Water Chestnuts - "They're Not Talking About Chinese Food"

(Alfred Cofrancesco, U.S. Army Corps of Engineers, at www.forestryimages.org)

(http://www.iisgcp.org/EXOTICSP/waterchestnut.htm)

Originating from European, African, and Asian waters, Trapa natans, commonly called the water chestnut, began to invade the American northeast around the 1870s. Some of its offenses include the clogging of waterways and ponds, as well as significantly altering native aquatic habitats, one of which includes the mighty and already infested, Lake Champlain.

Water chestnuts inhabit shallow areas of freshwater lakes and ponds as well as slow-moving streams and rivers, upon which, the formation of impenetrable mats of floating vegetation begins. They also favor nutrient-rich waters with a pH range of 6.7 to 8.2. The Burlington bay area of Lake Champlain fluctuates around a pH of 8, making it a great medium for water chestnut habitation. To put the severity of Trapa invasion into perspective, the author of this article lists species distribution history throughout the Northeast, and immediately proceeds this by singling out Lake Champlain. Of all the aquatic bodies listed, the Charles River, the Hudson River-Mohawk River drainage basin, and even Lake Ontario, Lake Champlain was the only one mentioned to be a "major infestation of more than 300 acres... throughout some 55 miles... between New York and Vermont" (O'Neill, 2006). 

(Alfred Cofrancesco, U.S. Army Corps of Engineers, www.forestryimages.org)

Water chestnut populations are mainly kept in check by parasitism provided by native insect species. Devoid of such insects, Lake Champlain currently has no natural predation defenses against and remains susceptible to such invasive attacks.

( Vermont Department of Natural Resources)

 These attacks introduced various physical, ecological ,and economic impacts that were previously absent. Firstly, the dense mats of vegetation prove to be a hazard to recreational lake users as the sharp, spiny nuts can puncture swimmers. Mat density also severely limited light penetration for other species. This, along with the plant's decomposition, creates a trophic cascade since reduced oxygen levels and increased fish kill resembles the effects of eutrophication. So, water chestnuts can severely and easily out-compete native aquatic species, and deteriorate the biodiversity of the entire habitat. Moreover, the species provides little to no nutritional or habitat value to other fish or waterfowl species.


It is possible to control the spread of a water chestnut invasion, but is easiest to do so in the early stages; thus, early detection and rapid response are key to preventing infestations. Small, early populations can be easily hand-pulled, while larger populations require the more costly use of mechanical harvesters or aquatic herbicides. Even so, these solutions are merely temporary, as new mats of chestnuts will once again grow back next season from the bed of the waterbody. It is estimated that a treatment of 10 years would be needed in order to completely eradicate such an invasion. The article goes on to mention that New York and Vermont alone have spent $4.3 million dollars from 1982-2001 on water chestnut control measures on Lake Champlain (O'Neill, 2006).

( The Nature Conservancy, www.nature.org/aboutus/careers/index.htm)

(Vermont Department of Natural Resources)

References
O'Neill, C. R. (2006, February). Sea grant new york. Retrieved from http://www.waterchestnut.org/Assets/PDF/wcfactsheet.pdf