Some of the world’s worst introduced invasive noxious water weeds have escaped from garden ponds into local Australian waterways. Native provenance water plants and any edge plants play an important role in nutrient buffering, bank stabilisation and sediment trapping.
Oxygen is the single most important water quality parameter and submerged native plants help to oxygenate the water. Native aquatic plants also play an important role in providing habitat for many organisms, particularly birds, amphibians, fish and many insects and other small pond creatures. Floating plants give shade, reduce evaporation rates, provide shelter for small fish, and keep the water temperature more constant.
Introduced noxious plant species blanket the entire water surface, causing oxygen depletion – this destroys the under-surface ecosystem and kills native aquatic species They compete with native species and reduce biodiversity, and impact on the aquatic habitat of bird species and cause them to relocate or die.
Some free floating plants that are declared noxious weeds in Australia include the introduced salvinia, (Salvinia molesta), the water hyacinth (Eichhornia crassipes), water lettuce (Pistia stratiotes), and the noxious weed alligator weed (Alternanthera philoxeroides) which may also grow on land.
Not all aquatic plants produce viable seed but spread and multiply from fragments of stem, root or leaves. Examples include noxious water weeds Salvinia and Alligator weed, and South American Parrotfeather. Other aquatic weeds produce seed and are also able to propagate from stem, root or leaf fragments.
So how did these introduced weeds get here? Most were brought in legally and illegally, for fish tanks. In Queensland in the 1980's, the Queensland Dept of Primary Industries illegally bought in over 400 plants from around the World to provide feed for cattle. Although not all were released, one that has created huge problems in Queensland waterways is Hymenacne. This invasive plant blocks waterways, in tropical and subtropical areas. Although it does not grow in water over 4 feet deep, it has smothered streambanks, replacing native rushes and other edge plants.
Control of these introduced noxious water weeds is very difficult. Sprays kill wildlife such as frogs, fish, and insects, and also polute the waterways. Hand removal is expensive and time consuming. In some ponded ares dredges have been used to remove surface weeds, but the weeds always grow back from leaf and stem pieces.The best option for controlling aquatic plants in a body of water is to take the necessary steps to prevent the problem from occurring in teh first place.
An example of the devastation that can result from uncontrolled aquatic noxious water weeds is the salvinia infestation that occurred in the Hawkesbury–Nepean River in 2004, which cost $1.6 million to control.
Salvinia, or hymenacne, or water hyacyinth, and/or alligator weed can be found in almost every waterway, dam and creek in Queensland, NSW, and Victoria, along with many other imported water plants that are considered less of a weed. Removal or effective control of these plants is almost impossible. This blog reports on the issues of noxious water plants in Australia.
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