Scientists concerned over lake oxygen levels

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(Host) Just about all living things need oxygen to survive.

And it’s the lack of oxygen that has scientists worried about Lake Champlain.

Dissolved oxygen levels in the depths of the Lake’s northeast arm have declined steadily for over a decade.

Researchers say it’s a new and alarming sign of worsening water pollution.

VPR’s John Dillon has the story:

(Dillon) The lake is dead calm as Tim Burke motors out from Keeler Bay in South Hero.

Burke works for the Conservation Law Foundation, a regional environmental group. In the winter, he rides the political currents in the Statehouse. In the summer, at least on nice days, his office is a small aluminum boat.

(Burke) “We use the boat to patrol the lake, to investigate sources of pollution, but also to reach out to people who use the lake to hear about their concerns, to educate them about water quality problems in the lake.”

(Dillon) We’re headed for a spot of water north of Savage Island. The trouble is not on the surface, but about 135 feet down.

New research has documented a steady decline in oxygen levels near the lake bottom.

Burke explains that fish, especially species like trout and salmon, prefer abundant amounts of oxygen, around 6 to 8 parts per million. This low oxygen zone has levels as low as 2 or 3 parts per million.

(Burke) “Cold water fish can’t live in water without a good supply of oxygen. But it’s also just an indication that water quality is deteriorating.

(Dillon) Here’s the basic formula for Lake Champlain water pollution. Nutrients, such as phosphorus from sewage, farm fields and suburban lawns, wash into the lake. The phosphorus acts as a fertilizer and stimulates toxic algae blooms. And when the tiny organisms die, they sink to the bottom and use up oxygen as they decompose.

(Burke)”The decline in dissolved oxygen levels at this spot in the Inland Sea correlates to increases in phosphorus levels at the same place.”

(Dillon) The problem is not unique to Lake Champlain. About a third of the country’s medium to large size lakes suffer from some level of eutrophication. That’s the term for nutrient-caused pollution.

Eric Smeltzer is the state’s Lake Champlain specialist who discovered the low-oxygen problem. He studied 15 years of water samples from this deepest part of the lake’s northeast arm.

His research paper describes an “alarming acceleration” of eutrophication in this part of the lake.

(Smeltzer) “It’s an additional cause for alarm. But the bottom line is it’s just one more reason that we really need to reduce phosphorus levels in the lake.”

(Dillon) The Gulf of Mexico has an area known as the “dead zone” where oxygen levels are too low to support life. This area of Lake Champlain isn’t dead, but it may need life support.

(Smeltzer) “Oxygen is not zero down there, but it can get as low as 3 or 4 milligrams per liter, which is probably lower than trout like. So I think some of the organisms that are less tolerant of low oxygen levels are going to avoid that area or become stressed.”

(Dillon) The Conservation Law Foundation says Smeltzer’s research is the first to document the low oxygen problem in Lake Champlain. It’s one more sign that the big lake is under stress.

For VPR News, I’m John Dillon in South Hero.

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