Mystery of Granger Pond

I was just beginning to tell Whitney King the Mystery of Granger Pond, when he surprised me by confidently jumping into the tale.

"Second week in August, right?" said King, a Colby College chemistry professor.

Well, yeah … maybe.

Usually the water in Granger, a 125-acre pond in Denmark, is crystal clear. But in August water clarity declined alarmingly and kept dropping. The water turned distinctly green. In his 35 years on the pond, camp owner Bob Simmons had never seen anything like it.

"I'm looking down at the pond now from my cottage," Simmons told me in early October. "I used to be able to see all the rocks very clearly. And I can see them - but it's murky."

Granger Pond clearly had an algae bloom, but the speed at which it developed was dramatic and puzzling. The phosphorous and chlorophyll levels hadn't increased significantly and there seemed to be no reason, such as recent development, why they should. Granger only has about a dozen camps and little boat traffic.

"It just doesn't make sense right now, so it's kind of a mystery," said my co-worker Colin Holme, field services director of the Lakes Environmental Association (LEA) in Bridgton.

Algae are microscopic plants that live in the surface waters of lakes. They're usually present in such small numbers that they're not visible to the human eye. But when they get extra nutrients, particularly phosphorous, algae can become so abundant they become unpleasantly visible. An algae "bloom" is actually an algae population explosion. The state lists about 40 lakes that commonly experience algae blooms, which reduce water clarity and, depending on the type of algae, produce yellowish-brown, blue-green or even red scum. There also may be a bad odor. An algae bloom turns a gorgeous lake into a place you wouldn't want to stick your toe, much less your face.

Water clarity is measured with a simple device invented in the 1860s by Pietro Secchi, a Jesuit priest and scientific advisor to Pope Pius IX. A Secchi disk is black and white and about 8 inches in diameter. You lower it into a lake with a measured line. Then, with a water scope cutting down glare, you note at what depth the disk disappears from view. Lakes with a Secchi disk reading of less than 2 meters are considered impaired.

In Granger, the Secchi disk could be seen at 6 or 7 meters early this summer, but "by August it was at 3 meters and by September it went to the high 2s and then the low 2s," Holme said.

LEA sent an algae sample to Roy Bouchard at the Maine Department of Environmental Protection, hoping to pinpoint the type, which might help explain the cause of the bloom. But Nov. 30, Bouchard emailed Holme that he couldn't identify it, though it "it appears to be a blue-green algae of rather small dimensions …"

When I was told King about Granger's mysterious bloom, he thought the answer was pretty clear. He and his Colby students have been studying East Pond in the Belgrades, which commonly experiences algae blooms. They've placed sensors that continuously measure temperature in the deepest area and they also measure dissolved oxygen, phosphorous and water clarity.

It looked as if East Pond would escape an algae bloom this year until an event in early August that King not only saw, but felt.

"I was coming back to shore as fast as I could as the thunderstorms rolled in. We got off the lake just in time, but I was soaked," he said. "We had two inches of rain in one day."

Camp roads turned to muck and soil - with phosphorous - washed into the lakes. That "runoff event" triggered algae blooms in a number of lakes, King said. In East Pond "it brought the phosphorous up about 3 parts per billion in a week," he said. "That's not very much but it's enough to trigger a bloom if everything else is sort of right."

As soon as I hung up the phone, I checked Maine Newsstand, the database where daily newspaper stories are archived. Sure enough, big storms moved across much of the state Aug. 3. And on Aug. 6 there was a record rainfall in Portland of 2.29 inches, while Gray reported .80 inches. However, weekly rainfall totals compiled by LEA in Bridgton don't show quite as big a "runoff event." Just .92 inches rain was recorded for the week ending Aug. 7. There was more, 1.28 inches, during the week ending July 24.

So perhaps The Mystery of Granger Pond is solved. But perhaps we'll never know for sure. And maybe there's another chapter coming next year.