Water hyacinth (Eichhornia crassipes), a species that originated in South America, has been widely distributed in the world. It is a free-floating aquatic macrophyte that typically grows about 0.5m height and up to 1m in tropical areas. Recently, it is considered as an invasive species in many places due to its destruction on water and aquatic biodiversity. It will affect more countries with its expansion into higher latitudes due to climate change (Villamagna & Murphy, 2010).

Fig. 1. Water hyacinth (Eichhornia crassipes) (credits: Ted Center/USDA)

How water hyacinths become weeds?

Water hyacinth was introduced in China as a good fodder plant since 1901 (Chu et al, 2006). In the period with low level of agricultural development when serious food competition existed between humans and domestic animals, water hyacinth played an important part in China. However, farmers reduce familial feeding using water hyacinth gradually with the improvement of agricultural technology and development of urbanization. As a result of rapidly spreading from family ponds into inner rivers, water hyacinth population has become a severe environmental problem nowadays as its dominant situation in water because of the nutrient content of water increased with the improving industrialization level. Among the 7 billion economic loss caused by invasive species, water hyacinth which results in impeding water flows, paralyzing navigation, and damaging irrigation and hydroelectricity facilities occupies the largest proportion (Chu et al, 2006). Since 1990, water hyacinth became a synonym for “pollution” in China. It costed huge amount of money while the pollution cannot be completely eradicated such as Dianchi Lake, Taihu Lake and the Pearl River. According to the statistics, the amount of water hyacinth harvested was increased from 0.5 tons per day in 1975 to 500 tons per day in 2000 (Lu et al, 2007). In addition, water bodies of approximately 19 provinces or cities were infected by water hyacinth (Lu et al, 2007).

Fig. 2. Water hyacinth chokes the Pearl River

Threats to the aquatic biodiversity

The presence of water hyacinth is mainly determined by its unique biological characteristics, global warming of greenhouse effect and the accelerated eutrophication process (Yan et al, 2017). This invasive weed colonized the ecosystem around the growing environment as it spread. It is well known that the structure of a macrophyte community is significant for determining phytoplankton, zooplankton and fish communities. Nevertheless, the high reproductive capacity of water hyacinth poses a great threat to biodiversity as it is more competitive than other species. Water hyacinth can even grow more than 1.5 meters above the water level under sufficient nutrient supply and expand to twice in amount in two weeks (Yan et al, 2017). When it forms to be a dense monoculture, it can alter the structure and function of ecosystem by changing the physical and chemical aquatic environment through interfering with the food chains and nutrient cycling (Shanab et al, 2010). Moreover, dense water hyacinth would reduce the amount of light reaching the submerged plants which consume the dissolved oxygen in the water. The reduction of dissolved oxygen content will then affect the plankton diversity and ultimately affect aquaculture yields. The decrease in DO also promotes a shift of fish species from high oxygen demanding species to lower oxygen tolerating species while most fish species prefer DO level more than 4 mg/L (Yan et al, 2017).

How to control?

Since the pollution of water hyacinth is a seasonal outbreak, the control measures used in many parts of China are combination of manual and mechanical salvage. Although studies have shown that biological control such as neochetina bruchi is more effective without damaging crops. However, this method is still in the experimental stage in China because it is not certain whether this species will show a strong ecological invasion in China.

Current studies suggest that water hyacinth is difficult and unlikely to be completely eradicated partly because of the high cost of mechanical harvesting and disposal (Yan et al, 2017). Additional, the management of water hyacinth includes a series of decisions, policies and actions based on environment which makes the decision makers to be solid consideration. Future research may be focus on developing low cost salvage techniques.

References

Chu, J. J., Ding, Y., & Zhuang, Q. J. (2006). Invasion and control of water hyacinth (Eichhornia crassipes) in China. Journal of Zhejiang University-Science B, 7(8), 623-626.

Lu, J., Wu, J., Fu, Z., & Zhu, L. (2007). Water hyacinth in China: a sustainability science-based management framework. Environmental management, 40(6), 823.

Shanab, S. M., Shalaby, E. A., Lightfoot, D. A., & El-Shemy, H. A. (2010). Allelopathic effects of water hyacinth [Eichhornia crassipes]. PLoS One, 5(10), e13200.

Villamagna, A. M., & Murphy, B. R. (2010). Ecological and socio‐economic impacts of invasive water hyacinth (Eichhornia crassipes): a review. Freshwater biology, 55(2), 282-298.

Yan, S. H., Song, W., & Guo, J. Y. (2017). Advances in management and utilization of invasive water hyacinth (Eichhornia crassipes) in aquatic ecosystems–a review. Critical reviews in biotechnology, 37(2), 218-228.

Photos:

Figure 1. https://www.feedipedia.org/node/160

Figure 2. http://www.4thmedia.org/2011/07/invasive-plant-chokes-pearl-river/

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Yuan Cheng

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