Effects of Water Hyacinth (Eichhornia Crassipes) on Water Quality and Composition and Abundance of Phyto- and Zooplankton in the Littoral Region of Koka Reservoir, Ethiopia
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Date
2019-05-05
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Addis Ababa University
Abstract
Invasion of aquatic habitats by non-native species is a global environmental challenge with serious ecological, social and economic consequences demanding urgent action. Water hyacinth, Eichhornia crassipes (Martius) Solms, is one of the world’s most rampant invasive aquatic plants recognized as one of the top 10 worst weeds in the world. Its appearance in Koka Reservoir was reported in 1965 and has become a threat to the aquatic ecosystem. Although several limnological studies have been made on the reservoir, the effects of water hyacinth on water quality and plankton have not been addressed. Samples were collected monthly from three weed-infested and three non-infested sites from March to July 2018 to assess its effect on water quality, plankton composition and abundance in the reservoir. Potential toxicity of water hyacinth extract was also investigated using white albino mice. During this investigation, the differences between weed-infested and non-infested sites in DO, NO3-N, NO2-N, SRP, TP, NH3, TSS, Turbidity, Silica and Secchi disk depth were significant (P<0.05), with lower values in the weed-infested sites except values of TSS, Silica and Turbidity higher in the weed infested sites. The phytoplankton community, which was constituted of 62 species, was dominated by Bacillariophyceae (mainly Aulacoseira granulata) followed by Cyanophyceae (Cylindrospermopsis spp., Microcystis aeruginosa, and Anabaena flos-aquae) and Chlorophyceae in both non-infested and weed-infested sites. The variations in the abundance of phytoplankton and zooplankton between the two sites were significant (p<0.05). The phytoplankton species Monorophidium griffithii and Gyrosigma obtusatum and the zooplankton taxa Lecane monostylahomata, Lecane leontita, Trichocerca djurellasejunctipes, Euchlanis menta, and Platyias quadricornis var. bervispinus were found only in the weed-infested sites. Significant differences in Shannon’s index (H'), species richness (d) and species evenness (j) of zooplankton and species richness (d) of phytoplankton were also observed between the two sites, with higher mean values in the non-infested sites than in the weed-infested sites (p<0.05). Rotifers, followed by Copepods and Cladocerans in the same order, were the most abundant at both sites. The relative density of Rotifers and Cladocerans was higher in the non-infested sites, while that of Copepods was higher next to Rotifesrs in the weed-infested sites. Results of the experimental test on the toxicity of water hyacinth on white albino mice showed unusual changes although the death of the treated mice was not observed suggesting the potential toxic effect of the weed on aquatic biota that would occur with an increase in dose and duration of administration. The existing infestation level of water hyacinth poses a significant effect on water quality, composition and abundance of phytoplankton and zooplankton. The current environmental conditions are favorable for the optimum growth of the weed and further proliferation of the weed and spread to new areas are possible worsening its adverse effect to the ecosystem. Thus, continuous monitoring and development of a sustainable management strategy and regulation of agricultural and urban wastes, have to be addressed.
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Phytoplankton, Mice, Toxicity Test, Zooplankton