Socio-ecological Impacts of Water Hyacinth ( Eichhornia Crassipes ) Under Dry Climatic Conditions : The Case of Shagashe River in Masvingo , Zimbabwe

In Zimbabwe, aquatic environments continue to endure water hyacinth (Eichhornia Crassipes) invasions. The intricate and distinctive characteristics of water hyacinth make it one of the most ecologically resilient aquatic plants enabling it to invade major water systems. There is still paucity of scientific knowledge about the social and ecological ramifications of this macrophyte. In this study, we assessed the social and ecological effects of water hyacinth along Shagashe River. The mixed methods research design was adopted as the strategy of inquiry. Sampling sites were selected to compare two environments along the river, one under the cover of water hyacinth and the other without water hyacinth. Moreover, the sampling was done in two distinct periods i.e. the dry season and wet season. In each of these sections and periods, 15 sampling points were selected using the stratified random sampling criteria. Ecological data for the two sections were compared by means of one way analysis of variance (ANOVA). A comparison was also done on the social data from the two sections of the river and also from the two seasons. Ecological data was collected mainly through field measurements of biodiversity, sedimentation rate and velocity. Laboratory testing of evaporation rate and water parameters augmented the ecological data collection processes. Data on sociological aspects was collected mainly through interviews, questionnaire surveys and the story telling approach. Results show that the water hyacinth infested environment had low phytoplankton productivity, low dissolved oxygen, high sedimentation rates, high water loss and reduced river velocity among other ecological doi: 10.26502/jesph.96120027


Introduction
Half of the world's rivers are heavily polluted and most of them run through developing countries [1].In most less economically developed countries, sewer systems usually draw untreated sewage into rivers.This is due to the fact that most developing countries cannot afford to build waste treatment plants and do not enforce laws for controlling water pollution.According to [1], most cities in developing countries discharge most of their untreated sewage directly into rivers, streams and lakes.Rapid rates of urbanisation are also a characteristic of developing countries [2].As urban centres grow spatially and demographically they are confronted by waste disposal problems which result in water pollution [3,4].This largely contributes to the pollution of rivers traversing urban areas in most African countries resulting in the proliferation of water hyacinth (Eichhornia Crassipes) in the polluted water ways.
Nutrients and temperatures are key determinants of water hyacinth growth and reproduction [5].Daily, about 2 million tons of sewage industrial and agricultural wastes are discharged into the world's water ways [1].These wastes introduce nutrients such as nitrates and phosphates, which create conducive environment for rapid growth of the weed [6,7].In nutrient rich waters, water hyacinth grows at a fast rate that the surface it covers doubles in twelve days [8].
Water hyacinth has become a global problem with approximately 56 countries in the world including the USA struggling to remove it from water bodies [9].In the USA, approximately 11 million dollars is spent every year in Florida, Laisan and Texas to control this weed [10].It is especially pervasive throughout South East Asia, South USA, Central and West Africa and Southern Africa [11,12].According to [13], there is no clear record of how, why and when water hyacinth was introduced to water bodies outside its native range.People have been enticed to carry the weed as an ornament because of its attractive purple flower.However more important explanations for its spread can be attributed to its capacity to quickly multiply, strive and outcompete in alien lands, away from its natural predators.
Water hyacinth has spread throughout vital fresh water bodies and wetlands of Africa.Infestations of this weed are reaching crisis proportions in important fresh water bodies in Africa [14].This is causing environmental, economic and social problems and accumulated damages that can easily be valued in the order of billions of dollars [15].This has direct effects on communities that in one way or another depend on the environmental services or production from affected water bodies [16].In Lake Victoria Basin, the macrophyte covers about 12,000 ha and is affecting livelihoods of more than 40 million people in Kenya, Tanzania and Uganda [17].Other infested water bodies in Africa include Lake Malawi, the Zambezi River, Tano Lagoon, River Niger in West Africa, Incomati River in Mozambique, Kafue River in Zambia, Pangani River in Tanzania and Lake Naivasha in Kenya [8].Changes to water hyacinth density have the potential to affect other ecological and human communities in areas where it is established.These changes may be perceived as positive or negative depending on the designated or beneficial uses of water body [18].
Zimbabwe has not been an exemption to the problem of water hyacinth.It is reported to have been present in Zimbabwe as early as 1940 [19] and has subsequently spread to other parts of the country.Its invasion of Lake Chivero and Manyame River has been well documented along with the resulting problems it has created [7] Shagashe River in Masvingo Province is one of the infested water ways in Zimbabwe [7].The growth of water hyacinth in Zimbabwe is mainly attributed to the failure by councils to control water pollution by raw sewage [20].
Despite the occurrence of water hyacinth in the water bodies in Zimbabwe and specifically in the dry climates of agro-ecological region V, its social and ecological impacts are only superficially understood.There is need to establish area specific impacts of the macrophyte in order to come up with area specific solutions.The problem of water pollution is predicted to persist given the financial and capacity challenges faced by the local authorities.
Consequently, water bodies including lakes, dams and rivers have been greatly affected and are likely to continue being affected.This translates to the continuation of the existence of water hyacinth on most of the water bodies.In these affected areas are human settlements that rely on these water bodies for various economic, social, ecological services.Whether the presence of water hyacinth in water bodies is a socio-ecological blessing or curse is an issue veiled in obscurity.
Moyo et al. [7] presented an integrated management framework to control water hyacinth infestation in Shagashe River to manageable levels.Moyo and Mapira [21] tested for the effectiveness of water hyacinth in phytoremediation in Shagashe River.Another study by [22] assessed the remediation potential of selected parameters by water hyacinth.Recent literature on the management of water hyacinth mainly focuses on its removal.
However, the impacts of the macrophyte to the ecological systems and surrounding communities have not yet been established.Specifically, no study has studied the socio-ecological impacts of the macrophyte along Shagashe River.
It is the purpose of this study to establish the socio-ecological impacts of the water hyacinth with specific reference to Shagashe River in Masvingo through ecological assessments and social impact analysis.

