Phytoremediation Capacity of Water Hyacinth ( Eichhornia crassipes ) as a Nature-Based Solution for Contaminants and Physicochemical Characterization of Lake Water

: Water hyacinth ( Eichhornia crassipes ) is a potential accumulator of water pollutants in aquatic ecosystems, and its presence in water systems can affect water quality. This study used different ﬁeld measurements and laboratory tests of lake water to determine the impact of water hyacinth phytoremediation capacity. A total of eight sampling stations were used for the two lakes: Lake Koka and Lake Ziway, Ethiopia. Sampling stations were selected from sites infested with water hyacinth (low, medium, and high) and non-water hyacinth aquatic plants during wet or rainy and dry or non-rainy seasons to compare the effects of plants on water quality in the two lakes. All the sampled stations had various human interventions. The water samples were tested for the selected physico-chemical properties, namely, phosphate, nitrate, pH, electrical conductivity (EC), the ﬁve-day biological oxygen demand (BOD 5 ), water temperature, and heavy metals (Chromium (Cr), Lead (Pb), Cadmium (Cd), Zinc (Zn), and Copper (Cu)). These water quality variables were compared by means of ANOVA. Despite the chemical oxygen demand (COD) of Lake Ziway, this study found no signiﬁcant ( p > 0.05) variation in the concentrations of Cu, EC, pH and water temperature between wet and dry seasons in either lake. Variations in Zn concentration and other physico-chemical parameters (EC, BOD 5 , COD, nitrate, phosphate) between low, medium, and high levels of water hyacinth were signiﬁcant in both lakes ( p < 0.05). Water hyacinth has shown signiﬁcant phytoremediation nature during wet and dry seasons. The lowest average heavy metal, phosphate, and nitrate concentrations; and signiﬁcant pH and temperature variations were observed in Lakes Koka and Lake Ziway, among water hyacinth and other grass-infested sites. These ﬁndings suggest water hyacinth plant as a promising nature-based solution for removing undesirable chemicals from contaminated water bodies.


