Introduction:
Canadian waterweed (Elodea canadensis).
Elodea canadensis a submergent, aquatic plant, native to North America, has spread rapidly and easily throughout the world. Particularly in Europe, this species is very invasive and is considered a weed due to its ability to grow and multiply fairly rapidly in many diverse habitats and conditions. It is capable of causing problems of economic importance, habitat alteration, competition and threat to biodiversity. In addition, this species is not easily manageable. For these reasons, this species has been the focus of many experiments and research in the hopes of establishing a greater knowledge of growth habits, the true threat it causes, and possible prevention methods.
Description:
Elodea canadensis is a submerged, rather densely bushy, aquatic perennial. This aquatic herb has stems that branch out between 20 and 30 cm in length, which tends to form dense monospecific stands that can cover hundreds of acres. The joints of the stems are brittle. The leaves are oblong-linear and are in groups of three. The numerous overlapping, dark green, transulcent, and minutely toothed leaves are about 1 cm long, and 2-3 mm wide. In addition, the leaves have a non-waxy texture and are rigid. This species contains flowers, either white or pale purple, that appear at the surface of the water . The flowers have also been described in color as being rose-white. The flowers are carried to the surface on a long slender stalk, which is 2-15 cm long, with a sheathing, two-lobed spathe. In addition, there are fruits, which are capsule having a length of less than 1 cm and 3 mm in width. The roots are white, unbranched and thread-like. The plant has multiple apical growth points. In winter the stems build turions, specialised overwintering buds.
E. canadensis can be classified as a species of intermediate palatability. However, this species is poorly consumed by invertebrates. It is able to transport and fix carbon by using 4-carbon acids to supplement the 3-carbon acid pathway. It is also able to use bicarbonate as a carbon source in alkaline conditions either directly or by converting bicarbonate into carbon dioxide by acidification of the cell walls. This plant has been reported from sites in lakes of a very wide range of depths, and it is generally considered relatively highly tolerant to low light conditions. In addition, this species is able to form new side shoots, even when leaves are missing or the stem has turned brown as a result of herbivory, therefore concluding that the fragments of this species have high regenerative capacities.
Elodea species have a wide range of phosphorus content in their biomass and they are able to store this nutrient in their roots to be used for growing when phosphorus levels
Canadian waterweed (Elodea canadensis) Distribution in North America shown in green.
in water are low. E. canadensis is also able to take up phosphors from the sediment by its roots, so reducing the phosphorus concentration in the water column in most cases is not able to reduce its growth.
Occurs in:
Estuarine habitats, lakes.
Habitat description:
Elodea Canadensis has a wide range of conditions in which it can grow. It can grow in very shallow to deep water and in slightly mineralized and acid water in siliceous sediments to heavily mineralized water in calcareous sediments. However, it prefers mesotrophic waters. This species can even grow slowly under ice cover and can survive inside the ice. Dense stocks can also partly survive, when the water level sinks and the plants on the banks are exposed to dryness for several weeks. (Experiments with E. nuttallii but E. canadensis will show the same tolerance to dryness, P. Podraza, unpublished data).In its native habitat, E. canadensis resides in surface standing waters, surface running waters: shallow lakes, ponds, pools, ditches and streams with slow moving water. In its invaded habitat, it can survive in the same environments; however it can survive in up to 3 meters of water depth in slow moving water, and in exceptional cases up to 16 meters in depth. It tolerates pH values from 6.0 to 7.5 and temperatures from 1 to 25 degrees in celcius. The foliage can stand much battering by turbulence, but, being poorly anchored or not at all, this species will not persist in waters with a continuously fast flow and favours still or sluggish conditions.
Management information:
Close up of Canadian waterweed (Elodea canadensis).
Physical: Mechanical removal of the biomass will temporarily reduce the populations and their proliferation. However, as the plant spreads through fragmentation, it is essential to prevent the spread of plant fragments by creating filters downstream before any mechanical treatment is carried out. All plants removed must be carefully disposed of to prevent dissemination of fragments. This plant can be easily cut and controlled for short periods by mechanical control methods. The cut weed should be removed from the water to avoid deoxygenation. However the growing rate of E. canadensis is very fast and the effects of mowing only last for a few weeks (P. Podraza, pers. comm.). Continued mowing of the invasive water plant species Myriophyllum spicatum has led to its disappearance from the system in some cases. However this has not been successful with a similar species E. nuttalli and it is thought that it would also be unsuccessful with E. canadensis.
Other appropriate methods of mechanical control include removal by hand, raking, chains, weed bucket, weed boat or dredging. E. canadensis is adapted to stagnant or slow flowing waters. Increasing flow velocity in running waters can reduce the plant density.
Chemical: Diquat and copper sulphate or chelates of copper can be used in stagnant water. The addition of copper is reputed to improve control compared with diquat alone, and is also advantageous because algae are inhibited. However copper is toxic to most crustacean species, affects fish reproduction and may impact the food web structure, e.g. by reducing the zooplankton densities. Terbutryne is used for control of various submerged weeds. Acrolein gives temporary control in flowing water. It is injected into the water and allowed to flow over the weed beds.
Environmental: Shade will control most submerged aquatic plants. This can be achieved by planting trees on the south side of waterbodies or by using a floating sheet of opaque material.
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