Study area
The study was carried out in Masvingo Province along Shagashe River (Figure 1).The area is located in agroecological region five (v) of the country.The region is semi-arid with average annual rainfall below 450 mm.It supports extensive livestock production and game ranging.The river Shagashe drains into Zimbabwe's largest J Environ Sci Public Health 2018; 2 (1): 36-52 inland water body, Lake Mtirikwi.Masvingo is a mediumsized city with a population of 88 554 [23].The city has experienced phenomenal spatial and demographic growth [24].Water scarcity at the original site forced the city to relocate to the confluence of Mucheke and Shagashe Rivers where it has survived up to present day.The industrial activities and domestic sewage have polluted the two rivers resulting in the proliferation of water hyacinth.

Research design
The mixed methods approach was adopted in which both qualitative and quantitative methods were used.The research required both numerical and descriptive data hence the need for combining the two methods.

Water samples:
Water sampling was undertaken in accordance to NWL/SAZ: 558: 1999/22/05 (sampling from surface waters) which stipulates that, samples should be taken at points where water is flowing and samples should be sterilized among other precautions [25] Water samples were collected directly from each sampling point with 500ml plastic containers washed with nitric acid to remove any form of contaminants.These were stored immediately in a cooler box in order to ensure that the physical properties of the water samples were maintained and transported to the laboratory for analysis.Water samples along Shagashe River were collected and analysed after every two weeks over two distinct periods; the dry season and wet season between October 2013 and August 2014.
From the two periods, the same 15 sampling sites were assessed.

Sampling for biodiversity:
The sampling frame for biodiversity measurement was determined using the species area curve as shown in Figure 2. Initially, a frame 30*30cm in size was designed and species were counted.
The size of the frame was subsequently increased to 50*50cm, 80*80cm, 100*100cm up to 200*200cm.The objective was to come up with a quadrat with the optimum number of species.Figure 2 shows the species area curve used in the determination of the optimum quadrat size.The 100*100 cm quadrat had the optimum number of species.Biodiversity data was then collected from the 100*100 cm quadrats that were put in the established nine sampling points in each river section.Within each section, the quadrats were placed in form of a radial arm (Figure 3).The radial arm is designed to facilitate the capture of all variations within the river segment through considering 4 points.That is one from the centre, one from the N, one from the SW and the other one from the SE.Angles between arms were 120 o and its length 5 m.

