Academics

Invasive species, whether plant or animal, occupy ecosystems and can cause devastating impacts to the native environment with some of the damage being irreversible. For example, water hyacinth, which is native to the Amazon River Basin of South America, was introduced to freshwater systems in over 50 countries as an ornamental plant and has since caused significant ecological and socioeconomic effects (Villamagna and Murphy 2010). Its success as an invader is attributed to its ability to outcompete native vegetation and to the absence of consumers found within its native range (Villamagna and Murphy 2010). And once it is established, water hyacinth is very hard to remove due to is rapid reproduction rates and its dense layers which form a mat over the water’s surface. Water hyacinth threatens the diversity of native species and can cause changes to the physical and chemical structure of the aquatic environments they invade which eventually leads to a disruption in food chains and nutrient cycling (Shanab et al., 2010). This is due to the fact that the plant grows and spreads rapidly in large areas over short time periods creating these dense layers (Center and Spencer 1981). It is because of these two traits, the density and growth rate, that water hyacinth is such a threatening invasive species. Within its invasive range, water hyacinth can alter water clarity, impact community composition of phytoplankton, zooplankton and fish, and have negative socioeconomic impacts. Because of these reasons, freshwater bodies would be positively affected by its complete removal until methods are found to control its growth.  

The leaves of water hyacinth are fanlike and slightly cupped, and this shape makes a very effective sail and allows the plants to spread easily over water bodies when the wind blows (Albright et al., 2004). Their ability to spread allows them to rapidly take over in canals, rivers, and lakes of surrounding areas, which makes controlling the plant that much harder. Not only does their spread contribute to their success, but frequent water level fluctuations provide suitable ecological conditions for seed germination and seedling establishment (Wilson 2005). 

Water hyacinth is also able to spread to new areas quickly because of its ability to regenerate. It reproduces asexually by breaking apart into pieces, each of which develops into a separate plant (Ndimele et al., 2011). Seeds germinate quickly, and new plants can grow from stolon in 6-18 days. During regular growth, three phases aid in their ability to regenerate rapidly (Wilson 2005). The first phase occurs after winter freeze causes damage to the developing shoots and it involves the reapportioning of the biomass distribution (Center and Spencer 1981). In this phase the plant finds new and different ways to distribute its area and volume. The second phase begins in the early spring and is distinguished by three different sub-phases of rapid growth which include increased branching and ramet production, high leaf densities, and high foliar height diversity (Center and Spencer 1981). This phase mostly occurs during the early stages of growth of the leaves and it purposes to increase the number of cloned individuals. The third phase of growth begins in late spring and involves increases in leaf size and the development of a balanced number of leaves per plant cloned in the second phase (Center and Spencer 1981). The leaves of a water hyacinth are round to oval in shape, four to eight inches in diameter, and their veins are very dense and abundant (Center and Spencer). All three phases support an increase in leaf size and can be used to explain why the plant is able to form thick layers on the water’s surface.  

The density of the water hyacinth is another characteristic of the plant that categorizes it as a pest species. Since the plant is able to reproduce so rapidly, it can quickly grow to very high densities (Wilson 2005). Much of the leaf’s thickness is related to its vein density, which causes the leaf to stand straight up (Wilson 2005). It is these many layers of abundant leaves, and their shape and large size, which cause issues in the areas in which they invade because of their ability to shade out native plant life by taking up all of the space on the surface of the water. The water hyacinth’s thick and fibrous root system assists in increasing the already high density of the plant as well (Wilson 2005). The root system allows the plant to not only spread across the surface of the water but also to add to the thick layers of the water hyacinth within the water, which is a huge problem, especially for overall water quality.  

Due to the dense, mat-like layers that water hyacinth tends to form on the surface of freshwater bodies, the plant causes an alteration in water clarity; this change in water clarity has many significant effects on the aquatic ecosystem (Villamagna and Murphy 2010). The most well documented effects are the lowering of phytoplankton productivity and the dissolution of oxygen concentrations beneath the mats (Villamagna and Murphy 2010). These mats decrease dissolved oxygen concentrations by preventing the transfer of oxygen from the air to the water’s surface while also blocking light used for photosynthesis by phytoplankton and other vegetation (Shanab et al., 2010). And unlike phytoplankton and other aquatic plants, water hyacinth does not release oxygen into the water (Toft et al., 2003). Therefore, water hyacinth smothers native plant life, and continues to reproduce at rapid rates, while also preventing natural plant life from reproducing and surviving.  