Introduction
Water hyacinth is an invasive alien plant species that migrated from South America to different continents in the world [1][2][3][4].In the 19th century, its invasion spread over Africa, and in the mid-19th century, it dominated many East African rivers and lakes, including Ethiopian fresh water bodies causing economic, social, and environmental loss [5,6].It is one among the top ten worst weeds in the world, and it is classified as a noxious weed in several African countries [7,8].Water hyacinth has proven to be a substantial cause of economic and environmental difficulties in many subtropical and tropical places Water 2023, 15, 2540 2 of 13 throughout the world [9,10].Ethiopia is part of tropical sub-Saharan Africa where in the country about 35 known invasive alien plant species, including water hyacinth, currently exist and become one of the impairment sources of fresh water bodies [11][12][13][14].Additionally, continued exploitation and unintended contamination of aquatic habitat causes impairment on physical, chemical, and biological character of fresh water ecosystem [15,16].Generally, water bodies are exposed for many intentional and unintentional contaminants that can cause environmental and public health problems [17,18].The problems are associated with development activities.These activities are basically useful for development, but expose the life of many to health risk factors.For instance, the industry of aquaculture production, especially in many Asian countries, discharge domestic wastes, industrial effluents, etc., which can have harsh effects on the local environment and public health [19][20][21].For example, chemicals that are used to treat fish at fish farms can produce huge amounts of effluent, which can affect human health and the immediate locality.Moreover, fish in fish farms get sick from a contagious virus and parasite infestations.Then, the diseased fish have a chance to escape from the facility, and are able to contaminate healthy wild stocks.Largescale human activities producing dangerous discharge of waste at populated localities.But, in many developing countries, waste discharge and septic tanks are characterized by open bottoms or peculiar channels, which facilitate the seepage in depth or sometimes direct connection with the nearby streams [18,19].A great deal of study revealed that there is heavy metal contamination and unwanted nutrients in aquatic ecosystems [17,18,20,21].Therefore, the remediation of water body needs strong focus in Africa and in many more continents globally.
In normal circumstances, fresh water bodies have a specific premised physico-chemical standard; however, the invasion of weeds like water hyacinth trigger significant impacts on the deviation of water physico-chemical character from the permission level [22][23][24].Farmers who cross invaded water bodies to access their farms cannot do so in the presence of the dense mats of the weeds, resulting in high agricultural and economic losses [7,25].Smallholder farming was affected by the water hyacinth invasion in a number of ways, including decreased farm output profits, financial difficulty, and the destruction of crops due to the hyacinth's obstruction of water bodies [25].Water hyacinth influenced crop productivity, fishing, cattle feed, water supply, water transportation, and other economic activities [7].As the abundance of water hyacinth increased, the degree of challenge for fishing and fish market activity also increased.The invasion has a number of repercussions on fishing and fish trading, including decreased fish catch, difficulty using fishing gear, decreased profit, and higher fishing costs [7].These impacts have a significant impact on the long-term viability of fishing and fish trading [7].In the research communities, the plentiful water hyacinth acts as a habitat for disease-carrying insects such as mosquitoes, which cause malaria and many more vector carriers to a breeding ground.As a result, respondents assessed the water hyacinth invasion to have had a detrimental impact on their health.Despite the fact that many respondent participants perceived malaria infection to be the leading cause of illness in their communities.Prior to the introduction of water hyacinth into the water bodies, the current predominance of the disease in the study communities was widely perceived to be primarily due to the presence of the weed [25,26].On the other hand, water hyacinth has remarkable economic advantages.One of the studies conducted on the benefits of water hyacinth concluded that after acid pretreatment and post-washing step, the biogas yield increased due to the increased sugar and ethanol yield during saccharification and fermentation of water hyacinth [27].Different organic acids showed varying yields in ethanol and biogas yield showing different acids affecting the pretreatment efficiency [27].Despite the widely held belief that the water hyacinth was an invasion, a few fishermen and fish sellers observed that the water hyacinth provided protection for fish [7].Moreover, water hyacinth was used for compost and bio char [28].In addition, water hyacinth fast growth and quick expansion related with its high takeup ability for nutrients and minerals found in the aquatic system [29,30].Its expansion continued through competing the available nutrients in the aquatic ecosystem and this Water 2023, 15, 2540 3 of 13 view is supported by the study findings in the lab test conducted under greenhouse conditions [9,22,23,31].The weed's nature of minerals absorption and nutrients take-up capacity from the soil sustained to dominate native aquatic plant biodiversity [32,33].In most cases, fresh water pollutants are either organic and inorganic compounds, or natural and manmade contaminants, and sometimes heavy metals [1,33].Heavy metals have unique ability to be accumulated in the surface sediment, an in a variety of fish and mussel bodies at different concentrations [19,20].Different discharges of domestic and industrial waste can cause a critical health effect.Therefore, regular monitoring of heavy metal concentration and nutrients in the water environment can significantly help environmental protection, food safety, and human health [17,18,21].Consequently, remedial plant studies suggested that water hyacinth has removal efficiency of organic and inorganic contaminants, heavy metals, and nutrients form the water habitat [2,9,22].Water hyacinth has been reported as a potential tool for the removal of heavy metals (Pb, Cr, Cd, Zn, and Cu), nutrient contaminant compounds such as (NO 3 − , PO 4 3− ), adjust pH, and organic and inorganic matters (COD, BOD 5 ) taken up from lake water [23,34,35].Henceforth, in the context of environmental conservation, plants with unique efficiency on chemical removal ability can play a role in phytoremediation [22,34,[36][37][38].The plants with phytoremediation capacity remove chemicals from the contaminated sites without disrupting the environment, instead applying their inherent capabilities [22,36].Currently, seeking an option for cleansing the environment is an important research topic for many reasons [23,34].Therefore, in this research, a comparative study was undergone aimed to evaluate nature-based solution prospects of water hyacinth on removal of some lake water contaminants and maintaining standard water physico-chemical character.This study specifically focused on comparison of wet and dry season physico-chemical levels of pollutants in the lakes; the effect of water hyacinth on the physico-chemical levels of pollutants in the lakes; and comparison of the physico-chemical levels of pollutants in the lakes at the lake covered by water hyacinth and any other grasses such as Aeschynomene elaphroxylon, Echinochloa stagnina (Retz.),etc.