Biodiversity measurements:
The study assessed the influence of water hyacinth on biodiversity.To assess species diversity, the Shannon-Weaver Index, which usually combines aspects of richness and evenness (H), was used.This method is widely recognised as a successful tool for the evaluation and quantification of plant and animal diversity, and an easy and practical measure of area diversity [26].
This index was calculated using the formula:

H = -Sum (P 1 In (P 1 ))
(Equation 1) Where the summation is over all species and P 1 is the relative abundance of species in the quadrat.This index measures the average degree of uncertainty in predicting to what species chosen at random from a collection of S species and N individuals will belong (Lugwig, 1988).Species evenness (E) was also calculated using the formula:

E= H/In (S) (Equation 2)
Where H is the Shannon Weaver index and S is species richness observed within the quadrat.This index assumes that when all species in the sample are equally abundant evenness should be at maximum and decreases towards zero as the relative abundance of species diverges away from evenness [27] 2.3.4Water testing: Water samples were collected using standard procedure as outlined in APHA Manual Water Analysis and tested using standard methods as described by the reference laboratory standard operating procedure manuals for fresh and waste water quality at University of Zimbabwe, Biological Sciences Laboratory.Fifteen samples were collected from the sampling points in the months of May and November.A total of 8 parameters were tested 4 being physical and 3 chemical.Samples were collected in 500ml clean sterilized plastic labelled containers with screw caps.The containers were rinsed several times to make sure that they are free from contaminants.Depth per each point was measured using a standard meter rule while velocity was determined using a float and stop watch.The collected samples were preserved in an ice box and transported to the lab for analysis within 24 hours.
Parameters were tested to check if they are influenced by the presence or absence of water hyacinth.

Water evaporation experiment:
An experiment was carried out to ascertain the effect of water hyacinth on water loss from water bodies.Water from the river was collected into evaporation pans.Evaporation pan A was filled with water and covered with live water hyacinth extracted from Shagashe River while evaporation pan B was the control pan not covered with water hyacinth.Same amount of water was put into the two pans.Assessment was done for eight days where water level was recorded from both pans after every 24 hours.This necessitated comparison of the two evaporation pans to determine the one mostly affected in terms of water loss.

Insect infestation experiment
We also tested whether the presence of water hyacinth attracts nuisance insects or not.The presence of insects may affect the aesthetic value of the environment and may also attract insects that cause discomfort due to biting.In this experiment, water and water hyacinth were put in pan A whilst in pan B we put water without hyacinth.Repeated observations of presence or absence of insects were done for eight days.

Secondary data sources
The study used previously published documents on water hyacinth in Shagashe River.Secondary information on the problem of river pollution was drawn from various sources such as Masvingo City council, ZINWA Masvingo branch and The Mirror, a weekly newspaper.Other sources include Environmental Management Agency data sheets on water parameters.

Interviews
An interview is a conversation between two people where questions are asked by the interviewer to elicit facts or statements from the interviewee [28].Interviews were used to collect data from various stakeholders.Responsible authorities from relevant stakeholders such as Zimbabwe National Parks and Wildlife Management, Mtirikwi Sub Catchment Council and Environmental Management Agency were interviewed on information about the social and ecological impact of water hyacinth.

Questionnaire survey
Questionnaires were distributed in water hyacinth infested and non-infested sections for comparative purposes, a total of 50 questionnaires were distributed to collect data on social and ecological effects of water hyacinth.The questionnaires were distributed to both men and women since they have different levels of interaction with the river.
People who had resided in the area for at least 5 years were targeted because they had stayed in the area long enough to notice the changes that were occurring in the river as well as felt the social impact due to the presence of water hyacinth.They also have the history of the river for the period they have stayed in the area as well as how the growth of water hyacinth has affected their various social benefits from the river.

