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Keywords: Squam Lakes, variable milfoil, Eurasian milfoil, aquatic ecosystem, invasive plant, exotic species, ecological monitoring Photographs copyright Karlene V. Schwartz and cannot be reproduced without permission of the photographer |
 Variable Milfoil |
"It's Up To YOU To Control Aquatic Nuisance Species" a New Hampshire Department of Environmental Services flyer announces. What is an aquatic nuisance species? Nuisance species affect the integrity of freshwater biological communities and also the use of freshwater as a resource for humans. Variable milfoil (Myriophyllum heterophyllum), water chestnut (Trapa natans), fanwort (Cabomba caroliniana), and Brazilian elodea (Egeria densa) are just four of the aquatic species considered exotic nuisances in New Hampshire, a state in which they are not native. Uninformed people inadvertently introduce exotics into a water body by dumping aquaria in a lake or by introducing nuisance plants purchased from the nursery trade. Exotic nuisance plants can hitch a ride from lake to lake on boats, boat trailers, dive gear, bait pails, and personal watercraft.
Exotic aquatic plants are among the greatest threats to water bodies because each exotic species has the potential to reduce biological diversity. Fragments of nuisance species are often each capable of forming another plant and so disperse widely in a short time. A plant-clogged lake becomes less attractive to swimmers and divers, who might become entangled in the clogging weeds. Heavy aquatic plant growth makes water less attractive to canoeists, kayakers, and rowers. Weed strands trail behind boat propellers. Fishermen and -women are annoyed by loops of plant clinging to their fishing lines. Exotics may reduce lakefront property values by as much as 16%, according to a 2001 University of New Hampshire report (cited in Attention Boaters - Are you unknowingly spreading Exotic Aquatic Plants, published by New Hampshire Department of Environmental Services, Aquatic Species Program, Concord NH.). More importantly, dense growth of nuisance submerged plants may impact fish populations by stunting fish growth. When out-of-control exotic plants decompose, the level of dissolved oxygen in a water body drops. The oxygen decline is sometimes sufficient to trigger a fish-kill. Invasion of exotic species may also compete with native species.
Variable milfoil, Myriophyllum heterophyllum, a nuisance aquatic plant, grows up to seven meters (22 feet) tall in an infested lake, emerging from the water surface. This milfoil species is native to streams and ponds from Florida to New Mexico. When people introduce milfoil into water outside its natural range, the plant lacks natural controls that exist in its native waters. Variable milfoil readily establishes itself and the population may explode. The result can be impossible to eradicate, pricey to control.
By 2002, about 50 water bodies in New Hampshire were invaded by variable milfoil. Although it is illegal to transport and introduce exotic aquatic plants in New Hampshire, it was only a matter of time before milfoil was carried from an infested lake to the two Squam Lakes in central New Hampshire. Squam and Little Squam are well-known for their pristine waters, but even in the Squam Lakes, variable milfoil has become a troublesome aquatic culprit.
When an infestation of milfoil was documented in the Squam Lakes, Squam Lakes Association (SLA), was quick to act on its mission:
“The Squam Lakes Association is dedicated to conserving for the public benefit the natural beauty, peaceful character and unique resource values of the lakes and surrounding areas. In cooperation with local and state authorities and other conservation organizations, the Association promotes the protection, careful use and shared enjoyment of the lakes, forests, open spaces and wildlife of the Squam Lakes region.”
SLA hired an ecosystem management consultant who identified and monitored invasive and/or alien plants as a facet of the bioinventory of the Squam Lakes. The Association devised a plan to manage invasive aquatic plants that involved:
An environmental biologist who is an Americorps member hosted by the SLA coordinated the Weed Watcher program. She provided each volunteer Weed Watcher with a kit developed by the New Hampshire Department of Environmental Services to train volunteers and lake residents to regularly monitor and report exotic plants in New Hampshire water bodies and reduce dispersal of nuisance species. The kit has a plant identification guide illustrated with forty-one plants that might be encountered in and around a lake. Exotic/invasive species—Myriophyllum heterophyllum (variable milfoil) and Myriophyllum spicatum (Eurasian milfoil)—are shown and described as well as their native look-alike Myriophyllum humile. Additional sections of the kit help neophyte Weed Watchers learn to conduct an exotic weed-watch survey, as well as provide a list of New Hampshire lakes known to have exotic plants and fact sheets about exotics. Using these materials, a Weed Watcher surveys a selected portion of a lake monthly from June through August. If a suspicious species is spotted, the Weed Watcher collects a sample which is sent to the NH Department of Environmental Services for identification. If it is a nuisance species, the biologist determines the action necessary to control the infestation.
