Myriophyllum aquaticum has the potential for high environmental impact if introduced to the Great Lakes. The U.S. EPA (2008) predicted that parrot feather could have a high impact and spread rate in the Great Lakes, as it is adaptive to a variety of environments. According to Les and Mehrhoff (1999), rapid spread has been relatively common in this macrophyte’s North American invasion history (Les and 1999).
Dense infestations of parrot feather can rapidly overtake small ponds and sloughs, changing their physical and chemical properties, including impeding water flow, which can result in increased flood duration and intensity. The spread of aquatic nonindigenous plants into a waterbody can also lead to increased rates of evapotranspiration and water loss (Rosa et al. 2009).
Furthermore, parrot feather can dramatically alter ecosystems by shading out algae, pondweeds, and coontail on which waterfowl feed (Ferreira and Moreira 1994, Washington State Department of Ecology 2011). Floating mats of parrot feather have been measured at up to 26 kg of fresh weight in Europe and are capable of reducing the oxygen content (Fonseca 1984 cited in Moreira et al. 1999, Hussner 2008 in Hussner 2009). In Germany, the infestation of these mats created anoxic, shaded conditions in shallow waters, and appeared to be correlated with a decline in native macrophyte diversity (Hussner 2008 in Hussner 2009).
A laboratory study indicated that parrot feather will outcompete native species in high-nutrient sediment (Xie et al. 2010). Furthermore, a mesocosm experiment sugggested that parrot feather has an advantage over algae species when nitrogen levels are elevated (Wersal and Madsen 2011).Stiers et al. (2011) compared Belgian lake sites and found that native species richness was 57% lower in heavily invaded sites relative to uninvaded sites. Parrot feather cover was also negatively correlated with invertebrate species richness and abundance, possibly due to dense mats of parrot feather reducing oxygen levels(Stiers et al. 2011). Utricularia vulgaris (rare in Belgium, native to the Great Lakes region) and Hydrocharis morsus-ranae (a vulnerable IUCN Red List species in Belgium and invasive in the Great Lakes) were absent in heavily invaded sites but present in semi-invaded sites (Steirs et al. 2011).
Parrot feather can also alter the cycling of heavy metals in aquatic systems. Cardwell et al. (2002) found that parrot feather accumulated the highest overall levels of metals (zinc, cadmium, copper, and lead) in its tissues of all 15 aquatic plants that underwent testing. The consumption of parrot feather by grazers could increase the bioaccumulation of heavy metals in the food web.
Myriophyllum aquaticum has the potential for high socio-economic impact if introduced to the Great Lakes.
Parrot feather infestations have been reported in both natural and man-made water bodies, including lakes, ponds, canals, drainage and irrigation ditches, and lagoons. Plants and floating mats of vegetation are sometimes uprooted, choking waterways, inhibiting navigation, and potentially blocking pumps or drainage (Engineer Research and Development Center 2007, Sheppard et al. 2006). Dense growth can also diminish the recreational value and seriously affect the perceived aesthetic qualities of infested waterways (Banfield 2008, Washington State Department of Ecology 2011).
Parrot feather monocultures provide prime mosquito habitat; higher parrot feather density has been correlated with higher mosquito egg and larval abundance (Orr and Resh 1992), which may lead to increased prevalence of mosquito-born diseases.
One account by South African farmers also reported that tobacco crops gained a red tint (reducing the sale value of the crop) when irrigated with water from an area colonized by parrot feather roots (Cilliers 1999).
Myriophyllum aquaticum has the potential for moderate benefits if introduced to the Great Lakes.
Assessment protocols have been developed using parrot feather as a primary indicator species of sediment toxicity in potentially polluted areas (Feiler et al. 2004, Knauer et al. 2008).
Parrot feather is an important species in the aquarium trade and can be found in shops in both the American and Canadian Great Lakes regions (Marson et al. 2009a, Rixon et al. 2005). It is reportedly sold as an “oxygenating plant” in Europe (Sheppard et al. 2006).
Parrot feather may provide cover for some aquatic organisms (Washington State Department of Ecology 2011). Parker et al. (2007) found that beavers (Castor canadensis) in Georgia fed on M. aquaticum to the extent that invasive populations were reduced, although no strong preference for this plant species over others was documented.
Parrot feather could be used for nitrogen and phosphorus remediation (e.g., in a constructed wetland remediating nutrient runoff), but Polomski et al. (2009) found that other invasive macrophytes (Eichhornia crassipes and Pistia stratiotes) had equal or greater uptake efficiency levels relative to parrot feather. Parrot feather can also aid in environmental remediation of soil and water contaminated with chlorinated solvents, trinitrotoluene (TNT), and other nitrogenated explosive/aromatic compounds (Medina et al. 2000, Nwoko 2010).