Murky, oxygen-deprived ponds benefit from alum approach
By Doreen Leggett, from The Cape Codder newspaper
Dleggett@cnc.com
MASHPEE - There is always a worry of a fish kill when alum is used as a solution for nutrient-choked lakes.
And scientists did discover a dead fish while looking around the edges of Ashumet Pond after an alum treatment earlier this month. But it had nothing to do with the chemical.
"It likely died of old age," said Ed Eichner, water scientist at the Cape Cod Commission.
The buildup of phosphorus in Ashumet Pond is predominately from a plume that emanates from a wastewater treatment plant on the Massachusetts Military Reservation. The plant was closed in 1995, but the plume still exists and phosphorus streams into the pond near the parking lot and boat landing.
Eichner is one of many who are keeping an eye on the military-funded solution to the phosphorus problem in the pond, which is in Mashpee and Falmouth.
"A lot of people are interested," said Spence Smith, the project manager and part of the Air Force Center for Environmental Excellence. "It's touchy with acid ponds like the Cape. It looks like we have a good result here."
Bob Sherman, Mashpee's conservation agent, said that he thought the application went well, but the real test will be in mid-October. That is when the lake "turns over" and the colder water rises; if the alum hasn't done its job, there will be a bloom.
The application was timed with the stratification of the pond in late summer when there is no mixing between the shallow and deeper waters of the pond.
"All the chemicals tested have come out within the norms of what they expected," said Sherman, adding that the town and its consultant had done a lot of planning with AFCEE.
If the alum treatment in Ashumet Pond proves successful, it is likely that more and more pond lovers will be looking at the chemical as a way to fight the blossoming amount of phosphorus in other Cape waters.
Eichner said the recent interest in alum, which has been used in ponds across the nation for 30 years, has less to do with the chemical than the condition of the Cape's waters and a growing awareness that ponds are being affected by too much development.
"I think we are starting to see more problems in our lakes," he said. "A lot of it is a reflection of all the things that have gone on on the Cape in 20 years."
Long Pond, in Brewster and Harwich, is on the cusp of getting close to $300,000 in state monies (Ed.: this earlier grant request was denied late in 2001...) to conduct an alum treatment and do some work to reduce the input of nutrients at the 740-acre pond.
Excess phosphorus in a pond acts as an out-of-control fertilizer, oftentimes creating large algae blooms. When the blooms die, they suck up a tremendous amount of oxygen. The bottom of the ponds are left without oxygen, making them inhospitable for many forms of life, most notably fish.
Particularly worrisome is that the amount of phosphorus in the ponds has grown to such levels that they don't even need outside influences (septic systems and road run-off being two prime examples) anymore. Locked up in the pond sediment, phosphorus feeds itself by being released in oxygen-starved water and fostering blooms which continue the cycle.
Alum is part of the battle against eutrophication, but management is the key to winning the war. Eichner said alum buys time for pond managers to work with residents and others to cut down on nutrients. Many towns are looking at ways to address growth and wastewater, he said, naming Orleans and Chatham in addition to Mashpee and Falmouth.
Alum is not the only solution for minimizing the impacts of phosphorus. In the Long Pond study, the consulting firm ENSR listed close to 20 ways to treat the pond, including aeration (which pumps oxygen into the water), herbicides, flushing and mechanical removal. In some cases dredging is used and the nutrient-rich material is used on golf courses.
ENSR's David Mitchell, who worked on the Ashumet Pond project, said they too looked at a number of options, but alum was the top choice.
The chemical has been used on the Cape at least once before, in Barnstable's Hamblin Pond in 1995, where it caused a massive fish kill. Researchers say improper application was the cause, not the alum itself. None of the players at Ashumet were involved in the Hamblin Pond application, which, despite the fish kill, has resulted in clearer water and increased oxygen levels. The effects of alum last about 20 years.
Alum's role is two-fold: it scours phosphorus from the water column and creates a barrier so the phosphorus in the sediments can't escape. Although alum, aluminum sulfate, does the work, another chemical, sodium aluminate, is equally important, acting as a buffer for the more acidic alum, explained Gerry Smith. Both chemicals are injected into the lake simultaneously in a 2:1 ratio.
Smith, the owner of Aquatic Control Tech, has been in the business for more than 20 years and has worked on 400 ponds and lakes. A number of those projects involved alum, but the work his company did on Ashumet was likely the first of its kind in the nation.
The alum is typically applied at the surface or injected a maximum of 20-25 feet under the surface. At Ashumet, the injection was done at a depth of 35 feet.
Spence Smith explained that the fish in the pond didn't stray below 25 feet because there was no oxygen, but the team, which included Bob Sherman, decided to play it safe and add another 10 feet.
Gerry Smith (no relation) said his company had to construct longer equipment for the barge that they typically use for alum treatments. A series of paired nozzles, two-feet apart across a 30-foot long boom, inject the chemicals. Researchers watching the application through a special viewfinder can see the alum drifting to the bottom.
"The [alum flakes] get bigger and fatter as they go down," explained Mitchell. "It looks a lot like driving through a snowstorm."
Fish can also be seen on the viewfinder, swimming happily above the alum.
Spence Smith said they have few worries of the treatment harming anything below 35 feet.
"There isn't much life there," he said.
To make sure they had calibrated the dosage properly, the team did a test patch in early September and that worked well. Only five acres, the deepest portions of the 28-acre pond, were treated.
The project was spurred by residents who worried about the quality of their pond. Unlike Long Pond, which has experienced algae blooms and fish kills, Ashumet is in relatively good condition, but it is deteriorating.
The alum treatment is only part of the three-part project, which also includes adding iron to the sediments along the pond's shore and long-term monitoring.