth 2006 honors graduate Cayelan Carey hasstudied Lake Sunapee’s bloom for two summers. Her work was done for her honors thesis, and results have been submitted to scientific journals. The second summer’s work validated the findings of the 2005 study and added further lab and lake experiments to expand her work. Carey presented findings to LSPA’s annual meeting in July 2006, and to the Board at the end of her summer 2006 work. (See the Beacon, September 2005 and July 2006 for articles on her methodology and preliminary results.)
What Gloeo Looks Like
Gloeo in the lake water looks like little (1/16" diameter) round yellow-green dots. They are suspended throughout the lake water (the water column). Gloeo has appeared in Sunapee’s water for the last several summers. At the surface, the colonies tend to form little clumps (1-2" wide) of many colonies together. If the winds and lake surface are just right, the colonies can end up all floating together to form a greenish surface scum. When in the water column, Gloeo looks enough like the pine pollen that we are used to seeing in June that many observers do not register that this yellow-green stuff is different from, and appears at a different time than, the pine pollen we usually notice in the spring.
Role of Phosphorus
Lake Sunapee is categorized as oligotrophic, or a lake that is clear, with low nutrients, high oxygen, and sparse plant growth. While the nutrient levels in the lake water, though rising, are at levels typical of oligotrophic lakes, Carey found that the sediment in Sunapee contains very high amounts of the nutrient phosphorus – closer to the levels expected in a eutrophic lake. (Eutrophic lakes have an abundance of nutrients, algae and plant life that deplete the oxygen in the water, reducing fish and other biological life forms in the lake.
Carey discovered that the trapped sediment phosphorus plays a role in the life cycle of Gloeo. When there are increases in the amount of phosphorus, the number of Gloeo colonies that enter the water can increase dramatically. Carey found that peaks in sediment phosphorus are followed by peaks in the presence of Gloeo in the water. The interval between these peaks is the exact amount of time needed for Gloeo in the sediment to develop into the colonies that enter the water column.
Carey conducted a separate experiment in 2006 to definitively test the effect of phosphorus pulses on the migration of Gloeo colonies from the sediment to the water column. (See page 4.) The experiment demonstrated that increases in sediment phosphorus significantly trigger the migration of Gloeo into the water. This finding, states Carey, “indicates that the most effective way to reduce Gloeo blooms is to limit the amount of phosphorus entering the sediment, particularly phosphorus that enters the lake in pulses.”
Sources of Sunapee’s Phosphorus
The presence of phosphorus in Lake Sunapee’s sediment may have come from many sources over the years: in the 19th century, sheep farming, clear cut fields and lumbering; in the 20th century and today poor waste handling practices (cess pools and failing septic systems); and in more recent years, runoff from roads and house sites, the use of detergents (especially dishwasher) containing phosphates, and improperly functioning septic systems. Whatever the sources, the amount of phosphorus in the sediment means that Gloeo blooms on Lake Sunapee are likely to become more of an issue for lake users. The key to reducing them is limiting the amount of phosphorus – the one key nutrient for Gloeo – getting into the lake sediment.
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