Management methods for Cabomba caroliniana in the Netherlands
Cabomba caroliniana (Cabombaceae, EPPO List of Invasive Alien Plants) has been traded as an aquarium plant for decades in the Netherlands. It was first recorded in the Meuse River in 1986, but was only reported as posing a problem in 2005 in the Loosdrecht Lakes. The different behaviour of the species in various sites in the Netherlands was an incentive to investigate biotic and abiotic factors that might explain these disparities, as well as practical management options.
In cold temperate climates, C. caroliniana can overwinter through vegetative forms. In autumn, it forms ‘turion-like’ structures which can break off from the plant. Buoyant fragments can be carried over long distances by water currents. These fragments lose their buoyancy at the beginning of the winter and sink to the sediment surface.
Biotic and abiotic (temperature, oxygen, pH, conductivity and transparency of water samples) variables measured show that there are no limiting factors for the species to grow prolifically in any water in the Netherlands. The species responds favorably to free CO2 in the water corresponding to low pH levels and high light intensities.
Management tests were also undertaken in the field. When blocking sunlight with opaque geotextile, all macrophytes under cover died. The effects of reopening over a long period of time remain unknown.
An experiment on regular dredging consisted of completely removing vegetation from a canal with C. caroliniana present over a 100% of the area. The plants were removed with a weed cutting bucket which scraped the soft sediment layer over a distance of 100 metres. These experiments highlighted that such a method will not result in the permanent removal of C. caroliniana and other macrophytes, even if it is applied twice a year.
Another experiment consisted of completely removing vegetation from a canal (C. caroliniana covering 100% of the area) over a distance of 100 metres by using a powerful water stream (‘hydro venture system’) to resuspend the vegetation as well as the soft sediment after which the loose material was removed. This method allows a temporary removal of the species.
The study also showed that the current velocity is the decisive factor hampering establishment. As a consequence all slow flowing and still waters are potentially at risk.
Sources
Van Valkenburg JLCH, Roijackers RMM ; Léonard R (2011) Cabomba caroliniana Gray in the Netherlands. In: Bohren C, Bertossa M, Schönenberger N, Rossinelli M, Conedera M. (ed) 3rd International Symposium of Environmental Weeds and Invasive Plants. Abstracts. October 2 to 7 2011. Monte Verità, Ascona, Switzerland.
Available from Internet
http://www.wsl.ch/epub/ewrs/sessions/detail_EN?id=110;session=7;type=oralpresentations. Birmensdorf, Swiss Federal Institute for Forest, Snow and Landscape Research WSL.