The Study Area
The lakes included in this study are Lake Koka and Lake Ziway (Figure 1.).In General, the rift-valley region and in particular the district of Lake Koka and Lake Ziway at upper Awash River Basins of the rift valley show the two lakes are vulnerable for many natural processes and anthropogenic activities [39][40][41].For instance, at upper Awash River Basins of the rift valley, predominantly, the districts of Lake Koka and Lake Ziway are the center for many agricultural activities, and hydrological features, in Ethiopia [39].Lake Koka is a man-made lake built in the 1960s to generate hydroelectric power (Figure 1).The lake has a surface area of around 200 km 2 , a mean depth of 9 m, and a mean surface water temperature of 19 • C. Lake Koka is located at the coordinates of longitude 39 • to altitude 39 • 10 E in between 8 • 2 and 8 • 26 N latitude.The Awash and Modjo rivers provide inflow to the lake.Agriculture is the main activity in the basin, and Acacia trees are widely scattered.Basically, in Ethiopia, these locations are susceptible for continued exploitation that cause natural biodiversity loss, climate changes, precipitation, etc.Therefore, these activities are major factors for surface water pollution that conveys climate change impact and invasive alien species infestation.
Lake Ziway is located at the coordinates of 8.0074 N and 38.8416 E (Figure 1).Lake Ziway is the sole freshwater lake among the natural lakes in the middle rift valley basin.It serves as a water supply source for Ziway and its surroundings.Furthermore, more water is being drawn from the lake to irrigate small and large-scale private and state-owned farms.Lake Ziway is located around 165 km south of Addis Ababa, at an elevation of 1638 m above sea level.It has an average depth of 4 m and an area of around 435 km 2 .Lake Ziway of Ethiopia is a worm-monomictic lake that never freezes throughout the year.The lake's two main feeder rivers, Meki and Ketar, flow from the eastern and western highlands, respectively [6,40].The present study location was at the districts of Lake Koka and Lake Ziway of upper Awash River Rift Valley.The two lakes are situated in the rift-valley of upper Awash River Basins in a coordination, found at central Ethiopia.Lake Koka and Lake Ziway are known as the Central Ethiopian largest freshwater lake and there is a road crossing the two lakes that apparently connect the two.Water hyacinth has infiltrated the lakes and established itself along the lake water banks [14,41].
owned farms.Lake Ziway is located around 165 km south of Addis Ababa, at an elevation of 1638 m above sea level.It has an average depth of 4 m and an area of around 435 km 2 .Lake Ziway of Ethiopia is a worm-monomictic lake that never freezes throughout the year.The lake's two main feeder rivers, Meki and Ketar, flow from the eastern and western highlands, respectively [6,40].The present study location was at the districts of Lake Koka and Lake Ziway of upper Awash River Rift Valley.The two lakes are situated in the riftvalley of upper Awash River Basins in a coordination, found at central Ethiopia.Lake Koka and Lake Ziway are known as the Central Ethiopian largest freshwater lake and there is a road crossing the two lakes that apparently connect the two.Water hyacinth has infiltrated the lakes and established itself along the lake water banks [14,41].

Sample Sites
In this study, physico-chemical characterization of Lake Koka and Lake Ziway water quality was conducted for a period of one year (1 September 2021-30 August 2022) considering wet and dry seasons.The driest season was October to January, and the rainy season was June to September.In the study location, within these two seasons, the water hyacinth plant invasion is usually most visible from a distance.In order to assess the physico-chemical pollutant concentration in the lakes' water, four water samples from each lake were taken at four different sites purposefully.A total of eight sampling stations were carefully selected for the two lakes.The stations SK1L, SK2M, SK3H, SZ1L, SZ2M, and SZ3H were collected from low infected, medium, and high infected sites by the water hyacinth.The stations SK4G and SZ4G were collected from others grasses affected sites from Lake Koka and Ziway, respectively.The classification high, low, and medium was based on observation, expertise recommendation, and local communities' suggestion.Later, the value of water hyacinth abundance score for all the selected sites were rated as to the scale score procedure of invasive species proposed by Phillps, 1992, as cited in Firehun, 2017 [42].Therefore, in this present study, scale score: 5 = completely masked the water body; 4 = a