Physical management of milfoil-infested areas consisted of installation of bottom barriers, manual extraction of individual milfoil plants and application of herbicide. The SLA purchased a supply of bottom barrier material and laid down several thousand square feet on the lake bottom and in the channel connecting Little Squam and Squam Lake. Milfoil-infested areas near marinas and large boathouses were posted restricting boating to minimize breakup of milfoil plants. Near one marina with particularly heavily infestation on Little Squam Lake the herbicide Diquat was applied in a 1.5 acre area. Diquat use required a state permit and posting restrictions. Lakeshore abutters were notified and provided with drinking water. In about two weeks most, but not all, of the milfoil had died. Monitoring of the infested areas continues. In addition to laying bottom barrier and application of herbicide, milfoil plants were handpicked by SLA and New Hampshire Department of Environmental Services divers.
A program to educate the public about aquatic plants was developed and implemented by SLA staff with input from the NH Dept. of Environmental Services. Live variable milfoil was displayed in an aquarium at the SLA headquarters to show visitors the physical characteristics of the submerged plant. Brochures picturing milfoil were presented to lakeshore property owners and other SLA members. The brochure instructs people to:
1) look for signs that warn of invasive plants,
2) remove and dispose of these species,
3) wash and dry all equipment before using their boat, trailer, trailer hitch, fishing or diving gear again
4) drain and flush the live wells of the boat, the boat engine cooling system, dive gear and bait buckets
5) inspect all gear before launching in another water body to paddle, dive, fish, or boat and
6) remember that it is illegal to transport aquatic exotic plant species in New Hampshire.
The National Oceanic and Atmospheric Administration (NOAA) granted $260,000 to the New Hampshire Lakes Association to staff boat launches with Lake Hosts and for milfoil education. The SLA received $4,700 in grants to staff boat launch ramps with Lake Hosts who instruct boaters about invasive exotic plants and train them to inspect their boats. The SLA served as a regional training center for Lake Hosts and trained over 40 people. Several boat ramps on the Squam Lakes were staffed with Lake Hosts on weekends and holidays. The shoreline of the Squam Lakes is within the jurisdiction of five towns: Ashland, Center Harbor, Holderness, Moultonborough and Sandwich. SLA solicited cooperation from these towns to manage aquatic nuisance species and several agreed to cooperate by welcoming boat Lake Hosts at their town beaches. But a drawback of this system is that boaters are not fully informed about nuisance aquatic species when launching at times or sites lacking Lake Hosts.
Information about aquatic nuisance species is posted at the State Of New Hampshire Public Boat Access Ramp in Holderness, which provides access to the Squam Lakes. Information about milfoil is also provided at the SLA's own low-impact boat access point. Here canoeists, kayakers, and sailors may rent craft from the SLA or launch their private boat. Off-lake boats are inspected for invasive aquatic plants before entering Squam and as they leave the lakes. The SLA newsletter and website (http://www.squamlakes.org) feature updates about milfoil.
In the Squam Lakes, the main objective—to reduce milfoil growth and prevent milfoil fragments from spreading to additional areas of the Lakes was attained. But, these lakes must be continually monitored for new areas of infestation. As a result of early detection and prompt management, beaches of the Squam Lakes are clear of plant fragments, boat traffic lanes are free of weeds, waterfront property values have held up and fishing and swimming are generally fine. And—most critical of all—milfoil has not displaced beneficial wildlife.
Although the SLA decided to spend up to $50,000 in the year 2002 to aggressively address the management of invasive milfoil, the solution is temporary. Watching for milfoil, applying herbicide, hand-pulling of plants, and emplacement of bottom barriers will continue for the foreseeable future. In the future, research may eventually discover an aquatic herbivore or other biological control agent that could be introduced into an infested lake to control or eradicate the milfoil population without further upsetting the native ecosystem.
Maine Volunteer Lake Monitoring Program. A Field Guide to Invasive Aquatic Plants. P.O. Box 445, Turner ME 04282-0445. Telephone 207 225-2070.
"Stop the Spread of Exotic Aquatic Plants" [an illustrated brochure listing 14 exotic aquatic plants listed as prohibited species in New Hampshire and how to help prevent their spread]. New Hampshire Department of Environmental Services, Watershed Management Bureau, 6 Hazen Drive, Concord NH 03301. Telephone 603 271-2693. http://www.des.state.nh.us/wmb/exoticspecies/
The Loon Flyer. Summer 2002. Published by the Squam Lakes Association, P.O. Box 204, Holderness NH 03245.
The views and opinions expressed in all articles that appear in "Conservation Perspectives" are those of the authors and do not necessarily reflect those of NESCB.