Water hyacinth (Eichhornia crassipes), which is locally known as ’Emboch’ in Ethiopia, is a perennial, herbaceous, free floating aquatic plant. It is an invasive weed of waters that doubles itself within 5–15 days (Villamagna and Murphy, 2010). The most favourable conditions for the optimum growth of water hyacinth are nutrient-rich water, temperatures ranging from 28°C to 30°C, pH value between 6.5 and 8.5, salinity <2%, 20 mg N L water –1, 3 mg P L water –1, and 53 mg P L water –1. (Fernandez et al, 1990; Gaikwad and Gavande, 2017).
Partly because of the increasing temperature as a result of climate change and non-point sources of nutrients entering water bodies from agricultural lands through erosion, the aforementioned environmentally favourable conditions have been fulfilled and the weed has invaded Lake Tana (since 2011) (Minychl et al, 2019) and Aba-Samuel or Koka Dam water in Ethiopia. The weed has also spread to Awash River, Abay River, and Baro-Akobo River, where the above environmental conditions exist.
The weed does not appear in water bodies of Ethiopia where the average daily temperature is below the aforementioned ranges. However, other species of aquatic weeds are flourishing in these water bodies which are found in less warmer areas in the country such as central Ethiopia.
The weed poses a serious problem to the management of water resources. The invasion by the weed disrupts water transportation system, affects human health, hydroelectric operations, hydraulics of canals and rivers, creates flooding hazards, increases evapotranspiration of water bodies, affects fishing, irrigation, navigation, livestock, and aquatic biodiversity. The weed also depletes oxygen in the water because of algal growth, thereby reducing the fish population in the water (Epstein, 1998)
Apart from the high temperature (28°C to 30°) and the favourable water pH, the major causes of proliferation of the weed in the major waters of Ethiopia, such as Lake Tana and Koka Artificial Lake, are non-point nutrient sources nitrogen and phosphorus from the use of fertilizers in agricultural lands. Runoff from agricultural lands contains phosphorus (P) and nitrogen (N) because of the application of fertilizers and pesticides. The minimum requirement for the survival of water hyacinth is 5.5 mg N L water –1 and 1.66 mg P L water –1.
It is difficult to eradicate the weed by removing it physically once it establishes itself (Villamagna and Murphy, 2010; Minychl et al, 2019). Other methods of controlling or eradicating the weed such as biological control, use of herbicides, etc. are often used (Center et al., 1999). However, in Ethiopia, the best long-term insurance against growth of this weed on a water body seems to be preventing erosion coming as runoff from agricultural lands and flow of sewage from sewers in urban centres into the water bodies. These sources are the ones that enrich the water bodies with the nutrients required by the weed to grow. Therefore, Ethiopia should design sound strategies to control runoff from agricultural lands and flow of urban sewage into the water bodies to control the weed on a sustainable basis.
About the Author
Prof. Nigussie Dechassa is a plant nutritionist, agronomist, and horticulturist and has an experience of more than 20 years in teaching, research, mentoring, and publication. He has also successfully led a number of development-oriented international agricultural research projects. He has a strong track record in teaching, research, training, and leadership as well as in working with a number of international project partners. He has also comprehensive editorial skills. Prof. Nigussie Dechassa holds a PhD Degree in Plant Nutrition/Horticulture from the Leibniz University of Hanover, MSc Degree in Tropical and sub-Tropical Horticulture and Crop Science from the University of London, and a BSc Degree in Plant Sciences from Haramaya University of Agriculture (now Haramaya University).