Sample Sites
In this study, physico-chemical characterization of Lake Koka and Lake Ziway water quality was conducted for a period of one year (1 September 2021-30 August 2022) considering wet and dry seasons.The driest season was October to January, and the rainy season was June to September.In the study location, within these two seasons, the water hyacinth plant invasion is usually most visible from a distance.In order to assess the physico-chemical pollutant concentration in the lakes' water, four water samples from each lake were taken at four different sites purposefully.A total of eight sampling stations were carefully selected for the two lakes.The stations SK 1 L, SK 2 M, SK 3 H, SZ 1 L, SZ 2 M, and SZ 3 H were collected from low infected, medium, and high infected sites by the water hyacinth.The stations SK 4 G and SZ 4 G were collected from others grasses affected sites from Lake Koka and Ziway, respectively.The classification high, low, and medium was based on observation, expertise recommendation, and local communities' suggestion.Later, the value of water hyacinth abundance score for all the selected sites were rated as to the scale score procedure of invasive species proposed by Phillps, 1992, as cited in Firehun, 2017 [42].Therefore, in this present study, scale score: 5 = completely masked the water body; 4 = a dense and serious infestation; 3 = wide spread throughout the water body; sample analysis.The sampling station selection was based on human intervention, through industry, city and agricultural actions land graving, and many more related anthropogenic activities.Water plants are free-floating plants, and therefore, field-based measurement carried on a temporal basis is recognized as the standard measurement [43,44].Therefore, a change due to flotation is under control and less likely to affect the result.In the present study, field-based measurement has been carried on a temporal basis between the period September 2021 and August 2022.
Detailed description of water sample habitat by water hyacinth infestation level and site is given in Table 1.At sites SK 1 L and SZ 1 L, there was less human activity but the nearby villagers have been practiced agricultural activities surrounding the lakes.The second sites (SK 2 M, SZ 2 M) were relatively located at industrial zone, recreation center, or fishing and fish marketplaces with more human activity than the first site.The third sites (SK 3 H, SZ 3 H) were categorized as the area with the highest industrial influence, agricultural impacts, and heavy human activities carrying zone than both site 1 and 2. The fourth stations (SK 4 G, SZ 4 G) were the lakes' water body covered by other grasses excluding water hyacinth.The purposes of including the fourth sites in the study were to consider other grasses impact in comparison with the water hyacinth invaded lakes' water.The comparison was basically to assess the effect of water hyacinth, in two different lakes, Lake Koka and Lake Ziway, widely known as the Ethiopian rift valley lakes of fresh water bodies.

Lakes' Water Physico-Chemical Variables Test
In this study, two types of lakes' water test, namely in situ at the study sites and ex situ water sample test were conducted.The ex-situ test in the laboratory was held for many of the selected physico-chemical variables except for unstable physico-chemical variables such as EC, pH, and water.As mentioned earlier, one of the water hyacinths studied and reported topics for many researchers was its potential on heavy metals removal, and some nutrients uptake capacity by its root from the water body.Based on this review, in this current study, water hyacinth's heavy metals removal tendency and selected nutrients uptake capacity assessed following the plant's level of invasion at different location in the study lakes.In this research, parts of the lake covered by other plant species, rather than water hyacinth, were also assessed to compare the selected heavy metals removal tendency and nutrients uptake performance of those plants with the water hyacinth.

