On October 16, Matt Ricker, a graduate student in URI professor Frank Golet’s wetlands ecology class retrieved a leaf of an unfamiliar plant from Belleville Pond in North Kingstown.

Discovery specimen from Matt Ricker and Frank Golet

Professor Golet and RINHS staff confirmed the leaf as coming from a water chestnut. On October 18 two survey staff members returned to the find site and confirmed a patch about 20 meters in diameter, containing some hundreds of individuals. The plants, which are annuals, are already beginning to die back, with leaves and rosettes floating loose from their stems and leafless stem heads sinking to the bottom. Numerous seed pods were observed, caught in submerged vegetation or in mats of floating algae. The population is in a meter of water, on loose and unconsolidated organic sediment bottom. It is about 50 meters from shore in the northwest section of the pond.

A brief reconnaissance of nearby areas of the pond did not locate any other patches. At first glance, based on the number of individuals, the species appears to have been present since at least the 2006 growing season, though probably not for long before that, given its apparently still restricted distribution. The lat. & long. of the patch (determined using Google Earth Plus) are: 41* 33′ 56.51 N x 71* 28′ 58.69 W.

Find site

Belleville Pond is located in the town of North Kingstown. The pond is a well known fishing, waterfowling, and passive recreation location accessible by canoe from a ramp in Ryan Park, off of Oak Hill Road. Belleville Pond is part of the Annaquatucket River system, a relatively small watershed with headwaters a mile or so to the northwest, discharging through a series of historic impoundments into Narragansett Bay at Bissel Cove a mile or so to the southeast. The river includes the state-run Lafayette fish hatchery.

Map of Belleville Pond and contiguous waters in the Annaquatucket watershed to assist with reconnaissance for other T. natans patches.

Water chestnut (Trapa natans) is native to Eurasia (and is not related to the water chestnut commonly found in stir-fry). It was introduced to North America in the 19th century as a horticultural plant and it promptly escaped to the wild. It can grow vigorously and densely in shallow, nutrient-rich waters, obliterating native pond habitat, clogging waters to most recreational uses, and presenting a significant physical hazard to swimmers and waders due to its diabolical, barbed seed pods. Concerted efforts have been made to limit its spread, with variable results, throughout the past century. New York and Vermont spent almost half a million dollars controlling it in Lake Champlain in 2006.

Water chestnut seed pod from Belleville Pond. Each pod has four, centimeter-long spines, each with numerous needle-sharp, backward-pointing barbs.

Fact sheets on water chestnut, including more photos, diagnostic drawings, control measures, etc., at:
invasive.org
IPANE
Vermont DEC
Maine Center for Invasive Aquatic Plants

The discovery of water chestnut in Rhode Island is an extremely serious development, though not entirely a surprise, given its distribution in nearby states. In fact, the small size and apparently low distribution are good news. Also good news is the fact that the plant have seeded already and we have about 8 months to prepare an eradication plan. Water chestnut is an annual, so control efforts can be effective if undertaken before seed is set. Unfortunately, water chestnut seed can remain viable, in pond mud, for 5-12 years so reconnaissance and control will be a long term commitment.

RINHS is in touch with freshwater ecologists at DEM and around the state and region as well as with grassroots watershed and aquatic recreation groups about the discovery and we expect to convene a meeting on the issue later in the fall. At this meeting the technical requirements for eradication will be described and we will begin planning an eradication campaign for spring and early summer of 2008. If you want to keep in touch with developments or are interested in participating in the meeting, please contact David Gregg at RINHS. Please visit rinhs.org for regular updates. RINHS members can receive email updates: membership information.

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