Waterway warriors

Fans turn out to rid their beloved Nashua River of invasive plant

For years, avid duck hunter Doug Conner watched as water chestnuts slowly but surely spread throughout his beloved Nashua River. The invasive plant resembles a lily pad, but grows thick enough to clog acres of open water with dense leaves and underwater tendrils that choke out native flora and fauna.

"The only thing that could get through there is an airboat," said Conner, pointing to a green carpet of water chestnuts as he plied the Pepperell Pond area of the river in his camouflage-colored motorboat. "A duck couldn't even make it through there."

Now Conner and others are getting their hands dirty to stop the spread of water chestnuts, which state environmental officials have identified as one of their top concerns in Boston-area waterways. Last Sunday, local conservationists organized a water chestnut "pull," when around 40 volunteers took to the Nashua to yank tons of plants from its calm waters.

The pull was designed to remove water chestnuts from areas of the river too shallow for tractor-sized, floating harvesting machines to enter. Using a $300,000 state grant secured by area legislators, the Groton-based Nashua River Watershed Association contracted this summer with Aquatic Control Technology of Sutton to conduct the mechanical harvesting.

The mechanical harvester and hand pull are expected to remove around 450 tons of water chestnuts from 45 acres of the river in the next few weeks, said Martha Morgan, NRWA water programs director. She expected another mechanical harvesting and hand pull to take place next year, too, she said.

Already, Conner said, the river is cleaner. "On both sides of the river, except for 100 feet in the middle, it was infested," said Conner, a Pepperell resident. "If you had been here a month ago, you'd have seen a green blanket."

Conner and others at the event said they wanted to help clean up the river because it's central to their lives. "I've hunted and fished on this river for the past 10 years," said Conner. "I felt like if you're going to take something out, you've got to put something in."

George Crochiere, a Pepperell resident who regularly kayaks on the river, said he would spend five hours at the hand pull because he didn't want to see water chestnuts invade other rivers northwest of Boston. "They'll float downstream, and the Merrimack will get it," he said. "Then it will be in Lowell."

It's not hard to pull a water chestnut. One simply reaches over the edge of one's boat, grabs a floating cluster of the plant's leaves, and hauls them and their long wispy stems up. In less than an hour, a puller can fill a few laundry baskets to the brim with plants. They are attached to silt in the river bottom, but only loosely.

"It's a floating weed," said Phil Rogers, a Pepperell resident who was out on the river in his canoe. "You just pull it up. That's the easy part."

Pullers have to wear gloves, however. The water chestnut's seed, from which it derives its name, is a rock-hard, spiny black nut when fully developed. "It will go right through your shoes," said Conner.

The nuts' spines are why the water chestnut spreads so rapidly, said Anne Monnelly, acting director of water resources at the state Department of Conservation and Recreation.

It's believed a Harvard University botanist inadvertently released the water chestnut into Massachusetts' ecosystem more than a century ago, said Monnelly. Since then, it has invaded around 20 water bodies in the state, mostly in the Boston area, she said. The plant is native to Africa, Asia, and Europe, but is not the same as the edible water chestnut used in Asian cooking.

The nuts become lodged in boats' bilges, on ropes, and anywhere else they might cling. "They'll stick in the down in the geese," said Conner. "They fly to another body of water and drop them off. Once you get one, then the infestation starts."

The nuts float to the bottom of rivers and ponds and, when they germinate, release a stem as long as 16 feet that reaches up to the surface before blooming into 10 to 15 rosettes, or leafy clusters, said Monnelly. Each rosette can produce as many as 20 seeds.

With so many seeds, said Monnelly, water chestnuts can quickly proliferate in slow-moving waters with soil rich enough to support them. They suck up oxygen, displace other plants and fish and, when they die, alter the chemical composition of the water, harming native species.

"It really changes the ecology because you get this mat that is blocking out sunlight to many of the plants below," said Monnelly. "It is also reducing recreational values because you can't get through it. When it dies, you get this mass of biomass as it gets broken down."

On the plus side, water chestnuts are relatively easy to eliminate. They aren't perennial plants, so if they are removed from the water before they drop their seeds, they won't reproduce, said Monnelly. The trick is to catch them when they've germinated, but before their seeds have matured, and to come back again to grab the plants that remain.

"With water chestnuts, you really can't expect to remove it in one year," she said. "There's a seed base in the sediment. . . . You usually need to come back, we say, once every three years."

The state recently removed 130 tons of water chestnuts from Fiske Pond in Natick, said Monnelly. A hand pull last month on the Charles River yielded three dumpsters of plants.

Another volunteer at the Nashua hand pull, Marion Stoddard, who was instrumental in cleaning up the river when it was grossly polluted from paper mills in the 1960s, was dismayed at the spread of the water chestnuts. But their appearance isn't all bad, she said.

Years ago, Stoddard didn't anticipate the Nashua would ever suffer from an excess of vegetation, she said, adding that she also didn't foresee how organized the river's friends would be.

"It's clean enough to have this problem. Everybody is keen about helping. They use and enjoy the river. They want to help protect it."

John Dyer can be reached at johnjdyerjr@gmail.com.