Observations
In this study, observations were used to collect data.An observation guide was drafted in order to guide the researchers during data collection.Observation is a fundamental way of finding out about the world around us.
Observation provides direct access to the phenomena under study.The observations were also used to assess the estimated percentage coverage of water hyacinth at selected points along the channel as well as noting the observed plant and animals present.

Story telling approach
Some identified people along Shagashe River were asked to tell stories related to their use of water in Shagashe River.The story telling approach captures some information that would otherwise be left out in a formal guided interview or a questionnaire survey [29].From the stories related, important information was obtained regarding the socio-ecological impacts of water hyacinth.Stories were collected from both the area with water hyacinth and the area without water hyacinth for comparative purposes.

Water loss:
In this study, it was established that water hyacinth significantly affects water levels along the river.Results from a 14 day experiment shows a significant decrease (p =0.0001, α= 0.05) in the level of water from water hyacinth infested pan.There is also a significant decrease (p=0.0001,α= 0.05) in water level on the noninfested pan.Despite the fact that both pans had a significant water loss, there is a significant difference in the rate at which the two sources are losing water through evaporation and transpiration (Figure 4).Water hyacinth covered water surfaces lost water by 1.5 times more than loss from non-water hyacinth surfaces.There is a significant (p=0.001,α= 0.05) difference in water loss from a water hyacinth infested and a non-infested water source.By the end of 14 days, the depth of water of the evaporation pan which contained water hyacinth had dropped from 140mm to below 60mm.On the other hand, the evaporation pan which did not contain water hyacinth dropped from 140mm to 70mm.The trend shows that over a long period of time the difference in the rate of water loss continues to increase.Hence, water is lost at a higher rate in water hyacinth covered water bodies as compared to open water bodies.This view was also supported by the data obtained from questionnaires where 97.3% of the respondents in the water hyacinth infested area acknowledged that they face water challenges during periods of high infestation.It is therefore the position of this study that water hyacinth results in increased rate of water loss.
Thus, water hyacinth may exacerbate ecological stress especially in the face of climate change which is marked by an increase in temperatures in the region.This may pose challenges to some aquatic species that depend on water.
Hippopotamus have been reported to migrate from some sections of the river due to excessive water loss during the dry season.Several other aquatic species are likely to be affected by this water loss and this disturbs the functional dexterity of river ecosystems.

Biodiversity loss:
Species richness data shows that during the dry season, when water hyacinth density and cover are high, plant species diversity is low.Conversely, the wet season, when water hyacinth is low, had high diversity.Figure 5 shows the difference in species richness between period of high infestation (dry season) and that of low infestation (wet season).Each sampling point was assessed twice, during the dry and wet season.The Shannon index of diversity calculated for the two periods also shows that diversity is high when water hyacinth cover is low or absent.This point to the fact that water hyacinth has an effect on species richness and evenness.Dry season sample quadrats had an average of 2 species including the water hyacinth whilst wet season quadrats had an average of 4 species.Thus, in terms of species richness, water hyacinth infestation is associated with low plant species diversity.In most cases where 1 species was recorded in a quadrat it was the water hyacinth weed which was mainly dominant.The macrophyte proved to be the dominant species which eliminates other water weeds.
Furthermore, calculation of species evenness has shown that the distribution of water weeds is more even where there is no water hyacinth and more uneven where there is water hyacinth.The water haycinth infested quadrats had an average of 0.19 whilst the non infested quadrats had an average of 0.73.This shows that in terms of both richness and evenness, water hyacinth causes a decrease in biodiversity.
These findings confirm [5]'s ascertions that water hyacinth suffocates the productivity of other species, especially phytoplankton productivity.It is postulated that water hyacinth blocks sunlight from reaching lower areas within the water bodies.This affects the process of photosynthesis in other aquatic weeds and consequently affects productivity.

