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To control spread of weeds, Corps mulls grass carp, herbicide for lake
SoVaNow.com / December 06, 2012The U.S. Army Corps of Engineers is considering an assault on hydrilla in Buggs Island Lake that could include herbicide treatments and the introduction of Chinese grass carp, measures that have also been employed on nearly Lake Gaston for years to control the highly-invasive noxious weed.
The Corps held a public meeting at the Kerr Dam project near Boydton on Nov. 15 to explore options for weed control on Buggs Island Lake and seek out public input on a preferred method for addressing the problem.
Preliminary reports from a recent environmental assessment done on Buggs Island Lake indicate that hydrilla — a highly invasive aquatic weed blamed for clogging waterways and interfering with recreational activities — is alive and well in the 48,900 acre lake. Chris Powell, a Corps conservation biologist, says the areas infested with the weed are rapidly increasing.
At first, the problem was mainly limited to the North Carolina side of the lake. The shallowness of the water due to the gradual slope of the shoreline in that area was more conducive to hydrilla growth, Powell said. Now, weeds are just as often spotted in coves and boat launch sites throughout the Virginia side of the lake.
Michael Womack, Operations Project Manager for John H. Kerr Reservoir, noted that dense vegetative mats of hydrilla are interfering with public use of the lake by restricting access around boat ramps, docks and coves, and limiting opportunities to swim, fish from the shoreline and enjoy other water activities.
Hydrilla also may be killing eagles and waterfowl because of a type of blue-green algae that grows on top of the weed mats. These algae are potentially toxic to birds and it is believed that waterfowl are poisoned by eating hydrilla containing the toxic algae. When eagles eat smaller infected waterfowl, they succumb to the disease as well. More than 100 eagle deaths are believed to be a result of the disease.
Powell added that experience has shown the problem must be addressed before Buggs Island Lake is overtaken by a dense mat of hydrilla. The Corps has been involved in hydrilla eradication and control in the southeastern United States for nearly 40 years.
Since its discovery, hydrilla has caused significant economic damage, Powell said. In 1991 hydrilla forced the St. Stephen Powerhouse at Lake Moultrie, S.C. to cease operations for seven weeks. The project surrendered $2 million in revenue from the loss of power generation and spent more than $2.5 million to repair the clogged plant, dredge the nearby waterway to eliminate the underground tubers and to restock lost fish.
For Buggs Island Lake, which already has experienced problems with inadequate levels of dissolved oxygen, hydrilla poses an additional threat to biodiversity.
Powell said the preferred treatment plan is a combination of chemical and biological controls, the latter to include Asian grass carp, which are prodigious eaters of the weed. The fish typically must be restocked as they are rendered sterile to keep them from becoming a noxious species unto themselves. Grass carp and herbicide treatments have been a mainstay of the weed control program on Lake Gaston, which has been ongoing since hydrilla was discovered there some two decades ago.
Powell said he does not recommend manual controls or mechanical harvesting since these methods can further spread invasive plants due to fragmentation. Additionally, mechanical controls remove native plants along with hydrilla and create disposal issues.
The Lake Gaston Weed Control Council’s weed management program — which is carried out in conjunction with the state of North Carolina’s Department of Environment and Natural Resources (NCDENR) — includes annual surveys, biological assessment of the tuber growth, herbicide applications as necessary and grass carp to assist in the removal of plants and tubers.
The Council, on its website, acknowledges that Sonar treatments control the hydrilla plant, but are not effective on the tuber bank in the sediment — the underground root from which hydrilla grows.
Powell highlighted the importance of tuber control by noting the seemingly intermittent pattern of the infestation: “Kerr Lake Reservoir has been in existence for 60 years, but the hydrilla problem has only occurred in the last five or so years. Why now, what has happened or changed?” Even though the Corps cannot answer that question, Powell said biologists understand that hydrilla can lie dormant in underground tubers for many years. Once it receives sufficient light exposure, the plant will emerge from dormancy. As the hydrilla grows and spreads, “It degrades the habitat for and displaces native aquatic vegetation.”
Osceola County, Florida, which has battled hydrilla infestations for decades, was awarded a $2.881 million dollar grant by the Environmental Protection Agency (EPA) to find new and cost-effective ways to manage hydrilla. In the end, officials concluded that grass carp and the use of herbicides specifically registered and approved for use in aquatic environments were the most effective tools for dealing with the problem.
Both Powell and Womack agree that, whatever method is chosen, the intent of the Buggs Island Lake Aquatic Vegetation Management Program is to maintain a healthy and sustainable ecosystem dominated by native aquatic vegetation, especially since elimination of hydrilla in Buggs Island Lake is not realistic given both the wide geographic extent of the current infestation.
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