Despite this, it is also important to note that not the all of the impacts this invasive plant has on water quality within an ecosystem are negative; there are some benefits of its presence within the invasive range. Other effects water hyacinth has on water quality include higher sedimentation rates within the plant’s complex root structure and stabilization of pH levels and temperature (Villamagna and Murphy 2010). These tend to be positive impacts that increase the productivity within freshwater systems with rapid moving water. Water hyacinth, with the help of gravity, removes suspended solids that are near the surface of the water, making once turbid water, clear (Toft et al., 2003). This is beneficial for the aquatic ecosystem because it causes an increase in nutrients within the soil below the water’s surface. The stabilization of pH and temperature within the water system also directly relate to an increase of mixing within the water column which helps to prevent stratification (Villamagna and Murphy 2010). Both pH and temperature stabilization inhibit the ability of layers in the water that act as barriers to form which could otherwise cause anoxia - a state of reduced dissolved oxygen which negatively impacts surrounding aquatic vegetation (Toft et al., 2003). The overall ability of water hyacinth to absorb nutrients makes it a biological alternative to water treatment, especially when considering concentration of certain harmful elements (Villamagna and Murphy 2010). 

Furthermore, water hyacinth leaf tissue was found to have the same mercury concentration as the sediment beneath, suggesting that harvesting water hyacinth could help control mercury concentration (Villamagna and Murphy 2010). Mercury is harmful when it contaminates water systems because it can be absorbed by fish and other aquatic animals. These exposed animals have trouble ridding their bodies of mercury, and it accumulates in tissue with every link in the food chain (Villamagna and Murphy 2010). For vertebrates, mercury affects their development, as well as their neurological and hormonal systems. Fish are seen to form loose, sloppy schools and respond slower to predator presence (Villamagna and Murphy 2010), while ducks have been observed to lay fewer eggs, and to have ducklings that do not respond well to their calls (Villamagna and Murphy 2010). Therefore, overall, the presence of a natural water treatment like invasive water hyacinth can positively impact aquatic ecosystems in some respects.  

 Yet once again, from a socioeconomic perspective, there are many costs associated with the presence of water hyacinth. Its invasion into freshwater systems presents a problem for many human uses, more specifically to boating access, navigability, and recreation, as well as to pipe systems for agriculture, industry and municipal water supply (Villamagna and Murphy 2010). These can be huge issues especially in smaller bodies of water where water hyacinth grows at increasingly high rates (Toft et al., 2003). The mats of water hyacinth across the water’s surface make it almost impossible to navigate through waters. These dense mats also have a huge impact on fishing areas as they reduce fish catchability. Water hyacinth can greatly affect a fishery if it causes changes in fish community structure, or if catchability of already harvested species is altered (Villamagna and Murphy 2010). This decrease is caused by the inability to reach once common fishing grounds that are now blocked by the dense layers of water hyacinth. Not only do the water hyacinth obstruct boats, but they prevent certain fish species from being able to breed and reproduce as well (Villamagna and Murphy 2010) thereby negatively effecting the entire fishing industry of that body of water in multiple ways. And an important thing to note is that some of the biological impacts and socioeconomic impacts of water hyacinth invasion may not be immediately realized (Villamagna and Murphy 2010). Instead, damages may increase over time or as a result of biological and economic interactions.  

In summary, water hyacinth greatly affects aquatic ecosystems within the invasive range in numerous ways ranging from ecological to socioeconomic impacts. Currently, researchers are looking for low-cost ways to remove the plant safely. Although there are benefits to water hyacinth in the invasive range, freshwater bodies would be positively affected by its complete removal until methods are found to control its growth. Initial management of water hyacinth outside of its native range focused on eradication, but due to the difficulty of this approach, efforts have shifted towards reducing plant density levels that minimize economic and ecological impacts (Agidie et al., 2018). One main reason that eradication is no longer thought to be feasible is due to the discovery that seeds of water hyacinth have the ability to lie dormant for 15-20 years during drought periods and to begin to germinate and renew their growth cycle once reflooding occurs; this means that the direct removal of the plant would not guarantee that new populations would not return in the future from undetected seeds that were left (Ndimele et al., 2011). Mechanical, chemical and biological control methods are commonly used to control water hyacinth, but no one method is suitable for all situations as each method has advantages and disadvantages (Villamagna and Murphy 2010). 

Mechanical control options include harvesting plants and in-situ cutting (Greenfield et al., 2007). Mechanical control immediately opens physical space for fish, boat traffic, fishing, and recreation. Although there are disadvantages to this method, including the possibility of an increase in water hyacinth populations, it is overall more effective than harvesting the plant. This is because water hyacinth is comprised of 90% water, which makes is very heavy to transport, and locations to dispose of the plant are very hard to find and are often costly (Villamagna and Murphy 2010). For these reasons, many managements have begun to concentrate efforts into chemical control rather than mechanical.   