Lakes' Water Quality Measurement by Physico-Chemical Character
The lakes' water physico-chemical characters measured were: pH, temperature, electrical conductivity, nutrients, the five-day biological oxygen demand (BOD 5 ), chemical oxygen demand (COD), dissolved oxygen (DO), and heavy metals.The pH and electrical conductivity were analyzed by using pH meter and Electric Conductivity Meter in Siemens per meter (S•m −1 ).Nitrate and orthophosphate concentration were measured by using the UV-Vis spectrophotometer (Hach DR6000™, LPV441.99.00002,Ames, IA, USA).Nitraver ® 5 and PhosVer ® 3 reagent powder pillows were used for the analysis of nitrate and phosphate, respectively.The lakes' water sample dissolved oxygen (DO) was measured by Portable Dissolved Oxygen Meter.The five-day biological oxygen demand (BOD 5 ) of the lakes' water sample was determined using the digital BOD incubator (TS 606/4-i), which operates at 20 • C. The heavy metal composition of the lakes' water samples were analyzed using Atomic Absorption Spectroscopy.Moreover, the water samples odor was quantitatively stated by observation and on its smell, which was noted as whether the water had an objection to the noise or not.Likewise, to consider seasonal variation of the water hyacinth impact, at wet and in dry seasons, the data were collected for selected heavy metals (Pb, Cr, Cd, Zn, and Cu), nutrients (NO 3 − , PO 4 3− ), organic and inorganic matters (COD, BOD 5 ), pH, and physico-chemical variable concentration of the lakes' water sample.Any deviation of lake water physico-chemical character from the permitted standard of freshwater bodies due to plant invasion was considered.During the samples analysis, checkups and calibration were taken as precautions before and after measuring and registering all data.

Water Sampling
Water samples were collected from the lakes according to the sampling design.Collections of the samples were conducted by using 250 mL polyethylene containers pre-cleaned by soaking into nitric acid and chilled.The samples were temporarily stored in sampling box followed by storing at 4 • C before ex situ analysis in the laboratory.The samples were transferred to the laboratory with 24 h as recommended by EPA and WHO.For this entire study, all the water sampling materials and laboratory equipment were used from Addis Ababa University and Addis Ababa Science and Technology University, which are located approximately 165 km from the field of study.

Sample Analysis
In this study, water quality variables such as: Cr, Pb, Cd, Zn, Cu, Ca, and PO 4 3− , NO 3 − , COD, and BOD 5, temperature and pH were tested, and data properly tabulated and statistically analyzed by applying one-way analysis of variance (ANOVA).The analysis was carried out by statistical package for social sciences (SPSS) software version 26 (IBM Corporation, Armonk, NY, USA).

Comparison of Wet and Dry Season Physico-Chemical Levels of Pollutants in the Lakes
Lake Koka and Lake Ziway: the physico-chemical analysis of the samples observation during the wet season (between July and August 2021) and dry season (between January and February 2022) is presented in Tables 2 and 3.The selected months were purposively chosen considering the highest dry and wet seasons of Ethiopian weather and climate.As shown in Tables 2 and 3, Cr and Cd were not detected at both wet and dry seasons for both lakes (Lake Koka and Lake Ziway).For both lakes, Pb was detected mainly during the dry season.Low concentration of Cu (0.03-0.07 mg/L) was detected in the samples collected from Lake Koka.As indicated in Table 2, the variation in the concentration of heavy metals (Pb, Zn), nutrients (PO 4 3 -P, NO 3 -N), and biological organic matter (BOD 5 ) were significant (p < 0.05) (Table 4) between the wet and dry seasons in Lake Koka.For Lake Koka, only the concentration of EC, PO 4 3 -P (during the dry season), NO 3 -N, and the values of temperature and pH did not exceed the WHO standard value.In this regard, Lake Ziway showed a similar result, except concerning the concentration of EC, which exceeded the WHO standard value (Table 3).
As indicated by the results, the variation in the concentration of heavy metals Pb and Zn, nutrients (PO 4 3 -P, NO 3 -N), and biological organic matter (BOD 5 ) were significant (p < 0.05) (Table 4) between the wet and dry seasons in Lake Koka.Considering the heavy metals analyzed, Pb and Zn were detected in all sampling sites, while Cr and Cd were not detected in the two lakes (Tables 2 and 3).Heavy metals in water bodies are insignificant in non-polluted environments.However, heavy metals major contributor to surface water could be geogenic origin or anthropogenic activities, namely, industrial, mining, sewage, and agricultural sources [39].According to Gimeno-García et al. [45], Pb and Zn were the main components of superphosphate fertilizers and pesticides.The mean level of Pb and Zn (Table 4) in Koka and Ziway were significantly lower compared to the mean Pb levels (0.31-1.36 mg/L) and Zn levels (0.46-1.56 mg/L) in Awash river and this is similarly reported by Eliku et al. [40].The current mean levels of heavy metals observed are quite higher than their concentration compared to the nearby Awash river concentration levels as reported by Teklay et al. [46].The variation in the levels of the concentrations may be due to the increment of the economic activities around the two lakes.Agricultural activities and animal manure waste caused the variation of the nutrient (NO 3 -N and PO 4 3 -P) concentration during wet and dry season [46,47].In both lakes, Zn mean concentration during the wet and dry season observed exceeding its threshold limit concentration in drinking water as settled by WHO.As indicated in Tables 2 and 3, Pb concentration was exceeding the settled standard level during the dry season of the year in both lakes.Moreover, EC, COD, and BOD recorded were above the standard level in both lakes.Nitrate, pH, and temperature were within the allowable level by WHO.In both lakes, the phosphate above the standard limit were observed during the wet season, which might be due to the application of phosphate based inorganic fertilizers in the agricultural field around these lakes.However, according to Gizaw et al. (2021), phosphate concentration exceeding 0.01 mg/L and nitrate concentration exceeding 10 mg/L could cause eutrophication of lakes [48].Despite COD in Lake Ziway, this study reveals that there was not significant (p > 0.05) variation in concentrations of Cu, EC, pH, and temperature between wet and dry seasons in both lakes (Table 4).