Physicochemical characteristics
As a consequence of the dense mats formed by the interlocking of individual water hyacinth plants, water quality along Shagashe River has been affected.Several water parameters (i.e.physical, chemical and biological) have ecological importance.Alteration of these parameters is associated with ecological changes.Water samples along Shagashe River were collected and analysed after every two weeks over two distinct periods; the dry season and wet season between October 2013 and August 2014.From the two periods, 15 sampling sites were assessed.Table 1 shows the results of the analyses.The values shown in Results show that during the period of maximum water hyacinth cover (May to October) the concentration of most physical parameters is high.During periods of minimum water hyacinth concentration (November to April) the concentration of the physical parameters is reduced.High density and cover of water hyacinth is associated with high levels of turbidity, conductivity, total dissolved oxygen, temperatures and pH.It is the position of this study, however, that water hyacinth does not explain 100 percent of these parameters since there could be other factors regulating parameter level such as the dilution effect due to changes in volume and velocity.

Turbidity and total suspended solids:
Turbidity describes the clarity and haziness of the water.From the conducted water parameter analysis, it was noted that turbidity is high in water hyacinth infested areas and season.
The season of high water hyacinth density had an average of 29.75 turbidity whilst the average for the season with low or no water hyacinth had an average of 16.89.There is a significant (p<0.05)difference in the levels of turbidity between these two periods.It is thus the position of this paper that water hyacinth contributes to the increase in turbidity in Shagashe River.Turbidity mostly affects growth of aquatic plants at the bottom of the water surfaces by inhibiting access to sunlight.Since plants are at the bottom of the food chain, chances of quality sustenance of the food ecosystem will be affected.Water clarity is also an indicator of potential primary productivity.High turbidity could be resulting from high sedimentation rate which is exacerbated by water hyacinth.There is high sedimentation rate within the water hyacinth's complex root structure which traps sediments and phytoplankton resulting in high turbidity.This blocks sunlight from deeper waters hence inhibiting photosynthesis which greatly reduces oxygen levels in the water.Thus, the high level of turbidity will not favour abundance of zooplankton organisms.The role of zooplankton in the energy transfer from primary producers to organisms of higher trophic levels cannot be overemphasized.It is therefore the position of this study that high turbidity resulting from the presence of water hyacinth in the river has some ecological implications.
There was also a significant difference in total suspended solids between season of water hyacinth infestation and that of low or no water hyacinth.This is due to the fact that water hyacinth mats trap detritus and phytoplankton.
The suspended solids observed include silt, plankton and industrial waste.They affect aquatic ecosystems through clogging fish gills, reducing growth rates, decreasing resistance to disease, and preventing egg and larval development.Particles that settle out can smother fish eggs and those of aquatic insects, as well as suffocate newlyhatched larvae.The material that settles also fills the spaces between rocks and makes these microhabitats unsuitable for various aquatic insects, such as mayfly nymphs, stonefly nymphs and caddisfly larva.

pH:
Results from water parameter analysis show that the presence of water hyacinth in Shagashe River contributes to the changes in water pH.Although there is no significant difference (p > 0.05) between pH levels for the two seasons, the period with high water hyacinth density and cover has more acidic water.However, the pH levels for Shagashe River even during periods of high water hyacinth density are still within the natural range of between 6-8.Whilst the pH has not reached toxic level, the decrease poses negative consequences to the marine ecosystems through interference with life cycle of aquatic organisms.The pH values were generally lower for most seasons in the infested portions of the river.The water hyacinth plants can stand both highly acidic and highly alkaline conditions, but more vibrant growth is supported by neutral water bodies [30].Water hyacinth plants do not survive in water media with pH equal to or less than 4.0 [31].Given that in Shagashe River the average value for all seasons is 7, water hyacinth is expected to proliferate.

