mcdude
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The Suncook River and Milfoil
From the Baysider 9/28/06
To get a good look at the plants growing on the bottom of the Suncook River, the section above the Barnstead Parade dam was lowered by two feet (as pictured here on Sept. 21), and then by four feet, and then by six feet. The Barnstead Milfoil Control Committee found what they both feared and expected: Lots of milfoil. The photo below was taken by a reader, revealing milfoil covering the river bottom, like so much green spaghetti.
The level of the Suncook River has been lowered over the past week, and the Barnstead Milfoil Control Committee was troubled by the amount of milfoil revealed in some stretches of the river – and puzzled by the absence of it in other stretches.
The committee, preparing for a chemical treatment of the river this spring, had been planning to drop the level of the river by eight feet below its normal level, but concerns about native fish species compelled NH Fish and Game officials to limit the fall draw down to six feet below normal, a level which was expected to be reached by Wednesday, Sept. 27. Under normal circumstances, the river can be as deep as 20 feet in the main channels.
It was thought that the current in the main channel would have discouraged the growth of the aquatic weed in and near the channels, but that turned out to be at least partially incorrect. One purpose of the draw down was to survey the river while the water is low, and see just how close it comes to the main channel. Ed Neister, of the Milfoil Control Committee, said milfoil was seen to grow very close to the main channel, where the committee members were traveling in their boat. "They saw in spots a forest under the boats – not a good sign."
The planned chemical treatment will use an aquatic herbicide 2,4-D, which is effective in targeting and killing only the aquatic weed milfoil, must be absorbed by the plant in specific concentrations if it is to be effective.
The plan to treat the river in the spring is to lower the river, thereby causing the current to recede to the main channel so that the "flats" can be treated while the water is still.
For the sections near the river's channel, Neister fears, those patches will have to be hand-pulled by divers, which will be especially time-consuming and arduous in the river's flow.
In the wide, shallow areas, known as the "flats" or "broads," the lower water levels revealed wide swaths of milfoil, some patches stretching for many acres. One reason for the study was to confirm the presence of the plant, but another benefit is that the exposed plants will dry, desiccate and defoliate. The roots of the plant won't die, and they will begin to grow back next year, but the amount of biomass will be reduced, which will increase the effectiveness of the planned treatment.
As thick as the milfoil is in some areas of the river, there are other parts where NH DES Water Biologist Jody Connor found a moderate amount of milfoil mixed in with native plants, and other areas where native plants are dominant and milfoil is absent. Connor had studied the Suncook River, cove by cove, immediately prior to the beginning of the draw down, to map the presence of the milfoil. He described the river as being moderately infested on average.
It may only be moderate over the entire stretch of the river, but Neister says the plant is completely taking over in the soft, silted parts of the river. In those areas, the plants were observed growing right up to the shoreline.
Puzzling to Neister and Connor is that once they got upstream from the cove where the Crooked Run River connects with the Suncook, milfoil is completely absent. This is especially puzzling because Brindle Pond and Suncook Lake, both of which have or have had milfoil infestations, feed into upstream sections of the Suncook River. And it isn't that there aren't any suitable habitats for milfoil in that stretch of the river. Neister said there are plenty of places where he expected to see it, but it just wasn't there. "It really confuses us… it should have been there."
Why is there milfoil above and below this section, and yet no milfoil for this one stretch? "That's a good question. I don't have any answers to that at this point," said Connor.
Scott Decker, NH Fish and Game official, raised concerns prior to the draw down about the effect to fish populations, especially the swamp darter and bridle shiner, both of which are small prey fish. After the river was drawn down, he canoed up and examined the scene for himself. He didn't see any dead or dying fish stranded in the "flats," although he did see several fishing birds, such as herons and cormorants.
Although the weed is seen as a nuisance and potential threat to the ecosystem by some, Decker said that eliminating the milfoil could cause some short-term ecosystem turbulence.
"Even though it's a non-native plant, when you're taking away that much plant matter, you're taking away habitat." He said that smaller fish have been observed to use milfoil patches in Lake Winnipesaukee as habitats.
From his experience on Lower Suncook Lake, Neister said that fish will use milfoil when it is less dense, usually within the first couple of years of an infestation, but that it then becomes too dense even for the small fish. "It very quickly takes over the area, and becomes a suffocating thing," he said.
The dam operators will slowly begin to bring the river up to its normal level today, Sept. 28, and it will begin to fill up quickly once Suncook Lake is lowered for its normal fall period, expected to begin in the first days of October.
The Milfoil Control Committee will use the information and experience gained from this draw down to apply for a spring treatment, in which the river will again be drawn down for the chemical treatment.
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