The Effect of Water Hyacinth on the Physico-Chemical Levels of Pollutants in the Lakes
As depicted in Tables 5 and 6, the variation of Zn concentration between low, medium, and high level water hyacinth infested was significant (p < 0.05) in both lakes.Other heavy metals, namely, Cr, Pb, Cd, and Cu, were not detected in the presence of water hyacinth despite the concentration of Pb, Cd, and Cu in some sites of the two lakes (Tables 5 and 6).This observation demonstrated that water hyacinth has significant effects in removing heavy metals from water during wet and dry seasons.Many researchers reported that water hyacinth has the capacity to take up heavy metals (Pb, Cr, Cd, Zn, and Cu) nutrient (NO 3 − , PO 4 3− ), pH, organic and inorganic matters (COD, BOD 5 ) from lake water.For instance, Liao and Chang [38] looked at the water hyacinth's capacity to absorb and transport the heavy metals Cd, Pb, Cu, Zn, and Ni in the order of Cu > Zn > Ni > Pb > Cd.Phyto-remedial capability of water hyacinth for heavy metals namely Pb, Cd, Hg, and Zn scavenging also demonstrated by Sasidharan et al. [49].Similar results are also reported by Kumar et al. [50].Moreover, the ANOVA values for physico-chemical levels of EC, BOD, COD, nitrate, and phosphate were found to be significant (p < 0.05) for the different water hyacinth levels in the lake.This also demonstrated the capacity of water hyacinth towards the absorbance of aforementioned pollutants [49].Similar results concering the present observations were reported by treating wastewater from mining using water hyacinth constructed wetland, which reported water hyacinth as the most efficient plant at removing phosphorus, COD, and EC with removal rates of 97.3%, 70.5%, and 22.2%, respectively [51].Despite Lake Ziway, significant variation (p < 0.05) in pH was observed for Lake Koka.Moreover, the variation of temperature at different levels of water hyacinth was observed statistically significant (p < 0.05) in Lake Ziway.This might be due to the shading of the water hyacinth biomass from the direct sunlight during dry season, which causes to raise surface water temperature.As indicated in Table 7, Cr and Cd were not detected in both lakes infested by water hyacinth and other grasses.Regardless of water hyacinth and other grasses, Cu was also not detected in Lake Koka during dry season and both during wet and dry seasons in Lake Ziway.Lowest mean Zn concentration (0.39 mg/L) was recorded during the dry season for samples collected from water hyacinth infested compared to the samples collected from the other grasses infested sites (0.72 mg/L) in Lake Koka.Moreover, lower mean phosphate concentration during wet and dry season and lower mean nitrate concentration only at dry season were observed and their variation significance were supported by ANOVA value indicated in Tables 5 and 6.Lowest mean heavy metal, phosphate concentration, and nitrate concentration implies that water hyacinth infested lake absorbs more heavy metal like Zn and nutrients (phosphate and nitrate) compared to other grasses infested sites in Lake Koka.In Lake Koka, significant pH and temperature variation were significantly observed between water hyacinth and other grasses infested sites.Despite Zn and BOD 5 concentration, this shown trend for Lake Ziway was reported by Sidek et al. [51] and Getnet et al. [14].