Chemical control is less labor intensive and expensive than mechanical control (Agidie et al., 2018). One eco-friendly chemical that is currently being used for control is acetic acid. Acetic acid has been found to affect the stem, stolen, and leaf parts of the plant sufficiently in a very short amount of time (Agidie et al., 2018). It was observed that acetic acid caused a discoloration of the leaves, and an overall decrease in plant biomass (Agidie et al., 2018). This is due to the fact that acetic acid is poisonous to water hyacinth, and higher concentrations of the chemical cause rapid death. A disadvantage of using chemical control is that herbicides are less selective: they can kill non-target algae, which are a critical foundation of aquatic food webs (Villamagna and Murphy 2010). Although important to consider, overall, it can be noted that acetic acid chemical could be a promising option to control water hyacinth populations.  

Biological control is another alternative to both mechanical and chemical control programs. Biological control programs are promising because they avoid the introduction of toxic chemicals into the environment, they are not labor or equipment intensive, and they have the potential to be self-sustaining (Villamagna and Murphy 2010). Common biological control options for water hyacinth include the introduction of various insect species that are pathogenic to the plant, such as the mottled water hyacinth weevils, which are beetles from the water hyacinth’s native range. The adults of these insects produce feeding scars on the leaves and petioles of the water hyacinth (Villamagna and Murphy 2010). And in the larval stage, the insect tunnels into the petioles and the crown of the plant, which results in biotic stress, reduced flowers and seeds, and less vigorous growth (Villamagna and Murphy 2010). The main disadvantage to using biological methods such as these is their effects take a long time and results may not be seen for years, but they are also promising as they could be the safest and most eco-friendly method of control.  

Overall, the water hyacinth disturbs water communities and causes great ecological damage to both plants and animals within the ecosystem. The ripple effect of destruction caused by this aquatic plant is numerous and almost irreversible within the invasive range, which is why control and removal of the plant is so important. Although there are some benefits to the presence of water hyacinth, aquatic ecosystems would be more successful with its complete eradication. Efforts to develop programs that employ mechanical, chemical, or biological means to control water hyacinth populations, and potentially a combination of all of these types, should therefore continue to be of focus in order to determine and put into practice the least costly and most beneficial program. 

Works Cited

Agidie, A., S. Sahle, A. Admas, and M. Alebachew. 2018. Controlling water hyacinth, Eichhornia crassipes (Mart.) Solms using some selected eco-friendly chemicals. Journal of Aquaculture 9:1-3. 

Albright, T. P., T. G. Moorhouse, and T. J. McNabb. 2004. The rise and fall of water hyacinth in Lake Victoria and the Kagera River Basin, 1989-2001. Journal of Aquatic Plant Management 42:73-84 

Center, T. D., and N. R. Spencer. 1981. The phenology and growth of water hyacinth (Eichhornia crassipes (Mart.) Solms) in a eutrophic north-central Florida lake. Aquatic Botany 10:1-32.  

Greenfield, B. K., G. S. Siemering, J. C. Andrews, M. Rajan, S. P. Andrews, and D. F. Spencer. 2007. Mechanical shredding of water hyacinth (Eichhornia crassipes): effects on water quality in the Sacramento-San Joaquin River Delta, California. Estuaries and Coasts 30:627-640.  

Ndimele, P. E., C. A. Kumolu-Johnson, and M. A. Anetekhai. 2011. The invasive aquatic macrophyte, water hyacinth {Eichhornia crassipes (mart.) Solm-Laubach: Pontedericeae}: problems and prospects. Research Journal of Environmental Sciences 5:509-520. 

Shanab ,S. M. M., E. A. Shalaby, D. A. Lightfoot, and H. A. El-Shemy. 2010. Allelopathic effects of water hyacinth [Eichhornia crassipes]. PLoS One 5:10. 

Toft, J. D., C.A. Simenstad, J. R. Cordell, and L. F. Grimaldo. 2003. The effects of introduced water hyacinth on habitat structure, invertebrate assemblages, and fish diets. Estuaries 26:746-758. 

Villamagna, A. M., and B. R. Murphy. 2010. Ecological and socio‐economic impacts of invasive water hyacinth (Eichhornia crassipes): a review. Freshwater Biology 55:282-298.  

Wilson, J. R., N. Holst, and M. Rees. 2005. Determinants and patterns of population growth in water hyacinth. Aquatic Botany 81:51-67.