Conductivity:
In this study, conductivity was high in water hyacinth infested areas and in the period of high infestation.The range of values for the infested areas and period was between 290-304 μs cm -1 while sections and the period with low or no water hyacinth values ranged between 252-264 μs cm -1 .Statistical tests reveal that conductivity in water hyacinth infested sections of the river and period was significantly higher (p<0.05)than sections and period with low or no water hyacinth.The implication of these results is that water hyacinth is found in areas and times when there is mineralisation and where there is high nutrient concentration.In addition, this could be due to the fact that water hyacinth contributes to the amount of salts in the water bodies since conductivity gives an estimate of salt concentration in water.Hence water hyacinth alters the conductivity of water bodies.

Nitrates:
Nitrate concentrations are low during the period of high water hyacinth infestation.The average nitrate concentration value was 6.84 mg L -1 during this period.The concentrations were high during the period of low infestation with an average of 11.21 mg L -1 .The significant difference (P<0.05) between these two periods could be attributed to the dilution effect which is associated with the rainy season.On the other hand, it can be attributed to the absorption of nitrates by water hyacinth.Several studies [22,30] have shown that water hyacinth absorbs nitrates.As a result this indicates that, water hyacinth thrives in polluted water bodies.The macrophyte has river [7].Water shortage challenges are mostly encountered this season and this has affected the local communities negatively.

Lack of access to clean water:
More than 90% of the respondents of questionnaires distributed during the infested period noted that the proliferation of water hyacinth results in lack of debris free or clean water.86% of the respondents also highlighted reduced access to water point.The proliferation of the invasive weed reduces accessibility to water collection points for various domestic uses such as washing, bathing and watering gardens.
The reduction of water levels in the channel leads to shortages of water needed for domestic use and livestock watering.The reduction in water levels in Shagashe River may also directly affect the levels of water in Lake Mtirikwi which may later result in water shortages in the city of Masvingo since Lake Mtirikwi is the sole supplier of the water used in the city.If water hyacinth is not controlled Masvingo city may end up having severe water challenges in the near future.
All respondents from the water hyacinth free period reported deriving various social benefits of the river.They indicated that they are able to perform other domestic activities such as washing and bathing without challenges.
Access of water points is not a challenge in this section.Villamagna [13] notes that water transparency is an attractive water quality in a water body that is primarily for recreation and other domestic uses.

Impact on religious activities:
8% of the respondents in the water hyacinth infested area indicated the effect of water loss on some religious activities such as baptism.The macrophyte inhibits the religious practice of baptism since the weed will be floating in most of the pools where the activity may be done.In order to engage in such an activity they have to travel long distances to non-infested areas.Although no respondents in the water hyacinth free section indicated that they engage in baptism events, they highlighted that if such events were to be held, no problems were going to be encountered since the water have not been affected through infestation by water hyacinth.
Generally, the water hyacinth weed has affected social lives of the community along Shagashe negatively.The community in the lower course can no longer derive benefits from the river mainly due to the growth of the invasive weed.People can no longer perform some recreational activities and reduction in the number of fish catches has affected the supplementation of their diets.

Conclusion
We conclude that, water hyacinth does more harm than good along Shagashe River both socially and ecologically.
The study found that the communities along Shagashe River are exposed to a number of social problems due to the presence of water hyacinth.These include physical discomfort due to mosquito bites.The macrophyte seems to create a comfortable habitat and breeding ground of mosquitoes.The river has lost its aesthetic and recreational

Figure 1 :
Figure 1: Location of the study area.

Figure 4 :
Figure 4: Water loss from water hyacinth infested and non-infested evaporation pans.

Figure 5 :
Figure 5: Differences in species richness between high water hyacinth infestation period and low infestation period.

4. 2 . 3
Total dissolved solids: Total dissolved solids values varied in water hyacinth infested areas and open areas from the obtained results of tests conducted in May and November.In May when the sampling area had water hyacinth showed high values of total dissolved solids while November open water had a lower value.There was a significant difference in the values of total dissolved solids between water hyacinth infested areas as compared to open water areas.TDS is closely linked to turbidity and hence affect the penetration of sunlight to deeper waters.

Table 1
are averages of replicates taken from different samples.

Table 1 :
Variations in water quality between water hyacinth infested and non-infested water in different seasons along Shagashe River.Mean value ± S.E (n=15).