Conclusions
Despite seasonal fluctuations, significant variations in pollutant physico-chemical levels were found in both lakes.Cr and Cd were not detected in both wet and dry seasons for both lakes.For both lakes, Pb was detected mainly during the dry season.Low concentration of Cu (0.03-0.07 mg/L) was detected in the samples collected from Lake Koka.For Lake Koka, only the concentration of EC, PO 4 3− (during the dry season), NO 3 , and the values of temperature and pH did not exceed the WHO standard value.In this respect, the concentrations of EC which exceeded WHO standard values were found to be similar in Lake Ziway.In both lakes, the threshold limit concentrations of Zn in drinking water set by WHO were exceeded during the wet and dry seasons.Despite COD in Lake Ziway, this study shows no significant (p > 0.05) variation in Cu, EC, pH and temperature between wet and dry seasons in either lake.This observation demonstrated that water hyacinth has a significant effect in removing heavy metals from water during wet and dry seasons.Moreover, the ANOVA values for physico-chemical levels of EC, BOD, COD, nitrate and phosphate were found to be significant (p < 0.05) for the different water hyacinth levels in the lake.This also demonstrated the capacity of water hyacinth towards the absorbance of water pollutants.Lowest mean heavy metal, phosphate, and concentration nitrate concentration implies that water hyacinth infested lake absorbs more heavy metals and nutrients (phosphate and nitrate) compared to other infested grass sites in Lake Koka and Lake Ziway.In both the wet and dry seasons, it was found that the water hyacinth had a substantial impact on the physico-chemical levels of pollutants in the lakes.Funding: This study was carried out with the support of UNISA (University of South Africa).
2 = large patches or many individuals; 1 = occasional patches individuals; or tr = trace, a few individuals only.And the value of rating scale used for estimation of water hyacinth infestation level: high = 4 to 5, medium = 2-3, low = tr to 1.The samples were collected using dark plastic bottles, temporarily stored in sampling boxes and stored at 4 • C prior to Water 2023, 15, 2540 5 of 13

Author
Contributions: E.E.C.: idea conceptualization, proposal development, methodology setup, data curation and analysis, investigation, writing original draft, editing, and revision of the manuscript, visualizing Corresponding.Authors: L.N. and M.C.: Supervisors and Co-Supervisor of the project from the start to the end.All authors have read and agreed to the published version of the manuscript.

Table 1 .
Description of water sample habitat by water hyacinth infestation level and site.

Table 2 .
Average physico-chemical parameters of Lake Koka water during wet and dry seasons.

Table 3 .
Average physico-chemical parameters of Lake Ziway water during wet and dry season.

Table 5 .
ANOVA the effect of water hyacinth on the physico-chemical levels of pollutants during wet and dry seasons at Lake Koka.Not analyzed, SD-standard deviation, * p < 0.05-significant, W -wet, D -dry.

Table 6 .
ANOVA the effect of water hyacinth on the physico-chemical levels of pollutants during wet and dry seasons at Lake Ziway.Comparison of the Physico-Chemical Levels of Pollutants in the Lakes at the Lake Covered by Water Hyacinth and Any Other Native Grasses Note(s): NA-Not analyzed, SD-standard deviation, * p < 0.05-significant, W -wet, D -dry.

Table 7 .
ANOVA for the comparison of the physico-chemical levels of pollutants in the lakes at the lake covered by water hyacinth and other grasses.